The Development of Virtual Testing Model for Korea High Speed Train

1S.R. Kim, 2J.S. Koo, 3T.S. Kwon, 4H.S. Han

Korea University of Science and Technology, Daejeon, Korea1; Seoul National University of Technology, Seoul, Korea2;

Korea Institute of Machinery and Materials, Daejeon, Korea4

Abstract

This paper describes the development and evaluation of a flexible collision dynamics model for KHST as an effective crashworthiness assessment method. It has 1D and 3D FE train models. It is designated as VTM because it could be utilized instead of full rake train test. The VTM has largely two noticeable characteristics in the modeling aspect. One is that it incorporates complete flexible parts and reflects the force-displacement behavior of suspension and connection devices. Another is that it considered the full rake consists of 20 vehicles with three 3D models and seventeen 1D models. Because of modeling configurations, the VTM simulation makes it possible to predict all behavior obtained by 1D, 2D and 3D multibody dynamics models. In addition, it can describe the twisting deformation mode of car body, other unexpected buckling mode, and so on. This VTM can be utilized to develop passive safety devices and structures as standard products. For instance, it can be used to evaluate the specifications of buffer stops or energy absorbers, and the front structural designs, such as the headstock and honeycomb block. This paper simulated four kinds of collision scenarios to evaluate the VTM for KHST. The first scenario describes a collision situation with a movable 15ton truck at 110kph. The second scenario gives the description of an oblique collision situation with a movable 15ton truck at 110kph. The third scenario shows a head-on collision with a same train at the relative velocity of 60kph. The last scenario shows a head-on collision with a same train at the relative velocity of 16kph. These results were compared with those of the previous studies in other papers, and the usefulness of the VTM is assessed and discussed. Keywords : Korea High Speed Train(KHST), Virtual Testing Model(VTM), Finite Element(FE), Crashworthiness

1. Introduction

While train collisions are an extremely rare occurrence, when one happens, heavy casualties are unavoidable. For this reason, many European countries and USA have developed design methods to minimize damages in the event of a train collision [1-4]. Moreover, in an effort to improve train crashworthiness, these countries have raised the safety guidelines for passenger trains [5]. One aspect of such efforts to minimize the damages and the number of casualties in the event of a collision is to apply design that can minimize damage to the car body by predicting the situations in which a train collision might occur. The most ideal technique providing the highest reliability in predicting collision behavior is to use a real train collision, but this requires massive amounts of time and expense, so such a technique is rarely used. Therefore, simulation method is particularly important in the train collision field.

So far, crashworthiness has been assessed by four modeling techniques [6-10]. The first is to sequentially analyze and evaluate the partial structure of a train by using a 3D finite element modeling technique [6]. The second is to analyze the crushing characteristics of the entire train by applying the crushing characteristics obtained from the second technique to a 1D train model [7]. The third is to use a 2D modeling technique to estimate overriding [8]. The fourth is a technique to predict the behavior of an entire train by using a 3D multi-body dynamics model. Although these methods have been efficiently applied in computer equipment environments without much difficulty, they have many restrictions in terms of their ability to predict the nonlinear collision behavior that occur in an actual collision. In other words, the aforementioned evaluation methods have the shortcoming that they cannot consider interactions sequentially occurring among each member, suspension, bogie and the body, which is a weakness. To supplement this weakness, we developed a VTM which could be adopted as a more improved model to evaluate crashworthiness for KHST. More than anything else, a couple of purposes can be met even with one simulation. That is, the VTM will provide numerical results that are superior to those able to be obtained when the other four modeling techniques are applied respectively. KHST was designed to be operated with a 20 car consist. The first three cars were generated using the 3D finite element model, while the remaining 17 cars were generated using the 1D element model. Upon colliding, most of the collision energy is absorbed by the first three cars, which is the reason why these cars were generated using the 3D finite element model. The train unit can be largely categorized into two parts, the body and the bogie. These two parts are linked with several restraint devices, and this linking has a great influence on the dynamic behavior of the train. Therefore, to describe the collision behavior more realistically, the VTM was modeled by taking such dynamic elements into consideration [11]. In order to assess the VTM for KHST, some typical accident scenarios for obstacles or train-to-train collisions were applied to the simulation, and the simulation results were compared with the results obtained from other modeling techniques.

