Universitat Stuttgart Research Articles

An Automated Low-Cost Analog and Mixed-Signal DfT Method Using Testing Diodes

Analog and mixed-signal circuitry forms a substantial part of automotive electronics, and their test application time contributes predominantly to the overall test time. The authors present a low-cost design-for-test technique that allows a high-level of parallelism. —Hans-Joachim Wunderlich, Universitat Stuttgart

Data-Driven Formal Reasoning and Their Applications in Safety Analysis of Vehicle Autonomy Features

Analyzing the safety of automotive systems at the application level is -especially challenging as often very complex or even incomplete models are available. The authors combine formal reasoning with simulation data to effectively -validate safety or estimate worst case situations of automotive control systems. —Hans-Joachim Wunderlich, Universitat Stuttgart

An Optimized Test During Burn-In for Automotive SoC

Early life failures have to be excluded to fulfill the high reliability needs of automotive electronics. While burn-in test may be an effective technique, it is also a very significant cost factor. This article presents strategies for stress test parallelization. —Hans-Joachim Wunderlich, Universitat Stuttgart

Automotive Functional Safety Assurance by POST with Sequential Observation

Power-on self-test is an efficient means for covering safety-critical faults in automotive systems. This paper presents a multicycle logic BIST technique that avoids fault masking after multiple cycles by sequential observation using a new scan cell structure. —Hans-Joachim Wunderlich, Universitat Stuttgart

ADAGE: Automatic DfT-Assisted Generation of Test Stimuli for Mixed- Signal Integrated Circuits

This paper presents an integrated workflow for design-for-test and test signal generation of mixed-signal circuits. The DfT phase pre-partitions the core under test and allows an efficient automatic generation of test signals. —Hans-Joachim Wunderlich, Universitat Stuttgart

Addressing Functional Safety Challenges in Autonomous Vehicles with the Arm TCL S Architecture

Triple modular redundancy is an option to satisfy the strict safety requirements for autonomous driving. This article introduces a solution at CPU core level, which minimizes the possible single point of failures. Additional effort is spent to mitigate the fault-recovery routines and the assisting infrastructure. —Hans-Joachim Wunderlich, Universitat Stuttgart

Ka-band High-speed Communication Systems on Small Satellites for Future Advanced Communication Networks and Earth Observations

The goal of this paper is to describe the capabilities and application methods of Ka-band communication systems for small satellites indicating contributions to future advanced communication networks and Earth observations. This study is based on the actual experience on the design of the Ka-band high-speed communication system of the small satellite Flying Laptop, which is developed at the Institute of Space Systems of the Universitat Stuttgart. The objectives of the Ka-band communication system is to demonstrate high-speed communications with a data rate of up to 500 Mbit/s as well as to conduct scientific Earth observations. Flying Laptop satellite is also equipped with a Ku-band signal transmitter. The attenuation of the two transmission signals in Ka-/Ku-bands are measured with ground stations to estimate the local precipitation rate. The mathematical background and operational scenario of this measurement is summarized. The received Ka-band transmission signal is measured in different meteorological conditions to identify attenuation characteristics of the Ka-band signal due to rain, clouds, trace gases and so forth, which is of great interest for utilization of Ka-band frequencies for future broadband communications.

Thrust Measurement of the Hybrid Electric Thruster TIHTUS by a Baffle Plate

A novel, two-stage, electric thruster is under development at Institut fiir Raumfahrtsysteme at Universitat Stuttgart. The first stage is an arcjet, and the second stage uses inductive heating of the arcjet plume. Because of the complex setup of the thruster, it is impossible to mount the two-stage system on a thrust stand without causing unwanted momentum onto the stand by the numerous supply lines. Thrust is, therefore, inferred using a baffle plate by means of a variation of power- and mass-flow ratios between the two stages. To interpret the results, the present paper also provides radially resolved measurement of total pressure from which thrust can be determined. It is shown that the thrust obtained from the two measurement methods are in good agreement with each other and range between 1.7 and 2.5 N for the respective operating conditions of the thruster. At constant total input power of 50 kW to the thruster, thrust decreases as power is diverted from the first stage to the second (inductive) stage at a constant mass-flow rate. However, when power is applied to both stages, thrust increases as the mass-flow rate is diverted to the second stage at a constant total mass-flow rate of 300 mg/s.

