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28 February 2023, Volume 57 Issue 2 Previous Issue   
Naval Architecture, Ocean and Civil Engineering
Supporting Structure Optimization of Offshore Large-Scale Vertical Axis Wind Turbine Based On BESO Algorithm
HE Wenjun, SU Jie, ZHOU Dai, HAN Zhaolong, BAO Yan, ZHAO Yongsheng, XU Yuwang, TU Jiahuang
2023, 57 (2):  127-137.  doi: 10.16183/j.cnki.jsjtu.2021.448
Abstract ( 182 )   HTML ( 413 )   PDF (12945KB) ( 138 )  

The research on large-scale offshore vertical axis wind turbine is of great significance to the development of ocean wind energy. For the safety of wind power, it is very important to study the reasonable supporting structure of the large-scale wind turbine. In this paper, an supporting structure optimization of a large-scale vertical axis wind turbine based on the variable deletion rate bidirectional evolutionary structural optimization (BESO) algorithm is proposed, and the reliability of structural optimization is verified by analyzing the dynamic response. The results show that this inverse proportional BESO algorithm can effectively improve the optimization iteration rate, and has a wide applicability to the optimal design of vertical axis wind turbine supporting structure. Compared with the initial structure, the wind-induced dynamic response of the topological new structure model under wind load is significantly reduced. The findings can be used to optimize the structural design of vertical axis wind turbine.

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Strata Responses Due to Pumping from Deep Confined Aquifers of Multi-Aquifer-Aquitard System in Shanghai
PENG Chenxin, LI Mingguang, ZHEN Liang, LI Yaoliang, ZHANG Zhebin
2023, 57 (2):  138-147.  doi: 10.16183/j.cnki.jsjtu.2021.386
Abstract ( 121 )   HTML ( 510 )   PDF (3860KB) ( 51 )  

When pumping in confined aquifers, vertical leakage could be found in the multi-aquifer system in soft deposits, and the responses of groundwater flow and strata deformation are complicated. Based on pumping tests in an ultra-deep underground project, this study performs a 3D finite-difference modeling to investigate the responses of groundwater and strata to pumping in the second and third confined aquifers. It considers the hydro-mechanical coupled and small strain stiffness characteristics of soils in the analysis, and discusses and compares the spatiotemporal distribution characteristics of drawdown and deformation induced by pumping in different confined aquifers. The results indicate that the ground settlement induced by pumping in the second confined aquifer is greater though the groundwater drawdown is smaller, and the compression of dewatering aquifers caused by dewatering in the second and third aquifers accounts for 56.18% and 77.69% of the settlement, respectively. It could be attributed to the connectivity between the second confined aquifer and its overlying aquitards, which results in a greater influential depth. In addition, the compressibility of shallow strata is significantly greater than that of deep strata. The study is significant for the dewatering construction and environmental deformation control of ultra-deep excavations.

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Effects of Relative Humidity on Tensile Property Degradation of GFRP Rebars in Seawater and Sea Sand Concrete Environment
WANG Wenhua, ZHAO Qi, ZHANG Daxu, ZHANG Peifu, CHEN Peng
2023, 57 (2):  148-160.  doi: 10.16183/j.cnki.jsjtu.2022.034
Abstract ( 86 )   HTML ( 290 )   PDF (2813KB) ( 42 )  

By establishing a quantitative analysis method of relative humidity, pore solution saturation, and corrosion reaction rate of concrete, the influence of environmental relative humidity on the mechanical properties of glass fiber reinforced polymer (GFRP) in seawater sea-sand concrete environment has been studied. Based on the pore size distribution of concrete and the surface tension formula of pore solution, the relationship between the relative humidity and pore solution saturation of seawater sea-sand concrete is established. It is assumed that the pore solution is uniformly smeared in concrete. Therefore, the concentration of corrosive ion OH- can be obtained. The corrosion rate and strength retention rate of GFRP bars under the action of OH- are evaluated using the etching model. The accuracy of the current method is verified by experimental results. Based on the climate statistics of some coastal cities in China, the influence of relative humidity on the strength retention rate of GFRP bars in seawater and sea sand concrete environment is predicted under the conditions of representative ambient temperature and water-cement ratio. The increase of relative humidity promotes the performance degradation of GFRP bars. According to relevant standards, the relations between relative humidity and service life of GFRP bars in seawater sea-sand concrete environment have been predicted.

