scholarly journals Dynamic Response Analysis of a Floating Bridge Subjected to Environmental Loads

2018 ◽  
Author(s):  
Zhengshun Cheng ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Wind Wave ◽  
Bending Moment ◽  
Response Analysis ◽  
Ultimate Limit State ◽  
Wave Loads ◽  
Frequency Wave ◽  
Environmental Loads ◽  
Load Effects ◽  
Floating Bridge ◽  
Sway Motion

Designing floating bridges for wide and deep fjords is very challenging. The floating bridge is subjected to wind, wave, and current loads. All these loads and corresponding load effects should be properly evaluated, e.g. for ultimate limit state design check. In this study, the wind-, wave- and current-induced load effects of an end-anchored floating bridge are numerically investigated. The considered floating bridge, about 4600 m long, was an early concept for crossing Bjørnafjorden, Norway. It consists of a cable-stayed high bridge part and a pontoon-supported low bridge part, and has a number of eigen-modes, which might be excited by the relevant environmental loads. Numerical simulations show that the sway motion and strong axis bending moment along the bridge girder are primarily induced by wind loads, while variations of heave motion and weak axis bending moment are mainly induced by wave loads. Current loads mainly provide damping force to reduce the variations of sway motion and strong axis bending moment. Turbulent wind can cause significantly larger low-frequency resonant responses than second-order difference-frequency wave loads.

Numerical Modeling and Dynamic Analysis of a Floating Bridge Subjected to Wind, Wave, and Current Loads

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Zhengshun Cheng ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Axial Force ◽  
Wind Wave ◽  
Bending Moment ◽  
Wave Loads ◽  
Environmental Loads ◽  
Turbulent Wind ◽  
Load Effects ◽  
Floating Bridge ◽  
Bridge Girder ◽  
Sway Motion

Designing reliable and cost-effective floating bridges for wide and deep fjords is very challenging. The floating bridge is subjected to various environmental loads, such as wind, wave, and current loads. All these loads and associated load effects should be properly evaluated for ultimate limit state design check. In this study, the wind-, wave-, and current-induced load effects are comprehensively investigated for an end-anchored curved floating bridge, which was an early concept for crossing the Bjørnafjorden. The considered floating bridge is about 4600 m long and consists of a cable-stayed high bridge part and a pontoon-supported low bridge part. It also has a large number of eigen-modes, which might be excited by the environmental loads. Modeling of wind loads on the bridge girder is first studied, indicating that apart from aerodynamic drag force, aerodynamic lift and moment on the bridge girder should also be considered due to their significant contribution to axial force. Turbulent wind spectrum and spatial coherence play an important role and should also be properly determined. The sway motion, axial force, and strong axis bending moment of the bridge girder are mainly induced by wind loads, while the heave motion, weak axis bending moment, and torsional moment are mainly induced by wave loads. Turbulent wind can cause significant larger low-frequency eigen-mode resonant responses than the second-order difference frequency wave loads. Current loads mainly contribute damping and reduce the variations of sway motion, axial force, and strong axis bending moment.

Extreme Response Analysis of an End-Anchored Floating Bridge

2019 ◽  
Author(s):  
Zhengshun Cheng ◽  
Zhen Gao ◽  
Torgeir Moan
Keyword(s):  
Axial Force ◽  
Limit State ◽  
Bending Moment ◽  
Contour Method ◽  
Response Analysis ◽  
Ultimate Limit State ◽  
Extreme Response ◽  
Structural Responses ◽  
Floating Bridge ◽  
Extreme Responses

Abstract During the design of a floating bridge, extreme structural responses are required to be properly evaluated for ultimate limit state (ULS) design check. This study addresses the estimation of extreme structural responses for an end-anchored curved floating bridge. The floating bridge, about 4600 m, consists of a cable-stayed high bridge part and a pontoon-supported low bridge part. The long-term extreme responses are approximated by using a engineering approach, i.e., the environmental contour method. The sea state with 100-year environmental conditions is considered, and a 90% fractile is used to calculate the short-term extreme responses by using the Gumbel method and the mean up-crossing rate (MUR) method based on 100 1-hour simulations with different seeds. The extreme responses are expressed as μ + κσ, where μ and σ are the ensemble mean and standard deviation, and κ is a multiplying factor. Numerical results show that structural responses are close to Gaussian distributed. κ of axial force and strong axis bending moment along the bridge girder estimated by both the Gumbel and MUR methods vary in the vicinity of 4. κ estimated by the two method deviates, especially for axial force. Moreover, for both methods the estimated κ deviates more significantly if fewer ensembles are used.

