#### Table of Content

28 May 2020, Volume 54 Issue 5
 Motion Modeling and Numerical Simulation Study of Underwater Multi-Cable Multi-Body Towed System WANG Fei, DING Wei, DENG Deheng, WU Xiaofeng 2020, 54 (5):  441-450.  doi: 10.16183/j.cnki.jsjtu.2020.05.001 Abstract ( 1463 )   PDF (1531KB) ( 555 )   Aimed at the underwater multi-cable multi-body towed system, a mathematical model and the corresponding numerical solution are proposed to predict and analyze its dynamic characteristics in various conditions. The model consists of three parts: the governing equation of cables is given based on the lumped mass method; the underwater towed body, as a key part of the system, is accurately described by the 6 degree-of-freedom governing equations for submarines; the other tiny towed body in the system is simplified as a mass point and is incorporated into the cable node governing equation because of its small dimension. Coupling boundary conditions for towed cable and body are given to unite the three parts together, which is numerically solved by using the 4th order Runge-Kutta integration method. Finally, numerical simulations for a four-cable and two-body towed system are conducted to study its dynamic response in various conditions, and some conclusions are drawn from the results.
 An Integrated Model-Based and Data-Driven Method for Early Fault Detection of a Ship Rudder Electro-Hydraulic Servo System XU Qiaoning,AI Qinglin,DU Xuewen,LIU Yi 2020, 54 (5):  451-464.  doi: 10.16183/j.cnki.jsjtu.2020.05.002 Abstract ( 929 )   PDF (9410KB) ( 361 )   This paper offers an integrated model-based and data-driven early fault detection scheme for a ship rudder electro-hydraulic servo system (RESS). First, the state equation of RESS is established, the common faults in the system are analyzed, and the uncertain factors in the system are classified. To reduce the influences of various uncertainties, a hybrid processing method with several steps is proposed next. Using the system input and output data in normal state, the uncertain model parameters can be identified, and then a robust fault detection observer is designed to eliminate the influences of system inherent nonlinearity and unknown external force. To deal with the remaining uncertainties and disturbances, a neural network based compensation model using actual and observed system data is constructed, which can further reduce the influences of uncertainties and to detect the early faults effectively. Both simulation and experimental results show that the combined method is efficient and can be used for on-line fault detection.
 Preventive Maintenance and Replacement Policy for Series Deteriorating Production System Considering Generalized Time Value DU Yu，LI Yuqing，ZHANG Xiufang，PAN Ershun 2020, 54 (5):  465-472.  doi: 10.16183/j.cnki.jsjtu.2020.05.003 Abstract ( 811 )   PDF (889KB) ( 260 )   A series production system consisting of multiple processes and facility was studied considering degradation process as a random process in line with Gamma distribution. Opportunistic maintenance was introduced when preventive maintenance (PM) was conducted to reduce system downtime. Maintenance time was regarded as a function of degradation degree and maintenance times. A degradation degree recovery factor was used to describe the evolution process of facility degradation degree before and after maintenance. Considering the generalized time value, cost function of facility and system model was established according to the decision of maintenance and replacement based on cost-effectiveness and availability. The numerical example optimized the maintenance thresholds and calculated the replacement time and PM times of each facility. The results show that the generalized time value can accelerate the aging of facility, shorten service life, and provide a new idea for enterprise to make maintenance and replacement policy.
 Floating and Melting Process of an Ice Particle ZHANG Yulong，ZHANG Peng，MA Fei 2020, 54 (5):  473-480.  doi: 10.16183/j.cnki.jsjtu.2020.05.004 Abstract ( 1154 )   PDF (2664KB) ( 369 )   In order to understand the flow and heat transfer characteristics of phase change slurry, the floating and melting process of an ice particle in water is numerically studied. The free-floating process of an ice particle under various forces is numerically modelled, and the melting process of solid particle is described by enthalpy-porous method. The model is implemented to study the floating and non-uniform melting process of an ice particle at different temperature variations and internal supercooling degrees. The morphological change of ice particle and the thermo-fluidic characteristics during floating and melting process are obtained. It is found that the internal supercooling degree of ice particle delays the melting of ice particle.
