钢纤维混凝土Ⅰ型破坏断裂分析

钢纤维混凝土是拉应力敏感材料,在外荷载作用下,裂纹端部会产生微裂纹形成微裂区。这一特征使线弹性断裂力学不能直接分析钢纤维混凝土的断裂。同时钢纤维混凝土开裂后,钢纤维在开裂区通过提供拉应力,限制裂纹的扩展。针对钢纤维混凝土这两个特征,本文用理论和实验的方法,对钢纤维混凝土I型断裂的裂纹产生和裂纹扩展进行了研究,并得到可用有效裂纹长度代替真实裂纹长度和用闭合力等效钢纤维阻裂作用的结论。最后用线弹性断裂力学方法计算钢纤维混凝土I型断裂的临界应力强度因子和钢纤维拉应力。     

季冻区组合式矩形渠冻胀数值模拟研究

季节性冻土地区渠道衬砌冻胀破坏现象普遍,在土体冻融环境影响下容易发生开裂、坍塌等破坏现象,这将严重影响渠系工程的安全运行,因此对季冻区渠道衬砌的冻胀破坏研究具有十分重要意义。以实际工程项目为原型,采用有限元方法,基于ABAQUS平台,对组合式矩形渠进行数值模拟分析,研究了一次与多次冻融循环的土体冻结融化规律,分析了冻融循环后土体的残余应力及残余变形,验证了组合式矩形渠在10 a结构强度满足要求,不会影响正常运行。     

考虑土体剪胀特性的土质边坡稳定性极限分析

剪胀特性是土体的重要特性之一,然而,经典的塑性力学理论高估了土体的剪胀性质,从而使土体强度背离实际情况。通过等效内摩擦角的方法,对原有的土体抗剪强度进行修正,反映出土体剪胀性对土体强度的影响。通过构建对数螺旋形式的破坏机构,推导出相应的内能耗散和外力功率表达式,结合极限分析理论和强度折减方法,建立边坡安全系数的求解方法。结果表明,该方法的计算结果是合理的。随着剪胀角的不断增大,边坡安全系数增大的速度变慢,这种变化趋势是非线性的。针对不同的土质特性,提出相应的剪胀角取值建议。     

具有中心穿透裂纹缺陷的矩形板极限拉伸强度分析

本文利用弹塑性有限元分析结果对现有的裂纹板的拉伸极限强度简化公式进行了修正，得到了与实验结果比较吻合的修正公式，并且以受单向拉伸、具有中心穿透裂纹的正方形板为例，借助弹塑性断裂力学的理论推导了断裂控制基础上该材料的极限拉伸强度计算公式，从而从理论上解释了修正公式的合理性。     

土体抗剪强度指标相关性特征研究

本文从摩擦力学角度阐述了土体抗剪强度指标之间相关性的理论基础,提出了分析抗剪强度指标相关性的一般步骤,通过工程实例与前人成果的对比,得出土体抗剪强度指标正负相关性受多种因素影响的结论.     

偏压固结软黏土循环特性试验研究

关于软黏土循环强度弱化的研究已经有了很多成果。然而在工程上为了削弱循环荷载对土体的影响,一般会采取打塑料排水板、堆载预压等软基处理手段来提高土体强度,从而减弱循环荷载对土体的弱化作用。以烟台港原状淤泥质粉质黏土为研究对象,通过室内动三轴试验,探究土体在静偏应力固结后累积孔压的发展规律和循环强度的弱化规律。根据孔压数据拟合出软黏土的孔压模型,再利用等效超固结比理论将孔压模型与强度弱化规律相结合,得到了适用于偏压固结之后整个动态循环过程的强度变化公式。     

绞吸挖泥船绞刀切削过程数值模拟及刀臂曲线优化

为了研究绞吸挖泥船切削过程土体与绞刀相互作用的功率消耗和切削产量情况,基于离散元理论,结合实船施工数据,采用PFC3D程序,将土体离散为有限单元,模拟绞刀切削土体过程,监测绞刀功率消耗和切削产量,与实船数据对比分析,验证数值模拟的可靠性,在此基础上对现有绞刀刀臂曲线进行改进优化。     

