Yesterday, Wim Kleermaker graduated at the TU Delft on a research project he conducted on our slurry test circuit at Damen Dredging Equipment. Specifically, he was investigating the wear behaviour in our dredge pumps. The noteworthy aspect of this project, was that Wim was supervised by our colleague Suman Sapkota. As long time readers in the audience might remember Suman was my own pupil some years ago1.
Wear is a very common process in the dredging industry and one of the main cost factors in a project2. It is beneficial to know the amount of wear to expect in a certain condition and be able to predict the budget to reserve for this nuisance. This is only possible when we as a manufacturer will be able to predict the wear rate and pattern can provide the information to the operator for his estimates. We do have historical data that will allow us to provide a ball park figure, but a more analytical approach might assist us in particular unusual cases. Furthermore, it will also provide us insight in the impact of certain design decisions for the wear performance of a certain pump design. For Wim’s graduation, he had to approach this academically: come up with a simulation model and verify this with measurements.
The measurements were done in our slurry pump test circuit. This circuit has been highlighted a couple of posts back3. For Wim’s experiments, he used an impeller under a certain operating condition and mixture properties. Before and after a representative period, the condition of the impeller was measured and the difference is a measure of the wear experienced.
Wear (or scientifically: erosion) is related to the impact of the particles on the material surface. In order to know the kinetic energy of the particles, the flow field has to be known. As the flow fleild cannot be measured directly at the test circuit, we have to resort to Computation Fluid Dynamics. We already know of Suman’s graduation, to look for patterns in the flow lines, but Wim has extended the procedure to also quantitively estimate the related erosion.
Although there is only a limited amount of data available, comparing the results of the CFD estimation and the measured erosion are looking promising. This is certainly a workflow that will provide us the unique tools for engineering better pumps and assisting customers in their specific projects.
Although Wim will not join our ranks in the dredging community and pursue a different career in another interesting industry, we are sure he will be constructive and dedicated colleague at Marin.
Another magazine dropped on my doormat, albeit a digital edition of ‘Damen Nieuws’1. The internal magazine for Damen colleagues. It featured an article with Suman Sapkota and me. Suman is our pump design specialist2 and at a Damen wide R&D convention he presented a poster on his pump design workflow within Damen Dredging Equipment. This caught the attention of the editorial board and we were interviewed on what we actually do for a living. Although we can’t share the exact details of the article or the poster, it is still an interesting message that we can highlight here.
The design of a dredge pump is based on the required specifications(1). The most important properties of the pump are: efficiency, NPSH, wear and ball passage. The first important property we try to fix is the ball passage3. We do use our own geometry generator(2) that assist us in creating a pump with a big ball passage. Unlike normal pumps, dredge pumps have to cope with debris and boulders that have to pass the impeller. The bigger chunks that can pass, the more uptime the dredge will have. Once we are satisfied with the geometry, we feed this through a file format converter(3). The resulting 3D file can be used on several platforms. This will enable us to create the digital solid for the engineering4, but it also gives us the negative volume, also known as fluid. Then to do mathematical operations on the digital fluid, we have to divide the volume into tiny cells. This process is called meshing.(4) When the mesh is available, the fluid flow through the mesh can be simulated with computational fluid dynamics.(5) All the fluid properties of every cell are calculated and the results are shared with the adjoining cells. This can be repeated until all properties of the cells don’t change very much anymore, a stable solution. Integrating all the properties of the cells give the resulting performance of the pump.
The estimated performance can be evaluated against the four properties.(6) The head times the capacity divided by the power required will give the efficiency. That is one of the items we wanted to know, as it relates to how much fuel will be consumed. The other parameter obtained from the CFD is the NPSH, or roughly: the suction performance. Wear cannot be estimated yet, but we are working on that2. Although the calculated turbulence might give a clue what wear to expect. If the properties are not satisfying our requirements we make an iteration in the geometry for improving the performance. However, changing the geometry will usually result in a smaller ball passage. If the parameters are OK to our requirements we have a pump design.(7) Manufacturing it is a completely different game.5
The design process of the dredge pump takes quite some effort and we are continually looking to improve the workflow6. Eventually we would like to be able to cater for all special requirements each individual customer might have.
Working for a dredge manufacturer, I am happy we design and produce our own pumps. It gives us the confidence, that when we supply dredges, they are as we like them to be. Another benefit is in discussions with the customer. It is easier when we can sit at the table as experts on their equipment assit them in finding a solution for their dredge.
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.
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.
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.