水翼艇翼航时稳性探讨

文章探讨V形割划式水翼艇翼航时初横稳性的计算,主要涉及水翼艇翼航时水翼浸深、横倾时左右翼升力的合力、回复力矩和稳性临界速度;提出了水翼艇翼航时稳性临界航速的概念和计算方法.文中的计算和讨论可为V形割划式水翼艇的设计提供参考.     

船舶结构的搁浅数值仿真研究

文章用数值仿真法研究了船舶结构搁浅中的内部力学问题,分析了典型双层底结构的损伤变形、受力和能量耗散结果。研究表明,损伤变形集中于搁浅的区域,搁浅力学问题主要考虑局部的船体结构;肋板的存在显著地增加船底结构的抗搁浅能力,使礁石的垂向贯入量会略有减小;当纵桁远离搁浅区域时,它的吸能能力无法发挥,抗搁浅作用明显削弱。     

三维复杂群桩水流力特性数值模拟研究

本文利用ANSYS Fluent,通过建立的三维水动力数值模型研究了矩型圆柱群桩在不同桩距条件下的水流纵向水流力、横向水流力及总水流力分布规律。同时,对目前实际工程中常用的菱型、圆型及哑铃型圆柱群桩在不同桩距下的纵向水流力、横向水流力及总水流力进行了研究。     

Workers wanted: Changing employee accessibility with industrial development ─ Evidence from Foxconn

In response to the trends of manufacturing revitalization and workforce shortage in the U.S., this study investigates how Foxconn changes accessibility to industrial employees by automobile and by transit in Southeast Wisconsin. Results suggest that there is a mismatch between the Foxconn site and the areas with high accessibility to industrial employees. With a great demand for labor, Foxconn reduces employee accessibility by automobile throughout the region, while its impact on employee accessibility by transit is more localized. The results inform industrial firm locations, workforce housing development, and transportation service provisions. The analysis framework shifts the angle of accessibility research to focusing on the perspective of employers, and it can be applied to investigate future large-scale economic development projects.     

浮码头与旁靠船舶的运动响应特性研究

本文基于三维势流理论，采用数值分析方法研究了浮码头与散货船旁靠系泊的运动特性。考虑缆绳和护舷的非线性特性，探求了波浪周期对浮体运动、系缆力的影响规律。研究结果表明：考虑间隙内水体运动影响，旁靠散货船在横浪条件下的纵摇和纵荡运动有所增大。浮码头在计算工况下，缆绳受力较大，在某些工况条件下超出了国际系缆力标准的要求，旁靠散货船的缆绳在计算工况下均未超标，满足要求。研究结果为浮码头系泊系统的设计及工程运营提供理论参考。     

Fatigue damage estimation in non-linear systems using a combination of Monte Carlo simulation and the First Order Reliability Method

For non-linear systems the estimation of fatigue damage under stochastic loadings can be rather time-consuming. Usually Monte Carlo simulation (MCS) is applied, but the coefficient-of-variation (COV) can be large if only a small set of simulations can be done due to otherwise excessive CPU time. The reason is that the fatigue damage estimation is very sensitive to the largest values from the simulations. The paper suggests the additional use of the First Order Reliability Method (FORM) to get a better estimation of the tail in the distribution of the estimated fatigue damage and thereby reducing the COV. For a specific example dealing with stresses in a tendon in a tension leg platform the COV is thereby reduced by a factor of three.     

扣件DI弹条非正常部位断裂原因分析及结构优化

通过对DI弹条非正常部位断裂的研究,发现扣件安装时弹条与铁垫板安装孔发生接触,致使弹条在中肢与尾部圆弧过渡区域产生应力集中,发生早期疲劳断裂。本文在研究弹条结构及安装方式的基础上,在弹条的中肢与尾部圆弧过渡区域引入"凹面"结构,对弹条进行结构优化,并通过扣压力和疲劳性能检测、实验室疲劳断裂检验、现场试铺检验等对带有优化"凹面"结构的DI弹条性能进行检测。结果表明:优化后的弹条扣压力和疲劳性能均合格,且能有效抑制因接触产生的非正常部位断裂,提高弹条性能。     

Sea state estimation based on vessel motion responses: Improved smoothness and robustness using Bézier surface and L1 optimization

Floating structures oscillate in waves, where these wave-induced motions may be critical for various marine operations. An important consideration is thereby given to the sea states at the planning and operating stages for an offshore project. The most important information extracted from a sea state is the directional wave spectrum, indicating wave direction, significant wave height, and wave spectrum peak period. Among several available methods of measuring and estimating the directional wave spectrum, the wave buoy analogy technique based on vessel motion responses is an in situ and almost real-time solution without extra costs of devices. If the forms of the wave spectra are not predefined in the estimation, the method is called a nonparametric approach. Its most remarkable advantage is the flexible form, but the smoothness should be regulated. After the discrete Fourier transform has been applied to the measured vessel motions, smoothing is necessary. However, this process results in disturbed vessel cross-spectra and a lowpass characteristic of the windowing function. This paper presents a nonparametric approach for directional wave spectrum estimation based on vessel motion responses. It introduces novel smoothness constraints using Bézier surface and includes a more robust estimate using L1 optimization. Both techniques are applied to the wave buoy analogy for the first time. Numerical simulations are conducted to verify the proposed algorithm.     

Experimental study of freak wave impacts on a tension-leg platform

This study investigates the freak wave impinging on a tension-leg platform through wave flume experiments. The freak waves are generated using the focused wave theory. By adjusting the wave focusing location, different incident wave scenarios at the structure location are produced. Simultaneous measurements of wave shape evolutions upon impingement, wave impact pressures on the platform deck, platform motions and tether forces are carried out for synchronized analyses of the wave kinematics/dynamics and structural responses. The variation of these parameters with the incident wave profile is studied. It is found that although applying less intensive local impact pressures as compared to the highly-breaking freak wave, the slightly-breaking or non-breaking freak wave imposes the same level of adverse effect on the platform's global stability in terms of motions and tether forces. In addition, the high-crest freak wave causes violent motions of the floating platform, which are likely to induce snap loads of large amplitude and high occurrence frequency in tethers. The published results would provide useful benchmarks for validating numerical and analytical models.     

Hybrid analytic-FEM approach for dynamic response analysis of air-cushion vehicle skirts

Focused on the assessment method for dynamic behavior of the skirts of an air cushion vehicle (ACV), this paper proposes a hybrid analytic-FEM approach, within which the self-developed subroutine considers the transient skirt-water contacting force through suggested semi-analytical formula based on the empirical results from CFD simulations of the equivalent flat-plate model. The dynamic explicit algorithm of FEM is adopted to solve the large deformation problem of flexible skirts. The validity of the approach has been confirmed by comparing with previous numerical results as well as published experimental results of steady seal deformation tests at University of Michigan. Afterward, more simulations for demonstration cases are carried out to study the complex dynamic response of the skirts under different skirt-water contacting conditions. The proposed method can obtain more reliable results than traditional analytical method and be more efficient than fluid-structure interaction simulations, thus providing a practical balanced approach aiming at the dynamic response analysis for whole skirts and contributing to the skirts dynamics performance assessment of an ACV.