Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering http://pid.sagepub.com/

A new hybrid particle swarm optimization approach for structural design optimization in the automotive industry Ali R Yildiz Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering published online 23 May 2012 DOI: 10.1177/0954407012443636 The online version of this article can be found at: http://pid.sagepub.com/content/early/2012/05/22/0954407012443636 A more recent version of this article was published on - Sep 14, 2012

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Original Article

A new hybrid particle swarm optimization approach for structural design optimization in the automotive industry

Proc IMechE Part D: J Automobile Engineering 0(0) 1–12 Ó IMechE 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954407012443636 pid.sagepub.com

Ali R Yildiz

Abstract This paper presents an innovative optimization approach to solve structural design optimization problems in the automotive industry. The new approach is based on Taguchi’s robust design approach and particle swarm optimization algorithm. The proposed approach is applied to the structural design optimization of a vehicle part to illustrate how the present approach can be applied for solving design optimization problems. The results show the ability of the proposed approach to find better optimal solutions for structural design optimization problems.

Keywords Structural design optimization, particle swarm optimization, Taguchi’s method, robust design

Date received: 13 October 2011; accepted: 6 March 2012

Introduction The optimal design of structures includes sizing, shape and topology optimization. There has been extensive research focused on shape optimization due to its great contribution to cost, material and time savings in the procedures of the engineering design. The purpose of shape optimization is to determine the optimal shape of a continuum medium to maximize or minimize a given criterion (often called an objective function), such as minimize the weight of the body, maximize the stiffness of the structure or remove the stress concentrations, subjected to the stress or displacement constraint conditions. Computer-aided optimization has been commonly used to obtain more economical designs. Numerous algorithms have been developed to solve structural design optimization problems in the last four decades. The early works on this topic mostly use various mathematical techniques. These methods are not only time consuming in solving complex nature problems, but also they may not be used efficiently for finding global or near global optimum solutions. In the past few decades, a number of innovative approaches, such as tabu search, genetic algorithm, simulated annealing, particle swarm optimization algorithm, ant colony algorithm and immune algorithm, have been developed and widely applied in various fields of science.1–13

Fast convergence speed and robustness in finding the global minimum are not easily achieved at the same time. Fast convergence requires a minimum number of calculations, increasing the probability of missing important points; on the other hand, the evaluation of more points for finding the global minimum decreases the convergence speed. This leads to the question: ‘how to obtain both fast convergence speed and global search capability at the same time?’ There have been a number of attempts to answer this question, while hybrid algorithms have shown outstanding reliability and efficiency in application to the engineering optimization problems.14–20 Therefore, researchers are paying great attention to hybrid approaches in order to answer this question, particularly to avoid premature convergence towards a local minimum and to reach the global optimum results. There is an increasing interest in applying the new approaches and in further improving the performance of optimization techniques for the solution of structural design optimization problems. Although Department of Mechanical Engineering, Bursa Technical University, Bursa, Turkey Corresponding author: Ali R Yildiz, Department of Mechanical Engineering, Bursa Technical University, Bursa, Turkey. Email: [email protected]

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Proc IMechE Part D: J Automobile Engineering 0(0)

some improvements regarding structural design optimization issues are achieved, the complexity of design problems presents shortcomings. The main goal of the present research is to develop an effective approach to solve real-world design optimization problems. A new hybrid approach based on robustness issues is used to help better initialize particle swarm optimization algorithm search. The aim has been to reach optimum designs by using Taguchi’s robust parameter design approach coupled with particle swarm optimization algorithm. In this new hybrid approach, signal-to-noise (S/N) values are calculated and ANOVA (analysis of variance) tables for each of the objectives are formed using S/N ratios, respectively. According to results of ANOVA tables, appropriate interval levels of design parameters are found, and then initial search population of the particle swarm optimization algorithm process is defined according to these interval levels. Optimum results of the design problem are then obtained using particle swarm optimization algorithm. The developed new hybrid optimization approach is applied to a vehicle part design optimization problem taken from the automotive industry to demonstrate the application of the present approach to real-world design problems. The results of the proposed approach show that the proposed optimization method converges rapidly to the global optimum solution and provides reliable and accurate solutions. The organization of the paper is as follows. The third section presents a detailed review on optimization approaches. The particle swarm optimization (PSO), Taguchi’s method and the proposed hybrid approach are presented in the third section. A case study from automobile industry is solved in the fourth section. The paper is concluded in the fifth section.

Literature review Recently, new approaches in the area of optimization research are presented to further improve the solution of optimization problems with complex nature. Over the past few years, studies on evolutionary algorithms have shown that these methods can be efficiently used to eliminate most of the difficulties of classical methods. Evolutionary algorithms are widely used to solve engineering optimization problems with complex nature. Various research works have been carried out to enhance the performance of evolutionary algorithm.1–23 For instance, Yildiz and Saitou2 developed a novel approach for multi-component topology optimization of continuum structures using a multi-objective genetic algorithm to obtain Pareto optimal solutions that exhibits trade-offs among stiffness, weight, manufacturability and assemble ability. Yildiz and Saitou2 present a method for synthesizing structural assemblies directly from the design specifications without going through the two-step process. Given an extended design domain

with boundary and loading conditions, the method simultaneously optimizes the topology and geometry of an entire structure and the location and configuration of joints considering structural performance, manufacturability and assemble ability. The developed approach is applied to multi-component topology optimization of a vehicle floor frame. The PSO algorithm originally developed by Eberhart and Kennedy24 is inspired with social behavior, such as bird flocking or fish schooling, which is used successfully in the solution of optimization problems. The PSO algorithm has been used in many areas of optimization studies. The use of PSO algorithms in the optimum solution of problems resulted in better solutions compared to classical methods.6,25–32 The PSO algorithm was applied to the shape optimization of a torque arm and to the size optimization of truss structures taken from literature by Fourie and Groenwold.6 In their PSO algorithm, the concept of craziness is redefined and elitism operator borrowed by GA was used. Their results showed that PSO algorithms were better than GA and the gradient-based recursive quadratic programming algorithm. Perez and Behdinan26 proposed a particle swarm approach for structural design optimization. The effectiveness of the improved PSO algorithm on structural optimization is shown through the use of four classical truss optimization examples. Results from the three tested cases using an improved PSO illustrate the ability of the algorithm to find optimal results which are better than, or at the same level of, other structural optimization methods. Venter and Sobieszczanski-Sobieski32 used PSO algorithm for multidisciplinary optimization of a transport aircraft wing. Some researchers have used the robustness issues to solve optimization problems.33–37 Robinson et al.38 present a review paper which focuses largely on the work done since 1992 and a historical perspective of parameter design is also given. Kunjur and Krishnamurty39 presented a robust optimization approach that integrates optimization concepts with statistical robust design techniques. Although Taguchi’s methods have been successfully applied to processes in the design and manufacturing, they are also criticized for their efficiency.36,40 Hybrid methods are also used to enhance the performance of evolutionary algorithm. Yildiz et al.15 developed a hybrid robust genetic algorithm (HRGA) based on Taguchi’s method and genetic algorithm. After the approach was validated by multi-objective welded beam design problems, it was applied to structural design optimization problem of an automobile component from industry. The immune algorithm is hybridized with a hillclimbing local search algorithm by Yildiz,16 and the hybrid approach is applied to multi-objective disc brake and manufacturing optimization problems from the literature.

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Yildiz18 developed a new hybrid particle swarm optimization approach to solve optimization problems in design and manufacturing areas by hybridizing the particle swarm algorithm with receptor editing property of immune system. Tsai et al.41 proposed a hybrid algorithm in which the Taguchi’s method is inserted between crossover and mutation operations of a genetic algorithm. The Taguchi method is incorporated in the crossover operations to select the better genes to achieve crossover and, consequently, enhance the performance of the genetic algorithm. It is known that the PSO algorithm is more efficient than genetic algorithm (GA) at exploring the solution space, but it does not guarantee the global optimum as in other evolutionary methods. The introduction of hybrid methods comes from the increasing need to tackle complex real-world problems. Some of the hybrid approaches in literature have been made on the hybrid particle swarm.20,42,43 Yildiz and Solanki20 developed a new hybrid optimization approach based on PSO and immune algorithm. The proposed approach is used for multi-objective optimization of vehicle crashworthiness. Fan et al.42 proposed a hybrid approach algorithm based on the Nelder–Mead simplex search method and PSO algorithm. The approach was applied to the optimization of multi-modal functions. Their results indicated that the proposed algorithm was better than hybrid GA, continuous GA, simulated annealing (SA) and tabu search in finding optimal solutions for multimodal functions. Xia and Wu43 proposed a hybrid approach based on the hybridization of the PSO and SA and they applied this to the multi-objective flexible job-shop scheduling problem as a case study. The proposed hybrid approach is applied to the design optimization of a vehicle component to illustrate how the present approach can be applied for solving structural design optimization problems.

given and, finally, the proposed hybrid approach is explained.

Particle swarm optimization algorithm The PSO algorithm was developed by Eberhart and Kennedy.24 It is a biologically inspired algorithm which models the social dynamics of bird flocking. A large number of birds flock synchronously, change direction suddenly, scatter and regroup iteratively, and finally perch on a target. This form of social intelligence not only increases the success rate for food foraging but also expedites the process. The PSO algorithm facilitates simple rules simulating bird flocking and serves as an optimizer for continuous non-linear functions. The general principles of the PSO algorithm are outlined as follows.