 Flow Characteristics and Heat Transfer of Swirl Cooling in Three-Pass Channel WANG Kai,XIA Tian,RAO Yu 2020, 54 (5):  481-489.  doi: 10.16183/j.cnki.jsjtu.2020.05.005 Abstract ( 709 )   PDF (7961KB) ( 260 )   A transient thermal liquid crystal experiment and the numerical simulation were conducted on the three-channel swirling cooling structure inside the turbine blade. The results were compared with those of the ordinary turning channel at when Reynolds number is 40000. By conducting the transient experiment, high precision distribution of Nusselt numbers and the pressure loss along the channel were obtained. Combined with the numerical calculation results, the following conclusions were drawn: the swirl channel significantly enhanced the heat transfer capacity and the heat transfer uniformity of the system. Compared with the ordinary turning channel, the average Nusselt numbers on the wall of the second and third processes were increased by 60% and 57%, respectively. The impact loss and the throttling loss at the turning position were the main pressure losses of the three-channel structure. The pressure coefficient of the whole system of the swirl channel was about three times that of the ordinary turning channel, and it increased with Reynolds number. Numerical calculation indicated that the total pressure loss in the swirl channel was reduced by 25% compared with the static pressure loss. It was more scientific and reasonable to use the total pressure to analyze the pressure coefficient along the channel.
 Jet Flame Propagation Characteristics of Methane/Air Mixture in a Large Bore Constant Volume Chamber Based on MATLAB Image Processing Method XU Xiaochen, LI Xiang, HUANG Zhong, JU Dehao, LÜ Xingcai, HUANG Zhen 2020, 54 (5):  490-498.  doi: 10.16183/j.cnki.jsjtu.2020.05.006 Abstract ( 981 )   PDF (5564KB) ( 434 )   To explore the ignition characteristics of methane/air mixture generated by the pre-chamber turbulent jets, experimental studies were conducted in a large bore constant volume chamber. The flame image batch processing was conducted by using MATLAB software to obtain the flame characteristic parameters. By analyzing the pressure variations and flame images taken by a high-speed camera, the effects of air-fuel equivalence ratios and pre-mixed pressures on jet flame ignition process and flame propagation were studied. The results show that the jet flames in the main chamber are asymmetry, which can be even worse when the air-fuel equivalence ratio is lower due to the asymmetric orientation of the spark plug. As the initial pressure or air-fuel equivalence ratios increase, the flame propagation becomes slower. Furthermore, with the lower air-fuel equivalence ratio (λ=08), the flame propagation tends to be more sensitive to the back pressure variation.
 A New Electronic Skin with High Sesitivity Based on Sandwich Structure CHEN Le，WANG Ying，LI Haihua 2020, 54 (5):  499-506.  doi: 10.16183/j.cnki.jsjtu.2020.05.007 Abstract ( 1031 )   PDF (17741KB) ( 219 )   Electronic skin with high sensitivity and fast response time has great application prospects in human body signal monitoring and robotics. By imitating the structure of human skin, this paper proposes a self-locking type of electronic skin, whose upper layer is a regular pyramid array, and the lower layer is irregular undulations. The device has a maximum sensitivity of 190.4kPa-1, a minimum detection pressure of 32Pa, a response time of 8ms, a recovery time of 8 ms, and an excellent stability under 3000 cycles of loading. The device has a simple preparation process and the mold can be recycled to meet the conditions of mass production. The device is applied to distinguishing different mechanical forces and monitoring physiological signals of the human body. It shows good performance and has great development potential.
 Soft Gripper Grasping Based on Complete Grasp Configuration and Multi-Stage Network LIU Wenhai,HU Jie,WANG Weiming 2020, 54 (5):  507-514.  doi: 10.16183/j.cnki.jsjtu.2020.05.008 Abstract ( 1013 )   PDF (17218KB) ( 246 )   Visual guided robotic grasping of soft gripper depends on correct grasp position, grasp angle and grasp depth, and therefore a complete grasp configuration model and a multi-task loss function for soft gripper are proposed. A two-stage deep learning network based on anchor and rotating blocks is designed to realize direct map from image to multi-gripper grasping. The performance of the network is analyzed by public cornell grasping dataset and self-built dataset. The results show that the two-stage network based on multi-task loss and anchor with rotated blocks improves the accuracy of multi-output grasp detection and increases the success rate of robotic grasping. Finally, the soft robotic grasping system is constructed and the robotic grasping experiment results show that the proposed method provides a certain robustness to vision error, achieves 96% grasp success rate at different fruits, and exhibits a good generalization ability to grasp fruit peel.
