| 1. |
- Diedrichs, Ben, et al.
(författare)
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Crosswind stability of high-speed train on a high embankment
- 2007
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - 0954-4097 .- 2041-3017. ; 221:2, s. 205-225
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Tidskriftsartikel (refereegranskat)abstract
- This work presents aerodynamic results of crosswind stability obtained numerically and experimentally for the leading control unit (class 808) of Deutsche Bahn AG's high-speed train Inter-CityExpress 2. The train model is on top of a 6 m high embankment in accordance with the proposed European code for interoperable trains, the so-called technical specifications for interoperability. The purpose of the study is to convey the predictive accuracy that typical steady-state computational fluid dynamics-Reynolds average Navier-Stokes methods (industry standard) return and to contribute to the understanding of the aerodynamics for the current application. Attention is drawn to the aerodynamics around the train and embankment when subjected to a steady block profile crosswind of 30 degrees yaw angle on the basis of the onset velocity far upstream the embankment. The Re (Reynolds number) of the embankment cases is 4.6 x 10(6). Calculated results are obtained with the commercial code STAR-CD, with exclusively hexahedral meshes with a total cell count of 13.5 x 10(6). Results are obtained when the train stands on the windward and leeward tracks on top of the embankment. These results are first compared with a flat ground case from a previous study. Then experimental data are obtained in a high-pressure wind tunnel with a model scale of 1:100. Re effects are compensated by raising the ambient pressure by a factor of 60, which increases the air density and thus the Re by a similar factor. Calculated results are in fair agreement with the experiments, where both the calculations and the experiments predict the leeward case to be the more critical one. In addition, the related consequences on the mechanical behaviour, i.e. the stability of the car, are briefly addressed by means of a quasi-static mechanical analysis. The results of the present study indicate that the 6 m high embankment concerning the current train reduces the permissible crosswind speed with approximately 20 per cent.
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| 2. |
- Diedrichs, Ben, et al.
(författare)
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Large eddy simulations of a typical European high-speed train inside tunnels
- 2004
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. - 0768013194
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Konferensbidrag (refereegranskat)abstract
- This article presents our results of external aerodynamics, obtained with Large Eddy Simulations(LES), about a typical European passenger-stock insidetunnels. The focal points are the aerodynamic forces andtheir typical frequencies applied to the tail. Two trainlengths and three tunnels are employed in the study tomodel the conditions of double and single-track bores.Owing to the relatively high numerical cost associated with LES for external train aerodynamics we could only afford sufficient spatial grid resolution on our shortest train. The flow simulations confirm the existence of coherent structures alongside the body that give rise to continuously propagating pressure disturbances. These disturbances with a relatively small amplitude and high spatial frequency cannot affect the ride comfort. Still,they are found to influence the flow separation about the tail, which is regarded as one of the candidate mechanisms to impair the ride comfort and running stability.
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| 3. |
- Diedrichs, Ben, et al.
(författare)
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Large eddy simulations of the flow around high-speed trains cruising inside tunnels
- 2004
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Ingår i: ECCOMAS 2004 - European Congress on Computational Methods in Applied Sciences and Engineering. ; , s. 1-21
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Konferensbidrag (refereegranskat)abstract
- Stability and ride comfort of high-speed rolling stock are, for reasons of external aerodynamics, dependent on the external design in conjunction with properties of the vehicle dynamics and the design of the infrastructure, herein referring to the confining tunnel walls. It is a fact that some Japanese high-speed trains are quite prone to tail vehicle vibrations only inside tunnels, while (to the authors' knowledge) other nation's comparable train systems are not. In this context the current work describes our results of external aerodynamics, calculated with large eddy simulations, about two simplified train models inside two double track tunnels with comparable blockage ratio. These models are based on the German Inter-City Express 2 and the Japanese Series 300 Shinkansen trains. The focal points of this study are the origin of unsteady aerodynamic tail forces, their spectral characteristics and the impact of spontaneously emerging coherent flow structures adjacent to the train's surfaces. Full scale tests of the above trains have shown that only the Shinkansen train is subjected to a reduced ride comfort inside tunnels, with a quite obvious lateral vibration at about 2 Hz at top speed (300 km/h). Our unsteady flow calculations have successfully predicted the more detrimental lateral aerodynamic forces. In addition, a spectral analysis of the unsteady side force resulted in a quite prominent frequency at the Strouhal number of 0.09 (based on the speed and height of the train), which correlates well with the Japanese full scale tests.
