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.     

Asymptotic field of mode Ⅱ dynamic growing crack in visco-elastic material

A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity, namely, (σε) ∝r^-1/(n-1). The asymptotic solutions of separatied variables of stress, stain and displacement in crack-tip field are obtained by asymptotic analysis, and the results of numerical value of stress and strain in crack-tip field are obtained by shooting method. Through numerical calculation, it is shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. By the asymptotic analysis to the crack-tip field, the fracture criterion of mode Ⅱ dynamic growing crack of visco-elastic materials is put forward from the point of view of strain.     

船首形状对自由液面水下航行体阻力影响的试验研究（英文）

In this paper, towing tank experiments are conducted to study the behavior of flow on a model of the underwater vehicle with various shapes of bows, i.e. tango and standard bows in free surface motion tests. The total resistances for different Froude numbers are considered experimentally. The towing tank is equipped with a trolley that can operate in through 0.05–6 m/s speed with ±0.02 m/s accuracy. Furthermore, the study is done on hydrodynamic coefficients i.e. total, residual and friction resistance coefficients, and the results are compared. Finally, the study on flow of wave fields around bows is done and wave filed around two bows are compared. The Froude number interval is between 0.099 and 0.349. Blockage fraction for the model is fixed to 0.005 3. The results showed that the residual resistance of the standard bow in 0.19 to 0.3 Froude number is more than the tango bow in surface motion which causes more total resistance for the submarine. Finally, details of wave generated by the bow are depicted and the effects of flow pattern on resistance drag are discussed.     

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.     

Numerical study of viscous wave-making resistance of ship navigation in still water

The prediction of a ship＇s resistance especially the viscous wave-making resistance is an important issue in CFD applications. In this paper, the resistances of six ships from hull 1 to hull 6 with different hull forms advancing in still water are numerically studied using the solver naoe-FOAM-SJTU, which was developed based on the open source code package OpenFOAM. Different components of the resistances are computed and compared while considering two speed conditions （12 kn and 16 kn）. The resistance of hull 3 is the smallest while that of hull 5 is the largest at the same speed. The results show hull 3 is a good reference for the design of similar ships, which can provide some valuable guidelines for hull form optimization.     

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.     

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.     

Influence of external restraint distribution on welding buckling of thin plate butt joint北大核心CSCD

［Objectives］It is easy to produce buckling distortion when welding thin plate butt joints, which affects the construction period, cost and performance, but this can be controlled by applying external restraints. ［Methods ］ First, a butt welding test of a thin plate under external restraints is carried out, and the out-of-plane deformation is measured by the optical surface scanning method. At the same time, finite element (FE) models in a free state and external restraint state are established, and the thermal mechanical phenomena of the two models are subjected to thermal-elastic-plastic FE analysis (TEP FE). The influence of different external restraint distributions on the welding buckling distortion of the joints is then studied, and reasons for controlling welding buckling distortion are analyzed from the perspective of longitudinal plastic strain and longitudinal contraction force.［Results ］ The out-of-plane deformation of the corresponding model is in good agreement with the measured results, and milder than the out-of-plane deformation of the model in a free state. When external restraints are applied, the longitudinal plastic strain of the weld and its adjacent metal decreases, and the longitudinal contraction force of the thin plate also decreases.［Conclusions ］ The results verify that external restraints can effectively control welding buckling distortion, and the control effects are different depending on the external restraint distribution. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Asymmetric regular sampling SPWM method based on tangent-secant midpoint approximation applied to intermediate frequency inverter power supply北大核心CSCD

［Objective］In order to reduce the switching frequency of an intermediate frequency inverter power supply, ensure the quality of the output waveform and realize digitalization easily, a SPWM sampling method based on a tangent-secant midpoint approximation is proposed. ［Methods］It is proven by deduction that the quantitative relationship of the natural sampling method can be approximated, and a Matlab/Simulink simulation model is built. The algorithm is designed and applied to an intermediate frequency inverter device, and the correctness of the proposed method is verified in the two aspects of simulation and experiment. ［Results］The simulation results show that the total harmonic distortion (THD) of the output waveform based on the tangent-secant midpoint approximation method is 2.64%, lower than the 3.99% of the symmetrical regular sampling method. The waveform quality of the tangent-secant midpoint approximation method is obviously better than that of the symmetrical regular sampling method, as it not only reduces the switching frequency but also takes into account the requirements of THD. ［Conclusions］SPWM sampling based on tangent-secant midpoint approximation is applied to the intermediate frequency power supply and is able to effectively overcome the shortcomings of the low-quality output waveform and high switching frequency of the symmetrical regular sampling method. Both theoretical analysis and engineering practice verify the rationality and correctness of the proposed method, and it can be widely extended to the field of intermediate frequency power supply installation. © 2022 Journal of Clinical Hepatology. All rights reserved.     

