In shipyards, the plate thickness together with the steel grade and the joint type are commonly considered as major inputs in the design practice of welding joint. This paper focuses on the effects of the plate thickness on the welding distortion and residual stress. T-joints of DH36 marine steel with thickness of 6 mm, 8 mm, and 10 mm have been selected and investigated. To conduct the investigation, a thermal elasto-plastic analysis procedure has been established in conjunction with ABAQUS. A double ellipsoid heat source model was implemented through ABAQUS user subroutine DFLUX by authors. Experimental measurements were also performed to validate the numerical procedure by comparing the analysis results regarding the molten pool morphology, welding temperature history, and welding induced distortion and residual stress to those obtained from tests. For the considered T-joints of DH36, results have demonstrated that the plate thickness has significant influence on the distortion angle but negligible influence on the maximum residual stress. The data obtained from this study could be a direct assistance for welding engineers in shipyards to design T-joints of DH36 that frequently adopted in hull structures of ships and other facilities in ocean engineering.

In this article, a full-order sliding mode controller with echo state network (ESN-FOSMC) disturbance compensation is proposed for the trajectory tracking and vibration suppression of underwater flexible manipulators (UFM). To improve the robustness under lumped disturbances and reduce the computational complexity of traditional recurrent neural networks method, ESN, a continuous recurrent neural network, is used to approximate and compensate model uncertainties and hydrodynamic disturbances. A FOSMC is designed to ensure accurate tracking of joints and end-effectors, and proportional-derivative (PD) control method is utilized to further suppress flexible vibration. The adaptive law of ESN is formulated by using Lyapunov method, integrating the ESN method with sliding mode control method. Then, Lyapunov method is used to prove the stability of the control system. Finally, the virtual prototype system of the UFM is established to validate the effectiveness of the proposed control method. Simulation results present that, compared with the nonsingular fast terminal sliding mode controller and a FOSMC with radical basis functions (RBF-FOSMC) neural network disturbance compensation, the ESN-FOSMC achieves superior tracking accuracy with reduced vibration.

This paper presents a composite controller for trajectory tracking of moving-base underwater flexible manipulators (UFM). Firstly, a dynamics model of the moving-base UFM is established, and the model is decomposed into a slow-varying subsystem and a fast-varying subsystem by using the singular perturbation method. Then, an adaptive non-singular fixed-time sliding mode controller based on a high-order sliding mode observer is proposed for the slow-varying subsystem. In this controller, the high-order sliding mode (HOSM) observers are used to estimate and compensate for lumped disturbances, and adaptive super-twisting algorithm is used to reduce sliding mode chattering, which overcomes the disadvantage that the traditional adaptive method is prone to overestimation. To further suppress the system chattering, a HOSM observer is used to obtain the flexible mode derivatives for the fast-varying subsystem to achieve the suppression of vibration modes. The main advantages of this controller are its non-singularity, fast finite-time convergence and good vibration suppression. Extensive simulation results have validated the effectiveness of the proposed control method.

This paper aims to investigate the influence of welding sequences and boundary conditions on welding-induced residual stress and residual deformation of DH36 steel T-joint fillet welds through experimental and numerical methods. A series of typical experiments of successive and simultaneous double-sided welding conditions are conducted to explore both the magnitude and distribution of temperature field, residual stress and residual deformation. Meanwhile, thermal elastic-plastic finite element analysis based on a double ellipsoidal heat source model is performed to investigate the heat transfer and deformation mechanism during the welding process. The influencing factors are further explored to determine and quantify the residual stress and residual deformation induced by different welding sequences and boundary conditions. There is generally well agreement between the experimental and numerical results in terms of temperature field, residual stress, residual deformation and molten pool morphology. The results show that the welding sequences have an important influence on the magnitude and distribution of residual stress and residual deformation. Continuous simultaneous double-sided welding can significantly reduce residual stress and residual deformation to obtain better-quality welds. Boundary conditions have a significant effect on the distribution and magnitude of residual deformation and little effects on residual stress. Tightening the ends of the flange plate with bolts during the welding process can significantly reduce the deformation.

It is of great significance to expand the functions of submarines by carrying underwater manipulators with a large working space. To suppress the flexible vibration of underwater manipulators, an improved sparrow search algorithm (ISSA) combining an elite strategy and a sine algorithm is proposed for the trajectory planning of underwater flexible manipulators. In this method, the vibration evaluation function is established based on the precise dynamic model of the underwater flexible manipulator and considering complex motion and vibration constraints. Simulation results show that the ISSA algorithm requires only 1/3.68 of the time of PSO. Compared to PSO, SSA and the opposition-based learning sparrow search algorithm (OBLSSA), the optimization performance is improved by 17.3%, 13.1% and 9.7%, respectively. However, because the complex dynamics model of the underwater flexible manipulator leads to large computational effort and a long optimization time, ISSA is difficult to apply directly in practice. To obtain a large number of optimization results in a shorter time, an incremental Kriging-assisted ISSA (IKA-ISSA) is proposed in this paper. Simulation results show that IKA-ISSA has good nonlinear approximation ability and the optimization time is only 3% of that of the ISSA.

