Effects of Strong Cross Winds on High-Speed Trains a Risk Assessment Approach

Transcription

1 PSAM Effects of Strong Cross Winds on High-Speed Trains a Risk Assessment Approach Gerd Matschke, Thorsten Tielkes, Peter Deeg and Burkhard Schulte-Werning Deutsche Bahn AG, Research and Technology Centre, Department of Aerodynamics, Voelckerstrasse 5, Munich, Germany, Aerodynamik@bku.db.de Peter Locher, Charles Fermaud and Hans Bohnenblust Ernst Basler + Partners Ltd., Zollikerstrasse 65, 8702 Zollikon, Switzerland, Peter.Locher@ebp.ch Abstract For several years Deutsche Bahn AG (German Rail) has been investigating the risks from the operation of lightweight end coaches due to cross winds. The methodology, which can be applied to all types of rail traffic, is described for high-speed trains. It involves the computation of permissible wind speeds using wind tunnel and simulation techniques, followed by a quantitative assessment of the frequency with which the permissible wind speed is exceeded at the leading vehicle. Safety criteria are used to derive to which extent countermeasures are necessary to guarantee safe railway operations. The methodology was approved by the responsible federal authorities and is successfully being applied in practice. 1. Background and description of the problem Since 1872 there have been at least 28 railway accidents involving passenger trains in Japan due to cross winds [1]. The great majority of all known accidents occurred on narrow gauge lines at wind speeds considerably in excess of 30 m/s. The authors are aware of only three accidents world-wide in which passenger trains running on standard gauge lines were affected. At Deutsche Bahn AG (DB) two new generations of high-speed trains have been introduced since The use of a driving trailer in the ICE2 respectively the electrical multiple-unit concept implemented in the ICE3 together with the systematic use of lightweight materials made the construction of end coaches possible whose weight is approximately 53 tonnes. Since it cannot be ruled out that strong cross winds pose a hazard to these light vehicles, the issue has been investigated by DB in an extensive research programme that has been running since 1994 [2]. Similar research has been done by the railway operators in Japan [3], Britain [4] and Sweden. Existing high-speed railway lines in Germany allow maximum train speeds

2 PSAM5 of 280 km/h, while new lines are designed for 300 km/h. For lightweight bodied vehicles a speed of 200 km/h has been shown to be sufficiently safe even in the presence of strong gusts. The approach adopted by DB is to increase the speed, which has been 200 km/h so far for such vehicles, whilst ensuring by suitable countermeasures that the risks due to cross winds do not increase accordingly. Peak wind speeds of 25 m/s are exceeded on embankments or high bridges on German high-speed lines on an average of 3 days per year. Strong winds from the west prevail so that sections of track that run north-south are most exposed to cross winds. A detailed methodology for establishing an adequate level of protection has been worked out, which is applicable to all rail traffic. This methodology is illustrated by application to high-speed rail traffic with light end coaches, as safety requirements are the most stringent in this case. 2. Methodology of risk assessment and safety planning The risks posed by cross winds to rail traffic are mainly influenced by vehicle properties (such as weight, location of centre of gravity, shape and running gear), line parameters (such as curve radii, cant and quality of track geometry), vehicle speed and the probability of occurrence of strong cross winds. Figure 1 provides an overview of the methodology adopted to guarantee safe train operation. The approach is broken down into four main steps. Step 1: Vehicle-specific permissible cross wind speeds Safety p roof Param eters of the vehicle, track and superstructure Characteristic wind curve Step 2: Line-specific risk assessment Train speed, track geometry Permissible wind speed Probability of strong winds W ind statistics, characteristics of surroundings Frequency F CWC of exceeding the permissible wind speed Step 3: Risk appraisal Com parison with safety target F CWC F CWC,target? if YES: No m easures Step 4: Planning of safety measures if NO: Possible measures Š reduction of train speed Š modifications at the vehicle Š wind-protection measures Figure 1: Methodology with four main steps

