Introduction
In various industrial scenarios, it is possible to observe interactions between a solid object and a fluid in flow. When the fluid in flow is of interest, it is possible to apply the technique of computational fluid dynamics(CFD). If you are interested in this subject, check out some of the texts on the Kot Blog on the subject in the links below:
The Federal Remediation Technologies Roundtable (FRTR) defines the dredging process as the removal, treatment and/or relocation of contaminated sediments or submerged contaminants [1]. This definition converges with the description of the environmental recovery dredging process described by the Brazilian Navy's Directorate of Ports and Coasts, which establishes it as "The act of removing material and sediments from the bed of bodies of water, with a specific purpose [...] Carried out for the improvement of environmental or sanitary conditions". [2]. This type of dredging is carried out to reduce the risk of materials posing some kind of threat to human health or the environment.
The equipment used to carry out dredging is known as a dredger and is commonly classified as a mechanical dredger, a hydraulic dredger or a pneumatic dredger. It is also possible to find hybrid models of these machines. In short, their operation can be described as [1]:
- Mechanical dredgers: equipment that dredges using mechanical devices, such as excavators;
- Hydraulic dredgers: equipment that dredges using the addition of water to form a fluid with the material to be removed, which can be pumped through pipes;
- Pneumatic dredgers: equipment that dredges using air pumping to suck up material with a small amount of water;
- Hybrid dredges: an arrangement of equipment that uses mechanical and hydraulic components to remove material.
Figure 1 shows a schematic of the dredging, dewatering and water treatment process.
Figure 1: Example of dredging, dewatering and water treatment. [1]
Kot has carried out a CFD analysis of the drag on the floats of a dredger's feed pipe. The dredgers in question are responsible for removing tailings from the reservoir resulting from the bauxite ore washing process. These tailings are transported through a pipe to the reservoir wall. This pipe, in turn, is dragged by the dredger which, in contact with the fluid, generates a drag force contrary to the movement of the vessels.
Objective
The main objective of the study was to assess the drag force exerted by the movement of the dredgers, in order to enable the sizing of the wire rope and anchor bollards.
Development
When starting the analysis, the model was created and the boundary conditions - such as the flow of water perpendicular to the pipe - were defined and used. Figures 2 and 3 below show the computer model generated for the study and the mesh used in the model, respectively.
Figure 2: Model used in CFD analysis. [3]
Figure 3: Final mesh of the CFD model. [3]
Some of the results obtained from the calculations and analyses carried out can be seen in Figures 4 to 7.
Figure 4: Velocity profiles around the pipe [m/s] [3].
Figure 5: Pressure distribution [Pa]. [3]
Figure 6: Velocity vectors around the pipe - Top view. [3]
Figure 7: Velocity profile around the pipe - Top view. [3]
The objective of the study was completed with the help of the drag force equation. The computational analyses and analytical calculations to determine the maximum drag load acting on the pipes and dredgers showed that the drag coefficients are too high for the application, which influences the dredger's movement path, as shown in Figure 8.
Figure 8: Schematic view of dredge movement. [3]
CFD CFD analyses have a wide range of applications in the industrial contextnot only in design conditions, but also to evaluate real scenarios of existing systems. These studies make it possible to understand the physics and mathematics of complex events that are not visible to the naked eye.
Kot has experience in this area and can help you with your company's needs. Contact our team for more information!
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References:
[1] https://frtr.gov/matrix/Environmental-Dredging/#Introduction
[2] RULES OF THE MARITIME AUTHORITY FOR WORKS, DREDGING, RESEARCH AND MINING OF MINERALS UNDER, OVER AND ON THE SHORES OF BRAZILIAN JURISDICTIONAL WATERS
[3] Kot Collection
