23 results on '"offshore platform"'
Search Results
2. 海洋环境荷载下半潜式平台上承房屋钢框架结构的动力响应特征.
- Author
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李富民, 刘永强, 赵婕, and 郭震
- Subjects
SEA breeze ,FINITE element method ,STEEL framing ,STRUCTURAL frames ,OCEAN ,EARTHQUAKES ,EFFECT of earthquakes on buildings - Abstract
Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2022
- Full Text
- View/download PDF
3. Seismic response analysis of fixed jacket-type offshore structures based on power spectrum density Driven input.
- Author
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Abdel Raheem, Shehata E., Abdel Aal, Elsayed M., AbdelShafy, Aly G. A., and Fahmy, Mohamed F.M.
- Subjects
OFFSHORE structures ,POWER density ,SEISMIC response ,POWER spectra ,FINITE element method ,TRANSFER functions ,RANDOM vibration - Abstract
Offshore platforms in seismically active areas should be properly designed to survive within the face of intense earthquakes without a global structural collapse. This paper scrutinizes the seismic performance of a newly designed and established jacket type offshore platform based on the API-RP2A normalized response spectra during seismic events. A finite element model is developed from a typical jacket type offshore platform taking into the effect of the interaction among structure, pile, and soil components. The seismic responses of jacket type offshore platforms subjected to random earthquake excitations are evaluated by means of the power spectral density (PSD) analysis. Dynamic characteristics, the response function, output PSD and transfer functions for various elements of the platform are discussed. The spectrum compatible PSD is directly used to estimate the peak structural responses and determine the dynamic response of offshore jacket platforms that meet the required level of engineering practice for preliminary design. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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4. In-Place Analysis for Structural Integrity Assessment of Fixed Steel Offshore Platform.
- Author
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Abdel Raheem, Shehata E., Abdel Aal, Elsayed M., Abdel Shafy, Aly G. A., Fahmy, Mohamed F. M., and Omar, Mohamed
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OFFSHORE structures , *FINITE element method , *DRILLING platforms , *MAXIMA & minima , *WATER depth , *BEHAVIORAL assessment , *STEEL - Abstract
In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures. The structural integrity of platform components under the maximum and minimum operating loads of environmental conditions is required for risk assessment and inspection plan development. In-place analyses have been executed to check that the structural member with all appurtenances has robustness and capability to support the applied loads in either storm condition or operating condition. A nonlinear finite element analysis is adopted for the platform structure above the seabed and the soil–pile–jacket interaction to estimate the in-place behavior of a typical fixed offshore platform. The analysis includes an interpretation of the dynamic design parameters based on the available site-specific data, together with foundation design recommendations for in-place loading conditions. The SACS software is utilized to calculate the natural frequencies, dynamic amplification factors, and the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have important effects on the results of the in-place analysis behavior. The incidence angle of seismic waves is an essential parameter, where, for some crucial angles, the internal forces and the maximum deformations can be doubled or more in comparison with the ones corresponding to other, less crucial angles. Therefore, the incidence angle considerably affects the response quantities. The results confirm that the in-place analysis is quite essential for the reliable design of new offshore platforms and the assessment of existing offshore structures. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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5. Pile-soil-structure interaction effect on structural response of piled jacket-supported offshore platform through in-place analysis.
- Author
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Raheem, Shehata E. Abdel, Aal, Elsayed M. Abdel, AbdelShafy, Aly G. A., Fahmy, Mohamed F. M., and Mansour, Mahmoud H.