3 PSAM Step 1: Determination of vehicle-specific permissible cross wind speeds The time-dependent contact forces between wheel and rail are calculated for a given gust scenario using multi-body simulations. Aerodynamic coefficients measured in a wind tunnel, the main characteristics of running gear, irregularities in track geometry and superstructure behaviour are being taken into account. The results of these simulations are summarised in so-called characteristic wind curves (CWC). They describe for a particular vehicle how the permissible wind speed, at which the contact forces between wheel and rail fall below specified limits, varies as a function of vehicle speed and uncompensated lateral acceleration. The threshold values for the contact forces are chosen in a conservative way, which is common practice in railway engineering. Even a significant violation of these values does not immediately cause a derailment. This was quantitatively demonstrated for a lightweight driving trailer, which has not yet experienced a wind induced accident despite 30 years of operation with over one billion kilometres and almost certainly numerous violations of the permissible wind speed. For high-speed trains, however, neither statistically-based arguments nor computational methods are available to specify quantitatively derailment probabilities in case of cross wind speeds above the permissible value. Step 2: Line-specific probabilistic risk assessment A quantitative description of the occurrence of strong winds must be based on probabilistic methods. In order to be able to make comparisons with other hazards to railway operations, a quantitative assessment of the individual or societal risks arising as a result of derailments due to cross winds would be desirable. However, due to lack of knowledge about probabilities of wind induced derailments, it is assumed that the risks are proportional to the frequency with which the permissible wind speed is exceeded at the vehicle. As all safety measures directly act on this frequency such a simplification is useful for practical applications. The frequency of exceeding a vehicle s CWC is determined quantitatively for homogeneous sections of track (typical length: 100 m) as follows: - Determination of the local permissible wind speed on the basis of the CWC - Determination of the probability of occurrence of strong winds as a function of cross wind speed. This step involves transferring direction dependent statistical wind data from representative measuring stations to the line by the German weather service. Line direction, locality of track (embankment, bridge, cutting), surface roughness of the surrounding area and the presence of structures close to the track (particularly, noise protection walls and buildings) are being taken into account.

4 PSAM5 - Estimate of the frequency of the permissible wind speed being exceeded at the leading vehicle (f CWC,i ). By assuming that train operation and occurrence of strong winds are not correlated, this frequency can be computed for section i by use of formula 1: ptrain, i pcwc, i fcwc, i = (1) F CWC = f CWC, i (2) t gust p train,i is the probability of the presence of a train, p CWC,i is the probability that the relevant permissible wind speed is exceeded at a given moment, and t gust is the assumed mean duration of a gust. By taking the sum over all sections according to formula 2, an overall frequency F CWC can be calculated, which refers to an entire high-speed line and a given kilometric train performance. Step 3: Risk appraisal The decision which risk level posed by cross winds to planned high-speed train operation is acceptable is based on article 2 of the German Railway Construction and Operation Regulations. According to this regulation, the safety level once achieved must not be lowered as a result of constructional or operational modifications (principle of proof of equal safety according to GAMAB: Globalement Au Moins Aussi Bon ). Following an agreement with the German federal railway authorities, the currently authorised ICE2 service on the Hanover - Wuerzburg high-speed line with a maximum speed of 200 km/h has been adopted as a reference, defining the cross wind safety target for all high-speed train operations in Germany. The comparison is based upon the frequency F CWC in formula 2 and referred to 1 million train kilometres with a lightweight leading vehicle operating between two main stations. There is no local safety target concerning the values of f CWC,i on individual sections. Step 4: Planning of safety measures If the frequency F CWC calculated for a planned service exceeds the target value, measures must be taken so that F CWC is reduced to a value below. The main types of countermeasures are: - Reducing train speed (permanently or during periods of strong winds [5]), - Wind-protection measures (walls or fences as windbreakers), - Constructional modifications to the vehicle (e.g. lowering the centre-ofgravity, improved aerodynamics, adding extra weight) - Improving the quality of the track geometry Generally, a optimal set of measures are implemented so that the required safety level can be achieved most economically. i

