MODELLING AND SIMULATION


Multibody Simulation for All


GEMMA CHURCH EXAMINES THE DEMOCRATISATION OF MULTIBODY DYNAMICS (MBD) SIMULATION AND THE IMPACT OF ADVANCING ELECTRIFICATION


The field of multibody dynamics analysis is not a new endeavour. From Galileo’s investigations into


falling masses to Newton’s infamous apples, these past experiments still form the basis of many of today’s dynamic problems. ‘More than a hundred years later,


Lagrange introduced a formulation for constrained multibody systems, which remains the bedrock of multibody analysis,’ continued Pawan Soami, product manager for the Multibody Dynamics Module and the Composite Materials Module in Comsol Multiphysics. ‘ However, with the advent of increasing computing power and advanced numerical techniques, new demands are being imposed on multibody dynamics analysis.’ These demands can be broken down


into two key areas: better integration with structural analysis (including flexible multibody dynamics) and flexible joints, according to Soami, who added: ‘Flexible multibody dynamics means not all parts are considered rigid, but some parts are represented by a fully fledged elastic linear or nonlinear finite element model. ‘An example could be a wiper or door slam analysis, where the blades or seals need to be modelled as a hyperelastic material. Similarly, when modelling contact between two constrained bodies, it is often critical to find the stresses on the contact boundary, which means the boundary needs to be flexible,’ he explained. The representation of impacts is another key challenge, according to Ondrej Frantisek, corporate research at ABB Process Automation. ‘It is often the reason why one must switch to much more complicated modelling methods – for


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example, finite element method analysis. If the impacts of two bodies would deliver more precise results, the multibody simulation would be mostly preferred as it is a leaner approach.’


Another issue is friction modelling,


according to Frantisek, ‘especially its stick- slip effect, which is not well implemented. Again, this would be a reason for changing to the finite element method. The last challenge to mention is the availability of interfaces to other simulation software if coupled field simulation is required.’ It’s clear that MBD simulations are


increasing in scale and complexity because of the increasing product complexity. Alex Pett, product manager for Ansys Motion, said: ‘ The world of MBD has been changing rapidly over the last decade. Products are more complicated, have greater levels of control systems and often involve multiple different areas of physics.’ Electrification is ‘the biggest trend in


MBD,’ according to Christopher Baker, head of system dynamics at Hexagon’s Manufacturing Intelligence Division. ‘Gone are days of purely mechanical systems. Electronics are now pervasive in almost all mechanical applications. With these integrated electrical systems comes the complexity of testing them to ensure there are no unexpected responses and performance requirements are met.’ Autonomous vehicles, for example,


”Gone are days of purely mechanical systems. Electronics are now pervasive in almost all mechanical applications”


include a range of sensors and control systems. Baker said: ‘The only practical way to test these electro-mechanical systems through the full range of operating conditions is through simulation. ‘We are seeing a lot of demand for MBD in the development of controls for high-speed robotic systems, where it is important to factor in the stiffness and mass of the components to minimise vibration and provide accurate and reliable operation,’ Baker added. This rising product complexity and


advancing electrification have a knock-on effect on the MBD software itself. Pett said: ‘Traditional MBD codes often struggle to analyse these kinds of products due to their focus solely on the rigid structure. Ansys Motion addresses this by having rigid and flexible solvers combined within one solver scheme, meaning a super-fast solve time for large and complex models.’ Pett added: ‘Combine this with the


fact that Motion is embedded within the Ansys ecosystem, giving the possibility to couple to other physics solvers: acoustic, electromagnetic, fluids and particle-based


Autumn 2021 Scientific Computing World 23 g


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