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

 

Ben Sloof Nominated For KIvI Best Offshore Graduate Student

3D simulation of a hopper loading process

Ben Sloof was one of the best graduate students we had here at our company. For his thesis1, he tackled a complex problem and managed to model this in a reliable simulation. Now he is nominated for best Offshore Graduate Student. Today, there will be a KIvI Offshore lecture evening with a ceremony to award the prize2. Once again3, Ben will deliver a capturing pitch on his thesis. So, let’s review what he has achieved.

Van Rhee and similar ‘Euler’ models

At the chair of Dredging Technology of professor van Rhee, a lot of effort is put in describing the hopper loading in so called ‘Euler’ models. This is where you calculate the flow of the fluid and derive the flux of material that is carried within. Ben is standing on the shoulders of giants here, as by now there are a lot of models available4. We opted to use an existing simulation platform: OpenFOAM. One of the plugins for this open source program is DriftFlux, where the valuable grains are treated as a continuum fluid moving through the rest of the fluid. The extra effort of Ben, was to modify this DriftFlux plugin to account for settling and scour. This is in itself is already an unprecedented feat. Complicated by the unstructured calculations within DriftFlux and OpenFOAM. Nonetheless, after careful verification, he was able to perform interesting simulations of the hopper loading process.

Concentration and Velocity

After careful examination of the simulations, Ben started to see patterns in the flow. These set him on a track to build a whole new model. This new layer model credibly describes the process as well, without the complexity of a CFD simulation. As the development of a multi-fraction version of the OpenFOAM platform is still in progress, final verification is still pending. At least, the differences we see between the single fraction model and reality can be explained by what can be expected. It is open to further expansion with future research and can be used as a starting point for the next improvement.

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

And that is an insight worthy of extra appraisal: finally cracking the riddle of the sands settling in the hopper. We hope you will receive the prize. You deserve it.

Good luck Ben, we wish you all the best on your future voyages to unknown destinations. We are sure you’ll be blessed and a blessing, wherever you go.

Setting sail to distant shores

References

  1. Graduation of Ben Sloof: Hopper Loading Model and Overflow Losses
  2. KIvI Evening: Johan Sverdrup Platform Installatie
  3. Hopper Loading: What Happens Beneath the Surface
  4. IADC Young Author Award for 1DH Hopper Loading Model of Jordy Boone

See also

 

Don’t rock the boat, don’t tip the boat over

DOP Dredge ‘Roanoke’, Long Island, USA

We were quietly enjoying our dinner on a relaxed evening in our vacation. Suddenly, we were rudely disturbed by rumble and clatter from across the valley. For our eyes developed a rock slide. Just as sudden as it started it was already over. Perplexed, we were too slow to capture the event and put it on social media. Afterwards, I took some pictures of the rubble. As you can see, it was not even a proper rock slide, more the collapse of a retaining wall.

Retaining wall collapse, Sóller, Mallorca, Spain, June 21, 2018

Come to think about it, it was not the first collapse I witnessed. Back in 2006, I was visiting our DOP dredge at Roanoke on Long Island, NY in the USA. I had to do some measurements and general inspection. I was below decks connecting the data recorder to the drive system and had to check something with the dredge master. Just when I climbed on deck, he yelled at me to hold on. Immediately a torrent of water and sand was flung horizontally over the dredge. Some stones cracked a window in the control cabin. Within seconds a tsunami lifted the dredge for about a meter and we kept rocking until the reflecting waves in the pit eventually subsided.

DOP Dredge Roanoke with pit bank in the foreground, before it collapsed. Older bank collapses in the background.

That was one big bank collapse to me. A bank collapse is a known, although undesirable phenomenon in dredging1. It is a result of dredging methods, relying on the development of an active bank to produce a heavy slurry, that is sucked up. However, the sediment does not consist of a uniform block of sand. Usually, the sediment is deposited in different layers, each with their own geo technical properties. These result in varying propagation velocities of the active banks. When a ‘faster’ sand is under a ‘slower’ sand, the upper layer is not supported anymore and collapses. As the bank slumps down, it displaces an enormous volume of water and this often causes a tidal wave of its own. At Roanoke, the effects were aggravated by the fact, that the upper bank ran all the way to above water level.

Progression of an active bank and bank collapse

As this bank collapse can be expected when dredging with active banks and different sand layers, dredging companies are very keen on predicting these nasty consequences. Not only for the safe working condition of the crew, but also to prevent material damage and eventually for a stable and reliable delivered profile. Exactly this is what is being investigated by dr. Askarinejad in the Laboratory of Geo-Engineering at the Technical University Delft2. He has a beautiful rig, where exactly those conditions can be simulated and measured. With a neat trick he tips the whole test facility to form an instable bank. This makes the bank collapse on demand3.

Static liquefaction tank TU Delft (Credit: dr. A. Askarinejad)

Basically, this is exactly what we can demonstrate with the ‘breaching exhibit ‘ in our dredging experience4. Of course you are welcome to come over. For those who are not in the circumstance to visit us, you can also visit the National Dredging Museum as they now have a breaching exhibit of their own5.

Handover of our old breaching exhibit to the National Dredging Museum

References

  1. Breaching Process OE 4626, van Rhee, TU Delft
  2. Amin Askarinejad, TU Delft
  3. Statische liquefactietank , Delft Integraal
  4. Loose sand, how hard can it be?
  5. Baggermuseum krijgt model van Damen Dredging, Binnenvaartkrant

See also