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| 4. |
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| 5. |
- Diedrichs, Ben, et al.
(författare)
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Nonlinear interaction of laminar three-dimensional disturbances in plane Poiseuille flow
- 1996
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Ingår i: Advances in turbulence VI. - : Kluwer Academic Publishers. - 792341325 ; , s. 333-334
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Konferensbidrag (refereegranskat)abstract
- Results are presented of an experimental study of localized disturbances in a plane Poiseuille flow, with emphasis on the nonlinearities of localized (laminar) disturbances. It is found that the nonlinear interaction (NI) of the center of the structure in general appears in connection with large velocity gradients in the streamwise and spanwise directions of the disturbances. At the outer regions of the composite disturbance, the NI follows the negative amplitudes of the velocity
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| 6. |
- Diedrichs, Ben
(författare)
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On computational fluid dynamics modelling of crosswind effects for high-speed rolling stock
- 2003
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 217:3, s. 203-226
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Tidskriftsartikel (refereegranskat)abstract
- This work addresses crosswind stability exemplified for the German Railway Deutsche Bahn AG high-speed train ICE 2. The scope of the work is to describe the flow by means of computational fluid dynamics past the leading two cars of the train for yaw angles in the range 12.2-40.0degrees. Three track formations are utilized. The basic results are the set of independent aerodynamic coefficients for the lead and subsequent cars. The results are to some extent compared with experimental data for ICE 2 and also with data obtained for the Swedish high-speed train X2000. A numerical sensitivity study is undertaken to quantify differences in the above results dependent on the grid density and quality, turbulence model, numerical scheme, location of inlet and outlet boundaries, turbulence intensity and flow simulation software.
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| 7. |
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| 8. |
- Diedrichs, Ben, et al.
(författare)
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On the aerodynamics of car body vibrations of high-speed trains crusing inside tunnels
- 2008
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Ingår i: ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS. - : Informa UK Limited. - 1994-2060 .- 1997-003X. ; 2:1, s. 51-75
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Tidskriftsartikel (refereegranskat)abstract
- Aerodynamically induced car body vibrations of high-speed trains inside tunnels have for approximately two decades been recognized as a problem in Japan, while other nations' high-speed rail services have not reported similar problems. In order to shed light on this contradiction the scope of the present paper is to primarily explore tail car vibrations of Deutsche Bahn AG's high-speed train ICE 2 and Japan Railways series 300 Shinkansen train. Despite similarities of these two trains the problems are reported only for the latter. Several large eddy simulations are carried out to predict the aerodynamics around simplified and smooth models of the above mentioned trains inside tunnels. The results focus on the ability to resolve PPD (propagating pressure disturbances) generated alongside the bodies, unsteady aerodynamic forces and their corresponding frequencies. Mesh refinement studies are undertaken for both train models, where mesh independence is quite a challenge for this type of application. Affordable meshes appropriate for LES could only be achieved for models confined to a typical car length. For smooth models and for a model with three generic inter-car gaps, the high spatial frequency of the resolved PPD does not make them sufficient to upset the ride quality of a car. A low frequency mode that strongly affects the forces of the tail of the Shinkansen models is described, which is caused by the confinement of the tunnel walls. A study of the implications of the lateral distance to the wall is further investigated. The findings reveal that the effects of the low frequency mode intensify with a narrow wall clearance, corresponding to the nominal lateral position of the train.
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| 9. |
- Diedrichs, Ben, et al.
