数控肋骨冷弯机自动控制检测方法的改进

分析了传统的数控肋骨冷弯机控制方法与机构,阐述了统线测量控制法的基本原理。据此建立了新的控制检测方法和数学模型,提出了基于弦线测量控制法的新的控制检测方法。     

Comparison of aluminium sandwiches for lightweight ship structures: Honeycomb vs. foam

The use of lightweight aluminium sandwiches in the shipbuilding industry represents an attractive and interesting solution to the increasing environmental demands. The aim of this paper was the comparison of static and low-velocity impact response of two aluminium sandwich typologies: foam and honeycomb sandwiches. The parameters which influence the static and dynamic response of the investigated aluminium sandwiches and their capacity of energy absorption were analysed. Quasi – static indentation tests were carried out and the effect of indenter shape has been investigated. The indentation resistance depends on the nose geometry and is strongly influenced by the cell diameter and by the skin – core adhesion for the honeycomb and aluminium foam sandwich panels, respectively. The static bending tests, performed at different support span distances on sandwich panels with the same nominal size, produced various collapse modes and simplified theoretical models were applied to explain the observed collapse modes. The capacity of energy dissipation under bending loading is affected by the collapse mechanism and also by the face-core bonding and the cell size for foam and honeycomb panels, respectively. A series of low-velocity impact tests were, also, carried out and a different collapse mechanism was observed for the two typologies of aluminium sandwiches: the collapse of honeycomb sandwiches occurred for the buckling of the cells and is strongly influenced by the cell size, whereas the aluminium foam sandwiches collapsed for the foam crushing and their energy absorbing capacity depends by the foam quality. It is assumed that a metal foam has good quality if it has many cells of similar size without relevant defects. A clear influence of cell size distribution and morphological parameters on foam properties has not yet been established because it has not yet been possible to control these parameters in foam making. The impact response of the honeycomb and foam sandwiches was investigated using a theoretical approach, based on the energy balance model and the model parameters were obtained by the tomographic analyses of the impacted panels. The present study is a step towards the application of aluminium sandwich structures in the shipbuilding.     

均匀外压下有几何缺陷球壳的破坏压力

将球壳缺陷部分看作受球壳其余部分弹性约束的独立扁球壳,提出了弹性屈曲压力的分析方法,并得出临界弧长的解析结果。还对非弹性屈曲破坏问题提出了工程实用的处理方法。共作十四个铝球壳和四个钢球壳模型试验。     

基于RANS 升力法的轴流泵多方案优化设计

传统升力法参考与设计泵性能接近的母型泵以完成两栖车喷水推进轴流泵设计,该方法设计的轴流泵水动力性能存在缺陷和不足,本文基于RANS法,借助于商用软件ICEM（前处理）和CFX（后处理）对传统升力法设计的轴流泵水动力性能缺陷和不足进行改进。在验证RANS法准确性的前提下,在某型两栖车喷水推进器的升力法设计过程中,母型泵与设计泵性能参数相差较大的情况下,通过RANS法对影响轴流泵水动力性能的相关参数进行优化,表明通过弦长优化方案和翼型拱度优化方案的轴流泵改进设计均能达到预期优化目标,其弦长变化比 或拱度变化比 时,其轴流泵的水动力性能较佳,满足最终设计方案需求。     

主管受拉K型管节点抗冲击性能有限元研究

偶然荷载引起的撞击会造成海洋平台中的管桁架严重损伤,尤其是管节点的破坏,严重时会导致整个平台的损坏,因此管节点是海洋平台设计研究中的一个重要内容.本文以海洋平台中常见的K型管节点为研究对象,利用有限元软件ABAQUS研究了3个主管在受拉状态下的K型管节点的抗冲击性能.在研究过程中以几何参数和荷载参数为主要变量,分析了各相关参数对管节点的抗冲击性能的影响.确定了K型管节点在冲击荷载作用下的破坏模态.在对冲击力、位移、能量耗散等时程曲线的分析中揭示了抗冲击性能工作机理.研究结果表明:支主管的径厚比以及支管的拉压状态对管节点所受到的最大冲击力和节点变形具有较显著的影响.     

