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1.
《中国海洋大学学报(英文版)》2020,(5)
Jacket-type offshore platforms are widely used for oil, gas field, and energy development in shallow water. The design of a jacket structure is highly dependent on target environmental variables. This study focuses on a strategy to estimate design loads for offshore jacket structures based on an environmental contour approach. In addition to the popular conditional distribution model, various classes of bivariate copulas are adopted to construct joint distributions of environmental variables. Analytical formulations of environmental contours based on various models are presented and discussed in this study. The design loads are examined by dynamic response analysis of jacket platform. Results suggest that the conditional model is not recommended for use in estimating design loads in sampling locations due to poor fitting results. Independent copula produces conservative design loads and the extreme response obtained using the conditional model are smaller than those determined by copulas. The suitability of a model for contour construction varies with the origin of wave data. This study provides a reference for the design load estimation of jacket structures and offers an alternative procedure to determine the design criteria for offshore structures. 相似文献
2.
Offshore jacket platforms are widely used in offshore oil and gas exploitation. Finite element models of such structures need to have many degrees of freedom (DOFs) to represent the geometrical detail of complex structures, thereby leading to incompatibility in the number of DOFs of experimental models. To bring them both to the same order while ensuring that the essential eigen- properties of the refined model match those of experimental models, an extended model refinement procedure is presented in this paper. Vibration testing of an offshore jacket platform model is performed to validate the applicability of the proposed approach. A full-order finite element model of the platform is established and then tuned to meet the measured modal properties identified from the acceleration signals. Both model reduction and modal expansion methods are investigated, as well as various scenarios of sensor arrangements. Upon completion of the refinement, the updated jacket platform model matches the natural frequencies of the measured model well. 相似文献
3.
Environmental load is the primary factor in the design of offshore engineering structures and ocean current is the principal environmental load that causes underwater structural failure. In computational analysis, the calculation of current load is mainly based on the current profile. The current profile model, which is based on a structural failure criterion, is conducive to decreasing the uncertainty of the current load. In this study, we used prototype monitoring data and the empirical orthogonal function(EOF) method to investigate the current profile in the South China Sea and its correlation with the design of underwater structural strength and the dynamic design of fatigue. The underwater structural strength design takes into account the size of the structure and the service water depth. We propose profiles for the overall and local designs using the inverse first-order reliability method(IFORM). We extracted the characteristic profile current(CPC) of the monitored sea area to solve dynamic design problems such as vortex-induced vibration(VIV). We used random sampling to verify the feasibility of using the EOF method to calculate the CPC from the current data and identified the main problems associated with using the CPC, which deserve close attention in VIV design. Our research conclusions provide direct references for determining current load in this sea area. This analysis method can also be used in the analysis of other sea areas or field variables. 相似文献
4.
HUANG Weiping* and WANG Xiaoyan Institute of Coastal Offshore Engineering Ocean University of China Qingdao P. R. China 《中国海洋大学学报(英文版)》2007,6(1):85-89
1 Introduction Health monitoring of structures, especially large spacestructures intended for long-term operation, is essential indeveloping short-term or long-term repair plans. Becausethe maintenance, replacement, and time out of service arecostly, it i… 相似文献
5.
Safety assessment of offshore platforms is an urgent task. Such assessments are now focusing on the structure, maintenance, and retirement of a platform. Some methods employed have many shortcomings. For example, they cannot make the reliability adequately explicable. Therefore, a mathematical tool, the unascertained measure, was introduced. First, the basic knowledge of the unascertained sets was introduced briefly. Second, the unascertained measure was defined and credible identification was set up. The method has been introduced into the fields for safety assessment of a jacket loadout procedure. Engineering practices showed that it can complete the safety assessment systematically and scientifically without any assumption. The work should have significance in theory and practice for offshore engineering. 相似文献
6.