- Subjects
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SOIL structure , *BEHAVIORAL assessment , *SOIL-structure interaction , *BENDING moment , *FINITE element method , *WATER depth - Abstract
In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures, in addition to the structural integrity of platforms components under the maximum and minimum operating loads when subjected to the environmental conditions. In-place analysis have been executed to check that the structural member with all appurtenance's robustness have the capability to support the applied loads in either storm or operating conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the dynamic characteristics of the platform model and the response of platform joints then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have significant effects in the results of the in-place analysis behavior. The most of bending moment responses of the piles are in the first fourth of pile penetration depth from pile head level. The axial deformations of piles in all load combinations cases of all piles are inversely proportional with penetration depth. The largest values of axial soil reaction are shown at the pile tips levels (the maximum penetration level). The most of lateral soil reactions resultant are in the first third of pile penetration depth from pile head level and approximately vanished after that penetration. The influence of the soil-structure interaction on the response of the jacket foundation predicts that the flexible foundation model is necessary to estimate the force responses demands of the offshore platform with a piled jacket-support structure well. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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6. Effect of Geometric Parameters and Combined Loading on Stress Distribution of Tubular T-Joints.
- Author
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BELHOUR, Samira, KAHOUL, Hafida, BELLAOUAR, Ahmed, and MURER, Sébastien
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STRESS concentration , *TUBULAR steel structures , *AXIAL loads , *OFFSHORE structures , *FINITE element method , *NUMERICAL analysis , *BENDING stresses - Abstract
Steel tubular structures are widely used in the construction of offshore platforms and T-type junctions are extensively used in this domain. The tubular members are welded, which generates significant stress concentrations at the edges. The stress levels reached in these critical places are used to assess lifetimes based on fatigue curves from tests conducted on standard samples. This study is devoted to the modeling and analysis of T-type welded tubular structures for the determination of hot spots stresses (HSS) at the chord/brace intersection, A numerical analysis was carried out to study the effect of a combined loading composed of an axial loading and a continuation of rational bending, that best assimilate real conditions, as well as the effect of normalized geometric parameters a, ß, on the distribution of stress concentration (area and values) of T-joints. The mechanical behaviour has been modeled in 2D using quadrangular and triangular thin-shell elements by the finite element method (FEM). It is the most appropriate approach because it considers all geometric complexities and singularities of the structure, while the efforts as well as the computation time are considerably reduced compared to an experimental study or to complex FE models implementing solid elements. In this study, we use the COMSOL-MULTIPHYSICS® software. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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7. Analytical modelling of structure-borne sound transmission through I-junction using Chebyshev-Ritz method on cascaded rectangular plate–cavity system.
- Author
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Chin, Cheng Siong and Ji, Xi
- Subjects
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TRANSMISSION of sound , *CHEBYSHEV systems , *RITZ method , *RECTANGULAR plates (Engineering) , *FINITE element method - Abstract
Highlights • Study of structure-borne sound transmission of cascaded plate–cavity system. • Application of Chebyshev-Ritz method. • Comparable numerical accuracy as compared to finite element method. • Numerical examples are simulated for different configurations. • Better prediction of sound transmission via tuning of cascaded plate–cavity system. Abstract A Chebyshev-Ritz based analytical model is proposed to investigate I-junction within the structural–acoustic model of a cascaded rectangular plate–cavity system. By considering of the structural interconnection force and the moment at edges and structural-acoustic interaction on the interface, the structural and acoustic systems are coupled. Two-dimensional and three-dimensional Chebyshev Polynomial series are used to present the unknown panel displacements and the sound pressure field variable inside the cavities, respectively. The effectiveness and correctness of the proposed model on an I-junction in a typical marine offshore platform are verified with those calculated from Finite Element Analysis. The influence of boundary conditions, structural coupling, plate properties, and size of the source-to-receiver cavities on the offshore platform on structure-borne sound transmission are analyzed and addressed. Numerical examples are simulated for several different configurations. It is shown that the boundary conditions, structural coupling manner, plate properties, and the volume ratio of the source-to-receiver cavity will change the structure-borne sound transmission characteristics of the cascaded rectangular plate–cavity system. With the proposed approach, a better prediction can be obtained for structure-borne sound transmission via proper tuning of the cascaded rectangular plate–cavity system on the offshore platform. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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8. Numerical simulation and re‐design optimization of impressed current cathodic protection for an offshore platform with biofouling in seawater.
- Author
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Wang, W., Li, W.‐H., Song, L.‐Y., Fan, W.‐J., Liu, X.‐J., and Zheng, H.‐B.