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Wave Run-Up Prediction of Semi-Submersible Platforms Based on Long Short-Term Memory Network
LI Yan, XIAO Longfei, WEI Handi, KOU Yufeng
2023, 57 (2):  161-167.  doi: 10.16183/j.cnki.jsjtu.2021.310
Abstract ( 83 )   HTML ( 139 )   PDF (2601KB) ( 40 )  

Wave run-up and air-gap are key issues for the safety of semi-submersible platforms. Real-time wave run-up prediction is helpful to ensure the safety of offshore activities. Based on the long short-term memory (LSTM) network, the extreme short term online prediction method is developed for predicting the wave run-up of semi-submersible platforms using wave and motion sequences. With the help of large sets of data from the model test, the LSTM model is trained and tested. The study shows that when the forecast durations are 6 s and 12 s, the average accuracy of the prediction results are 92.90% and 84.09%, and the relative errors of the maximum wave run-up height are lower than or equal to 19.69% and 30.66%, respectively. In addition, the model has a stable and exact prediction of extreme values of wave run-up height when the forecast duration is within 6 s, which confirms its ability to provide valid technical support for the early warning of wave slamming and overtopping during the operation of offshore platforms.

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Numerical Simulation of Crashback Condition of a Propeller Based on OpenFOAM
GUO Haipeng, ZOU Zaojian, LI Guangnian
2023, 57 (2):  168-176.  doi: 10.16183/j.cnki.jsjtu.2021.305
Abstract ( 103 )   HTML ( 13 )   PDF (14062KB) ( 55 )  

The hydrodynamic characteristics of a propeller under the crashback condition are closely related to the crash stopping ability of a ship, which directly affect the ship navigational safety. In this paper, a numerical study on the hydrodynamic characteristics of a propeller and the flow field around the propeller under the crashback condition is conducted based on the Reynolds-averaged Navier-Stokes solver in the open source computational fluid dynamics platform OpenFOAM. Taking the 5-blade propeller DTMB4381 model as the study object, the ahead and crashback conditions are numerically simulated. The numerical results are compared with international open model test data to validate the effectiveness of the numerical method in the prediction of the hydrodynamic characteristics of the propeller under different conditions. Based on the obtained hydrodynamic loads and flow field details, the local flow field characteristics changing with the advance velocity and the relation between the local flow fields and the global hydrodynamic forces are explored, which provides theoretical basis for the evaluation of ship crash stopping ability.

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Modification of Velocity Formulations in a Two-Layer Boussinesq-Type Model for Water Waves
LIU Zhongbo, HAN Qingliang, REN Shuangshuang, WANG Yan, FANG Kezhao
2023, 57 (2):  177-182.  doi: 10.16183/j.cnki.jsjtu.2021.337
Abstract ( 88 )   HTML ( 134 )   PDF (857KB) ( 36 )  

In order to improve the accuracy of velocity formulation in a Boussinesq-type wave model, with a two-layer Boussinesq-type model with the highest spatial derivative of 2 being chosen as the research object, a third-order term with constant coefficient is proposed to modify the velocity formulation. The coefficient is optimized by minimizing the error between the summation of the integration of horizontal and vertical velocities of the equation and that of the analytical linear Stokes wave velocity components in the range of 0<kh< 8 (where k is wave number, h is still water depth). At a 1% tolerance error, the applicable water depths of the modified formulations for horizontal and vertical velocities are up to kh=7.34 and kh=7.83, respectively, which are larger than those of the original formulations. The evolution of the steady-state wave and the focused wave is numerically simulated by using the numerical model. The horizontal velocity under the maximum surface elevation crest is in good agreements with the analytical solution of stream function and published experimental data, which verifies the effectiveness of the modified formulations. The studies show that the velocity accuracy of the improved equation is greatly improved. This method provides an important reference for the improvement of velocity field of other Boussinesq-type models.

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Thermal Environment Monitoring and Analysis of an Enclosed Gymnasium with Double-Layered Membrane Roof in Summer
SONG Yinbo, YIN Yue, YAN Yongsheng, WANG Xiaoqing, CHEN Wujun, REN Sijie
2023, 57 (2):  183-193.  doi: 10.16183/j.cnki.jsjtu.2021.259
Abstract ( 76 )   HTML ( 9 )   PDF (12452KB) ( 29 )  