运用非连续变形分析（DDA）和有限元方法(FEM)对砌体结构进行震动分析。建模中将砌体结构的砖、柱、过梁以及楼板等视为独立的弹性体分别作有限元划分,弹性体之间运动由接触界面的张开、闭合和滑动控制来实现,通过防止弹性体间的侵入来校正弹性块体系统的位移与应变最小二乘拟合结果。弹性块体间滑动采用库仑摩尔定律控制砂浆的作用与失效,输入相当于地震烈度Ⅸ度的加速度峰值的迁安波对砌体结构模型进行震力分析,研究相应震动过程。算例表明,DDA和FEM组合的方法能很好地模拟砌体结构受地震作用的动力响应过程。在较大地震作用下,砌体结构首先从底层开始开裂破坏并导致结构倒塌,与农村砌体结构震害现象吻合较好。 相似文献
7.
With the increasing application of floating platforms in deep waters and harsh environments,a proper assessment of the reliability of floating structures is important to ensure that these structures can operate safely during their design lives.This study outlines a practical methodology for reliability analysis of a semi-submersible platform based estimating the probability distribution of the extreme response in rough sea conditions(survival conditions).The Constrained NewWave(CNW)theory combined with Monte Carlo simulations was first applied to simulate the random wave surface elevation process in the time domain.A Gumbel distribution was the best fitting to describe the dynamically sensitive extreme response statistics under extreme waves(drift and mooring tension).The derived probability distribution of the extreme response was subsequently used in estimation of the associated limit state func-tion,and a reliability analysis of the floating structure was conducted using the Monte Carlo method.A semi-submersible platform in a water depth of 1500 m subjected to extreme wave loads was used to demonstrate the efficiency of the proposed methodology.The probability of failure of the semi-submersible when considering mooring lines tension is greater than considering drift. 相似文献
8.
Vertical axis wind turbines(VAWTs) are advantageous for the development of large-scale offshore wind power because the drive system is located at the bottom of the turbine. This study investigates the structural strength of a tri-floater floating foundation supporting a 2.6 MW Darrieus VAWT. Finite element models of the floating foundation were developed using space plate-beam elements. The environmental loads, such as the aerodynamic loads, static wind loads, and wave-current loads, were considered. The general strengths of the floating foundation were calculated for the normal operating case(a cut-out wind speed of 25 m s~(-1) and blade rotation of 12 r min~(-1) were used to analyze the most unfavorable loads) and an extreme case(wind speed of 40 m s~(-1) and parked blades), and the weak components of the structure were analyzed. The results show that the floating foundation meets the strength requirements and the structural stress is highest when the wave, wind, and current are in a collinear direction. The main and secondary supporting bars transmit the loads between the stand columns and the tower foundation, and their stresses are higher than those in the other components. In the actual design, these supporting bars should be strengthened. The aerodynamic loads are very important and should be considered in the structural strength analysis of the floating foundation and the floating wind turbine system. 相似文献
9.
【目的】研究提高船舶主机燃料的综合利用率。【方法】结合MAN 6S50ME型船舶柴油机的余热能量特性和循环热力过程特点,分别建立基本循环、缸套水预热循环和回热循环等三种船舶余热利用有机朗肯循环系统模型,对三种余热利用系统的热力性能与经济性能进行计算和分析。【结果与结论】在三种循环系统中,缸套水预热循环的综合性能更具优势,在循环压力为2000 kPa时,系统的综合性能达到最优,循环净功为555.35 kW,热效率可达18.27%,循环发电净收益提高39.64%。研究结果可为船舶柴油机余热利用系统的设计和优化提供一定的理论指导。 相似文献
10.
Compared to traditional mode shape identification methods such as eigensystem realization algorithm (ERA), this article proposes a mode shape identification method based on estimated residues of measured data and the theoretical relationship between the estimated residues and the mode shapes from the state space model is obtained by defining a coefficient matrix. A mass-spring model with five degrees of freedom (DOFs) is utilized to demonstrate the approach. The numerical results indicate that the estimated residues are the mode shapes of structures, but with a coefficient matrix to maintain consistency with the mode shapes from the ERA. Using MATLAB a complicated numerical jacket platform is built to further study the proposed method. The results show that mode shapes consistent with those from the ERA could be obtained by taking the defined coefficient matrix into account, which is also demonstrated by a physical beam model that was built at Ocean University of China. 相似文献
11.