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FINITE element method , *SEAWATER , *REMOTE submersibles , *MAGNESIUM oxide , *STEEL - Abstract
A finite element model (FEM) of the offshore platform with biofouling is developed here to predict the effectiveness of the ICCP under seawater. Remotely operated vehicle (ROV) test verified that the offshore platform was fully covered by a coating‐like biofouling to protect the structures from corrosion. FE‐SEM and EDS tests demonstrated that the biofouling deposits on the offshore platform mainly contained magnesium oxides, biofouling deposits, and corrosion products doped with calcium oxides. The polarization relationships of platform steel with biofouling coverage were used as boundary conditions for the numerical simulation. Furthermore, the factors including output current, anode location, seawater conductivity, and biofouling coverage rate, which influenced the protective effectiveness, were comparatively evaluated by FEM. Then, a re‐design two‐anode ICCP system was employed to keep offshore platform in protective condition. A ROV monitored the potential distributions of the legs and demonstrated that numerical simulation results of ICCP had a good agreement with measured data. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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9. 底座关键焊缝裂纹探测与扩展寿命预测.
- Author
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葛运春, 周国强, 吴泽民, and 冷建成
- Abstract
Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
- Published
- 2017
- Full Text
- View/download PDF
10. Numerical analysis on the HSS and SIF of multi-planar DX-joint welds for offshore platforms.
- Author
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Liu, Guijie, Zhong, Benlei, Tian, Xiaojie, Chen, Pengfei, and Mu, Weilei
- Subjects
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OFFSHORE structures , *NUMERICAL analysis , *STRESS intensity factors (Fracture mechanics) , *FATIGUE cracks , *FINITE element method , *STRESS concentration - Abstract
Among offshore platform structures, multi-planar tubular joints are usually in the most dangerous positions and generate fatigue cracks the earliest. In this study, DX-joints were regarded as the research object, and finite element method was adopted to conduct systematic research on the fatigue properties of multi-planar tubular joint welds. Axial, in-plane bending moment, and out-of-plane bending moment loads were applied to explore the stress distribution along the weld path and the hotspot location under different load conditions. Results indicated that the hotspot stress (HSS) location of DX-joints changed with the variation in the combined stress ratio. Through HSS analysis, cracks were prefabricated at the hotspot location of DX-joints to analyze the change rule of the stress intensity factor (SIF). The influence of different loads, crack lengths, and crack depths on SIF was studied to estimate the growth trend of the weld crack and its dominance. The findings can provide theoretical guidance for fatigue damage and safety assessment of offshore platforms. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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11. Safety evaluation of LD27-2 WHPB platform based on rod pumping
- Author
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Yanqun Yu, Xiaoguang Huang, and Zhiming Yin
- Subjects
020209 energy ,Offshore platform ,Mechanical properties ,02 engineering and technology ,010502 geochemistry & geophysics ,01 natural sciences ,Stress (mechanics) ,0202 electrical engineering, electronic engineering, information engineering ,Safety coefficient ,Oil field ,Petroleum refining. Petroleum products ,Rod pumping ,0105 earth and related environmental sciences ,Petrology ,Hydraulic pumping unit ,QE420-499 ,Geotechnical Engineering and Engineering Geology ,Finite element method ,Probability model ,Wind engineering ,General Energy ,Joint distribution of extreme ,Offshore geotechnical engineering ,Submarine pipeline ,TP690-692.5 ,Marine engineering - Abstract
The development of heavy oil with high efficiency is a worldwide difficulty for offshore oil field. The technology of rod pumping provides a possible effective way for offshore heavy oil thermal recovery, but the safety of working platform is the prerequisite for the implementation of this new technology. In this paper, the mechanical model of LD27-2 WHPB platform is established, and the safety performance of the platform under hydraulic pumping unit (HPU) load is evaluated. The distribution of the combined HPU load accords with the classical probability model. When the HPUs are all synchronous, the combined load reaches its maximum. The finite element-based platform safety analysis under the extreme condition is carried out. Under the combined action of wave current, wind load and the extreme HPU load, the maximum stress of the jacket is 83.2 MPa, and the safety coefficient is 4.33, indicating the overall strength of LD27-2 WHPB platform meets the safety requirement.
