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Viewing 1 to 30 of 3324
2011-04-12
Technical Paper
2011-01-0245
Zhenfei Zhan, Yan Fu, Ren-Jye Yang
Computer Aided Engineering (CAE) has become a vital tool for product development in automotive industry. Increasing computer models are developed to simulate vehicle crashworthiness, dynamic, and fuel efficiency. Before applying these models for product development, model validation needs to be conducted to assess the validity of the models. However, one of the key difficulties for model validation of dynamic systems is that most of the responses are functional responses, such as time history curves. This calls for the development of an objective metric which can evaluate the differences of both the time history and the key features, such as phase shift, magnitude, and slope between test and CAE curves. One of the promising metrics is Error Assessment of Response Time Histories (EARTH), which was recently developed. Three independent error measures that associated with physically meaningful characteristics (phase, magnitude, and slope) were proposed.
2011-04-12
Journal Article
2011-01-0238
Vicente Romero
This paper1 explores some of the important considerations in devising a practical and consistent framework and methodology for working with experiments and experimental data in connection with modeling and prediction. The paper outlines a pragmatic and versatile “real-space” approach within which experimental and modeling uncertainties (correlated and uncorrelated, systematic and random, aleatory and epistemic) are treated to mitigate risk in modeling and prediction. The elements of data conditioning, model conditioning, model validation, hierarchical modeling, and extrapolative prediction under uncertainty are examined. An appreciation can be gained for the constraints and difficulties at play in devising a viable end-to-end methodology. The considerations and options are many, and a large variety of viewpoints and precedents exist in the literature, as surveyed here. Rationale is given for the various choices taken in assembling the novel real-space end-to-end framework.
2011-04-12
Technical Paper
2011-01-0177
Pascal Theissen, Johannes Wojciak, Kirstin Heuler, Rainer Demuth, Thomas Indinger, Nikolaus Adams
Unsteady aerodynamic flow phenomena are investigated in the wind tunnel by oscillating a realistic 50% scale model around its vertical axis. Thus the model is exposed to time-dependent flow conditions at realistic Reynolds and Strouhal numbers. Using this setup unsteady aerodynamic loads are observed to differ significantly from quasi-steady loads. In particular, the unsteady yaw moment exceeds the quasi-steady approximation by 80%. On the other hand, side force and roll moment are over predicted by quasi-steady approximation but exhibit a significant time delay. Using hotwire anemometry, a delayed reaction of the wake flow of Δt/T = 0.15 is observed, which is thought to be the principal cause for the differences between unsteady and quasi-steady aerodynamic loads. A schematic mechanism explaining these differences due to the delayed reaction of the wake flow is proposed.
2011-04-12
Technical Paper
2011-01-0176
Sinisa Krajnovic
The paper discusses an appropriate usage of large eddy simulation (LES) in external vehicle aerodynamics. Three different applications, wheelhouse flow, gusty flow and active flow control, are used to demonstrate how LES can be used to obtain new knowledge about vehicle flows. The three examples illustrate the information that can be extracted using LES in vehicle aerodynamics and show the potential of LES in explorations of this complex flow.
2011-04-12
Journal Article
2011-01-0172
David Sims-Williams
This paper provides a published counterpart to the address of the same title at the 2010 SAE World Congress. A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, due to the unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of road side obstacles. This last term is of greatest significance. Various works related to the characterization, simulation and effects of on-road turbulence are compared together on the turbulence spectrum to highlight differences and similarities. The different works involve different geometries and different approaches to simulating cross wind transients but together these works provide guidance on the most important aspects of the unsteadiness. On-road transients include a range of length scales spanning several orders of magnitude but the most important scales are in the in the 2-20 vehicle length range.