Hybrid particle swarm optimization algorithm for structural optimization In this paper, a new hybrid optimization approach, named HRPSO (hybrid robust particle swam optimization algorithm), is developed to solve structural design optimization problems. In the proposed optimizations approach, the refinement of the population space is introduced by Taguchi’s method. The bounds selected on the design variables are first used for the initial swarm, then they are applied throughout particle swarm algorithm for finding optimal design parameters. The aim is to overcome the limitations caused by larger population regarding computational cost and quality of solutions for global optimization. First, some brief explanations about the particle swarm optimization algorithm and Taguchi’s method are

Particle representation. The particle in the PSO is a candidate solution to the underlying problem and moves iteratively about the solution space. The particle is represented as a real-valued vector containing an instance of all parameters that characterize the optimization problem. We denote the ith particle by Pi = (Pi1 , Pi2 , . . . , pid )T 2 Rd where d is the number of parameters. Swarm. The PSO explores the solution space by flying a number of particles, called swarm. The initial swarm is generated at random and the size of swarm is usually kept constant through iterations. At each iteration, the swarm of particles search for target optimal solution by referring to previous experiences. Personal best experience and swarm’s best experience. The PSO enriches the swarm intelligence by storing the best positions visited so far by every particle. In particular, particle i remembers the best position among those it has visited, referred to as pbesti , and the best position by its neighbors. There are two versions for keeping the neighbors’ best position, namely lbest and gbest. In the local version, each particle keeps track of the best position lbest attained by its local neighboring particles. For the global version, the best position gbest is determined by any particles in the entire swarm. Hence, the gbest model is a special case of the lbest model. Particle movement. The PSO is an iterative algorithm according to which a swarm of particles fly about the solution space until the stopping criterion is satisfied. At each iteration, particle i adjusts its velocity vij and position pij through each dimension j by referring to, with random multipliers, the personal best position (pbestij ) and the swarm’s best position (lbestij , if the local version is adopted) using equations (1) and (2) as follows vij = vij + c1 r1 pbestij pij + c2 r2 lbestij pij

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ð1Þ

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Proc IMechE Part D: J Automobile Engineering 0(0) X S=N ratio = 10 log y2i =n

and pij = pij + vij

ð2Þ

where c1 and c2 are the cognitive coefficients and r1 and r2 are random real numbers drawn from U(0, 1). Thus, the particle flies toward pbest and lbest in a navigated way while still exploring new areas by the stochastic mechanism to escape from local optima. Clerc and Kennedy25 have pointed out that the use of a constriction factor is needed to insure convergence of the algorithm by replacing equation (2) with the following vij = K vij + c1 r1 pbestij pij + c2 r2 lbestij pij ð3Þ

and 2 K = pﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ 2 u u2 4u

ð4Þ

where u = c1 + c2 , u . 4. Typically, u is set to 4.1 and K is thus 0.729.

Stopping criterion. The PSO algorithm is terminated with a maximal number of iterations or the best particle position of the entire swarm cannot be improved further after a sufficiently large number of iterations.

Taguchi method The Taguchi method is a universal approach, which is widely used in robust design (Robinson et al.,38 Tsai et al.41 and Phadke45). There are three stages to achieve Taguchi’s objective: (1) concept design, (2) robust parameter design (RPD), and (3) tolerance design. The robust parameter design is used to determine the levels of factors and to minimize the sensitivity of noise. That is, a parameter setting should be determined with the intention that the product response has minimum variation while its mean is close to the desired target. Taguchi’s method is based on statistical and sensitivity analysis for determining the optimal setting of parameters to achieve robust performance. The responses at each parameter setting were treated as a measure that would be indicative of not only the mean of some quality characteristic, but also the variance of that characteristic. The mean and the variance would be combined into a single performance measure known as the S/N ratio. Taguchi classifies robust parameter design problems into different categories depending on the goal of the problem and for each category as follows. Smaller the better. For these kind of problems, the target value of y, that is, quality variable, is zero. In this situation, S/N ratio is defined as follows

ð5Þ

Larger the better. In this situation, the target value of y, that is, quality variable, is infinite and S/N ratio is defined as X S=N ratio = 10 log 1=y2i =n ð6Þ Nominal the best. For these kind of problems, the certain target value is given for y value. In this situation S/N ratio is defined as X ð7Þ S=N ratio = 10 log y2 =s2 Taguchi’s method uses an orthogonal array and analysis of mean to analyze the effects of parameters based on statistical analysis of experiments. To compare performances of parameters, the statistical test known as the analysis of variance (ANOVA) is used. Further details and technical merits about robust parameter design can be found in work by Phadke.45 Most of the structural design optimization problems in the automotive industry have usually uncontrollable variations in their design parameters with complex nature. There is a need to overcome the shortcomings due to the traditional optimization methods and also to further improve the strength of recent approaches to achieve better results for the real-world design problems. Therefore, in this research, an integrated approach to solve structural design optimization problem is proposed based on Taguchi’s parameter design and particle swarm optimization algorithm. The architecture of proposed hybrid approach is given in Figure 1. Taguchi’s robust parameter design is introduced to help to define robust initial population levels of design parameters and to reduce the effects of noise factors to achieve better initialize particle swarm optimization algorithm search. The problem with larger populations is that the particle swarm optimization algorithm may

Figure 1. Hybrid particle swarm optimization algorithm based multi-objective design optimization approach. ANOVA: analysis of variance; S/N: signal to noise.

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tend to converge and stick around certain solutions which may not be the best ones. This is handled with the help of robust parameter levels which are embedded into particle swarm optimization algorithm process as being initial population intervals. In other words, the design space is restricted and refined based on the effect of the various design variables on objective functions. The purpose of the ANOVA tables is to help differentiate the robust designs from the non-robust ones. Finally, optimum results of multi-objective problem are obtained by applying particle swarm optimization algorithm through cloning, mutation and receptor editing operations. The present approach is considered in two stages as follows: 1.

2.

Stage 1: Determine efficient solution space for structural design optimization variables using Taguchi’s method. Stage 2: Apply particle swarm optimization algorithm to find structural design variables.

In the first stage, Taguchi’s robust parameter design procedure is used to find the levels of variables for efficient search space as follows:

identify the objectives, constraints and design parameters; determine the settings of the design parameter levels; conduct the experiments using orthogonal array; compute S/N ratios and ANOVA analysis; find the optimal settings of design parameters.

The main issue of experimental analysis is the ANOVA analysis which is formed using S/N ratios for each of the objectives. According to the results of ANOVA, appropriate levels of design parameters are found, and then the initial search population of particle swarm optimization algorithm process is defined according to levels. Finally, optimum results of the optimization problem are obtained by applying particle swarm optimization algorithm process in two steps as follows:

define initial population set; use particle swarm operators to create the next generation; evaluate objective function and constraints; repeat the loop until the optimum solutions are found.

In this paper, a new hybrid approach is proposed to improve the performance of the particle swarm optimization algorithm. Our argument behind the proposed approach is that the strength of one algorithm can be used to improve the performance of another approach in the optimization process. The combination of

Taguchi’s method and particle swarm optimization algorithm results in a solution which leads to better parameter values for structural design optimization problems. The algorithm of proposed hybrid approach can be outlined as follows: BEGIN Step 1: Taguchi’s method Begin 1.a Choose convenient orthogonal array from Taguchi’s standard orthogonal arrays 1.b Define levels and intervals 1.c For i:=1 to NOE (number of experiments) do begin Compute objective function values end; 1.d Choose convenient S/N ratio type (smaller the best or larger the best or nominal the best) based on minimization or maximization of objective functions 1.e For i:=1 to NOE do begin Compute S/N ratios end; 1.f Constitute Anova table for objective functions using S/N ratios 1.g Determine optimum levels and intervals using percentage contribution to performance using Anova table Use these levels and intervals for forming initial population end; ‘Generate optimal solution set using particle swarm optimization algorithm and computed robust initial population space’ Begin Input Use Initial population found in previous part of the program as input to particle swarm optimization algorithm Step 2: Particle swarm algorithm 2.a Generate initial swarm population with random positions and velocities While maximum iterations or minimum error criteria is not attained for i:=1 to NOP (number of particles) do begin 2.b Calculate fitness value for each particle 2.c For each particle, If the fitness value is better than the best fitness value (lbest) in history set current value as the new lbest 2.d Determine the best fitness value of all the particles as the gbest 2.e Calculate velocity of every particle according to equation (1) 2.f For each particle Update position of every particle according to equation (3) end; END.

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Proc IMechE Part D: J Automobile Engineering 0(0) The bar bending stress (sx) is calculated from the following equation sðxÞ =

6PL x4 x23

ð17Þ

The bar buckling load is found from the following equation qﬃﬃﬃﬃﬃﬃﬃ rﬃﬃﬃﬃﬃﬃ x23 x64 4:013 E 36 x3 E Pc ðxÞ = (1 ) ð18Þ L2 2L 4G The bar displacement is computed using the following equation

Figure 2. Welded beam structure.

Evaluation of the proposed approach using test problem In this section, the results of a well-known welded beam optimization problem and discussions regarding the proposed approach are given through the test problem. A welded beam design optimization problem, which is often used for the evaluation of design optimization methods, is used to illustrate the implementation procedure of the proposed approach for solving optimization problems. Figure 2 shows design variables and structure of the welded beam. The objective function is to minimize the cost under the given loading conditions. The beam has a length of 14 in. and P=6000 lb force is applied at the end of the beam.46–49 The problem includes seven constraints. The design variables are thickness of the weld h(x1 ), length of the weld l(x2 ), width of the beam t(x3 ), and thickness of the beam b(x4 ): The mathematical model of the welded beam optimization problem is defined as Objective functions f1 ðxÞ = 1:10471x21 x2 + 0:04811x3 x4 ð14:0 + x2 Þ

ð8Þ

Constraints g1 ðxÞ = t max t(x)50

ð9Þ

g2 ðxÞ = smax s(x)50

ð10Þ

g3 ðxÞ = x4 x1 50

ð11Þ

g4 ðxÞ = Pc (x) P50

ð12Þ

g5 ðxÞ = dmax = d(x)50

ð13Þ

g6 ðxÞ = x1 0:12550

ð14Þ

g7 ðxÞ = 5 1:10471x21 x2 + 0:04811x3 x4 ð14:0 + x2 Þ50

ð15Þ

The weld stress t(x) has two components which are t9 and t99:t9 is the primary stress, whereas t99 is the secondary torsional stress ( ). t(x) is computed using the following equation rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ x2 2 2 + ðt 99 Þ t ðxÞ = ðt 9 Þ + t 99 :t 9 ð16Þ 2R

dðxÞ =

4PL3 EX33X4

ð19Þ

Step 1: Four design variables are used to define the objective and seven constraint functions. The design variables are h(x1 ), l(x2 ), t(x3 ) and b(x4 ). The objective is to minimize the cost f1 ðxÞ under the given loading conditions subject to constraints. The bending stress, buckling load, and weld stress are defined with notations as s(x), Pc ðxÞ and t(x). The values of loads and stresses are given as P = 6000 lb, t max = 13,600 psi, and smax = 30,000 psi. Step 2: In this step, experiments are designed to evaluate the effects of four design variables related to the objective function. The selection of an orthogonal array for a given problem depends on the number of factors and their levels. Taguchi has tabulated 18 basic orthogonal arrays, which are called standard orthogonal arrays. In most of the problems, one of the standard orthogonal arrays is considered to plan a matrix experiment. The suitable orthogonal array with regard to four design variables at four levels each is chosen as L16 . The equations for calculating S/N ratios for quality characteristics are logarithmic functions based on the mean square quality characteristics. In this problem, smaller the better characteristic is considered to compute S/N ratios based on the objectives as smaller the better for cost and deflections. Therefore, the responses for each experiment are computed using the following equation (see Table 1) X S=N ratio = 10 log( y2i =n) ð20Þ L16 orthogonal array is used to simulate the experiments. The levels and S/N ratios are tabulated for 16 experiments as shown in Table 1. The intervals of parameters for four levels are given as 0.125\x1 \5, 0.1\x2 \10, 0.1\x3 \10, 0.125\x4 \5. The ANOVA for objective is formed using S/N ratios as shown in Tables 2 and 3. Step 3: In the previous step, the experiments are designed to evaluate the effects of four design parameters with respect to objective function. In this step, the intervals of the design parameters are found using ANOVA regarding the effects of factors on the

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Table 1. S/N ratios of the welded beam design optimization problem. Exp. no.

