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B.J. Nieuwboer
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When dredging rock using a Cutter Suction Dredger the high amount of spillage is problematic, since it prevents an energy efficient removal process. This papers presents a coupled DEM-FVM method to simulate spillage, that can be used for optimizing the design and working method of the Cutter Suction Dredger. In these simulations, the challenge was to model relatively large particles in a complex and rotating geometry. To ensure stability and reduce computational time we used smoothing kernels to map the forces and the concentration between the discrete elements and the fluid mesh. The method is validated for the fluid flow in the rotating cutter head. This model incorporates all physical processes to predict flow induced spillage in cutter heads within feasible calculation times.
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When dredging rock using a Cutter Suction Dredger the high amount of spillage is problematic, since it prevents an energy efficient removal process. This papers presents a coupled DEM-FVM method to simulate spillage, that can be used for optimizing the design and working method of the Cutter Suction Dredger. In these simulations, the challenge was to model relatively large particles in a complex and rotating geometry. To ensure stability and reduce computational time we used smoothing kernels to map the forces and the concentration between the discrete elements and the fluid mesh. The method is validated for the fluid flow in the rotating cutter head. This model incorporates all physical processes to predict flow induced spillage in cutter heads within feasible calculation times.
Modelling Spillage in Rotating Cutter Suction Heads
A combined Finite Volume and Discrete Element Model
Due to an increased demand for transport, ships become larger, needing a larger navigable depth. For these reasons a waterway needs to be dredged and a Cutter Suction Dredger is a vessel suitable for this operation.
A Cutter Suction Dredger is a floating vessel which removes sand, clay or soft rock from sea or river beds. It has a cutter head with pickpoints attached to it. By rotating and swinging, the pickpoints are pushed into the soil, disintegrating it. The soil enters the cutter head where it is mixed with water. From inside the cutter head it is hydraulically transported to the vessel via the suction mouth and pipe. The rotational speed of the cutter head can be varied by the vessel operator. When increasing the rotational velocity and swing speed, more production can be obtained. However, this leads to an outflow of water and dredged material near the ring, spilling the soil.
When the Cutter Suction Dredger is employed for cutting sand, the sand particles are easily kept in suspension due to the rotating motion before it is sucked up. A cutter suction dredger is also used for cutting rock, leading to large pieces, which are more influenced by gravity and the centrifugal force. Due to these forces, the pieces are thrown out of the cutter head more easily than smaller sand particles. The pieces of rock which are thrown out of the cutter are considered spilled. This spillage is unfavourable since this material has to be dredged a second time or is left on the sea floor. When the material is left on the sea floor, a larger layer of soil needs to be dredged for creating the same navigable depth.
To reduce spillage, the processes contributing to spillage should be quantified in order to design a better cutter head or working method. This dissertation contributes to this goal by presenting a validated model for simulating the spillage of rock particles inside a rotating cutter head. Such a model can be used to quantify different processes and test new cutter head designs…
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A Cutter Suction Dredger is a floating vessel which removes sand, clay or soft rock from sea or river beds. It has a cutter head with pickpoints attached to it. By rotating and swinging, the pickpoints are pushed into the soil, disintegrating it. The soil enters the cutter head where it is mixed with water. From inside the cutter head it is hydraulically transported to the vessel via the suction mouth and pipe. The rotational speed of the cutter head can be varied by the vessel operator. When increasing the rotational velocity and swing speed, more production can be obtained. However, this leads to an outflow of water and dredged material near the ring, spilling the soil.
When the Cutter Suction Dredger is employed for cutting sand, the sand particles are easily kept in suspension due to the rotating motion before it is sucked up. A cutter suction dredger is also used for cutting rock, leading to large pieces, which are more influenced by gravity and the centrifugal force. Due to these forces, the pieces are thrown out of the cutter head more easily than smaller sand particles. The pieces of rock which are thrown out of the cutter are considered spilled. This spillage is unfavourable since this material has to be dredged a second time or is left on the sea floor. When the material is left on the sea floor, a larger layer of soil needs to be dredged for creating the same navigable depth.
