The tubular pipes of Jacket platform may be frequently subjected to repeated impact loadings from vessels and dropped objects during the operation life, which may lead to serious damages to the platform. In this paper, the numerical studies on dynamic behavior of tubular pipe subjected to repeated impact loadings was performed. The deformation profile and permanent deflection in numerical simulation were compared with those in experiment, and good agreement was achieved. Besides, the mechanism of deformation accumulation and energy absorption were analyzed. Results showed that, the tubular pipe mainly produced transverse expanding and local dent, the global bending was very small. The permanent deflection at the middle of the pipe increased as the impact numbers increased, while the increment decreased. In addition, with the increase of impact number, the elastic deformation energy stored by the tubular pipe increased, and the plastic deformation energy decreased.
{"title":"Numerical Studies on Dynamic Behavior of Tubular Pipes Under Repeated Impacts","authors":"Ling Zhu, Xiang Wang, K. Guo, Binxing Ma","doi":"10.1115/omae2020-19270","DOIUrl":"https://doi.org/10.1115/omae2020-19270","url":null,"abstract":"\u0000 The tubular pipes of Jacket platform may be frequently subjected to repeated impact loadings from vessels and dropped objects during the operation life, which may lead to serious damages to the platform. In this paper, the numerical studies on dynamic behavior of tubular pipe subjected to repeated impact loadings was performed. The deformation profile and permanent deflection in numerical simulation were compared with those in experiment, and good agreement was achieved. Besides, the mechanism of deformation accumulation and energy absorption were analyzed. Results showed that, the tubular pipe mainly produced transverse expanding and local dent, the global bending was very small. The permanent deflection at the middle of the pipe increased as the impact numbers increased, while the increment decreased. In addition, with the increase of impact number, the elastic deformation energy stored by the tubular pipe increased, and the plastic deformation energy decreased.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125337709","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Modeling of fatigue crack growth plays a key role in risk informed inspection and maintenance planning for fatigue sensitive structural details. Probabilistic models must be available for observable fatigue performances such as crack length and depth, as a function of time. To this end, probabilistic fracture mechanical models are generally formulated and calibrated to provide the same probabilistic characteristics of the fatigue life as the relevant SN fatigue life model. Despite this calibration, it is recognized that the rather complex fracture mechanical models suffer from the fact that several of their parameters are assessed experimentally on an individual basis. Thus, the probabilistic models derived for these parameters in general omit possible mutual dependencies, and this in turn is likely to increase the uncertainty associated with modeled fatigue lives. Motivated by the possibility to reduce the uncertainty associated with complex multi-parameter probabilistic fracture mechanical models, a so-called normalized fatigue crack growth model was suggested by Tychsen (2017). In this model, the main uncertainty associated with the fatigue crack growth is captured in only one parameter. In the present contribution, we address this new approach for the modeling of fatigue crack growth from the perspective of how to best estimate its parameters based on experimental evidence. To this end, parametric Bayesian hierarchical models are formulated taking basis in modern big data analysis techniques. The proposed probabilistic modeling scheme is presented and discussed through an example considering fatigue crack growth of welds in K-joints. Finally, it is shown how the developed probabilistic crack growth model may be applied as basis for risk-based inspection and maintenance planning.