X1

X2

X3

X4

S/N (Objective)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0.125 0.125 0.125 0.125 1.75 1.75 1.75 1.75 3.375 3.375 3.375 3.375 5 5 5 5

0.1 3.4 6.7 10 0.1 3.4 6.7 10 0.1 3.4 6.7 10 0.1 3.4 6.7 10

0.1 3.4 6.7 10 3.4 0.1 10 6.7 6.7 10 0.1 3.4 10 6.7 3.4 0.1

0.125 1.75 3.375 5 3.375 5 0.125 1.75 5 3.375 1.75 0.125 1.75 0.125 5 3.375

39.82 214.04 227.09 235.25 218.19 221.52 227.57 233.51 227.59 237.02 238.53 242.02 223.30 239.51 246.10 248.83

objective function. The effective parameters with respect to the objective are x2 and x1 with 39.2 and 35.5% contributions as shown in Tables 2 and 3 respectively. Therefore, the levels of 1 and 2 are considered as 0.125 (level 1) and 1.75 (level 2) for x1 and 0.1 (level 1) and 3.4 (level 2) for x2 , since the smaller the better category is applied for the objective function. The intervals for x1 and x2 are level 1\x1 \level 2 and level 1\x2 \level 2. The contributions for x3 and x4 are weak for the objective as 8.9 and 9.9%, respectively. Therefore, the predefined intervals are selected without any change as 0.125 and 10 (level 1\x3 \level 4) for x3 , 0.125 and 5 (level 1\x4 \level 4) for x4 . In summary, the parameter settings are found as 0.125\ x1 \1.75, 0.1\x2\ 3.4, 0.1\x3 \10, 0.125\ x4 \5 (level 1\x1 \level 2, level 1\x2 \level 2, level 1\ x3 \level 4, level 1\x4 \level 4) for the objective function. Step 4: The initial population of PSO algorithm is randomly generated for individuals within the range of the solution space bounded by 0.125\x1 \1.75, 0.1\x2 \3.4, 0.1\x3 \10, 0.125\x4 \5 (level 1\ x1 \level 2, level 1\x2 \level 2, level 4 for x3 , level 1\x4 \level 4). Steps 5–7: From steps 5 to 7, HRPSO searches for the optimal solutions using the refined population range obtained in the previous step. The PSO operators are then applied to compute the optimal values. The parameters used by the proposed hybrid approach for optimization process are the following:

(a) number of individuals: 50; (b) maximum number of generations: 500; (c) number of objective function evaluations: 25,000. The best solutions obtained by the above mentioned approaches are listed in Tables 2 and 3, and their statistical simulation results are given in Table 4 for welded beam design problem. When considering the number of function evaluations, the best solution computed and the statistical analysis results are taken into account together, it is concluded that HRPSO provided better solutions for this problem among the other results46–51 given in Tables 2, 3 and 4. The worst solution found by HRPSO is better than the best solutions found by Siddall46 and Ragsdell and Phillips.47 The use of the HRPSO improves the convergence rate by computing the best value 1.72485 with the smallest function evaluation 25,000 and standard deviation values. As can be seen from Table 4, HRPSO gives the best results reported in the literature for welded beam design problem.

Structural design optimization using improved hybrid particle swarm algorithm The hybrid approach proposed in the third section is applied to solve a structural design optimization problem taken from automotive industry for the optimal design of an automobile component in this section. The objective functions are due to the volume and the frequency of the part which is to be designed for minimum volume and avoiding critical frequency subject to strength constraints. In this research, then structural optimization is performed using the present approach. In the first stage, the experiments are designed to evaluate the effects of four design variables related to objective functions. The four design variables X1, X2, X3 and X4 are selected as shown in Figure 3. The feasible range of design variables without shape distortions is considered as 90\X1\150, 185\X2\ 230, 10\X3\25 and 30\X4\45. Matrix experiments are designed using L16 orthogonal arrays and S/N ratios are conducted for each objective as given in Table 5. Smaller the better and larger the better characteristics are applied to compute S/N ratios based on each objective as smaller the better for volume and larger the better for frequency.

Table 2. ANOVA of the objective function for the welded beam problem.

X1 X2 X3 X4

Level 1

Level 2

Level 3

Level 4

Ss

% Contribute

29.14 27.31 217.26 217.32

225.20 229.67 230.09 227.34

236.29 234.82 231.93 232.78

239.44 239.90 230.79 232.62

2248.99 2478.34 567.47 631.07

35.58 39.21 8.98 9.98

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Table 3. Comparison of the best solution welded beam design problem by different methods. Design variables

HRPSO

Akay and Karabog˘a51

Huang et al.50

He and Wang49

Coello and Montes48

Ragsdell and Phillips47

Siddall46

x1 x2 x3 x4 g1(x) g2(x) g3(x) g4(x) g5(x) g6(x) g7(x) f(x)

0.205730 3.470489 9.036624 0.205730 0.000000 20.000002 0.000000 23.432984 20.080730 20.235540 0.000000 1.724852

N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 1.724852

0.203137 3.542998 9.033498 0.206179 244.57856 244.66353 20.003042 23.423726 20.078137 20.235557 238.02826 1.733462

0.202369 3.544214 9.048210 0.205723 212.83979 21.247467 20.001498 23.429347 20.079381 20.235536 211.68135 1.728024

0.205986 3.471328 9.020224 0.206480 20.074092 20.266227 20.000495 23.430043 20.080986 20.235514 258.6664 1.72822

0.245500 6.19600 6.19600 0.24550 25743.82 24.71509 0.00000 23.02028 20.12050 20.23420 23604.275 2.385937

0.2444 6.2189 8.2915 0.2444 25743.50 24.01520 0.00000 23490.46 20.23424 20.11940 23.02256 2.38154

Table 4. Statistical results of different methods for welded beam problem. Design variables

Best

Mean

Worst

Standard deviation

Function evaluations

HRPSO Akay and Karaboga et al.51 Huang et al.50 He and Wang49 Coello and Montes48 Ragstell and Phillips47 Siddall46

1.724852 1.724852 1.733461 1.728024 1.728226 2.3859373 2.3815433

1.73418 1.741913 1.768158 1.748831 1.7926 N/A N/A

1.75322 2 1.824105 1.782143 1.99340 N/A N/A

0.00051 0.03100 0.022194 0.012926 0.074713 N/A N/A

25,000 30,000 240,000 200,000 80,000 N/A N/A

Figure 3. Design variables. Table 5. Experimental results and S/N ratios for volume and frequency. Exp. no.

X1 (mm)

X2 (mm)

X3 (mm)

X4 (mm)

F1 (Volume)

F2 (Frequency)

S/N1 Volume

S/N2 Frequency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

90 90 90 90 110 110 110 110 130 130 130 130 150 150 150 150

185 200 215 230 185 200 215 230 185 200 215 230 185 200 215 230

10 15 20 25 15 10 20 25 20 25 10 15 25 20 15 10

30 35 40 45 40 45 30 35 45 40 35 30 35 30 45 40

98,815.7 125,002.7 157,199.9 195,402.7 108,202.7 97,419.2 143,602.7 177,798.1 109,602.7 133,800.7 96,017.3 120,210 102,998.8 106,200.7 103,399.8 94,617.3

6.9 8.4 9.3 9.2 6.5 6.1 6.3 6.5 4.9 4.7 4.4 4.5 3.4 3.4 3.5 3.4

299.89 2101.93 2103.92 2105.81 2100.68 299.77 2103.14 2104.99 2100.79 2102.52 299.64 2101.59 2100.25 2100.52 2100.29 299.51

16.77 18.51 19.41 19.34 16.3 15.69 16.05 16.33 13.88 13.62 12.99 13.2 10.84 10.83 11.11 10.83

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Table 6. Results of the analysis of variance for volume.

X1 X2 X3 X4 Error Total

Level 1

Level 2

Level 3

Level 4

S

DOF

M

F

Cont. (%)

2102.89 2100.4 299.71 2101.29

2102.15 2101.19 2101.12 2101.71

2101.14 2101.75 2102.09 2101.66

2100.14 2102.98 2103.4 2101.67

17.19 11.82 26.66 0.11 0.24 56.05

3 3 3 3 3 15

5.73 3.94 8.88 0.03 0.08

69.98 48.10 108.5 0.47

30.6 21.1 47.5 0.2 2.4 100

Table 7. Results of the analysis of variance for frequency.

X1 X2 X3 X4 Error Total

Level 1

Level 2

Level 3

Level 4

S

DOF

M

F

Cont. (%)

18.51 14.45 14.07 14.21

16.09 14.66 14.78 14.67

13.42 14.89 15.04 15.04

10.9 14.92 15.03 15.01

129.9 0.69 2.75 2.02 0.2 135.5

3 3 3 3 3 15

43.3 0.23 0.91 0.67 0.06

650.8 3.5 13.8 10.1

95.81 0.515 2.033 1.491 0.151 100

Figure 4. The optimal structural layout.