Experimental study on the collapse strength of wide stiffened panels

Five specimens are tested under axial compression until collapse to investigate the ultimate strength of wide stiffened panels with four stiffeners. To avoid the side bays collapse and reduce the influence of the clamped boundary condition on the collapse behaviour, the tests are made on panels with two half bays plus one full bay in the longitudinal direction with simply supported condition at the end edge of loading. Initial loading cycles are used to release the residual stresses of the stiffened panels and the gap between the stiffened panels and the supported steel block. Strain gauges are installed on the plates and the stiffeners to record the distribution of strain. This series of experiments is compared to a series of tests with narrow panels (two stiffeners), which allows analysing the effect of the width on the strength of stiffened panels.     

轮缘推进器水动力性能数值分析

轮缘推进器作为一种新型的推进方式,取消了螺旋桨推进中轴系的设置,具有舱容占比小、噪声低和振动小等优点,可用于潜艇、鱼雷或者是游艇等海洋航行器,有广泛的应用前景。本文基于STAR-CCM+仿真软件,针对推进器流场进行数值模拟,采用SST k-ω模型完成对轮缘推进器水动力性能的数值计算,分析了建模时简化推进器驱动环间隙及桨叶弦长和螺距比对推进器水动力性能的影响。     

Effect of non-symmetrical corrosion imperfection on the collapse pressure of subsea pipelines

The effects of non-symmetrical corrosion defects (about the major or minor axis of the ellipse) on the collapse modes and collapse pressures of subsea pipelines are studied using the Finite Element (FE) method. The corrosion defects are represented by a groove of a given length, width, and depth which is created by the “element death” technology. Parametric studies are conducted and the influences of corrosion location angle, length, width, and depth on the collapse pressure are discussed. Several significant and interesting results are achieved: (1) The collapse modes are mainly affected by the corrosion location angle, width, and depth; (2) The collapse pressure of a pipe may increase as the corrosion length, width, or depth increases when the corrosion location angle is small; (3) The longer the corrosion length, the larger the effect of corrosion location angle on the collapse pressure; (4) For collapses controlled by corrosion defect (0.3≤h/t ≤ 0.7), the relationship between the collapse pressure and corrosion location angle follows a simple cosine function. For collapses controlled by the ovality (h/t < 0.3), the relationship can be expressed by the combination of straight-line and cosine function.     

Evaluation of ultimate strength of stiffened panels under longitudinal thrust

A series of collapse analyses is performed applying nonlinear FEM on stiffened panels subjected to longitudinal thrust. MSC.Marc is used. Numbers, types and sizes of stiffeners are varied and so slenderness ratio as well as aspect ratio of local panels partitioned by stiffeners keeping the spacing between adjacent longitudinal stiffeners the same. Initial deflection of a thin-horse mode is imposed on local panels and that of flexural buckling and tripping modes on stiffeners to represent actual initial deflection in stiffened panels in ship structures. On the basis of the calculated results, buckling/plastic collapse behaviour of stiffened panels under longitudinal thrust is investigated. The calculated ultimate strength are compared with those obtained by applying several existing methods such as CSR for bulk carriers and PULS. Simple formulas for stiffened panels, of which collapse is dominated fundamentally by the collapse of local panels between longitudinal stiffeners, are also examined if they accurately estimate the ultimate strength. Through comparison of the estimated results with the FEM results, it has been concluded that PULS and modified FYH formulas fundamentally give good estimation of the ultimate strength of stiffened panels under longitudinal thrust.     

横向干货补给系统高架索的静力学分析

考虑挠曲对高架索索长的影响,利用微元法得到更为精确的高架索挠度表达式,将其进行二阶泰勒展开并代入悬挂点轨迹方程。重点研究补给过程中货物运输的安全性,通过数值计算发现补给过程中的落水危险点并不会发生在最大挠度处,而更接近接收端。探讨了高架索张力和补给距离对高架索静挠度的影响。     

基于ANSYS的预应力混凝土桁架桥设计

结合某预应力混凝土桁架桥的概念设计,基于单元刚度矩阵集成和ANSYS有限元数值模型为计算方法,分析研究该桥在静力荷载作用下的响应。通过分析腹杆及弦杆的挠度和应力分布,研究该桥的受力特点,并提出桁架桥的优化设计建议。     

不同纵摇轴位置下的二维柔性鳍推进性能与流场特性研究

利用FLUENT软件数值计算了二维柔性鳍作升沉纵摇运动时的推力系数及推进效率,探讨了修正Bose变形方程、均匀载荷和非均匀载荷悬臂梁变形方程等三种柔性模式下纵摇轴位置对摆动鳍推进性能的影响,其中纵摇轴在尾缘处能够获得更大的推力,而最高的推进效率分别对应修正Bose模式下纵摇轴距首缘1／3弦长处和悬臂梁柔性变形模型下纵摇轴距首缘2／3弦长处．同时计算分析了斯特劳哈尔数、最大攻角等参数对柔性鳍水动力性能的影响,建立了最大推力系数和最高推进效率所对应的参数区间,其中低St数的最高推进效率发生在低αmax,高St数的最高推进效率发生在高αmax．     

