Journal of Engineering and Thermal Sciences
Not a member yet
1200 research outputs found
Sort by
Vibration analysis of the beam structure under the moving mass
Get PDFAnalytical solution of vibration of simply supported beam under the action of centralized moving mass and two numerical methods using life and death element method and displacement contact method are analyzed in this paper. The results show that vertical acceleration resulted from speed and centrifugal acceleration resulted from load moving must be taken into consideration for large quality and high speed. The characteristics and applicable situations of the two numerical methods are also studied to provide a basis for analyzing and considering structural dynamic problems of moving load mass
Dynamic analysis of a train-bridge system to vessel collision and running safety of high-speed trains
Get PDFA dynamic analysis model is established for a train-bridge system subjected to a vessel collision-load. A (32+48+32) m continuous bridge with PC box girders and a CRH2 high-speed train are considered as a case study. The whole histories of the train running on the bridge are simulated while the vessel collision load acting on the pier, based on which the dynamic responses of the bridge and the running safety indices of the train on the bridge are evaluated. The results show that the dynamic responses of the bridge are greatly increased by the vessel collision load, resulting in a big influence on the running safety of high-speed train
Integrating a verified vehicle-bridge system model into fatigue assessment of steel railway bridge
Get PDFEffectively evaluating the fatigue behavior of aging bridge structures is an urgent task for engineers and researchers, as more and more existing bridges approach the end of their service life. Determining the fatigue load effects due to moving trains is a key aspect of the available assessment frameworks (e.g., the S-N approach). In this paper, a vehicle-bridge system model is integrated into the fatigue assessment procedure employing S-N lines. The system model is used to obtain fatigue stresses generated by moving train loads. The integration is proven able to aid in effective prediction of fatigue damage and remaining fatigue life of railway bridges
The roller bearing fault diagnosis methods with harmonic wavelet packet and multi-classification relevance vector machine
Get PDFRoller bearings are widely used elements in rotary machines. How to monitor the working conditions of roller bearings are focus study in the world. Monitoring the vibration signals of roller bearings is important indirect mean for that they reveal the characteristics and feature of roller bearing faults. Therefore, monitor the vibration signals and diagnose the working states of roller bearings are widely used to ensure the safety operation of the machines. This paper studies a novel roller bearing faults discrimination method with harmonic wavelet packet and Multi-classification Relevance Vector Machine (MRVM). Indeed, the fault discrimination is a pattern recognition process including feature extraction and faulty patterns recognition. Therefore, this paper collects vibration signals and decomposes them with harmonic wavelet packet. After the wavelet coefficients of each node are available, compute the vector energy by corresponding coefficients. The feature vector is prepared after the vector energy has been standardized. With MRVM, the paper proposes three fault discrimination methods in order to identify good bearing, bearing with inner race fault, bearing with outer race fault and bearing with roller fault. The Decision Tree (DT) model, One Against Rest (OAR) model and One Against One (OAO) model are used to propose the classification methods respectively. The proposed OAO model is simplified in order to improve the computation efficiency and simplify the architecture of the model. Finally, capture the vibration signal from the roller bearing stand of electric engineering lab and the roller bearing fault simulation stand QPZZ-II to illustrate the proposed methods. The proposed feature extraction method with harmonic wavelet packet is compared with conventional wavelet packet. With the previous feature vectors, the accuracy and efficiency of the three fault discrimination methods are compared. The accuracy and efficiency of three fault discrimination methods are compared under different conditions including developing faults, noise involving and several faults developing simultaneously. Experiment results show that the proposed feature extraction method is more effective than conventional method and the simplified OAO-RVM model possess the best fault discrimination accuracy and DT-RVM model possesses the better computation efficiency
DC modulation controller parameters tuning based on improved multi-signal Prony algorithm
Get PDFTo aim at the puzzle of DC modulation controller parameters tuning in large-scale AC/DC interconnected power systems, in this paper a multi-signal Prony algorithm is proposed which can simultaneously extracts oscillation modes from multiple signals compared with traditional Prony analysis method. In the algorithm, current setting value increment at rectifier side serves as system input, and AC liaison transmission line active power increment acts as the resulting output under consideration of systems initialization state. Through the improved multi-signal Prony identification on the output time-domain response data under specified input, an equivalent linear model with order reduced is obtained. Based on the identified results, the adjustments are then implemented on the controller parameters using the pole placement method. Through theoretical analysis and IEEE four generators system tests, the simulation results show that to add the DC modulation controller with parameters tuned by the improved Prony algorithm can significantly increase the oscillation damping of AC/DC interconnected systems, and improve the systems operation stability