含裂纹平板结构有限元模型的建立及有限元分析

带有裂纹压力平板的安全评定可以通过断裂力学理论来进行,这也是国内外对结构做安全评定的主要理论依据。从上世纪中叶至今,断裂力学理论应用研究有了突破式的发展。在实际的工程应用中,评定一些含裂纹的结构的安全性,可以直接参考应用的断裂参数几乎没有。本文以断裂力学为基础,采用有限元分析方法,应用ANSYS软件创建带有裂纹的平板有限元模型。进一步分析计算,得到线弹性条件下不同参数条件下的应力强度因子K值,再对裂纹尖端的应力场进行分析应用,对比数据结果,探究裂纹尖端应力应变场的影响因素。     

降雨对非饱和土边坡稳定性的影响分析

随着岩土工程的深入研究,对非饱和土边坡的研究也日益发展。本文依据Bishop及Fredlund的非饱和土抗剪强度理论,揭示了基质吸力对土体抗剪强度的贡献尤为重要。运用Fredlund提出的总黏聚力法对降雨引起的基质吸力变化导致的边坡变形进行分析,得出了降雨导致基质吸力减小甚至散失引起的土体抗剪强度减小,将威胁到边坡稳定性的结论。     

成层土地基基础极限承载力的模型试验研究

本文通过大量的室内模型试验对地基土体分层情况下基础的极限承载力进行了试验研究，得到成层土地基极限承载力的大小与持力层土体强度、厚度的变化规律；并且根据试验结果分别对港口工程和土木工程中常用的迈耶霍夫和汉纳的理论计算方法、汉森加权平均法、扩散角法以及魏锡克的理论计算方法这四种成层土地基极限承载力计算方法进行了验证。其结果表明对于成层土地基基础极限承载力的理论计算，由魏锡克和迈耶霍夫的理论所得的计算结果与试验测量值最接近。最后运用有限元的方法对成层土条件下地基土体的变形及位移情况进行了模拟计算进一步验证了魏锡克理论的合理性。     

船舶操纵数学模型在港口航道设计中的应用

本文介绍了船舶操纵数学模型的组成,并对其在港口、航道设计中应用的典型列车进行了介绍,指出了船舶操纵数学模型的进一步发展方向和它在港口、航道设计中的应用前景。     

Numerical study on breaking phenomena of ships’ waves in narrow and shallow waterways

The environmental impact of a ships waves, such as the risk of erosion of coasts and riverbanks, and unacceptable ship movements in a restricted waterway, is now a significant ship design criterion. Therefore, it is necessary to predict ship-wave phenomena accurately in a restricted waterway. In this study, a numerical investigation of the breaking phenomena of a ships waves in restricted waterways was carried out. Incompressible Navier–Stokes and continuity equations were employed. The equations are discretized by a finite-difference method in a curvilinear coordinate system. The interface capturing method was applied to simulation of a ships waves, including wave-breaking. A modification of the level-set method is proposed to find the free surface shape clearly and without difficulty of the implemation of the boundary conditions for the distance function. In order to obtain a high resolution of wave height, a constrained interpolated profile (CIP) algorithm is adopted. In order to check the advantage of the CIP method, computations by two numerical methods, the CIP and the 3rd-order up-wind scheme, were compared. The computations for a Wigley hull in restricted waterways were performed and compared with experiments. The phenomena of ships waves in restricted waterways are discussed in order to understand the mechanism of wave-breaking in relation to the change in water depth along a waterway.     

Ductile crack initiation behavior in steels with compressive prestrain

It is well known that compressive prestrain reduces ductility in steels. On the other hand, it has also been found that high stress triaxiality reduces equivalent plastic strain at the onset of ductile fracture. In this research, plate specimens and notched bar specimens, which were prestrained in compression with bending, were used in reversed bending tests, and the effect of compressive prestrain on ductile crack initiation in steels was investigated. It was found that small ductile cracks occurred from the microscopic wrinkles which were formed on the concave surface with compressive prestrain. The critical relationship between stress triaxiality and equivalent plastic strain at ductile crack initiation was investigated by finite-element analysis. It was found that ductile crack initiation in steels with compressive prestrain can be estimated qualitatively by the relationship between stress triaxiality and equivalent plastic strain.     