Collapse strength of hatch cover of bulk carrier subjected to lateral pressure load

A series of elastoplastic large deflection FEM analyses has been performed on hatch covers of bulk carriers subjected to lateral load. Two types of hatch covers are considered which are the folding type and the side-sliding type. For the folding-type cover, one size is considered which is for Handy size bulk carrier, whilst for the side-sliding-type cover, two sizes are considered which are for Panamax and Cape size bulk carriers. For each type, two hatch covers are selected which are designed in accordance with the old ICLL rule and new IACS rule, respectively. Calculated collapse strengths are compared with individual design loads, and a strength assessment is performed. On the basis of collapse behaviour observed in FEM analyses, a simple method is proposed to evaluate the collapse strength of a hatch cover subjected to lateral load. It is confirmed that the collapse strength is accurately predicted by the proposed method.     

Numerical investigation on the ultimate strength behaviour and assessment of continuous hull plate under combined biaxial cyclic loads and lateral pressure

The ultimate strength of continuous hull plate under combined biaxial cyclic loads and lateral pressure is investigated in the present paper by using nonlinear finite element method. Geometric nonlinearity due to large deflection and material nonlinearity induced by kinematic hardening and isotropic hardening are both accounted for. A parametric study is designed and completed to examine the longitudinal ultimate compressive strength behaviours in the cycles on the basis of a large number of load-shortening curves. Effects of series of parameters especially the plate slenderness ratio, transverse cyclic compression, lateral pressure and cycle number are analyzed with details. It is found that the strength characteristic and collapse mode are highly affected by the coupling influence of the mentioned factors as well material behaviours. A dimensionless unified formulation as a function of the decisive factors is empirically proposed to accurately assess the ultimate strength of continuous hull plate in various cycles.     

The effect of weld residual stress on fracture toughness at the intersection of two welding lines of offshore tubular structure

Due to the spatial complexity and fabrication characteristics of offshore platforms, it is inevitable to encounter overlaps or proximity of weld lines in tubular joints. Several international standards such as American Petroleum Institute (API), American Welding Society (AWS), and American Institute of Steel Construction (AISC) regulate the minimum distance between primary weld beads; however, any logical and detailed background of this limitation has not been presented. For a non-compliant weld joint where the regulation is not met, fracture toughness calculation is a typical index to verify the structural integrity.This research consists of two parts. First, weld residual stress distributions are calculated by a 3D thermo-mechanical nonlinear Finite Element Analysis. Two crossing welds, a T-weld crossing on a butt weld, are simulated in one model. A separate tee and a butt welding simulations are also performed for a comparative purpose. Second, SIFs and J-integral values are calculated at the surface and deepest crack tip locations for four different types of semi-elliptical surface cracks. Four cracks are embedded into the weld model and the residual stress distribution from the 3D thermo-mechanical FEA are mapped to a 3D FE crack model as initial conditions. An additional axial tensile load is also imposed. SIF values are compared with those using the weighting function method for the butt weld model subject to three load cases, i.e., tensile stress only, weld residual stress only, and both of them. From the simulation, a tubular joint containing a chord girth weld intersected with weld beads of brace is found to show lower the SIF values than that having only a girth weld on chord.     

Assessment of IACS-CSR implicit safety levels for buckling strength of stiffened panels for double hull tankers

The present study aims at applying structural reliability methods to assess the implicit safety levels of the buckling strength requirements for longitudinal stiffened panels implemented in the IACS Common Structural Rules (CSR) for double hull oil tankers. The buckling strength requirements considered are used in the initial stage of the hull girder scantlings’ design to control the buckling capacity of longitudinal stiffened panels subjected to the compressive loads induced by the hull girder vertical bending. The following buckling collapse failure modes are explicitly considered in the design formulation: uniaxial buckling of the plating between stiffeners, column buckling of stiffeners with attached plating and lateral-torsional buckling or tripping of stiffeners.The paper presents the procedure used to assess the implicit safety levels of the strength requirements for the three buckling collapse failure modes above mentioned, which includes the optimization of the scantlings of the plate panels and longitudinal stiffeners in order to reflect the minimum strength required by the formulation. A first order reliability formulation is adopted, and stochastic models proposed in the literature are used to quantify the uncertainty in the relevant design variables. A sample of five oil tankers representative of the range of application of the IACS-CSR design rules is considered. The effect of corrosion in the implicit safety levels is quantified based on the three corrosion levels of the Net Thickness Approach (NTA) adopted in the design rules. Sensitivity analyses are also performed to quantify the relative contribution or importance of each design random variable to the implicit safety levels.     