Degradation of slopes due to shallow landslide and the subsequent erosional processes are a big challenge on the application of soil bioengineering techniques; that is the use of plants as main structural components of a slope protection and conservation system. An optimal application of soil bioengineering techniques should include not only the technical factor of plants as structural components but also the ecology of species and the plant adaptations to disturbances, which is crucial if a longterm successful slope restoration system is intended. Ferns are a dominant understory vegetation species in the forest of Japan, but its characteristics and influences on the recovery of shallow landslide scars have not been fully studied yet. This study aims to find out the ecological characteristics of fern species through the calculation of ecological indicators and the quantification of the morphological features of specimens growing on disturbed and non-disturbed forest slopes in Japan. Gleichenia japonica was found as the vegetation species with biggest ecological indicators on both slopes. The analysis of morphological characteristics of the specimens growing on both sites showed that the development of the specimens is focused in below-ground characteristics. The pull-out force of Gleichenia japonica root system as an indicator of ecological adaptation to a constraint environment and morphological characteristics quality is influenced by height and root length according to the principal component analysis. The eco-morphological characteristics of species can be used as an indicator of an optimal element in soil bioengineering establishment for slope conservation proposes. The long and fibrous root system could be placed on forest roads, steep or small slopes where space limitation is an issue for the establishment of bigger species and if the slope conditions allow it, it can control soil losses due to rainfall and provide stability. 相似文献
12.
大梁子铅锌矿床位于扬子地块西南缘的川西南矿集区内，矿体展布明显受构造控制。针对该矿床构造分级控矿规律与控矿构造组合样式不清的问题，基于矿田地质力学理论与方法，通过不同级别的典型控矿构造力学性质鉴定及不同期次构造筛分，厘清了控矿构造组合样式及其形成机理。研究表明，成矿构造体系为印支晚期NE向构造带，在NW-SE向主压应力作用下，矿床内形成的不同级别构造分级控制了矿床、矿体和矿脉的展布；形成不同尺度的控矿构造组合样式:矿床尺度的走滑为主断裂-褶皱构造组合、矿体尺度的为“多”字型、“入”字型及“黑色破碎带”构造组合。本研究为该矿床深部及外围找矿勘查提供了重要依据。 相似文献
13.
本文介绍了陕北黄土高原油区TM图象的隐伏断裂和环状构造解译标志,建立了该区延安一带的构造格架,并分析了构造特征,提出了隐伏断裂控制环状构造的观点。最后,通过油气分布同新建构造格架的对比研究,认为环状构造集中区或隐伏断裂交叉部位是油气藏储存的良好构造部位。 相似文献
14.
我国城市地下电缆通道结构,在其设计寿命周期内容易受到复杂的环境和人类工程活动的影响而发生失效破坏,并造成巨大的社会经济损失和影响,因此需要针对其结构的破坏规律和加固修复方法展开研究,进而有效避免工程灾害的发生。为了探究电缆通道的结构失效问题及其加固修复方法,参考地下管道结构特点,采用工程实例与数值模拟相结合的方法,研究了电缆通道本体结构破坏的类型、分级,结构的应力应变分布及其裂缝的分布规律。工程实例表明其结构损伤形式通常有8种,4个级别;数值模拟结果显示该类结构损伤大都集中在结构失效的危险区域。从适用范围、修复效果和成本等方面对相关的结构加固修复方法——明挖修复、注浆加固修复和非开挖喷涂修复方法进行了对比和分析,对比结果表明非开挖喷涂修复方法适用性较强,施工便捷,安全高效。通过结合对结构破坏和加固修复方法的研究,可以为解决我国的地下电缆通道中可能存在的结构失效问题提供参考。 相似文献
15.
