considerations on limits of dredging processes - Delft Dredging ...

Miedema, S.A., "Considerations on limits of dredging processes". 19th Annual Meeting & Technical Conference of the Western Dredging Association. Louisville Kentucky, May 16-18, 1999.

CONSIDERATIONS ON LIMITS OF DREDGING PROCESSES S.A. Miedema1 ABSTRACT In hydraulic dredging, two main dredging processes occur. On one hand, soil has to be excavated and on the other hand, the soil has to be transported. When excavating soft soil, the excavating process is limited by bulldozing or clogging of the cutterhead resulting in a high-excavated production. This causes a high-density mixture to be transported hydraulically. In this case usually vacuum, pressure or sedimentation occurring in the hydraulic system limits the hydraulic transportation process. Which of these is the real limit, depends on the type of soil and on the pipeline and pump layout. When excavating hard to dig soil, the excavating process is limited by the cutter torque available. The excavated production will be low, so the hydraulic system will not give limitations. The paper describes the different processes involved for sand cutting and transportation and gives some tools on how to determine the transition between excavating limitations and hydraulic limitations. By means of simulations and calculations, both limitations will be illustrated. INTRODUCTION TO SAND CUTTING In dredging, the excavation of soil is one of the most important processes. It is known that on the largest cutter suction dredges thousands of kW's are installed on the cutter drive. To predict the forces on excavating elements, two-dimensional cutting theories are used. Van Os 1977 [12], Verruijt 1985 [14], Miedema 1987 [6] and 1989 [7] and van Leussen & van Os 1987 [13] described the two-dimensional cutting theory for water saturated sand and its applications extensively. The aim of developing such theories is to predict the loads on excavating elements like cutter heads, drag heads, etc. It is however also possible to predict the production, when the soil mechanics parameters, the geometry of the excavating element and the available power are known. The soil mechanics parameters are described by van Leussen & Nieuwenhuis in 1984 [5]. The cutting process of a cutter head is very complicated. Not only do the blades have a three-dimensional shape; also, the velocities on the blades are three-dimensional, with respect to their direction, due to a combination of the swing velocity and the circumferential velocity. Figure 1 shows the 3D shape of a cutterhead. Other excavating elements such as dredging wheels, blades in dragheads and trenchers, may not look that complicated, but will also require the three-dimensional cutting theory to fully describe the cutting process. In 1994, Miedema [8] described the three-dimensional cutting theory.

1Associate

Professor, Chair of Dredging Technology, Director of Education, Mechanical Engineering, Delft University of Technology.

Copyright: Dr.ir. S.A. Miedema


To derive forces, torque, power, specific energy and production from the abovementioned theories, requires complicated calculations, while the soil mechanics parameters of the sand have to be known. Mostly, only the SPT (Standard Penetration Test) value of the sand is known. In 1995 Miedema [9] described how to determine the production of a hydraulic dredge based on cutting theories for sand cutting.

Fig. 1: The 3D shape of a cutterhead. In 1975, Hatamura and Chijiiwa [3] distinguished three failure mechanisms in soil cutting. The "shear type", the "flow type” and the "tear type". A fourth failure mechanism can be distinguished, the "curling type", as is known in metal cutting. Although it seems that the curling of the chip cut is part of the flow of the material, whether the "curling type" or the "flow type" occurs depends on several conditions. The "flow type", "tear type" and "curling type" occur in clay, while the "tear type” and, under high hydrostatic pressure, the "flow type” occur when cutting rock. The "shear type" occurs in materials with an angle of internal friction, but without cohesion like sand. Figure 2 illustrates the four failure mechanisms as they might occur when cutting soil. Although the "shear type" is not a continuous cutting process, the shear planes occur so frequently, that a continuous process is assumed. The Mohr-Coulomb failure criteria is used to derive the cutting forces. This derivation is made under the assumption that the stresses on the shear plane and the blade are constant and equal to the average stresses acting on the surfaces.



Fig. 2: Failure mechanisms in soil cutting. THE EQUILIBRIUM OF FORCES. The forces acting on a straight blade when cutting soil, can be distinguished as: 1. A force normal to the blade N2. 2. A shear force S2 as a result of the soil/steel friction N2·tan[δ]. 3. A shear force A as a result of pure adhesion between the soil and the blade. This force can be calculated by multiplying the adhesive shear strength of the soil with the contact area between the soil and the blade. 4. A force W2 as a result of water under pressure on the blade. These forces are shown in figure 3. If the forces N2 and S2 are combined to a resulting force K2 and the adhesive force and the water under pressure distribution is known, then the resulting force K2 is the only unknown force on the blade.



Fig. 3: The forces acting on the blade. The forces acting on the layer cut are: 1. 2. 3. 4. 5.

The forces occurring on the blade as mentioned above. A normal force acting on the shear surface N1. A shear force S1 as a result of internal fiction N1·tan[φ]. A force W1 as a result of water under pressure in the shear zone. A shear force C as a result of pure cohesion. This force can be calculated by multiplying the cohesive shear strength with the area of the shear plane. 6. A gravity force G as a result of the weight of the layer cut. 7. An inertial force I, resulting from acceleration of the soil.

The normal force N1 and the shear force S1 can be combined to a resulting grain force K1. By taking the horizontal and vertical equilibrium of forces, an expression for the force K2 on the blade can be derived. Figure 4 illustrates the forces on the layer of soil cut. The forces shown are valid in general. In sand, several forces can be neglected. In fact the forces resulting from the water underpressure dominate the cutting of water saturated sand. From literature, it is known that, during the process of cutting sand, the pore volume of the sand increases. This is caused by the phenomenon dilatancy (see figure 5 and 6). With a certain cutting velocity vc there has to be a flow of water to the shear zone, the area where the pore volume increases. This causes a decrease in the pore pressure of the pore water and because the soil stress remains constant, the grain stress will increase. Van Os [12] 1977 stated: "If it is the aim of the engineer to know the average cutting forces needed to push the blade through the soil, he can take an average deformation rate δe/δt to insert into the Biot equation. But it should be noted that this is purely practical reasoning and has nothing to do with Theoretical Soil Mechanics". Van Os and van Leussen



Fig. 4: The forces acting on the layer cut. published their cutting theory in 1987 [13]. Van Leussen and Nieuwenhuis [5] discussed the relevant soil mechanical parameters in 1984. Miedema [6] 1987 uses the average deformation rate as stated by van Os [12] 1977 but instead of inserting this in the Biot equation; the average deformation rate is modeled as a boundary condition in the shear zone. Although the cutting process is not solely dependent upon the phenomenon dilatancy, the above mentioned research showed that for cutting velocities in a range from 0.5 to 5 m/sec the cutting process is dominated by the phenomenon dilatancy, so the contributions of gravitational, cohesive, adhesive and inertial forces can be neglected, thus the cutting equations can be simplified to (Miedema, 1987 [6]): The non-cavitating cutting process:

c ⋅ ρ ⋅ g ⋅v ⋅ h ⋅b ⋅e = F k

(1)

c ⋅ ρ ⋅ g ⋅v ⋅ h ⋅b ⋅e = F k

(2)

2

1

w

c

i

h

m

2

2

w

c

i

v

m

The cavitating cutting process: = d 1 ⋅ ρ ⋅ g ⋅ ( z + 10 ) ⋅ hi ⋅ b

(3)

F = d ⋅ ρ ⋅ g ⋅ (z + 10) ⋅ h ⋅ b

(4)

F

h

v

w

2

w


i


Fig. 5: The occurrence of dilatation when cutting water saturated sand. SPECIFIC ENERGY. To determine the production of excavating elements as a function of the SPT value of the soil, the specific energy method is used. The specific energy is the amount of energy (work) required for the excavation of one cubic meter of in-situ soil. The dimension of specific energy is kNm/m3 or kPa. The specific energy depends on the type of soil (soil mechanical parameters), on the geometry of the excavating element (dredging wheel, crown cutter, etc.) and on the operational parameters (haulage velocity or trail velocity, revolutions, face geometry, etc). Beside the above, the effective specific energy will be influenced by other phenomena such as spill, wear and the bulldozer effect. The maximum production can also be limited by the hydraulic system. The production can be derived from the specific energy by dividing the available power by the specific energy.