- Published
- 2020
12. Weak-mode identification and time-series reconstruction from high-level noisy measured data of offshore structures.
- Author
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Liu, Fushun, Li, Huajun, and Lu, Hongchao
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TIME series analysis , *OFFSHORE structures , *NOISE measurement , *DAMPING (Mechanics) , *FOURIER transforms , *FINITE element method - Abstract
The identification of true weak modes buried in high-level, noisy, measured data from offshore structures is a practical but challenging problem because weak modes are typically eliminated as noise and rarely, yield a discrete time series. This study proposes a weak-mode identification and time-series reconstruction method for offshore structures when high-level noise is present. A theoretical development proposed in this study extends the traditional modal analysis to reconstructing the discrete time series of weak modes, thereby removing its previous limitations to only frequencies, damping ratios and mode shapes. Additionally, a second development proposed in this study makes the reconstructed time series not simply a combination of harmonic components from a Fourier transform but rather complex exponentials; the damping of the test structure is thus estimated with a better accuracy. A third theoretical development avoids variations in the results from different original signals by handling multiple signals simultaneously. The proposed approach primarily includes three steps: (1) estimate the poles and corresponding residues of high-level, noisy, measured data by converting high-order difference equations to first-order difference equations; (2) isolate the poles of weak modes by assigning multiple rough-pole windows, and subsequently extract the corresponding residues based on the row number of the isolated pole vector; and (3) identify and reconstruct the time series of the weak modes of interest in the form of complex exponentials. The most primary advantage of the proposed process in engineering applications is that the pole windows can be easily obtained and assigned from the relationship between the frequencies and their poles. Three numerical examples are studied: the first presents the detailed numerical operation of the proposed method, the second extends the proposed method from managing one signal to managing multiple signals, and the third demonstrates the advantage of the approach compared with traditional methods. The numerical results indicate that the original signals can be decomposed into multiple complex exponentials with representative poles and corresponding residues, and that the new signals representing weak modes could be reconstructed by assigning a range of frequencies in terms of their relations with the poles. To study the performance of the proposed method when applied to offshore structures such as offshore platforms and marine risers, the experimental data from the high mode VIV experiments sponsored by the Norwegian Deepwater Programme (NDP) are used firstly. The results show that two dominant frequencies corresponding to the in-line and cross-flow directions can be identified simultaneously even one mode is very weak compared with the other, and the time series of the weak mode could be reconstructed with a rough frequency window. Then sea-test data of two offshore platforms are used: one was collected from the JZ20-2MUQ offshore platform when it was excited by ice, and the other was collected from the WZ11-4D platform when it was excited by waves. The results further demonstrated that a large model order is required to estimate all poles and residues of the original noisy signals, and that the row number corresponding to a weak mode of the isolated pole matrix could be easily determined via finite element analysis or engineering experiences. Therefore, the proposed approach provides not only modal parameters, such as frequencies and damping ratios of true weak modes buried in high-level noise, but also the discrete time series of the weak mode. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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13. Long term effectiveness of life extension methodologies applied to offshore structures.
- Author
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Haagensen, P.J., Larsen, J.E., and Vårdal, O.T.
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OFFSHORE structures , *FATIGUE cracks , *DRILLING & boring , *RETROFITTING , *PEENING , *FINITE element method - Abstract
This paper documents developments in fatigue cracking of a floating platform that required repair and upgrading during 1999–2000. The Veslefrikk B (VFB) platform was built in 1985 for drilling exploration but was converted to a production platform in 1989. Shortly thereafter extensive fatigue cracking was discovered and several repairs were made. However, extensive fatigue cracking continued and a retrofitting program was implemented, using various types of grinding and peening techniques. In 1999 the platform was temporarily decommissioned and dry-docked for a comprehensive repair and upgrading program, following the International Institute of welding (IIW) guidelines for weld improvement methods [1] , this was completed in only four months. However, after a few more years of service fatigue damage again necessitated new repairs. The majority of cracks occurred in the hull skin plates and caused water leakage. It is noteworthy that cracking this time occurred only in areas of the structure that were left untreated in the first retrofitting program due to low levels of stress from FE analyses in these areas. The paper describes the original repair and strengthening program, and the types of subsequent fatigue damage that necessitated new repairs. The recent life extension program has resulted in the safe operation of the platform for an estimated additional period of 20 years. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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14. Joint parameter-input estimation for virtual sensing on an offshore platform using output-only measurements.