To reduce spillage, the processes contributing to spillage should be quantified in order to design a better cutter head or working method. This dissertation contributes to this goal by presenting a validated model for simulating the spillage of rock particles inside a rotating cutter head. Such a model can be used to quantify different processes and test new cutter head designs…
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Due to an increased demand for transport, ships become larger, needing a larger navigable depth. For these reasons a waterway needs to be dredged and a Cutter Suction Dredger is a vessel suitable for this operation.
A Cutter Suction Dredger is a floating vessel which removes sand, clay or soft rock from sea or river beds. It has a cutter head with pickpoints attached to it. By rotating and swinging, the pickpoints are pushed into the soil, disintegrating it. The soil enters the cutter head where it is mixed with water. From inside the cutter head it is hydraulically transported to the vessel via the suction mouth and pipe. The rotational speed of the cutter head can be varied by the vessel operator. When increasing the rotational velocity and swing speed, more production can be obtained. However, this leads to an outflow of water and dredged material near the ring, spilling the soil.
When the Cutter Suction Dredger is employed for cutting sand, the sand particles are easily kept in suspension due to the rotating motion before it is sucked up. A cutter suction dredger is also used for cutting rock, leading to large pieces, which are more influenced by gravity and the centrifugal force. Due to these forces, the pieces are thrown out of the cutter head more easily than smaller sand particles. The pieces of rock which are thrown out of the cutter are considered spilled. This spillage is unfavourable since this material has to be dredged a second time or is left on the sea floor. When the material is left on the sea floor, a larger layer of soil needs to be dredged for creating the same navigable depth.
To reduce spillage, the processes contributing to spillage should be quantified in order to design a better cutter head or working method. This dissertation contributes to this goal by presenting a validated model for simulating the spillage of rock particles inside a rotating cutter head. Such a model can be used to quantify different processes and test new cutter head designs…
A Cutter Suction Dredger is a floating vessel which removes sand, clay or soft rock from sea or river beds. It has a cutter head with pickpoints attached to it. By rotating and swinging, the pickpoints are pushed into the soil, disintegrating it. The soil enters the cutter head where it is mixed with water. From inside the cutter head it is hydraulically transported to the vessel via the suction mouth and pipe. The rotational speed of the cutter head can be varied by the vessel operator. When increasing the rotational velocity and swing speed, more production can be obtained. However, this leads to an outflow of water and dredged material near the ring, spilling the soil.
When the Cutter Suction Dredger is employed for cutting sand, the sand particles are easily kept in suspension due to the rotating motion before it is sucked up. A cutter suction dredger is also used for cutting rock, leading to large pieces, which are more influenced by gravity and the centrifugal force. Due to these forces, the pieces are thrown out of the cutter head more easily than smaller sand particles. The pieces of rock which are thrown out of the cutter are considered spilled. This spillage is unfavourable since this material has to be dredged a second time or is left on the sea floor. When the material is left on the sea floor, a larger layer of soil needs to be dredged for creating the same navigable depth.
To reduce spillage, the processes contributing to spillage should be quantified in order to design a better cutter head or working method. This dissertation contributes to this goal by presenting a validated model for simulating the spillage of rock particles inside a rotating cutter head. Such a model can be used to quantify different processes and test new cutter head designs…
In dredging soil is excavated with dredging equipment. One of the main types of equipment is the cutter suction dredge (CSD). The CSD consists of a floating pontoon, with in the back a spud pole penetrating the soil. In the front there is a ladder, which can rotate around a horizontal bearing. By means of this rotation the cutter head, mounted at the end of the ladder, can be positioned in the bank. Also, at the end of the ladder two swing wires are connected (port and starboard wires) enabling the CSD to rotate around the spud pole and thus letting the cutter head make a circular movement through the bank. During this rotation, with a circumferential swing velocity vs at the centre of the cutter head, the cutter head (also rotating around its axis with a certain rpm) is excavating the soil. The theoretical soil production Qc equals the cross section of the cutter head in the bank cutting, perpendicular to the swing velocity vs times the swing velocity vs. The cutter head consists of the cutter axis connected to the hub, 5 or 6 arms on one side connected to the hub and on the other side connected to the ring and a suction pipe to catch the soil cut and transport the soil to its destination.