Uncertainty analysis of propulsion shafting vibration北大核心CSCD

［Objective］In view of the insufficient safety and reliability of the traditional deterministic vibration analysis of ship propulsion shafting system, the vibration response analysis of the shafting system under uncertain excitation conditions is carried out. ［Methods］Using non-random vibration analysis based on non-probabilistic convex model process, the uncertain excitation and vibration response are described in the form of the upper and lower bounds of the interval to reduce dependence on a large amount of excitation sample data. Compared with the calculation results in the relevant literature, the validity of the program for solving the response bound of the two-degrees-of-freedom (2-DOFs) system is verified, and the uncertain vibration problem of the shafting system is then explored on this basis. ［Results］The results show that when the shafting system is excited by [−30 N, 30 N] propeller laterally, a displacement response of the magnitude of about 10−6 m is generated at the bearing. It is also indicate that the shafting system is excited in a certain interval, so a certain interval response must be produced. ［Conclusions］Applying the non-probabilistic convex model process and non-random vibration analysis to the field of the uncertain vibration analysis of ship propulsion shafting system, the vibration displacement response bound of the shafting under uncertain excitation conditions can be obtained with fewer excitation samples, thereby providing useful references for improving the robustness of the dynamic response prediction of ship propulsion shafting systems. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Statistical Analysis of Ship Collisions with Bridges in China Waterway

Having carried out investigations on ship collision accidents with bridges in waterway in China, a database of ship collision with bridge (SCB) is developed in this paper. It includes detailed information about more than 200 accidents near ship' s waterways in the last four decades, in which ships collided with the bridges. Based on the information a statistical analysis is presented tentatively. The increase in frequency of ship collision with bridges appears, and the accident quantity of the barge system is more than that of single ship. The main reason of all the factors for ship collision with bridge is the human errors, which takes up 70%. The quantity of the accidents happened during flooding period shows over 3 - 6 times compared with the period from March to June in a year. The probability follows the normal distribution according to statistical analysis. Visibility, span between piers also have an effect on the frequency of the accidents.     

Study on fast calibration of a ULA's gain and phase error

Array calibration is important in engineering practice. In this paper, fast calibration methods for a ULA's gain and phase errors both in far and near fields are proposed. In the far field, using a single sound source without exact orientation, this method horizontally rotates the array exactly once, performs eigen value decomposition for the covariance matrix of received data, then computes the gain and phase error according to the formulas. In the near field, using the same single sound source, it is necessary to rotate the array horizontally at most three times, build equations according to geometric relations, then solve them. Using the formula proposed in this paper, spherical waves are modified into plane waves. Then eigen values decomposition is performed. These two calibration methods were shown to be valid by simulation and are fast, accurate and easy to use. Finally, an analysis of factors influencing estimation precision is given.     

Study on fast calibration of a ULA＇s gain and phase error

Array calibration is important in engineering practice. In this paper, fast calibration methods for a ULA＇s gain and phase errors both in far and near fields are proposed. In the far field, using a single sound source without exact orientation, this method horizontally rotates the array exactly once, performs eigen value decomposition for the covariance matrix of received data, then computes the gain and phase error according to the formulas. In the near field, using the same single sound source, it is necessary to rotate the array horizontally at most three times, build equations according to geometric relations, then solve them. Using the formula proposed in this paper, spherical waves are modified into plane waves. Then eigen values decomposition is performed. These two calibration methods were shown to be valid by simulation and are fast, accurate and easy to use. Finally, an analysis of factors influencing estimation precision is given.     

Seabed collision emergency decision-making of AUV based on safety domain model北大核心CSCD

［Objectives］To ensure safety and prevent seabed collisions in complex unknown underwater environments, this study proposes a seabed safety domain model and tiered emergency response strategies. ［Methods］A vertical motion simulation model is established and verified by surpassing the test results, then used to calculate the active and passive safety domain distance of an autonomous underwater vehicle (AUV), thereby establishing a seabed safety domain model. An AUV emergency control system and emergency strategies are then built on the basis of the dynamic safety domain model. The trim and distance from the seabed of the AUV are used to calculate the current and future risk factors. Based on the weighted sum, the comprehensive risk factor is employed to provide the AUV with emergency response strategies.［Results］Lake tests with the AUV sailing at a fixed depth and height show a strong dependency of the comprehensive risk coefficient on seabed height when it is close to the boundary of the AUV's active safety domain. In the opposite case, there is a weak dependency of the comprehensive risk coefficient on seabed height. The results show that the proposed AUV emergency control system can reduce emergency false alarms caused by frequently changing riverbed heights and sailing altitudes close to the seabed. In such cases, reasonable emergency strategies can be realized under complex rough terrain.［Conclusions］The AUV seabed safety domain model and tiered emergency response strategies based on vertical motion equations proposed herein can be applied to evaluate seabed collision risk in various cases. Finally, this paper provides emergency response strategies to avoid seabed collision accidents, which can enhance the safety of AUV navigation. © 2023 Chinese Journal of Ship Research. All rights reserved.     