- Author
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Song, Mingming, Christensen, Silas, Moaveni, Babak, Brandt, Anders, and Hines, Eric
- Subjects
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KALMAN filtering , *OFFSHORE structures , *STRAIN gages , *FINITE element method , *PROPRIOCEPTION , *BAYESIAN field theory - Abstract
• A recursive window-based Bayesian inference approach is formulated and validated. • It is implemented for joint input-parameter estimation of an offshore structure. • Strain time histories at hotspots are accurately predicted through virtual sensing. • The proposed method outperform modal expansion method for virtual sensing. This paper presents a recursive Bayesian inference framework for joint parameter-input identification, and virtual sensing for strain time history prediction of an offshore platform using sparse output-only measurements. The studied offshore platform, known as FINO3, is in the North Sea and is instrumented with a variety of sensors, including accelerometers and strain gauges. Offshore platforms are fatigue critical structures due to harsh marine environmental conditions and continuous cyclic wind and wave loads. Therefore, continuous monitoring of strain time histories at hotspot locations of offshore structures is important for reducing maintenance cost and avoiding unexpected failures. A windowed unscented Kalman filter (UKF) is employed to estimate an uncertain modeling parameter (foundation stiffness) and unknown input load time histories using output-only acceleration and strain measurements. The input loads are divided into overlapping windows, and windowed inputs and model parameters are combined as an augmented state vector in the UKF framework. Then strain time histories at critical locations are estimated through a virtual sensing strategy using the estimated input loads and model parameter. A traditional modal expansion approach combined with model updating is also implemented for the purpose of verification and comparison. The proposed method is first demonstrated through a numerical study using a finite element model of FINO3, where accurate model parameter and input estimations are obtained. Then the approach is further investigated using the actual measurements on FINO3. More accurate strain predictions are provided by the UKF than the modal expansion approach, which recommends the proposed UKF method for fatigue monitoring and input estimation. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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15. Numerical simulation of gear surface hardening using the finite element method.
- Author
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He, Bin, Huang, Shan, and He, Xiaolin
- Subjects
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SURFACE hardening , *COMPUTER simulation , *ELASTOPLASTICITY , *GEARING machinery , *FINITE element method , *NUMERICAL analysis - Abstract
This paper was devoted to presenting a systematic approach based on finite element method to numerical analysis of gear surface hardening with the consideration of the contact problem. After the contact finite element method theory of gear and rack was introduced, the numerical analysis of gear surface hardening was discussed in detail. The element selection of gear-rack hardening layer based on finite element method was proposed, the algorithm characteristics of gear-rack elastic-plastic contact problems were also put forward, and the material properties and constitutive relations of gear-rack hardening layer were then discussed in detail. The gear-rack elastic-plastic contact analysis results were discussed, and the experimental results with the laser treatment were analyzed with the microstructure changes of the laser hardening layer to measure the performance of the hardening layer. The wear simulating test of gear results in improving the wear resistance greatly, and this surface hardening treatment has been officially put into engineering application. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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16. Modal parameter estimation for jacket-type platforms using noisy free-vibration data: Sea test study
- Author
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Li, Huajun, Li, Ping, and Hu, Sau-Lon James
- Subjects
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PARAMETER estimation , *FINITE element method , *ACCELERATION (Mechanics) , *ACCELEROMETERS , *SIGNAL processing , *DAMPING (Mechanics) - Abstract
Abstract: Accurate estimate of the modal parameters of an offshore structure is crucial to many practical engineering issues, such as finite element (FE) model updating/validation, damage detection, etc. Using noisy acceleration signals collected from a step-relaxation test of a jacket-type offshore platform, we estimate its modal frequencies and damping ratios by an extended Prony''s method, which includes a noise removal procedure to yield filtered signals before implementing the classical Prony''s method on the filtered signals. To validate the applicability of the proposed approach, numerical simulations were firstly performed. Investigating corrupted relaxation response signals simulated from a FE model of the test platform, we conclude that the proposed approach is very accurate on estimating the modal parameters. A significant improvement can be achieved when the filtered, rather than the originally measured, signals are used. Using sea test data measured from accelerometers mounted at three different locations of the test platform, we find that the modal parameters estimated from the filtered signals of the three locations separately are in excellent agreement. [Copyright &y& Elsevier]
- Published
- 2012
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17. Mechanical Modeling of the Not Welded Tubular Y and T-Joints of the Offshore Steels.