{"title":"On Normalized Fatigue Crack Growth Modeling","authors":"Sebastian T. Glavind, Henning Brüske, M. Faber","doi":"10.1115/omae2020-18613","DOIUrl":"https://doi.org/10.1115/omae2020-18613","url":null,"abstract":"\u0000 Modeling of fatigue crack growth plays a key role in risk informed inspection and maintenance planning for fatigue sensitive structural details. Probabilistic models must be available for observable fatigue performances such as crack length and depth, as a function of time. To this end, probabilistic fracture mechanical models are generally formulated and calibrated to provide the same probabilistic characteristics of the fatigue life as the relevant SN fatigue life model. Despite this calibration, it is recognized that the rather complex fracture mechanical models suffer from the fact that several of their parameters are assessed experimentally on an individual basis. Thus, the probabilistic models derived for these parameters in general omit possible mutual dependencies, and this in turn is likely to increase the uncertainty associated with modeled fatigue lives. Motivated by the possibility to reduce the uncertainty associated with complex multi-parameter probabilistic fracture mechanical models, a so-called normalized fatigue crack growth model was suggested by Tychsen (2017). In this model, the main uncertainty associated with the fatigue crack growth is captured in only one parameter. In the present contribution, we address this new approach for the modeling of fatigue crack growth from the perspective of how to best estimate its parameters based on experimental evidence. To this end, parametric Bayesian hierarchical models are formulated taking basis in modern big data analysis techniques. The proposed probabilistic modeling scheme is presented and discussed through an example considering fatigue crack growth of welds in K-joints. Finally, it is shown how the developed probabilistic crack growth model may be applied as basis for risk-based inspection and maintenance planning.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129978155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper aims to introduce a novel method in terms of risk analysis and control of FPSO oil and gas processing system. The Failure Mode and Effect Analysis (FMEA) is implemented to identify the critical equipment and typical failure modes, in order to improve the accuracy and pertinence of model establishment. A Petri Net model is then developed based on FMEA results and the correlation analysis between different components. The input reliability data are primarily collected from Offshore and Onshore Reliability Data (OREDA), and the maintenance information is assessed by industry experts, using fuzzy synthetic evaluation method. This paper focuses on the accuracy, rapidity and feasibility in the modeling and solution process, and considers the influence of weather factors on the maintenance operation and limited maintenance crew number, forming a complete set of reliability and maintenance strategy optimization analysis method of FPSO oil and gas processing system. The results contain system reliability, availability, and maintenance information. The proposed approach can reveal the risk feature of the system and provide corresponding risk control scheme.
{"title":"Reliability Analysis of FPSO Oil and Gas Processing System Based on Petri Net","authors":"Jichuan Kang, Xin Geng, Liping Sun, P. Jin","doi":"10.1115/omae2020-18163","DOIUrl":"https://doi.org/10.1115/omae2020-18163","url":null,"abstract":"\u0000 This paper aims to introduce a novel method in terms of risk analysis and control of FPSO oil and gas processing system. The Failure Mode and Effect Analysis (FMEA) is implemented to identify the critical equipment and typical failure modes, in order to improve the accuracy and pertinence of model establishment. A Petri Net model is then developed based on FMEA results and the correlation analysis between different components. The input reliability data are primarily collected from Offshore and Onshore Reliability Data (OREDA), and the maintenance information is assessed by industry experts, using fuzzy synthetic evaluation method. This paper focuses on the accuracy, rapidity and feasibility in the modeling and solution process, and considers the influence of weather factors on the maintenance operation and limited maintenance crew number, forming a complete set of reliability and maintenance strategy optimization analysis method of FPSO oil and gas processing system. The results contain system reliability, availability, and maintenance information. The proposed approach can reveal the risk feature of the system and provide corresponding risk control scheme.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"81 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132745050","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. M. Ng, Biramarta Isnadi, Luong Ann Lee, Syahnaz Omar, S. N. Saminal, Wan Hariz Fadli Wan Shafie, R. Khan
The objective of this paper is to present the digitalization of Structural Integrity Management for PETRONAS, via a web-based Structural Integrity Compliance System (SICS). Developed initially as a software application to manage the vast database for integrity management of offshore fleet, the system covers the substructure, topside structures, onshore civil and structural assets and ship-shaped floating structure modules. The system is developed in line with API RP 2SIM, taking the SIM process of Data-Evaluation-Strategy-Program. The Data captured in the system inclusive of the design, construction, characteristics, inspection, foundation and metocean data required for evaluation of the likelihood of failure. While the life safety, environmental pollution & business loss data is assigned to evaluate the consequence of failure. After successful implementation of substructure module, the system has been expanded to capture data and evaluate risk of other types of assets, namely the topside structures, onshore civil and structural assets and at last, a module developed for a ship shaped floating structure. A centralized database to manage the integrity a large aging fleet provides good visibility to the management in order to prioritize resources (budget, manpower and logistic) for inspection and maintenance, at the same time reducing the risk of operation disruption due to non-compliance. The system has created much cost saving through Risk-Based Underwater Inspection (RBUI) and risk-based anomalies repair. SICS consists of the risk ranking sub-module and also other decision making tools including Strengthening-Modification and Repair (SMR) Toolkit, and Technical Limits Weight Control (TLWC) Tool. These toolkits are codified to provide quick decision making to management to evaluate the feasibility of SMR scheme or modification involving additional topside weights.
