Journal of Engineering and Thermal Sciences
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Study on vibration characteristics of ship mining system under composite load
Get PDFThe load that borne by ship mining system is very complex. The vibration of lifting pipe can be significantly affected by ocean current and wind load, which has a key impact on material lifting, ore bin storage and ship towing. Considering the composite load condition, the vibration control equation of mining ship is established based on the transverse swing mechanism of ship hull, and the variation law of transverse disturbance is obtained. The dynamic equation is constructed according to the bearing characteristics of the lifting system and the D’Alembert principle. The Wilson method is used to analyze and obtain the transverse vibration spectrum response of the lifting pipe under different wind loads, hull disturbance velocity and water depth. Based on the analogy method and hammering method, the vibration feedback test-bed of the lifting system is built, and the time-domain and frequency-domain vibration characteristics of the lifting pipe model under different water depths are obtained. The results show that in shallow water, the disturbance of mining ship and the composite load of ocean current are the key factors affecting the vibration amplitude of lifting pipe respectively. With the increase of water depth, the characteristic frequency and amplitude of the system decrease, and the amplitude gradually presents a discontinuous phenomenon
Experimental study of the lap motion trajectory of vibratory finishing machine
Get PDFVibratory equipment is widely used for performing various finishing processes, machining and forcing of different parts and materials. Numerous researchers and technologists pay specific attention to the possibilities of implementing vibration-driven machinery for conducting the lapping and polishing operations on flat surfaces. The present paper is dedicated to studying the laps kinematic parameters of the vibratory finishing machine actuated by six electromagnets. The paper’s scientific novelty consists in the experimental verification of the previously modelled and simulated circular trajectories of the laps under different operational conditions. The methodology of research contains two basic stages: changing the excitation frequency at the constant traction force and changing the traction force at the constant excitation frequency. The improved 3D-design of the vibratory finishing machine was developed in the SolidWorks software. The experimental prototype was implemented in practice, and full-scale tests were carried out using the WitMotion sensors and software. Based on the obtained experimental data, the trajectories of the machine’s laps were constructed and analyzed in the MathCad software. The research results substantiate the possibilities of providing circular oscillations of the laps at different operational conditions. The results can be used by technologists and engineers while choosing the appropriate design and control parameters for similar vibratory equipment intended for lapping and polishing of flat surfaces
The influence of the truss bar on the dynamic behavior of a Warren truss by changing the modulus of elasticity
Get PDFThe paper presents the natural frequencies shift of a Warren truss with seven elements in the case that members of the structure are weakened by considering that the modulus of elasticity with a lower value. Taking into consideration that the slenderness ratio has a constant value and the transverse section of the truss bars is changed, the relative frequency shift for the first seven vibration mode were calculated by using the values obtained from numerical modal analysis. The conclusions reveal the fact from the dynamic behavior of the structure it can be obtained templates to identify the weakened truss bar of the structure
Studies on tensile and tear fracture of the S8210 tarpaulin
Get PDFThe tarpaulin of PVC-coated S8210 wagons is a composite textile membrane. This material is resistant to atmospheric factors (wind, rain, snow, etc.), durable for many practical applications and can be manufactured in various colors and prints. PVC membrane material is inexpensive, soft and easy to manufacture. These materials are widely used in large-opening spatial structures due to excellent mechanical behavior and beautiful textures. The tarpaulins are made by the method of welding with high frequency currents from the material S8210. In the present paper, the tensile and tearing mechanical properties of tarpaulins intended to protect goods carried by railway wagons are presented. The results of this study can be used in establishing the appropriate utilization of the fabric, in accordance to the warp and weft directions
Research on intelligent detection of pavement damage based on CNN
Get PDFIn order to timely detect road damage under complex constraints, the road damage mechanism was used to reclassify the types of road damage, the VGG-19 model was applied to identify and detect less road damage images intelligently through convolutional neural network and transfer learning and at the same time, the road damage situation was detected using the Softmax classifier and the feasibility and accuracy of the method were verified on the basis of the detection set. The results show that the detection and recognition accuracy of the model proposed in this paper reaches 86.2 %, an increase of 6.2-49.8 percentage points than the detection results of other convolutional neural network models. Therefore, it can be concluded that the transfer learning- and convolutional neural network-based road damage intelligent detection methods proposed in this paper are feasible, and this research is helpful to realize high-precision real-time intelligent detection of road damage
Editor’s Letter. Use of computational simulation by Finite Element Method in Jaw Functional Orthopedics. Is it possible and feasible?