2011-04-12
Technical Paper
2011-01-0171
Dirk Baeder, Thomas Indinger, Nikolaus Adams, Friedhelm Decker
Computational Fluid Dynamics (CFD) is state of the art in the aerodynamic development process of vehicles nowadays. With increasing computer power the numerical simulations including meshing and turbulence modeling are capturing the complex geometry of vehicles and the flow field behavior around and behind a bluff body in more detail. The ultimate goal for realistic automotive simulations is to model the under-hood as well. In this study vehicle simulations using the finite volume open source CFD program OpenFOAM® are validated with own experiments on a modified generic quarter-scale SAE body with under-hood flow. A model radiator was included to take account of the pressure drop in the under-hood compartment. Force and pressure measurements around the car, total-pressure and hot-wire measurements in the car flow field and surface flow patterns were simulated and compared with the experiment.
2011-04-12
Technical Paper
2011-01-0170
Ashok D. Khondge, Sandeep Sovani, Gunjan Verma
Thorough design exploration is essential for improving vehicle performance in various aspects such as aerodynamic drag. Shape optimization algorithms in combination with computational tools such as Computational Fluid Dynamics (CFD) play an important role in design exploration. The present work describes a Free-Form Deformation (FFD) approach implemented within a general purpose CFD code for parameterization and modification of the aerodynamic shape of real-life vehicle models. Various vehicle shape parameters are constructed and utilized to change the shape of a vehicle using a mesh morphing technique based on the FFD algorithm. Based on input and output parameters, a design of experiments (DOE) matrix is created. CFD simulations are run and a response surface is constructed to study the sensitivity of the output parameter (aerodynamic drag) to variations in each input parameter.
2011-04-12
Technical Paper
2011-01-0153
Makoto Tsubokura, See Yuan Cheng, Takuji Nakashima, Yoshihiro Okada, Takahide Nouzawa
We investigate the pitching stability characteristics of sedan-type vehicles using large-eddy simulation (LES) technique. Pitching oscillation is a commonly encountered phenomenon when a vehicle is running on a road. Attributed to the change in a vehicle's position during pitching, the flow field around it is altered accordingly. This causes a change in aerodynamic forces and moments exerted on the vehicle. The resulting vehicle's response is complex and assumed to be unsteady, which is too complicated to be interpreted in a conventional wind tunnel or using a numerical method that relies on the steady state solution. Hence, we developed an LES method for solving unsteady aerodynamic forces and moments acting on a vehicle during pitching. The pitching motion of a vehicle during LES was produced by using the arbitrary Lagrangian-Eulerian technique. We compared two simplified vehicle models representing actual sedan-type vehicles with different pitching stability characteristics.
2011-04-12
Technical Paper
2011-01-0158
Stephane Cyr, Kang-Duck Ih, Sang-Hyun Park
Aerodynamic simulation results are most of the time compared to wind tunnel results. It is too often simplistically believed that it suffice to take the CAD geometry of a car, prepare and run a CFD simulation to obtain results that should be comparable. With the industry requesting accuracies of a few drag counts when comparing CFD to wind tunnel results, a careful analysis of the element susceptible of creating a difference in the results is in order. In this project a detailed 1:4 scale model of the Hyundai Genesis was tested in the model wind tunnel of the FKFS. Five different underbody panel configurations of the car were tested going from a fully paneled car to a car without panels. The impact of the moving versus static ground was also tested, providing over all ten different experimental results for this car model.
2011-04-12
Technical Paper
2011-01-0161
Tsuneaki Ishima, Yasushi Takahashi, Haruki Okado, Yasukazu Baba, Tomio Obokata
In CFD (Computational Fluid Dynamics) verification of vehicle aerodynamics, detailed velocity measurements are required. The conventional 2D-PIV (Two Dimensional Particle Image Velocimetry) needs at least twice the number of operations to measure the three components of velocity ( u,v,w ), thus it is difficult to set up precise measurement positions. Furthermore, there are some areas where measurements are rendered impossible due to the relative position of the object and the optical system. That is why the acquisition of detailed velocity data around a vehicle has not yet been attained. In this study, a detailed velocity measurement was conducted using a 3D-PIV measurement system. The measurement target was a quarter scale SAE standard vehicle model. The wind tunnel system which was also designed for a quarter scale car model was utilized. It consisted of a moving belt and a boundary suction system.