Forecasting research of overpressure of explosive blast in subway tunnels
Get PDFIn case of an explosion happening inside the subway tunnel, blast waves interacts with the structure in an enclosed space. Both the overpressure and duration of blast increase. On the basis of experimental research, we establish a calculation model of blast effects in a tunnel. Its applicability has been verified by comparing the numerical results and the experimental findings. Then the blast effects in subway tunnel have been analyzed. It has been found out such factors as the tunnel shape, charge position, and distance to the explosion center all have a great influence on blast effects. The overpressure of blast in the subway tunnel is summarized and the formula is proposed. Compared to data of explosion tests at home and abroad, the formula has been proven to have some applicability. It may be provide some reference to the design of antiknock loads of subways and evaluation of casualties
A high-throughput WSN for structural health monitoring
Get PDFA challenge with existing WSNs used for structural health monitoring (SHM) is how to increase the data transmission rate (DTR) for large amounts of sampling data. To handle this issue, this paper proposes a new design method of a high-throughput WSN with multi-radio sink node (M-RSN) which can increase the data transfer ability of WSN. Additionally, a tight scheduled approach and multi-radio time synchronization method are designed for the stable implementation of the proposed network. A high data throughput of 1020 Kbps of the developed network has been proved. To evaluate the effectiveness and robustness of the proposed network designing method, experiments for aircraft composite wing boxes monitoring are carried out. The evaluation results have shown the advantages of the proposed methods
Topology optimization for minimizing frequency response of constrained layer damping plates
Get PDFThis paper presents a topology optimization method to design the optimal layout of Constrained Layer Damping (CLD) material in structures subjected to harmonic excitations or stationary random excitations. A finite element model is used to describe the dynamic performances of the CLD structure. Since energy dissipation arises only from the viscoelastic (VEM) layer, the modulus of elasticity of the VEM layer is complex. The complex mode superposition method is employed to calculate the steady-state response of the CLD structure under harmonic excitations. According to Pseudo-Excitation Method (PEM), the vibration analysis of stationary stochastic excitations can be transformed to the analysis of harmonic excitations. The minimization of frequency response at specified one point or several points in structures are selected as optimization objective. The Solid Isotropic Material with Penalization (SIMP) method is adopted to interpolate the CLD material. The sensitivity is derived by means of the adjoint variable method which is more efficient than the direct variable method. The Method of Moving Asymptote (MMA) is used to search the optimal layout of CLD material on structures. Numerical examples are given to illustrate the efficiency and verification of the proposed approach
Comparison of the noise level and the skid resistance of asphalt pavement mixtures on road surface
Get PDFTraffic noise is a major environmental source of pollution both in developed and in developing countries. Pavement surface texture affects many vehicle and road characteristics; therefore, efforts are needed to develop more advanced techniques for evaluating pavement texture. The selection of an appropriate pavement as the best method to control the main cause of road noise, the sound absorption resulting from contact wheel vehicles and pavement is proposed. In this study skid resistance of porous asphalt and conventional asphalt were measured. The correlation R2 and P value of the linear regression was used for skid resistance and noise. Various pavement characteristics were measured and their effects on noise levels were evaluated using principal components regression, in addition to ordinary least-squares regression. This research confirmed that open graded pavements exhibit reduced tire noise compared to dense and gap graded mixes and quantified this reduction for typical mixes in Tehran. Correlation between Skid resistance of asphalt pavements and noise levels were determined using the statistical program
Experimental study on the bursting vibration effect in ground surface of large-diameter and high-pressure steel pipe
Get PDFIn order to study the harmful effects of seismic waves generated by the bursting of large-diameter high-pressure gas pipelines, through two half-buried three-pipe air bursting tests and with the use of three-vector velocity sensors, vibration speeds in three different directions when pipe bursting seismic waves propagate along the surface can be obtained. Propagation characteristics and spectral characteristics of pipe bursting seismic waves can be gained by comparison and the Fourier transform analysis of the autocorrelation function. According to results, major seismic wave energy concentrates in 0-100 Hz frequency range where the maximum power spectral density corresponds to a frequency, which is less than 10 Hz and has strong destructive impacts on the buildings around the pipelines. Linking test results to safety threshold that have been studied allows some data to be acquired. When natural gas pipelines are under construction, the safe distance between parallel buried pipelines is 60-70 m; from pipelines to traffic tunnels and mine workings the safe distance is 50-100 m; from pipelines to the buildings it is100-240 m