Ph.D. on Efficient Dredging

IHC Systems congratulates Jelmer Braaksma obtaining his Ph.D. degree

Monday February 4th 2008 saw a lot of IHC Systems’ representatives and other IHC Merwede crew gathering in a festive mood with scientists and family and friends of Jelmer Braaksma in the Senate Chamber of Delft University of Technology, The Netherlands.

In that decent ambiance Jelmer, who joined IHC Systems in 2003, skilfully defended his doctoral thesis Model-Based Control of Hopper Dredgers before a distinctfully toga-clad promotional committee, in which near his direct promotor prof. dr. R. Babuška, among others such well-known people in the dredging world as prof. dr. ir. R. de Keyser, prof. dr. ir. C van Rhee and prof. ir. W.J. Vlasblom were seated, as well as IHC Systems’ research department manager, ir. C. de Keizer.

Jelmer’s research was focused on optimisation of dredging process and performance of trailing suction hopper dredgers. Obtaining optimum performance involves the control of five sub-processes, viz. drag head-excavation, pump and pipeline performance, power train, sailing and the sedimentation process in the hopper. All these are intertwined, and together constitute a dredging cycle which is essential for efficient operation of the vessels in economic and ecological terms.

As in particular the sedimentation process in the hopper cannot quantitatively be observed by the operator, he cannot incorporate this process in his control strategy. So, the performance of the dredging operation is only observable at the end of a complete cycle.

Now Jelmer succeeded in developing an optimisation strategy for the process by applying a model predictive control (MPC) strategy on the whole process. Therefore modelling was at stake, the gathering and analysis of enormous amounts of practice derived data for calibration and validation purposes, as well as nonlinear programming methods. Dredging Contractor DEME allowed IHC Systems and Jelmer to intensively gather data on board of their ships, for which courtesy IHC Systems is very thankfully.

MPC among others applies online parameter estimations and observes power constraints as well as constraints originating from the pumping and sailing process such as vacuum limitations and engine power. In general it has proven that MPC outperforms usual control strategies and optimizes the dredging stage of the process with approximately 20% for fine sand – and so the complete dredging cycle. Another result of the study is the insight that drag head models and vessel/cut-force models should receive attention.

Number 5 of the thesis’ propositions perfectly illustrates the cooperative spirit and fresh way of thinking of the young doctor: “The sharing of information, which the competition might have anyway, is not harmful for the competitive position, but rather it stimulates the development of new technology in the dredging industry.”

The photograph below shows that the promotion committee unanimously decided Jelmer worthy of carrying the title doctor from now. We at IHC Systems naturally are proud of our young colleague and cordially congratulate him and his girl-friend Grietje – who had designed the tasteful cover of the thesis – with his promotion and express the hope to share long times in Jelmer’s knowledge and further development.