波流共同作用下泥沙扩散系数沿垂线分布的探讨

为了计算波流共同作用下含沙量沿垂线的分布,建立了沿垂线分布的泥沙扩散系数模型。通过悬沙模型反求泥沙扩散系数的方法来拟合系数。实测资料表明该模型可以比较准确地直接计算泥沙扩散系数沿垂线的分布。     

基于计算流体动力学的流量系数研究

为了研究某液压装置中节流阀的流量系数与孔口雷诺数之间的关系,该文利用计算流体动力学软件FLUENT,构造结构化网格,采用层流模型或标准湍动能-湍动能耗散率(k-ε)模型,对节流阀内部层流或紊流流动进行数值模拟.经过对不同孔口雷诺数工况的数值模拟计算发现:节流阀流量系数与孔口雷诺数关系比较符合文献[7]中提出的短孔流量系数的计算公式,表明了文中提出的基于计算流体动力学的数值模拟是可行的.     

混凝土成熟度和氯离子扩散系数的相关性及在某工程中的应用

采用化学结合水法、氯离子快速测定法（RCM法）和混凝土成熟度测定法研究了56 d龄期内混凝土氯离子扩散系数和混凝土成熟度的关系。结果表明：混凝土氯离子扩散系数不仅随养护龄期的延长而降低,还随养护温度的升高而降低,延长养护龄期或提高养护温度均可提高胶凝材料的水化程度;室内养护混凝土试件的氯离子扩散系数与混凝土成熟度值之间呈幂函数关系,二者具有很好的相关性（R2=0.976）,利用室外养护混凝土试件的数据进行验证计算,其理论计算值与实测值具有较好的吻合性,可根据混凝土成熟度实测值预测出混凝土的氯离子扩散系数;在本工程中,沉管隧道接触海水时混凝土成熟度的推荐值为21064℃·h,控制边界值为13926℃·h,考虑外部养护温度和水化热对混凝土成熟度产生影响时,可对混凝土接触海水的龄期通过后计算进行适当的调整。     

基于海洋暴露试验的氯离子扩散系数时空模型研究

在我国腐蚀条件最为恶劣的海南八所港,对3种配合比的混凝土试件进行实海暴露试验,通过测定浪溅区条件下氯离子在混凝土中侵入量,研究氯离子有效扩散系数随时间和深度的演变,为准确预测混凝土结构的使用寿命提供参考。     

海洋环境下港口工程混凝土界面过渡区氯离子扩散系数模型

通过现场暴露物理试验,实测得到了港口工程混凝土及相对应的水泥砂浆试件中氯离子的浓度分布结果,经回归分析分别得到了这两种试件的氯离子扩散系数。以此为基础,定量评估了粗骨料的稀释、曲折和界面过渡区效应对混凝土中氯离子扩散系数的影响,并建立了混凝土界面过渡区氯离子扩散系数模型。基于混凝土中氯离子扩散的细观数值模拟方法,验证了所建立的混凝土界面过渡区氯离子扩散系数模型的正确性。对细观数值模拟结果的分析可知:界面过渡区对混凝土中仅考虑粗骨料的稀释和曲折效应的氯离子扩散系数的提升效应不可忽略,应充分考虑界面过渡区的存在对混凝土中氯离子浓度分布和扩散特性的影响。     

系泊船舶在横浪作用下撞击能量计算参数C_m取值研究

船舶附加水体质量系数C_m的取值对计算系泊船舶在横浪作用下的撞击能量具有十分重要的影响,目前国内外相关文献对该参数取值差异较大,且国内水运行业规范的参数取值偏小,给结构安全带来一定隐患。经过对取值规定的比较,并参照计算公式、结合工程实例分析计算结果,得知国内现行规范C_m的取值明显小于国内外相关规范和研究报告的取值。建议20万吨级以上船舶增大C_m取值为1.7~2.0。     

系泊船舶在横浪作用下撞击能量计算参数Cm 取值研究

船舶附加水体质量系数Cm的取值对计算系泊船舶在横浪作用下的撞击能量具有十分重要的影响,目前国内外相关文献对该参数取值差异较大,且国内水运行业规范的参数取值偏小,给结构安全带来一定隐患。经过对取值规定的比较,并参照计算公式、结合工程实例分析计算结果,得知国内现行规范Cm的取值明显小于国内外相关规范和研究报告的取值。建议20万吨级以上船舶增大Cm取值为1.7～2.0。     

Numerical simulations of fatigue crack initiation and propagation based on re-tensile plastic zone generating load criterion for in-plane gusset welded joints

Many accidents are caused by fatigue in welded built-up steel structures, and so it is important to estimate the fatigue lives of such structures quantitatively for safety reasons. By assuming that fatigue cracks cannot grow without an accumulation of alternating tensile/compressional plastic strain, one of the authors identified an improved effective stress intensity factor range ΔK _RPG based on the re-tensile plastic zone generating (RPG) load, which represents the driving force for fatigue cracks, and suggested that ΔK _RPG should be used as the parameter to describe fatigue crack growth behavior. The “FLARP” numerical simulation code in which ΔK _RPG is implemented as the fatigue crack growth parameter, was developed in order to predict fatigue crack initiation and propagation behavior. In this paper, it is demonstrated that FLARP gives accurate estimates for fatigue life by comparing the estimated fatigue crack growth curves and S–N curves with the experimental results for in-plane gusset welded joints, which are used in many welded steel structures. Moreover, the effect of induced bending moment due to the linear misalignment in the out of plane direction on the fatigue strength of in-plane gusset welded joints is investigated through numerical simulations.     

