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Interpore 2026: The Cutting Of Clay in A Herschel-Bulkley Model

Proudly holding my poster for the Interpore conference

This week, I’ll be in Nantes at the Interpore 2026 conference1. This is an academic conference on everything porous, ranging from catalysts, to food, to foams, to biology and even soil mechanics. And that is a topic where my research fits in. I submitted an abstract for a poster on the work done by our intern Prasanna Ramadurai2 on the applicability of Herschel-Bulkley fluid modelling for the simulation of the cutting of clay. The accompanying presentation can be found here.

The elemental physics of clay deformation with the rate process theory

As a refresher, clay is a funny substance. The constituent particles of various minerals that form small plates, that are electrostatically charged. Due to these charges, they tend to cling together. When you deform the mass, there develops a shear plane. The particles move over each other with alternating repelling and attracting electric fields. This discrete path is reminiscent of how in particle physics moving steps are only possible when there is enough energy to push the particle past an activation threshold. This was initially postulated by Boltzmann3 and subsequently formalised by Arrenius and Glasstone in the rate process theory. Miedema further applied this to the deformation of clay4. Depending on the amount of water present, it can behave like the clay can behave like thick water or soft rock. Both captured by the same equations. Eventually the resulting shear stress curve is very similar to a Herschel-Bulkley fluid.

Shear stress model by Miedema and comparable fluid models

The work of Prasanna focused on exploring a workflow to simulate the deformation of clay using Ansys Fluent for CFD. This package does not support the deformation model as described by Miedema. But, as the resulting behaviour should be similar to the Herschel-Bulkley model, the H-B viscosity could be used. As previously described here, Prasanna managed to find the appropriate settings and setup to achieve credible results.

Result of the experiments and the simulation compared

As Fabian Kruis5 has previously done experiments in the soil bin test rig, we do have reference data from actual measurements. Fabian has recorded the deformation and analysed the internal movements with PIVlab. The vector field from PIVlab is very similar to the vector field calculated by Ansys Fluent with the Herschel-Bulkley viscosity model. However, translating the deformation to stresses and ultimately to the cutting forces on the blade is still to be improved. The results from Ansys overestimate the measured forces.

Next to the poster, I also prepared a presentation. This presentation can be accessed through the conference portal, or directly from here. Off course, when you are at the conference, you can approach me there. Or through the contact details her on this website.

Resulting shear plane angles from PIVlab and Ansys

References

Oldtimer Club at Damen: Dredges on the Road

Last week, we received the Oldtimer Club Nijkerk1 at our yard. Vehicles of every age and type gathered at the quayside next to our dredges and the club members were entertained in our office and factory on presentations and guided tours. I was happy to present part of my ‘History of Dredging’ story2. It was an engaging lecture for people that are actively involved in keeping rolling history alive. They were very excited to see how we have transported our dredges over time.

Transport of a single pontoon by Stoof Breda

When our predecessor company ‘De Groot’ started it’s business in Nijkerk, the idea was to be as close as possible to the emerging Zuiderzeewerken, the reclamation of the IJsselmeerpolders3. Most of the equipment could be launched from site and towed to the project site for mobilisation. Still, sometimes it was faster to deliver the equipment by truck, especially when it was small enough to fit on the loading bed.

Over time, the dredges increased in size, as did the trucks. And when the hull did not fit on the bed anymore, an (extendable) trailer could be utilised. Any additional equipment, spuds, pipeline, wires, etc. Could be loaded on separate trucks or later into containers for transport. As our products grew in size, this was the way we delivered the dredges. Also influenced by the constraint of the motorway bridge and the lock to the IJsselmeer. It has been a familiar sight to see trucks from the company ‘De Haan’ loading the dredges and bring them either to a port for shipment. Or sending directly to the client by road.

Suction dredge on transport by de Haan Transport

The modular design of our dredges has been a selling point for easy transport and quick mobilisation. This workaround turned out to be an advantage to our customers. The assembly at the destination can be done by local cranes. We can provide supervision and assistance on location. Even our biggest CSD’s have been road transported. e.g. The CSD650 was transported on 10 trucks and 7 containers. When you encounter this convoy on the road it is quite impressive.

Convoy of a dismounted CSD650 on 17 trucks

References

Ewout van Duursen 25 Years: Monitoring the Hopper Process

Ewout van Duursen (l) and colleague installing monitoring software on TSHD Tommy Norton

Regularly, I do write about the adventures of a student internship or graduation that I am involved in. And it really helps those young aspiring engineers to be in the limelight of attention. Today there is a different story on my website, the 25 year work anniversary of my esteemed colleague Ewout van Duursen1. A fitting opportunity to celebrate his achievements during his long career at Damen Dredging Equipment. Ewoud’s specialties are drive systems and programming. And especially in applications for trailing suction hopper dredges. One of the products he has been working on tirelessly are hopper process monitoring systems2.

Dredge master console with hopper process monitoring installed

A good TSHD monitoring system will show a number of processes for operating a trailing suction hopper dredge.

Trailing suction pipe visualisation
Pump performance monitoring
Hopper loading monitoring and draught measurement
Survey and positioning
Recording and reporting

One aspect I want to highlight is the hopper loading and draught measurement. There are some details that might be confusing at first.

Screen shot of a sample hopper loading process

Take for instance a nominally 1000 cube hopper. It may be rectangular 32 m long, 9 m wide and 4 m deep, without any obstructions for simplicity. The mathematical capacity would be 1152 m³. But you don’t want to have the cargo spilling over the coaming. The maximum water level might be 0.5 m below the coaming making the volume 1008 m³. The maximum height of the telescopic overflow may be 0.7 m below the coaming level, as the water draws down about 0.2 m from stagnation level to the rim of the overflow. This measurable volume is now 950 m³.

Diagram of various hopper loading volumes

And the cargo does not only have volume, it also has a mass. And as Archimedes already discovered, mass displaces its weight in volume of water. During design of the vessel and the hopper, the loaded sand is assumed to have a certain density, e.g. 1.6 ton/m³. But the density for the hopper may only be 1.5 ton/m³, as one has to accommodate for the transport water that also enters the hopper. So, you can’t fill the 950 m³ with 1521 ton of sand. The vessel can only carry 1426 ton of total cargo. This is 713 m³ sand of 1.6 ton/m³ and 237 m³ mixture of 1.2 ton/m³. It sounds disappointing when your 1000 cube hopper only carries 713 m³ of valuable sand. The 1.5 ton/m³ hopper density is rather low and the vessel is probably more intended for silt and mud with a lower in situ density. With mud of 1.5 ton/m³ density, you can load the hopper to the rim. And when you encounter heavier sand with e.g. a density of 1.8 ton/m³, don’t try to fill the hopper with this 713 m³ mentioned before. You’ll sink your ship. A good hopper loading monitoring system will enable you to monitor filling of the hopper to the maximum safe cargo capacity.

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

Interpore 2026: The Cutting Of Clay in A Herschel-Bulkley Model

References

See also

Oldtimer Club at Damen: Dredges on the Road

References

See also

Ewout van Duursen 25 Years: Monitoring the Hopper Process

References

See also