For any floating body, statical stability curves play a critical role in its stability analysis. In this article, a force‐oriented approach, in conjunction with finite element procedure, is proposed in order to compute those curves of floating bodies with complicated hull forms. The hull surface is meshed by triangular elements. The buoyant force and restoring moments are directly computed through the load redistribution of the hydrostatic pressure over the facet of each triangular element. Computations of a statical stability curve require a series of floating conditions that lead to the change of waterline with respect to the hull surface. In order to do all computations by using a unique finite element mesh, techniques regarding nodal coordinate update and non‐matching element treatment are developed. The procedure has been established and the algorithm has been developed. Results from three examples with simple but representative geometries are compared to those by hand calculations to verify the accuracy of the approach. Then, two standard reference hull forms, a very large crude carrier (KRISO KVLCC2) and a trimaran (NPL Round Bilge 4a), have been investigated to demonstrate the validation of the approach. Results of all examples show that the proposed approach is insensitive to the mesh pattern.

文中针对不同浮态下船舶排水量的测量,提出一种基于约束模型试验的船舶排水量直接测量技术.首先,给出了基于约束模型试验的船舶排水量测试仪器的装置组成和测试原理.接着,对三种典型模型进行了排水量测量试验,并将试验结果与理论结果进行了对比分析,结果高度吻合,说明该装置能够以较高的精度完成船舶排水量的测量.因此,该装置可以作为一种船舶设计时确定船舶排水量的补充方法.

The hydroelastic analysis of the propeller-shafting system in the non-uniform wake is a key step for designing a modern propeller-shafting system. The hydroelastic responses of the propeller-shafting system in the wake of ships are predicted by applying a three-dimensional time-frequency combined panel approach in conjunction with the finite element method. A fully non-penetration boundary condition applied on the deformed blade surface is conducted. The correction of both the incoming flow velocities and the normal vectors imposed on the blade surface of the transient vibration and the equilibrium positions is considered. The added-mass and -damping matrices due to strongly coupled fluid-structure interaction are derived. By comparing the present findings to numerical solutions calculated using the commercial tool Ansys Mechanical, the accuracy of the suggested technique is verified. It is observed that the added damping is higher, and the amplitudes of bearing forces are smaller, by applying the fully non-penetration boundary condition compared with the results obtained by imposing the other two simplified non-penetration conditions. This indicates that the designers need to imply the fully non-penetration condition on the deformed surfaces to predict the hydroelastic dynamics of the propeller-shafting system, especially in the case of high skew propellers. In addition, the amplitudes of the exciting forces after considering the fluid and propeller-shaft system interaction can be larger or smaller than those ignoring the interaction. The results depend on the phase difference and the mode shape.

This paper proposes a composite controller (CC) to improve the accuracy of trajectory tracking and suppress the vibration of two-link underwater flexible manipulators. A dynamic model of the flexible manipulators considering hydrodynamic force is established by combining the Lagrange equation and Morison formula. Then, the dynamic model is divided into a flexible dynamic subsystem and rigid dynamic subsystem, and a decomposed dynamic control strategy is presented for the two subsystems. In particular, an adaptive fuzzy sliding mode control scheme (AFSMC) with good robustness to compensate for uncertain factors is designed to track the joint trajectory and suppress vibration. Next, the trajectory tracking control of two-link underwater flexible manipulators is simulated to investigate the performance of the framework. The results show that the hydrodynamic force and flexible deformation markedly affect the input torque of the joint, and the traditional sliding mode controller (SMC) is superior to proportional integral derivative (PID) control in managing hydrodynamic force disturbance and inferior in suppressing flexible vibration. The proposed composite controller based on adaptive fuzzy sliding mode control CC(AFSMC) is more effective in restraining the vibration of flexible manipulators and resisting hydrodynamic force disturbance than PID and CC(SMC).

"船舶流体力学"是船舶与海洋工程(081901)本科专业的专业基础课程之一.以面向行业需求为抓手、以夯实流体力学基础为根本,结合课堂教学实践,文章对国内已有船舶流体力学教材内容进行分析,在此基础上提炼出"船舶流体力学"教学所需解决的核心问题,并就"船舶流体力学"教材大纲编写提出初步建议.明确了"船舶流体力学"课程的定位,厘清了船舶流体力学与相关课程的关系,有助于提高"船舶流体力学"课程及后续专业核心课程的教学效果.

