Table of Content

28 January 2020, Volume 54 Issue 1 Previous Issue    Next Issue

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Research and Application of the Capture Area Obtaining Method for Waterjet GUO Jun,CHEN Zuogang,DAI Yuanxing,CHEN Jianping 2020, 54 (1):  1-9.  doi: 10.16183/j.cnki.jsjtu.2020.01.001 Abstract ( 1148 )   PDF (3238KB) ( 521 )   Save The momentum flux method recommended by the International Towing Tank Conference (ITTC) needs to determine the capture area of waterjet. A simple and practical method to obtain the capture area based on streamline method is proposed. MATLAB is adopted to greatly simplify the post-processing of obtaining the capture area and enhances the efficiency. On this basis, by solving the RANS equation and applying the steady multi-reference frame (MRF) model, the performance of the waterjet is numerical calculated and analyzed at different rotational speeds. It is found that the method can accurately get the shape of the capture area, and the parametric expressions of the capture area are given. The shape of the capture area, the velocity distribution of the pump intake and the position of the separation point of the lip flow all change with the rotational speed. The proposed method is practical and can be used to predict the performance of the waterjet. References | Related Articles | Metrics

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Strength Check Method of Blade Edge Under Concentrated Ice Load Condition YE Liyu, WANG Chao, GUO Chunyu, CHANG Xin 2020, 54 (1):  10-19.  doi: 10.16183/j.cnki.jsjtu.2020.01.002 Abstract ( 1101 )   PDF (3822KB) ( 437 )   Save During the design process of ice-class propellers, it is necessary to check the blade edge strength to avoid the gap on the blade under ice contact, which may affect the propeller performance of hydrodynamic force, cavitation, noise, etc. To quickly check the blade edge strength, based on the rules in IACS URI3 and the finite element method (FEM), the strength check method of blade edges is established under the concentrated ice load conditions. Considering the particularity of the propeller, an automatic meshing method has been developed by dividing the propeller into many 8-node hexahedron elements along radial, chordwise and thickness directions, which can help to mesh the propeller blades reasonably according to the loading position. The FEM is applied to calculate the stress and deformation distributions of the propeller blade under the concentrated ice load. Taking the PC3 ice-class propeller as an example, the blade edge strength is analyzed and checked. The results show that large stress is concentrated on the blade edge which is prone to cause the damage. References | Related Articles | Metrics

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Study on Oblique Water Entry of Wedge Applying Improved Volume of Fluid Method XIE Hang,REN Huilong,TAO Kaidong,FENG Yikun 2020, 54 (1):  20-27.  doi: 10.16183/j.cnki.jsjtu.2020.01.003 Abstract ( 1043 )   PDF (2765KB) ( 411 )   Save Some improvements based on volume of fluid (VOF) method were done to exactly track the free surface with air pocket during the water entry. A continuum surface force (CSF) model was introduced to serialize the pressure on the interface of air and water. A convective term was added to minimize the numerical dissipation of volume fraction, and the level-set function was coupled to keep the sharpness of free surface. Oblique water entry problems of wedge with various inclination angles were simulated numerically based on the improved VOF method, and the characteristics of pressure and free surface were analyzed. The research shows that the free surface can be exactly reconstructed, and the same resolution can be realized in the improved VOF method through reducing 1/3 total number of mesh. The cavitation during oblique water entry is better reflected by the numerical simulation, and the slamming pressure peak agrees well with the published experimental data. When the deadrise angle is below 10°, an obvious air effect will appear. The error between numerical and experimental results is 10%, while it reaches up to 40% in the analytical solution. The results suggest that the air greatly influences the slamming pressure and the numerical high-precision results can be obtained through the improved VOF method. References | Related Articles | Metrics