The difference between the theoretical production and the real production is the spillage. So, this is
the percentage of the theoretical production not entering the suction pipe. ...
The difference between the theoretical production and the real production is the spillage. So, this is
the percentage of the theoretical production not entering the suction pipe. ...
In dredging soil is excavated with dredging equipment. One of the main types of equipment is the cutter suction dredge (CSD). The CSD consists of a floating pontoon, with in the back a spud pole penetrating the soil. In the front there is a ladder, which can rotate around a horizontal bearing. By means of this rotation the cutter head, mounted at the end of the ladder, can be positioned in the bank. Also, at the end of the ladder two swing wires are connected (port and starboard wires) enabling the CSD to rotate around the spud pole and thus letting the cutter head make a circular movement through the bank. During this rotation, with a circumferential swing velocity vs at the centre of the cutter head, the cutter head (also rotating around its axis with a certain rpm) is excavating the soil. The theoretical soil production Qc equals the cross section of the cutter head in the bank cutting, perpendicular to the swing velocity vs times the swing velocity vs. The cutter head consists of the cutter axis connected to the hub, 5 or 6 arms on one side connected to the hub and on the other side connected to the ring and a suction pipe to catch the soil cut and transport the soil to its destination.
The difference between the theoretical production and the real production is the spillage. So, this is
the percentage of the theoretical production not entering the suction pipe.
The difference between the theoretical production and the real production is the spillage. So, this is
the percentage of the theoretical production not entering the suction pipe.
One of the main types of equipment is the cutter suction dredge (CSD). The theoretical soil production Qc equals the cross section of the cutter head in the bank cutting, perpendicular to the swing velocity vs times the swing velocity vs. If the theoretical soil production is 100%, usually less than 100% will enter the suction pipe. The real production. The difference between the theoretical production and the real production is the spillage. So, this is the percentage of the theoretical production not entering the suction pipe.
Now in practice it is more difficult to define the spillage, because often a number of swings at different levels is necessary to excavate a bank. The spillage of a previous swing may be cut a second time during the current swing and thus enter the suction pipe in the current swing. So, the spillage of one swing does not have to be spillage overall. In this report however just one swing is considered, assuming a fresh bank, where all the soil that does not enter the suction pipe is considered spillage.
The model is derived based on the Euler equation for centrifugal pumps, including inner and outer radii and blade angles. The model is first calibrated based on the limited experimental data mentioned in den Burger (2003). This paper covers the theory and the validation, with many experimental data of Miltenburg (1983), a cold case never published before. This paper shows the state of the art of the spillage modeling. ...
Now in practice it is more difficult to define the spillage, because often a number of swings at different levels is necessary to excavate a bank. The spillage of a previous swing may be cut a second time during the current swing and thus enter the suction pipe in the current swing. So, the spillage of one swing does not have to be spillage overall. In this report however just one swing is considered, assuming a fresh bank, where all the soil that does not enter the suction pipe is considered spillage.
The model is derived based on the Euler equation for centrifugal pumps, including inner and outer radii and blade angles. The model is first calibrated based on the limited experimental data mentioned in den Burger (2003). This paper covers the theory and the validation, with many experimental data of Miltenburg (1983), a cold case never published before. This paper shows the state of the art of the spillage modeling. ...
One of the main types of equipment is the cutter suction dredge (CSD). The theoretical soil production Qc equals the cross section of the cutter head in the bank cutting, perpendicular to the swing velocity vs times the swing velocity vs. If the theoretical soil production is 100%, usually less than 100% will enter the suction pipe. The real production. The difference between the theoretical production and the real production is the spillage. So, this is the percentage of the theoretical production not entering the suction pipe.
Now in practice it is more difficult to define the spillage, because often a number of swings at different levels is necessary to excavate a bank. The spillage of a previous swing may be cut a second time during the current swing and thus enter the suction pipe in the current swing. So, the spillage of one swing does not have to be spillage overall. In this report however just one swing is considered, assuming a fresh bank, where all the soil that does not enter the suction pipe is considered spillage.