本文的目的是通过基于网络的结构完整性合规系统(SICS)为马来西亚国家石油公司介绍结构完整性管理的数字化。该系统最初是作为一个软件应用程序开发的，用于管理海上船队完整性管理的庞大数据库，该系统涵盖了下层结构、上层结构、陆上土木和结构资产以及船型浮动结构模块。系统按照API RP 2SIM，采用数据-评估-策略-计划的SIM流程进行开发。系统中捕获的数据包括设计、构造、特征、检查、基础和气象海洋数据，这些数据是评估故障可能性所需的。同时分配生命安全、环境污染和业务损失数据，评估失效后果。在子结构模块成功实施后，该系统已扩展到捕获数据和评估其他类型资产的风险，即上层结构，陆上土建和结构资产，最后是为船型浮式结构开发的模块。管理大型老化机队完整性的集中数据库为管理层提供了良好的可见性，以便优先考虑检查和维护的资源(预算，人力和物流)，同时降低因不合规而导致运营中断的风险。通过基于风险的水下检查(RBUI)和基于风险的异常修复，该系统节省了大量成本。SICS由风险排序子模块和其他决策工具组成，包括加固-修改和修复(SMR)工具包和技术限制重量控制(TLWC)工具。这些工具集可以为管理层提供快速决策，以评估SMR方案的可行性或涉及额外上部重量的修改。
{"title":"Structural Integrity Management (SIM) via a Digitalized Structural Integrity Compliance System","authors":"S. M. Ng, Biramarta Isnadi, Luong Ann Lee, Syahnaz Omar, S. N. Saminal, Wan Hariz Fadli Wan Shafie, R. Khan","doi":"10.1115/omae2020-19064","DOIUrl":"https://doi.org/10.1115/omae2020-19064","url":null,"abstract":"\u0000 The objective of this paper is to present the digitalization of Structural Integrity Management for PETRONAS, via a web-based Structural Integrity Compliance System (SICS). Developed initially as a software application to manage the vast database for integrity management of offshore fleet, the system covers the substructure, topside structures, onshore civil and structural assets and ship-shaped floating structure modules.\u0000 The system is developed in line with API RP 2SIM, taking the SIM process of Data-Evaluation-Strategy-Program. The Data captured in the system inclusive of the design, construction, characteristics, inspection, foundation and metocean data required for evaluation of the likelihood of failure. While the life safety, environmental pollution & business loss data is assigned to evaluate the consequence of failure. After successful implementation of substructure module, the system has been expanded to capture data and evaluate risk of other types of assets, namely the topside structures, onshore civil and structural assets and at last, a module developed for a ship shaped floating structure.\u0000 A centralized database to manage the integrity a large aging fleet provides good visibility to the management in order to prioritize resources (budget, manpower and logistic) for inspection and maintenance, at the same time reducing the risk of operation disruption due to non-compliance. The system has created much cost saving through Risk-Based Underwater Inspection (RBUI) and risk-based anomalies repair.\u0000 SICS consists of the risk ranking sub-module and also other decision making tools including Strengthening-Modification and Repair (SMR) Toolkit, and Technical Limits Weight Control (TLWC) Tool. These toolkits are codified to provide quick decision making to management to evaluate the feasibility of SMR scheme or modification involving additional topside weights.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131675723","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The climate change may affect the long-term wave statistics and consequently affect the cumulative fatigue damage. This paper aims to project the trend of annual fatigue damage of offshore floating structures and to detect the climate change impact on the future fatigue damage by coupling a conventional fatigue design method with climate and wave models. Firstly, climate scenarios are selected to project the global radiative forcing level over decadal or century time scales. Secondly, climate models are used to simulate atmosphere circulations and to obtain the wind field data. Thirdly, wave conditions are simulated by coupling wind driven wave models to climate models. Fourthly, stress analysis and fatigue assessments are conducted to project the annual fatigue damage. At last, control simulations are carried out in order to identify the range of natural variability and to detect the human-induced change. A case study is presented in the Sable field offshore South Africa. The results indicate that the significant wave height is considerably influenced by the human-induced climate change. However, this change induced by human activities is still partially masked by the dominant natural variability. In addition, both the significant wave height and the annual fatigue damage increase over century time-scales.
