Graduation Gijs Ter Meulen: Drag Analysis And Model For Forces And Production

Gijs proudly presenting his MSc. certificate.

We have another bright new MSc. engineer in dredging technology1: Gijs ter Meulen. Tuesday, he presented and defended his thesis on the forces and production of a trailing suction head. For this thesis project he was working at our research and development department at Damen Dredging Equipment2.

Trailing suction hopper dredges have become the tool of the trade for modern dredging contractors. They are versatile, flexible and able to transport sand over great distances. They load their cargo in their holds, by sucking up the sediment from the sea bottom with a big trailing suction head. This head looks like an out of size vacuum cleaner head.

Typical drag head on a railing suction hopper dredge.

Usually, it is very difficult to comprehend what is going on in and around the drag head. There is some laboratory research done, but not all results are freely available. Other knowledge is solely based on the experience of well-seasoned dredge masters. I do have respect for the experience of dredge masters, but their stories are hardly usable for an academic model description. So, Gijs took on the challenge to piece together a model, that satisfies our curiosity and fits with the experiences.

Concise development of the drag head model by Gijs ter Meulen.

For this project, he identified several steps, which we briefly touch upon here:

  1. The processes and forces around the drag head3 were all investigated on their cause and effect.
  2. A model was set up, where each process and their interaction with the others were identified.
  3. One main process in the drag head is the jetting production. A powerful jet of water is injected into the soil and this erodes part of the sediment under the drag head4.
  4. Another main process is the cutting production5. What is not eroded away by the jets, is removed by the teeth at the back of the visor.
  5. As the contribution of the processes to the forces and the production is known, the total performance can be calculated.

Along the way, this gave us very useful insight in the capabilities of the drag head and the trailing system, all the way to the requirements for the propulsion. Now, we will be able to continue to improve our drag heads even further. Any other students who would like to participate in that project are welcome to contact us5.

Gijs takes a new step in his career path. He is going to work for a well esteemed customer of us, so we will see him around in the dredging industry. Thanks Gijs, bon voyage!

Gijs, good luck with your future career in dredging.

References

  1. MSc Offshore & Dredging Engineering, TU Delft
  2. Innovation, Damen Dredging Equipment
  3. Designing Dredging Equipment [OE4671], Vlasblom
  4. Sand erosion with a traversing circular jet, Robert Weegenaar
  5. The Cutting of Sand, Dredging Engineering
  6. Internships, Damen Dredging Equipment

See also

Graduation Suman Sapkota: Where wear parts were worn down

Suman Sapkota signing his Master of Science degree

Yesterday, Suman Sapkota graduated at the University of Twente on: ‘Technical and Sustainability Analysis of Sediment Erosion of Impeller Blades of Dredge Pumps’. We are very proud he worked for us on this topic and graduated with a grade 8 for it. As such, he stands in a long line of Master students1, who graduate with an 8 or even higher2. We value good students and we like to work with them only if the work they deliver is useful for us. This requires an intensive supervision and the results are correspondingly. This does not guarantee a good result, but you can always try3.

Suman graduated on a topic covered by the chair of ‘Sustainable Energy Technology’4. The objective was to study the economic and environmental impact of worn wear parts. When wear parts have to be rejected too early, they increase their environmental footprint. On the other end, if an impeller is severely worn, the efficiency decreases and the environmental footprint increases also. Our question was whether it was possible to improve the design of the dredge pump for a longer lifetime by checking the wear rate of the improvement in a simulation. To understand the problem and answer the question Suman had to start investigating the wear process itself.

Introduction sediment erosion in dredging applications

From literature he evaluated different erosion models. Basically, what is the effect when a defined particle impacts the concerned surface under certain conditions. And the conditions will be depending on the flow pattern and the influence of the fluid on the particle trajectories. The second research part was the investigation of this flow pattern and simulated with a CFD application. The flow pattern and the particle properties were combined. This way, the movement of the particles can be traced from inlet to outlet.