The membrane structure roof is widely used in large-span buildings such as stadiums and gymnasiums because of its full use of natural light sources and flexible forms. In order to solve the prominent problems such as poor thermal insulation performance and prone to external environmental factors, the multi-layer membrane structure design, laying of insulation layers, and other schemes are applied to engineering practice. However, there is still a gap in the relevant research of thermal environment monitoring and analysis. In order to study the thermal environment of the double-layer PTFE (polytetrafluoroethylene)-aerogel roof, multi-point thermometers were uniformly arranged to monitor, and the overall temperature field was constructed using the measured data. A thermophysical model which could accurately reflect the change of temperature field was established, whose average error was less than 5%. With the laying of roof insulation layer as the variable, three working conditions, i.e., no insulation layer, only rock wool insulation layer, and all aerogel insulation layer were constructed based on the model. The comparison indicates that the laying of aerogel reduces the average temperature of indoor space by 2.0 ℃, the original working condition has the best thermal insulation effect, and the average temperature difference between indoor and outdoor is 9.6 ℃. This paper can provide reference for the thermal insulation design of membrane structure roofs.

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Materials Science and Engineering
Thermal Conductivity of Bulk Attapulgite Prepared by Pressureless Sintering
SUN Xucheng, ZHAO Xiaofeng, YANG Fan
2023, 57 (2):  194-200.  doi: 10.16183/j.cnki.jsjtu.2021.254
Abstract ( 53 )   HTML ( 13 )   PDF (4529KB) ( 20 )  

To explore the potential of attapulgite as thermal barrier materials, bulk attapulgite samples were prepared by pressureless sintering. The effects of sintering temperature on the phase composition, porosity, microstructure, and thermal conductivity of bulk attapulgite were investigated. With increasing sintering temperature, bulk attapulgite transforms from predominant quartz phase (700 ℃) to coexistence of quartz and enstatite phases (800—900 ℃), and to coexistence of quartz, enstatite and cristobalite phases (1000—1200 ℃). Meanwhile, the microstructure of the bulk attapulgite changes from random, loose packed fiber-like porous morphology, to dense structure with a random distribution of MgO·SiO2 grains inside the SiO2 matrix to result in a significant decrease in porosity. The thermal conductivity of bulk attapulgite increases with increasing temperature. When sintered at 700 ℃, bulk attapulgite presents a temperature-independent thermal conductivity with an ultra-low value of 0.16 W/(m·K) at room temperature. Attapulgite, with its natural abundance and low cost, along with the ultra-low thermal conductivity, has a great potential as thermal barrier materials.

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Off-Axis Tensile Test and Numerical Simulation of Unidirectional Thermoplastic Composite Laminates
ZHANG Jian, CHEN Xiuhua, CHEN Yong, FANG Yin
2023, 57 (2):  201-212.  doi: 10.16183/j.cnki.jsjtu.2021.352
Abstract ( 78 )   HTML ( 9 )   PDF (13908KB) ( 58 )  

As a high-performance thermoplastic composite material, AS4/PEEK has been widely used in aerospace, military, automotive, and other fields. After conducting the off-axial tensile test of unidirectional AS4/PEEK laminates with different angles, the relevant stress-strain curves and tensile strengths, as well as fracture plane angles are obtained. In simulation, a 3D elastic-plastic model where the parameters are determined by trust-region reflective algorithm is used to describe the nonlinear mechanical behavior of AS4/PEEK laminates. In combination with the LaRC05 criterion and the crack zone theory, a user material subroutine VUMAT based on Abaqus is developed and applied to the numerical simulation of off-axis tensile test. The numerical results show that the 3D elastic-plastic damage constitutive model can accurately simulate the plastic effect of AS4/PEEK laminates and the tensile strength predicted by the numerical method agrees well with those from the test. The proposed 3D elastic-plastic damage model provides an accurate and effective method for the comprehensive analysis of plastic deformation and damage of thermoplastic composites.

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Material Model of Membrane Structure in Rainstorm
PANG Yan, QING Qiang, WANG Shasha, ZHANG Xiangyu, GONG Jinghai
2023, 57 (2):  213-220.  doi: 10.16183/j.cnki.jsjtu.2021.365
Abstract ( 73 )   HTML ( 10 )   PDF (7018KB) ( 34 )  

When encountering heavy rain, the membrane surface with a relatively small slope is easy to accumulate water. Accurately simulating the deformation of the membrane surface at this time will help ensure the safety of the structure. The linear constitutive model of membrane material used in existing research is not suitable for simulating the deformation of membrane structure in rainstorm. This study conducts a uniform load test on a membrane structure to simulate the mechanical behavior of the membrane surface in rainstorm and obtains the deformation form of the structure when water is accumulated. The linear constitutive model and the double broken line constitutive model of membrane material are used in the finite element model of the membrane structure for load analysis. By comparing the deformation of the finite element model and the actual structure, it selects the constitutive model suitable for simulating the deformation of the membrane structure in heavy rain. The numerical simulation results show that the structural deformation simulated by the double broken line constitutive model is closer to the deformation measured in the experiment than the linear constitutive model. The research results can provide a reference for the selection of the membrane constitutive model and the analysis of membrane structure in rainstorm.