Q =P E

(5)

a

s

An accurate calculation of the specific energy and thus the production can be carried out only when all off the parameters influencing the cutting process are known. If an estimate has to be made of the specific energy and the production, based on the SPT value only, a number of assumptions will have to be made and a number of approximations will have to be applied. These assumptions and approximations will



Fig. 6: Equipotential and flow lines, showing the pore pressures. maximize the specific energy and thus minimize the production. In other words, the specific energy as calculated in this paper is an upper limit, whilst the calculated production is a lower limit. Wear, spill and limitations such as the bulldozer effect are not taken into consideration. Once the specific energy and the production per 100 kW are known, the production, giving an available power, can be calculated. This production can be either realistic, meaning that the bulldozer effect will not occur, or not realistic meaning that this effect will occur. In the last case, the maximum production will have to be calculated from the limitations caused by the bulldozer effect. From the maximum production derived, the maximum swing velocity, giving a certain bank height and step size, can be determined. The type of cutting process is determined by the soil mechanical properties of the soil to be dredged, the geometry of the excavating element and the operational parameters. SPECIFIC ENERGY AND PRODUCTION IN SAND. As discussed previously, the cutting process in sand can be distinguished in a noncavitating and a cavitating process, in which the cavitating process can be considered to be an upper limit to the cutting forces. Assuming that during an SPT test in watersaturated sand, the cavitating process will occur, because of the shock wise behaviour during the SPT test, the SPT test will give information about the cavitating cutting process. Whether, in practice, the cavitating cutting process will occur, depends on the soil mechanical parameters, the geometry of the cutting process and the operational parameters. The cavitating process gives an upper limit to the forces, power and thus the



specific energy and a lower limit to the production and will therefore be used as a starting point for the calculations. For the specific energy of the cavitating cutting process, the following equation can be derived according to Miedema [6, page 148]:

E

s

=

F ⋅ v = ⋅ ρ ⋅ g ⋅ (z + 10) d h ⋅b ⋅v h

c

1

i

(6)

w

c

In Miedema [9], a derivation is given on the relation between de SPT value and the value of the only unknown in equation 6, the coefficient d1. Specific energy 2500 2250 2000 1750

kPa

1500 1250 1000 750 500 250 0 0

10 Waterdepth 0 m

20 Waterdepth 5 m

30

40

Waterdepth 10 m

50 SPT Waterdepth 15 m

60

70

Waterdepth 20 m

80 Waterdepth 25 m

90

100

Waterdepth 30 m

Production per 100 kW

m^3/hour

10000

1000

100 1

10 SPT Waterlevel 0 m

Waterlevel 5 m

Waterlevel 10 m

Waterlevel 15 m

100 Waterlevel 20 m

Waterlevel 25 m

Specific energy and production for a 30 degree blade and a cavitating cutting process in sand as a function of the reduced SPT value.

Fig. 7: The specific energy and maximum production.


Waterlevel 30 m


With this relation, the maximum specific energy can be determined for a range of waterdepths as shown in figure 7. Once the maximum specific energy is known, the production can be determined given the available power. Figure 7 shows the production per 100 kW as a function of the maximum specific energy and the SPT value of the sand. These graphs are based on research in the Laboratory of Dredging Technology (T.U. Delft). Results of this research can be found in Miedema [6, 8 & 9]. Figure 8 shows a cross-section of the cutting rig in the laboratory. The above decribes the limitations of the cutting process as a result of power limitations. There are two other important limitations, clogging and the bulldozer effect. Clogging occurs when the layer cut does not fit between two blades of the cutterhead. This deformed layer thickness depends on the swing velocity, the revolutions, the number of blades, and the cutting angle and depends on the type of sand through the angle of the shear plane.

Fig. 8: A cross section of the Dredging Technology Laboratory (T.U. Delft).



The thickness of the deformed layer cut can be determined with:

h

def

=

v ⋅ 60 ⋅ ⋅ sin(α + β ) sin( β ) n ⋅p s

(7)

o

Fig. 9: The deformed layer thickness and the free running angle. Figure 9 shows the deformed layer thickness. From this figure, it is obvious, that the throughput also depends strongly on the shape of the blades. The throughput can be defined as the shortest distance between the carrier line on the cutting edge of a blade and the back of the previous blade. When the deformed layer thickness does not fit anymore between two blades, the cutterhead becomes clogged first and then starts to bulldozer, because there is no way out for the sand. From equation 7, it is obvious that this will occur with a high swing velocity/revolutions ratio. Another phenomenon that may cause the cutterhead to bulldozer is, when the sand hits the back of the blade of the cutterhead. Figure 9 shows the free running angle based on the circumferential velocity γ1. Because of the swing velocity the actual free running angle γ2 is smaller. When the value of the actual free running angle approaches zero, the sand will be pushed away by the back of the blade. This effect is determined by the free running angle, the circumferential velocity, the swing velocity and the direction of the circumferential velocity. One can see from figure 9 that this effect is at a maximum when the circumferential velocity is vertical. Resuming it can be stated that clogging and bulldozing will limit the maximum cutting production at low SPT values, while the available power will limit the maximum production at low SPT values. The transition between the limiting factors depends on the geometry of the cutterhead, the power installed and on the operation parameters.



INTRODUCTION TO HYDRAULIC TRANSPORT.

A multi pump/pipeline system consists of components with different dynamic behaviour. To model such a system, one should start with simple mathematical descriptions of the sub-systems, to be able to determine the sensitivity of the behaviour of the system to changes in one of the sub-systems. The following sub-systems can be distinguished: - The pump drive - The centrifugal pump - The sand/water slurry in the pipeline - Flow control (if used) The system is limited by cavitation at the entrance of each pump on one hand and by sedimentation of the solids resulting in plugging of the pipeline on the other hand.The system is also limited by the power installed and the torque speed curve of each individual pump. Cavitation will occur at high line velocities and/or at high solids concentrations in the suction pipe of the pump considered. Sedimentation will occur at line velocities below the so called critical velocity. The critical velocity depends on the grain distribution and on the solids concentration. In between these two limitations a stable transportation process is required. A steady state process is possible only if the solids properties and the solids concentration are constant in time. In practice however this will never be the case. Solids properties such as the grain size distribution will change as a function of time and place as will the solids concentration. The resistance of the slurry flow depends on the solids properties and concentration. If the total resistance of the slurry flow in a long pipeline is considered, changes of the solids properties and concentration at the suction mouth will result in slow changes of the total resistance, since only a small part of the pipeline is filled with the new slurry while most of the pipeline remains filled with the slurry that was already there, except from the slurry that has left the pipeline at the end. If the relatively short suction line is considered, this results in a much faster change of the vacuum at the inlet of the first pump. The total head of a pump however, responds immediately to changes of the solids properties and concentration. If a sudden increase of the concentration is assumed, the total head of a pump will increase almost proportionally with the concentration. This will result in a higher flow velocity, but, because of the inertia of the slurry mass in the pipeline, the slurry mass will have to accelerate, so the flow velocity responds slowly on changes of the total head. The increase of the total head also causes an increase of the torque and power of the pump drive, resulting in a decrease of the pump drive revolutions and thus of the total head. Because of the inertia of pump and pump drive, there will not be an immediate response. It is obvious that there is an interaction between all the different sub-systems. These interactions can be ranged from very slow to immediate. To be able to model the system, first the characteristic behaviour of the sub-systems should be known. THE PUMP DRIVE.

Pump drives used in dredging are diesel direct drives, diesel/electric drives and diesel/hydraulic drives. In this paper the diesel direct drive, as the most common arrangement, is considered.