5 PSAM Results and planning of safety measures The most important results from the investigations about the risks due to cross winds for the ICE2 driving trailer on the Hanover Wuerzburg and Hanover Berlin high-speed lines can be summarised as follows: - The lowest permissible wind speed of 22 m/s occurs in curves with a high noncompensated lateral acceleration. For straight sections of track, the permissible wind speed is at or above 29 m/s, depending upon the actual speed of the train. - The frequency with which the CWC is exceeded varies widely depending on the characteristics of the particular sections of line investigated, cf. Figure 2. Particularly critical are curves on exposed embankments or bridges when the wind impinges on the train from the inside of the curve frequency of exceeding the CWC (lower line) [per 100 m-sections and year] distance along railway line [km] train speed (upper dotted curve, one direction) [km/h] Figure 2: Frequency of exceeding the CWC along a typical high-speed line (peaks correspond to curves on embankments or bridges) - At a maximum vehicle speed of 280 km/h, the cumulative value F CWC along the entire high-speed line is on average five times higher than that at 200 km/h. - Because the prevailing wind direction is from the west, the danger posed by cross winds on the north-south Hanover Wuerzburg line is about an order of magnitude greater than that on the east-west Hanover Berlin line. - Since the reference risk is the one associated with the 200 km/h ICE2 service on the high-speed line Hanover - Wuerzburg, any increase in the speed of the ICE2 will require the implementation of appropriate countermeasures. In order for the ICE2 with leading trailer to run at the targeted maximum speed of 280 km/h, approximately 10 km of wind barriers would be required along the

6 PSAM5 most susceptible sections of track. An alternative approach is the installation of a wind warning system which would automatically trigger a speed reduction when strong winds are forecast [5]. 4. Summary and conclusions The methodology described in this paper is suitable for making a transparent and quantitative comparison of the hazards posed by cross winds to different vehicles on selected railway lines. Safety criteria have been defined which allow a clear decision about the extent to which countermeasures are necessary to guarantee the safe running of trains with lightweight end coaches. The methodology has already proved its worth in practical applications and has been approved by the German federal railway authorities. It has been adopted by DB as a guideline. Given that in the future operation with lightweight end coaches will be common practice with many railways, the existing methodology may form a useful starting point for other railways when dealing with the problems posed by cross winds to rail traffic operations. DB therefore proposes to incorporate the knowledge gained into the relevant European standards or directives such as TSI or CEN TC256. DB is already co-operating in the area of the risks due to cross winds with the East Japan Railway Company and proposes to intensify existing partnerships with various European railways. References 1. Fujii T., Maeda T., Ishida H., Imai T., Tanemoto K. and Suzuki M., Wind- Induced Accidents of Train/Vehicles and Their Measures in Japan, Quarterly Report of Railway Technical Research Institute, Vol. 40, No. 1, March Matschke G., Schulte-Werning B., Measures and Strategies to Minimise the Effect of Strong Cross Winds on High Speed Trains. Proceedings of WCRR World Congress of Railway Research, Florence, Italy, Vol. E, , Kunieda M., Theoretical Study on the Mechanics of Overturn of Railway Rolling Stock (in Japanese), The Railway Technical Research Institute, No. 793, Cooper R.K., The Probability of Trains Overturning in High Winds, Proc. Of the 5 th International Conference of Wind Engineering, Fort Collins, Colorado, Matschke G., Tielkes Th., Schulte-Werning B., Locher P., Fermaud Ch., Bohnenblust H., A Short-Term Wind Warning System to Counteract the Effects of Cross Wind on High Speed Trains. Paper for PSAM 5, International Conference of Probabilistic Safety Assessment and Management, Osaka, Japan, 2000