2. Three-dimensional virtual testing model for KHST

KHST was designed to absorb 5.74MJ in the front end in an early development stage. The energy absorption components of the front end are composed of a gas-hydro buffer, an expansion tube, a headstock, a honeycomb block. Figure 1 shows the force-displacement characteristics of the front end of KHST. This modeling technique is intended to obtain the influence of interactions between car units, chain actions, and unexpected deformation behavior to occur after collision. So, the virtual testing model is anticipated to be useful for the prediction of real train test results. It is also expected to minimize the crashworthiness evaluation efforts by replacing 2D, 3D multibody dynamics analysis, and real crash test. The VTM is created as a 3D finite element model for LS-DYNA solver like Table 1. Its goal is to predict nonlinear collision behavior through a reasonable collision dynamics model. The VTM includes 20 vehicles in the train set, as shown in Figure 2. The first three cars are created in 3D nonlinear deformable models, and the other seventeen cars are done in 1D spring/damper elements which are defined from the crushable or uncrushable zone of car body during collision. KHST is designed to absorb most of energy in front head zone, and the reminder in car bodies and side buffers between power car and motorized trailer car. The main materials related to crashworthy design are E24-4, E36-3, and E490D in Table 2. E24-4 is mild steel and easily crushed. E36-3 and E490D are used to support the structure from weight and collision impact force. The total number of elements of the VTM is 777080.

Figure 1: Crush characteristics curve of the front end of KHST.

Table 1: Modelling strategy and element information of VTM.

Figure 2: FE model of the full rake KHST.

Materials E ν ρ yσ Object

E24-4 210 GPa 0.3 7800 3/kg m 240 MPa Headstock, Pivot bolster, Under sheet floor

E36-3 210 GPa 0.3 7800 3/kg m 360 MPa Cantrail, Torque rear cross

member, Vertical post , Pivot bolster, Under-frame bay

Longitudinal member

E490D 210 GPa 0.3 7800 3/kg m 490 MPa Side sill, Upper sheet, Centre sill, Honeycomb 5 GPa 0.3 77 3/kg m 1000 GPa Honeycomb structure

Table 2: Material properties used in the power car of KHST.

One of the characteristics of VTM is to reflect dynamic components like suspension and connection devices. Figure 3 and 4 show dynamic components in the power bogies and the articulated bogies, and they have each characteristic curve in terms of force-displacement behaviour. Suspensions in bogies are divided into two types, primary suspension and secondary suspension. The bogie is restrained by a pivot between car body and bogie. Power

car and motorized trailer are linked with side buffers with an anti-climbing grip to prevent to overriding during collision. Also, there are 4 dampers between motorized trailer car and trailer car to mitigate the running vibration.

Figure 3: Suspensions and connections of the power car bogies (front, rear).

Figure 4: Suspensions and connections of the motorized trailer bogies (front, rear).

3. Analysis using VTM

Several numerical analyses were performed to evaluate the applicability of the VTM for collision scenarios in Figure 5. So, as described in Table 1, the energy absorption capability of the crushable front end is compared with 1D dynamic analysis. Also, the influence of dynamic components on nonlinear behavior of cars can be discussed. Besides, some unexpected buckling modes can be treated in the VTM. The four kinds of scenarios are used for analysis, and Figure 5 describes each collision scenario. Impact force, internal energy and crush length are monitored to compare each numerical result. Simulation of the VTM was performed by using LS-DYNA solver installed IBM supercomputer in KISTI (Korea Institute of Science and Technology Information). It takes 56hours to simulate the VTM up to 400msec with this computer system.

3.1 Collision analysis with a truck at 110kph from TSI

This scenario was referred from the TSI scenario, and its accident situation describes a collision with 15 ton truck at 110 kph. This scenario requires no intrusion into minimum survival space,

scenario 1 scenario 2 scenario 3 scenario 4

Figure 5: Description of four types of scenarios on collision.

no overriding, and passenger’s deceleration at less than 5g. The simulation results were summarized in Table 3. Theoretical total kinetic energy is 364.4 MJ for 780 ton, and numerical total kinetic energy is 364.5 MJ for 780.5 ton. The change of the total energy is less than 0.11% for the scenario 1. It is assumed that the numerical errors will be quite small, since the relative error of the total energies is very small. The left figure in Figure 6 is the results on scenario 1. No intrusion into driver’s zone happened, and no overriding happened between the power car and the motorized trailer car.

3.2 Collision analysis with an oblique truck at 110 kph

This scenario is similar to the TSI scenario, but the truck is positioned with 120° angle. The noticeable figure from this simulation results is that the power car body is twisted and saw-tooth lateral buckling happens after collision.