At nominal operating speed, the maximum load coincides with the nominal full torque point. If the torque is less then the nominal full torque, the engine speed usually rises slightly as the torque decreases. This is the result of the control of the speed by the governor. The extent of this depends upon the type of governor fitted. If the engine load increases above the full torque point, the speed decreases and the engine operates in the full fuel range. With most diesel engines the torque will increase slightly as the speed decreases, because of a slightly increasing efficiency of the fuel pumps. When the load increases further, insufficient air is available to produce complete combustion and the engine stalls. The torque drops rapidly and heavily polluted gasses are emitted. The smoke limit has been reached. The speed range between the full torque point and the smoke limit is often referred to as the constant torque range. The torque/speed characteristic of the diesel engine can thus be approximated by a constant full torque upon the nominal operating speed, followed by a quick decrease of the torque in the governor range. THE CENTRIFUGAL PUMP.

The behaviour of centrifugal pumps can be described with the Euler impulse moment equation: ⎛ ⎛ Q ⋅ cot( β i ) ⎞ Q ⋅ cot( β o ) ⎞ ⎟⎟ − ρf ⋅ u i ⋅ ⎜⎜ u i − ∆pE = ρf ⋅ u o ⋅ ⎜⎜ u o − 2 ⋅ π ⋅ ro ⎠ 2 ⋅ π ⋅ ri ⎠ ⎝ ⎝

(8)

For a known pump this can be simplified to:

(

∆pE = ρf ⋅ C1 − C2 ⋅ Q

)

(9)

Because of incongruity of impeller blades and flow, the finite number of blades, the blade thickness and the internal friction of the fluid, the Euler pressure ∆p E has to be corrected with a factor k, with a value of about 0.8. This factor however does not influence the efficiency. The resulting equation has to be corrected for losses from frictional contact with the walls and deflection and diversion in the pump and a correction for inlet and impact losses. The pressure reduction for the frictional losses is:

∆ph .f . = C3 ⋅ ρf ⋅ Q 2

(10)

For a given design flow Qd the impact losses can be described with:

(

∆ph .i . = C4 ⋅ ρf ⋅ Qd − Q

)

2

The total head of the pump as a function of the flow is now:


(11)


(

)

(

)

2⎞ ⎛ ∆pp = k ⋅ ∆pE − ∆ph .f . − ∆ph .i . = ρf ⋅ ⎜ k ⋅ C1 − C2 ⋅ Q − C3 ⋅ Q 2 − C4 ⋅ Qd − Q ⎟ ⎠ ⎝

(11)

Based on this theory, the characteristics of a pumps used is given in figures 10. The pump is limited by the constant torque behaviour of the corresponding diesel engine in the full fuel range. Pump Power 7200

1680

5760

1260

4320

kW

kPa

Pump Head 2100

840 420

2880 1440

0 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec

0 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec

Pump Efficiency

Pump Torque 180

0.800

144

0.600

108

-

kNm

1.000

0.400 0.200

72 36

0.000 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec

0 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec

Pump Revolutions 500

80

400

60

300

rpm

kPa

Pump NPSH 100

40 20

200 100

0 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec Pump Revolutions 260 rpm

Input: 330 rpm

295 rpm

330 rpm

365 rpm

400 rpm

0 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec

Pump Pipeline System Windows V2.01 05-12-1996 - 10:27:16 Pump File: C:\PPSW\Pump\Main.Pmp Torque Limited

Fig. 10: The characteristics of the main pump and the booster pump. Figures 10 gives the pump characteristics for clear water. If a mixture is pumped however, the pump head increases because of the mixture density and the pump efficiency decreases because a heterogeneous mixture is flowing through the pump. The decrease of the efficiency depends upon the average grain diameter, the impeller diameter and the solids concentration and can be determined with (according to Stepanoff):

(

( ) ) / D⎞⎠

⎛ ηm = ⎝1 − C t ⋅ 0.466 + 0.4 ⋅ Log10 d 50

(12)

PRESSURE LOSSES WITH HOMOGENEOUS WATER FLOW. When clear water flows through the pipeline, the pressure loss can be determined with the well known Darcy-Weisbach equation: ∆p w = λ ⋅

L 1 ⋅ ⋅ ρ ⋅ c2 D 2 w


(13)


The value of the friction factor λ depends on the Reynolds number: Re =

c⋅ D ν

(14)

PRESSURE LOSSES WITH HETEROGENEOUS FLOW. For the determination of the pressure losses of a heterogeneous flow many theories are available, like Durand/Condolios/Gibert, Fuhrboter, Jufin/Lopatin and Wilson. In this paper the Durand/Condolios/Gibert theory will be used, further referred to as the Durand theory. Durand assumes that the clear water resistance in a pipeline should be multiplied by a factor depending on the line speed, the grain size distribution and the concentration. Miedema, 1996 [11] added the inertial pressure to the equation.

(

)

n

∆pm = ∆pw ⋅ 1 + Φ ⋅ Ct + ∑ ξ n ⋅ 12 ⋅ ρm ⋅ c 2 + ρm ⋅ g ⋅ H g + ρm ⋅ L ⋅ c&

(15)

1

In which: −3 / 2

⎛ c2 ⎞ Φ = 180 ⋅ ⎜ ⋅ Cx ⎟ ⎝g⋅ D ⎠

(16)

and: Cx =

g⋅d v2

(17)

The second term in the right hand side gives the resistance of all bendings, valves, etc. The third term gives the resistance of the geodetic height and the fourth term the inertial c resistance. Since Frfl = is the Froude number for the flow in the pipeline and g ⋅ Dp

v is the Froude number for the settling process of a grain, equation 16 can g⋅d also be written as: Frgr =

Φ = 176 ⋅ Frfl−3 ⋅ Frgr1.5

(18)

In normal sands, there is not only one graindiameter, but a grain size distribution has to be considered. The Froude number for a grain size distribution can be determined by integrating the Froude number as a function of the probability according to:


4800 4320

6000 4800 3600 2400 1200 0

Flow in m^3/sec

3360 2880 2400 1920

9600 7200 4800 2400 0

960 480 0 0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.60 4.00 Flow in m^3/sec Vcrit

Water

Rho: 1.144

Rho: 1.258

Rho: 1.372

Rho: 1.486

Rho: 1.600

1.0 1.2 1.4 1.6 1.8 2.0 Density in ton/m^3

4.00 3.20 2.40 1.60 0.80 0.00

1440 Prod. in m^3/hour

Total Head in kPa

12000

1.0 1.2 1.4 1.6 1.8 2.0 Density in ton/m^3

3840

Pressure in kPa

Total Power in kW

Pump Pipeline System Windows V2.01 05-12-1996 - 10:29:55 C:\PPSW\PIPELINE\Pipeline.Inp in Default Sand

Prod. in m^3/hour


0

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Length of discharge line in m

0

1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Length of discharge line in m

6000 4800 3600 2400 1200 0

1700 1340 980 620 260 -100 0

410

820

1230

1640 2050 2460 Distance from suction mouth in m

2870

3280

3690

4100

Fig. 11: Characteristics of the pump/pipeline system. Frgr =

1

∫

0

1 g⋅d dp v

(19)

When the flow decreases, there will be a moment where sedimentation of the grains starts to occur. The corresponding line speed is called the critical velocity. Although in literature researchers do not agree on the formulation of the critical velocity, the value of the critical velocity is often derived by differentiating equation 15 with respect to the line speed c and taking the value of c where the derivative equals zero. This gives:

c cr =

(

g ⋅ D p ⋅ 90 ⋅ C t Cx

)

2/ 3

(20)

At line speeds less then the critical velocity sedimentation occurs and part of the crosssection of the pipe is filled with sand, resulting in a higher flow velocity above the sediment. Durand assumes an equilibrium between sedimentation and scour, resulting in a Froude number equal to the Froude number at the critical velocity.



c cr

Frcr =

g ⋅ Dp

( 90 ⋅ C )

2/ 3

t

=

(21)

Cx

By using the hydraulic diameter concept, at lines speeds less then the critical velocity, the resistance can be determined. Resistance in kPa 18900

17010

15120

13230

11340

9450

7560

5670

3780

1890

0 0.00

0.40

Water

0.80

1.20

Durand

1.60

2.00 Flow in m^3/sec

Wilson Fine

2.40

Wilson Coarse

2.80

3.20

Durand Critical Velocity

3.60

4.00

Wilson Critical Velocity

Fig. 12: A comparison between Durand and Wilson. Figure 12 shows the water resistance, the mixture resistance and the critical velocity according to Durand [2] and Wilson [15] for a fine sand. Durand and Wilson match well in this case for fine sands, but for coarse sands they differ quite a lot.