(författare)
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Quasistatic modelling of wheel-rail reaction due to crosswind effects for various types of high-speed rolling stock
- 2004
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 218:2, s. 133-148
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a quasi-static tool developed to assess the performance swiftly of crosswind stability for three types of rolling stock with conventional, semi-trailer and Jacobs bogie running gear configurations. The prediction accuracy of the results returned by the tool for the quasistatic assumption is fair in comparison with results of more advanced multibody simulation software that is commercially available. The codes, which are based on steady equilibrium equations for the wheels and axles, bogie frames and vehicle body/bodies, handle arbitrarily canted embankments and circular curves. To a large extent the accuracy hinges on the bodies' lateral displacements relative to the contact points between the wheels and rails; therefore proper modelling of the suspension systems and bump stops are found to be important. Examples are given of the limitations associated with the quasi-static approach, studying the following: (a) the combined wind and track scenario in Deutsche Bahn AG's guideline, (b) the effects of typical track irregularities for high-speed transportation as a function of train speed and (c) the effects of oscillating crosswind. It has also been found relevant to demonstrate some of the large differences regarding provisions regulating crosswind safety. To this extent the present results are compared with those derived with the British Group Standard and also with results presented in the guideline of Deutsche Balm AG. In addition, examples are given of the differences found of the permissible crosswind speed using calculated (with CFD-RANS) and experimentally obtained aerodynamic loads.
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| 10. |
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| 11. |
- Diedrichs, Ben
(författare)
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Three-dimensional disturbances : considering starting profiles and optimal profiles in Couette and Poiseuille flow
- 1996
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Ingår i: Physics of fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 8:5, s. 1149-1158
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the velocity profile on transient (algebraic) growth of three-dimensional disturbances in channel flow is investigated. Only streamwise-independent perturbations are considered and the effect of a single forcing Orr-Sommerfeld mode is studied. This restriction is motivated by previous investigations, which show that the largest possible (global optimal) energy growth of a disturbance is generally obtained for streamwise-independent perturbations. Analytic solutions for the energy growth on starting profiles for plane Couette and plane Poiseuille flow are deduced and the findings reveal that the most favorable profiles for transient growth are indeed the fully developed ones. An isoperimetric method to compute optimal profiles is then presented with the purpose to increase the energy growth compared to the fully developed profiles. These profiles are dependent on the spanwise wave number, as well as the perturbation growth time. A numerical investigation show that significant energy magnification can take place on such a profile, even at short growth times of the perturbation. It is further established that these profiles are stable only for low Reynolds number.
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| 12. |
- Diedrichs, Ben, et al.
(författare)
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Vehicle dynamics of a high-speed passenger car due to aerodynamics inside tunnels
- 2007
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - 0954-4097 .- 2041-3017. ; 221:4, s. 527-545
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Tidskriftsartikel (refereegranskat)abstract
- High train speeds inside narrow double-track tunnels using light car bodies can reduce the ride comfort of trains as a consequence of the unsteadiness of the aerodynamics. This fact was substantiated in Japan with the introduction of the series 300 Shinkansen trains more than a decade ago, where the train speed is very high also in relatively narrow tunnels on the Sanyo line.The current work considers the resulting effects of vehicle dynamics and ride comfort with multi-body dynamics using a model of the end car of the German high-speed train ICE 2. The present efforts are different from traditional vehicle dynamic studies, where disturbances are introduced through the track only. Here disturbances are also applied to the car body, which conventional suspension systems are not designed to cope with.Vehicle dynamic implications of unsteady aerodynamic loads from a previous study are examined. These loads were obtained with large eddy simulations based on the geometry of the ICE 2 and Shinkansen 300 trains.A sensitivity study of some relevant vehicle parameters is carried out with frequency response analysis (FRA) and time domain simulations. A comparison of these two approaches shows that results which are obtained with the much swifter FRA technique are accurate also for sizable unsteady aerodynamic loads. FRA is, therefore, shown to be a useful tool to predict ride comfort in the current context.The car body mass is found to be a key parameter for car body vibrations, where loads are applied directly to the car body. For the current vehicle model, a mass reduction of the car body is predicted to be most momentous in the vicinity of 2 Hz.
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| 13. |
- Favre, Tristan, et al.
