Review 2023 - FEMFAT LAB​​​​​​​​​​​​​​

The transformation of the mobility industry has an deep impact on development methodologies and the way how we will use data over the entire life cycle of an product. How can utilize this new enabler technologies to create a smart and sustainable mobility for our future?

This paper discusses an iterative algorithm for coupling arbitrarily many dynamic subsystems (simulation and/or test bench) into an overall system. One conceivable application would be the coupling of globally distributed numerical simulations and test benches (HIL) to form an overall dynamic system. Another example is the coupling of two test benches on two different test fields to one overall system, because the monolithic overall system would be too large for one test field.  

Similar to virtual iteration, this is an iterative method in which the control signals of the subsystems are modified until all cutting quantities are approximately equal. Besides the disadvantage that several runs of all involved subsystems are necessary to achieve a coupled overall system, the following advantages can be mentioned: (1) The coupling does not neglect any dynamics or nonlinearities. (2) Secrecy is guaranteed, since only transfer functions from the individual subsystems are required. (3) There is no communication between the subsystems during a run. Thus, no special requirements for data exchange are necessary. Data transfer via email is conceivable. (4) No controllers are necessary. (5) If numerical subsystems and test benches are to be coupled (HIL), then the mathematical models can be arbitrarily complex. No real-time capability is necessary. 

In addition to an explanation of the method, two examples are shown. The first example is a purely numerical example with three subsystems. It is shown that the distributed simulation converges to the same solution as if a monolithic overall system is considered. In the second example, a model car is considered on a four poster test rig. The vehicle on the four poster is a multibody simulation model. Two shock absorbers are considered as hardware on the test rig. It is shown that the cutting quantities are approximately equal in a few iterations. 

Virtual and accurate load case definition is one challenge in modern off-road vehicle development to ensure correct dimensions and lightweight design in an early development stage. AVL have developed a methodology therefor based on vehicle multibody system simulations with MSC Adams and FTire, whereby an agricultural tractor of a serial production was chosen as test object for this research project. 

For this purpose, acceleration measurements at the wheel hubs taken in the field (short wave road profiles, i.e.: cleats) have been evaluated and analyzed, and their comparison with the virtually achieved simulation results were the basis for fine adjustment of the simulation model, especially in view of accurate tire parametrization. 

To proof the new methodology, a further test track has been built up in the field, acceleration signals at the wheel hubs were measured again, whereby virtual simulations were performed with the fine-tuned model parallelly. As a result, the comparison between measured and simulated signals indicated a strong correspondence, which justifies the conclusion that a virtual multibody system simulation delivers a sufficiently accurate load case definition. It also confirms the possibility to accurately fine-tune FTire parameters for large tires. 

The main advantages of this methodology are that it leads to a significant cost reduction and acceleration in the development process, and it provides a good insight to the dynamic behavior of the vehicle (tractor). Furthermore, parameter optimization can be carried out cost-efficiently, too.  

Three workflow examples will be presented for typical load cases with different ways of performing strength and lifetime analyses on basis of an agricultural tractor. Requirements of the model setup and parametrization will be discussed, and the boundary conditions for the test procedures on the hydro pulse system will be derived, too. Finally, the results (e.g.: damage values) achieved on the hydro pulse system will be compared with the ones derived by finite element and mechanical fatigue analysis. 

First example is the Merry-Go-Round test which is a well-known tractor test procedure, and the second one is the pendulum impact test which should ensure safety for dynamic articulation of the tractor front axle. In both cases, the load case definition is performed using cutting loads obtained from rigid multibody system simulations considering no flexible structure (except tires, springs, damper, bushings, stops, etc.). 

The third workflow example refers again to the Merry-Go-Round test. However, in this case two flexible components (i.e.: exhaust system and DPF) mounted to the tractor chassis body are included in the vehicle multibody system simulation, whereby the flexibility of the structures has been considered via Craig Bampton method. The load cases for the finite element and mechanical fatigue analysis are obtained from the multibody system simulation results of cutting loads and component accelerations, based on rainflow counting and statistical methods. A lifetime assessment using Femfat will be presented as result. 

Dynamic simulation using virtual roads plays an important role in the concept phase of vehicle development. Digital customer roads or proving grounds are often not available, therefore standard tracks will be used but should lead to an equivalent result.

Full vehicle simulations of a truck were performed with different roads. The target values for the assessment of the truck are known from measured road load data. The simulated roads were mixed to a test program to achieve these target values. A fatigue analysis of rear axle parts were performed to evaluate the procedure.

The resulting test program can be used in the future to assess similar vehicles in an early stage of the development. 

Dynamic simulation results depend strongly on the used excitation data. Input signals from test track, test rig or 3D road scans are often not available, extremely expensive or cannot be measured. The method of virtual iteration (VI) represents a well-rounded solution to handle this problem. Using an iteration process with simulation analogous to physical test rig allows to adjust external loadings applied on a structure in such a way that internal measurements, i.e. proper load flow, can be reproduced with desired accuracy (solution of a non-linear inverse problem).

FEMFAT LAB 3D road can additionally generate the virtual road based on measured internal measured signals by full vehicle simulations using a tire model.

The workshop introduces to the method of virtual iteration with focus on generating 3D roads predicted from RLD measurements.

In the “digital age”, leadership—in the meaning of the skill for “working on a system/business model”—is of paramount importance. Rapid technological change coming with digitalization enters all aspects of life, so businesses are forced to undertake extensive transformation processes. A strategic and pervasive positioning of information technology (IT) as business enabler and fundament of business models is of essence. Cultural business conflicts with the positioning of other operational units are unavoidable. Traditional methods of management are certainly being tested. The “digital society” needs executives with new competencies and businesses based upon fundamentally changed business cultures.

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