2011-04-12
Technical Paper
2011-01-0163
Robert Lietz, Burkhard Hupertz, Neil Lewington, Rafael Silveira, Christian Taucher
A benchmark study was conducted to assess the capability of an open source CFD based process to accurately simulate the physics of the flow field around various vehicle types. The ICON FOAMpro process was used to simulate the flow field of four baseline geometries of a Truck, CD-Car, B-Car and an SUV. Further studies were carried out to assess the effects of geometry variations on the predicted aerodynamic lift and drag. A Detached-Eddy Simulation (DES) approach was chosen for the benchmarks. In addition to aerodynamic lift and drag values, the results for surface pressure data, surface and wake flow fields were calculated. These results were compared with values obtained using Ford's existing CFD processes.
2011-04-12
Journal Article
2011-01-0166
David Sims-Williams, David Marwood, Adam Sprot
The rear end geometry of road vehicles has a significant impact on aerodynamic drag and hence on energy consumption. Notchback (sedan) geometries can produce a particularly complex flow structure which can include substantial flow asymmetry. However, the interrelation between rear end geometry, flow asymmetry and aerodynamic drag has lacked previous published systematic investigation. This work examines notchback flows using a family of 16 parametric idealized models. A range of techniques are employed including surface flow visualization, force measurement, multi-hole probe measurements in the wake, PIV over the backlight and trunk deck and CFD. It is shown that, for the range of notchback geometries investigated here, a simple offset applied to the effective backlight angle can collapse the drag coefficient onto the drag vs backlight angle curve of fastback geometries.
2011-04-12
Technical Paper
2011-01-0523
William Nicholas Dawes, William Kellar PhD, Simon Harvey PhD, Neil Eccles PhD
Successful product development, especially in motorsport, increasingly depends not just on the ability to simulate aero-thermal behavior of complex geometrical configurations, but also the ability to automate these simulations within a workflow and perform as many simulations as possible within constrained time frames. The core of these aero-thermal simulations - and usually the main bottleneck - is generating the computational mesh. This paper describes recent work aimed at developing a mesh generator which can reliably produce meshes for geometries of essentially arbitrary complexity in an automated manner and fast enough to keep up with the pace of an engineering development program. Our goal is to be able to script the mesh generation within an automated workflow - and forget it.
2013-04-08
Journal Article
2013-01-1228
Graciela Becci, Gunwant Dhadyalla, Alexandros Mouzakitis, James Marco, Andrew David Moore
Testing real-time vehicular systems challenges the tester to design test cases for concurrent and sequential input events, emulating unexpected user and usage profiles. The vehicle response should be robust to unexpected user actions. Sequence Covering Arrays (SCA) offer an approach which can emulate such unexpected user actions by generating an optimized set of test vectors which cover all possible t-way sequences of events. The objective of this research was to find an efficient nonfunctional sequence testing (NFST) strategy for testing the robustness of real-time automotive embedded systems measured by their ability to recover (prove-out test) after applying sequences of user and usage patterns generated by combinatorial test algorithms, considered as “noisy” inputs. The method was validated with a case study of an automotive embedded system tested at Hardware-In-the-Loop (HIL) level. The random sequences were able to alter the system functionality observed at the prove-out test.
2014-01-15
Journal Article
2013-01-9091
Dongfang Jiang
To get a sequence retainable rainflow cycle counting algorithm for fatigue analysis, an alternate equivalent explanation to rainflow cycle counting is introduced, based on which an iterative rainflow counting algorithm is proposed. The algorithm decomposes any given load-time history with more than one crest into three sub-histories by two troughs; each sub-history with more than one crest is iteratively decomposed into three shorter sub-histories, till each sub-history obtained contains only one single or no crest. Every sub-history that contains a single crest corresponds to a local closed (full) cycle. The mean load and alternate load component of the local cycle are calculated in parallel with the iterative procedure.