 Constant Force Control Method for Robotic Disk Grinding Based on Floating Platform ZHANG Tie,WU Shenghe,CAI Chao 2020, 54 (5):  515-523.  doi: 10.16183/j.cnki.jsjtu.2020.05.009 Abstract ( 1013 )   PDF (2771KB) ( 328 )   In order to keep the control accuracy of robotic grinding and improve quality of grinding workpiece, a robotic grinding system based on the floating platform is developed and a constant force grinding strategy of linear active disturbance rejection control (LADRC) is proposed.The robotic floating grinding system mainly includes robots, force feedback sensors, grinding system and floating platform mechanism.Taking the robotic grinding system as the research object, grinding contacting force model between the workpiece at the end of the robot and the grinding disc is established.According to the nonlinear robot grinding model, the extended state observer is designed. The closed-loop stability of LADRC is analyzed, and the corresponding grinding experiments are designed to verify the feasibility of LADRC algorithm. Finally experiments and analyses show that LADRC can realize an effective robotic constant force control for disk grinding.Comparing with proportion integration differentiation (PID) control, LADRC can significantly reduce the force fluctuation during the grinding process and greatly decrease the surface roughness of abrasive workpiece.
 X-Rudder Autonomous Underwater Vehicle Control Allocation Based on Improved Quadratic Programming Algorithm LI Yueming,WANG Xiaoping,ZHANG Junjun,CAO Jian,ZHANG Yinghao 2020, 54 (5):  524-531.  doi: 10.16183/j.cnki.jsjtu.2020.05.010 Abstract ( 1082 )   PDF (1299KB) ( 368 )   Aiming at the problem of allocation accuracy and computational efficiency of X-rudder autonomous underwater vehicle (AUV) attitude control with four independent rudder blades, an improved quadratic programming algorithm is proposed to reduce the calculation amount while satisfying the allocation accuracy. The Lagrange multiplier method is used to replace the smooth Newton method used in the sequence quadratic programming method to optimize the solution calculation. The method effectively reduces the iterative cycle calculation while preserving the calculation accuracy of sequence quadratic programming. The results of X-rudder AUV motion control in the simulation environment show that the improved control allocation algorithm can reduce the calculation time by 40%, and the control allocation deviation is not more than 003N·m. The effect of AUV attitude control is good.
 Virtual Matching Method Based on Finite Element Simulation in Automotive Panel WANG Wei，WANG Min，HU Juncong，BAO Yidong，JIN Xia，CHEN Wenliang 2020, 54 (5):  532-543.  doi: 10.16183/j.cnki.jsjtu.2020.05.011 Abstract ( 1030 )   PDF (6040KB) ( 547 )   A virtual matching method based on finite element simulation in automotive panel is proposed. In the virtual environment of finite element analysis, the rapid assembly analysis on models of automotive panels, connectors and external sample rack is performed, and the deformation prediction of automotive panel is obtained. The sensitivity of the adjustable parts is analyzed to gain the adjustment strategy of reference point zeroing, and the sample point position data are extracted to judge the matching quality of automotive panel. An application example of automobile hood assembly is used to verify the proposed method. And the simulation data and test data of sample points are compared. It is concluded that the simulation data are nearly consistent with the test data. The maximum deviation is less than 0.6mm. The results show that the proposed method is feasible and effective to verify that the automobile panel meets the requirements of body assembly.
 Influence of Fluorine on Calcium Deficient Hydroxyapatite Synthesis and Improvement of Thermo Stability RAO Qunli,FAN Xiaolan,GU Xiang,LI Lingling 2020, 54 (5):  544-550.  doi: 10.16183/j.cnki.jsjtu.2020.05.012 Abstract ( 926 )   PDF (3309KB) ( 229 )   Fluoridating holds considerable promising for improving thermos stability of calcium-deficient hydroxyapatite with reserving pristine good biocompatibility and bio-activity. In this paper, synthetic products and their thermo stability are studied with different fluorine additions under the same chemical precipitation condition by X-ray diffraction (XRD). Dicalcium phosphate dihydrate (DCPD) is the main product with few hydroxyapatite (HA) when no fluorine is added; mixture of calcium-deficient fluoridated hydroxyapatite (D-FHA) and DCPD appears in products when fluorine is added, and only D-FHA remains in products of Sample 04F. Influence of fluorine on the synthetic process is proved to accelerate the transformation from DCPD to D-FHA. Synthetic products are further sintered to investigate the thermo stability. Dehydration occurs only in Sample 00F and Sample 02F when heated at 200℃, which does not appear in Samples 04F—10F. D-FHA of Sample 04F begins to decompose into β-Ca3(PO4)2 and β-Ca2P2O7 at 600℃. The temperature of D-FHA decomposition rises and the stability improves with the increasing fluorine addition.