(författare)
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Detached-Eddy Simulations Applied to Unsteady Crosswind Aerodynamics of Ground Vehicles
- 2010
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Ingår i: Progress in hybrid rans-les modelling. - Berlin : SPRINGER-VERLAG. - 9783642141676 ; , s. 167-177
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Konferensbidrag (refereegranskat)abstract
- Crosswind stability is an important safety issue for manufacturers of cars, buses and rail vehicles. Since side wind conditions are unsteady phenomena they require time-dependent techniques to simulate the flow. In this study, a hybrid RANS-LES methods, Detached-Eddy Simulation, is applied to evaluate headwind and unsteady crosswind situations for a simple model of car. A grid refinement study is carried out to evaluate the accuracy of the calculations. Convergence in the force coefficients while refining the grid suggests that a certain level of grid convergence is reached. A similar conclusion is drawn from the unsteady simulations.
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| 14. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Time-Dependent Simulations for the Directional Stability of High Speed Trains Under the Influence of Cross Winds or Cruising Inside Tunnels
- 2005
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Ingår i: FLUID DYNAMICS APPLICATIONS IN GROUND TRANSPORTATION: Simulation, a primary delepment tool in the automotive industry, Lyon, France, 26-27 October 2005.
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Konferensbidrag (refereegranskat)abstract
- Large eddy simulation (LES) technique is used to study safety and comfort issues of cross-wind stability and lateral vehicle vibrations in double-track tunnels. A simplified train model is used to study flows at yaw angles of 90 and 35 degrees of the cross wind and Reynolds numbers of 300 000 and 370 000, respectively. LES results are compared with the experimental data and good agreement was found. For the LES investigation of lateral vibrations in tunnel, two high-speed trains are used, the German ICE2 and the Japanese Shinkansen S300. It is found that the lateral oscillations of the Shinkansen train originate from the shape of the rear end. Besides, the small vortices formed at the front of the train, on the center side of the tunnel, are found to govern the separation at the rear of the Shinkansen train. The frequency of the lateral oscillations of the Shinkansen train in LES is St=0.09 compared to St=0.1 measured at full scale tests. In the same time no dominant frequency is found on the ICE2 train.
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| 15. |
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| 16. |
- Thomas, Dirk, 1978-, et al.
(författare)
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Dynamics of a high-speed rail vehicle negotiating curves at unsteady crosswind
- 2010
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - London : Professional Engineering Publishing. - 0954-4097 .- 2041-3017. ; 224:F6, s. 567-579
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Tidskriftsartikel (refereegranskat)abstract
- Rail vehicles in everyday operation experience large lateral influences from curves and track imperfections, yielding large suspension deflections and displacements of the carbody relative to the track. Aerodynamic loads caused by crosswind may deteriorate the conditions that can result in vehicle overturning. This study investigates the influence of crosswind on a highspeed rail vehicle negotiating a curve. A multi-body simulation model of a high-speed rail vehicle is subjected to unsteady aerodynamic loads. The vehicle response is studied for different gusts, and variations of some vehicle parameters are performed.
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| 17. |
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| 18. |
- Thomas, Dirk, 1978-, et al.
(författare)
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Rail vehicle response to lateral carbody excitations imitating crosswind
- 2015
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Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 229:1, s. 34-47
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Tidskriftsartikel (refereegranskat)abstract
- Repeatable field tests to measure the vehicle response to unsteady crosswinds are not practical due to safety and economic reasons. Simulations are therefore necessary to gather information on the vehicle response to crosswind. However, in turn, these simulations need to be validated. This study presents results of measured quasi-static and dynamic responses of a stationary rail vehicle due to defined lateral carbody excitations imitating unsteady crosswind, which are reflected by multibody simulations. The vehicle responses are measured in terms of suspension deflections, lateral carbody accelerations and vertical wheel/rail forces. The vehicle dynamic response to a gust-like event results in an overshoot of wheel unloading. In general the measurements and simulations show good agreement. However, the simulations partly overestimate the responses slightly and an influence due to airspring levelling can be observed in the measured values of quasi-static load cases.
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