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Hydrodynamic Optimization Design Method for Guide Vane of Water-Jet Contractive-Flow Pump CAI Youlin,FAN Sheming,CHEN Gang,LIANG Jun,WANG Lixiang 2020, 54 (1):  28-34.  doi: 10.16183/j.cnki.jsjtu.2020.01.004 Abstract ( 1008 )   PDF (4673KB) ( 401 )   Save To solve the hydrodynamic problem of a new type of water-jet contractive-flow pump caused by the smaller radial dimension and higher load on guide vane, a hydrodynamic design method of the three-dimensional controllable velocity moment for water-jet contractive-flow pump guide vane is proposed. A guide vane meridian plane is optimized by controlling the flow area change based on a contractive-flow impeller, and the overall contraction from pump inlet to outlet is realized. Based on the principle of controllable velocity moment, the velocity moment distribution on meridian plane is given according to the outlet flow field of an impeller and the characteristics of contractive-flow guide vane. The design of guide vane is accomplished by a three-dimensional controllable velocity moment method and the model of the guide vane is formed. The internal flow field and external characteristics of the contractive-flow pump are calculated by applying a numerical simulation test method which has been verified. The numerical simulation result shows that the pump efficiency increases from 87% in the original design model to 90%. The axial length of the guide vane is shortened by 20%. The design and the optimization effects are remarkable, and the improved design can meet the requirement of engineering application.The hydrodynamic problem is solved. References | Related Articles | Metrics

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Influence of Empirical Relation Uncertainty for Water Entrainment on Layer-Averaged Numerical Modeling of Turbidity Currents ZHANG Weikai,HU Peng 2020, 54 (1):  35-42.  doi: 10.16183/j.cnki.jsjtu.2020.01.005 Abstract ( 839 )   PDF (1741KB) ( 484 )   Save Combining with the existing experimental data of water entrainment for turbidity currents, uncertainties of empirical coefficients, E1 and E2, in empirical formula were investigated using the method of Gibbs sampling based on Bayesian theory. A total of 2×105 sample values for E1 and E2 were obtained. Through statistics, the maximum probability (E1,E2) values are similar to the original formula. By inputting these sample values of (E1,E2) into a fully coupled mathematical model, the evolution of the turbidity currents over a steep slope is simulated. The results indicates that the range of the computed current thickness, velocity, sediment’s volume fraction and bottom deformation increases with distance. If the sample values of (E1,E2) with the highest frequency were used, the model may underestimate the current thickness and sediment volume fraction, and over-estimate the current velocity and bottom deformation. The range of hydraulic parameters calculated with 95% (E1,E2) sample values inputted into turbidity current models is much larger than that with 25% (E1,E2) sample values, which indicates that the model is very sensitive to the value of (E1,E2). References | Related Articles | Metrics

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Experiment Simulation of Submarine Clayey Slope Failure Induced by Gas Hydrate Dissociation SONG Xiaolong,ZHAO Wei,NIAN Tingkai,JIAO Houbin 2020, 54 (1):  43-51.  doi: 10.16183/j.cnki.jsjtu.2020.01.006 Abstract ( 991 )   PDF (9851KB) ( 479 )   Save In view of the insufficient recognition of the failure mechanism of submarine clayey slope induced by gas hydrate dissociation, the effect of gas on submarine slope after gas hydrate dissociation was simulated by means of venting. Furthermore, multiple of experiments were carried out under different combinations of soil strength, embedment depth of gas hydrate, flow rate and dissociation zone. Combining with the image processing, the deformation and the evolutionary process of slope surface and slope body were deeply investigated. The deformation and failure characteristics of submarine clayey slope induced by hydrate dissociation were initially revealed. On this basis, a limit equilibrium method was used to establish the critical pressure analytic expression of submarine slope failure, which is theoretically explained the critical pressure value in the failure process of slope deformation. The results show that the deformation and failure processes of the submarine slope are divided into four stages: the accumulation of air pressure, the elastic compression of soil, the upheaval failure of slope, and the deformation stability of slope. Although, there is a deviation between the calculated and experimental results of gas critical pressure, it can reflect the true level of the critical pressure to some extent. The research results can provide some references for the further understanding of the deformation and failure mechanism of submarine clayey slope induced by gas hydrate dissociation, and the developments of the stability analysis theory and evaluation method. References | Related Articles | Metrics

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Development of a Wave-Absorbing Device with Multiple Porous Plates for Circulating Water Channel and Simulation on Its Performance DING Junjie,MA Ning,GU Xiechong 2020, 54 (1):  52-59.  doi: 10.16183/j.cnki.jsjtu.2020.01.007 Abstract ( 1170 )   PDF (4224KB) ( 630 )   Save Based on the k-ε turbulence model, a numerical wave flume was established to develop a pervious wave-absorbing device with multiple porous plates using CFD software STAR-CCM+. The volume of fluid (VOF) method was used to track the free surface and the wave was generated with the module of VOF WAVE with the wave-damping zone placed at the end of the flume. The results of regular waves verify the numerical method compared with the analytic solutions. The reflection and transmission coefficients of the wave absorbing device change with different wavelengths, wave heights and water-current conditions. The results showed that these coefficients increase with the increasing wavelength. The reflection coefficient increases and the transmission coefficient decreases with the increasing wave height. The reflection and transmission coefficients have a marked decrease because of the wave-current interaction. A conclusion is drawn that the wave-absorbing device has good wave-absorbing performance. References | Related Articles | Metrics