{"title":"Projection and Detection Procedures for Long-Term Wave Climate Change Impact on Fatigue Damage of Offshore Floating Structures","authors":"T. Zou, M. Kaminski, Hang Li, L. Tao","doi":"10.1115/omae2020-18350","DOIUrl":"https://doi.org/10.1115/omae2020-18350","url":null,"abstract":"\u0000 The climate change may affect the long-term wave statistics and consequently affect the cumulative fatigue damage. This paper aims to project the trend of annual fatigue damage of offshore floating structures and to detect the climate change impact on the future fatigue damage by coupling a conventional fatigue design method with climate and wave models. Firstly, climate scenarios are selected to project the global radiative forcing level over decadal or century time scales. Secondly, climate models are used to simulate atmosphere circulations and to obtain the wind field data. Thirdly, wave conditions are simulated by coupling wind driven wave models to climate models. Fourthly, stress analysis and fatigue assessments are conducted to project the annual fatigue damage. At last, control simulations are carried out in order to identify the range of natural variability and to detect the human-induced change. A case study is presented in the Sable field offshore South Africa. The results indicate that the significant wave height is considerably influenced by the human-induced climate change. However, this change induced by human activities is still partially masked by the dominant natural variability. In addition, both the significant wave height and the annual fatigue damage increase over century time-scales.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124761375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Welding is an effective method for joining metallic structures which are very common in the construction of ships and offshore platforms. However, welded joints are prone to fatigue failure under cyclic loading due to the associated high residual stresses. In order to assess the fatigue crack propagation (FCP) accurately, precise evaluation of stress intensity factors (SIFs) is a key parameter. The residual stress distribution on the crack face of welded joints is usually non-uniform and also depends on boundary conditions. Therefore, an efficient technique is required to calculate SIFs for welded joints under non-uniform stress distribution. In this study, SIFs of semi-circular surface cracked welded joints are calculated by using the influence function method (IFM). The IFM has been introduced as an efficient method to evaluate SIFs under arbitrary stress distribution. The influence coefficient databases (ICDB) are developed for welded joints and flat plate models using IFM in this study. As the crack face traction (CFT) integral is employed in this developed influence coefficients (IC), the SIFs given by IFM are more accurate compared to the previously established solutions without CFT-integral. The ICDB and SIFs evaluated by using welded joint and flat plate models are compared and discussed. This study reveals the difference between ICDB of flat plates and welded joints, and estimation error of calculated SIFs for welded joints by using flat plate ICDB.
{"title":"Comparative Study on Stress Intensity Factors for Surface Cracks in Welded Joint and Flat Plate by Using the Influence Function Method","authors":"Phyo Myat Kyaw, Osawa Naoki, Gadallah Ramy, Tanaka Satoyuki","doi":"10.1115/omae2020-19261","DOIUrl":"https://doi.org/10.1115/omae2020-19261","url":null,"abstract":"\u0000 Welding is an effective method for joining metallic structures which are very common in the construction of ships and offshore platforms. However, welded joints are prone to fatigue failure under cyclic loading due to the associated high residual stresses. In order to assess the fatigue crack propagation (FCP) accurately, precise evaluation of stress intensity factors (SIFs) is a key parameter. The residual stress distribution on the crack face of welded joints is usually non-uniform and also depends on boundary conditions. Therefore, an efficient technique is required to calculate SIFs for welded joints under non-uniform stress distribution.\u0000 In this study, SIFs of semi-circular surface cracked welded joints are calculated by using the influence function method (IFM). The IFM has been introduced as an efficient method to evaluate SIFs under arbitrary stress distribution. The influence coefficient databases (ICDB) are developed for welded joints and flat plate models using IFM in this study. As the crack face traction (CFT) integral is employed in this developed influence coefficients (IC), the SIFs given by IFM are more accurate compared to the previously established solutions without CFT-integral. The ICDB and SIFs evaluated by using welded joint and flat plate models are compared and discussed. This study reveals the difference between ICDB of flat plates and welded joints, and estimation error of calculated SIFs for welded joints by using flat plate ICDB.