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Material Properties of Granular Ice Layers Characterized Using a Rigid-Body-Penetration Method: Experiments and Modeling

Technical University of Darmstadt-Markus Schremb, Kenan Malicevic, Louis Reitter, Ilia Roisman, Cameron Tropea
Published 2019-06-10 by SAE International in United States
Accretion and shedding of ice layers is a serious problem for various engineering applications. In particular, ice layers growing due to ice crystal impingement on warm parts of an aircraft jet engine pose a severe hazard since they seriously affect safe operation of an aircraft. The material properties, and in the first place the strength of an ice layer, are crucial for the mechanisms leading to, and taking place during, both accretion and shedding of an ice layer. In the present study, the apparent yield strength of dry granular ice layers is examined employing a novel rigid-body-penetration approach. Dynamic projectile penetration into granular ice layers of varying porosity and ice grain size is experimentally investigated for different projectile impact velocities using a high-speed video system and post-processing of the captured video data. The obtained data for the total penetration depth of the projectile is used to calculate the apparent yield strength of the ice layer based on theoretical modeling of the projectile dynamics during penetration. Finally, the experimental method and theoretical modeling employed in the…
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Scale-Resolving Simulation of an ‘On-Road’ Overtaking Maneuver Involving Model Vehicles

Technical University of Darmstadt-Suad Jakirlic, Lukas Kutej, Cameron Tropea
AVL LIST GmbH-Branislav Basara
Published 2018-04-03 by SAE International in United States
Aerodynamic properties of a BMW car model taking over a truck model are studied computationally by applying the scale-resolving PANS (Partially-averaged Navier-Stokes) approach. Both vehicles represent down-scaled (1:2.5), geometrically-similar models of realistic vehicle configurations for which on-road measurements have been performed by Schrefl (2008). The operating conditions of the modelled ‘on-road’ overtaking maneuver are determined by applying the dynamic similarity concept in terms of Reynolds number consistency. The simulated vehicle configuration constitutes of a non-moving truck model and a car model moving against the air flow, the velocity of which corresponds to the car velocity. The presently modelled ‘on-road’ overtaking maneuver is designed by reference to the complementary ‘quasi stationary’ event investigated experimentally in full-scale wind tunnel of the BMW Group in Munich/Ascheim by fixing the truck model at eight discrete positions relative to the car model, Schreffl (2008); accordingly, the results obtained are discussed also by reference to these measurements, in addition to the results of the realistic ‘on-road’ investigations. The turbulence modelling focus of the present work is on the validation of the…
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Critical Assessment of Some Popular Scale-Resolving Turbulence Models for Vehicle Aerodynamics

SAE International Journal of Passenger Cars - Mechanical Systems

Technical University of Darmstadt-Suad Jakirlic, Lukas Kutej, Cameron Tropea
Audi AG-Peter Unterlechner
  • Journal Article
  • 2017-01-1532
Published 2017-03-28 by SAE International in United States
Some widely-used scale-resolving turbulence models are comparatively assessed in simulating the aerodynamic behavior of a full-scale AUDI-A1 car configuration. The presently considered hybrid RANS/LES (RANS – Reynolds-Averaged Navier-Stokes; LES – Large-Eddy Simulation) models include the well-known DDES (Delayed Detached-Eddy Simulation) scheme and two further variable-resolution formulations denoted by PANS (Partially-Averaged Navier-Stokes; Basara, 2011) and VLES (Very LES; Chang et al., 2014). Whereas the DDES method represents the originally proposed formulation based on the one-equation Spalart-Almaras model (Spalart et al. 2006), whose RANS/LES interface position is directly correlated to the underlying grid resolution, the other two models represent ‘true’ seamless formulations, providing a smooth transition from Unsteady RANS to LES in terms of a dynamic “resolution parameter” variation. The latter parameter is evaluated by contrasting the length scale related to the residual turbulence of both PANS and VLES methods to the grid spacing. The dynamics of residual motion in both methods is modelled by a four equation model (Hanjalic et al., 2004). All computations are performed by the OpenFOAM code. The PANS and VLES formulations, in…
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Implementation of an Open-Loop Controller to Design the Longitudinal Vehicle Dynamics in Passenger Cars