ANOVA for each objective is formed using S/N ratios for the first and second objective functions as shown in Tables 6 and 7. The optimal settings for X1, X2, X3 and X4 variables are computed as X1=90, 185\X2\230, 10\X3\20 and X4=30. Then, the problem is solved using particle swarm optimization algorithm. The parameters used by the proposed hybrid approach for optimization process are the following: (a) number of individuals: 30; (b) maximum number of generations: 80; (c) number of objective function evaluations: 2400.

In the present approach, PSO algorithm begins its search with a set of solutions for which its population range is defined by Taguchi’s method as given above. The structural layout results of the present approach using PSO algorithm and robust design based on Taguchi’s method for the design of vehicle part is given in Figure 4. The results of present hybrid approach for the design of vehicle part are given in Table 8. The numbers of function evaluations are also listed for each approach in Table 6. The HRPSO has the smallest function evaluation number. It is seen that shape design optimization performance is improved compared to other approaches.

Conclusions This research describes a new design optimization strategy based on particle swarm optimization algorithm and Taguchi’s parameter design to develop an innovative design optimization approach for solving structural design optimization problems. Taguchi’s robust parameter design is introduced to help to define robust initial population levels of design parameters to achieve better initialize particle swarm optimization algorithm

Table 8. Comparison of the design optimization results for vehicle component.

Topology design CAD optimum design Genetic algorithm PSO algorithm Hybrid PSO approach

X1 (mm)

X2 (mm)

X3 (mm)

X4 (mm)

Volume (cm3)

Frequency (Hertz)

Stress (MPa)

Function evaluations

110 130.8 98.9 98.9 90

190 200.5 188.6 188.6 185

17 15 11 11 10.1

32 40.3 36 36 30

117,001 107,973 101,223 95,823 87,685

6.3 4.6 6.8 7.2 8.6

280.8 286.6 271.2 283.2 297.3

2 50,000 10,000 4500 2400

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search. The design solution space of particle swarm optimization algorithm is refined based on the effect of the various design variables on objective functions. The proposed approach is applied to a vehicle component taken from the automotive industry. It is seen that better results can be achieved with the present hybrid approach. Funding This research received no specific grant form any funding agency in the public, commercial, or not-for-profit sectors. References 1. Yildiz AR. A new design optimization framework based on immune algorithm and Taguchi’s method. Comput Ind 2009; 60(8): 613–620. 2. Yildiz AR and Saitou K. Topology synthesis of multicomponent structural assemblies in continuum domains. Trans ASME J Mech Des 2011; 133: 011008-1–011008-9. 3. Bureerat S and Limtragool J. Performance enhancement of evolutionary search for structural topology optimisation. Finite Elem Analysis Des 2006; 42(6): 547–566. 4. Bureerat S and Srisomporn S. Optimum plate-fin heat sinks by using a multi-objective evolutionary algorithm. Engng Optimization 2010; 42(4): 305–323. 5. Durgun I and Yildiz AR. Structural design optimization of vehicle components using cuckoo search algorithm. Mater Testing 2012; 3: 185–188. 6. Fourie PC and Groenwold AA. The particle swarm optimization algorithm in size and shape optimization. Struct Multidisciplinary Optimization 2002; 23: 259–267. 7. Yildiz AR. Hybrid immune-simulated annealing algorithm for optimal design and manufacturing. Int J Mater Product Technol 2009; 34: 217–226. 8. Luh GC and Chueh CH. Multi-objective optimal design of truss structure with immune algorithm. Comput Structs 2004; 82: 829–844. 9. Lyu N and Saitou K. Topology optimization of multicomponent structures via decomposition-based assembly synthesis. Trans ASME J Mech Des 2005; 127: 170–183. 10. Yildiz AR. A new design optimization framework based on immune algorithm and Taguchi method. Comput Ind 2009; 60; 613–620. 11. Saka MP. Optimum geometry design of geodesic domes using harmony search algorithm. Adv Struct Engng 2008; 10: 595–606. 12. Yildiz AR. Optimal structural design of vehicle components using topology design and optimization. Mater Testing 2008; 50; 224–228. 13. Woon SY, Querin OM and Steven GP. Structural application of a shape optimization method based on a genetic algorithm. Struct Multidisciplinary Optimization 2001; 22: 57–64. 14. Luh GC and Chueh CH. Multi-modal topological optimization of structure using immune algorithm. Comput Methods Appl Mech Engng 2004; 193: 4035–4055. 15. Yildiz AR, Ozturk N, Kaya N and Ozturk F. Hybrid multi-objective shape design optimization using Taguchi’s method and genetic algorithm. Struct Multidisciplinary Optimization 2007; 34: 277–365.

16. Yildiz AR. An effective hybrid immune-hill climbing optimization approach for solving design and manufacturing optimization problems in industry. J Mater Process Technol 2009; 209: 2773–2780. 17. Yildiz AR and Ozturk F. Hybrid enhanced genetic algorithm to select optimal machining parameters in turning operation. Proc IMechE Part B: J Engineering Manufacture 2006; 220: 2041–2053. 18. Yildiz AR. A novel particle swarm optimization approach for product design and manufacturing. Int J Adv Mfg Technol 2009; 40: 617–628. 19. Yildiz AR. A novel hybrid immune algorithm for global optimization in design and manufacturing. Robotics and Computer Integrated Mfg 2009; 25: 261–270. 20. Yildiz AR and Solanki KN. Multi-objective optimization of vehicle crashworthiness using a new particle swarm based approach. Int J Adv Mfg Technol 2012; 40: 617– 628. 21. Yildiz AR. Hybrid Taguchi-differential evolution algorithm for optimization of multi-pass turning operations. Appl Soft Comput. Epub ahead of print 31 January 2012. DOi:10.1016/j.asoc.2012.01.012. 22. Yildiz AR, Kaya N, Alankus OB and Ozturk F. Optimal design of vehicle components using topology design and optimization. Int J Veh Des 2004; 34: 387–398. 23. Yildiz AR. A new hybrid differential evolution algorithm for the selection of optimal machining parameters in milling operations. Appl Soft Comput 2012 (in press). 24. Eberhart R and Kennedy J. A new optimizer using particle swarm theory. In: IEEE sixth international symposium on micro machine human science, 1995. 25. Clerc M and Kennedy J. The particle swarm explosion, stability, and convergence in a multidimensional complex space. IEEE Trans Evolut Comput 2002; 6; 58–73. 26. Perez RE and Behdinan K. Particle swarm approach for structural design optimization. Comput Structs 2007; 85: 1579–1588. 27. Haq AN, Sivakumar K, Saravanan R and Karthikeyan K. Particle swarm optimization algorithm for optimal machining allocation of clutch assembly. Int J Advd Mfg Technol 2006; 27: 865–869. 28. Bochenek B and Forys P. Structural optimization for post-buckling behaviour using particle swarms. Struct Multidisciplinary Optimization 2006; 32: 521–531. 29. Natarajan U, Saravanan R and Periasamy VM. Application of particle swarm optimisation in artificial neural network for the prediction of tool life. Int J Advd Mfg Technol 2006; 28: 1084–1088. 30. Tandon V, El-Mounayri H and Kishawy H. NC end milling optimization using evolutionary computation. Int J Machine Tools Mf 2002; 42: 595 605. 31. Vahed ARR and Mirghorbani SM. A multi-objective particle swarm for a flow shop scheduling problem. J Combinatorial Opt 2007; 13: 79–102. 32. Venter G and Sobieszczanski-Sobieski J. Multidisciplinary optimization of a transport aircraft wing using particle swarm optimization. Struct Multidisciplinary Optimization 2004; 26: 121–131. 33. Khoei AR, Masters I and Gethin DT. Design optimization of aluminium recycling processes using Taguchi technique. J Mater Process Technol 2002; 127: 96–106. 34. Chen SX, Low TS and Leow B. Design optimization of a nonlinear magnetic media system using finite element

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analysis and Taguchi method. Int J Comput Math Elect Electron Engng 2002; 21: 2223–2234. Lee KH, Shin JK, Song SI, Yoo YM and Park GJ. Automotive door design using structural optimization and design of experiments. Proc IMechE Part D: J. Automobile Engineering 2003; 217: 855–865. Nair VN. Taguchi’s parameter design: a panel discussion. Technometrics 1992; 34: 127–161. Wu FC and Wu CC. Optimization of robust design for multiple quality characteristics. Int J Prod Res 2004; 42: 337–354. Robinson TJ, Borror CM and Myers RH. Robust parameter design: a review. Qual Reliab Engng Int 2004; 20: 81–101. Kunjur A and Krishnamurty S. A robust multi-criteria optimization approach. Mech Mach Theory 1997; 32: 797–810. Box G. Signal-to-noise ratios, performance criteria, and transformations. Technometrics 1998; 1: 1–17. Tsai JT, Liu TK and Chou JH. Hybrid Taguchi genetic algorithm for global numerical optimization. IEEE Trans Evolutionary Comput 2004; 84: 365–377. Fan SSK, Liang YC and Zahara E. Hybrid simplex search particle swarm optimization for the global optimization of multimodal functions. Engng Optimization 2004; 36: 401–418. Xia WJ and Wu ZM. A hybrid particle swarm optimization approach for the job-shop scheduling problem. Int J Advd Mfg Technol 2006; 29: 360–366. Deb K. Multiobjective optimization using evolutionary algorithms. Chichester: John Wiley, 2001. Phadke SM. Introduction to quality engineering. Asian Productivity Organization, 1989. Siddall JN. Analytical design-making in engineering design. Prentice-Hall, 1972. Ragsdell KM and Phillips DT. Optimal design of a class of welded structures using geometric programming. ASME J Engng Ind 1976; 98: 1021–1025. Coello CAC and Montes EF. Constraint-handling in genetic algorithms through the use of dominance-based tournament selection. Adv Engng Inf 2002; 16: 193–203. He Q and Wang L. An effective co-evolutionary particle swarm optimization for constrained engineering design problems. Engng Applic Artif Intell 2007; 20: 89–99. Huang FZ, Wang L and He Q. An effective coevolutionary differential evolution for constrained optimization. Appl Math Comput 2007; 186; 340–356. Akay B and Karaboga D. Artificial bee colony algorithm for large-scale problems and engineering design optimization. J Intell Mfg 2010. DOI: 10.1007/s10845-010-0393-4.

