Introduction

Currently, in various industrial settings, interactions between a solid object and a flowing fluid can be observed. In this regard, when the focus of the study is the flowing fluid, the technique of computationalfluid dynamics (CFD) can be applied. If you are interested in this subject, check out the links below for some of the posts on the Kot Blog on this topic:

 

• • Computational Fluid Dynamics: the physics and mathematics involved in CFD analysis;

 

• • CFD simulation: learn about its main uses in industry;

 

• • Succes story: CFD analysis in a moving hood;

The Federal Remediation Technologies Roundtable ( FRTR) defines the dredging process as the removal, treatment, and/or relocation of submerged contaminated sediments or contaminants [1]. Similarly, this definition aligns with the description of the environmental remediation dredging process outlined by the Brazilian Navy’s Ports and Coasts Directorate, which defines it as “The act of removing material and sediments from the bed of water bodies for a specific purpose […] carried out to improve environmental or sanitary conditions.” [2]. This type of dredging is performed to reduce the risks of the materials posing any kind of threat to human health or the environment.

The equipment used for dredging is known as dredgers and is commonly classified as mechanical dredgers, hydraulic dredgers, or pneumatic dredgers. In addition, hybrid models of these machines are also available. 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 conducted a study analyzing the drag forces on the floats of a dredge’s feed pipe using CFD analysis. These dredges are responsible for removing tailings from the reservoir that result from the bauxite ore washing process. Subsequently, these tailings are transported through a pipe to the reservoir wall. This pipe, in turn, is dragged by the dredger, which, upon contact with the fluid, generates a drag force opposite to the movement of the vessels.

Objective

The main objective of the study was to evaluate the drag force exerted by the movement of the dredgers, in order to determine the appropriate sizing of the steel cable and the anchor heads.

Development

First, at the start of the analysis, the model was created, and the boundary conditions—such as water flow perpendicular to the pipe—were defined and applied. Figures 2 and 3 show the computational 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 7: Velocity profile around the pipe - Top view. [3]

Finally, the study’s objective was achieved using the drag force equation. Thus, the computational analyses and analytical calculations to determine the maximum drag force acting on the pipes and dredgers showed that the drag coefficients are very high for this application, which influences the dredger’s movement trajectory, as shown in Figure 8.

Figure 8: Schematic view of dredge movement. [3]

In conclusion, CFD analyses have a wide range of applications in an industrial context, not only under design conditions but also for evaluating real-world scenarios in existing systems. These studies enable a physical-mathematical understanding of complex events and/or those 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