Manuel Rexer

Technical University of Darmstadt

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Peter F. Pelz

Technical University of Darmstadt

Nicolas Brötz

Technical University of Darmstadt

Florian Hoppe

Klinikum Oldenburg

Jakob Hartig

Technical University of Darmstadt

Maximilian Knoll

Krankenhaus der Barmherzigen Brüder Trier

M Schaeffner

Technical University of Darmstadt

Christopher M. Gehb

Technical University of Darmstadt

Christian Bölling

Museum für Naturkunde

Matthias Weigold

Technical University of Darmstadt

Philipp Hedrich

Technical University of Darmstadt

Cooperative Institutions

Technical University of Darmstadt

Institut für Umformtechnik (Germany)

Materials Science & Engineering

Heidelberg University

Ingenieurgesellschaft Auto und Verkehr (Germany)

Darmstadt University of Applied Sciences

University of Stuttgart

Humboldt-Universität zu Berlin

Fraunhofer Institute for Structural Durability and System Reliability

Fraunhofer Society

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Our Specific Approach on Mastering Uncertainty

Springer tracts in mechanical engineering (2021)

Peter F. Pelz Robert Feldmann Christopher M. Gehb Peter Groche Florian Hoppe

Abstract This chapter serves as an introduction to the main topic of this book, namely to master uncertainty in technical systems. First, the difference of our approach to previous ones is highlighted. We then discuss process chains as an important type of technical systems, in which uncertainty propagates along the chain. Five different approaches to master uncertainty in process chains are presented: uncertainty identification, uncertainty propagation, robust optimisation, sensitivity analysis and model adaption. The influence of the process on uncertainty and methods depends on whether it is dynamic/time-varying and/or active. This brings us to the main strategies for mastering uncertainty: robustness, flexibility and resilience. Finally, three different concrete technical systems that are used to demonstrate our methods are presented.

Robustness

Propagation of uncertainty

Identification

Sensitivity Analysis

Resilience

10.1007/978-3-030-78354-9_3

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Fluid dynamic vibration absorber for cabin suspension

Nicolas Brötz Manuel Rexer Peter F. Pelz

Truck drivers spend all day moving goods.They are exposed to vibrations every time they drive.Modern cabin suspension and an air-suspended seat already offer a high level of comfort.This, however, is designed for vertical dynamics and you can observe the cab of a truck performs large pitching vibrations during acceleration.These are examined here.A pitch model of the cabin is set up for this purpose.On the basis of this model it is examined which reduction of the vibration can be achieved by the use of a hydraulically translated vibration absorber.The advantage of this absorber is the use of the hydraulic transmission to reduce the heavy mass at high absorber inertia.4 kg of fluid mass act as 131 kg absorber mass reducing vibrations by more than 10%.The conventional vibration absorber is inacceptable due to the additional load.The investigation based on VDI 2057 Part 1 shows that driving comfort can be increased.

Suspension

Dynamic Vibration Absorber

10.25368/2020.103

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Foam accumulators: packaging and weight reduction for mobile applications

Manuel Rexer Peter Kloft Frank Bauer Jakob Hartig Peter F. Pelz

Standardized parts like hydraulic accumulators are used in nearly every hydraulic system, in many cases even several.Therefore, even small changes in size and weight of accumulators can save considerable material costs.In mobile applications, hydraulic accumulators are used among others in hydro-pneumatic suspension systems.There is a strong focus on miniaturization and weight reduction, as the components always have to be transported with the vehicle.Energy density and energy content of conventional hydraulic accumulators cannot be maximized at the same time.This limitation can be overcome by adding a heat capacity with large surface into the gas volume of the accumulator.The heat capacity enlarges the isothermal frequency range and therefore enlarges the energy density of the accumulator at the given frequency and the given size.In this paper an experimental comparison of conventional hydraulic accumulators and accumulators with foam inserts shows, that at a specific frequency band, the stiffness of foam filled accumulators is significantly lower than of conventional accumulators.The energy density is about 11 % higher than in conventional accumulators.Consequently, a space reduction of about 18 % is possible.

Hydraulic accumulator

Accumulator (cryptography)

10.25368/2020.26

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Analysis, Quantification and Evaluation of Uncertainty

Springer tracts in mechanical engineering (2021)

M Schaeffner Eberhard Abele Reiner Anderl Christian Bölling Johannes Brötz

Abstract This chapter describes the various approaches to analyse, quantify and evaluate uncertainty along the phases of the product life cycle. It is based on the previous chapters that introduce a consistent classification of uncertainty and a holistic approach to master the uncertainty of technical systems in mechanical engineering. Here, the following topics are presented: the identification of uncertainty by modelling technical processes, the detection and handling of data-induced conflicts, the analysis, quantification and evaluation of model uncertainty as well as the representation and visualisation of uncertainty. The different approaches are discussed and demonstrated on exemplary technical systems.

Identification

Uncertainty Quantification

Representation

Sensitivity Analysis

10.1007/978-3-030-78354-9_4

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Mastering Model Uncertainty by Transfer from Virtual to Real System

Lecture notes in mechanical engineering (2021)

Nicolas Brötz Manuel Rexer Peter F. Pelz

Abstract Two chassis components were developed at the Technische Universität Darmstadt that are used to isolate the body and to reduce wheel load fluctuation. The frequency responses of the components were identified with a stochastic foot point excitation in a hardware-in-the-loop (HiL) simulation environment at the hydropulser. The modelling of the transmission behaviour influence of the testing machine on the frequency response was approximately represented with a time delay of $$10\,\mathrm {ms}$$ 10ms in the frequency range up to $$25\,\mathrm {Hz}$$ 25Hz . This is considered by a Padé approximation. It can be seen that the dynamics of the testing machine have an influence on the wheel load fluctuation and the body acceleration, especially in the natural frequency of the unsprung mass. Therefor, the HiL stability is analysed by mapping the poles of the system in the complex plane, influenced by the time delay and virtual damping. This paper presents the transfer from virtual to real quarter car to quantify the model uncertainty of the component, since the time delay impact does not occur in the real quarter car test rig. The base point excitation directly is provided by the testing machine and not like in the case of the HiL test rig, the compression of the spring damper calculated in the real-time simulation.