Appendix Analysis of variance (ANOVA) ANOVA is a standard statistical technique to interpret the experimental results. The percentage contribution

of various process parameters to the selected performance characteristic can be estimated by ANOVA. Thus information about how significant the effect of each controlled parameter is on the quality characteristic of interest can be obtained. ANOVAs for raw data have been performed to identify the significant parameters and to quantify their effect on the objective function. The ANOVA based on the raw data identifies the factors which affect the average response rather than reducing variation. In ANOVA, total sum of squares (SST ) is calculated by SST =

XN i=1

2 (Yi Y)

ð21Þ

where N is the number of experiments in the orthogonal array, N=9, Yi is the experimental result for the ith experiment and Y is given by 1 XN Y = Y i=1 i N

ð22Þ

The total sum of the squared deviations SST is decomposed into two sources: the sum of the squared deviations SSP due to each process parameter and the sum of the squared error SSe : SSP can be calculated as SSP =

i2 (SYj )2 1 hXN Y i j=1 i=1 N t

Xt

ð23Þ

where p represent one of the experiment parameters, j the level number of this parameter p, t the repetition of each level of the parameter p, SYj the sum of the experimental results involving this parameter p and level j. The sum of squares from error parameters SSe is SSe = SST SSA SSB SSC

ð24Þ

The total degrees of freedom is DT = N 1, and the degrees of freedom of each tested parameter is DP = t 1. The variance of the parameter tested is Vp = SSp =Dp . Then, the F-value for each design parameter is simply the ratio of the mean of squares deviations to the mean of the squared error (Fp = Vp =Ve ). The percentage contribution r can be calculated as rP =

SSP SST

ð25Þ

Table 9 shows experimental results for L9 orthogonal array. Table 10 shows the results of ANOVA for the objective function. It can be seen from Table 10 that X2 and X3 are the most significant parameters for the objective function.

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Table 9. Experimental results. Exp. no.

X1

X2

X3

Obj. function

1 2 3 4 5 6 7 8 9

850 850 850 900 900 900 950 950 950

120 250 500 120 250 500 120 250 500

4.00 4.08 4.17 4.08 4.17 4.00 4.17 4.00 4.08

0.585 0.627 0.598 0.585 0.685 0.530 0.585 0.555 0.576

Table 10. Results of the analysis of variance for the objective function. Source

DOF

Sum of squares

Mean square

Contribution (%)

X1 X2 X3 Error Total

2 2 2 2 8

0.00176 0.00463 0.00663 0.00251 0.01553

0.00088 0.00231 0.00331 0.00126

11.35 29.79 42.68 16.18 100

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A new hybrid particle swarm optimization approach for structural design optimization in the automotive industry Ali R Yildiz Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering published online 23 May 2012 DOI: 10.1177/0954407012443636 The online version of this article can be found at: http://pid.sagepub.com/content/early/2012/05/22/0954407012443636 A more recent version of this article was published on - Sep 14, 2012

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Original Article

A new hybrid particle swarm optimization approach for structural design optimization in the automotive industry

Proc IMechE Part D: J Automobile Engineering 0(0) 1–12 Ó IMechE 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0954407012443636 pid.sagepub.com

Ali R Yildiz

Abstract This paper presents an innovative optimization approach to solve structural design optimization problems in the automotive industry. The new approach is based on Taguchi’s robust design approach and particle swarm optimization algorithm. The proposed approach is applied to the structural design optimization of a vehicle part to illustrate how the present approach can be applied for solving design optimization problems. The results show the ability of the proposed approach to find better optimal solutions for structural design optimization problems.

Keywords Structural design optimization, particle swarm optimization, Taguchi’s method, robust design

Date received: 13 October 2011; accepted: 6 March 2012

Introduction The optimal design of structures includes sizing, shape and topology optimization. There has been extensive research focused on shape optimization due to its great contribution to cost, material and time savings in the procedures of the engineering design. The purpose of shape optimization is to determine the optimal shape of a continuum medium to maximize or minimize a given criterion (often called an objective function), such as minimize the weight of the body, maximize the stiffness of the structure or remove the stress concentrations, subjected to the stress or displacement constraint conditions. Computer-aided optimization has been commonly used to obtain more economical designs. Numerous algorithms have been developed to solve structural design optimization problems in the last four decades. The early works on this topic mostly use various mathematical techniques. These methods are not only time consuming in solving complex nature problems, but also they may not be used efficiently for finding global or near global optimum solutions. In the past few decades, a number of innovative approaches, such as tabu search, genetic algorithm, simulated annealing, particle swarm optimization algorithm, ant colony algorithm and immune algorithm, have been developed and widely applied in various fields of science.1–13

Fast convergence speed and robustness in finding the global minimum are not easily achieved at the same time. Fast convergence requires a minimum number of calculations, increasing the probability of missing important points; on the other hand, the evaluation of more points for finding the global minimum decreases the convergence speed. This leads to the question: ‘how to obtain both fast convergence speed and global search capability at the same time?’ There have been a number of attempts to answer this question, while hybrid algorithms have shown outstanding reliability and efficiency in application to the engineering optimization problems.14–20 Therefore, researchers are paying great attention to hybrid approaches in order to answer this question, particularly to avoid premature convergence towards a local minimum and to reach the global optimum results. There is an increasing interest in applying the new approaches and in further improving the performance of optimization techniques for the solution of structural design optimization problems. Although Department of Mechanical Engineering, Bursa Technical University, Bursa, Turkey Corresponding author: Ali R Yildiz, Department of Mechanical Engineering, Bursa Technical University, Bursa, Turkey. Email: [email protected]

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some improvements regarding structural design optimization issues are achieved, the complexity of design problems presents shortcomings. The main goal of the present research is to develop an effective approach to solve real-world design optimization problems. A new hybrid approach based on robustness issues is used to help better initialize particle swarm optimization algorithm search. The aim has been to reach optimum designs by using Taguchi’s robust parameter design approach coupled with particle swarm optimization algorithm. In this new hybrid approach, signal-to-noise (S/N) values are calculated and ANOVA (analysis of variance) tables for each of the objectives are formed using S/N ratios, respectively. According to results of ANOVA tables, appropriate interval levels of design parameters are found, and then initial search population of the particle swarm optimization algorithm process is defined according to these interval levels. Optimum results of the design problem are then obtained using particle swarm optimization algorithm. The developed new hybrid optimization approach is applied to a vehicle part design optimization problem taken from the automotive industry to demonstrate the application of the present approach to real-world design problems. The results of the proposed approach show that the proposed optimization method converges rapidly to the global optimum solution and provides reliable and accurate solutions. The organization of the paper is as follows. The third section presents a detailed review on optimization approaches. The particle swarm optimization (PSO), Taguchi’s method and the proposed hybrid approach are presented in the third section. A case study from automobile industry is solved in the fourth section. The paper is concluded in the fifth section.

Literature review Recently, new approaches in the area of optimization research are presented to further improve the solution of optimization problems with complex nature. Over the past few years, studies on evolutionary algorithms have shown that these methods can be efficiently used to eliminate most of the difficulties of classical methods. Evolutionary algorithms are widely used to solve engineering optimization problems with complex nature. Various research works have been carried out to enhance the performance of evolutionary algorithm.1–23 For instance, Yildiz and Saitou2 developed a novel approach for multi-component topology optimization of continuum structures using a multi-objective genetic algorithm to obtain Pareto optimal solutions that exhibits trade-offs among stiffness, weight, manufacturability and assemble ability. Yildiz and Saitou2 present a method for synthesizing structural assemblies directly from the design specifications without going through the two-step process. Given an extended design domain

with boundary and loading conditions, the method simultaneously optimizes the topology and geometry of an entire structure and the location and configuration of joints considering structural performance, manufacturability and assemble ability. The developed approach is applied to multi-component topology optimization of a vehicle floor frame. The PSO algorithm originally developed by Eberhart and Kennedy24 is inspired with social behavior, such as bird flocking or fish schooling, which is used successfully in the solution of optimization problems. The PSO algorithm has been used in many areas of optimization studies. The use of PSO algorithms in the optimum solution of problems resulted in better solutions compared to classical methods.6,25–32 The PSO algorithm was applied to the shape optimization of a torque arm and to the size optimization of truss structures taken from literature by Fourie and Groenwold.6 In their PSO algorithm, the concept of craziness is redefined and elitism operator borrowed by GA was used. Their results showed that PSO algorithms were better than GA and the gradient-based recursive quadratic programming algorithm. Perez and Behdinan26 proposed a particle swarm approach for structural design optimization. The effectiveness of the improved PSO algorithm on structural optimization is shown through the use of four classical truss optimization examples. Results from the three tested cases using an improved PSO illustrate the ability of the algorithm to find optimal results which are better than, or at the same level of, other structural optimization methods. Venter and Sobieszczanski-Sobieski32 used PSO algorithm for multidisciplinary optimization of a transport aircraft wing. Some researchers have used the robustness issues to solve optimization problems.33–37 Robinson et al.38 present a review paper which focuses largely on the work done since 1992 and a historical perspective of parameter design is also given. Kunjur and Krishnamurty39 presented a robust optimization approach that integrates optimization concepts with statistical robust design techniques. Although Taguchi’s methods have been successfully applied to processes in the design and manufacturing, they are also criticized for their efficiency.36,40 Hybrid methods are also used to enhance the performance of evolutionary algorithm. Yildiz et al.15 developed a hybrid robust genetic algorithm (HRGA) based on Taguchi’s method and genetic algorithm. After the approach was validated by multi-objective welded beam design problems, it was applied to structural design optimization problem of an automobile component from industry. The immune algorithm is hybridized with a hillclimbing local search algorithm by Yildiz,16 and the hybrid approach is applied to multi-objective disc brake and manufacturing optimization problems from the literature.