- Author
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Belhour, S., Bellaouar, A., Benidir, M., and Lachi, M.
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MECHANICAL models ,WELDED joints ,STEEL ,NUMERICAL analysis ,ANSYS (Computer system) ,MECHANICAL behavior of materials ,STRESS concentration ,FINITE element method - Abstract
In this work a numerical modeling with ANSYS program of the mechanical behavior of the not welded tubular junction structures of the offshore has been considered. The objective is to determine the stress field and displacement of the structure in particular, at the chord/brace intersection of the Y-joint and T-joint under the action of wind and sea wave. [ABSTRACT FROM AUTHOR]
- Published
- 2012
18. Fatigue crack growth prediction method for offshore platform based on digital twin.
- Author
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Fang, Xin, Wang, Honghui, Li, Wenjing, Liu, Guijie, and Cai, Baoping
- Subjects
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FATIGUE crack growth , *FATIGUE cracks , *FRACTURE mechanics , *OFFSHORE structures , *BAYESIAN analysis , *DIGITAL technology , *FINITE element method - Abstract
To accurately predict the crack growth trend of marine structures, this paper proposes a fatigue crack growth prediction method for offshore platforms based on digital twin. First, a digital twin model for offshore platforms is established, and the key technical procedures required for each part of the model are given. Subsequently, to implement consistency maintenance between the virtual model and the physical entity during the digital twin usage, a finite element surrogate model approach based on Gaussian process is performed, which integrates with the crack growth consistency maintenance strategy using dynamic Bayesian network. Finally, according to service condition characteristics of the offshore platform, a crack growth experiment under mixed-mode multi-step loading is designed to verify the effectiveness of the proposed method. The results show that the method not only reduces the influence of uncertain factors on crack growth prediction under complex loads, but also achieves accurate of crack growth through dynamic tracking. • A digital twin five-dimensional model for offshore platform is proposed. • Summarized the key technical methods for building digital twin model. • A fatigue crack growth prediction method based on digital twin is proposed. • A fatigue crack growth experiment under mixed-mode multi-step loading was designed according to the marine environment. • The proposed method can achieve dynamic following and accurate prediction of fatigue crack growth. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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19. CONSTRUCTION OF THE MEGA-FRAME PLATFORMS BASED ON TOPOLOGICAL OPTIMIZATION.
- Author
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Dong Zhao, Dongmei Cai, Mingzhe Zhang, and Shaoli Cai
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MATHEMATICAL optimization ,TOPOLOGY ,SIMULATION methods & models ,DRILLING platforms ,OFFSHORE structures ,FINITE element method ,VIBRATION (Mechanics) ,MECHANICAL loads - Abstract
The article discusses the use of topological optimization in constructing simulated mega-frame platforms (MFP). It is said that based on analyses the MFP does not show mode shape distortion and exhibit the best performance in terms of static and dynamic capability. The use of finite element method (FEM) software in simulating vibration control in platforms exposed to random excitation wave loads is tackled. The vertical loads and horizontal loads suffered by the MFP are detailed.