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116684329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To register the wave loads acting on offshore floating structures, wave buoys have been the generally accepted as the most accurate method. However, over the last couple of years, hindcast data has become increasingly accurate. The availability of this data allows assessment of the response of offshore floating structure without the need of local wave buoys. The accuracy when using hindcast data to assess fatigue accumulation on FPSO hulls is assessed in this paper. For this analysis, calculations have been executed for multiple spread-moored production units in the West-Africa region. The purposely deployed wave buoys provide a full wave spectrum including multiple wave components and directional variation of the wave energy. This data is used to derive statistical data description of the sea state. In this paper, we consider the use of WaveWatch III, ERA-5 and Copernicus hindcast models. These are all models which provide sea state descriptions on a global scale. The statistical data from the hindcast models is compared against the reference data provided by the wave buoys. Overall, the three models provide decent results in this mild environment. However, it is found that Copernicus provides more accurate estimates for the larger wave heights. Fatigue analyses have been executed. The full spectral data provided by the wave buoys is used to conduct a spectral fatigue assessment. The hindcast models generally provide more limited details of the sea state, information such as spectral shapes and directional spreading may be missing. Understanding the influence of these missing characteristics is vital for reliable long term fatigue assessment. Multiple fatigue analyses have been executed to examine the sensitivity to these missing characteristics. It has been shown that the multi-modality of the sea state and spectral shape are the most important parameters driving the deviation between the fatigue assessment based on hindcast data and wave buoy data. These differences can accumulate to a factor of 2 on lifetime consumption. The influence of the accuracy of the statistical parameters provided by the hindcast models and wave spreading is considerably less with a typical contribution of around 30% on lifetime consumption.
为了记录作用在近海浮式结构上的波浪荷载，波浪浮标被普遍认为是最准确的方法。然而，在过去的几年里，预测数据变得越来越准确。这些数据的可用性可以在不需要当地波浪浮标的情况下评估近海浮动结构的响应。本文对利用后置数据评估FPSO船体疲劳积累的准确性进行了评估。为了进行这一分析，已经对西非地区的多个扩展系泊生产单元进行了计算。有目的地部署的波浪浮标提供了一个完整的波浪谱，包括多个波浪分量和波浪能量的方向变化。该数据用于导出海况的统计数据描述。在本文中，我们考虑使用WaveWatch III, ERA-5和哥白尼后置模型。这些都是在全球范围内提供海况描述的模型。将预报模型的统计数据与浮标提供的参考数据进行比较。总的来说，这三种模型在这种温和的环境中提供了不错的结果。然而，发现哥白尼对较大的波高提供了更准确的估计。进行了疲劳分析。利用波浪浮标提供的全光谱数据进行频谱疲劳评估。一般来说，后播模式提供的海况细节比较有限，可能缺少频谱形状和方向扩展等信息。了解这些缺失特征的影响对于可靠的长期疲劳评估至关重要。已经进行了多次疲劳分析，以检验对这些缺失特性的敏感性。结果表明，海况和波谱形状的多模态是导致基于后播数据的疲劳评估与波浪浮标数据偏差的最重要参数。这些差异可以累积到寿命消耗的2倍。后验模型提供的统计参数的精度和波的传播对寿命消耗的影响要小得多，典型的贡献约为30%。
{"title":"Feasibility of Using Hindcast Data for Fatigue Assessment of Permanently Moored Offshore Units in West-Africa","authors":"R. Hageman, P. Aalberts, D. L'hostis, A. Ledoux","doi":"10.1115/omae2020-18794","DOIUrl":"https://doi.org/10.1115/omae2020-18794","url":null,"abstract":"\u0000 To register the wave loads acting on offshore floating structures, wave buoys have been the generally accepted as the most accurate method. However, over the last couple of years, hindcast data has become increasingly accurate. The availability of this data allows assessment of the response of offshore floating structure without the need of local wave buoys.\u0000 The accuracy when using hindcast data to assess fatigue accumulation on FPSO hulls is assessed in this paper. For this analysis, calculations have been executed for multiple spread-moored production units in the West-Africa region. The purposely deployed wave buoys provide a full wave spectrum including multiple wave components and directional variation of the wave energy. This data is used to derive statistical data description of the sea state.\u0000 In this paper, we consider the use of WaveWatch III, ERA-5 and Copernicus hindcast models. These are all models which provide sea state descriptions on a global scale. The statistical data from the hindcast models is compared against the reference data provided by the wave buoys. Overall, the three models provide decent results in this mild environment. However, it is found that Copernicus provides more accurate estimates for the larger wave heights.\u0000 Fatigue analyses have been executed. The full spectral data provided by the wave buoys is used to conduct a spectral fatigue assessment. The hindcast models generally provide more limited details of the sea state, information such as spectral shapes and directional spreading may be missing. Understanding the influence of these missing characteristics is vital for reliable long term fatigue assessment. Multiple fatigue analyses have been executed to examine the sensitivity to these missing characteristics.\u0000 It has been shown that the multi-modality of the sea state and spectral shape are the most important parameters driving the deviation between the fatigue assessment based on hindcast data and wave buoy data. These differences can accumulate to a factor of 2 on lifetime consumption. The influence of the accuracy of the statistical parameters provided by the hindcast models and wave spreading is considerably less with a typical contribution of around 30% on lifetime consumption.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132380111","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. L. Simão, P. Videiro, Mauro Costa de Oliveira, L. Sagrilo