The Advanced URANUS Navier-Stokes Code for the Simulation of Nonequilibrium Re-entry Flows

In order to predict the thermal and mechanical loads during re-entry, the URANUS (Upwind Relaxation Algorithm for Nonequilibrium Flows of the University of Stuttgart) has been being developed at the Institute of Space Systems (IRS) of the Universitat Stuttgart. For the accurate determination of the thermochemical conditions, advanced thermochemical relaxation models for the gas-phase as well as sophisticated gas-surface interaction models have been developed. The Navier-Stokes equations for the 11-component air flow, which consists of N2, O2, NO, N, O, N2+, O2+, NO+, O+, N+ and e-, have been derived by the Chapman-Enskog method from the Boltzmann-Equation. The linearized system of equations is solved fully coupled and fully implicitly, employing Newton's method. In the paper, the modelling is described in some detail and selected simulation results are presented.

Formal add to traditional methods in software engineering

Traditional, informal techniques in software engineering reach their limits when complex systems are to be developed efficiently. The Institute for Formal Methods in Computer Science of the Universitat Stuttgart states: Tools like IDEs, automatic code generation from graphical descriptions, visualization techniques like UML diagrams, and others are certainly necessary. However, they often lack the ability to support detailed and provably sound reasoning about complex systems. Formal methods in software engineering provide approaches to close that gap.

Impact of constitutive models on the numerical analysis of underground constructions

The constitutive model frequently used in numerical calculations of tunnel excavation is linear-elastic perfectly plastic with a Mohr–Coulomb (MC) failure criterion. Generally, this leads to shallower and wider surface settlement troughs than those observed experimentally. It is therefore necessary to use adapted constitutive models for the design of underground works. In this paper, three constitutive models are implemented in a two-dimensional simulation of an underground excavation in plane strain: a linear-elastic perfectly plastic model (the MC model), an elastoplastic model with isotropic hardening [the hardening soil (HS) model, Schanz et al., Beyond 2000 in computational geotechnics, Balkema, Rotterdam, pp. 281–290, 1999] and an extension of this model which implies an evolution of the stiffness modulus in the small-strain range according to the strain level (the HS model with small-strain stiffness “HS-Small”, Benz, Small-strain stiffness of soils and its numerical consequences. Ph.D. thesis, Universitat Stuttgart, 189 pp., 2007). The study is based on the results of drained triaxial compression tests representing an overconsolidated clay (Gasparre, Advanced laboratory characterisation of London clay. Ph.D. thesis, Imperial College London, 598 pp., 2005); and is then applied to a shallow tunnel. The impact of the constitutive model is highlighted as well as the limits of the simplest constitutive model.

Experimental investigations on the stability of riprap layers on overtoppable earthdams

In Germany small dams (<10 m) on flood retention reservoirs are often provided with an overtoppable dam section for flood relief. In case of overtopping a protection of the dam body is absolutely mandatory as the mainly cohesive dam material is not capable to withstand the affecting erosive forces of the flow. There is a big number of possibilities how to protect the dam whilst overtopping. Some of the most common construction types of slope protection layers for a sufficient dam protection such as riprap and placed stones, have been tested in large scale physical models at the Hydraulic Laboratory at Universitat Stuttgart. Thereby different experiments for the failure scenarios “erosion of single stones”, “sliding of the protection layer” as well as “disruption of the protection layer” have been conducted and analysed aiming to find some design criteria for the construction of such dams.

Winding and unwinding ATP synthase

![][1] ATP synthase turns one way to make ATP and the other to break it down. Borsch Like a revolving door, bacterial ATP synthase turns two ways, according to Manuel Diez, Michael Borsch (Universitat Stuttgart, Germany), and colleagues. One direction makes ATP, whereas the other

Ein vereinheitlichtes Modell für Vormischflammen als gasdynamische Diskontinuität

