Plastic mechanism analysis of structural performances for stiffeners on bottom longitudinal web girders during a shoal grounding accident

A theoretical model is introduced in this paper for structural performance of stiffeners on double-bottom longitudinal girders in a shoal grounding accident. Major emphasis is placed on establishing the characteristic deformation mechanism of stiffeners and identifying major energy dissipation patterns. Numerical simulations using the LS-DYNA nonlinear finite-element program were carried out to examine thoroughly the progressive deformation process during sliding deformation. Stiffener deformations were observed to fall into two categories: stiffeners fully contacted with the indenter, and stiffeners subjected to indirect deformation due to energy transfer from attached girders. Grounding performance of stiffeners is substantially influenced by that of the attached plating, and therefore a review of the existing deformation models of longitudinal girders (i.e. Simonsen 1997, Midtun 2006 and Hong 2008) was included. Hong's model of bottom girders was found not capable of representing the effects of stiffeners, and a new model of girders was thus developed. Based on observation of the numerical deformation process and the new analytical girder model, a kinematically admissible model of stiffeners on bottom longitudinal girders was built. Using the methods of plastic mechanism analysis, simplified analytical expressions for energy dissipation by girder-attached stiffeners, both fully contacted and noncontacted, were formulated, and equations for grounding resistance were subsequently obtained. The theoretical expressions agree favorably with results from nonlinear finite-element simulations and capture two significant characteristics of the problem: that energy varies little with indentation for stiffeners that fully contacting the indenter, and that energy is independent of slope angle for indirectly deformed stiffeners. The proposed theoretical model helps to predict analytically shoal grounding performance of stiffeners on longitudinal girders with reasonable accuracy.     

同步建设构皮滩水电站通航设施促进乌江综合开发利用

阐述乌江航运的重要地位和作用,全面分析缓建通航设施对经济发展造成的不利影响,呼吁同步建设通航设施,促进河流综合开发利用。     

三峡工程变动回水区上洛碛滩航道整治

分析川江上洛碛滩滩险特性、碍航原因及三峡水库分别按156m和175m蓄水位运行时期该滩的滩势变化,并根据实测资料分析本整治工程(156m蓄水位运行期)的效果。     

长江下游安庆港及其航道泥沙沉积原因的分析

安庆河道位于长江下游，长度50km。安庆港位于安庆河道北岸。从1880年至1984年，长达23．2km的安庆港岸线很稳定，岸线平均水深大于9．6m，安庆水道平均水深大于13．9m，成为长江中下游天然深水港。1984年以来，安庆港被泥沙沉积，安庆水道因江心洲浅滩的沉积趋向恶化，在枯水期安庆港西区和江心洲浅滩的水深分别小于4m和3．6m，影响航运。本文根据地理调查，近120年航行图的比较，对航道水深的测量，对官洲河岸整治、封堵汉道、采砂作了评述，着重研究了1984年以来安庆河道主流线变化和安庆港与江心洲浅滩的沉积。这些研究成果对安庆港及其航道治理和长江中下游港口与航道建设均有重要的参考价值。     

多因素数学模型在温州瓯江口浅滩围涂工程研究中的应用

建立了波浪、潮流、盐度、悬沙、底床冲淤等多种因素数学模型,在模型验证的基础上,对瓯江口温州浅滩围涂工程海区的波浪场、潮流场、盐度场、悬沙场、底床冲淤场进行了数值模拟研究,对温州浅滩围涂工程对瓯江泄洪、瓯江南北口分流比、乐清湾养殖业、瓯江口港口航道及状元岙深水区、南口口外滩地的影响进行了分析论证。分析研究结果表明,温州浅滩围涂工程是可行的。     

硬式扫床在松花江三姓浅滩二期航道整治工程中的应用

通过对松花江三姓浅滩的整治,详细介绍目前黑龙江航道局所使用的硬式扫床器的结构型式、工作原理、实施步骤及扫床工作定位方法等。     

红水河峡龙滩航道整治工程及效果

分析了红水河峡龙滩滩险特性、碍航原因,并介绍了整治工程方案及其整治效果。     

Investigation on structural performance predictions of double-bottom tankers during shoal grounding accidents

An investigation is carried out in this paper for the predictions of structural performance of double-bottom tankers during ship grounding over the “shoal” type seabed obstacles. Hong and Amdahl developed a simplified analytical model for the unstiffened double bottom. This method is carefully studied, verified and then used as the first stage of our prediction. The second stage is concerned with stiffeners since stiffeners are indispensable components for double-bottom tankers. A prevailing way to handle is to smear stiffeners onto their attached plating known as the smeared thickness method. However, the effective ratio in this method is dubious in such shoal grounding accidents. Proper values of this parameter are determined in stage two, and then together with the method in stage one, constitute a reliable and efficient tool for structural performance predictions of double-bottom structures in shoal grounding accidents.A double-bottom tanker is chosen as object for the case study. Finite element models of the hold both stiffened and unstiffened are created for numerical simulations using the LS_DYNA software. Simulation cases cover a wide range of slope angles of the indenter and indentations. Numerical results show that Hong and Amdahl's model in stage one is capable of predicting energy dissipation with high precision but poor accuracy for grounding resistances, and a possible reason may be the neglect of vertical resistance. The updated smeared method proposed in stage two is also proved to be capable of grasping major characteristics of stiffeners. Results and conclusions drawn from this paper can be conveniently applied for assessments of the performance of ship double-bottom structures during shoal sliding grounding scenarios, and will benefit the application of accidental limit state design concept in the ship design stage.     

江苏如东人工岛建设对周边水动力及泥沙冲淤的影响

在南黄海辐射沙洲这样一个水动力和泥沙环境都相当复杂的区域建设浅水人工岛,不仅要考虑人工岛本身的稳定型问题,还要深入地认识浅水人工岛建设引起的流场和泥沙冲淤是否造成目前潮流动力场和"水道—沙洲"系统格局的较大变异、自然演变的趋势性过程是否因人工岛建设而加速或逆转。通过整体潮流泥沙物理模型研究了西太阳沙人工岛工程对滩槽演变趋势的影响和工程区滩冲槽淤的短期波动,探讨了如东人工岛工程建设后,岛周围水动力和泥砂冲淤的变化规律,提出了相应的防冲措施。结果表明,拟建人工岛工程建设引起的水流动力变化主要在西太阳沙附近的浅水区,并局限在1.5倍人工岛直径范围内,对邻近水道深槽区的潮流动力没有影响。人工岛工程没有改变西太阳沙周边各水道潮流动力场格局,没有引致水道间潮流动力此消彼长的变化、未改变控制西太阳沙"水道-沙洲"系统演变的动力泥沙环境,西太阳沙核心部位的稳定主要取决于西太阳沙北侧潮流动力增强的自然演变过程。就人工岛建设而言,东北岛壁前沿有效的防冲护底措施对沙洲核心部位稳定和减少北水道深槽淤积泥沙来源均有积极意义。     

从河床演变观点评荆江碾子湾河道的整治

长江下荆江河段的碾子湾河道长度只有２８ｋｍ,分布着严重碍航的碾子湾浅滩,藕池口浅滩,石首锐弯与被泥沙沉积的石首港。１９８０年以来碾子湾河道发生严重的侵蚀与沉积。１９９５年２月至３月因碾子湾浅滩严重沉积使航道恶化,断航达２９天,约５００多艘江轮与６万多名旅客相继滞留在碾子湾河道上,在长江中游近代航运史上实属罕见。本文从近４０多年来碾子湾的河床演变和鱼尾洲护岸工程角度评述碾子湾道与石首港恶化的原因,这