Crack detection using a frequency response function in offshore platforms

Structural cracks can change the frequency response function (FRF) of an offshore platform. Thus, FRF shifts can be used to detect cracks. When a crack at a specific location and magnitude occurs in an offshore structure, changes in the FRF can be measured. In this way, shifts in FRF can be used to detect cracks. An experimental model was constructed to verify the FRF method. The relationship between FRF and cracks was found to be non-linear. The effect of multiple cracks on FRF was analyzed, and the shift due to multiple cracks was found to be much more than the summation of FRF shifts due to each of the cracks. Then the effects of noise and changes in the mass of the jacket on FRF were evaluated. The results show that significant damage to a beam can be detected by dramatic changes in the FRF, even when 10% random noise exists. FRF can also be used to approximately locate the breakage, but it can neither be efficiently used to predict the location of breakage nor the existence of small hairline cracks. The FRF shift caused by a 7% mass change is much less than the FRF shift caused by the breakage of any beam, but is larger than that caused by any early cracks.     

Fast evaluation of ship-bridge collision force based on nonlinear numerical simulation

The max collision force of ship-bridge collision is one of the most important references for bridge design. By means of nonlinear digital simulation method, the collision forces of the collisions between rigid bridge pier and ship bow were calculated out for four different ships, whose tonnages are 5 000, l0 000,50 000 and 60 000 DWT respectively. Curves of collision force-penetration and absorbed energy-penetration are obtained, and the data of the max loads are then summarized. On the basis of these curves and data, a set of curves describing the relationships between max collision forces and tonnages of the ships are successfully presented, by which the max collision forces of the ships-bridge with different tonnages and in different velocities can be estimated easily and reliably.     

天然气泄漏扩散状态模拟及后果分析

本文以一个地下调压室为研究对象,对燃气管道泄漏后的扩散模型进行了深入研究和比较,确定调压室内燃气泄漏后的扩散过程可以使用浮力修正的k-ε双方程湍流模型。通过采用CFX软件对室内燃气泄漏后的扩散状态进行模拟,得到了天然气泄漏后的浓度、温度以及流场分布规律,并根据模拟结果分析了燃气泄漏后室内是否存在爆炸的危险。     

大直径PHC桩竖向承载特性数值模拟研究

以珠海高栏港码头结构为工程背景,对码头的大直径PHC桩的数值模拟技术和承载特性进行研究。首先采用ABAQUS进行数值模拟,并将数值模拟结果与试验结果进行对比分析,验证了有限元分析的可行性,然后通过桩径、桩长,桩侧土和桩端土等一系列参数的变化,探讨这些参数对PHC桩Q-S曲线的影响。结果表明,有限元计算出的位移比实测结果高出2%~20%,桩长超过50 m的PHC桩属于超长桩。