Bandgap optimization for chiral acoustic metamaterials based on material selection method北大核心CSCD

［Objectives］This study seeks to expand the bandgap frequency band, reduce the bandgap starting frequency and analyze and optimize the bandgap parameters of acoustic metamaterials. ［Methods］The influence of geometrical and material parameters on the bandgap properties of acoustic metamaterials is analyzed, and a method for maximizing the bandgap width is proposed. The multi-objective optimization problem is converted into a single objective optimization problem by normalizing the bandgap frequency coefficients. Structural material conversion is achieved via the material selection optimization method, and the optimization equations of bandgap parameters are established on the basis of weight-lightening. For chiral acoustic metamaterials, the material properties (density and wave velocity) and geometric parameters (scatterer diameter, ligament thickness and coating thickness) are defined as design variables, and the comprehensive optimization of structural parameters and material selection of acoustic metamaterials based on weight-lightening are implemented. ［Results］The optimization results show that the bandgap width increases by 27.7% and the lower bound frequency decreases by 1048 Hz, thereby achieving the goal of expanding the bandgap width based on lightweight acoustic metamaterials. The acoustic transmission analysis of the finite chiral acoustic metamaterial structure is then carried out to verify the effectiveness of the proposed method. ［Conclusions］The results show that the goal of lightweight acoustic metamaterials can be effectively achieved by integrating the comprehensive optimization of structural parameters and materials. As such, this study provides references for the design of new-type acoustic metamaterials. © 2023 Authors. All rights reserved.     

Fuzzy sliding mode control method for vertical motion of autonomous underwater gliders北大核心CSCD

［Objective］This paper proposes a fuzzy sliding mode controller based on T-S fuzzy logic for the vertical plane motion control of an autonomous underwater glider (AUG) with limited actuator capability. ［Methods］In the fuzzy sliding mode controller, the fuzzy switching rate is used to replace the switching rate in the fixed time controller to effectively suppress buffeting. The fuzzy switching rate is obtained by fitting the switching rate of the fixed time controller with T-S fuzzy rules. Based on the limited capabilities of AUG actuators, a saturation auxiliary system is designed to improve the actuator saturation effect. Finally, the performance of the system is verified by Lyapunov stability analysis and numerical simulation. ［Results］The results show that the AUG under the fuzzy sliding mode controller and the saturation auxiliary system can converge in finite time. The effectiveness of the fuzzy sliding mode controller and the saturation auxiliary system are verified by numerical simulation. ［Conclusions］By making comparisons with the fixed-time controller, it is verified that the two controllers have similar control performance, and the buffeting of the fuzzy sliding mode controller is lesser. © 2022 Journal of Clinical Hepatology. All rights reserved.     

A new source number estimation method based on the beam eigenvalue

Most source number estimation methods based on the eigenvalues are decomposed by covariance matrix in MUSIC algorithm. To develop the source number estimation method which has lower signal to noise ratio and is suitable to both correlated and uncorrelated impinging signals, a new source number estimation method called beam eigenvalue method (BEM) is proposed in this paper. Through analyzing the space power spectrum and the correlation of the line array, the covariance matrix is constructed in a new way, which is decided by the line array shape when the signal frequency is given. Both of the theory analysis and the simulation results show that the BEM method can estimate the source number for correlated signals and can be more effective at lower signal to noise ratios than the normal source number estimation methods.     

Cooperative path following control of UAV and USV cluster for maritime search and rescue北大核心CSCD

［Objectives ］ This paper studies a three-dimensional (3D) cooperative path-following control problem in the process of maritime search and rescue for a heterogeneous unmanned cluster system composed of unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs).［Methods ］ First, kinematic models of the UAVs and USVs are established under a fixed coordinate system and body coordinate system. In order to design a 3D path-following controller suitable for motion control, an air coordinate system is established, and the path tracking error models of the UAVs and USVs are established in the Serret-Frenet coordinate system. Next, a 3D line-of-sight (LOS) guidance law is designed at the kinematic level, and a cooperative path-following control method suitable for heterogeneous clusters of marine vehicles is proposed, allowing the UAVs and USVs to track the preset parameterized path. Finally, the stability of the control system is analyzed based on the Lyapunov stability theory.［Results］The simulation results verify the effectiveness of the proposed cooperative path-following control method for heterogeneous clusters of marine vehicles.［Conclusions］The results of this study can provide references for maritime search and rescue by using the proposed cooperative path-following control method. © 2022 Journal of Clinical Hepatology. All rights reserved.     