循环水槽隔板设计与水槽倾斜研究

  目的  风洞和循环水槽是很重要的流体力学试验设备。为高效地形成风洞或循环水槽的气动力学/水动力学设计方案,开发了基于CFD的风洞循环水槽设计系统程序。  方法  该程序集实体三维建模、网格自动生成、黏性流场求解及CFD计算后处理结果输出等功能于一身,在操作流程上实现从初始参数录入到优化目标参数输出一键操作的设想,用自动化的程序节省修改模型和网格过程所花费的人力和时间成本。通过参考上海交通大学风洞循环水槽对程序进行校验。  结果  结果表明,该软件在风洞的设计及性能预报方面具有很好的可信度和便捷性。  结论  该程序具有一定的理论方法创新和较高的工程应用价值。     

The dynamics of deep water subsea lifting operations in super-harmonic resonance via the harmonic balance method

The dynamics of deep water subsea lifting operations experiencing super-harmonic resonance is analysed in this study. The harmonic balance method is used to solve the non-dimensional equation of motion of the system and the results are compared with time domain integration and with an equivalent energy dissipation model for typical subsea lifting scenarios. It is demonstrated that 1:3 and 1:5 super-harmonic resonances represent significant features of the response of the system and can lead to large dynamic forces in the cable, which may violate the structural limits of the system in real operations. The harmonic balance method presents results almost as accurate as the time domain integration but up to 25 to 35 times faster, while the equivalent energy dissipation model is not able to represent the super-harmonic resonances. Consequently, taking into account the dynamics introduced by super-harmonic resonances is necessary in the analysis of subsea lifting operations, as it can be the limiting design criterion in certain scenarios, and the harmonic balance method can be used as a fast and accurate method to solve this problem.     

Research on the coefficient of sound absorption in turbid water

China’s coastal waters are turbid and the properties of the seabed are complex. This negatively impacts the performance of underwater detection equipment. The properties of sound absorption in turbid water are not well understood. In this paper, the coefficient of sound absorption in turbid water was measured by the reverberation technique. All work was done in a reverberation barrel made of seamless aluminum. First, pure water was poured into the reverberation barrel and its reverberation time measured. Next, various concentrations of turbid water were poured into the barrel and their reverberation time measured. After all data had been gathered, the coefficient of sound absorption in turbid water of different concentrations was calculated. From this we determined a law of sound absorption in turbid water as summarized in the paper.     

Effects of adhesive type on the mechanical properties of adhesive joints between polyurethane top coats and polyurethane-based adhesives after accelerated atmospheric ageing

The performance of a sealed stainless steel bracket system, adhesively bonded with two polyurethane-based adhesives (flexible adhesive, stiff adhesive) onto a marine polyurethane top coat, is investigated. The investigated joint connections on the coatings exhibited a high mechanical stability even after accelerated ageing (salt spray exposure, cyclic temperature variations, high relative humidity). The aged joints retained up to 81% of their tensile strength and up to 92% of their lap-shear strength. The torsional rigidity of the adhesive joint exceeded the required clamping torque of the designed bolt. A cyclical lifetime of >9·10⁶ load cycles was estimated. Effects of cyclic ageing on the creep performance of the adhesive joint were found to be insignificant. Under tensile loads, the joints with stiff adhesive material exhibited a linear-elastic performance without the capability to deform prior to failure. The joints with the flexible adhesive material, in contrast, exhibited a behavior typically for ductile materials featuring a pronounced yield plateau prior to failure. Failure loads were higher, and displacement was notably lower, for the joints with stiff adhesive material. All joint connections met the requirements for a safety factor for the design for marine applications (11.6 for the flexible adhesive; 14.3 for the stiff adhesive). When the flexible adhesive is applied, the cohesive strength of the adhesive material is the limiting design factor. When the stiff adhesive is utilized, the load carrying capacity is higher, and the interface between priming coat and steel substrate is the limiting design area of the joints. The strength utilization of the adhesive materials depended on the particular structure of the entire joint configuration, particularly on the interface between steel substrate and the coating material. A number of assessment factors, namely stress limit factor, coating adhesion factor and safety factor, are introduced and discussed for tensile and shear loads.     