THE PUMP /PIPELINE SYSTEM DESCRIPTION. In a steady state situation, the revolutions of the pumps are fixed, the line speed is constant and the solids properties and concentration are constant in the pipeline. The working point of the system is the intersection point of the pump head curve and the pipeline resistance curve. The pump curve is a summation of the head curves of each pump according to equation 11. The resistance curve is a summation of the resistances of the pipe segments and the geodetic head according to equation 15. Figure 11 shows this steady state situation for the system used in the case study at 6 densities ranging from clear water upto a density of 1.6 ton/m3. In reality, the solids properties and concentration are not constant in time at the suction mouth. As a result of this, the solids properties and concentration are not constant as a function of the position in the pipeline.



Fig. 13: The pump/pipeline layout as used in the case studies of Miedema [11]. To be able to know these properties as a function of the position in the pipeline, the pipeline must be divided into small segments. These segments move through the pipeline with the line speed. Each time step a new segment is added at the suction mouth, while part of the last segment leaves the pipeline. Because the line speed is not constant, the length of the segment added is not constant, but equals the line speed times the time step. For each segment the resistance is determined, so the resistance as a function of the position in the pipeline is known. This way also the vacuum and the discharge pressure can be determined for each pump. If vacuum results in cavitation of one of the pumps, the pump head is decreased by decreasing the pump density, depending on the time the pump is cavitating. The dynamic calculations are carried out in the time domain, because most of the equations used are non-linear. The time step used is about 1 second, depending on the speed of the PC and the other tasks Windows has to carry out. Figure 14 shows cavitation as a limiting condition on the booster pump of the system described in figure 13. The simulations are described fully in Miedema [11]. The cavitation in this case is a result of a density wave.

CONCLUSIONS. In this paper, many limiting conditions for the operations of cutter suction dredgers are described. For the cutting process these are: 1. Power and torque limitations



2. A thick deformed layer cut, resulting in cloggingand the bulldozer effect 3. A negative free running angle, resulting in the bulldozer effect. For the hydraulic transport process these are: 1. Sedimentation, resulting in clogging of the pipeline 2. Power and torque limitations, resulting in a decrease of the pump head, which can be used for a more stable process. 3. Cavitation, resulting in a fast pressure drop of the pump and a consequent decrease of the line velocity.

rpm

320 240 160 80 0 00:00

00:03

00:06

00:09

00:12

00:15 Time

00:18

00:21

00:24

00:27

00:30

00:21

00:24

00:27

00:30

00:21

00:24

00:27

00:30

00:21

00:24

00:27

00:30

Pump power vs time 3000 2400 kW

Pump Pipeline System Windows V2.01 May 14, 1996, 12:29:52 PM Pump 3 Time Series

Pump speed vs time 400

1800 1200 600 0 00:00

00:03

00:06

00:09

00:12

00:15 Time

00:18

Pump vacuum vs time (-=vacuum, +=pressure) 100.0

kPa

60.0 20.0 -20.0 -60.0 -100.0 00:00

00:03

00:06

00:09

00:12

00:15 Time

00:18

Pump discharge pressure vs time 700

kPa

560 420 280 140 0 00:00

00:03

00:06

00:09

00:12

00:15 Time

00:18

Fig. 14: Cavitation as a limiting condition on the booster pump. Because of the dynamics of the two processes involved, it is hardly impossible to predict when one of the limits is reached, as would be for a stationary process. The only way to carry out predictions is to use a simulation program. For a stationary situation the following rules can be applied: Step 1: Determine the production curve according to figure 7. Step 2: Determine the limits for the layer thickness and free running angle, based on swing velocity and revolutions of the cutterhead. Step 3: Adjust figure 7 for the limiting conditions. Step 4: Determine the critical velocity for the hydraulic system at the required density (figure 11) and for the sand properties. Step 5: Determine the cavitation limits for each pump in the system. Step 6: Adjust figure 7 for the hydraulic limits. Step 7: Never excavate a production beyond the limits of the adjusted figure 7.



LITERATURE. [ 1] Bree, S.E.M. de 1977, "Centrifugal Dredgepumps". IHC Holland 1977. [ 2] Gibert, R., "Transport Hydraulique et Refoulement des Mixtures en Conduites". [ 3] Hatamura, Y, & Chijiiwa, K., "Analyses of the mechanism of soil cutting". 1st report, Bulletin of the JSME, vol. 18, no. 120, June 1975. 2st report, Bulletin of the JSME, vol. 19, no. 131, May 1976. 3st report, Bulletin of the JSME, vol. 19, no. 139, November 1976. 4st report, Bulletin of the JSME, vol. 20, no. 139, January 1977. 5st report, Bulletin of the JSME, vol. 20, no. 141, March 1977. [ 4] Huisman, L. 1995, "Sedimentation and Flotation". Lecture Notes, Delft University Of Technology 1973-1995. [ 5] Leussen, W. van & Nieuwenhuis J.D., "Soil Mechanics Aspects of Dredging". Geotechnique 34 No.3, pp. 359-381, 1984. [ 6] Miedema, S.A., "The Calculation of the Cutting Forces when Cutting Water Saturated Sand, Basical Theory and Applications for 3-Dimensional Blade Movements with Periodically Varying Velocities for in Dredging Usual Excavating Elements" (in Dutch). PhD thesis, Delft, 1987, the Netherlands. [ 7] Miedema, S.A., "On the Cutting Forces in Saturated Sand of a Seagoing Cutter Suction Dredger". Proc. WODCON XII, Orlando, Florida, USA, April 1989. And Terra et Aqua No. 41, December 1989, Elseviers Scientific Publishers. [ 8] Miedema, S.A., "On the Snow-Plough Effect when Cutting Water Saturated Sand with Inclined Straight Blades". ASCE Proc. Dredging 94, Orlando, Florida, USA, November 1994. [ 9] Miedema, S.A., "Production Estimation Based on Cutting Theories for Cutting Water Saturated Sand". Proc. WODCON IV, November 1995, Amsterdam, The Netherlands 1995. [10] Miedema, S.A. 1996, "Pump Pipeline System Windows V2.01". Software, Delft 1996. [11] Miedema, S.A., "Modelling and Simulation of the Dynamic Behaviour of a Pump/Pipeline System". 17th Annual Meeting & Technical Conference of the Western Dredging Association. New Orleans, June 1996. [12] Os, A.G. van, "Behaviour of Soil when Excavated Underwater". International Course Modern Dredging. June 1977, The Hague, The Netherlands. [13] Os, A.G. van & Leussen, W. van, "Basic Research on Cutting Forces in Saturated Sand". Journal of Geotechnical Engineering, Vol. 113, No.12, December 1987. [14] Verruijt, A., "Offshore Soil Mechanics". Delft University of Technology, 1985-1994. [15] Wilson, K.C. & Addie, G.R. & Clift, R. 1992, "Slurry Transport Using Centrifugal Pumps". Elsevier Science Publishers Ltd. 1992.