改进的脉冲声管法(英文)

Based on existing low-frequency water-filled impedance tube testing facilities, which is a part of the Low Frequency Facility of the Naval Undersea Warfare Center in Beijing, an improved water-filled pulse tube method is presented in this short paper. This proposed study is significantly different from the conventional pulse tube method because of the capability for a single plane damped sine pulse wave to generate in the water-filled pulse tube with a regular waveform and short duration time of about 1ms. During the generation process of the pulse, an inverse filter principle was adopted to compensate the transducer response. The effect of the characteristics of tube termination can be eliminated through the generation process of the pulse. Reflection coefficient from a water/air interface was measured to verify the proposed method. When compared with the expected theoretical values, a relatively good agreement can be obtained in the low frequency range of 500-2 000 Hz.     

Multi-objective optimization study on dimensions of medium-sized cruise ship in concept phase北大核心CSCD

［Objective］Aiming at the problem of too many influencing factors and too little reference data for determining the dimensions of medium-sized cruise ships in the concept phase, a simplified multi-objective optimization method based on the fitting of dimensions and performance is proposed. ［Method］First, the dimension relations of medium-sized cruise ships are analyzed and the influence of the latest SOLAS requirements used to determine the optimization range. Second, the influence of cruise ship dimensions on space, resistance, stability and seakeeping are analyzed. Next, based on the principles of genetic algorithms, a multiobjective optimization algorithm with high robustness and high engineering adaptability is determined to establish a multi-objective optimization model for the concept design of medium-sized cruise ships. Finally, the Pareto solution obtained by multi-objective optimization is analyzed to provide initial references for determining the dimensions of the target cruise ship. ［Results］Implemented via a genetic algorithm, the optimization program proposed herein is applied in the concept design of a medium-sized cruise ship in order to optimize the initial dimensions, thereby achieving the expected outcome of providing reasonable initial dimensions for cruise ship design. ［Conclusion ］ The proposed simplified multi-objective optimization model can provide feasible initial dimensions for medium-sized cruise ships in the concept phase. As the Pareto solution obtained by multi-objective optimization has different focuses such as resistance and stability, the most suitable solution needs to be selected according to the design object. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Parameter optimization and parametric deviation influence for shock resistance of double-stage vibration isolation system with limiters北大核心CSCD

［Objectives］For marine nuclear power plants, the relative displacement of the pump supported by a vibration isolation system should be strictly restricted. In order to improve the shock resistance of a vibration isolation system with displacement limiters, the parameter optimization and parametric deviation influence are studied. ［Methods］The theoretical model of a double-stage vibration isolation system with typical limiter parameters is established, the analysis of the shock response characteristics of the system is carried out using the direct integration method, the optimal limiter parameters are obtained using a genetic algorithm, and the influence of parameter deviation on the shock resistance of the system is studied. ［Results］Limiter parameters significantly affect the shock response characteristics of the vibration isolation system. The optimal limiter parameters improve the shock resistance of the system, but parameter deviation has a great influence on shock resistance. Based on the influence of parameter deviation, a deviation control strategy is proposed in which the elastic parameter should have a positive deviation and the gap parameter a negative deviation. The simulation results show that the proposed strategy can effectively alleviate the shock resistance degradation caused by deviation.［Conclusions］The results of this study can be used to guide the design, manufacturing and variation control of limiters for vibration isolation systems. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Monocular visual servo-based stabilization control of underactuated unmanned surface vehicle北大核心CSCD

［Objectives ］ Aiming at the accurate posture stabilization problem of an under-actuated unmanned surface vehicle (USV) in GPS-denied environments, a monocular visual servo stabilization control scheme is proposed based on homography.［Methods］By virtue of the homography decomposition technique, posture errors with an unknown scale factor are directly reconstructed from current and desired images, which thoroughly removes the calibration of extrinsic camera parameters and priori information on visual targets; with respect to the under-actuation constraint, a periodic function to persistently excite the yaw angle is incorporated into the continuous time-variant output feedback controller, allowing the USV to be stabilized in the absence of image depth, movement velocities and model parameters.［Results］Under the framework of the Lyapunov theory, the closed-loop visual servo system of the USV is rigorously proven to be asymptotically stable by Barbalat lemma.［Conclusions］By installing an onboard monocular camera, USV posture errors can be precisely stabilized with the aid of the proposed visual servo strategy, providing significant technique support for practical applications including docking, berthing, dynamic positioning, etc. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Numerical analysis of transient fluid-structure interaction of warship impact damage caused by underwater explosion using the FSLAB北大核心CSCD