2004-11-02
Technical Paper
2004-01-3089
Lionel D. Alford, Aaron Altman
The typical aeronautical engineering approach to low Reynolds number flight studies has been to start with known high Reynolds number aerodynamic paradigms and attempt to match them by scaling to observations of birds and insects. On the other hand, the typical biological approach to natural flight aerodynamics has been to try to fit the observations of birds and insects into the typical known aerodynamic paradigms. Neither of these approaches has met with much success, and although we know more about the potential processes of natural flight, we have not been able to describe them using the framework of conventional aerodynamics. The investigation of low Reynolds number aerodynamic flows at the University of Dayton has led to a proposed new method of characterizing and describing the aerodynamics of natural flight. Lift in natural flight is theorized to be based in the spanwise flow along the curvature of a flapping wing.
2004-11-02
Technical Paper
2004-01-3088
J. Philip Barnes
The flight mechanics of dynamic soaring are described to explain how the albatross can sustain soaring flight over a waveless sea in any net direction, including upwind, by extracting energy from the wind velocity gradient with cyclic zoom maneuvers. A dynamic soaring force is postulated to be represented by a wind-aligned vector providing energy gain during both upwind ascent and downwind descent in the wind profile. Maneuver angles are specified consistent with both a dynamic soaring rule and the desired net progress over the water. The equations of motion for coordinated maneuvering in the wind profile are derived and numerically integrated for a range of trajectories as perceived by the albatross, and also as perceived by a stationary observer.
2004-11-02
Technical Paper
2004-01-3092
Zenovy S. Wowczuk, Kenneth H. Means, Victor H. Mucino, Gregory J. Thompson, James Smith, Jeffery R.X Auld, James E. Smith, Adam Naternicola, Lawrence Anthony Feragotti, Bruce J. Corso
The development of a standardized roll-on, roll-off (RoRo) sensor pallet system for a C-130 aircraft was conceived by the National Guard and the Counter Narco-Terrorism Technology Development Office to assist in counterdrug reconnaissance activities within the United States and surveillance and reconnaissance missions worldwide. West Virginia University was contracted to perform the design and development of this system because of their innovative design ideas. Before development, the design parameters were established by these two DoD agencies, their mission requirements and by the limitations of the C-130 aircraft. These limitations include using Commercial off the Shelf (COTS) and Government off the Shelf (GOTS) items when developing the system that must be universal on all C-130 aircrafts variants B thru H. Further design criteria are by the limitations of the C-130 aircraft and its existing mission requirements.
2004-11-16
Technical Paper
2004-01-3415
Marcelo Lopes de Oliveira e Souza, Gilberto da Cunha Trivelato
In this work we discuss some types of simulation environments and laboratories, their characteristics and applications to the simulation and control of aerospace vehicles. This includes: the basic definitions, types and characteristics of simulators and simulations (physical, computational, hybrid, etc.; discrete events, discrete time, continuous time, etc; deterministic, stochastic, etc.) their basic compromise (simplicity × fidelity), their man-machine interfaces and interactions (virtual, constructive, live, etc.), their evolution law (time, events, mixed, etc.), their architectures (“stand-alone”, PIL, HIL, MIL, DIS, HLA, etc.), and especially, their environments (discrete, continuous, hybrid, etc.) and laboratories (physical, computational, hybrid, etc.), and their applications to the simulation and control of aerospace vehicles. This is illustrated by some examples driven from the aerospace industry.