Technical University of Darmstadt-Stephan Rinderknecht
Daimler AG-Christoph Andre Malonga Makosi, Ralf Binz, Frank Uphaus, Frank Kirschbaum
Published 2017-03-28 by SAE International in United States
In order to offer a wide range of driving experiences to their customers, original equipment manufacturers implement different driving programs. The driver is capable of manually switching between these programs which alter drivability parameters in the engine control unit. As a result, acceleration forces and gradients are modified, changing the perceived driving experience. Nowadays, drivability is calibrated iteratively through road testing. Hence, the resulting set of parameters incorporated within the engine control unit is strongly dependent on the individual sentiments and decisions of the test engineers.It is shown, that implementing a set of objective criteria offers a way to reduce the influences of personal preferences and sentiments in the drivability calibration process. In combination with the expertise of the test engineers, the desired vehicle behavior can be formalized into a transient set point sequence to give final shape to the acceleration behavior. To control the longitudinal dynamic of the vehicle in order to meet the customer expectations regarding to this set point sequence an open-loop controller is used.To alleviate comfort reducing drive train oscillations (non-linearities…
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Eddy-resolving Simulations of the Notchback ‘DrivAer’ Model: Influence of Underbody Geometry and Wheels Rotation on Aerodynamic Behaviour

Technical University of Darmstadt-Suad Jakirlic, Lukas Kutej, Daniel Hanssmann, Cameron Tropea
AVL North America Inc.-Branislav Basara
Published 2016-04-05 by SAE International in United States
The present work deals with a computational study of a ‘DrivAer’ car model, the rear-end shape of which corresponds to the Notchback configuration (Heft et al. [1] and Heft [2]). The study investigates the effects of the underbody geometry and wheel rotation on the aerodynamic performance. The configurations with detailed and smooth underbody as well as with stationary and rotating wheels are considered. The computational model applied relies on a VLES (Very Large Eddy Simulation) formulation, Chang et al. [3]. The residual turbulence related to the VLES framework is presently modelled by a RANS-based (Reynolds-Averaged Navier-Stokes), four-equation (D(k,ɛ,ζ, f)/Dt) near-wall eddy-viscosity model, Hanjalic et al. [4]. In addition to the equations governing the kinetic energy of turbulence (kus) and its dissipation rate (ɛus), it solves a transport equation for the quantity , representing a key parameter, as it models the velocity scale in the expression for the corresponding turbulence viscosity. In addition to VLES, all considered flows are simulated within both RANS and Unsteady RANS (URANS) frameworks using the same background model formulation representing the…
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Knowledge Based CAx Tools for the Development of Environmentally Sound Products

Technical University of Darmstadt-Sebastian Leibrecht, Reiner Anderl
Published 2003-03-03 by SAE International in United States
Within the Collaborative Research Center 392 (SFB392) methods and tools for the development of environmentally sound products are developed at the Technical University in Darmstadt. They are based on a very detailed Life Cycle Assessment method (LCA, → [8]) and can be used for entire products, like cars, or components, like engines or catalyzers. Existing CAD and process data can be used for the assessment using direct connections to CAD systems or data import via STEP files. The basic principle of the tools is to implement the required expert knowledge in an object oriented information model. An object oriented model is much easier to understand, adapt, extend, validate and maintain than programming source code, and is much easier to implement in computer programs than other kinds of models. This enables effective cooperative work and easy adaptation of the tools to the fast changing boundary conditions of industrial application.
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Towards a Representation Scheme for Feature-Based Parametric Assembly Modelling