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Yildiz18 developed a new hybrid particle swarm optimization approach to solve optimization problems in design and manufacturing areas by hybridizing the particle swarm algorithm with receptor editing property of immune system. Tsai et al.41 proposed a hybrid algorithm in which the Taguchi’s method is inserted between crossover and mutation operations of a genetic algorithm. The Taguchi method is incorporated in the crossover operations to select the better genes to achieve crossover and, consequently, enhance the performance of the genetic algorithm. It is known that the PSO algorithm is more efficient than genetic algorithm (GA) at exploring the solution space, but it does not guarantee the global optimum as in other evolutionary methods. The introduction of hybrid methods comes from the increasing need to tackle complex real-world problems. Some of the hybrid approaches in literature have been made on the hybrid particle swarm.20,42,43 Yildiz and Solanki20 developed a new hybrid optimization approach based on PSO and immune algorithm. The proposed approach is used for multi-objective optimization of vehicle crashworthiness. Fan et al.42 proposed a hybrid approach algorithm based on the Nelder–Mead simplex search method and PSO algorithm. The approach was applied to the optimization of multi-modal functions. Their results indicated that the proposed algorithm was better than hybrid GA, continuous GA, simulated annealing (SA) and tabu search in finding optimal solutions for multimodal functions. Xia and Wu43 proposed a hybrid approach based on the hybridization of the PSO and SA and they applied this to the multi-objective flexible job-shop scheduling problem as a case study. The proposed hybrid approach is applied to the design optimization of a vehicle component to illustrate how the present approach can be applied for solving structural design optimization problems.

given and, finally, the proposed hybrid approach is explained.

Particle swarm optimization algorithm The PSO algorithm was developed by Eberhart and Kennedy.24 It is a biologically inspired algorithm which models the social dynamics of bird flocking. A large number of birds flock synchronously, change direction suddenly, scatter and regroup iteratively, and finally perch on a target. This form of social intelligence not only increases the success rate for food foraging but also expedites the process. The PSO algorithm facilitates simple rules simulating bird flocking and serves as an optimizer for continuous non-linear functions. The general principles of the PSO algorithm are outlined as follows.

Hybrid particle swarm optimization algorithm for structural optimization In this paper, a new hybrid optimization approach, named HRPSO (hybrid robust particle swam optimization algorithm), is developed to solve structural design optimization problems. In the proposed optimizations approach, the refinement of the population space is introduced by Taguchi’s method. The bounds selected on the design variables are first used for the initial swarm, then they are applied throughout particle swarm algorithm for finding optimal design parameters. The aim is to overcome the limitations caused by larger population regarding computational cost and quality of solutions for global optimization. First, some brief explanations about the particle swarm optimization algorithm and Taguchi’s method are

Particle representation. The particle in the PSO is a candidate solution to the underlying problem and moves iteratively about the solution space. The particle is represented as a real-valued vector containing an instance of all parameters that characterize the optimization problem. We denote the ith particle by Pi = (Pi1 , Pi2 , . . . , pid )T 2 Rd where d is the number of parameters. Swarm. The PSO explores the solution space by flying a number of particles, called swarm. The initial swarm is generated at random and the size of swarm is usually kept constant through iterations. At each iteration, the swarm of particles search for target optimal solution by referring to previous experiences. Personal best experience and swarm’s best experience. The PSO enriches the swarm intelligence by storing the best positions visited so far by every particle. In particular, particle i remembers the best position among those it has visited, referred to as pbesti , and the best position by its neighbors. There are two versions for keeping the neighbors’ best position, namely lbest and gbest. In the local version, each particle keeps track of the best position lbest attained by its local neighboring particles. For the global version, the best position gbest is determined by any particles in the entire swarm. Hence, the gbest model is a special case of the lbest model. Particle movement. The PSO is an iterative algorithm according to which a swarm of particles fly about the solution space until the stopping criterion is satisfied. At each iteration, particle i adjusts its velocity vij and position pij through each dimension j by referring to, with random multipliers, the personal best position (pbestij ) and the swarm’s best position (lbestij , if the local version is adopted) using equations (1) and (2) as follows vij = vij + c1 r1 pbestij pij + c2 r2 lbestij pij

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ð1Þ

4

Proc IMechE Part D: J Automobile Engineering 0(0) X S=N ratio = 10 log y2i =n

and pij = pij + vij

ð2Þ

where c1 and c2 are the cognitive coefficients and r1 and r2 are random real numbers drawn from U(0, 1). Thus, the particle flies toward pbest and lbest in a navigated way while still exploring new areas by the stochastic mechanism to escape from local optima. Clerc and Kennedy25 have pointed out that the use of a constriction factor is needed to insure convergence of the algorithm by replacing equation (2) with the following vij = K vij + c1 r1 pbestij pij + c2 r2 lbestij pij ð3Þ

and 2 K = pﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ 2 u u2 4u

ð4Þ

where u = c1 + c2 , u . 4. Typically, u is set to 4.1 and K is thus 0.729.

Stopping criterion. The PSO algorithm is terminated with a maximal number of iterations or the best particle position of the entire swarm cannot be improved further after a sufficiently large number of iterations.

Taguchi method The Taguchi method is a universal approach, which is widely used in robust design (Robinson et al.,38 Tsai et al.41 and Phadke45). There are three stages to achieve Taguchi’s objective: (1) concept design, (2) robust parameter design (RPD), and (3) tolerance design. The robust parameter design is used to determine the levels of factors and to minimize the sensitivity of noise. That is, a parameter setting should be determined with the intention that the product response has minimum variation while its mean is close to the desired target. Taguchi’s method is based on statistical and sensitivity analysis for determining the optimal setting of parameters to achieve robust performance. The responses at each parameter setting were treated as a measure that would be indicative of not only the mean of some quality characteristic, but also the variance of that characteristic. The mean and the variance would be combined into a single performance measure known as the S/N ratio. Taguchi classifies robust parameter design problems into different categories depending on the goal of the problem and for each category as follows. Smaller the better. For these kind of problems, the target value of y, that is, quality variable, is zero. In this situation, S/N ratio is defined as follows

ð5Þ

Larger the better. In this situation, the target value of y, that is, quality variable, is infinite and S/N ratio is defined as X S=N ratio = 10 log 1=y2i =n ð6Þ Nominal the best. For these kind of problems, the certain target value is given for y value. In this situation S/N ratio is defined as X ð7Þ S=N ratio = 10 log y2 =s2 Taguchi’s method uses an orthogonal array and analysis of mean to analyze the effects of parameters based on statistical analysis of experiments. To compare performances of parameters, the statistical test known as the analysis of variance (ANOVA) is used. Further details and technical merits about robust parameter design can be found in work by Phadke.45 Most of the structural design optimization problems in the automotive industry have usually uncontrollable variations in their design parameters with complex nature. There is a need to overcome the shortcomings due to the traditional optimization methods and also to further improve the strength of recent approaches to achieve better results for the real-world design problems. Therefore, in this research, an integrated approach to solve structural design optimization problem is proposed based on Taguchi’s parameter design and particle swarm optimization algorithm. The architecture of proposed hybrid approach is given in Figure 1. Taguchi’s robust parameter design is introduced to help to define robust initial population levels of design parameters and to reduce the effects of noise factors to achieve better initialize particle swarm optimization algorithm search. The problem with larger populations is that the particle swarm optimization algorithm may

Figure 1. Hybrid particle swarm optimization algorithm based multi-objective design optimization approach. ANOVA: analysis of variance; S/N: signal to noise.

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tend to converge and stick around certain solutions which may not be the best ones. This is handled with the help of robust parameter levels which are embedded into particle swarm optimization algorithm process as being initial population intervals. In other words, the design space is restricted and refined based on the effect of the various design variables on objective functions. The purpose of the ANOVA tables is to help differentiate the robust designs from the non-robust ones. Finally, optimum results of multi-objective problem are obtained by applying particle swarm optimization algorithm through cloning, mutation and receptor editing operations. The present approach is considered in two stages as follows: 1.

2.

Stage 1: Determine efficient solution space for structural design optimization variables using Taguchi’s method. Stage 2: Apply particle swarm optimization algorithm to find structural design variables.

In the first stage, Taguchi’s robust parameter design procedure is used to find the levels of variables for efficient search space as follows:

identify the objectives, constraints and design parameters; determine the settings of the design parameter levels; conduct the experiments using orthogonal array; compute S/N ratios and ANOVA analysis; find the optimal settings of design parameters.

The main issue of experimental analysis is the ANOVA analysis which is formed using S/N ratios for each of the objectives. According to the results of ANOVA, appropriate levels of design parameters are found, and then the initial search population of particle swarm optimization algorithm process is defined according to levels. Finally, optimum results of the optimization problem are obtained by applying particle swarm optimization algorithm process in two steps as follows:

define initial population set; use particle swarm operators to create the next generation; evaluate objective function and constraints; repeat the loop until the optimum solutions are found.

In this paper, a new hybrid approach is proposed to improve the performance of the particle swarm optimization algorithm. Our argument behind the proposed approach is that the strength of one algorithm can be used to improve the performance of another approach in the optimization process. The combination of

Taguchi’s method and particle swarm optimization algorithm results in a solution which leads to better parameter values for structural design optimization problems. The algorithm of proposed hybrid approach can be outlined as follows: BEGIN Step 1: Taguchi’s method Begin 1.a Choose convenient orthogonal array from Taguchi’s standard orthogonal arrays 1.b Define levels and intervals 1.c For i:=1 to NOE (number of experiments) do begin Compute objective function values end; 1.d Choose convenient S/N ratio type (smaller the best or larger the best or nominal the best) based on minimization or maximization of objective functions 1.e For i:=1 to NOE do begin Compute S/N ratios end; 1.f Constitute Anova table for objective functions using S/N ratios 1.g Determine optimum levels and intervals using percentage contribution to performance using Anova table Use these levels and intervals for forming initial population end; ‘Generate optimal solution set using particle swarm optimization algorithm and computed robust initial population space’ Begin Input Use Initial population found in previous part of the program as input to particle swarm optimization algorithm Step 2: Particle swarm algorithm 2.a Generate initial swarm population with random positions and velocities While maximum iterations or minimum error criteria is not attained for i:=1 to NOP (number of particles) do begin 2.b Calculate fitness value for each particle 2.c For each particle, If the fitness value is better than the best fitness value (lbest) in history set current value as the new lbest 2.d Determine the best fitness value of all the particles as the gbest 2.e Calculate velocity of every particle according to equation (1) 2.f For each particle Update position of every particle according to equation (3) end; END.