Escalating demand in the oil and gas industry has led offshore structures to be installed in ever deeper waters and under severe environmental conditions. As the mooring system is a crucial element in floating offshore structures, a reliable estimation of its long-term response is a decisive step in any usual design procedure. In the long-term scenario, the environmental actions to which these structures are subjected to, such as waves, wind and current, are non-stationary processes. However, this long-term behavior is usually modeled as a series of short-term stationary conditions (typically 3-h). In a full long-term analysis approach, an estimate of the long-term N-year response can be obtained through a multidimensional integration over all these short-term environmental conditions. In this paper, this multidimensional integral is numerically evaluated by means of the Importance Sampling Monte Carlo Simulation (ISMCS) method, where the uniform distribution is used as the sampling function. Thus, all short-term environmental conditions have the same probability of being sampled, which assures that conditions with very low original probability of occurrence, but with knowingly higher contributions to the long-term response, are efficiently accounted for. The random variability of the short-term environmental parameters and their interdependencies are represented by a simplified joint probabilistic model which comprehends both wind sea and swell waves. The methodology is numerically validated for an idealized single-degree-of-freedom (SDOF) model and later investigated for a mooring line connected to an FPSO installed in Brazilian deep waters. It is shown that ISMCS provides good estimates for the long-term N-year response with a moderate amount of required simulations and can be a powerful tool in order to account for simultaneous occurrence of wind sea and swell waves in structural response evaluations.
{"title":"An Efficient Importance Sampling Method for the Long-Term Mooring Lines Response Estimation Considering Wind Sea and Swell","authors":"M. L. Simão, P. Videiro, Mauro Costa de Oliveira, L. Sagrilo","doi":"10.1115/omae2020-18175","DOIUrl":"https://doi.org/10.1115/omae2020-18175","url":null,"abstract":"\u0000 Escalating demand in the oil and gas industry has led offshore structures to be installed in ever deeper waters and under severe environmental conditions. As the mooring system is a crucial element in floating offshore structures, a reliable estimation of its long-term response is a decisive step in any usual design procedure. In the long-term scenario, the environmental actions to which these structures are subjected to, such as waves, wind and current, are non-stationary processes. However, this long-term behavior is usually modeled as a series of short-term stationary conditions (typically 3-h). In a full long-term analysis approach, an estimate of the long-term N-year response can be obtained through a multidimensional integration over all these short-term environmental conditions. In this paper, this multidimensional integral is numerically evaluated by means of the Importance Sampling Monte Carlo Simulation (ISMCS) method, where the uniform distribution is used as the sampling function. Thus, all short-term environmental conditions have the same probability of being sampled, which assures that conditions with very low original probability of occurrence, but with knowingly higher contributions to the long-term response, are efficiently accounted for. The random variability of the short-term environmental parameters and their interdependencies are represented by a simplified joint probabilistic model which comprehends both wind sea and swell waves. The methodology is numerically validated for an idealized single-degree-of-freedom (SDOF) model and later investigated for a mooring line connected to an FPSO installed in Brazilian deep waters. It is shown that ISMCS provides good estimates for the long-term N-year response with a moderate amount of required simulations and can be a powerful tool in order to account for simultaneous occurrence of wind sea and swell waves in structural response evaluations.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128374240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Barratt, H. Bingham, P. Taylor, T. V. D. Bremer, T. Adcock
The relative contributions of free waves and bound waves to the formation of an extreme wave event remains a topic of interest in offshore engineering. A variety of methods have been proposed for identifying and removing the bound wave components. The method of “phase separation” or “phase manipulation” repeats simulations/experiments of a wave field with an offset in the initial phase of the wave components and relies upon summation of the resulting wave fields to isolate the bound harmonics, following from a Stokes expansion in steepness; the method has proven effective in isolating bound harmonics but requires that all cases be repeated. Alternatively, the bound harmonics can be removed using a three-dimensional fast Fourier transform (3D-FFT) of the wave field. However, the Fourier transform requires periodicity in the signal and assumes homogeneity in space and stationarity in time, producing spurious modes otherwise. We compare the phase separation and 3D-FFT approaches for a steep, focusing wave group in deep water using the numerical simulation tool, OceanWave3D, and discuss the effectiveness of both methods.