Technical University of Darmstadt-J. Scharr
Fraunhofer-Institute for Computer Graphics-G. Brunetti
  • Technical Paper
  • 1997-25-0024
Published 1997-06-19 by ISATA - Dusseldorf Trade Fair in United Kingdom
Feaure-based parametric assembly modelling (FbPAM) is an approach to assembly modelling in CAD/CAM that integrates the advantages of features-based modelling and parametric modelling. The realization of FbPAM systems requires an appropriate representation scheme. Here, a parametric assembly feature representation (PAFRep) is introduced that incorporates the application data of a feature-based model with the generic data of a parametric model. The PAFRep represents explicitly assemblies and assembly relationships between parts as well as design or manufacturing features and their relationships. Application-specific data is mapped to generic form entities and to geometric and non-geometric parameters and constraints.
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Improved Wheel Speed and Slip Determination Considering Influences of Wheel-Suspension Dynamics and Tire Dynamics

Technical University of Darmstadt-Ralf Schwarz, Markus Willimowski, Rolf Isermann
ITT-Automotive Europe-Peter Willimowski
Published 1997-02-24 by SAE International in United States
The wheel speed and the slip are important signals for many modern automotive control systems. The performance of these systems strongly depends on the quality of the evaluated wheel speed and the slip. However, during car motion, especially during acceleration or braking, deflections of the flexibly mounted wheel suspension and of the tire disturb the measurement or rather the determination of these signals. In this paper an approach to increase the quality of the evaluated wheel-speed signal and the slip signal by considering these influences is introduced. The method considers the longitudinal motion of the wheel center, the tangential motion or rather the oscillations of the belt, the changing of the dynamic tire radius and the disturbances due to the angular motion of the wheel-speed sensor. To obtain the required kinematic values for the compensation, a mathematical model of the wheel suspension and of the tire is developed. The reconstructed signals are verified by means of measurement data taken during test drives with a BMW 318i. By comparing the slip as well as a μ-slip…
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Real-Time Supervision of the Diesel Engine Injection Process

Technical University of Darmstadt-Steffen Leonhardt, Ralf Schwarz, Rolf Isermann
Published 1997-02-24 by SAE International in United States
This paper deals with the supervision of the Diesel injection process. A new method to analyse the injection quality is presented which is based on the acquisition and evaluation of cylinder pressure signals. In this novel approach, a reconstructed “motored” pressure is substracted from the fired pressure signal resulting in independence from a possible sensor offset and a contrast amplification. To describe the shape of the difference pressure, features like the center of gravity or the secant length at certain pressure values are introduced. These numbers can be used for supervison of the injection pump (backward diagnosis) as well as for driving the engine at operating points with low exhaust production (feedforward control).The presented concept is supported by simulations and real-time measurements obtained from a swirl chamber Turbo Diesel stock car engine (4 cylinders, 1600 ccm).
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The Crankshaft of Internal Combustion Engines as a Source of Vibrations - Experimental Methods and Results

Technical University of Darmstadt-H. G. Engel, M. Leber
Carl Schenck AG-H. Schönfeld
  • Technical Paper
  • 945025
Published 1994-10-17 by Society of Automotive Engineers of China in China
In former investigations concerning engine vibrations the uneven mass distribution of crankshafts due to the location of counterweights was found to cause crankshaft bending. The well accepted balancing method of crankshafts, where holes are drilled into the counterweights, increases this problem due to occasionally asymmetric location of those drillings. This effect may bring about specific problems such as additional load on the engine block, a increasing noise level and even unwelcome movements of the flywheel. The objective of the described examinations was to investigate the behavior of a newly developed, fast running, 4-cylinder in-line SI engine with a light-alloy cylinder block under variation of the inner mass compensation of the crankshaft. An evident relationship was found between the extent of inner crankshaft imbalance and engine block bending occurring in the 1st order of engine speed. With a non-contact distance measuring device longitudinal and tumble flywheel movements in the 1st and 2nd order of engine speed were observed.