NOMENCLATURE. Sand Cutting: A b C c1,2 d1,2 e Es Fh Fv G g hb hi I km K1 K2 n no N1 N2 p Pa Q S1 S2 vc vs W1 W2 W3 z α β δ φ γ ρw

Adhesive force on blade Width of blade Cohesive force on the shear plane Coefficient non-cavitating cutting process Coefficient cavitating cutting process Fractional volume increase Specific energy Horizontal cutting force (direction of cutting velocity) Vertical cutting force (perpendicular to cutting velocity) Gravitational force resulting from weight Gravitational constant Height of blade Height of layer cut Inertial force on the shear plane Mean permeability Resultant force on the shear plane Resultant force on the blade Porosity Cutterhead revolutions Normal force on the shear plane Normal force on blade Number of blades cutterhead Available power Production Shear force on the shear plane Shear force on blade Cutting velocity Swing velocity Water underpressure force on the shear plane Water underpressure force on blade Water underpressure force on the back of the blade Waterdepth Blade angle Angle of shear plane Soil/interface friction angle Angle of internal friction Free running angle of blade Water density


N m N kPa N m/s N m/s2 m m m m/s N N rpm N N kW m3/s N N m/s m/s N N N m Deg. Deg. Deg. Deg. Deg. Ton/m3


Hydraulic transport: c C1,2,3,4 Cd Ct Cv Cx d D D Fr g H I k Kp L n p P Q r Re T u v α,β β ε ε Φ η ϕ ϕ& && ϕ λ ν ρ τ ξ ψ

Line speed Coefficients Drag coefficient Transport concentration Volumetric concentration Drag coefficient Grain diameter Impeller diameter Pipe diameter Froude number Gravitational constant Height Mass moment of inertia Constant Proportionality constant Length of pipeline Revolutions Pressure Power Flow Radius Reynolds number Torque Tangetial velocity Settling velocity grains Coefficients Blade angle Wall roughness Ratio Durand coefficient Efficiency Rotation angle of centrifugal pump Angular velocity of centrifugal pump Angular acceleration of centrifugal pump Friction coefficient Kinematic viscosity Density Time constant Friction coefficient Shape factor


m/sec

m m m m/sec2 m ton⋅m3 kNms/rad m rpm kPa kW m3/sec m kNm m/sec m/sec rad m rad rad/sec rad/sec2 m2/sec ton/m3 sec -

Bibliography Dr.ir. S.A. Miedema 1980-2010 1. Koert, P. & Miedema, S.A., "Report on the field excursion to the USA April 1981" (PDF in Dutch 27.2 MB). Delft University of Technology, 1981, 48 pages. 2. Miedema, S.A., "The flow of dredged slurry in and out hoppers and the settlement process in hoppers" (PDF in Dutch 37 MB). ScO/81/105, Delft University of Technology, 1981, 147 pages. 3. Miedema, S.A., "The soil reaction forces on a crown cutterhead on a swell compensated ladder" (PDF in Dutch 19 MB). LaO/81/97, Delft University of Technology, 1981, 36 pages. 4. Miedema, S.A., "Computer program for the determination of the reaction forces on a cutterhead, resulting from the motions of the cutterhead" (PDF in Dutch 11 MB). Delft Hydraulics, 1981, 82 pages. 5. Miedema, S.A. "The mathematical modeling of the soil reaction forces on a cutterhead and the development of the computer program DREDMO" (PDF in Dutch 25 MB). CO/82/125, Delft University of Technology, 1982, with appendices 600 pages. 6. Miedema, S.A.,"The Interaction between Cutterhead and Soil at Sea" (In Dutch). Proc. Dredging Day November 19th, Delft University of Technology 1982. 7. Miedema, S.A., "A comparison of an underwater centrifugal pump and an ejector pump" (PDF in Dutch 3.2 MB). Delft University of Technology, 1982, 18 pages. 8. Miedema, S.A., "Computer simulation of Dredging Vessels" (In Dutch). De Ingenieur, Dec. 1983. (Kivi/Misset). 9. Koning, J. de, Miedema, S.A., & Zwartbol, A., "Soil/Cutterhead Interaction under Wave Conditions (Adobe Acrobat PDF-File 1 MB)". Proc. WODCON X, Singapore 1983. 10. Miedema, S.A. "Basic design of a swell compensated cutter suction dredge with axial and radial compensation on the cutterhead" (PDF in Dutch 20 MB). CO/82/134, Delft University of Technology, 1983, 64 pages. 11. Miedema, S.A., "Design of a seagoing cutter suction dredge with a swell compensated ladder" (PDF in Dutch 27 MB). IO/83/107, Delft University of Technology, 1983, 51 pages. 12. Miedema, S.A., "Mathematical Modeling of a Seagoing Cutter Suction Dredge" (In Dutch). Published: The Hague, 18-9-1984, KIVI Lectures, Section Under Water Technology. 13. Miedema, S.A., "The Cutting of Densely Compacted Sand under Water (Adobe Acrobat PDF-File 575 kB)". Terra et Aqua No. 28, October 1984 pp. 4-10. 14. Miedema, S.A., "Longitudinal and Transverse Swell Compensation of a Cutter Suction Dredge" (In Dutch). Proc. Dredging Day November 9th 1984, Delft University of Technology 1984. 15. Miedema, S.A., "Compensation of Velocity Variations". Patent application no. 8403418, Hydromeer B.V. Oosterhout, 1984. 16. Miedema, S.A., "Mathematical Modeling of the Cutting of Densely Compacted Sand Under Water". Dredging & Port Construction, July 1985, pp. 22-26. 17. Miedema, S.A., "Derivation of the Differential Equation for Sand Pore Pressures". Dredging & Port Construction, September 1985, pp. 35. 18. Miedema, S.A., "The Application of a Cutting Theory on a Dredging Wheel (Adobe Acrobat 4.0 PDF-File 745 kB)". Proc. WODCON XI, Brighton 1986. 19. Miedema, S.A., "Underwater Soil Cutting: a Study in Continuity". Dredging & Port Construction, June 1986, pp. 47-53.

20. Miedema, S.A., "The cutting of water saturated sand, laboratory research" (In Dutch). Delft University of Technology, 1986, 17 pages. 21. Miedema, S.A., "The forces on a trenching wheel, a feasibility study" (In Dutch). Delft, 1986, 57 pages + software. 22. Miedema, S.A., "The translation and restructuring of the computer program DREDMO from ALGOL to FORTRAN" (In Dutch). Delft Hydraulics, 1986, 150 pages + software. 23. Miedema, S.A., "Calculation of the Cutting Forces when Cutting Water Saturated Sand (Adobe Acrobat 4.0 PDF-File 16 MB)". Basic Theory and Applications for 3-D Blade Movements and Periodically Varying Velocities for, in Dredging Commonly used Excavating Means. Ph.D. Thesis, Delft University of Technology, September 15th 1987. 24. Bakker, A. & Miedema, S.A., "The Specific Energy of the Dredging Process of a Grab Dredge". Delft University of Technology, 1988, 30 pages. 25. Miedema, S.A., "On the Cutting Forces in Saturated Sand of a Seagoing Cutter Suction Dredge (Adobe Acrobat 4.0 PDF-File 1.5 MB)". Proc. WODCON XII, Orlando, Florida, USA, April 1989. This paper was given the IADC Award for the best technical paper on the subject of dredging in 1989. 26. Miedema, S.A., "The development of equipment for the determination of the wear on pick-points" (In Dutch). Delft University of Technology, 1990, 30 pages (90.3.GV.2749, BAGT 462). 27. Miedema, S.A., "Excavating Bulk Materials" (In Dutch). Syllabus PATO course, 1989 & 1991, PATO The Hague, The Netherlands. 28. Miedema, S.A., "On the Cutting Forces in Saturated Sand of a Seagoing Cutter Suction Dredge (Adobe Acrobat 4.0 PDF-File 1.5 MB)". Terra et Aqua No. 41, December 1989, Elseviers Scientific Publishers. 29. Miedema, S.A., "New Developments of Cutting Theories with respect to Dredging, the Cutting of Clay (Adobe Acrobat 4.0 PDF-File 640 kB)". Proc. WODCON XIII, Bombay, India, 1992. 30. Davids, S.W. & Koning, J. de & Miedema, S.A. & Rosenbrand, W.F., "Encapsulation: A New Method for the Disposal of Contaminated Sediment, a Feasibility Study (Adobe Acrobat 4.0 PDF-File 3MB)". Proc. WODCON XIII, Bombay, India, 1992. 31. Miedema, S.A. & Journee, J.M.J. & Schuurmans, S., "On the Motions of a Seagoing Cutter Dredge, a Study in Continuity (Adobe Acrobat 4.0 PDF-File 396 kB)". Proc. WODCON XIII, Bombay, India, 1992. 32. Becker, S. & Miedema, S.A. & Jong, P.S. de & Wittekoek, S., "On the Closing Process of Clamshell Dredges in Water Saturated Sand (Adobe Acrobat 4.0 PDF-File 1 MB)". Proc. WODCON XIII, Bombay, India, 1992. This paper was given the IADC Award for the best technical paper on the subject of dredging in 1992. 33. Becker, S. & Miedema, S.A. & Jong, P.S. de & Wittekoek, S., "The Closing Process of Clamshell Dredges in Water Saturated Sand (Adobe Acrobat 4.0 PDF-File 1 MB)". Terra et Aqua No. 49, September 1992, IADC, The Hague. 34. Miedema, S.A., "Modeling and Simulation of Dredging Processes and Systems". Symposium "Zicht op Baggerprocessen", Delft University of Technology, Delft, The Netherlands, 29 October 1992. 35. Miedema, S.A., "Dredmo User Interface, Operators Manual". Report: 92.3.GV.2995. Delft University of Technology, 1992, 77 pages. 36. Miedema, S.A., "Inleiding Mechatronica, college WBM202" Delft University of Technology, 1992.