The crack tip fields of Mode Ⅱ stationary growth crack on bimaterial interface

A mechanical model is established for mode Ⅱ interfacial crack static growing along an elastic-elastic power law creeping bimaterial interface. For frictional contact of boundary conditions on crack faces, asymptotic solutions of the stresses and strains of near tip-crack are got. It was shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity and there is not the oscillatory singularity the field. Through numerical calculation, it is shown that the frictional coefficient η notably influence the crack-tip field.     

Damping of Oblique Ocean Waves by a Vertical Porous Structure Placed on a Multi-step Bottom

Oblique ocean wave damping by a vertical porous structure placed on a multi-step bottom topography is studied with the help of linear water wave theory. Some portion of the oblique wave, incident on the porous structure, gets reflected by the multi-step bottom and the porous structure, and the rest propagates into the water medium following the porous structure. Two cases are considered： first a solid vertical wall placed at a finite distance from the porous structure in the water medium following the porous structure and then a special case of an unbounded water medium following the porous structure. In both cases, boundary value problems are set up in three different media, the first medium being water, the second medium being the porous structure consisting ofp vertical regions-one above each step and the third medium being water again. By using the matching conditions along the virtualvertical boundaries, a system of linear equations is deduced. The behavior of the reflection coefficient and the dimensionless amplitude of the transmitted progressive wave due to different relevant parameters are studied. Energy loss due to the propagation of oblique water wave through the porous structure is also carried out. The effects of various parameters, such as number of evanescent modes, porosity, friction factor, structure width, number of steps and angle of incidence, on the reflection coefficient and the dimensionless amplitude of the transmitted wave are studied graphically for both cases. Number of evanescent modes merely affects the scattering phenomenon. But higher values of porosity show relatively lower reflection than that for lower porosity. Oscillation in the reflection coefficient is observed for lower values of friction factor but it disappears with an increase in the value of friction factor. Amplitude of the transmitted progressive wave is independent of the porosity of the structure. But lower value of friction factor causes higher transmission. The investigation is then carried out for the second ca     

Characteristics and calculation method of sound radiation of cylindrical shell with porous sound-absorbing material under acoustic excitation北大核心CSCD

［Objective］This paper aims to study the characteristics and calculation method of the vibration and sound radiation of single ring-stiffened cylindrical shells with porous fiber composite materials installed in the inner wall under acoustic excitation. ［Method ］ Based on the equivalent fluid theory model of Johnson–Champoux–Allard (JCA) and the transfer matrix of the multilayer medium, a theoretical formula of the sound absorption coefficient of multilayer sound absorption structures is derived. The three methods for calculating the vibration and sound radiation of a single ring-stiffened cylindrical shell with porous fiber materials under acoustic excitation, namely acoustic solid modeling of porous media, finite element model combined with theoretical formula and imposition of impedance boundary on sound absorption coefficient, are then verified and compared. Finally, the influences of sound-absorbing material's thickness, backed-air gap, static flow resistance, and material arrangement order on the acoustic absorption performance of the cylindrical shell are investigated. ［Results］The results show that laying porous fiber composite materials on the cylindrical shell internally can reduce the vibration and acoustic radiation of cylindrical shell structure. The sound absorption coefficient curve can quickly and effectively predict the resulting trend of the vibration and sound radiation of the cylindrical shell. ［Conclusion］The acoustic absorption performance of sound absorption structures can be effectively improved through the rational design of their properties and arrangement order of the sound-absorbing materials in order to achieve the purpose of vibration and noise reduction. © 2023 Chinese Journal of Ship Research. All rights reserved.     

Numerical analysis of impact resistance of honeycomb structures with different Poisson's ratios北大核心CSCD

［Objectives］This papers aims to analyze the impact resistance of honeycomb structure with different Poisson's ratio. ［Methods］Based on the explicit dynamic finite element method, this paper analyzes the dynamic mechanical properties of honeycomb structures with different Poisson's ratios under in-plane impact load, and explores the influence laws of Poisson's ratios on their impact resistance. Three typical honeycomb structures with negative/zero/positive Poisson's ratios (reentrant hexagon, hexagon and semi-reentrant hexagon) are selected, their geometric parameters are changed to give them the same relative density and different Poisson's ratios (−2.76 – +3.63), and their dynamic mechanical properties under low/medium/high-speed dynamic displacement loads are analyzed. ［Results ］ The results show that the zero Poisson's ratio semi-reentrant honeycomb structure has the best structural stability without transverse deformation under compression deformation; without structural instability, the platform stress has little correlation with the Poisson's ratio; and the compact strain and total energy absorbtion increases with the absolute value of the Poisson's ratio. Negative Poisson's ratio honeycomb structures with large t/l and small θ are suitable for applications with high platform stress (strong deformation resistance), and negative Poisson's ratio honeycomb structures with small t/l and small θ are suitable for high total energy absorbtion applications, while zero Poisson's ratio semi-reentrant honeycomb structures are suitable for applications with high platform stress (strong deformation resistance). ［Conclusions］This study can provide references for the type selection and geometric parameter design of side impact honeycomb structures. © 2023 Authors. All rights reserved.     

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.