- Published
- 2008
20. Evaluation of stress concentration for planar tubular joints
- Author
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A. Zeghloul, David Thevenet, Mohamad Fathi Ghanameh, Laboratoire de physique et mécanique des matériaux (LPMM), Université Paul Verlaine - Metz (UPVM)-Institut National Polytechnique de Lorraine (INPL)-Ecole Nationale d'Ingénieurs de Metz (ENIM)-Centre National de la Recherche Scientifique (CNRS), Mécanique des Structures Navales (MSN), and École Nationale Supérieure de Techniques Avancées Bretagne (ENSTA Bretagne)
- Subjects
welded tubular joints ,Materials science ,business.industry ,finite element method ,Metals and Alloys ,020101 civil engineering ,02 engineering and technology ,Bending ,Structural engineering ,Stress distribution ,offshore platform ,Geotechnical Engineering and Engineering Geology ,Condensed Matter Physics ,Brace ,0201 civil engineering ,020303 mechanical engineering & transports ,Planar ,0203 mechanical engineering ,stress distribution ,Materials Chemistry ,stress concentration ,business ,Joint (geology) ,Stress concentration - Abstract
WOS; International audience; In offshore tubular structures, a typical tubular joint may be subjected to three different types of basic loadings: axial, in-plane bending and out-of-plane bending, through its brace members. Each type will cause a different stress distribution at the joint intersection of structures. Moreover, the actual load condition of a tubular joint can be any combination of the above three basic load cases, for this reason, a combined loading was investigated in addition to these three basic loadings. This load is composed of an axial loading combined with a continuation of rotational bending loading obtained while rotate center of the brace around a circle. Different types of planar joints such as T, Y, X, K, DT, DY, DX, TY, TK, DTX, DTDY, and DTDK, with braces subjected to combined loading, were numerically analyzed to study the effect of those different cases of loading and different types of joints, on the stress concentration zone and values.
- Published
- 2006
21. Experimental and Numerical Study of Coupled Dynamic Response of a Mini Tension Leg Platform
- Author
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Anitha Joseph, Subroto Kumar Bhattacharyya, and V. G. Idichandy
- Subjects
Finite element method ,Engineering ,Hull-tether coupling ,Time domain analysis ,Morison-type wave loading ,Ocean Engineering ,Motion estimation ,Natural frequencies ,Tension leg platforms (TLP) ,Hull ,Wave frequency ,Nonlinear systems ,Tension-leg platform ,business.industry ,Tension (physics) ,Mechanical Engineering ,Natural resources exploration ,Structural engineering ,offshore platform ,Wave force ,Production platforms ,business ,Offshore platforms ,Petroleum prospecting ,Numerical analysis - Abstract
Role of mini tension leg platforms (TLP) in oil exploration and production in marginal deepwater fields is becoming increasingly important. Mini TLP combines the simplicity of a spar and favorable response features of a TLP. In this paper, the results of a detailed experimental and numerical investigation of the coupled dynamic behavior of a mini TLP are reported with special attention to hull-tether coupling. The experimental study has been carried out using a scaled model in wave flume with specially designed tethers whose first two "string" natural frequencies are excited by waves, thus achieving strong hull-tether coupling. The numerical study has been carried out using a nonlinear time domain finite element method specifically addressed to compliant offshore platforms using a combination of potential theory based wave loading and Morison-type wave loading. Extensive comparisons between numerical and experimental results have been made both for platform motions and deflected shapes of the tethers and conclusions drawn. Copyright ? 2004 by ASME.