［Objectives］This paper aims to address the numerical simulation problems of the dynamic response of ships subject to near-, medium- and far-field underwater explosions by establishing several numerical methods and calculation models. ［Methods］First, load and fluid-structure interaction models are established on the basis of the Eulerian finite element method and acoustic finite element method using the field-split technique, and FSLAB fluid-structure interaction software is developed. Next, near-, medium- and far-field underwater explosions are numerically simulated respectively. The shock wave propagation law, bubble shape and load evolution characteristics of near free-surface and near-wall underwater explosions are obtained, and the shock response characteristics of a spherical shell and ship subject to far-field underwater explosions are analyzed. Finally, the FSLAB software results are compared with the analytical solutions, reference solutions and experimental data. ［Results］The results show that the FSLAB fluid-structure interaction software developed in this paper is effective and accurate in simulating the impact damage of underwater explosions on warships. ［Conclusion］This study can provide a basis and support for the power assessment of underwater anti-explosion and shock design of warships. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Analysis of ultimate uniaxial compressive strength of stiffened panel considering influence of shear load北大核心CSCD

［Objective］This study aims to explore the law of the critical compression stress of stiffened panels under the influence of in-plane shear load, and whether in-plane shear load combined with lateral pressure will introduce a strong coupling effect. ［Method ］ To this end, nonlinear finite element (FE) software ABAQUS is used to perform numerical simulation analysis under combined loads on a group of FE models. A limit state equation/curve is then derived from the dimensionless calculation results based on the minimum square error method. ［Results］The results show that the influence law of in-plane shear load on the critical compression stress of stiffened panels is clarified, and a limit state equation of stiffened panels that considers the effect of shear load is obtained. ［Conclusion］The limit state equation in this paper can provide references for modifying the ultimate strength of stiffened panels under the influence of in-plane shear load. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Robust digital image watermarking against shearing based on haar orthogonal function system

In this paper, a robust digital watermarking method against shearing based on Haar orthogonal function system was introduced. The proposed method adopted the complete generalized orthogonal properties of Haar orthogonal function system to achieve the piece -based orthogonal transform on the image. The significant middle frequency coefficients in the transformation matrix are picked up, based on characteristics of the image visual system and the Haar orthogonal transform. The watermark is adoptively weighed to the middle frequency matrix. The method improves the validity of watermarking and shows excellent advantage against shearing attack. Experimental results show that the Haar orthogonal function system based watermark approach can provide an excellent protection under geometric attacks.     

Numerical evaluation method of lightning rod protection probability北大核心CSCD

［Objectives］Aiming at the current situation in which it is difficult to efficiently evaluate protection probability through traditional lightning rod evaluation methods, an efficient numerical evaluation algorithm is developed on the basis of an electrogeometric model (EGM) and attractive volume to realize the efficient calculation of lightning protection probability at any point in space.［Methods］This method first determines the attractive volume boundary of the lightning rod and protection object according to the interception process of the upward and downward leaders. The collection surface and exposure arc of the lightning stroke distance are then calculated, enabling the attractive risk and interception effect of the lightning rod to be quantified. Finally, the attraction and interception characteristics of the lightning rod are integrated to establish a numerical evaluation model of protection probability. To verify the accuracy of this method, the general rule of lightning rod protection probability is analyzed and the results compared with the existing analysis method.［Result］The evaluation results of this method show good agreement with those of classical leader progression model (LPM) theory.［Conclusions］ The method proposed herein has a high degree of quantification and can realize the efficient calculation of lightning protection probability at any point in space, which can provide useful references for lightning protection design work. © 2023 Authors. All rights reserved.     

等效波的散货船舱口角疲劳评估应力组合方法(英文)

The stress combination method for the fatigue assessment of the hatch corner of a bulk carrier was investigated based on equivalent waves.The principles of the equivalent waves of ship structures were given,including the determination of the dominant load parameter,heading,frequency,and amplitude of the equivalent regular waves.The dominant load parameters of the hatch corner of a bulk carrier were identified by the structural stress response analysis,and then a series of equivalent regular waves were defined based on these parameters.A combination method of the structural stress ranges under the different equivalent waves was developed for the fatigue analysis.The combination factors were obtained by least square regression analysis with the stress ranges derived from spectral fatigue analysis as the target value.The proposed method was applied to the hatch corner of another bulk carrier as an example.This shows that the results from the equivalent wave approach agree well with those from the spectral fatigue analysis.The workload is reduced substantially.This method can be referenced in the fatigue assessment of the hatch corner of a bulk carrier.     

