Tag: PhD project

CEDA Dredging Days 2024: My Presentation On Clay Cutting

Initial clay cutting tests for my PhD project CHiPS
Initial clay cutting tests for my PhD project CHiPS

Next week is the biannual CEDA Dredging Days event1. This time fully focused on presentations, networking and having a good time together with like minded people. Since a long time, it will not be in conjunction with the distractions of the Europort exhibition. Instead, it will be in the impressive WTC Rotterdam. This is an excellent opportunity to share with you the progress of my PhD project on clay cutting at the TU Delft2. As a teaser, I would like to share with you some observations from my literature study, already3. Starting to search for literature via Google results in this:

Literature on clay (Kushim, 3400BC)4
Literature on clay (Kushim, 3400BC)4

When estimating the cutting production of a dredge, the objective is to find the specific cutting energy for that dredge in combination with the soil properties and correctly chosen operational settings. The specific cutting energy is the amount of power needed to excavate a volume of soil from the bottom5. The funny thing is, when you work out the dimensions of the specific cutting energy, the unit is similar to a stress or pressure. So, there should be a direct relation between the specific cutting energy and a soil property. But which one? For cohesive soils as clay, there are: shear strength, cohesion, adhesion, tensile strength, yield strength. The VOUB course6 recommends to use an empirically derived relation between the cohesion and the deformation rate (which in turn is based on the operating settings) for the specific cutting energy.

Specific Cutting Energy Empirical (Bart van der Schrieck, 1996)
Specific Cutting Energy Empirical (Bart van der Schrieck, 1996)

In contrast to this empirical model, one could also start at the displacements of the clay particles and model the implications for the larger continuum mathematically. This has been investigated by Sape Miedema, who has published countless articles and an impressive book on the topic7. Following this through, the estimated specific cutting energy is in the same range as the empirical model. However, on closer inspection, there are some variations on the outer limits of the deformation rate.

Specific Cutting Energy Theoretical (Sape Miedema, 1992)
Specific Cutting Energy Theoretical (Sape Miedema, 1992)

This discrepancy is probably due applying the model under all conditions. Miedema already recommends to check for the validity of the assumptions in the model. At very thin cutting layers, the resulting chip may form a long curl. When cutting thick layers, the blade will cut out chunks. And those cutting types will have different force equilibriums, resulting in different cutting forces. Miedema suggested a three regime map of cutting types, which coincidently resembles the curves found empirically.

Cutting types (Sape Miedema, 1992)
Cutting types (Sape Miedema, 1992)

It appears, there are many more cutting types possible for a myriad of soil properties and operating conditions. However, the published results and proposed models are not directly applicable for the dredging industry. Either the conditions or assumptions differ (dry earth works for example) or parameters or data has been failed to included in the publication. This leads to some white spots in the knowledge that I hope to colour in with my future models and upcoming experiments8.

Clay cutting test rig at DDE in Nijkerk
Clay cutting test rig at DDE in Nijkerk

References

  1. Welcome to CEDA’s (revamped) Dredging Days 2024
  2. Personal Announcement: Going Back To School To Cut Some Clay
  3. CEDA Announcement of my presentation, LinkedIn
  4. What was the first (known) maths mistake? Matt Parker
  5. Experiencing The Cutting Edge Of Dredging Technology
  6. VOUB Cursus 1998, Deel X, hoofdstuk 12, VBKO
  7. The Delft Sand, Clay & Rock Cutting Model, Sape Miedema
  8. Mechanical excavation of clayey soils, a review of the physical phenomena occurring, Mark Winkelman et al (CEDA Dredging Days 2024)

See also

Cees van Rhee Passed Away, a Visionary Leader for the Dredging Community

Cees van Rhee at the TU Delft Dredging Technology Laboratory (Credit: TU Delft)
Cees van Rhee at the TU Delft Dredging Technology Laboratory (Credit: TU Delft)

This is an article I didn’t want to write. My professor Cees van Rhee passed away last weekend1. This was devastating news for his family and all those who surrounded him at the TU Delft. Cees was still enjoying life, he died doing his favourite hobby: fishing. Always looking ahead, he was determined to be my promotor for my PhD. project. I know him already so long. When he was doing his PhD. project, I was graduating on my masters in the same lab. It would be fitting to be his last PhD. student. Fate has decided differently. As he was a public figure, you will receive in the news probably some factual biographies about him2. But he was so much a person to me, that I want to highlight some of his thoughts and contemplations for you.

When Cees assumed his position as dredging professor3, he set three goals to work on:

  1. Bring the department of dredging engineering under a single faculty
  2. Improve the quality of research and education
  3. Make the dredging community conscious of designing equipment for performance

He managed to merge the civil engineering branch and the mechanical engineering branch of the dredging engineering department as one of his first feats as new professor. The second goal can be sensed from the enormous increase in publications during his tenure4. And not only in the usual dredging literature, but also in highly regarded scientific journals. A standard he also imposed on my own PhD. project. The final goal is a real dot on the horizon and is therefore harder to achieve. He engaged with the rest of the dredging community through his numerous activities for the CEDA. Bringing his academic perspective to the industry.