Evidence of double diffusion in the East China Sea

Double diffusion is an important phenomenon induced by the difference between the thermal conducting coefficient of the molecule and haline diffusive coefficient. Warm, salty water overlying cold, fresh water induces salt finger. On the contrary, when cold, fresh water overlies warm, salty water, diffusive convection occurs. In the East China Sea, double diffusion was observed during a cruise in September 2003. In order to describe the phenomenon precisely, Turner (TU) angle values are calculated station by station at Section YT. TU angle is a practical tool to indicate the water states. Different TU angle values represent salt finger, diffusive convection and stable stratification respectively. We map the distributions of the two forms of double diffusion at Section YT, and determine that the physical mechanism of the phenomenon is the mixing of water masses. The Changjiang Diluted Water (CDW) has great effect on the mixing of water masses, and the Kuroshio Water System dominates on the continental slope. Temperature and salinity varied in a manner consistent with double diffusion.     

极地船舶冰带区域关键节点研究

随着极地探索的不断发展,针对冰区航线的船体结构设计不再局限于传统的经验公式方法,人们更加关注作用于结构上的实际冰载荷及结构响应,研究冰载荷作用下的结构响应计算成为极地船舶结构设计中的关键部分。

首先,通过有限元方法对某极地航行船舶遭遇的碎冰、浮冰、层冰等冰载荷工况进行数值仿真,考虑材料应变率影响,计算冰载荷作用下的结构动态响应;然后,以结构响应等效为基准,进行动态响应的静态转换,并提出动静转化系数的概念;最后,给出不同冰载荷工况下动静转化系数的取值范围。

结果表明,船首结构在不同工况下动载荷响应的静载荷等效转换计算的转换系数为1.0～1.4之间。

船首结构冰致动力响应的准静态等效方法是合理可行的。

     

漫滩水流动量修正系数特性分析与模拟

以明渠深度平均二维水流模型为基础,研究了漫滩水流的动量修正系数.结果表明,漫滩瞬时动量修正系数迅速增大,随后快速减小;滩槽宽度比越大,动量修正系数变化程度越大,而传统断面平均法的计算结果恒为1,与实际情况存在较大差异,不能用于水流漫滩的模拟.为了反映动量修正系数的实际变化规律,提出了水流漫滩时断面动量修正系数新的计算方...     

Van der Meer公式中渗透系数P的研究进展及应用

在抛石斜坡堤的设计中,国际规范普遍采用Van der Meer公式对斜坡堤护面块石的稳定质量进行计算。该公式对渗透系数P的取值,根据堤心、倒滤层、护面层的不同配置给出了4种标准情形下的推荐值,分别为P=0.1、P=0.4、P=0.5和P=0.6。在工程实践中,斜坡堤并不完全符合任何一种标准情形,往往表现为两种标准情形的中间形态,尤其是对堤心砂设置倒滤层并铺设土工布的情况。介绍了Van der Meer对渗透系数的研究和近年来的研究进展,并将研究成果应用到工程实例中,可为海外类似工程的设计提供一定的借鉴。     

焊接温度场中复合换热系数的分析

在焊接温度场的模拟中,换热系数与焊件的冷却过程密切相关.根据传热学的相似理论,计算随时间变化的对流和辐射系数,将其转换为复合换热系数,实时地加入到温度场的计算过程中去,模拟得到焊件在空气中自然冷却时的温度场.与采用恒定换热系数得到的结果比较,文中提出的确定和施加换热系数的方法更为合理.     

水平力在高桩码头排架中的分配系数研究

利用ANSYS有限元结构分析软件对水平力在高桩码头排架中的分配系数进行研究,着重研究纵向排架间距和排架数量对分配系数的影响。分别选取5跨、6跨、7跨、8跨、9跨和10跨6种结构段,6m,7 m,8 m,9 m和10 m共5种间距情况进行建模计算与分析。结果表明,在计算实例条件下,纵向排架间距的变化对水平力在高桩码头排架中的分配系数影响较小,最大为4.93%,而分段跨数的影响则很大,最大达49.6%。对最不利排架的水平力分配系数与现行规范中的取值进行对比分析,根据分析结果对跨数多、排架间距大的大型码头的结构分析方法提出合理化建议。     

船舶碰撞运动的滞后特性

  目的  采用解析方法分析船舶碰撞动力特性较为快速和准确,其中外部动力学分析十分重要。  方法  为此,运用MATLAB程序实现船舶碰撞外部机理三维简化解析方法,计算两艘船舶碰撞的动能损失,并与二维解析方法的计算结果进行比对。在实现船舶碰撞动能损失快速计算解析方法的基础上,讨论碰撞高度、角度和位置对动能损失的影响。此外,还研究碰撞场景对保守恢复系数的影响和保守恢复系数对动能损失的影响。  结果  结果表明：三维解析方法得到的动能损失小于二维解析方法,碰撞高度对于动能损失有明显的影响;简化解析方法中,对于碰撞角度大于90°的场景,恢复系数简单地取0并不安全。  结论  在今后的外部动力学分析中,为了使动能损失的计算值更加准确,可以使用三维解析方法代替二维解析方法。     

华南地区两个码头海工混凝土结构耐久性调查

本文通过对深圳地区某码头和汕头地区某码头的结构调查,开展混凝土结构的耐久性调查与检测,为掌握混凝土耐久性有关参数的取值与变化规律提供参考。