- Published
- 2004
22. Structural monitoring of offshore platforms using impulse and relaxation response
- Author
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Lalu Mangal, V. G. Idichandy, and C. Ganapathy
- Subjects
Engineering ,Finite element method ,Environmental Engineering ,Monitoring ,condition monitoring ,Impulse (physics) ,Deck ,Data acquisition ,on-line technique ,Corrosive effects ,Underwater ,monitoring system ,offshore structure ,dynamic response ,Marine biology ,business.industry ,Continuous monitoring ,Fender ,System identification ,feasibility study ,Structural engineering ,offshore platform ,Vibration ,Water waves ,Ocean engineering ,Underwater foundations ,vibration ,business ,Offshore structures ,Offshore platforms - Abstract
Monitoring offshore platforms, long span bridges, high rise buildings, TV towers and other similar structures is essential for ensuring their safety in service. Continuous monitoring assumes even greater significance in the case of offshore platforms, which are highly susceptible to damage due to the corrosive environment and the continuous action of waves. Also, since a major part of the structure is under water and covered by marine growth, even a trained diver cannot easily detect damage in the structure. In the present work, vibration criterion is adopted for structural monitoring of jacket platforms. Artificial excitation of these structures is not always practicable and ambient excitation due to wind and waves may not be sufficient for collecting the required vibration data. Alternate methods can be adopted for the same purpose, for example, the application of an impact or a sudden relaxation of an applied force for exciting the structure. For jacket platforms, impact can be applied by gently pushing the structure at the fender while relaxation can be accomplished by pulling the structure and then suddenly releasing it using a tug or a supply vessel in both cases. The present study is an experimental investigation on a laboratory model of a jacket platform, for exploring the feasibility of adapting vibration responses due to impulse and relaxation, for structural monitoring. Effects of damage in six members of the platform as well as changes in deck masses were studied. A finite element model of the structure was used to analyze all the cases for comparison of the results as well as system identification. A data acquisition and analysis procedure for obtaining the response signatures of the platform due to the impulse and relaxation procedure was also developed for possible adoption in on-line monitoring of offshore platforms. From the study, it has been concluded that both impulse and relaxation responses are useful tools for monitoring offshore jacket platforms. The present work forms the basis for the development of an automated, on-line monitoring system for offshore platforms, using neural networks. ? 2000 Elsevier Science Ltd. All rights reserved.
- Published
- 2001
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23. Prediction of service fatigue strength of awelded tubular joint on the basis of the notch strain approach
- Author
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C.M Sonsino, D Flade, D. Radaj, and Publica
- Subjects
Cyclic stress ,Lebensdauerabschätzung ,notch stress ,crack propagation ,Industrial and Manufacturing Engineering ,Rißfortschritt ,Schweißverbindung ,General Materials Science ,Offshore Plattform ,Stress concentration ,loading spectrum ,Structural engineering ,structural fatigue strength ,Fatigue limit ,Finite element method ,Metall ,Mechanics of Materials ,Modeling and Simulation ,Service life ,Bauteil ,strength ,specimen ,Materials science ,metal ,welded loading ,Betriebsfestigkeit ,Residual stress ,Kerbspannung ,Fertigung ,strength evaluation ,Probestab ,Woehler curve ,Wöhlerlinie ,Joint (geology) ,Strain gauge ,Beanspruchungskollektiv ,corrosion ,Rohrverbindung ,business.industry ,Mechanical Engineering ,Festigkeitsbeurteilung ,theoretical method ,offshore platform ,Rechenverfahren ,Korrosion ,Beanspruchung ,offshore technology ,Festigkeit ,manufacturing process ,business ,Meerestechnik - Abstract
The applicability of the notch strain approach to the assessment of the fatigue strength and service life of a K-shaped tubular joint is investigated. The structural stresses in the hot spot area are calculated by the finite element method and compared with the results of relevant parametric formulae as well as of strain gauge measurements. The stress concentration factor at the weld toe is determined on the basis of a plane cross-sectional model of the weld at the hot spot. The elastic–plastic notch strains are derived therefrom using the cyclic stress strain curve of the material (finite element results and approximations according to Neuber and Sonsino). The fatigue strength of the tubular joint under constant-amplitude loading is predicted on the basis of the strain S–N curve. The service life under variable-amplitude loading in seawater is derived using the Miner rule. The notch strain approach for welded joints results in unacceptably large differences in the predicted strength and life values under similarly acceptable assumptions in respect of material state, local hardness and residual stress. The inhomogeneity of material and hardness at the weld toe seems to be the main reason for the discrepancies.
- Published
- 1998
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