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Proc IMechE Part D: J Automobile Engineering 0(0) The bar bending stress (sx) is calculated from the following equation sðxÞ =

6PL x4 x23

ð17Þ

The bar buckling load is found from the following equation qﬃﬃﬃﬃﬃﬃﬃ rﬃﬃﬃﬃﬃﬃ x23 x64 4:013 E 36 x3 E Pc ðxÞ = (1 ) ð18Þ L2 2L 4G The bar displacement is computed using the following equation

Figure 2. Welded beam structure.

Evaluation of the proposed approach using test problem In this section, the results of a well-known welded beam optimization problem and discussions regarding the proposed approach are given through the test problem. A welded beam design optimization problem, which is often used for the evaluation of design optimization methods, is used to illustrate the implementation procedure of the proposed approach for solving optimization problems. Figure 2 shows design variables and structure of the welded beam. The objective function is to minimize the cost under the given loading conditions. The beam has a length of 14 in. and P=6000 lb force is applied at the end of the beam.46–49 The problem includes seven constraints. The design variables are thickness of the weld h(x1 ), length of the weld l(x2 ), width of the beam t(x3 ), and thickness of the beam b(x4 ): The mathematical model of the welded beam optimization problem is defined as Objective functions f1 ðxÞ = 1:10471x21 x2 + 0:04811x3 x4 ð14:0 + x2 Þ

ð8Þ

Constraints g1 ðxÞ = t max t(x)50

ð9Þ

g2 ðxÞ = smax s(x)50

ð10Þ

g3 ðxÞ = x4 x1 50

ð11Þ

g4 ðxÞ = Pc (x) P50

ð12Þ

g5 ðxÞ = dmax = d(x)50

ð13Þ

g6 ðxÞ = x1 0:12550

ð14Þ

g7 ðxÞ = 5 1:10471x21 x2 + 0:04811x3 x4 ð14:0 + x2 Þ50

ð15Þ

The weld stress t(x) has two components which are t9 and t99:t9 is the primary stress, whereas t99 is the secondary torsional stress ( ). t(x) is computed using the following equation rﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ x2 2 2 + ðt 99 Þ t ðxÞ = ðt 9 Þ + t 99 :t 9 ð16Þ 2R

dðxÞ =

4PL3 EX33X4

ð19Þ

Step 1: Four design variables are used to define the objective and seven constraint functions. The design variables are h(x1 ), l(x2 ), t(x3 ) and b(x4 ). The objective is to minimize the cost f1 ðxÞ under the given loading conditions subject to constraints. The bending stress, buckling load, and weld stress are defined with notations as s(x), Pc ðxÞ and t(x). The values of loads and stresses are given as P = 6000 lb, t max = 13,600 psi, and smax = 30,000 psi. Step 2: In this step, experiments are designed to evaluate the effects of four design variables related to the objective function. The selection of an orthogonal array for a given problem depends on the number of factors and their levels. Taguchi has tabulated 18 basic orthogonal arrays, which are called standard orthogonal arrays. In most of the problems, one of the standard orthogonal arrays is considered to plan a matrix experiment. The suitable orthogonal array with regard to four design variables at four levels each is chosen as L16 . The equations for calculating S/N ratios for quality characteristics are logarithmic functions based on the mean square quality characteristics. In this problem, smaller the better characteristic is considered to compute S/N ratios based on the objectives as smaller the better for cost and deflections. Therefore, the responses for each experiment are computed using the following equation (see Table 1) X S=N ratio = 10 log( y2i =n) ð20Þ L16 orthogonal array is used to simulate the experiments. The levels and S/N ratios are tabulated for 16 experiments as shown in Table 1. The intervals of parameters for four levels are given as 0.125\x1 \5, 0.1\x2 \10, 0.1\x3 \10, 0.125\x4 \5. The ANOVA for objective is formed using S/N ratios as shown in Tables 2 and 3. Step 3: In the previous step, the experiments are designed to evaluate the effects of four design parameters with respect to objective function. In this step, the intervals of the design parameters are found using ANOVA regarding the effects of factors on the

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Table 1. S/N ratios of the welded beam design optimization problem. Exp. no.

X1

X2

X3

X4

S/N (Objective)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

0.125 0.125 0.125 0.125 1.75 1.75 1.75 1.75 3.375 3.375 3.375 3.375 5 5 5 5

0.1 3.4 6.7 10 0.1 3.4 6.7 10 0.1 3.4 6.7 10 0.1 3.4 6.7 10

0.1 3.4 6.7 10 3.4 0.1 10 6.7 6.7 10 0.1 3.4 10 6.7 3.4 0.1

0.125 1.75 3.375 5 3.375 5 0.125 1.75 5 3.375 1.75 0.125 1.75 0.125 5 3.375

39.82 214.04 227.09 235.25 218.19 221.52 227.57 233.51 227.59 237.02 238.53 242.02 223.30 239.51 246.10 248.83

objective function. The effective parameters with respect to the objective are x2 and x1 with 39.2 and 35.5% contributions as shown in Tables 2 and 3 respectively. Therefore, the levels of 1 and 2 are considered as 0.125 (level 1) and 1.75 (level 2) for x1 and 0.1 (level 1) and 3.4 (level 2) for x2 , since the smaller the better category is applied for the objective function. The intervals for x1 and x2 are level 1\x1 \level 2 and level 1\x2 \level 2. The contributions for x3 and x4 are weak for the objective as 8.9 and 9.9%, respectively. Therefore, the predefined intervals are selected without any change as 0.125 and 10 (level 1\x3 \level 4) for x3 , 0.125 and 5 (level 1\x4 \level 4) for x4 . In summary, the parameter settings are found as 0.125\ x1 \1.75, 0.1\x2\ 3.4, 0.1\x3 \10, 0.125\ x4 \5 (level 1\x1 \level 2, level 1\x2 \level 2, level 1\ x3 \level 4, level 1\x4 \level 4) for the objective function. Step 4: The initial population of PSO algorithm is randomly generated for individuals within the range of the solution space bounded by 0.125\x1 \1.75, 0.1\x2 \3.4, 0.1\x3 \10, 0.125\x4 \5 (level 1\ x1 \level 2, level 1\x2 \level 2, level 4 for x3 , level 1\x4 \level 4). Steps 5–7: From steps 5 to 7, HRPSO searches for the optimal solutions using the refined population range obtained in the previous step. The PSO operators are then applied to compute the optimal values. The parameters used by the proposed hybrid approach for optimization process are the following:

(a) number of individuals: 50; (b) maximum number of generations: 500; (c) number of objective function evaluations: 25,000. The best solutions obtained by the above mentioned approaches are listed in Tables 2 and 3, and their statistical simulation results are given in Table 4 for welded beam design problem. When considering the number of function evaluations, the best solution computed and the statistical analysis results are taken into account together, it is concluded that HRPSO provided better solutions for this problem among the other results46–51 given in Tables 2, 3 and 4. The worst solution found by HRPSO is better than the best solutions found by Siddall46 and Ragsdell and Phillips.47 The use of the HRPSO improves the convergence rate by computing the best value 1.72485 with the smallest function evaluation 25,000 and standard deviation values. As can be seen from Table 4, HRPSO gives the best results reported in the literature for welded beam design problem.

Structural design optimization using improved hybrid particle swarm algorithm The hybrid approach proposed in the third section is applied to solve a structural design optimization problem taken from automotive industry for the optimal design of an automobile component in this section. The objective functions are due to the volume and the frequency of the part which is to be designed for minimum volume and avoiding critical frequency subject to strength constraints. In this research, then structural optimization is performed using the present approach. In the first stage, the experiments are designed to evaluate the effects of four design variables related to objective functions. The four design variables X1, X2, X3 and X4 are selected as shown in Figure 3. The feasible range of design variables without shape distortions is considered as 90\X1\150, 185\X2\ 230, 10\X3\25 and 30\X4\45. Matrix experiments are designed using L16 orthogonal arrays and S/N ratios are conducted for each objective as given in Table 5. Smaller the better and larger the better characteristics are applied to compute S/N ratios based on each objective as smaller the better for volume and larger the better for frequency.

Table 2. ANOVA of the objective function for the welded beam problem.

X1 X2 X3 X4

Level 1

Level 2

Level 3

Level 4

Ss

% Contribute

29.14 27.31 217.26 217.32

225.20 229.67 230.09 227.34

236.29 234.82 231.93 232.78

239.44 239.90 230.79 232.62

2248.99 2478.34 567.47 631.07

35.58 39.21 8.98 9.98

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Table 3. Comparison of the best solution welded beam design problem by different methods. Design variables

HRPSO

Akay and Karabog˘a51

Huang et al.50

He and Wang49

Coello and Montes48

Ragsdell and Phillips47

Siddall46

x1 x2 x3 x4 g1(x) g2(x) g3(x) g4(x) g5(x) g6(x) g7(x) f(x)

0.205730 3.470489 9.036624 0.205730 0.000000 20.000002 0.000000 23.432984 20.080730 20.235540 0.000000 1.724852

N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 1.724852

0.203137 3.542998 9.033498 0.206179 244.57856 244.66353 20.003042 23.423726 20.078137 20.235557 238.02826 1.733462

0.202369 3.544214 9.048210 0.205723 212.83979 21.247467 20.001498 23.429347 20.079381 20.235536 211.68135 1.728024

0.205986 3.471328 9.020224 0.206480 20.074092 20.266227 20.000495 23.430043 20.080986 20.235514 258.6664 1.72822

0.245500 6.19600 6.19600 0.24550 25743.82 24.71509 0.00000 23.02028 20.12050 20.23420 23604.275 2.385937

0.2444 6.2189 8.2915 0.2444 25743.50 24.01520 0.00000 23490.46 20.23424 20.11940 23.02256 2.38154

Table 4. Statistical results of different methods for welded beam problem. Design variables

Best

Mean

Worst

Standard deviation

Function evaluations

HRPSO Akay and Karaboga et al.51 Huang et al.50 He and Wang49 Coello and Montes48 Ragstell and Phillips47 Siddall46

1.724852 1.724852 1.733461 1.728024 1.728226 2.3859373 2.3815433

1.73418 1.741913 1.768158 1.748831 1.7926 N/A N/A

1.75322 2 1.824105 1.782143 1.99340 N/A N/A

0.00051 0.03100 0.022194 0.012926 0.074713 N/A N/A

25,000 30,000 240,000 200,000 80,000 N/A N/A

Figure 3. Design variables. Table 5. Experimental results and S/N ratios for volume and frequency. Exp. no.