{"title":"Linearization of the Wave Spectrum: A Comparison of Methods","authors":"D. Barratt, H. Bingham, P. Taylor, T. V. D. Bremer, T. Adcock","doi":"10.1115/omae2020-18820","DOIUrl":"https://doi.org/10.1115/omae2020-18820","url":null,"abstract":"\u0000 The relative contributions of free waves and bound waves to the formation of an extreme wave event remains a topic of interest in offshore engineering. A variety of methods have been proposed for identifying and removing the bound wave components. The method of “phase separation” or “phase manipulation” repeats simulations/experiments of a wave field with an offset in the initial phase of the wave components and relies upon summation of the resulting wave fields to isolate the bound harmonics, following from a Stokes expansion in steepness; the method has proven effective in isolating bound harmonics but requires that all cases be repeated. Alternatively, the bound harmonics can be removed using a three-dimensional fast Fourier transform (3D-FFT) of the wave field. However, the Fourier transform requires periodicity in the signal and assumes homogeneity in space and stationarity in time, producing spurious modes otherwise. We compare the phase separation and 3D-FFT approaches for a steep, focusing wave group in deep water using the numerical simulation tool, OceanWave3D, and discuss the effectiveness of both methods.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"459 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120940366","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Jagite, H. L. Sourne, P. Cartraud, Š. Malenica, F. Bigot, J. D. Lauzon, Q. Derbanne
In the last ten years, the importance of whipping on the extreme hull girder loads has received much attention, but its consequence on the hull girder’s collapse is still unclear. The most common practice is to consider the structural behavior as linear-elastic in the hydro-elastic coupling, and as non-linear elasto-plastic in the ultimate strength evaluation. In order to investigate the influence of the non-linear structural behavior on the hydro-structure interaction responses, a new hydro-elastoplastic model is proposed to compute the non-linear whipping response. The structural part is modeled as two beams connected by a non-linear hinge, which follows the collapse behavior of a ship’s hull girder. The hydrodynamic problem is solved using the three-dimensional boundary element method, and the exact coupling between the structural model and the hydrodynamic one is made by making use of the shape function approach. Finally, the fully-coupled hydro-elastoplastic problem is solved directly in time-domain by numerical integration.
{"title":"A New Approach to Compute the Non-Linear Whipping Response Using Hydro-Elastoplastic Coupling","authors":"G. Jagite, H. L. Sourne, P. Cartraud, Š. Malenica, F. Bigot, J. D. Lauzon, Q. Derbanne","doi":"10.1115/omae2020-18200","DOIUrl":"https://doi.org/10.1115/omae2020-18200","url":null,"abstract":"\u0000 In the last ten years, the importance of whipping on the extreme hull girder loads has received much attention, but its consequence on the hull girder’s collapse is still unclear. The most common practice is to consider the structural behavior as linear-elastic in the hydro-elastic coupling, and as non-linear elasto-plastic in the ultimate strength evaluation. In order to investigate the influence of the non-linear structural behavior on the hydro-structure interaction responses, a new hydro-elastoplastic model is proposed to compute the non-linear whipping response. The structural part is modeled as two beams connected by a non-linear hinge, which follows the collapse behavior of a ship’s hull girder. The hydrodynamic problem is solved using the three-dimensional boundary element method, and the exact coupling between the structural model and the hydrodynamic one is made by making use of the shape function approach. Finally, the fully-coupled hydro-elastoplastic problem is solved directly in time-domain by numerical integration.","PeriodicalId":297013,"journal":{"name":"Volume 2A: Structures, Safety, and Reliability","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121758425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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