In response to the drivers for dredging: population growth, transport demand and sea level rise, he saw the following challenges:

  1. Continuous innovation to stay ahead of the competition
  2. Re-allocation of labour for the manufacturing of equipment
  3. Understanding the dredging processes on a fundamental level
  4. Development of AI for supporting optimal operation

These challenges are still valid and are a sign of his visionary academic approach to dredging. Most of the research are contributing to solve these challenges. As a leader of the department of Dredging Engineering he lead his colleagues into a solid self-supporting team of specialists. I think we are still in a good position to tackle the challenges, but have to be careful to maintain this advantage.

Cees left a legacy of a high academic standard for dredging engineering. Torn away from life and so many projects ongoing, there will be a lot of loose ends to tie. And I am proud, that I can be part of it. When I approached him for my PhD. plans, he suggested to follow certain ideas that have been slumbering around, but were dormant because by now everybody uses finite element applications to study those problems. He was really happy that I came along with my old school analytic competences to pick up that gauntlet. I have some promising preliminary results already. And I am so sorry, he will never be there to enjoy the results that confirm he was onto something good.

We will all miss you. Thank you Cees.

Cees van Rhee welcoming the audience at the 2019 CEDA Dredging Days (Credit: CEDA)
Cees van Rhee welcoming the audience at the 2019 CEDA Dredging Days (Credit: CEDA)

References

  1. In Loving Memory of Prof. dr. ir. Cees van Rhee, LinkedIn
  2. In Loving Memory of Prof. dr. ir. Cees van Rhee, CEDA
  3. Over grensvlakken en het verleggen van grenzen, TU Delft
  4. Cees van Rhee, ResearchGate

See also

Graduation of Ines Ben M’hamed: The Strength of Clay in a Test Rig

Ines Ben M’hamed defending her graduation thesis
Ines Ben M’hamed defending her graduation thesis

Last week, Ines Ben M’hamed graduated with good grades on her bachelor thesis. She did a project with us at the Research Department of Damen Dredging Equipment in Nijkerk. The topic was to investigate the strengthening of clay when it is subjected to shear. This deformation is a common phenomenon when cutting clay and as such a contribution to my own PhD project1 and consequently improving our products for these applications. A common problem with clay is clogging up the cutter head, but it is also not completely understood why the clay is behaving as it does and how much power is involved for the various regimes.

Fully covered cutter head in sticky clay

The effects of deformation on the behaviour of clay are much more pronounced than e.g. sand or rock. Rock does not deform, it just breaks. Sand deforms, but as it basically only involves hydraulic and mechanical forces, it is much better understood. Clay particles have wider range of interactions. Next to the hydraulic and mechanical forces, they may experience: adhesion and cohesion, molecular forces, electrostatic charges and chemical bonding in the higher temperature ranges. The general effect is that as the particles in the original situation may have a weak structure, the external disturbance causes the particles to get jostled around and all the mentioned interaction get a chance to hook on to each other.

Shear strengthening due to organising particles
Shear strengthening due to organising particles

The result is, that the particles get oriented and therewith a better opportunity to bond. The effect is a strengthening of the shear stress. As this strengthening is dependent on the strain rate, it is this strain rate, that is of interest for the prediction of the cutting forces. There are many publications available on what the consequences are of the strain rate on the Specific Cutting Energy. A well known model is by Sape Miedema2.

Strain Rate Effect on the Specific Cutting Energy (Credit: SA Miedema)
Strain Rate Effect on the Specific Cutting Energy (Credit: SA Miedema)

The trick with this model is, it depends on this strain rate effect. The sole experimental data available is by Hatamura and Chijiwa3 in 1975. They tested one type of clay on the three governing parameters: static shear strength, dynamic shear strength and the strain rate. There hasn’t been hardly any further experimental investigation into this problem. And as we regularly receive samples and soil reports that we can not test on these properties, it is also hard to predict the performance of our cutter heads. So, we decided to build our own cutting test rig.

Design of Ines’ cutting test rig
Design of Ines’ cutting test rig

This cutting test rig resembles the specifications to the original test rig of Hatamura. This will allow us to verify the parameters in the model ourselves. We also prepared the design with various option to enable us to allow assessment of clay samples that we receive from clients and service engineers. We hope to provide our customers with additional service in this problem. Currently, the parts of the test rig arrived very late and Ines was not able to include the build in her project. Respect for the good grade she received for her thesis. However, the parts are there and provide and excellent opportunity for the next graduation student to do their project with our company. Who dares?

Available parts for the cutting test rig
Available parts for the cutting test rig

References

  1. Personal Announcement: Going Back To School To Cut Some Clay, Discover Dredging
  2. The Delft Sand Clay & Rock Cutting Model, SA Miedema
  3. Analysis Of the Mechanism of Soil : 1st Report. Cutting Patterns of Soils, Hatamura & Chijiwa

See also