为了加强我国生态文明建设,深化绿色发展理念,尤其是对于长江经济带的保护和发展,集合各研究团队对长江经济带的生物生态本底数据、各类污染物监测与处理、自然灾害与防治、政策法规,以及绿色发展相关技术与平台的建设现状进行了调查.结果发现:长江经济带已在上述各方面均有所建树,但仍存在一些欠缺或不足,主要表现为缺乏统一管理和整体规划.针对上述不足,提出了建立整体的管理机制、出台"长江保护法"和建设大数据平台的建议.由于综合平台将有助于对长江经济带进行统筹管理,实现全面发展,因此建议规划建设综合性的国家科技平台"长江流域生物物种资源(含基因)库及生态环境保障设施".

This study aims to systematically study the fatigue crack propagation characteristics of the mooring system for a floating production storage and offloading vessel (FPSO) through the fracture mechanics-based approach. The remaining fatigue life of the mooring lines is predicted by a self-integrated program through the simulation of the crack growth behavior. Additionally, parametric studies are performed to investigate the influence of initial crack status (location/size/shape) on mooring crack propagation characteristics. Results illustrate that the remaining fatigue life at the uppermost position of mooring lines at the wave-ward side is similar, which is approximately 178 years longer than that of mooring lines at the wave-back side. Fatigue issues are the severest in the crown region, where the critical fatigue life is about 49% of that in the bend region and 19.9% of that in the straight region. With the increase of the initial crack size and aspect ratio, the remaining fatigue life experiences a remarkable decrease with amplitudes up to 47.8% and 30.1% respectively. The integrated evaluation program is a promising tool for the damage tolerance design of mooring system due to the excellent capability in predicting the remaining fatigue life and charactering the crack growth behavior.

This paper aims to propose a universal time-domain fatigue evaluation method for mooring fatigue analysis of marine structures utilizing a fracture mechanics-based approach. First, the tension history of the mooring lines is calculated in the time-domain through hydrodynamic analysis and converted into mooring tension cycles with corresponding ranges via the rain-flow counting method. Subsequently, mooring fatigue performance is characterized through a self-integrated program which can realize the automatic crack propagation, Stress Intensify Factor (SIF) calculation and fatigue life prediction. Finally, a comparative study is implemented to further investigate the fatigue performance at different evaluation positions of various mooring lines under various corrosion rates. Results illustrate that fatigue life is relatively longer for mooring lines on the wave-ward side and greater at both ends of each line for the applied semi-taut mooring system. Most residual mooring fatigue life is more than 129 years with an initial surface crack of a = 0.5 mm, and the crack growth rate accelerates dramatically when reaching about 2.1% of the chain diameter. Remaining fatigue life decreases significantly under increasing corrosion rates, which is typically reduced by 39.4%, 48%, 47.8% and 38.6% for mooring lines 2, 5, 8, and 11 at 0.2 mm/year corrosion rate.

"船舶静力学"课程是"船舶与海洋工程(081901)"专业本科教学的基础性专业核心课程.课程目的是培养学生完成船舶在静力载荷或等效静力载荷作用下的浮性与稳性的分析能力,其内容涉及流体静力学、理论力学、微积分、数值方法等多个方面.为了建设新时代"船舶与海洋工程(081901)"专业的课程体系,作者对国内设置船舶与海洋工程类高校课程教材内容进行了对比和聚类分析,并据此确定了"船舶静力学"课程的基本共性内容.这些共性内容主要包括船体几何描述、流体静力学、船舶浮性、船舶稳性、船舶静水力资料、重物的状态改变、自由液面、进水与破舱等八个方面.在上述分析的基础之上编写的课程讲义或教材,有望取得更好的教学效果.

Resistance is one of the important performance indicators of ships. In this paper, a prediction method based on the Radial Basis Function neural network (RBFNN) is proposed to predict the resistance of a 13500 transmission extension unit (13500TEU) container ship at different drafts. The predicted draft state in the known range is called interpolation prediction; otherwise, it is extrapolation prediction. First, ship features are extracted to make the resistance R-t prediction. The resistance prediction results show that the performance of the RBFNN is significantly better than the other four machine learning models, backpropagation neural network (BPNN), support vector machine (SVM), random forest (RF), and extreme gradient boosting (XGBoost). Then, the ship data is processed in a dimensionless manner, and the models mentioned above are used to predict the total resistance coefficient C-t of the container ship. The prediction results show that the RBFNN prediction model still performs well. Good results can be obtained by RBFNN in interpolation prediction, even when using part of dimensionless features. Finally, the accuracy of the prediction method based on RBFNN is greatly improved compared with the modified admiralty coefficient.

