Journal of Vibroengineering
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Consideration of the problem about vibration of automobile in one fourth model with taking road deformation and the loss of contact into account
Get PDFThis paper presents an approach to the problem about vibration of automobiles in one-fourth model where both road deformation and the loss of contact are taken into account. Contact characteristics such as the geometry of the contact area, pressure distribution, the relation between the contact force and the dimensions of the contact area, and therefore the change in dimensions of the contact area with respect to time are mentioned. Deformed road is modeled as an elastic beam which is simply supported at the two ends and lies on Kelvin’s visco-elastic ground. The differential equations of motion for both states of contact and losing contact are unified by introducing a so-called contact state parameter. The partial differential equation among the differential equations of motion of the vehicle-road coupled system is transformed into a system of all ordinary differential equations by applying the Bubnov-Galerkin’s method. A procedure for numerically solving the ordinary differential equations of motion of the vibration system under consideration is proposed and some numerical results for illustration are also presented in the paper
A novel regenerative snubber circuit for flyback topology converters
Get PDFSwitch mode power suppliers based on isolated flyback topology have voltage stresses on semiconductor switches caused by transformer leakage inductance. Those voltage stresses have to be mitigated by implementing active or passive clamp preferably with partial leakage energy recovery. In this paper a new integrated semi-active regenerative (lossless) snubber is proposed. The proposed snubber topology is featured by the snubber inductor integrated into the main transformer thus decreasing component count and saving the PCB space. Partial coupling of snubber inductor with a secondary side makes it possible to recover part of the transformer leakage energy directly to the secondary side with potential to increase snubber efficiency. The operation of the proposed snubber is analyzed and simulation results are presented. Interesting is that with the proposed snubber various side effects can be reached like reduction of RMS current in secondary side, ZCS and ZVS modes for secondary side rectifier and primary main switch along with achieved primary goal – voltage stress limitation and transformer leakage energy recovery
Indirect coupling method for structural analysis of refuge chamber
Get PDFStructural analysis is important in the design of a refuge chamber, which can ensure the structural safety of the refuge chamber in case of an explosion. In this paper, an indirect coupling method is utilized to calculate deformation of a refuge chamber under explosion, when gas explosion is simulated in a roadway model, and the pressure waves on different locations of chamber are extracted. The extracted pressure-time curves are applied to a detailed model of the refuge chamber to obtain deformation values. However, reliabilities and validities of the simulation results are not provided. Thereby, we conducted three groups of small-scale physical experiments for comparing the corresponding simulation results calculated by the indirect coupling method. Meanwhile, the theoretical values were obtained by the method of extracting the specific impulse. The results show that the simulation values fit well with the experimental and theoretical values. The process of applying a pressure-time curve to the model covers the specific impulse which acts on the prototype. This method can be used to calculate the deformation of complex equipment under explosion
Influence of truss rod damage on prestressed concrete chord-stayed truss T-frame bridge
Get PDFThe prestressed concrete cable-stayed truss T- frame bridge is a novel type and complex structure. Truss damage is a common form of distress in this type of bridge. For studying the mechanical properties of truss members under the condition of the truss rod, a finite element model is established for analyzing the damage or failure of the truss rod. The effects on the deflection and frequency are compared and analyzed under the condition of damage or failure of the truss rod. The results show that the damage of the truss members has a significant effect on the deflection and frequency of the main beam. The damage of the upper chord affects the deflection of the entire T-beam, and the damage scope of the web member is limited to the abdominal area. The relationship between the damage of the truss members and the deflection of the main beam is nonlinear. Damage to truss members results in a reduction in fundamental frequency. Whole bridge truss damage has a more significant effect on frequency. Upper chord damage has a more significant effect on frequency than web members
Experimental study on acceleration response laws of shallow-buried bias tunnels with a small distance
Get PDFBased on the similarity theory, a physical testing model with scale of 1:10 was designed and fabricated. The Wenchuan wave (WC-XZ), Darui artificial wave (DR-XZ) and Kobe wave (K-XZ) were adopted as excitation waves which was XZ directions (horizontal and vertical loading at the same time). A series of shaking table tests were carried out to study the effect of the types, directions and peaks acceleration of the seismic waves on the acceleration response laws of the shallow-buried bias tunnels with small distance. The results show that: (1) in the horizontal direction, the types of the seismic waves have a little effect on the acceleration response, but the law is opposite with Kobe wave being the most serious, followed by Darui artificial wave and Wenchuan wave in the vertical direction. (2) The existing slope has a significant effect on the acceleration response of the right hole which is different from that of the left hole. (3) The acceleration response of the tunnel in the vertical direction is more severe than that of the horizontal direction and the acceleration amplification factors in vertical direction are is generally 1.02-3.94 times that of the horizontal direction. (4) in the seismic design of tunnel, different seismic measures should be adopted in different directions. The results have a significant reference for the anti-seismic design of the tunnel
