影响电缆故障测试仪测试准确性的因素分析

电缆是信号设备的重要组成部分,XK2001型电缆故障智能测试仪是一套综合性的电缆故障探测仪,能对电缆的短路和电缆的断线、接触不良等故障进行测试。运用中,调整波速是测试的关键。     

大开口型船舶在不规则波中的波浪扭矩预报分析

综述了现有船舶波浪扭矩的计算分析方法，用STF切片理论方法计算了大开口船舶波浪扭矩的传递函数。根据不同波谱理论模型对不规则波中的扭矩作了统计预报，讨论了波浪扭矩予报对波谱的敏感性。研究结果表明，波浪扭矩对波谱谱型的依赖程度相当大；特征波浪周期对统计值的影响比有义波高大；对相同有义波高，PM谱相应的预报值比ITTC二参数谱的结果更偏于保守。     

水面舰船迎浪航行时大幅运动预报的切片算法

将预报船舶运动和波浪载荷的切片理论加以扩展，应用于有限深水中船舶迎浪航行时大幅纵向运动和波浪载荷的时域求解。预报结果体现出考虑了湿表面及化后引起的船舶运动和受力的非线性性质。本计算方法简便、实用，适用于船舶纵向大幅运动预报。     

隧道含水断层破碎带的探测与治理

以泉三高速公路三阳隧道含水断层为例,对比瑞利波、地质雷达和钻探三种探测技术及其探测成果,阐明瑞利波探测技术探测公路施工隧道含水断层破碎带具有探测精度高、受探测环境干扰小的优点,并论述了采用注浆方法治理该含水断层破碎带的技术。     

Experimental study on dynamic response of a floating offshore wind turbine under various freak wave profiles

This study performed experimental investigation on the dynamic response of an in-place floating offshore wind turbine (FOWT) under freak wave actions. Based on the method of wave profile modulation, various freak wave profiles embedded in unidirectional Gaussian seas were generated in wave basin and the action of these waves on the FOWT was measured and analyzed, which has not been done before. The motions of FOWT were analyzed in time domain as well as time-frequency domain. The effect of freak wave parameters on FOWT motions was addressed, i.e., freak wave height, freak wave period, large crest, and deep trough. The dynamic response of FOWT was observed as a spike at the occurrence of freak wave in a conventional random wave, where the impact of freak wave can last for 17 spectral peak periods of wave. Data analysis shows that the motions of FOWT increased linearly with the freak wave height. In addition, the occurrence of freak wave induced the coupled effect on surge and pith, which was strengthen with the increase of freak wave height and wave period. Compared to a large crest, a deep trough of freak wave led to stronger motions and was supposed to be a key concern on the safety of the FOWT. The novel findings in this study provided a reference for the design of survival load on a FOWT and benchmarks for validating numerical models.     

Wave spectrum estimation conditioned on machine learning-based output using the wave buoy analogy

In this work, a hybrid approach for wave spectrum estimation is proposed. Fundamentally, the approach is based on the wave buoy analogy, processing ship response measurements, via a framework combining machine learning and a physics-based method dependent on available transfer functions. Specifically, a non-parametric (Bayesian) estimate is obtained of the directional wave spectrum conditioned on integral wave parameters established by a convolutional neural network. The developed method is assessed in a case study considering about two years of data obtained from an in-service container ship. The method produces good results, significantly improved when compared to the initial estimate made without constraints.     

Sea trials of Sigma wave energy converter – slacking and snapping of TLP mooring lines

Sigma Energy has performed its foremost prototype tests of scaled wave energy converter in a real sea environment. The prototype was a point absorber with a cylindrical buoy, a mechanical power take-off system with a counterweight, moored to the seabed as a tension leg platform (TLP) with three equal tendons. In these extensive experiments, numerous device characteristics were measured and analysed. The present paper focuses on the dynamic forces in the mooring lines, and some unexpected and rare data obtained. It is well known that TLP tendons are prone to a brief loss of tension (the slacking) and that, after such events, high snapping forces of short duration can arise. Partly by intention, and partly due to underestimation of the dynamical forces, several such slacking-snapping incidents were recorded during the experiments. In some severe storms, the snapping forces were up to six times higher than the tendon pretension. The paper presents several recordings of dynamic forces and platform motion during these critical events. It analysis them, and gives a typical scenario under which they occur. It gives also some theoretical explanations, and numerical predictions of dynamical tendon forces, with their comparison to the experimental results.     

Hydrodynamic modelling of a multi-body wave energy converter using the Moving Frame Method

Significant wave energy conversion may be achieved with multiple floats with several modes of motion combining constructively to generate power. With the M4 system, power take off is at hinges to absorb resulting pitch motions. Complexity increases with number of floats and conventional vectorial multi-body dynamics may be conveniently replaced by the recently formulated moving frame method based on the calculus of variations to avoid free-body diagrams and joint reaction forces. Furthermore by utilising group theory to gather spatial rotations and angular velocities in a common structure, the obtained notation is general and straight-forward to apply for single and multi-body systems. This paper lays the foundations for incorporating hydrodynamic forces into the moving frame method. The method is applied to 3, 6 and 8 float cases in regular and irregular waves with results compared to the vectorial method and experimental measurements, showing close agreement. It is suggested that this is a more natural and general approach for complex multi-body, multi-hinge hydrodynamics systems.     

Required test durations for converged short-term wave and impact extreme value statistics — Part 1: Ferry dataset

For the design of maritime structures in waves, the extreme values of responses such as motions and wave impact loads are required. Waves and wave-induced responses are stochastic, so such responses should always be related to a probability. This information is not easy to obtain for strongly non-linear responses such as wave impact forces. Usually class rules or direct assessment via experiments or numerical simulations are applied to obtain extreme values for design. This brings up questions related to the convergence of extreme values: how long do we need to test in order to obtain converged statistics for the target duration? Or, vice versa: given testing data, what is the uncertainty of the associated statistics? Often the test or simulation duration is cut up in ‘seeds’ or ‘realisations’, with an exposure duration of one or three hours based on the typical duration of a steady environmental condition at sea, or the time that a ship sails a single course. The required number of seeds for converged results depends on the type of structure and response, the exposure duration, and the desired probability level. The present study provides guidelines for the convergence of most probable maximum (MPM) wave crest heights and MPM green water wave impact forces on a ferry. Long duration experiments were done to gain insight into the required number of seeds, and the effect of fitting. The present paper presents part 1 of this study; part 2 [1] presents similar results for wave-in-deck loads on a stationary deck box.