Particle tracking in CFD simulation of an impeller

Between inlet and outlet, the particles bounce against several areas of the blade. The bouncing can be counted and mapped. Together with the information of the impingement conditions and the erosion model, an estimation of the erosion rate can be made for different flow conditions and soil properties. The mapping can be transformed into an erosion density map. These maps can be checked for pump capacity and particle sizes.

Sediment erosion rate density map

With these maps, we can finally evaluate in advance where impellers will wear down and if we can improve their lifetime by modifying the design. Thus we can reduce their environmental footprint and contribute to a more sustainable business.

Suman, thank you very much for working for us. You were a pleasure to work with. We wish you good luck on your career and a happy life.

Congratulations to Suman Sapkota. Well done!

References

  1. Graduation reports, Discover Dredging
  2. Ben Sloof Nominated For KIvI Best Offshore Graduate Student
  3. Internship Vacancies, Damen
  4. Kipaji scholarship for Nepalese student, University of Twente

See also

 

Graduation of Ben Sloof: Hopper Loading Model and Overflow Losses

Ben Sloof signing his Master of Science degree

Do you remember Ben Sloof? Our young bright graduation student presenting at the Young CEDA Pitch Talks? Last week he graduated (with honours!) on ‘Numerical modelling of overflow losses and flow in Trailing Suction Hopper Dredgers’. You may have noticed that hopper loading was already a topic for previous posts about Ben Sloof and Jordy Boone at the CEDA Dredging Days. It results from the great interest in this part of the dredging process. And it still is a very dynamic field of research indeed, as in a short time frame various new models are presented. Who would ever think that dredging technology is a boring business? We are already dredging for ages, so what innovation could ever contribute to the progress of dredging? Well, I’ll explain what this new kid on the block found out now.

Overview of a hopper loading process with OpenFOAM simulation

Due to time constraints on a graduation project, Ben was limited to work on only a part of the hopper loading process. He worked only on the internal interface between mixture and sediment. Moving free surfaces of a filling hopper or a lowering water table from a reduced overflow height were left out of the scope. Still, it quite accurately describes the observed phenomena in the hopper loading process. We see a negative buoyant jet, we see the jet scour pit, recirculation and mixing in the fluid body and a ‘clear’ top layer which carries away the fines as it is skimmed away through the overflow weir. Deviation from the measurements can be explained by the difference in single fraction particle size.

Introduction to the key components of the proposed new ‘Layer Model’ (1DV)

With the observations from the CFD, Ben Sloof made his new ‘Layer Model’ with specifically a single fraction of particles. Then, he made an effort to correct the ‘Layer Model’ for physics of multiple fractions, with not too much improvement. Later on, he introduced a ‘fiddle factor’, that magically happened to be spot on. Further research and development of the model is currently under way to build a better foundation for this. Who knows, even Einstein had to introduce the ‘Cosmological Constant’ to fit his Theory of General Relativity to reality. Years later he was proved to be right1.

Comparison of van Rhee, Boone and Sloof

The performance of the models by van Rhee and Boone were already discussed2. Now, the validation of the Sloof ‘Layer Model’ is also included. Only after adjustment for the multi fraction in the results, the model nears the performance of the van Rhee model. Difference here is calculation speed. Sloof manages to estimate the hopper performance in seconds. This is why he rightfully received his degree with honours. He improved the speed AND accuracy of the calculation in a method, that would normally take the better part of a PhD study. I am looking forward to his future achievements.

Although this graduation assignment really helps us in refining our design process and gave some insight in the loading and overflow process, it still is an academic exercise. And any scientific model is just as good as the assumptions that were made at the beginning. In reality, the circumstances might be very different from what the model assumed, resulting in quit some different performance.

Heavy weather dredging (Retrieved from YouTube 18/10/2012, unknown source)

References

  1. Cosmological Constant Confirmed
  2. IADC Young Author Award for 1DH Hopper Loading Model of Jordy Boone

See also

Overview of hopper loading models by Ben Sloof
Nice report with an overview of the various hopper loading models

Dredging Engineering (lectures)

Dredging Engineering (papers)

Damen Standard TSHD

Damen MAD