2004-11-16
Technical Paper
2004-01-3472
Paulo Henriques Iscold Andrade de Oliveira, Ricardo Luiz Utsch de Freitas Pinto
This paper presents a numerical process for determination of optimal flight paths for competition soaring. The issue is reduction of flight time in order to soar towards an ascending thermal and climb, through thermal flying, to the initial altitude. The optimization procedure consists in the application of a Direct Method in order to obtain suboptimal solutions through parameterization of state variables, unlike a previous study by the same authors which was based on control parameterization. A mathematical programming procedure is used in order to determine the sub-optimal values for the parameterized state variables. The optimal control law, which is necessary for the generation of the sub-optimal state, is obtained through a step by step penalty technique. The obtained results demonstrate that the optimization of transitory phases is important for the minimization of total flight time.
2004-07-19
Technical Paper
2004-01-2366
Marc M. Cohen
This paper presents a preliminary modeling method, Habitat Multivariate Design Model (HMVDM), to estimate the volume, size, shape, and configuration required for the design of a space habitat. The specific habitat used for this analysis is the “Habot” mobile lunar base concept. The HMVDM methodology begins with values for mass and volume from quantitative summation tools such as the NASA Office of Biological and Physical Research (OBPR) Crew Accommodations Guide. From these tools, it derives a more detailed analysis of mass and particularly of volume. The estimated volume is input into the model, written as a spreadsheet-based analytical modeling tool. In this pilot study, the diameter of a cylindrical module serves as the single independent variable.
2004-07-19
Technical Paper
2004-01-2317
Valter Perotto, Vincenzo Mareschi
ALTAN (ALenia Thermal ANalyser) is a tool developed in Alenia Spazio, for the thermal simulation of satellites. Distinctive features of ALTAN are the description of the system in terms of thermal objects that can be considered as high level primitives, the accurate modelling of the energy sources (planets and sun) and of the optical properties, the integration in a single tool of the steps of radiative, conductive and thermal calculations and of the post-process of the results. An example of ALTAN application is given for Bepi-Colombo mission to Mercury, in particular the modelling of the highly variable planet temperature and the directional optical properties of the planet surface.
2004-07-19
Technical Paper
2004-01-2311
Jih-Run Tsai, Chia-Ray Chen, Lou-Chuang Lee, Chiuder Hsiao, Marco Molina, Maddalena Cova, Alberto Franzoso, Joseph Burger
The thermal vacuum / thermal balance test design and execution are described in the paper for the qualification campaign of 37 electronic units flown with the payload of ISS (International Space Station), i.e., AMS-02 (Alpha Magnetic Spectrometer). The tests are run in 10 separate test campaigns, across a time frame of 3 years (2002–2005). The tests have been carried on at NSPO (National Space Program Office in Taiwan), maximizing the time usage of thermal vacuum facilities. During each experimental campaign several units are tested at the same time, sharing the vacuum chamber volume. Because independent heaters are applied to each unit, the electronic crates can be tested at temperature levels different from one another. The reliability of thermal analysis is enhanced at each thermal balance test, with the final aim to fully validate the thermal mathematical model deviating less than 3°C from actual measurements.
2004-07-19
Technical Paper
2004-01-2319
Hume Peabody, Sharon Peabody
ThermPlot Pro is a Windows based, post-processing tool that interfaces with standard output files from many of the industry’s leading finite difference thermal modeling tools, including: SINDA/FLUINT, SINDA/G, ESATAN, TMG, TAK2000, and TSS. ThermPlot Pro takes the standard output from these tools and imports the data into a user created Microsoft Excel® workbook. From the ThermPlot interface, a user may define Tables or Plots of relevant data, group nodes together for simplification, create specialized parameters, or evaluate heat flow throughout a model using a specialized, interactive HeatMap workbook. Tabular data may include minimums, maximums, averages, or any selected timestep. It also includes the option to add user-defined limits to the tables and highlight data that is out of limit conditions. Plotted data allows the user full control over series properties (color, linetype, marker, etc) as well as control over the axes properties (minimum, maximum, major division, etc.)