X1 (mm)

X2 (mm)

X3 (mm)

X4 (mm)

F1 (Volume)

F2 (Frequency)

S/N1 Volume

S/N2 Frequency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

90 90 90 90 110 110 110 110 130 130 130 130 150 150 150 150

185 200 215 230 185 200 215 230 185 200 215 230 185 200 215 230

10 15 20 25 15 10 20 25 20 25 10 15 25 20 15 10

30 35 40 45 40 45 30 35 45 40 35 30 35 30 45 40

98,815.7 125,002.7 157,199.9 195,402.7 108,202.7 97,419.2 143,602.7 177,798.1 109,602.7 133,800.7 96,017.3 120,210 102,998.8 106,200.7 103,399.8 94,617.3

6.9 8.4 9.3 9.2 6.5 6.1 6.3 6.5 4.9 4.7 4.4 4.5 3.4 3.4 3.5 3.4

299.89 2101.93 2103.92 2105.81 2100.68 299.77 2103.14 2104.99 2100.79 2102.52 299.64 2101.59 2100.25 2100.52 2100.29 299.51

16.77 18.51 19.41 19.34 16.3 15.69 16.05 16.33 13.88 13.62 12.99 13.2 10.84 10.83 11.11 10.83

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Table 6. Results of the analysis of variance for volume.

X1 X2 X3 X4 Error Total

Level 1

Level 2

Level 3

Level 4

S

DOF

M

F

Cont. (%)

2102.89 2100.4 299.71 2101.29

2102.15 2101.19 2101.12 2101.71

2101.14 2101.75 2102.09 2101.66

2100.14 2102.98 2103.4 2101.67

17.19 11.82 26.66 0.11 0.24 56.05

3 3 3 3 3 15

5.73 3.94 8.88 0.03 0.08

69.98 48.10 108.5 0.47

30.6 21.1 47.5 0.2 2.4 100

Table 7. Results of the analysis of variance for frequency.

X1 X2 X3 X4 Error Total

Level 1

Level 2

Level 3

Level 4

S

DOF

M

F

Cont. (%)

18.51 14.45 14.07 14.21

16.09 14.66 14.78 14.67

13.42 14.89 15.04 15.04

10.9 14.92 15.03 15.01

129.9 0.69 2.75 2.02 0.2 135.5

3 3 3 3 3 15

43.3 0.23 0.91 0.67 0.06

650.8 3.5 13.8 10.1

95.81 0.515 2.033 1.491 0.151 100

Figure 4. The optimal structural layout.

ANOVA for each objective is formed using S/N ratios for the first and second objective functions as shown in Tables 6 and 7. The optimal settings for X1, X2, X3 and X4 variables are computed as X1=90, 185\X2\230, 10\X3\20 and X4=30. Then, the problem is solved using particle swarm optimization algorithm. The parameters used by the proposed hybrid approach for optimization process are the following: (a) number of individuals: 30; (b) maximum number of generations: 80; (c) number of objective function evaluations: 2400.

In the present approach, PSO algorithm begins its search with a set of solutions for which its population range is defined by Taguchi’s method as given above. The structural layout results of the present approach using PSO algorithm and robust design based on Taguchi’s method for the design of vehicle part is given in Figure 4. The results of present hybrid approach for the design of vehicle part are given in Table 8. The numbers of function evaluations are also listed for each approach in Table 6. The HRPSO has the smallest function evaluation number. It is seen that shape design optimization performance is improved compared to other approaches.

Conclusions This research describes a new design optimization strategy based on particle swarm optimization algorithm and Taguchi’s parameter design to develop an innovative design optimization approach for solving structural design optimization problems. Taguchi’s robust parameter design is introduced to help to define robust initial population levels of design parameters to achieve better initialize particle swarm optimization algorithm

Table 8. Comparison of the design optimization results for vehicle component.

Topology design CAD optimum design Genetic algorithm PSO algorithm Hybrid PSO approach

X1 (mm)

X2 (mm)

X3 (mm)

X4 (mm)

Volume (cm3)

Frequency (Hertz)

Stress (MPa)

Function evaluations

110 130.8 98.9 98.9 90

190 200.5 188.6 188.6 185

17 15 11 11 10.1

32 40.3 36 36 30

117,001 107,973 101,223 95,823 87,685

6.3 4.6 6.8 7.2 8.6

280.8 286.6 271.2 283.2 297.3

2 50,000 10,000 4500 2400

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search. The design solution space of particle swarm optimization algorithm is refined based on the effect of the various design variables on objective functions. The proposed approach is applied to a vehicle component taken from the automotive industry. It is seen that better results can be achieved with the present hybrid approach. Funding This research received no specific grant form any funding agency in the public, commercial, or not-for-profit sectors. References 1. Yildiz AR. A new design optimization framework based on immune algorithm and Taguchi’s method. Comput Ind 2009; 60(8): 613–620. 2. Yildiz AR and Saitou K. Topology synthesis of multicomponent structural assemblies in continuum domains. Trans ASME J Mech Des 2011; 133: 011008-1–011008-9. 3. Bureerat S and Limtragool J. Performance enhancement of evolutionary search for structural topology optimisation. Finite Elem Analysis Des 2006; 42(6): 547–566. 4. Bureerat S and Srisomporn S. Optimum plate-fin heat sinks by using a multi-objective evolutionary algorithm. Engng Optimization 2010; 42(4): 305–323. 5. Durgun I and Yildiz AR. Structural design optimization of vehicle components using cuckoo search algorithm. Mater Testing 2012; 3: 185–188. 6. Fourie PC and Groenwold AA. The particle swarm optimization algorithm in size and shape optimization. Struct Multidisciplinary Optimization 2002; 23: 259–267. 7. Yildiz AR. Hybrid immune-simulated annealing algorithm for optimal design and manufacturing. Int J Mater Product Technol 2009; 34: 217–226. 8. Luh GC and Chueh CH. Multi-objective optimal design of truss structure with immune algorithm. Comput Structs 2004; 82: 829–844. 9. Lyu N and Saitou K. Topology optimization of multicomponent structures via decomposition-based assembly synthesis. Trans ASME J Mech Des 2005; 127: 170–183. 10. Yildiz AR. A new design optimization framework based on immune algorithm and Taguchi method. Comput Ind 2009; 60; 613–620. 11. Saka MP. Optimum geometry design of geodesic domes using harmony search algorithm. Adv Struct Engng 2008; 10: 595–606. 12. Yildiz AR. Optimal structural design of vehicle components using topology design and optimization. Mater Testing 2008; 50; 224–228. 13. Woon SY, Querin OM and Steven GP. Structural application of a shape optimization method based on a genetic algorithm. Struct Multidisciplinary Optimization 2001; 22: 57–64. 14. Luh GC and Chueh CH. Multi-modal topological optimization of structure using immune algorithm. Comput Methods Appl Mech Engng 2004; 193: 4035–4055. 15. Yildiz AR, Ozturk N, Kaya N and Ozturk F. Hybrid multi-objective shape design optimization using Taguchi’s method and genetic algorithm. Struct Multidisciplinary Optimization 2007; 34: 277–365.

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Appendix Analysis of variance (ANOVA) ANOVA is a standard statistical technique to interpret the experimental results. The percentage contribution

of various process parameters to the selected performance characteristic can be estimated by ANOVA. Thus information about how significant the effect of each controlled parameter is on the quality characteristic of interest can be obtained. ANOVAs for raw data have been performed to identify the significant parameters and to quantify their effect on the objective function. The ANOVA based on the raw data identifies the factors which affect the average response rather than reducing variation. In ANOVA, total sum of squares (SST ) is calculated by SST =

XN i=1

2 (Yi Y)

ð21Þ

where N is the number of experiments in the orthogonal array, N=9, Yi is the experimental result for the ith experiment and Y is given by 1 XN Y = Y i=1 i N

ð22Þ

The total sum of the squared deviations SST is decomposed into two sources: the sum of the squared deviations SSP due to each process parameter and the sum of the squared error SSe : SSP can be calculated as SSP =

i2 (SYj )2 1 hXN Y i j=1 i=1 N t

Xt

ð23Þ

where p represent one of the experiment parameters, j the level number of this parameter p, t the repetition of each level of the parameter p, SYj the sum of the experimental results involving this parameter p and level j. The sum of squares from error parameters SSe is SSe = SST SSA SSB SSC

ð24Þ

The total degrees of freedom is DT = N 1, and the degrees of freedom of each tested parameter is DP = t 1. The variance of the parameter tested is Vp = SSp =Dp . Then, the F-value for each design parameter is simply the ratio of the mean of squares deviations to the mean of the squared error (Fp = Vp =Ve ). The percentage contribution r can be calculated as rP =

SSP SST

ð25Þ

Table 9 shows experimental results for L9 orthogonal array. Table 10 shows the results of ANOVA for the objective function. It can be seen from Table 10 that X2 and X3 are the most significant parameters for the objective function.

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Proc IMechE Part D: J Automobile Engineering 0(0)

Table 9. Experimental results. Exp. no.

X1

X2

X3

Obj. function

1 2 3 4 5 6 7 8 9

850 850 850 900 900 900 950 950 950

120 250 500 120 250 500 120 250 500

4.00 4.08 4.17 4.08 4.17 4.00 4.17 4.00 4.08

0.585 0.627 0.598 0.585 0.685 0.530 0.585 0.555 0.576

Table 10. Results of the analysis of variance for the objective function. Source

DOF

Sum of squares

Mean square

Contribution (%)

X1 X2 X3 Error Total

2 2 2 2 8

0.00176 0.00463 0.00663 0.00251 0.01553

0.00088 0.00231 0.00331 0.00126

11.35 29.79 42.68 16.18 100

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