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Numerical Simulation of Nonlinear Wave Based on an Improved Source Wave Method MA Zhe，ZHOU Ting，SUN Jiawen，FANG Kezhao，ZHAI Gangjun 2020, 54 (1):  60-68.  doi: 10.16183/j.cnki.jsjtu.2020.01.008 Abstract ( 1155 )   PDF (1235KB) ( 522 )   Save In the traditional mass source wave method, the accuracy is not high in the process of strong non-linear wave simulation, and the original setting of wave source area is complicated in different wave conditions. An improved method is proposed in this paper. Bidirectional quality outputs of the source area (lateral and vertical) are considered simultaneously, and the source function is improved and performed by theoretical derivation. The convergences of mesh and time step are verified based on the OpenFOAM program. The relative errors of second-order Stokes wave in amplitude and phase, comparing with traditional results, are discussed under different relative depths and different nonlinearity conditions. Then, a further simulation of the solitary waves propagation is performed. The numerical results show that the improved method can not only increase the efficiency but also improve the simulation accuracy of the mass source method in the high nonlinear range, especially when the nonlinearity parameter is 0.2, the amplitude error and the phase error are reduced by 21.7% and 46.5% respectively, compared to traditional ones. References | Related Articles | Metrics

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Opportunistic Maintenance Strategy for Multi-Unit Serial Systems Based on Dual Time Window YU Mengqi，SHI Kailong，ZHOU Xiaojun 2020, 54 (1):  69-75.  doi: 10.16183/j.cnki.jsjtu.2020.01.009 Abstract ( 818 )   PDF (828KB) ( 336 )   Save A decision model of opportunistic maintenance based on dual time window strategy is proposed for the multi-unit serial system. Instead of taking the arrival of a single unit’s optimal maintenance interval as the system shutdown condition in traditional single window strategy, dual time window strategy takes it as the trigger condition in maintenance decision. It decides the best maintenance equipment combination based on the maintenance time window for unit grouping, and introduces a new maintenance time window for preventive maintenance implementation to optimize the system downtime. On the basis of dual time window, the optimal maintenance strategy of the system is obtained by minimizing total maintenance cost of the system during the planning period. The example analysis shows that the dual window strategy is better than the single window strategy on total maintenance cost. References | Related Articles | Metrics

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High Accuracy Ultra Wideband Real Time Location System for Drug Rehabilitation Center SUN Mingyang,YAN Guozheng,LIU Dasheng,WANG Zhiwu,HAN Ding,ZHAO Kai,YANG Lei 2020, 54 (1):  76-84.  doi: 10.16183/j.cnki.jsjtu.2020.01.010 Abstract ( 1042 )   PDF (3240KB) ( 394 )   Save To satisfy the needs of intelligent supervision in drug rehabilitation center, a novel high-accuracy real-time location system based on ultra wideband (UWB) technology is proposed. Compared to ZigBee and Wi-Fi location systems, the UWB location system well improves the detection accuracy. The error sources of UWB system are analyzed and the delay parameter is corrected with a newly proposed parameter. The ranging function of system is used as geo-fencing, limiting the activity area of patients. The locating function of the system can calculate the position of patients and paint their positions on the screen simultaneously. Experiments indicate that the ranging error is lower than 7cm, the refresh rate is larger than 10Hz, the locating error is lower than 20cm, and the refresh rate is larger than 5Hz. The whole system has a good accuracy and real-time capability. References | Related Articles | Metrics