基于可靠度理论建立顺层岩质边坡稳定的可靠性分析方法，获得顺层岩质边坡可靠指标和失稳概率的计算表达式。以某高切坡为例分析其稳定状态和失稳概率，并据此探讨不同粘聚力、内摩擦角、炸药量和爆心距条件下边坡失稳概率的变化规律。计算结果表明，粘聚力对边坡的失稳概率影响较大；随着内摩擦角的增加，边坡失稳概率近乎线性减小；当单孔药量从10 kg增大到160 kg后，失稳概率增幅97.10%；当爆心距小于20 m时，边坡的失稳概率减小的速度很快，而爆心距超过20 m后边坡失稳概率减小的幅度较小。考虑爆破振动的时效性，爆破荷载使边坡失稳概率增大49.61%，单次爆破振动的影响时间约6 s。 相似文献
16.
The reliability of a vertical breakwater is calculated using direct integration methods based on joint density functions. The horizontal and uplifting wave forces on the vertical breakwater can be well fitted by the lognormal and the Gumbel distributions, respectively. The joint distribution of the horizontal and uplifting wave forces is analyzed using different probabilistic distributions, including the bivariate logistic Gumbel distribution, the bivariate lognormal distribution, and three bivariate Archimedean copulas functions constructed with different marginal distributions simultaneously. We use the fully nested copulas to construct multivariate distributions taking into account related variables. Different goodness fitting tests are carried out to determine the best bivariate copula model for wave forces on a vertical breakwater. We show that a bivariate model constructed by Frank copula gives the best reliability analysis, using marginal distributions of Gumbel and lognormal to account for uplifting pressure and horizontal wave force on a vertical breakwater, respectively. The results show that failure probability of the vertical breakwater calculated by multivariate density function is comparable to those by the Joint Committee on Structural Safety methods. As copulas are suitable for constructing a bivariate or multivariate joint distribution, they have great potential in reliability analysis for other coastal structures. 相似文献
17.
自“七五”以来,小秦岭区在区域地质构造特征,发展演化阶段,区域构造格局,金矿类型的系列性和序列性等诸多方面取得了不少新进展,初步建立起了小秦岭“折离-变质杂岩核”构造体系,从而为金的区域找矿、远景预测及新类型研究提供了一条全新的思路。 相似文献
18.
本文根据湘桂粤赣地区中泥盆世棋梓桥期台,盆(或沟槽)与隆、拗对应的独特构造古地理面貌,以及这种格局与层控矿床空间分布的关系,初步分析了该期华夏系(NE向)构造和东西向构造对岩相古地理的演化及其对层控矿床成矿作用的影响;总结了构造活动尤其是断裂活动控制岩相古地理的空间位置和延伸方向,促进台、盆分异,以及构造逐级控矿、构造体系复合控矿和断裂对层控矿床的控制作用;提出了以华夏系构造为主导对层控矿床的控相(沉积相—成矿沉积环境)、控位(矿床或矿体的储存空间)的控制作用。 相似文献
19.
综合减灾中,协同研判是一种十分有效的灾情汇聚分析手段。现有灾情协同研判系统存在灾情研判水平层次低、研判活动缺乏系统化管理、数据同步共享方式造成网络传输压力大等问题。数据集中的复制式模型是一种高效的协同系统模型,有效提高系统可靠性和降低网络传输量并兼顾空间数据一致性和数据存储效率。本文详细介绍了灾情研判技术流程和关键技术,充分利用复制式模型特点设计并实现了一个基于复制式模型的灾情协同研判系统。实验表明,该系统稳定可靠,能有效满足分布式、异步或同步灾情协同研判的要求。 相似文献
20.
Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with special focus on the low frequency (LF) fatigue damage. Several influential factors, including water depth, wave spectral parameters, and riser system, are considered. Numerical simulation of a semi-submersible platform with the mooring/riser system is executed under different conditions, and the fatigue damage of mooring lines is assessed by using the time domain analysis method as a benchmark. The effects of these factors on the mooring line tension and the fatigue damage are investigated and discussed in detail. Research results indicate that the LF fatigue damage only accounts for a very small portion of the total damage, although the LF components dominate the global motion response and the mooring line tension of the semi-submersible platform. However, it is demonstrated that the LF fatigue damage is clearly affected by the influential factors. The increase in water depth and spectral peak periods, and the existence of risers can weaken the contribution of the LF components to the mooring line fatigue damage, while the fatigue damage due to the LF components increases with the increase of significant wave height. 相似文献