海洋电缆弯曲加强器参数化设计与分析

为建立海洋电缆弯曲加强器参数化设计方法,使用有限元模型进行了弯曲加强器设计参数研究.基于海缆及其弯曲加强器的几何结构及受力特点,建立了基于多相耦合梁单元的平面有限元模型,可以计算并分析海缆及其弯曲加强器在一定角度的张力作用下的形变与等效应力分布.通过多个案例系统性地分析了弯曲加强器的主要设计参数,即根部直径、锥体段长度及材料弹性模量,对海缆弯曲挠度、曲率及等效应力分布的影响.文中原创性地提出了弯曲加强器组合设计参数φ(t,L,E).通过定量分析确定了其与海缆最大曲率之间的近似线性关系,并由此设计了参数化的弯曲加强器设计流程.通过设计实例验证了组合参数与海缆最大曲率之间关系的准确性和参数化设计流程的有效性.     

深海刚性跨接管弯管强度关键影响因素研究

深海刚性跨接管是水下生产系统的关键设备,其弯管处易因应力集中导致结构失效。依照理论与规范,并结合工程实例,通过数值模拟分析对影响跨接管弯管强度的关键因素进行研究,并对各影响因素展开敏感性分析。结果表明:跨接管结构形式是影响弯管强度的主要设计因素(M型跨接管可有效降低弯管的结构应力),弯管曲率半径影响较小;管道端部位移是影响弯管强度的主要载荷因素(重点分析此因素在不同方向的敏感性,发现轴向端部位移的影响最大);而工作温度对管道强度的影响很小。     

海洋沉积物中汞的释放通量及热力学研究

以胶州湾海泊河口和李村河口为对象,研究了其沉积物中的汞向海水的释放.结果表明,在静态条件下,沉积物汞向海水释放,平衡时海泊河口和李村河口沉积物汞的释放量分别为 0.070 5 ～ 0.117 μg/g 和 0.056 5 ～ 0.093 5 μg/g;汞的释放通量在前 2 h 最大,随后逐渐减小,通量与温度呈指数正相关.通过对汞释放的热力学分析,汞释放的反应热大于零,分别为 9.92 kJ·mol-1 和 9.98 kJ·mol-1,说明汞的释放是一个吸热过程;汞的释放是一个熵增过程;两个实验反应的标准自由能变分别为 2.34 ～ 3.22 kJ·mol-1和 1.19 ～ 2.20 kJ·mol-1,而且温度越高,ΔG0 越小,越利于反应向正方向进行.     

南四湖消落带底泥磷形态分布特征、影响因素及释放风险

南四湖是南水北调东线最大的调蓄湖泊,周期性水位涨落会形成大面积消落带,认知消落带底泥磷形态赋存特征、影响因素及释放潜能,对于保障东线调水水质具有重要的科学意义.本研究分析了南四湖消落带底泥磷形态分布特征,探讨了各形态磷与土地利用、母质类型及底泥理化因素之间的关系,评价了南四湖消落带底泥磷的污染程度并分析了其释放风险.结果发现,消落带底泥中总磷(TP)、无机磷(IP)、NaOH提取态磷(NaOH-P)、HCl提取态磷(HCl-P)和有机磷(OP)含量的平均值分别为745.37、510.51、50.42、460.09和234.86 mg/kg,以HCl-P为主的IP占比较高.南四湖消落带底泥各形态磷含量具有较高的空间异质性,TP、IP、OP、HCl-P和NaOH-P含量的变异系数分别为30.7%、36.9%、29.6%、37.6%和51.2%.自然湿地、乔木林地和水浇地等土地利用方式下的底泥NaOH-P、HCl-P、IP、OP和TP含量差异不显著.土壤类型对消落带底泥OP含量影响明显,但对TP、IP、NaOH-P和HCl-P含量则影响不大.NaOH-P含量与HCl-P含量具有显著正相关,与...     

环境因子对萱藻(Scytosiphon lomentaria)丝状体孢子放散的影响

在实验室条件下,以本实验室保存的萱藻丝状体为材料,研究了温度(7—27℃),光照强度[18—126μmol/(m2.s)]和丝状体生物量(0.1—1.6mg/ml)对萱藻孢子放散的影响。结果显示:(1)温度为12℃最适宜萱藻孢子的放散,在此温度下,孢子放散量大,放散速度快;(2)光照强度对孢子的放散具有重要影响,72μmol/(m2.s)为刺激萱藻孢子放散的最佳光照条件;(3)萱藻丝状体生物量过低,则孢子放散量较小无法达到采苗要求,而过高亦会抑制孢子的放散,生物量为0.8mg/ml时最适宜孢子的放散。     

Influence of experimental removal of large woody debris on spatial patterns of three‐dimensional flow in a meander bend