Chassis

10.1007/978-3-030-77256-7_4

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Material and process invariant scaling laws to predict porosity of dense and lattice structures in laser powder bed fusion

Materials & Design (2024)

A. Großmann Manuel Rexer Matthias Greiner Guillaume Meyer Jan Mölleney

Scaling laws represent an efficient way to describe complex physical phenomena efficiently and reliably by simplified relative quantities, which are holistic in the sense that they are invariant to changes in scale and therefore often universal. During part manufacturing in laser powder bed fusion additive manufacturing several such complex physical phenomena arise leading to unstable melt pool behavior and part porosity. Correlating processing parameters with melt pool quantities and eventually part properties such as porosity computationally efficiently can enable real-time build failure detection and process adaption leading to zero scrap rates in additive manufacturing. The efficient and reliable process-property correlation for dense materials is an ongoing field of research, whereas architected cellular and lattice structures, which are becoming more and more relevant in the context of additive manufacturing are rarely considered in this regard. In this contribution, a dimensionless number and the corresponding scaling law are derived to describe the correlation between porosity and process parameters for components manufactured by laser powder bed fusion. The scaling law is tested and validated for the commonly used alloys Ti-6Al-4V and AlSi10Mg on both dense and lattice structures regarding its suitability to predict the type and amount of porosity in additively manufactured components. The objective of this work is to foster reliable and predictable part quality and enable quality-driven build rate optimization.

Scaling law

Lattice (music)

10.1016/j.matdes.2024.112684

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Effects of Unsteady Heat Transfer on Behaviour of Commercial Hydro-Pneumatic Accumulators

arXiv (Cornell University) (2020)

Jakob Hartig Benedict Depp Manuel Rexer Peter F. Pelz

Hydraulic accumulators play a central role as energy storage in nearly all fluid power systems. The accumulators serve as pulsation dampers or energy storage devices in hydro-pneumatic suspensions. The energy carrying gas is compressed and decompressed, often periodically. Heat transfer to the outside significantly determines the transfer behaviour of the accumulator since heat transfer changes the thermodynamic state of the enclosed gas. The accumulators operating mode ranges from isothermal to adiabatic. Simulating fluid power systems adequately requires knowledge of the transfer behaviour of the accumulators and therefore of the heat transfer. The Engineer's approach to model heat transfer in technical system is Newton's law. However, research shows, that in harmonically oscillating gas volumes, heat flux and bulk temperature difference change their phase. Newton's law is incapable of representing this physical phenomenon. We performed measurements on two sizes of commercial membrane accumulators. Experimental data confirm the failure of Newton's approach. Instead the heat transfer can be modelled with an additional rate dependent term and independently of the accumulator's size. Correlation equations for the heat transfer and the correct accumulator transfer behaviour are given.

Hydraulic accumulator

Accumulator (cryptography)

10.48550/arxiv.2012.06526

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Much does not help much: 3D pareto front of safety, comfort and energy consumption for an active pneumatic suspension strut

Manuel Rexer Nicolas Brötz Peter F. Pelz

With regard to autonomous driving the demands on comfort are increasing.This makes it attractive to use active suspension systems.The system developed at TU Darmstadt is able to increase driving comfort up to 28 % while maintaining driving safety compared to a passive suspension system.This paper investigates the influence of available energy and power of the active system.The investigation is based on a simulation of a quarter car model and an uneven country road.This paper shows that the more energy the active system has at its disposition, the greater is the range between a comfortable and a sporty chassis.Furthermore the driving comfort can be increased by 28 % with constant driving safety.The average power required for this is 15 W and the maximum power is 300 W.

Chassis

Active suspension

Suspension

Active safety

10.25368/2020.91

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Citations (3)

Virtual Chassis Development – Reaching for Optimized Trade-off between Safety and Comfort

Proceedings (2024)

Mark Wielitzka Marcus Perner Martin Gebhardt Manuel Rexer Niklas Puff

Chassis

10.1007/978-3-662-70348-9_13

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Methods and Technologies for Mastering Uncertainty

Springer tracts in mechanical engineering (2021)

Peter Groche Eberhard Abele Nassr Al-Baradoni Sabine Bartsch Christian Bölling

Abstract Uncertainty affects all phases of the product life cycle of technical systems, from design and production to their usage, even beyond the phase boundaries. Its identification, analysis and representation are discussed in the previous chapter. Based on the gained knowledge, our specific approach on mastering uncertainty can be applied. These approaches follow common strategies that are described in the subsequent chapter, but require individual methods and technologies. In this chapter, first legal and technical aspects for mastering uncertainty are discussed. Then, techniques for product design of technical systems under uncertainty are presented. The propagation of uncertainty is analysed for particular examples of process chains. Finally, semi-active and active technical systems and their relation to uncertainty are discussed.

Identification

Representation

Propagation of uncertainty

10.1007/978-3-030-78354-9_5

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Citations (1)