The model is derived based on the Euler equation for centrifugal pumps, including inner and outer radii and blade angles. The model is first calibrated based on the limited experimental data mentioned in den Burger (2003). This paper covers the theory and the validation, with many experimental data of Miltenburg (1983), a cold case never published before. This paper shows the state of the art of the spillage modeling.
Now in practice it is more difficult to define the spillage, because often a number of swings at different levels is necessary to excavate a bank. The spillage of a previous swing may be cut a second time during the current swing and thus enter the suction pipe in the current swing. So, the spillage of one swing does not have to be spillage overall. In this report however just one swing is considered, assuming a fresh bank, where all the soil that does not enter the suction pipe is considered spillage.
The model is derived based on the Euler equation for centrifugal pumps, including inner and outer radii and blade angles. The model is first calibrated based on the limited experimental data mentioned in den Burger (2003). This paper covers the theory and the validation, with many experimental data of Miltenburg (1983), a cold case never published before. This paper shows the state of the art of the spillage modeling.
Spillage is a problem for many dredging projects that make use of a Cutter Suction Dredge (CSD). In addition to higher energy consumption for delivering the targeted depth, spillage can lead to a variety of environmental issues. Equally important is the operator's uncertainty as to how much spillage can be expected when drafting a tender. For this reason, this paper presents a tool to predict spillage rates when cutting sand or rock named the Sand-Rock Cutting Spillage Model. The tool focusses on centrifugal advection and rapid redeposition of sediment, the most significant spillage mechanisms. Centrifugal advection is defined as spillage due to the centrifugal forces acting on disintegrated soil inside the cutter as described in the Sand Cutting Spillage Model of Werkhoven et al. (2018). Rapid redeposition is induced by low mixture velocities that cause suspended particles to settle back onto the bank before reaching the suction mouth. This paper derives an improved mathematical foundation for the Sand Cutting Spillage Model and describes five model mechanisms that more accurately capture a number of observed dynamics. First, to more accurately predict cutter head flows, the internal and external cutter head densities are included. Second, the addition of axial flow in the cutter is investigated. Third, a formulation for the effects of rapid redeposition is incorporated. Fourth, an enhanced representation of the geometry of the cutter allows for a more accurate spillage prediction for the cutting of sand. The tool results compare well with measurements of Miltenburg (1983). For the cutting of rock, Den Burger (2003) observed that the downscaled rock material in his experiment easily settled at the cutter bottom. To this end, the fifth contribution of the Sand-Rock Cutting Spillage Model is the introduction of a concentration difference for rapid redeposition flow in comparison to other flow terms. The five mechanisms underlying the Sand-Rock Cutting Spillage Model bring the model in good agreement with experimental data for rock spillage rates by Den Burger (2003).
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Spillage is a problem for many dredging projects that make use of a Cutter Suction Dredge (CSD). In addition to higher energy consumption for delivering the targeted depth, spillage can lead to a variety of environmental issues. Equally important is the operator's uncertainty as to how much spillage can be expected when drafting a tender. For this reason, this paper presents a tool to predict spillage rates when cutting sand or rock named the Sand-Rock Cutting Spillage Model. The tool focusses on centrifugal advection and rapid redeposition of sediment, the most significant spillage mechanisms. Centrifugal advection is defined as spillage due to the centrifugal forces acting on disintegrated soil inside the cutter as described in the Sand Cutting Spillage Model of Werkhoven et al. (2018). Rapid redeposition is induced by low mixture velocities that cause suspended particles to settle back onto the bank before reaching the suction mouth. This paper derives an improved mathematical foundation for the Sand Cutting Spillage Model and describes five model mechanisms that more accurately capture a number of observed dynamics. First, to more accurately predict cutter head flows, the internal and external cutter head densities are included. Second, the addition of axial flow in the cutter is investigated. Third, a formulation for the effects of rapid redeposition is incorporated. Fourth, an enhanced representation of the geometry of the cutter allows for a more accurate spillage prediction for the cutting of sand. The tool results compare well with measurements of Miltenburg (1983). For the cutting of rock, Den Burger (2003) observed that the downscaled rock material in his experiment easily settled at the cutter bottom. To this end, the fifth contribution of the Sand-Rock Cutting Spillage Model is the introduction of a concentration difference for rapid redeposition flow in comparison to other flow terms. The five mechanisms underlying the Sand-Rock Cutting Spillage Model bring the model in good agreement with experimental data for rock spillage rates by Den Burger (2003).
