Grabs are used for unloading dry bulk cargo vessels such as iron ore or coal. The request for higher payloads, shorter cycletimes and longer lifetime results in a permanent desire of a more efficient grab.

Development of grabs and other types of bulk handling equipment is still a complicated process: predicting the performance of a new design is hard, as continuous models are not very suitable due to the particulate nature of the dry bulk material. The current design process of bulk handling equipment such as grabs is based on years of experience and consists of designing a prototype, building it in the factory and evaluating it at a test site. This is an expensive process involving high risks and long R&D times. Virtual prototyping is proven to be successful in predicting the performance of bulk handling equipment such as grabs and an efficient method to improve grab designs.

A validated model using the Discrete Element Method (DEM) and Multibody Dynamics (MBD) has been developed at TU Delft and is ready to be used for predicting the performance of a virtual prototype grab. This combined model computes the behavior of the individual particles as well as and the behavior of the grab. With this tool, the performance of virtual prototypes can be compared, indicating whether a design change is an improvement or not. As many variables can influence the performance of a grab, finding an optimal performance is a challenging task.



Currently there are three MSc thesis assignments available within this project:

  1. Optimisation of grab design by applying optimization techniques. So far OVAT (one variable at the time) has been used to change design variables and to measure the effect on the grab performance. This is a time inefficient method and does not reveal interrelations between parameters. Therefore this project will use state-of-the-art optimisation techniques, e.g. Design of Experiments, and tools, e.g. Minitab, to come to an increased grab performance in terms of payload, weight of the grab, etc.. The developed model is available to be used in this project, and will be used to study the effect of design and operational variables.
  2. Developing a DEM/MBD model for the handling of a more difficult to handle material such as iron ore fines. This material can behave more cohesive, consists of smaller particles and a wider particle size distribution compared to iron ore pellets and as a result other material models have to be used within the simulation environment. Material models have to be found and compared to be able to predict the behavior of the cohesive material in relation to the grab.
  3. Minimizing wear by a DEM supported approach. The developed tool and validated model will be used to study and minimize the wear. Promising directions can be applying non-smooth surfaces (based on bionic design) where the challenge is to reduce wear and have wear-resistant material under extreme conditions, while maintaining grab performance in terms of payload.


The research will be carried out together with the TU Delft, 3ME, section Transport Engineering and Logistics.

During this project the supervisory team exists of ir. Javad Mohajeri and Dingena Schott (section Transport Engineering and Logistics), Cees van Rhee (section Dredging Engineering) as well as the Engineering team at Nemag B.V..

The office location of the student is open for discussion (Delft and/or Zierikzee). A monthly allowance and travel expenses will be offered.



Interested in one of these projects? Students can apply for this position by sending an email to or



For more information contact us or apply for this position.

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Persoonlijke informatie


Want to know more about working at Nemag? Please contact our colleague.

ir. Michel Corbeau
General manager

+31 111 418 934

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Compare the grab glossary

Crane capacityIs the Safe Working Load of your crane in tons in grab duty, i.e. the total sum of grab dead weight and payload.

PayloadIs the nett load of cargo in the grab. Because it’s linked with the grab weight it will be filled in automatically.

Grab weightIs the Dead weight of your existing grab. Not sure? Check your grab manual, CE declaration, or on the ID plate on your grab.

Grab rope withdrawal lengthIs the length of the closing rope which needs to be pulled out in order to close the grab (not to confuse with the total reeved in grab rope length).

Not sure about the numbers?Check the grab manual. Don’t hesitate to contact us.

Riny Stoutjesdijk
Sales manager

+31 (0)653109307