This study reports the results of a large woody debris (LWD) removal experiment in a meander bend along a low‐energy stream in the Midwestern United States. The LWD obstacle was located in the center of the channel at the bend exit and consisted of a mature tree with an intact soil‐covered root wad and a large accumulation of logs, branches and pieces of lumber on top of and adjacent to the main tree. The results indicate that the LWD obstruction influenced 3D flow structure in this bend at all flow stages. The main effect of LWD is to dramatically decelerate flow throughout the majority of the bend, while locally accelerating flow where it passes through the narrow chute at the downstream end of the LWD obstruction. Results from the LWD removal experiment indicate that patterns of three‐dimensional flow structure in meander bends are sensitive to complete removal of LWD. After the removal of LWD from the bend, both downstream and secondary velocities increased and, though still weak, secondary flow intensified. Large, relatively stable, obstructions that span a significant portion of the channel may act as natural dams, effectively ponding water upstream of the LWD, thereby producing substantial convective deceleration of the flow. This research is the first to document three‐dimensional flow structure before and after a controlled removal of LWD from a meander bend. Studies of the type reported here represent a first step toward determining the ensemble of process interactions between LWD and bend dynamics. Copyright © 2006 John Wiley & Sons, Ltd.     

Initiation of the San Jacinto Fault and its Interaction with the San Andreas Fault: Insights from Geodynamic Modeling

The San Andreas Fault (SAF) is the Pacific-North American plate boundary, yet in southern California a significant portion of the relative plate motion is accommodated by the San Jacinto Fault (SJF). Here we investigate the initiation of the SJF and its interaction with the SAF in a three-dimensional visco-elasto-plastic finite-element model. The model results show that the restraining bend of the southern SAF causes strain localization along the SJF, thus may have contributed to its initiation. Slip on the SJF tends to reduce slip rate on the SAF and enhance deformation in the Eastern California Shear Zone. The initiation of the SJF and its interaction with the SAF reflect the evolving plate boundary zone as it continuously seeks the most efficient way to accommodate the relative plate motion.     

Dynamic simulation for tempo-spatial distribution of strain energy density in inhomogeneous stratified crust

IntroductionRupturetheorybasedonenergyconceptdisplaysthatstrainenergyanditsvariationinrockistheinvestigationrelevanttothebehaviorofrockdeformationandfracture.Itisoneofthemostimportantcriteriatodeterminethefractureposition,rupturingcondition,fracturedirectionaswellasrupturingscale.Therefore,toresearchonenergyfieldsofstrongearthquakes(focushasgreattheoreticalsignificancebothinunderstandingtheenergystateanditsvariationinthefocalarea,andincarryingoutexplicitpredictionforthetime,thelocationandthema…     

超大断面铁路隧道施工断面综合荷载释放过程研究

隧道开挖扰动会使影响范围内的围岩发生松弛,同时还产生一定的荷载作用于隧道结构。而在隧道开挖面推进时,作用于隧道结构上的荷载在应力调整过程中不断释放,最终在隧道结构及围岩达到稳定状态后荷载释放过程同时结束。通过数值分析及模型试验,对超大断面铁路隧道施时的隧道断面整体荷载释放过程进行了相关研究。研究了台阶法开挖过程中隧道洞壁不同特征点的荷载变化规律,并定义了能够表征隧道施工过程断面整体荷载释放状态的断面综合荷载释放率和荷载释放差异系数的概念,通过两者对隧道开挖断面整体荷载释放状态进行分析总结。在随后进行的隧道施工过程地质力学模型试验中,通过对开挖面推进洞壁不同位置围岩径向压力的变化规律进行监测,证明了数值模拟得到的结论,并进一步说明在隧道开挖的荷载释放过程研究中,应将整个断面作为研究对象,分析断面整体荷载释放状态,才能对隧道施工中的荷载释放过程有一个更加全面的认识。     

过渡段对连续弯道水流影响的数值模拟

通过分析不同长度的过渡段对连接连续弯曲河道后弯水流的影响,探讨航道整治工程设计中过渡段长度的确定依据。在模型试验资料验证的基础上,采用RNG k-ε湍流模型和VOF方法处理自由水面的水气两相流数学模型,对连续弯道水流进行模拟计算。对比不同过渡段长度条件下后弯水流特征的变化情况,发现增加过渡段长度可以减弱前弯对后弯水流的影响。当相对过渡段长度大于一定数值后,后弯的特征水流情况保持稳定,增加过渡段长度所引起的减弱前弯水流对后弯水流影响的效应基本丧失。以后弯水流条件趋于稳定为特征定义临界过渡段长度,可作为航道尺度设计中过渡段长度取值的计算基础。