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Cumulative Lateral Displacement of Single Pile Foundation Under Lateral and Vertical Cyclic Loadings HU Anfeng,XIAO Zhirong,JIANG Jinhua,FU Peng,NAN Bowen 2020, 54 (1):  85-91.  doi: 10.16183/j.cnki.jsjtu.2020.01.011 Abstract ( 1030 )   PDF (1381KB) ( 562 )   Save The stiffness degradation model of soft clay based on bidirectional cyclic loadings was presented to analyze the cumulative lateral displacement of single pile foundation under lateral and vertical cyclic loadings. The finite element software Abaqus was used to realize the stiffness degradation by secondary development method and study cumulative lateral displacement of single pile foundation under lateral and vertical cyclic loadings. Results indicate that under vertical and lateral cyclic loadings, lateral displacement at single pile head is larger than that only under horizontal cyclic loading. Minimum horizontal cyclic loading ratio is found under the analysis. When the horizontal cyclic loading ratio is smaller than the minimum, lateral displacement cannot cumulate in single pile foundation. There is a critical value of vertical cyclic loading in terms of its influence on pile lateral deformation. Lateral displacement of pile cannot be seriously affected by vertical cyclic loading when it is below that critical value. References | Related Articles | Metrics

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Influence of Node Local Oscillator Errors on Distributed Transmit Beamforming YUAN Ding,SUN Huixian,YAN Yunbin,QUAN Houde 2020, 54 (1):  92-99.  doi: 10.16183/j.cnki.jsjtu.2020.01.012 Abstract ( 823 )   PDF (1220KB) ( 362 )   Save Using the kernel density estimation method, a stochastic analysis of the performance of distributed transmit beamforming (DTBF) in the presence of node oscillator error is conducted. Considering carrier initial phase offset, carrier frequency offset and phase noise, the corresponding average beampattern and complementary cumulative distribution function are derived. Then the degradation factor and beampattern characteristic parameters are adopted to analyze the influence of local oscillator errors on far-field beam performance. Theoretical analysis and simulation results show that local oscillator error can result in the degradation of DTBF performance, the decrease of average main lobe level, the widening of main lobe, the expansion of sidelobe region, and the emergence of high beampattern sidelobe. Over time, the local oscillator error accumulates gradually, which makes the degradation become bigger and the energy focused on the target location become less. References | Related Articles | Metrics

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Experimental and Numerical Simulation Study on Flow-Induced Vibration Characteristics of Flat Strip ZHANG Botao，ZHU Yechen，MEI Yong，GONG Shengjie 2020, 54 (1):  100-105.  doi: 10.16183/j.cnki.jsjtu.2020.01.013 Abstract ( 1098 )   PDF (1979KB) ( 422 )   Save Flow-induced vibration will happen when the fuel assemblies in a reactor are flushed by the coolant at a high speed. And vibration of fuel rod cladding and spacer grid strips will lead to wear of fuel assemblies, which affects the operation security of nuclear power plant. In order to study the characteristics and the methods of flow-induced vibration of spacer grid strips, a flat stainless strip without structure is employed to carry on the flow-induced vibration experiments. A laser Doppler vibrometer is used to measure the vibration characteristics of the strip under waterflow conditions. The test results show that the “lock-in” phenomenon occurs when the frequency of vortex-induced vibration is near to the natural frequency. Vortex-induced vibration frequency is linear with the flow velocity within a certain flow rate range. Furthermore, the natural frequency of the flat strip in water is well predicted by applying wet modal simulation. References | Related Articles | Metrics

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Fatigue Life Prediction for Hydraulic Support Foundation Based on Grey System Model GM (1, 1) Improved Miner Criterion WANG Hui,JING Weichuan,ZHAO Guochao,JIN Xin 2020, 54 (1):  106-110.  doi: 10.16183/j.cnki.jsjtu.2020.01.014 Abstract ( 1003 )   PDF (2738KB) ( 429 )   Save Aiming at the problem that the error existing in traditional fatigue cumulative damage criterion (Miner criterion) for fatigue life prediction is quite larger, in order to improve the prediction precision of fatigue life for solid-filling hydraulic support and to ensure a safe and reliable service process, a grey system model GM (1,1) is used to improve the traditional Miner criterion. Taking ZZC8800/20/38 six-column supporting solid-filling hydraulic support foundation as the object of study, the stress analysis of the base under dangerous conditions was carried out through ANSYS, and the fatigue life prediction of the foundation was carried out with the fatigue test. The results show that compared with the traditional Miner criterion, the prediction precision of the improved Miner criterion increases by 4032%, which provides an effective method for the fatigue life prediction of the solid-filling hydraulic support, and has a certain reference significance for its security service. References | Related Articles | Metrics