Predicting interaction forces

In order to draw reliable conclusions regarding durability properties and energy efficiency within the development process of construction machines, it is inevitable to model both, the considered machine itself as well as the interaction with the environment in an appropriate quality and to predict sufficiently accurate interaction forces.

Simulation of Soil-Tool Interaction

Simulation of soil and wheel loader model interaction
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Simulation of soil and wheel loader model interaction when charging the bucket.

The high variability of construction and agricultural machinery leads to high demands on the product development. In particular, the interaction of the tool with the ground during excavation or plowing but also the interaction of a harvesting machine with the crop, etc. are hardly predictable. Until now, such complex interactions are usually determined by measurement and are therefore difficult to integrate into the virtual product development.

Therefore, the activities in this area are focused on the integration of the complex behavior of such materials. This makes it possible to compare variants of a machine under same conditions. Design changes may be analyzed for their impacts on the load on the machine or the flow of crop material through the machine.

Simulation of Particles

Methods of classical soil mechanics, e.g. Finite Element Method (FEM) with special material models for the nonlinear material behavior of the soil, fail in this application. A particular challenge is the separation of the material during excavation. Alternative simulation approaches, such as particle simulation can better deal with these conditions. In particular, the Discrete Element Method (DEM) is proven for simulations of this kind.

Besides the usage of the DEM in industrial projects, we also work on the development of particle methods. In this context, we have developed and implemented our own DEM code entitled »GRAnular Physics Engine (GRAPE)« for modeling and simulating soft soil. In particular, we focus on the prediction of correct reaction forces – which implies the necessity of an appropriate model parameterization – and the applicability in closed-loop scenarios.

Simulation of gravel and hauler model interaction
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Simulation of gravel and hauler model interaction when discharging the body.

Principle concept for coupling GRAPE
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Principle concept for coupling GRAPE to multibody construction equipment.

Simulation of Interaction

We have evolved, in cooperation with Volvo Construction Equipment AB (Sweden), a co-simulation framework  in the construction equipment development context that serves to simulate and analyze the interaction of construction machines with material.

We conceptually establish a force-displacement coupling for the co-simulation setup, that is in principle not confined to a certain construction machine but can be straightforwardly applied to wheel loaders, haulers, excavators, etc. Within the bilateral project, the construction machines are modeled in MSC.Adams but any known commercial multibody software can be integrated into the coupling framework.

The multibody construction equipment model provides kinematic states as input for GRAPE, which provides section forces as input for the multibody construction equipment model. The realization of the coupling concept requires specific co-simulation interfaces for the multibody construction equipment model and the GRAPE particles, as well as a co-simulation master algorithm organizing the data exchange and the prediction strategies. In this connection, MATLAB/Simulink is chosen as the platform for setting up the co-simulation scenario. The communication, i.e. the exchange of the coupling quantities, with the GRAPE server is realized via a TCP/IP network protocol so that it is possible to run GRAPE and MATLAB/Simulink together with the multibody software on different host PC's.


More details, numerical results and a verification based on real measurements are presented in selected publications listed below.

Realization of co-simulation framework for coupling GRAPE
© Fraunhofer ITWM

Realization of co-simulation framework for coupling GRAPE to multibody construction equipment.