37. Miedema, S.A. & Becker, S., "The Use of Modeling and Simulation in the Dredging Industry, in Particular the Closing Process of Clamshell Dredges", CEDA Dredging Days 1993, Amsterdam, Holland, 1993. 38. Miedema, S.A., "On the Snow-Plough Effect when Cutting Water Saturated Sand with Inclined Straight Blades (Adobe Acrobat 4.0 PDF-File 503 kB)". ASCE Proc. Dredging 94, Orlando, Florida, USA, November 1994. Additional Measurement Graphs. (Adobe Acrobat 4.0 PDF-File 209 kB). 39. Riet, E. van, Matousek, V. & Miedema, S.A., "A Reconstruction of and Sensitivity Analysis on the Wilson Model for Hydraulic Particle Transport (Adobe Acrobat 4.0 PDF-File 50 kB)". Proc. 8th Int. Conf. on Transport and Sedimentation of Solid Particles, 24-26 January 1995, Prague, Czech Republic. 40. Vlasblom, W.J. & Miedema, S.A., "A Theory for Determining Sedimentation and Overflow Losses in Hoppers (Adobe Acrobat 4.0 PDF-File 304 kB)". Proc. WODCON IV, November 1995, Amsterdam, The Netherlands 1995. 41. Miedema, S.A., "Production Estimation Based on Cutting Theories for Cutting Water Saturated Sand (Adobe Acrobat 4.0 PDF-File 423 kB)". Proc. WODCON IV, November 1995, Amsterdam, The Netherlands 1995. Additional Specific Energy and Production Graphs. (Adobe Acrobat 4.0 PDF-File 145 kB). 42. Riet, E.J. van, Matousek, V. & Miedema, S.A., "A Theoretical Description and Numerical Sensitivity Analysis on Wilson's Model for Hydraulic Transport in Pipelines (Adobe Acrobat 4.0 PDF-File 50 kB)". Journal of Hydrology & Hydromechanics, Slovak Ac. of Science, Bratislava, June 1996. 43. Miedema, S.A. & Vlasblom, W.J., "Theory for Hopper Sedimentation (Adobe Acrobat 4.0 PDF-File 304 kB)". 29th Annual Texas A&M Dredging Seminar. New Orleans, June 1996. 44. Miedema, S.A., "Modeling and Simulation of the Dynamic Behavior of a Pump/Pipeline System (Adobe Acrobat 4.0 PDF-File 318 kB)". 17th Annual Meeting & Technical Conference of the Western Dredging Association. New Orleans, June 1996. 45. Miedema, S.A., "Education of Mechanical Engineering, an Integral Vision". Faculty O.C.P., Delft University of Technology, 1997 (in Dutch). 46. Miedema, S.A., "Educational Policy and Implementation 1998-2003 (versions 1998, 1999 and 2000) (Adobe Acrobat 4.0 PDF_File 195 kB)". Faculty O.C.P., Delft University of Technology, 1998, 1999 and 2000 (in Dutch). 47. Keulen, H. van & Miedema, S.A. & Werff, K. van der, "Redesigning the curriculum of the first three years of the mechanical engineering curriculum". Proceedings of the International Seminar on Design in Engineering Education, SEFI-Document no.21, page 122, ISBN 2-87352-024-8, Editors: V. John & K. Lassithiotakis, Odense, 22-24 October 1998. 48. Miedema, S.A. & Klein Woud, H.K.W. & van Bemmel, N.J. & Nijveld, D., "Self Assesment Educational Programme Mechanical Engineering (Adobe Acrobat 4.0 PDF-File 400 kB)". Faculty O.C.P., Delft University of Technology, 1999. 49. Van Dijk, J.A. & Miedema, S.A. & Bout, G., "Curriculum Development Mechanical Engineering". MHO 5/CTU/DUT/Civil Engineering. Cantho University Vietnam, CICAT Delft, April 1999. 50. Miedema, S.A., "Considerations in building and using dredge simulators (Adobe Acrobat 4.0 PDF-File 296 kB)". Texas A&M 31st Annual Dredging Seminar. Louisville Kentucky, May 16-18, 1999.