Investigation of cavitation inception characteristics of hydrofoil sections via a viscous approach

Unlike traditional approaches based on potential theory, this work investigated the cavitation inception characteristics of hydrofoil sections by solving Reynolds-averaged Navier–Stokes (RANS) equations. The viscous effects at high Reynolds numbers were taken into account through calculation of the eddy viscosity using a k- model. This viscous approach delivers the lift and drag forces in a more self-contained way, which cannot be obtained directly from the potential theory. A comparison with smooth surface measurements validates the proposed numerical method. Two approaches to include the roughness effects are also described. The predictions of cavitation bucket characteristics based on potential theory are more conservative than those reached by the proposed viscous computations. Hydrofoil sections with different camber ratios, foil thicknesses, and Reynolds numbers were studied numerically. A decrease in the Reynolds number tends to increase the cavitation-free region without changing the shape of the steep region. An increase in foil thickness gives a range increase in the angle of attack where no cavitation is expected. An increase in the camber ratio moves the cavitation-free location of the angle of attack, and slightly increases its range.     

Ship resistance of quadramaran with various hull position configurations

Multihull ships are widely used for sea transportation, and those with four hulls are known as quadramarans. Hull position configurations of a quadramaran include the diamond, tetra, and slice. In general, multihull vessels traveling at high speeds have better hydrodynamic efficiency than monohull ships. This study aims to identify possible effects of various quadramaran hull position configurations on ship resistance for hull dimensions of 2 m length, 0.21 m breadth, and 0.045 m thickness. We conducted a towing test in which we varied the hull spacing and speed at Fr values between 0.08 and 0.62 and measured the total resistance using a load cell transducer. The experimental results reveal that the lowest total resistance was achieved with a diamond quadramaran configuration at Fr = 0.1-0.6 and an effective interference factor of up to 0.35 with S/L = 3/10 and R/L = 1/2 at Fr = 0.62.     

Elastic local buckling strength of stiffened plate considering plate/stiffener interaction and welding residual stress

An analytical formula for estimating elastic local buckling strength of a continuous stiffened plate subjected to biaxial thrust is derived considering the influence of plate/stiffener interaction and welding residual stresses. Through a comparison of calculated results with those by FEM eigenvalue analysis, high accuracy of the proposed formula is demonstrated. A series of buckling strength analyses is performed on the deck and bottom plating of actual ships. It has been found that:

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A simplified method for evaluating singular stress field and fatigue strength of U-shaped notch

In order to simplify the assessment method of notch stress and fatigue strength for cruciform welded structures in ocean engineering, a simple stress assessment formula based on singular strength values $a{s}_i$ and $b{s}_i$ was presented according to linear elastic fracture mechanics and notch stress strength theory. In view of the stress singularity caused by the V-notch, the stress of the corresponding U-notch was recommended and used for fatigue evaluation. Therefore, on the basis of V-notch stress formula, a simplified U-notch stress field evaluation formula was obtained by theoretical analysis and numerical calculation. After a series of verification, it is found that the stress distribution and fatigue strength evaluation formula for cruciform welded joints based on singular strength values proposed in this paper can simply and accurately predict the notch stress at welded joints. The result of fatigue strength evaluated by the simplified formula has a smaller scatter band.     

The rationality of conference pricing and output policies. Part 2

In Part 1 ^{* *}Maritime Studies and Management (1975) Vol 3, No. 2, pp. 103–111. of this article a background to the economics of conference operation was provided, and conference fleet planning and single voyage costs were discussed. This part of the paper will analyse the economic objectives of conferences and will consider the implications of ending the conference princing structure. Some recommendations are also offered.