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Ultrasonic Self-Fusion Rivet Welding of CF/PA6 to 6061 Aluminum Alloy
YANG Yuanduo, LI Yang, LIU Zeguang, WANG Kaifeng, AO Sansan
2023, 57 (2):  221-229.  doi: 10.16183/j.cnki.jsjtu.2021.289
Abstract ( 78 )   HTML ( 10 )   PDF (28050KB) ( 38 )  

In order to further improve the strength between carbon fiber reinforced thermoplastic (CFRTP) and lightweight metals, a novel ultrasonic self-fusion riveting method is proposed, in which carbon fiber reinforced polyamide 6(CF/PA6) is melted by ultrasonic welding and pressed into the prefabricated hole on the aluminum alloy plate to realize the join between CF/PA6 and aluminum alloy. The joining mechanism is mechanical self-locking. The results show that the overall mechanical performances increase with the increase of the number of holes. The optimal welding energy is 2 000 J and the maximum shear strength is (58.9 ± 7.1) MPa. According to the welding power and welding displacement signal, the ultrasonic self-fusion riveting process can be divided into the pressing stage, the energy director embedding stage, and the hole filling stage. When the energy is constant, with the increase of the number of holes, the energy director will be embedded into CF/PA6 earlier, and the welding time will be shortened. Compared with the welding energy, the number of holes has a greater impact on the welding process. Because ultrasonic self-fusion riveting mainly realizes the join between CFRTP and metal through mechanical self-locking, this method is not limited by metal types and has a broad application prospect.

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Failure Mechanism and Material Selection Method of CFRP/Steel Rivet-Bonding Joints
YU Haiyan, WU Hangyu
2023, 57 (2):  230-240.  doi: 10.16183/j.cnki.jsjtu.2021.344
Abstract ( 70 )   HTML ( 10 )   PDF (12124KB) ( 25 )  

To reveal the influence of material selection on joint properties in the joint design between carbon fiber reinforced polymer (CFRP) and steels, experiments of uniaxial tension and normal tension were performed on the bonded, riveted, and rivet-bonding joints, which were made of CFRP laminates and DC05, HC260Y, DP590, DP780, DP1180, and PHS1500 steel sheets. The failure modes and tensile strength of these joints were analyzed. The thickness ratio and bearing coefficient ratio of the CFRP parts and adjacent steel parts were summarized. The results show that the failure mode of the CFRP/steel joint depends on the mechanical properties of the material of the weaker side. During joint design, the strength and stiffness of the CFRP parts and adjacent parts should be as similar as possible. The thickness ratio of the CFRP parts and adjacent steel parts is recommended to be between 1.37 and 1.91, and the load bearing coefficient ratio is recommended to be between 0.9 and 1.52.

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Numerical Simulation and Experimental Study of Local Induction Heating of High Strength Steel Square Tube
WANG Yu, LIU Jing, MA Xiaoyan, HAN Jingtao
2023, 57 (2):  241-252.  doi: 10.16183/j.cnki.jsjtu.2021.360
Abstract ( 76 )   HTML ( 7 )   PDF (16456KB) ( 45 )  

In order to solve the forming problems such as difficult deformation and easy cracking of high strength steel square tubes, the local induction heating technology has been introduced based on the traditional cold forming process. An electromagnetic-temperature multi-field coupling model for local induction heating is established by using ANSYS parametric design language based on the magnetic vector potential and physical environment method. A numerical simulation is conducted at different heating process parameters, and the optimized parameters are used for experimental research. The simulation results show that the induction heating efficiency can be significantly improved by using magnetizers to increase the magnetic field intensity. As the heating frequency increase, the heating speed of the outer fillet area and the temperature difference between the outer and inner fillet area increase. As the heating power increases, the high temperature area and the peak temperature increase, but the outer fillet area is more prone to be overheated. The experimental results show that a high strength steel square tube with an extremely small fillet radius, increased corner thickness, but with no crack defect can be obtained by using the optimized heating process parameters. The average error between the simulated and measured heating temperature is about 7.57%, indicating that the finite element model has a good prediction accuracy.

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