大渡河桥隧道锚力学响应研究及承载力判定

隧道锚作为悬索桥锚碇形式的一种,具有工程量小、承载力大和对周边环境影响小的特点。为探究大渡河特大桥雅安岸隧道锚在巨大缆力作用下的力学响应规律和预测隧道锚极限承载能力,建立了大型非线性数值模拟模型,系统、细致地监测了施加缆力前后锚塞体单元主应力,锚塞体与围岩的相对位移,以及锚塞体整体位移以及锚塞体后端面的塑性区随缆力施加的变化趋势,并提出了一种基于锚塞体整体位移和锚塞体后端面塑性区的预测隧道锚极限承载能力的分析方法。最终得出施加缆力后,锚塞体最大主应力由大变小,最小主应力绝对值由小变大的力学规律,并通过超缆力分析预测大渡河特大桥隧道锚的极限承载力为7倍缆力。

开敞式液化天然气泊位平面布置优化

以唐山港曹妃甸港区某液化天然气码头为工程实例,结合工程区域风况、潮流、波浪等自然条件,采用物理模型试验和数值计算相结合的方式,对开敞水域液化天然气码头的码头走向、泊位长度、系缆墩布置进行优化设计,确定最优总平面布置形式。成果可为类似项目提供借鉴。

Dynamics analysis of planar armored cable motion in deep-sea ROV system

The armored cable used in a deep-sea remotely operated vehicle(ROV) may undergo large displacement motion when subjected to dynamic actions of ship heave motion and ocean current. A novel geometrically exact finite element model for two-dimensional dynamic analysis of armored cable is presented. This model accounts for the geometric nonlinearities of large displacement of the armored cable, and effects of axial load and bending stiffness. The governing equations are derived by consistent linearization and finite element discretization of the total weak form of the armored cable system, and solved by the Newmark time integration method. To make the solution procedure avoid falling into the local extreme points, a simple adaptive stepping strategy is proposed. The presented model is validated via actual measured data. Results for dynamic configurations, motion and tension of both ends of the armored cable, and resonance-zone are presented for two numerical cases, including the dynamic analysis under the case of only ship heave motion and the case of joint action of ship heave motion and ocean current. The dynamics analysis can provide important reference for the design or product selection of the armored cable in a deep-sea ROV system so as to improve the safety of its marine operation under the sea state of 4 or above.

Probabilistic Analysis and Fatigue Damage Assessment of Offshore Mooring System due to Non-Gaussian Bimodal Tension Processes

Both wave-frequency(WF) and low-frequency(LF) components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system.This paper conducts a comprehensive investigation of applicable probability density functions(PDFs) of mooring tension amplitudes used to assess mooring-line fatigue damage via the spectral method.Short-term statistical characteristics of mooring-line tension responses are firstly investigated,in which the discrepancy arising from Gaussian approximation is revealed by comparing kurtosis and skewness coefficients.Several distribution functions based on present analytical spectral methods are selected to express the statistical distribution of the mooring-line tension amplitudes.Results indicate that the Gamma-type distribution and a linear combination of Dirlik and Tovo-Benasciutti formulas are suitable for separate WF and LF mooring tension components.A novel parametric method based on nonlinear transformations and stochastic optimization is then proposed to increase the effectiveness of mooring-line fatigue assessment due to non-Gaussian bimodal tension responses.Using time domain simulation as a benchmark,its accuracy is further validated using a numerical case study of a moored semi-submersible platform.

Determination Method on Initial Pretension of Cables in Steel Mega Frame and Prestressed Composite Bracing Structure

Determining initial pretension values of pre-stressed cables is one of the key problems for a steel mega frame and pre-stressed composite bracing structure.Through the mechanical analysis of the composite bracing under vertical loading,the critical factors deciding the initial pretention value were found.According to these factors,a rule for the initial pretension value was put forward.The determination equations were acquired based on the principle of force equilibrium at nodes.The numerical results indicate that the internal force disequilibrium in composite bracings resulted from symmetrical load can be eliminated only in a symmetrical way,so that initial pretention values are decided only by vertical loads.The influencing coefficient leveling method,taking into account interactions between story and story,is accurate and feasible.

Thermal Analysis of Underground Power Cable System

The paper presents the application of Finite Element Method in thermal analysis of underground power cable system. The computations were performed for power cables buried in-line in the ground at a depth of 2 meters. The developed mathematical model allows determining the two-dimensional temperature distribution in the soil, thermal backfill and power cables. The simulations studied the effect of soil and cable backfill thermal conductivity on the maximum temperature of the cable conductor. Also, the effect of cable diameter on the temperature of cable core was studied. Numerical analyses were performed based on a program written in MATLAB.