The recently established Sanderforschungsbereich 606: Nonstationary combustion: transport phenomena, chemical reactions, technical systems at the Universitat Karlsruhe in cooperation with the Forschungszentrum Karlsruhe, the Universitat Stuttgart, and the DLR Stuttgart aims to improve the fundamental understanding and to further develop advanced combustion concepts, where time dependant processes are relevant. In these concepts premixed combustion is being applied to an increasing extent. In the present habilitation thesis premixed flames are considered resolving their time and space structures, thus omitting both space and time averaging. Experiments show that premixed flames are frequently thin compared to the hydrodynamic scales and may be viewed as a gasdynamic discontinuity separating the fresh mixture from the lighter products. Darrieus (1938 und 1945) and Landau (1944) independently proposed a model of a flame as a gasdynamic discontinuity, which consists of the Euler equations for the inviscid flow on either side of the flame and an ansatz for the flame propagation. In particular they assumed that the flame propagates at a constant speed and that the flows on either side of the flame are related to each other by jump conditions conserving mass and momentum, Markstein (1951) proposed a model where variations of the flame speed occur due to the curvature of the flame. In contrast to the previous heuristic models Sivashinsky (1976) derived a flame speed relation applying strict asymptotic methods. The model is applicable if the Lewis number (ratio of the diffusivities of heat and limiting species mass) is bounded away from unity. The jump conditions of the models by Markstein-, Sivashinsky- and Darrieus-Landau are identical. Finally, Matalon & Matkowsky (1982) derived a flame speed relation, valid for Lewis numbers close to unity, where flame speed is a function of flame stretch. In addition jump conditions where derived, which no longer conserve mass and momentum and which represent perturbative corrections of the Darrieus -Landau jump conditions. In this habilitation thesis tensor algebra is applied to derive a unified model, consisting of a new flame speed relation and new jump conditions, which is applicable for arbitrary Lewis numbers. In appropriate limits the models of Sivashinsky and Matalon-Matkowsky are recovered. Moreover a new distinguished limit allows for larger Lewis number deviations from unity as compared to the Matalon-Matkowsky theory thus bridging the Matalon-Matkowsky and the Sivashinsky theory. Considering shortwave corrugations of the flame not considered previously, results in new terms coupling neighboring flame elements. These terms damp short wave perturbations of the flame surface, and thus in contrast to previous theories the unified theory is applicable when the flame is unstable with respects to shortwave pulsating instabilities. Remarkable is the fact, that the flame speed relation and jump conditions depend on the precise location of the discontinuity surface. When Gibbs (1879) studied the free interface problem of two adjacent immiscible fluids, he made a similar observation. Depending on the choice of the interface an excess surface mass must be assigned to the interface. In contrast to previous theories the surface is chosen to yield a vanishing excess surface mass. This results in substantially simplified jump conditions.

Calculation of nonlinear drift instabilities in magneto-plasmadynamic thruster flows

This paper presents the latest results from calculations of the nonlinear development of instabilities in magneto-plasmadynamic (MPD) thruster flows. Linear instability analysis carried out at the Institut fur Raumfahrtsysteme of the Universitat Stuttgart yielded three basic instabilities for stationary MPD thruster flows: a space charge instability, an acoustic wave instability and an electron drift instability. Nonlinear analysis using the quasi-analytical method (QAM) developed by the authors not only yields these instabilities in the lower orders of the QAM hierarchy but also shows their nonlinear evolution in the higher order development, particularly that of the space charge instability which is actually shown to lead to current chopping. Calculation results for the normalized current density and electric field strength as functions of time for various relative gradients are presented.

A system dynamics approach to modeling fisheries management issues: Implications for spatial dynamics and resolution

AbstractNotes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universitat Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany or to Yaman Barlas, Dept. of Industrial Engineering, Bogazici University, 80815 Bebek, Istanbul, Turkey.

System dynamics, determinism, and choice: Toward a reconsideration of the image of “systems man”

AbstractNotes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universitat Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany.

Slicing a complex problem for system dynamics modeling

AbstractNotes and Insights is a forum for discussion and debate about current issues in the philosophy and application of the system dynamics approach, and a marketplace for the exchange of information about current research, policy issues, and teaching experiences. Manuscripts treating material particularly suited to presentation in short form (less than 2,000 words) should be sent to Erich Zahn, Betriebswirtschaft‐liches Institut, Abt. IV, Universitat Stuttgart, Keplerstr. 17, D‐7000 Stuttgart 1, Germany.Since formal modeling requires having a model boundary encompassing finite complexity so that deductive logic is possible, complex problems must be partitioned into simpler parts before being analyzed. There are many ways to slice a complex problem but not all create partitions that keep together processes contributing to effective policy design. This paper explores ways in which a complex problem may be appropriately sliced so that the models of partitions can serve as effective tools for policy design.

Authors

Authors

Dynamic Process Flowsheet Simulation - An Important Tool in Process Control

Abstract Comfortable tools for control system design and evaluation have gained increasing importance as useful aids in academia and industry. The limited nonlinear simulation capabilities of existing control system design packages are not sufficient for process and control system simulations. The development of detailed dynamic flowsheet simulators and their integration in a computer-aided design (CAD) environment is required for that purpose. The outline of the general purpose dynamic flowsheet simulator DIVA (Dynamische Simulation verfahrenstechnischer Anlagen), which is currently being developed at Universitat Stuttgart is presented below. An illustrative simulation example of a chemical production plant will demonstrate the function and the possibilities offered by the simulator.