A novel wind turbine fault diagnosis method based on generator current analysis
Get PDFGear meshing dynamic model is the most important part in the whole wind turbine system which is used to carry out operation conditions simulation in off-line case. By simulating the normal gear meshing and the gear meshing with broken teeth in wind turbine dynamic model respectively, the difference in generator current can be observed. The method we propose is to monitor the operating condition of the wind turbine based on the current transmitted to the generator end dynamically according to the meshing of the gear pair. Mechanical parameters have great influence on the system that will be transmitted to asynchronous generator, it works in a quite different approach compared with traditional method on vibration monitoring using sensors
Fault diagnosis of bearing vibration signals based on a reconstruction algorithm with multiple side Information and CEEMDAN method
Get PDFWhen bearing vibration of instruments is monitored, a large number of data are produced. This requires a massive capacity of storage and high bandwidth of data transmission whereby costs and complex installation are concerned. In this study, we aim to propose an effective framework to address such the amount of bearing signals to which only meaningful information is extracted. Based on the compressed sensing (CS) theory. We proposed a reconstruction algorithm based on the multiple side information signal (RAMSI) with a purpose to effectively obtain important information from recorded bearing signals. In the process of sparse optimization, the RAMSI algorithm was implemented to solve the n-11 minimization problem with the weighting adaptive multiple side information signals. Wavelet basis and Hartley matrix were applied for the reconstruction process, for which the effective sparse optimization processing of bearing signals was able to adaptively computed. The performance of our RAMSI-based CS theory was compared with the basis pursuit (BP) which is based on the alternating direction method of multiplier (ADMM) and orthogonal matching pursuit (OMP). The error indices of the reconstruction algorithms were evaluated. This proves that the performance of the sparse optimization algorithm from our proposed framework is superior to the BP based on the ADMM and OMP algorithm. After recovering vibration signals, some strong noise caused by the incipient fault characteristic of the bearing. The complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) method was performed to extract the bearing fault component from such noise. In terms of performance, the CEEMDAN method was compared to the standard ensemble empirical mode decomposition (EEMD) method. The results show that the CEEMDAN method yields a better decomposition performance and is able to extract meaningful information of bearing fault characteristic
The SH wave scattering of a heterogeneous hill in an elastic half-space
Get PDFBy combining the wave function expansion method with the auxiliary function, a closed series solution for the dynamic plane response is proposed considering horizontal circular heterogeneous topography under SH wave incidence. The displacement and stress residual is found to be small along the entire boundary, including the corner points; further, the solution can be used for the incidence of a high-frequency wave. In this study, the influence of the shear modulus ratio of a heterogeneous hill and a lower medium on the displacement amplitude spectrum and surface displacement is determined. The results show that the hardness of the medium in hill topography significantly influences out-of-plane surface motion. The surface displacement of the soft hill is significantly larger than that of the homogeneous hill, and the motion effects are enhanced considerably. In contrast, the hard hill weakens surface motion
Stress analysis of the discs of axial-flow microturbines
Get PDFThe article discusses the mesh creation techniques for models of discs of axial-flow microturbines. A universal method of optimization of such devices, in terms of their strength improvement, has been proposed. The research focused on microturbines that can operate in combination with ORC systems, especially the ones whose discs have many structural components such as pins or chamfers. Calculations were done using the commercial software ANSYS Workbench. Both tetrahedral and hexahedral grids were used in the analysed models. The calculation time needed for the grid preparation was regarded as an important parameter. Therefore, the reference model was created using the disc slice method. The results obtained for the models that included the full complex geometry of the disc were compared with the results obtained for the reference model. The mesh size coefficient was defined. It enabled to simplify the strength optimisation method for discs of axial-flow microturbine and also made it more universal. After carrying out all analyses and computations, it was possible to develop a scheme of conduct during the optimization of the aforementioned expansion devices
Seismic responses of concrete rectangular liquid storage structure with large height-width ratio
Get PDFConcrete rectangular liquid storage structure (CRLSS) with a large height-width ratio has good application prospects due to saving land resources. 3-D Solid element and 3-D Fluid element are used to simulate structure and liquid; and free surface is set to simulate the liquid sloshing behavior. Based on potential flow theory, a three-dimensional numerical model for CRLSS with large height-width ratio is established by ADINA. Results show that wall tensile stress exceeds the concrete tensile strength 2.39 MPa when liquid level height reaches to 11.70 m. There are the optimal baffle positions which can ensure that the wall tensile stress is less than the concrete tensile strength when PGA is 0.22 g, and the wall tensile stress reaches the minimum value when the baffle height is 3.6 m. Opening size has little effect on the wall tensile stress, but it has a significant effect on the baffle tensile stress. Seismic capacity of CRLSS with large height-width ratio designed by using the optimal baffle position can meet the requirements when PGA is 0.22 g, and it is necessary to carry out further comprehensive damping measures when PGA reaches 0.62 g. The arrangement of horizontal baffle can provide an effective way for the engineering application of large height-width ratio CRLSS