波浪中船体梁后极限强度特性的实验评估(英文)

Experimental investigations into the collapse behavior of a box-shape hull girder subjected to extreme wave-induced loads are presented.The experiment was performed using a scaled model in a tank.In the middle of the scaled model,sacrificial specimens with circular pillar and trough shapes which respectively show different bending moment-displacement characteristics were mounted to compare the dynamic collapse characteristics of the hull girder in waves.The specimens were designed by using finite element(FE)-analysis.Prior to the tank tests,static four-point-bending tests were conducted to detect the load-carrying capacity of the hull girder.It was shown that the load-carrying capacity of a ship including reduction of the capacity after the ultimate strength can be reproduced experimentally by employing the trough type specimens.Tank tests using these specimens were performed under a focused wave in which the hull girder collapses under once and repetitive focused waves.It was shown from the multiple collapse tests that the increase rate of collapse becomes higher once the load-carrying capacity enters the reduction path while the increase rate is lower before reaching the ultimate strength.     

Hydroelasto-plasticity approach to predicting the post-ultimate strength behavior of a ship’s hull girder in waves

Dynamic collapse behavior of a ship’s hull girder in waves is investigated; post-ultimate strength behavior is the focus. Firstly, a simulation method is proposed. Assuming that a plastic hinge is formed during the collapse of the hull girder, the whole ship is modeled as two rigid bodies connected amidship via a nonlinear rotational spring. The post-ultimate strength behavior, such as the reduction of load carrying capacity due to buckling and yielding, is reflected in the model. Hydrodynamic loads are evaluated by using nonlinear strip theory to account for the effect of large plastic deformations on the loads. A scaled model for validation of the simulation is designed and fabricated. Then a series of tank tests is conducted using the scaled model to validate the simulation results. Post-ultimate strength behavior characteristics in waves are clarified by using the numerical and tank test results. It is shown that the hull girder collapses rapidly after reaching ultimate strength, and then the plastic deformation grows until unloading starts at the collapsed section. Finally, several parametric dependencies of the extent of the collapse behavior are discussed based on a series of the simulations.     

用有限元法确定弹塑性材料结构的极限承载力

确定弹塑性材料结构的极限承载能力是结构设计中极其重要的一个问题,它通常是采用弹塑性非线性有限元方法来进行分析的.本文提出了利用基于一系列线弹性有限元解来获得弹塑性材料结构的极限承载能力的试验误差法,并将它与切线法和割线法进行了比较和讨论.在计算的每一步中,根据应力松弛系数降低杨氏弹性模量,并将结构的应力松弛系数和作为误差指标.当结构的误差指标小于给定的误差容限时就得到收敛解.本文方法可计算出结构受载后直到崩溃时应力、应变和载荷-变形曲线.数值实验表明,本文方法是有效的和可行的.     

Plastic design of laterally patch loaded plates for ships

Laterally loaded rectangular plates are used extensively in various marine structures, and they are often subjected to patch loading during ice action or accidental actions, such as collision and grounding. Therefore, focus is placed on investigating the resistance of laterally patch loaded plates. Plastic yield line theory has been adopted in this paper, since considerable plastic behavior is exhibited. The beneficial influence of the membrane effect during finite deformations is taken into account. The derivation of the “roof-top”-type patch loading mechanism using work energy principles is described in some detail. An alternative collapse model, as named “double-diamond” pattern herein, is proposed which could reduce the resistance and agrees better with the results from nonlinear finite element analysis (NLFEA) in plastic bending phase compared to the conventional “roof-top” model. Moreover, a plate length restriction factor is introduced to enhance the applicability of the present formulation when free formation of the collapse mechanism is restricted by the finite length of the plate. The developed formulae show reasonable agreement with the results from NLFEA of the plate resistance–deformation relationships. The resistance according to the proposed formulation is also compared with the recently developed International Association of Classification Societies (IACS) unified requirements for plating design for polar ships.