3.3 Head-on collision at 30kph

This scenario deals with head-on collision problem at the relative velocity of 60kph. The left figure in Figure 7 shows simulation results of this scenario 3. In this collision situation, noticeable figure is that a vertical buckling happens at driver’s door. From this result, we can know that suspensions and pivots are carefully considered as dynamic components because this phenomenon didn’t happen when bogies were modelled by rigid masses without suspension and pivot.

3.4 Head-on collision at 8 kph

This numerical analysis deals with light weight collision at the relative velocity of 16kph. In this simulation results, we can know they showed different numerical results, as shown in Table 3. It also depends on modeling characteristics of expansion tube behind the coupler. So, more study of expansion tube is needed.

Scenario 1 Scenario 2

Figure 6: Simulation results of VTM for scenario 1 and scenario 2.

Scenario 3 Scenario 4

Figure 7: Simulation results of VTM for scenario 3 and scenario 4.

Models List Scenario 1

Scenario 2 Scenario 3 Scenario 4

VTM 1D VTM VTM 1D VTM 1D

Crush force

Max. crush force [kN] 6781.4 4473.0 7419.7 5946.6 4465.0 4923 2000.0

Mean crush force

[kN] 3771.0 3785.0 4332.0 3798.0 3152.0 231 621.0

Energy absorption

Total absorbed energy

[MJ]

6.87 6.71 4.0945 6.53 5.45 0.012 0.5

Head zone [MJ] 4.44 5.29 3.3038 2.01 3.07 0.000953 1.6

Driver’s zone [MJ] 0.31 0.22 0.74358 0.22 0.06 0.000121 0

Power car body [MJ] 0.83 0.38 0.57284 3.45 0.67 0.000528 0.09

Crush length

Head zone [mm] 1014.0 1753.0 726.2 1104.9 1710.0 50 800.0

Driver’s zone [mm] 13.0 4.0 147.4 313.6 3.0 1 1.9

Power car body [mm] 197.3 20.0 219.0 614.2 19.0 0.4 5.5

Table 3: Crush Characteristics of VTM and 1D dynamic model for KHST.

4. Comparison and evaluation of simulation results

The numerical results of the VTM were compared with those of the 1D dynamic models in Table 3, as follows. In scenario 1, the most noticeable difference is in the crush length of the rear end of the power car body. The power car body of the VTM was crushed ten times more than the 1D dynamic models. From this result, it can be known that the maximum crash force gives some effects on crush and overriding of the rear end of the power car. In scenario 2, a saw-tooth lateral buckling happens after collision in the VTM, but it is impossible to describe this phenomenon with a 1D dynamic model. If a mutibody dynamic model is used, it will be possible [9]. The analysis using multibody dynamics cannot, however, show a twisting

buckling deformation, although it can show gross motion like zigzagging. The VTM predicts both saw-tooth lateral buckling and twisting deformation of the power car body. In scenario 3, the numerical results of the VTM predict the unexpected behaviour of the power car, and it is impossible to grasp the vertical buckling model from a mutibody dynamic model. The result results in Fig. 7 show a vertical buckling mode at the driver’s door zone. This phenomenon can be obtained only for the VTM. This result of the VTM shows why it is necessary in process of train crashworthiness evaluation In scenario 4, there are some differences in the simulation results of the light collision and it is needed to study modeling characteristics of coupler afterward.

5. Conclusion

This paper provides some study results of the VTM of KHST, and suggests it as more improved crashworthiness evaluation model. For assessment of the VTM, four kinds of representative scenarios were used, and the analysis results of the VTM were compared with those of 1D dynamic collision analysis. Through this study, it was obtained from the VTM that:

- In scenario 1, no intrusion into driver’s zone happened, and no overriding happened between the power car and the motorized trailer car. But, the maximum crash force gives some effects on crush and overriding of the rear end of the power car.

- In scenario 2, the power car body is twisted and saw-tooth lateral buckling happens after collision.

- In scenario 3, a vertical buckling mode happens at driver’s door in the VTM with dynamic components of bogies, but there is no vertical buckling in the VTM without dynamic components.

Accordingly, as considering the above results, VTM is a reliable modelling technique to be used in crashworthiness evaluation of a train set. It is especially effective in evaluation of train set instead of real train set test in aspect of cost and time. Nevertheless, the analysis time of VTM is still long when compared with other modeling method. But, it is expected to solve the problem according to fast growth speed of computer system.

Acknowledgements

This work was supported by the grant no. SR06008 from Korea Railway Research Institute (KRRI) funded by Ministry of Construction & Transportation (MOCT).

References

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