72 research outputs found
Vibration analysis of fluid filled pipework systems
No full textSIGLEAvailable from British Library Document Supply Centre-DSC:DXN037507 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Contribution a l'etude des systemes d'elevage mytilicole
No full textSIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
Fine flow field and unsteady hydrodynamic performance calculation for rudder cavitation
No full text[Objectives] In order to study the precise flow field of rudder cavitation and its related laws of unsteady hydrodynamic performance, [Methods] a propeller and rudder model of a certain ship is established, and a structure grid, SST k-ω turbulence model and VOF method are used to calculate the rudder cavitation. In order to understand the phenomenon of rudder cavitation, an observation experiment is carried out with a real ship. The calculated results are compared with the experimental results, proving the reliability of the numerical method. The periodic changes in rudder cavitation are then discussed and analyzed, and rudder cavitation is calculated on the basis of cavitation and non-cavitation under the two states of three kinds of rudder angles. [Results] The results show that when the cavitation range is small, it has little effect on average rudder force. As the cavitation range increases, its influence on average rudder force increases significantly while lateral rudder force decreases significantly. Once cavitation occurs, the amplitude of unsteady force increases greatly;the greater the cavitation range, the greater the amplitude of unsteady force. [Conclusions] The results of this study can provide technical support for assessing the hydrodynamic performance of rudders under cavitation conditions in the pursuit of optimal rudder design
Rail Corrugation Characteristics Deduced from a Wavelet Analysis of High-Speed Train Interior Noise and Vibration
No full textA method to deduce the characteristics of rail corrugation was developed and presented in this paper. It has been found that noise and vibration in the train vehicle were primarily contributed by rail corrugation and wheel polygonalisation. As the characteristics of wheel sets of a particular train can be assumed to be unchanged during a trip, rail corrugation along the tracks of the trip can be identified. Wavelet analysis was employed in analysing interior noise and vibration data collected inside a high-speed train vehicle traveling on a typical high-speed line in China. Noise and vibration data corresponding to increasing, decreasing, and unchanged train speeds were grouped and examined using time-frequency domain analysis. For both acceleration and deceleration speed conditions, the characteristic frequency of interior noise and vibration changes as the train speed changes, in a discontinuous pattern, and with a fixed speed-frequency ratio, which can be deducted as the pinned-pinned frequency of rail vibration and wavelength of rail corrugation in corresponding rail track sections. This method enables accurate restoration of rail corrugation characteristics, without having to apply for railway possession for rail corrugation tests onsite, which is an inexpensive yet reliable method to provide a basis for the formulation of line maintenance and rail grinding plans
A New Top-Mounted Shear-Hinge Structure Based on Modal Theory and Rubber-Pad Damping Theory
No full textSteel-spring floating-slab tracks (SSFSTs) are widely used as efficient vibration-damping beds, and in China, they are mainly used in subways and municipal railroads. The shear hinge is an important component that improves the stability of the line, and field research has found that the top-mounted shear hinge (TMSH) undergoes varying degrees of damage, which indirectly affects the safety and stability of line operation. In this work, we studied the causes of damage to TMSHs, designed a new TMSH structure with a rubber-pad layer installed based on modal theory and rubber-pad vibration-damping theory, and proved that the new structure can reduce the occurrence of damage by comparing it with the original TMSH structure. The main aspects of this study are as follows: Firstly, the ultimate load capacity of the existing and new TMSH structures was checked by establishing a refined finite-element model. Then, modal analysis and frequency-response function analysis were carried out based on modal theory and frequency-response function theory to reveal the causes of TMSH damage and prove that the new structure can effectively delay damage. Finally, the modal and vibration patterns of the two structures were obtained via indoor hammering tests and compared with the simulation results. The results show that the two TMSH structures are in line with the strength requirements, and the existing TMSH damage mainly results from the resonance between its natural frequency and the high-excitation frequency of the floating slab under long-term cyclic train loading, causing high-frequency vibration fatigue damage. It is also demonstrated that the new structure can effectively reduce the natural frequency of the TMSH so that its value is located in the region of low vibration on the floating slab. The excitation vibration levels of the TMSH mounted on the curved section of the 4.8 m floating slab and the 3.6 m floating slab were reduced by 9 dB and at least 3 dB, respectively. After adding rubber pads located in the 400–3000 Hz floating-slab high-vibration-level region of the TMSH damage-prone parts, the amplitude reduction, including lateral excitation of damage-prone parts, resulted in a vibration amplitude reduction of more than 30 dB. However, the vertical excitation of the mid-end and rear-end bolts slightly increased their amplitudes, whereas the shear-rod amplitude was reduced by 48 dB, and the front-bolt amplitude was reduced by 5.28 dB. The natural frequency and vibration pattern obtained from the hammering test were consistent with the simulation results, and the reliability of our conclusions was verified from both experimental and simulation perspectives
Structural Improvement of the ω-Type High-Speed Rail Clip Based on a Study of Its Failure Mechanism
No full textIn the circumstances of high-speed railways, the wheel-rail vibration is significantly aggravated by polygonal wheel wear and rail corrugation, which subsequently leads to the wheel-rail interaction at higher frequencies and potential failure of the rail fastening. In this paper, a ω-type clip of the fastening in the CRH high-speed rail was used to investigate the failure mechanism. First, a dynamic wheel-rail coupling model and a finite element analysis of the rail clip were developed, from which the rail vibration frequency and modal frequencies of the clip with different installation torques were obtained. The experimental tests and modal simulation results were mutually verified. In addition, the real-time vibration measurement and the wheel-rail wear monitoring were carried out at a CRH high-speed railway site. It was found that the resonant frequencies of the ω-type clip in the installation condition coincided with the excitation frequencies of the wheel-rail interaction induced by wheel-rail wear. The high-frequency dynamic failure mechanism of a typical ω-type clip, W300-1, is put forward for the first time. Moreover, a high-frequency rail clip fatigue test system was designed and developed specifically for this study. The loading excitation frequency of the clip test used was set as 590 Hz, and the loading amplitude was 0.05 mm. After 125-minute operation of the test system, the clip was broken at the expected location predicted by the FEA model. The high-frequency fatigue test result further verified that the failure mechanism of the ω-type clip was due to the resonance of the clip with its excitation force from the wheel-rail interaction. Finally, the clip was then structurally improved taking into account the stiffness and mass, which led to its resonant frequencies shifting away from the high-frequency excitation range, hence avoiding resonance failure of the subject clip
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