Issue 33

R. Sepe et alii, Frattura ed Integrità Strutturale, 33 (2015) 451-462; DOI: 10.3221/IGF-ESIS.33.50 461 V IBRATION ANALYSIS ith the growing use of advanced structures for railway vehicle design, determination of the structural dynamics characteristics is becoming increasingly important. From a space and loading perspective, it is beneficial to have the car body as long and as wide as possible, but due to the limits on the size of the car body cross- section, the structure can be rather long and slender with relatively low rigidity. A too flexible car body can lead to considerable structural deflection during travel, resulting in structural damage of it. During operation the car body is continuously excited due to the dynamic interaction between track, wheels, bogie and car body. To avoid resonances, as mentioned in [1], a common practical design rule is to keep the first natural frequency of the car body as high as possible, typically above 12 Hz. The elastic mode shapes and modal frequencies of a railroad car, which represent its dynamics characteristics, can be evaluated by using computational methods. To determine vibrational behaviour of vehicles, normal mode or free vibration analyses, as another eigenvalue problem, are performed. Tab. 10 shows the first three frequencies of the modified roof models. The least natural frequency is 50.81 Hz that is highest of the value of 12 Hz. This means that there are not problem of resonances. The first two elastic mode shapes of roof are shown in Fig. 16 and 17. The mode shape with the lowest frequency shows a vertical distortion of the roof structure, being the maximum normalized displacement localized in a fiberglass sheet. N° Frequencies [Hz] 1 50.81 2 50.84 3 51.29 Table 10 : Natural frequencies of the roof module. Figure 16 : Elastic mode shape for the first natural frequency. Figure 17 : Elastic mode shape for the second natural frequency. C ONCLUSIONS n this work static, buckling and vibration behaviors of a new roof structure for a refrigerated freight car subjected to different loading scenarios as defined in standards EN 12663, UIC CODE OR 577 and ERRI B12/RP17 were studied. Using a number of numerical cases the following important conclusions are shown: FE method is used to assess the structural behaviours of such roof structure. Three kinds of analyses were done: static analysis, linear buckling analysis and free vibrations. Development of work and main results and conclusions are summarized as follows: 1. Two stages of static analysis are performed. In the first stage the initial concept design of roof structure was analyzed and the structural weaknesses of designs were determined. Then the structure was opportunely modified and W I