51. Miedema, S.A., "Considerations on limits of dredging processes (Adobe Acrobat 4.0 PDF-File 523 kB)". 19th Annual Meeting & Technical Conference of the Western Dredging Association. Louisville Kentucky, May 16-18, 1999. 52. Miedema, S.A. & Ruijtenbeek, M.G. v.d., "Quality management in reality", "Kwaliteitszorg in de praktijk". AKO conference on quality management in education. Delft University of Technology, November 3rd 1999. 53. Miedema, S.A., "Curriculum Development Mechanical Engineering (Adobe Acrobat 4.0 PDF-File 4 MB)". MHO 5-6/CTU/DUT. Cantho University Vietnam, CICAT Delft, Mission October 1999. 54. Vlasblom, W.J., Miedema, S.A., Ni, F., "Course Development on Topic 5: Dredging Technology, Dredging Equipment and Dredging Processes". Delft University of Technology and CICAT, Delft July 2000. 55. Miedema, S.A., Vlasblom, W.J., Bian, X., "Course Development on Topic 5: Dredging Technology, Power Drives, Instrumentation and Automation". Delft University of Technology and CICAT, Delft July 2000. 56. Randall, R. & Jong, P. de & Miedema, S.A., "Experience with cutter suction dredge simulator training (Adobe Acrobat 4.0 PDF-File 1.1 MB)". Texas A&M 32nd Annual Dredging Seminar. Warwick, Rhode Island, June 25-28, 2000. 57. Miedema, S.A., "The modelling of the swing winches of a cutter dredge in relation with simulators (Adobe Acrobat 4.0 PDF-File 814 kB)". Texas A&M 32nd Annual Dredging Seminar. Warwick, Rhode Island, June 25-28, 2000. 58. Hofstra, C. & Hemmen, A. van & Miedema, S.A. & Hulsteyn, J. van, "Describing the position of backhoe dredges (Adobe Acrobat 4.0 PDF-File 257 kB)". Texas A&M 32nd Annual Dredging Seminar. Warwick, Rhode Island, June 25-28, 2000. 59. Miedema, S.A., "Automation of a Cutter Dredge, Applied to the Dynamic Behaviour of a Pump/Pipeline System (Adobe Acrobat 4.0 PDF-File 254 kB)". Proc. WODCON VI, April 2001, Kuala Lumpur, Malaysia 2001. 60. Heggeler, O.W.J. ten, Vercruysse, P.M., Miedema, S.A., "On the Motions of Suction Pipe Constructions a Dynamic Analysis (Adobe Acrobat 4.0 PDF-File 110 kB)". Proc. WODCON VI, April 2001, Kuala Lumpur, Malaysia 2001. 61. Miedema, S.A. & Zhao Yi, "An Analytical Method of Pore Pressure Calculations when Cutting Water Saturated Sand (Adobe Acrobat PDF-File 2.2 MB)". Texas A&M 33nd Annual Dredging Seminar, June 2001, Houston, USA 2001. 62. Miedema, S.A., "A Numerical Method of Calculating the Dynamic Behaviour of Hydraulic Transport (Adobe Acrobat PDF-File 246 kB)". 21st Annual Meeting & Technical Conference of the Western Dredging Association, June 2001, Houston, USA 2001. 63. Zhao Yi, & Miedema, S.A., "Finite Element Calculations To Determine The Pore Pressures When Cutting Water Saturated Sand At Large Cutting Angles (Adobe Acrobat PDF-File 4.8 MB)". CEDA Dredging Day 2001, November 2001, Amsterdam, The Netherlands. 64. Miedema, S.A., "Mission Report Cantho University". MHO5/6, Phase Two, Mission to Vietnam by Dr.ir. S.A. Miedema DUT/OCP Project Supervisor, 27 September-8 October 2001, Delft University/CICAT. 65.

(Zhao

Yi),

&

(Miedema,

S.A.),

" " (Finite Element Calculations To Determine The Pore Pressures When Cutting Water

Saturated Sand At Large Cutting Angles (Adobe Acrobat PDF-File 4.8 MB))". To be published in 2002. 66. Miedema, S.A., & Riet, E.J. van, & Matousek, V., "Theoretical Description And Numerical Sensitivity Analysis On Wilson Model For Hydraulic Transport Of Solids In Pipelines (Adobe Acrobat PDF-File 147 kB)". WEDA Journal of Dredging Engineering, March 2002. 67. Miedema, S.A., & Ma, Y., "The Cutting of Water Saturated Sand at Large Cutting Angles (Adobe Acrobat PDF-File 3.6 MB)". Proc. Dredging02, May 5-8, Orlando, Florida, USA. 68. Miedema, S.A., & Lu, Z., "The Dynamic Behavior of a Diesel Engine (Adobe Acrobat PDF-File 363 kB)". Proc. WEDA XXII Technical Conference & 34th Texas A&M Dredging Seminar, June 12-15, Denver, Colorado, USA. 69. Miedema, S.A., & He, Y., "The Existance of Kinematic Wedges at Large Cutting Angles (Adobe Acrobat PDF-File 4 MB)". Proc. WEDA XXII Technical Conference & 34th Texas A&M Dredging Seminar, June 12-15, Denver, Colorado, USA. 70. Ma, Y., Vlasblom, W.J., Miedema, S.A., Matousek, V., "Measurement of Density and Velocity in Hydraulic Transport using Tomography". Dredging Days 2002, Dredging without boundaries, Casablanca, Morocco, V64-V73, 22-24 October 2002. 71. Ma, Y., Miedema, S.A., Vlasblom, W.J., "Theoretical Simulation of the Measurements Process of Electrical Impedance Tomography". Asian Simulation Conference/5th International Conference on System Simulation and Scientific Computing, Shanghai, 3-6 November 2002, p. 261-265, ISBN 7-5062-5571-5/TP.75. 72. Thanh, N.Q., & Miedema, S.A., "Automotive Electricity and Electronics". Delft University of Technology and CICAT, Delft December 2002. 73. Miedema, S.A., Willemse, H.R., "Report on MHO5/6 Mission to Vietnam". Delft University of Technology and CICAT, Delft Januari 2003. 74. Ma, Y., Miedema, S.A., Matousek, V., Vlasblom, W.J., "Tomography as a Measurement Method for Density and Velocity Distributions". 23rd WEDA Technical Conference & 35th TAMU Dredging Seminar, Chicago, USA, june 2003. 75. Miedema, S.A., Lu, Z., Matousek, V., "Numerical Simulation of a Development of a Density Wave in a Long Slurry Pipeline". 23rd WEDA Technical Conference & 35th TAMU Dredging Seminar, Chicago, USA, june 2003. 76. Miedema, S.A., Lu, Z., Matousek, V., "Numerical simulation of the development of density waves in a long pipeline and the dynamic system behavior". Terra et Aqua, No. 93, p. 11-23. 77. Miedema, S.A., Frijters, D., "The Mechanism of Kinematic Wedges at Large Cutting Angles - Velocity and Friction Measurements". 23rd WEDA Technical Conference & 35th TAMU Dredging Seminar, Chicago, USA, june 2003. 78. Tri, Nguyen Van, Miedema, S.A., Heijer, J. den, "Machine Manufacturing Technology". Lecture notes, Delft University of Technology, Cicat and Cantho University Vietnam, August 2003. 79. Miedema, S.A., "MHO5/6 Phase Two Mission Report". Report on a mission to Cantho University Vietnam October 2003. Delft University of Technology and CICAT, November 2003. 80. Zwanenburg, M., Holstein, J.D., Miedema, S.A., Vlasblom, W.J., "The Exploitation of Cockle Shells". CEDA Dredging Days 2003, Amsterdam, The Netherlands, November 2003. 81. Zhi, L., Miedema, S.A., Vlasblom, W.J., Verheul, C.H., "Modeling and Simulation of the Dynamic Behaviour of TSHD's Suction Pipe System by using Adams". CHIDA Dredging Days, Shanghai, China, november 2003.