2004-07-19
Technical Paper
2004-01-2318
R. V. Gavrilov, A. M. Kislov, V. G. Romanenko
An applied program MIRAGE is intended for numerical modeling of radiant fluxes in mirror-lens optical systems of solar simulators. In the given area of the reference plane of a solar simulator the distribution of irradiance and its non-uniformity concerning of its average value as well as average irradiance and maximal angle of divergence of beam are calculated.
2004-07-19
Technical Paper
2004-01-2274
Vincenzo Mareschi, Valter Perotto, Matteo Gorlani, Danilo Lazzeri, Olivier Pin
Stochastic method is being used in several domains for design optimisation, but its application to spacecraft thermal control design is not yet consolidated. The paper presents an assessment of this technique applied to spacecraft thermal control design, made by Blue Engineering and Alenia Spazio under ESA contract, with the objective to assess the applicability of the method, the requirements for its implementation, the effects on the design process.
2004-07-19
Technical Paper
2004-01-2275
B. Cullimore, S. G. Ring, J. Baumann
Thankfully, the age of stand-alone fixed-input simulation tools is fading away in favor of more flexible and integrated solutions. “Concurrent engineering” once meant automating data translations between monolithic codes, but sophisticated users have demanded more native integration and more automated tools for designing, and not just evaluating point designs. Improvements in both interprocess communications technology and numerical solutions have gone a long way towards meeting those demands. This paper describes a small slice of a larger on-going effort to satisfy current and future demands for integrated multidisciplinary tools that can be highly customized by end-users or by third parties. Specifically, the ability to integrate fully featured thermal/fluid simulations into Microsoft’s Excel™ and other software is detailed. Users are now able not only to prepare custom user interfaces, they can use these codes as portals that allow integration activities at a larger scale.
2004-07-19
Technical Paper
2004-01-2273
D. Martin
Traditionally, the preliminary thermal design is behind the mechanical and electrical spacecraft design. Many factors contribute to this including a lack of detailed physical characteristics of the spacecraft and knowledge of the distribution of the thermal loads within the spacecraft. Therefore, the thermal design typically reacts to the mechanical and electrical designs. The thermal analyst gets a configuration and then tries to wrap an acceptable solution around it. The analyst relies on years of experience and trial and error to determine the appropriate design cases and create a thermal design. Depending on the experience level of the engineer, several iterations may be necessary to determine the worst-case design points and an acceptable thermal design.
2004-07-19
Technical Paper
2004-01-2276
R. V. Gavrilov, V. N. Fenchenko, A. M. Kislov, V. G. Romanenko
The software package for computerized modeling of thermal regimes of a spacecraft (S/C) provided with passive and active means of temperature control, under conditions of orbital flight mission and at thermo-vacuum testing conditions, is represented. The programs of the package have been developed in Object Pascal programming language. Description of the package programs and their basic functions is outlined. An example of calculations for thermal regimes of satellite, with its longitudinal axis oriented on the Sun, is represented.
2004-07-19
Technical Paper
2004-01-2304
Christian Vettore, Federico Pamio, A. A. Sochivko, I. P. Lukaschuk, A. S. Smoljaninov
This paper describes the Thermal Balance test that has been performed on the PAMELA telescope Pressurized Container (PC) to verify the performance of the PC Thermal Control System (TCS). The PC will be attached outside the Russian satellite RESOURS DK to be flown in2004 The thermal control system of the PAMELA PC is based on a mechanical pumped loop fed with Isooctane as working fluid. The test has been performed with PAMELA Structural Thermal Model (STM) inside the PC to have representative interfaces for the thermal control system. Simulation of close-to-real flight environmental heat loads have been accomplished in a vacuum chamber by means of a complex system of IR lamps suitably oriented toward the PC and mechanically mounted on a tubular structure outside the PC. Overall test results have been excellent; PAMELA thermal control system thermal/fluidic requested performance have been verified. PAMELA telescope thermal interfaces have been confirmed as well.
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