振荡浮子式双浮体波浪能装置的阵列特性（英文）

As the energy supply problem worsens, the development and utilization of marine renewable energy have become a research hotspot. The development of wave energy is moving from the near shore to the distant sea. The power-generation efficiency of a single two-floating-body wave-energy converter is relatively low. To fully utilize wave energy and improve the wave-energy capture rate of a fixed sea area, arranging a two-floating-body wave-energy converter array is necessary. This paper first introduces the basic theory of multi-floating flow field, time-domain calculation method, and influence factor of the waveenergy converter array. Then, the development of AQWA software in Fortran language considers the effect of power takeoff.A calculation method based on ANSYS–AQWA is proposed to simulate the motion of the oscillating-buoy two-floating-body wave-energy converter. The results are compared with the experimental results from the National Renewable Energy Laboratory.Finally, the ANSYS–AQWA method is used to study the power characteristics of simple and complex arrays of wave-energy converters. The average power generation of simple arrays is largest at 0°, and the average power generation of complex arrays does not change with the wave direction. Optimal layout spacing exists for the simple and complex arrays. These findings can serve as a valuable reference for the large-scale array layout of wave-energy converters in the future.     

A line impedance stabilization network for pulse current injection北大核心CSCD

［Objective］Aiming at the deficiency of the existing line impedance stability network (LISN) in the electromagnetic pulse protection capability, a LISN suitable for the pulse current injection (PCI) test of electrical and electronic equipment is proposed. ［Methods］Aiming at the characteristics of high peak value and fast rise of the pulse current in PCI testing, the circuit structure and physical structure of the LISN are improved on the existing basis through PSpice time-domain and frequency-domain simulation combined with engineering design requirements, thereby giving it good nanosecond pulse protection performance and impedance stability at the same time. Pulse current protection performance test and impedance curve test experiments are then designed and carried out.［Results］The experimental results show that the improved LISN can attenuate the injected pulse current by 60 times, while the error of its impedance curve is less than 5% compared with the Type 5 µH LISN in GJB 151B-2013. ［Conclusions］The proposed LISN has good impedance stability and decoupling ability, and can be used in the PCI testing of electrical and electronic equipment in order to protect the power supply and improve the repeatability of testing. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Simulation System Design of 3-D Panorama of Ship Motions in Wave

In this paper a 3-D panoramic simulation system of a ship is described which is developed with the MAXSCRTPT language and VC + + as programming tools on the platform of 3 Dsmax. The strip theory method is applied to the motion prediction of the mono-hull. The time history solutions of heave and pitch are obtained in the condition of head sea to provide the primary data on panoramic simulation. The simulation system has following functions: 1) digital simulation; 2 ) panoramic simulation; 3) environmental set-up; 4) render preview and output.     

多种边界条件下任意铺层层合板的基频解析解（英文）

In recent years, as the composite laminated plates are widely used in engineering practice such as aerospace, marine and building engineering, the vibration problem of the composite laminated plates is becoming more and more important. Frequency, especially the fundamental frequency, has been considered as an important factor in vibration problem. In this paper, a calculation method of the fundamental frequency of arbitrary laminated plates under various boundary conditions is proposed. The vibration differential equation of the laminated plates is established at the beginning of this paper and the frequency formulae of specialty orthotropic laminated plates under various boundary conditions and antisymmetric angle-ply laminated plates with simply-supported edges are investigated. They are proved to be correct. Simple algorithm of the fundamental frequency for multilayer antisymmetric and arbitrary laminated plates under various boundary conditions is studied by a series of typical examples. From the perspective of coupling, when the number of laminated plates layers N 8–10, some coupling influence on the fundamental frequency can be neglected. It is reasonable to use specialty orthotropic laminated plates with the same thickness but less layers to calculate the corresponding fundamental frequency of laminated plates. Several examples are conducted to prove correctness of this conclusion. At the end of this paper, the influence of the selected number of layers of specialty orthotropic laminates on the fundamental frequency is investigated. The accuracy and complexity are determined by the number of layers. It is necessary to use proper number of layers of special orthotropic laminates with the same thickness to simulate the fundamental frequency in different boundary conditions.     

K2_SPH方法及其在二维水波模拟中的应用(英文)

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian meshless particle method. However, its low accuracy of kernel approximation when particles are distributed disorderly or located near the boundary is an obstacle standing in the way of its wide application. Adopting the Taylor series expansion method and solving the integral equation matrix, the second order kernel approximation method can be obtained, namely K2_SPH, which is discussed in this paper. This method is similar to the Finite Particle Method. With the improvement of kernel approximation, some numerical techniques should be adopted for different types of boundaries, such as a free surface boundary and solid boundary, which are two key numerical techniques of K2_SPH for water wave simulation. This paper gives some numerical results of two dimensional water wave simulations involving standing wave and sloshing tank problems by using K2_SPH. From the comparison of simulation results, the K2_SPH method is more reliable than standard SPH.