82. Miedema, S.A., "The Existence of Kinematic Wedges at Large Cutting Angles". CHIDA Dredging Days, Shanghai, China, november 2003. 83. Miedema, S.A., Lu, Z., Matousek, V., "Numerical Simulation of the Development of Density Waves in a Long Pipeline and the Dynamic System Behaviour". Terra et Aqua 93, December 2003. 84. Miedema, S.A. & Frijters, D.D.J., "The wedge mechanism for cutting of water saturated sand at large cutting angles". WODCON XVII, September 2004, Hamburg Germany. 85. Verheul, O. & Vercruijsse, P.M. & Miedema, S.A., "The development of a concept for accurate and efficient dredging at great water depths". WODCON XVII, September 2004, Hamburg Germany. 86. Miedema, S.A., "THE CUTTING MECHANISMS OF WATER SATURATED SAND AT SMALL AND LARGE CUTTING ANGLES". International Conference on Coastal Infrastructure Development - Challenges in the 21st Century. HongKong, november 2004. 87. Ir. M. Zwanenburg , Dr. Ir. S.A. Miedema , Ir J.D. Holstein , Prof.ir. W.J.Vlasblom, "REDUCING THE DAMAGE TO THE SEA FLOOR WHEN DREDGING COCKLE SHELLS". WEDAXXIV & TAMU36, Orlando, Florida, USA, July 2004. 88. Verheul, O. & Vercruijsse, P.M. & Miedema, S.A., "A new concept for accurate and efficient dredging in deep water". Ports & Dredging, IHC, 2005, E163. 89. Miedema, S.A., "Scrapped?". Dredging & Port Construction, September 2005. 90. Miedema, S.A. & Vlasblom, W.J., " Bureaustudie Overvloeiverliezen". In opdracht van Havenbedrijf Rotterdam, September 2005, Confidential. 91. He, J., Miedema, S.A. & Vlasblom, W.J., "FEM Analyses Of Cutting Of Anisotropic Densely Compacted and Saturated Sand", WEDAXXV & TAMU37, New Orleans, USA, June 2005. 92. Miedema, S.A., "The Cutting of Water Saturated Sand, the FINAL Solution". WEDAXXV & TAMU37, New Orleans, USA, June 2005. 93. Miedema, S.A. & Massie, W., "Selfassesment MSc Offshore Engineering", Delft University of Technology, October 2005. 94. Miedema, S.A., "THE CUTTING OF WATER SATURATED SAND, THE SOLUTION". CEDA African Section: Dredging Days 2006 - Protection of the coastline, dredging sustainable development, Nov. 1-3, Tangiers, Morocco. 95. Miedema, S.A., "La solution de prélèvement par désagrégation du sable saturé en eau". CEDA African Section: Dredging Days 2006 - Protection of the coastline, dredging sustainable development, Nov. 1-3, Tangiers, Morocco. 96. Miedema, S.A. & Vlasblom, W.J., "THE CLOSING PROCESS OF CLAMSHELL DREDGES IN WATER-SATURATED SAND". CEDA African Section: Dredging Days 2006 - Protection of the coastline, dredging sustainable development, Nov. 1-3, Tangiers, Morocco. 97. Miedema, S.A. & Vlasblom, W.J., "Le processus de fermeture des dragues à benne preneuse en sable saturé". CEDA African Section: Dredging Days 2006 - Protection of the coastline, dredging sustainable development, Nov. 1-3, Tangiers, Morocco. 98. Miedema, S.A. "THE CUTTING OF WATER SATURATED SAND, THE SOLUTION". The 2nd China Dredging Association International Conference & Exhibition, themed 'Dredging and Sustainable Development' and in Guangzhou, China, May 17-18 2006. 99. Ma, Y, Ni, F. & Miedema, S.A., "Calculation of the Blade Cutting Force for small Cutting Angles based on MATLAB". The 2nd China Dredging Association

International Conference & Exhibition, themed 'Dredging and Sustainable Development' and in Guangzhou, China, May 17-18 2006. 100.

,"

" (download). The 2nd China Dredging Association International Conference & Exhibition, themed 'Dredging and Sustainable Development' and in Guangzhou, China, May 17-18 2006. 101. Miedema, S.A. , Kerkvliet, J., Strijbis, D., Jonkman, B., Hatert, M. v/d, "THE DIGGING AND HOLDING CAPACITY OF ANCHORS". WEDA XXVI AND TAMU 38, San Diego, California, June 25-28, 2006. 102. Schols, V., Klaver, Th., Pettitt, M., Ubuan, Chr., Miedema, S.A., Hemmes, K. & Vlasblom, W.J., "A FEASIBILITY STUDY ON THE APPLICATION OF FUEL CELLS IN OIL AND GAS SURFACE PRODUCTION FACILITIES". Proceedings of FUELCELL2006, The 4th International Conference on FUEL CELL SCIENCE, ENGINEERING and TECHNOLOGY, June 19-21, 2006, Irvine, CA. 103. Miedema, S.A., "Polytechnisch Zakboek 51ste druk, Hoofdstuk G: Werktuigbouwkunde", pG1-G88, Reed Business Information, ISBN-10: 90.6228.613.5, ISBN-13: 978.90.6228.613.3. Redactie: Fortuin, J.B., van Herwijnen, F., Leijendeckers, P.H.H., de Roeck, G. & Schwippert, G.A. 104. MA Ya-sheng, NI Fu-sheng, S.A. Miedema, "Mechanical Model of Water Saturated Sand Cutting at Blade Large Cutting Angles", Journal of Hohai University Changzhou, ISSN 1009-1130, CN 32-1591, 2006. 绞刀片大角度切削水饱和沙的力学模型, 马亚生[1] 倪福生[1] S.A.Miedema[2], 《河海大学常州分校学报》-2006年20卷3期 -59-61页 105. Miedema, S.A., Lager, G.H.G., Kerkvliet, J., “An Overview of Drag Embedded Anchor Holding Capacity for Dredging and Offshore Applications”. WODCON, Orlando, USA, 2007. 106. Miedema, S.A., Rhee, C. van, “A SENSITIVITY ANALYSIS ON THE EFFECTS OF DIMENSIONS AND GEOMETRY OF TRAILING SUCTION HOPPER DREDGES”. WODCON ORLANDO, USA, 2007. 107. Miedema, S.A., Bookreview: Useless arithmetic, why environmental scientists can't predict the future, by Orrin H. Pilkey & Linda Pilkey-Jarvis. Terra et Aqua 108, September 2007, IADC, The Hague, Netherlands. 108. Miedema, S.A., Bookreview: The rock manual: The use of rock in hydraulic engineering, by CIRIA, CUR, CETMEF. Terra et Aqua 110, March 2008, IADC, The Hague, Netherlands. 109. Miedema, S.A., "An Analytical Method To Determine Scour". WEDA XXVIII & Texas A&M 39. St. Louis, USA, June 8-11, 2008. 110. Miedema, S.A., "A Sensitivity Analysis Of The Production Of Clamshells". WEDA XXVIII & Texas A&M 39. St. Louis, USA, June 8-11, 2008. 111. Miedema, S.A., "An Analytical Approach To The Sedimentation Process In Trailing Suction Hopper Dredgers". Terra et Aqua 112, September 2008, IADC, The Hague, Netherlands. 112. Hofstra, C.F., & Rhee, C. van, & Miedema, S.A. & Talmon, A.M., "On The Particle Trajectories In Dredge Pump Impellers". 14th International Conference Transport & Sedimentation Of Solid Particles. June 23-27 2008, St. Petersburg, Russia. 113. Miedema, S.A., "A Sensitivity Analysis Of The Production Of Clamshells". WEDA Journal of Dredging Engineering, December 2008.

114. Miedema, S.A., "New Developments Of Cutting Theories With Respect To Dredging, The Cutting Of Clay And Rock". WEDA XXIX & Texas A&M 40. Phoenix Arizona, USA, June 14-17 2009. 115. Miedema, S.A., "A Sensitivity Analysis Of The Scaling Of TSHD's". WEDA XXIX & Texas A&M 40. Phoenix Arizona, USA, June 14-17 2009. 116. Liu, Z., Ni, F., Miedema, S.A., “Optimized design method for TSHD’s swell compensator, basing on modelling and simulation”. International Conference on Industrial Mechatronics and Automation, pp. 48-52. Chengdu, China, May 15-16, 2009. 117. Miedema, S.A., "The effect of the bed rise velocity on the sedimentation process in hopper dredges". Journal of Dredging Engineering, Vol. 10, No. 1 , 10-31, 2009. 118. Miedema, S.A., “New developments of cutting theories with respect to offshore applications, the cutting of sand, clay and rock”. ISOPE 2010, Beijing China, June 2010. 119. Miedema, S.A., “The influence of the strain rate on cutting processes”. ISOPE 2010, Beijing China, June 2010. 120. Ramsdell, R.C., Miedema, S.A., “Hydraulic transport of sand/shell mixtures”. WODCON XIX, Beijing China, September 2010. 121. Abdeli, M., Miedema, S.A., Schott, D., Alvarez Grima, M., “The application of discrete element modeling in dredging”. WODCON XIX, Beijing China, September 2010. 122. Hofstra, C.F., Miedema, S.A., Rhee, C. van, “Particle trajectories near impeller blades in centrifugal pumps. WODCON XIX, Beijing China, September 2010. 123. Miedema, S.A., “Constructing the Shields curve, a new theoretical approach and its applications”. WODCON XIX, Beijing China, September 2010. 124. Miedema, S.A., “The effect of the bed rise velocity on the sedimentation process in hopper dredges”. WODCON XIX, Beijing China, September 2010.