Nonstationary response of floating structures to random waves

Even if ocean waves are treated as a stationary random process, dynamic responses of floating structures to random waves at the transient state are always nonstationary. When nonstationary response statistics is desired, a common technique is to apply Monte Carlo simulations; however, its implementation is costly in computational time. Analytically, this article develops an efficient method for computing nonstationary response statistics, including evolutionary power spectrum and time-varying mean-square values. Assuming a hydrodynamic software has been employed to get various frequency response functions, a prerequisite of the proposed method is to get the elevation-to-motion transfer function formulated in its pole-residue form. The proposed method is applicable to arbitrary wave spectrum and has been based on pole-residue operations implemented in the Laplace domain to obtain closed-form solutions for the response evolutionary power spectrum. Numerical examples choose a single-degree-of-freedom Spar model and a six-degree-of-freedom Floating Production Storage and Offloading model to a Pierson–Moskowitz wave spectrum, and the correctness of the computed mean-square values is verified by Monte Carlo simulations.     

SBS改性沥青老化过程性能预测方程研究

建立SBS改性沥青在老化过程中性能衰变的非线性预测方程，通过薄膜烘箱试验验证了预测方程的可靠性，基于预测方程分析了SBS改性沥青老化过程中性能指标的变化速率。研究结果表明，非线性方程x(t)=(Lx₀)/[1+(L-1)e^-rt]可用以预测针入度、软化点、延度在SBS改性沥青老化过程中的变化规律；沥青针入度、软化点、延度的变化速率随老化时间的延长而逐渐下降，其中延度指标在老化初期的变化速率下降最快；可通过建立宏观性能指标与红外光谱a₁₇₀₀/a₁₆₀₀的关系方程，进行SBS改性沥青老化程度的预测评估。     

锚链多体系统最优化求解方法及其对比分析

为了在不添加额外方程或判断条件的情况下，求解锚链多体系统悬链和卧链共存的状态，提出利用最优化原理描述静态锚链多体系统的状态方程，即最小势能方程，并与传统的悬链线方程和多体系统一般力学方程进行对比分析。结果表明，该方法不需要进行复杂的受力分析，形式简单且物理意义明确。数值计算结果与传统方法在计算悬链时是一致的，且可在统一的框架下计算悬链和卧链同时存在的状态。     

An improved method for estimating internal solitary waves force on small circular cylindrical structures

Theoretically calculation and laboratory experiments were performed to investigate the horizontal force exerted by internal solitary wave (ISW) on small circular cylindrical structures. Improvement in calculation of drag force and inertia force by introducing two-drag-coefficient method and spatial derivative of velocity into the calculation of force by eigenfunction was made based on systematically study on theoretical foundations. Particle image velocimetry (PIV) method and high precision force sensor were used to measure the velocity and force exerted by ISW, respectively. ISW waveform was traced by analyzing image frames follow grayscale threshold method. For the first time, components of horizontal force were calculated from PIV data, which show good agreement with theoretical one. Moreover, series comparisons between experimental data and calculational results were carried out to examine the proposed method. The results show ideal accuracy of the method and significant improvement comparing to the traditional method.     

Numerical method of electromagnetic pulse response of conductor with complex load北大核心CSCD

[Objectives]Electromagnetic pulse can seriously affect and even destroy naval shipborne electronic information systems, weapons, equipment and so on. Due to the complexity of the antenna port load circuit, it is necessary to formulate a numerical method which can easily obtain the antenna load current. [Methods]The induced current of the terminal is obtained on the basis of the finite-difference time-domain (FDTD) and Holland model. According to the Thévenin equivalent circuit, the conductor is equivalent to the voltage source to realize decoupling between the conductor and load end, and the load circuit is solved using Simulink software.[Results]Compared with the traditional terminal model, this method is simple and feasible for high-order circuit processing. The effectiveness of the model is verified using non-linear elements and parallel capacitors and resistors as the load respectively. The results show that the calculation results of this method are consistent with those of the traditional methods. Finally, the antenna of the end-connected protect- or is calculated. The results show that the lead inductance caused by the installation of the protector is an important factor affecting the protection performance.[Conclusions]The method proposed in this paper can greatly reduce the simulation complexity of the coupling current of an antenna with a complex load, giving it useful reference value for the field of ship electromagnetic pulse protection design. © 2023 Editorial Department of Chinese Journal of Ship Research. All Rights Reserved.