Get PDFEffect of warp and weft uniaxial tension on the permeability of sand covered with geotextile
Get PDFThe permeability of sand covered with geotextile is affected by the permeability of geotextile, which is related to the tensile state of the geotextile. Considering the weaving mode of geotextile, the effects of warp tension and weft tension on the permeability of sand covered with geotextile were studied by experiment. Four different specifications of geotextiles were selected for warp and weft tension respectively. The changes of permeability parameters of sand covered with geotextile under non tension, warp and weft tension were measured by vertical permeability instrument, and the effects of warp and weft tension on permeability parameters such as seepage velocity, sand loss and gradient ratio were analyzed. The test results show that the water permeability and anti silting performance of the geotextile increase with the increase of tensile strain, and the soil conservation performance decreases with the tensile strain increasing. Meanwhile, the relationship between permeability and warp tensile strain is not monotonic. When the warp tensile strain 3%, the water permeability and anti silting performance of geotextile are the weakest, and the soil conservation performance is the strongest
Effect of damping ditch on blasting vibration reduction by field experiment and numerical simulation
Get PDFIn order to analyze the influence of a damping ditch on the blasting vibration, a large number of on-site monitoring tests with or without damping ditch were carried out based on the foundation pit excavation project. Based on the Sadovsky’s empirical formula, the optimized vibration velocity attenuation model was established by using the waveform subsection correspondence method and least square method. The calculation results are in good agreement with the measurement results. The average errors in radial direction and vertical direction are 17.04 % and 10.76 % respectively. A series of finite element models were established to study the influence of the damping ditch geometry on the damping effect. The experimental and numerical results show that the damping ditch can obviously reduce the blasting seismic effect, with the highest damping ratio in the area near blasting source. For different damping ditches, the damping ratio first increases and then decreases proportionally to the increase of distance between the measuring point and the blasting zone. The damping ditch depth has the best damping effect on blasting vibration, followed by the distance between the damping ditch and the blasting source, and finally the damping ditch width, which is consistent with the damping mechanism of theoretical analysis. The attenuation of the surface wave is only related to the damping ditch depth. The research results can provide a reference for the design of blasting vibration isolation
Analysis on the seismic wave caused by low frequency sound source in shallow sea based on multi-transmitting formula artificial boundary
Get PDFThe elastic waves propagating in seabed caused by sailing ships are called ship seismic waves, which can be used to identify ship targets. The wave components and the influences of source frequency, source depth and depth of seawater to the seismic waves are important to the application of seismic wave to detect ship targets. Thus, a forward numerical simulation of seismic waves in shallow sea excited by low frequency sources in time domain was carried out with finite element method based on the Multi-Transmitting Formula artificial boundary. The numerical results show that the body waves and conical waves decay faster in space, but the interface wave decays relatively slow. Multi-transmitting Formula (MTF) artificial boundary has achieved good transmitting effect for longitudinal wave, upstream and downstream acoustic wave and transverse wave. When the source frequency is very low and the seawater layer is shallow, due to the effect of low-frequency cutoff, there is no normal mode wave which can propagate without attenuation in the seawater waveguide, and only the interface wave is propagating near the sea bottom surface. When the frequency of the source or the depth of the seawater layer increases, the effect of low frequency cutoff in the shallow water waveguide is weakened, and the normal mode waves propagating in seawater layer are gradually excited. The intensity of the interface wave caused by low-frequency point sound source mainly depends on the distance between the source and the seafloor
Test and mechanism analysis for crack propagation by blasting in rock under the condition of unidirectional load
Get PDFIn deep rock blasting, there are different constraint conditions such as unidirectional loading, bidirectional loading and tridirectional loading due to in-situ stress. The similar model test of rock blasting under unidirectional load was carry out to study the law of crack propagation in rock by blasting in this study. A transparent material which conformed to the mechanical properties of hard rock is used to make specimens. A high-speed camera was used in some model blasts. After blasting the surface cracks on the specimen were measured, including the near zone and middle zone of blasting. The results showed that: (1) the radial main cracks in the specimens under initial static load propagated along the principal stress direction, which is different from that without initial stress, and there is almost no radial main crack in the direction perpendicular to the principal stress. (2) The average length of radial crack and diameter of circumferential fracture circle gradually decrease with the increase of unidirectional initial stress, but the diameter of compression crushing circle increase. (3) The maximum and average initial velocity of radial crack growth decrease with the increase of unidirectional initial stress