Mechanism of hydrodynamic aggregation of swimmers is an intriguing problem, which is usually studied by the immersed boundary (IB) method. In this paper, a loosely coupled partitioned algorithm is used to simulate this fluid-structure interaction (FSI) problem. Specifically, flow field is simulated by finite volume method, and structure field is approximated by solving the momentum equation and bending vibration equation of Euler-Bernoulli beam. First of all, this algorithm is validated through simulating collective behavior of two actively moving two-dimensional (2D) flexible plates in tandem configuration driven by the harmonic plunging motions of their leading edges with identical frequency and amplitude. Then, the hydrodynamic aggregations of multiple (two or three) 2D flexible plates in side-by-side configuration are studied. It is found that two different stable configurations (alternate-leading mode, AL and staggered-following mode, SF) are formed spontaneously in two parallel flexible plates, and are determined by the lateral spacing between them. In three parallel-plates scenario, the middle plate follows behind in SF mode, while the other two plates present AL and SF modes with different lateral spacings accordingly. Besides, the flow details in different configurations are illustrated and the corresponding propulsive properties (velocity, input power and efficiency) of plates are discussed.

An adaptive nonsingular fast terminal sliding mode control scheme with extended state observer (ESO) is proposed for the trajectory tracking of an underwater vehicle-manipulator system (UVMS), where the system is subjected to the lumped disturbances associating with both parameter uncertainties and external disturbances. The inverse kinematics for the system is obtained by the quaternion-based closed-loop inverse kinematic algorithm. The proposed controller consists of the modified nonsingular fast terminal sliding mode surface (NFTSMS) and ESO, and the adaptive control law. The utilized NFTSMS can ensure the fast convergence of the tracking errors, together with avoiding the singularity in the derivation. According to the ESO method, the estimation error of the lumped disturbance vector can realize the fixed-time convergence to the origin, along with replacing the sign function with the saturation function to attenuate the chattering. A continuous fractional PI-type robust term with adaptive laws is introduced to handle the unknown bound of the estimation error. The closed-loop system is proved to be asymptotically stable by the Lyapunov theory. Simulations are performed on a ten degree-of-freedom UVMS under four different strategies. Comparative simulation results show that the proposed controller can achieve better tracking performance and stronger robustness of the disturbance rejection.

This paper proposes an adaptive wave neural network nonsingular terminal sliding mode control (AWNN-NTSMC) strategy with force estimation, which is exploited to address the path tracking control problem of the underwater manipulator under lumped disturbances. The proposed control scheme contains three parts: a nonsingular terminal sliding mode surface (NTSMS) part, an AWNN part, and a force estimation part. The NTSMS is designed to make the system states achieve fast convergence in the sliding mode phase. The AWNN theory is utilized to approximate the lumped disturbances via online adjustment of the network parameters. The force estimation method is applied in compensating the effect of external force on the control system. Besides, a saturated function instead of the signum function is used aiming to the chattering suppression. Asymptotic stability of the closed-loop system is guaranteed by the Lyapunov stability. Finally, by using a six degree of freedom (DOF) underwater manipulator, comparative simulation results validate the better tracking performance and stronger robustness against disturbances of our proposed scheme.

The independent escape capsule, an important facility of submarine search and rescue (SAR) system, gains extensive attention recently. However, researches on its ejection performance are rare, not to mention the studies of structural design in terms of this theme. In this paper, the vibration-absorptive materials clinging to the inner wall of its housing are used, and hydrodynamic responses of the capsule at a particular orientation in steady, uniform currents under various design parameters such as rigidity, friction coefficient and thickness are simulated. In order to study this interdisciplinary problem of fluid-structure interaction and multi-body dynamics, a simulation model (loosely coupled scheme) based on Fluent (version 13.0.1) is adopted with complement of the contact force between the capsule and the vibration-absorptive materials. Specifically, Fluent is used to assess the hydrodynamic force acting on the capsule, distributed force mode and material mechanics method are adopted to obtain the contact force, and then fourth-order Runge-Kutta method is implemented to calculate the motion equations of the capsule. Discussion of motion characteristics of the capsule indicates that this vibration-absorptive design helps the ejection of the capsule. Mechanism of vibration-absorptive design is discussed and some design suggestions are given.

In this paper, a fractional integral sliding mode control (FISMC) strategy with a disturbance observer (DO) is proposed for the trajectory tracking problem of the underwater manipulator, under lumped disturbances namely parameter uncertainties and external disturbances. The modified fractional integral sliding mode surface (FISMS) is designed to guarantee the fast convergence of system states. The DO method and the second-order sliding mode control law are used in the controller design, in which the former is introduced to compensate the effect of the lumped disturbances. Also, a saturated function is selected to replace the sign function to attenuate the chattering phenomenon. The stability of the overall closed-loop system is proved via Lyapunov's finite-time stability theory. Numerical simulations are performed on a 6 degree of freedom (DOF) underwater manipulator. Simulation results demonstrate that the proposed control scheme can achieve better tracking performance and stronger robustness against disturbances, by comparing with the DO-based PD control and the DO-based PID-type linear sliding mode control (SMC).