This paper proposes a classification of the concurrent sources of Cutter Suction Dredger (CSD) spillage as well as a pseudo-analytical model for a-priori computation of spillage rates due to high rotational velocity-induced flow. As of yet, in literature, no analytical models exist that describe spillage due to centrifugal advection. Based on work performed by Miedema (2017) and Nieuwboer (2018), a preliminarymodel is set up that includes most relevant cutting variables, or a simplification thereof. However, in this preliminary model, the axial pump effect described in Den Burger is not explicitly accounted for and the pressures exerted on the cutterhead contour are heavily simplified. An adaptation of a governing dimensionless velocity ratio proposed by Steinbusch et al. (1999) and Dekker et al. (2003) is used for model calibration using experimental data for sand from Miltenburg (1983) and rock from Den Burger (2003). Model parameters were identified for which sand spillage can be estimated within a 5 percentage point bandwidth of the experimental data. Moreover, the shape of the model plot appears to resemble that of the data for sand accurately, i.e. the model behaves as expected. The preliminary model is not capable of accurately estimating rock spillage rates over a wide range of mixture velocities. This inaccuracy may be ascribed to the concurrence of other spillage sources. The preliminary proposed model may not entirely capture the centrifugal effect of the cutterhead for larger grain sizes. Recommendations are given for further research.
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This paper proposes a classification of the concurrent sources of Cutter Suction Dredger (CSD) spillage as well as a pseudo-analytical model for a-priori computation of spillage rates due to high rotational velocity-induced flow. As of yet, in literature, no analytical models exist that describe spillage due to centrifugal advection. Based on work performed by Miedema (2017) and Nieuwboer (2018), a preliminarymodel is set up that includes most relevant cutting variables, or a simplification thereof. However, in this preliminary model, the axial pump effect described in Den Burger is not explicitly accounted for and the pressures exerted on the cutterhead contour are heavily simplified. An adaptation of a governing dimensionless velocity ratio proposed by Steinbusch et al. (1999) and Dekker et al. (2003) is used for model calibration using experimental data for sand from Miltenburg (1983) and rock from Den Burger (2003). Model parameters were identified for which sand spillage can be estimated within a 5 percentage point bandwidth of the experimental data. Moreover, the shape of the model plot appears to resemble that of the data for sand accurately, i.e. the model behaves as expected. The preliminary model is not capable of accurately estimating rock spillage rates over a wide range of mixture velocities. This inaccuracy may be ascribed to the concurrence of other spillage sources. The preliminary proposed model may not entirely capture the centrifugal effect of the cutterhead for larger grain sizes. Recommendations are given for further research.
Although there have been many improvements in the design of cutter suction dredgers, a modern cutter still spills up to 40% of the cut rock in most unfavourable conditions. This spillage is the amount of rock that is cut loose by the cutter head, but is not sucked up by the dredge pump. This paper focusses on the flow phenomena of the water in the cutter. The flow partly causes this spillage. Previously, physical experiments have been performed to study the flow in a cutter head. In this paper the results of these measurements are used for the validation of an unsteady flow model. The cutter is modelled using Computational Fluid Dynamics with the OpenFOAM software. The modelled fluid velocities are averaged over one revolution and are compared with the time averaged velocities from experiments. This shows good agreement for different rotational speeds of the cutter head.
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Although there have been many improvements in the design of cutter suction dredgers, a modern cutter still spills up to 40% of the cut rock in most unfavourable conditions. This spillage is the amount of rock that is cut loose by the cutter head, but is not sucked up by the dredge pump. This paper focusses on the flow phenomena of the water in the cutter. The flow partly causes this spillage. Previously, physical experiments have been performed to study the flow in a cutter head. In this paper the results of these measurements are used for the validation of an unsteady flow model. The cutter is modelled using Computational Fluid Dynamics with the OpenFOAM software. The modelled fluid velocities are averaged over one revolution and are compared with the time averaged velocities from experiments. This shows good agreement for different rotational speeds of the cutter head.