Influence of Second-Order Difference-Frequency Wave Loads on the Floating Wind-Wave Hybrid Platform

2017 ◽  
Author(s):  
Hyebin Lee ◽  
Yoon Hyeok Bae ◽  
Kyong-Hwan Kim ◽  
Sewan Park ◽  
Keyyong Hong
Keyword(s):  
Wind Wave ◽  
Computational Effort ◽  
Second Order ◽  
Difference Frequency ◽  
Linear Wave ◽  
Wave Loads ◽  
Wave Load ◽  
Frequency Wave ◽  
Order Difference ◽  
Hybrid Platform

A wind-wave hybrid power generation system is a floating offshore energy platform which is equipped with a number of wind turbines and wave energy converters (WECs) to harvest energy from various resources. This wind-wave hybrid platform is moored by eight catenary lines to keep its position against wind-wave-current environment. In most cases, the resonant frequency of horizontal motion of moored platform is very low, so a resonance is hardly seen by numerical simulation with linear wave assumptions. However, the incident waves with different frequency components are accompanied by sum and difference frequency loads due to the nonlinearity of the waves. Typically, the magnitude of the second-order wave loads are small and negligible, but once the second-order wave loads excite the platform at its natural frequency, the resonance can take place, which results in adverse effects on the platform. In this paper, the second-order difference frequency wave load on the wind-wave hybrid platform is numerically assessed and time domain simulation by coupled platform-mooring dynamic analysis is carried out. As a result, the horizontal motions of the platform was highly excited and the increased motions led higher top tension of the mooring lines compared with the case of linear wave environment. Especially, the combination of the wind and wave loads excited the horizontal motions more and made the mooring top tension far higher than wave load was only applied. With regards to the second-order difference frequency wave load, the result with the Quadratic Transfer Function (QTF) is compared to the one with Newman’s approximation. As the simulation results between them was insignificant, the Newman’s approximation can be used instead of the complete QTF to reduce the computational effort.

Floating Bridge Technology: Prediction of Extreme Environmental Load Effects

2016 ◽  
Author(s):  
Bruno Villoria
Keyword(s):  
Environmental Load ◽  
Environmental Loads ◽  
Load Effects ◽  
Floating Bridge ◽  
Bridge Technology

The present paper describes the different concepts considered for the crossing of Bjørnfjorden. The emphasis is put on the methodology implemented for the estimation of the extreme environmental loads the chosen structure will be exposed to.

Joint Description Methods of Wind and Waves for the Design of Offshore Wind Turbines

2009 ◽  
Vol 43 (3) ◽  
pp. 23-33 ◽  
Author(s):  
Kim E. Mittendorf
Keyword(s):  
Wind Energy ◽  
Wind Wave ◽  
Limit State ◽  
Wave Model ◽  
Design Guidelines ◽  
Offshore Wind ◽  
Ultimate Limit State ◽  
Wave Loads ◽  
Offshore Wind Energy ◽  
The North

AbstractWind and wave loads are equally important for the design of offshore wind energy structures. For the design against an ultimate limit state or fatigue, the engineer has to estimate the combination of loads that are likely to occur simultaneously during the design life of the wind turbine. This is quite a complex task, involving different wind/wave models, load-calculation methods and statistical analysis of simultaneous extreme wind and wave conditions. Moreover, reliable and realistic methods for the assessment of the service life of an offshore wind energy converter under combined wind and wave loads are necessary. However, the current design guidelines (Det Norske Veritas or German Lloyd) provide hardly any information on how to model the wind and wave correlation. In this article, several approaches for obtaining the required wind-wave correlation for the design have been investigated. Manual wave forecasting methods, spectral sea state descriptions and numerical wave model data have been compared to simultaneously measured wind and wave data from the FINO research platform in the German Bight of the North Sea. The used approaches are general and can be easily applied to different data sets from different regions.

Wind/Wave Misalignment Effects on Mooring Line Tensions for a Spar Buoy Wind Turbine

2018 ◽  
Author(s):  
Luigia Riefolo ◽  
Fernando del Jesus ◽  
Raúl Guanche García ◽  
Giuseppe Roberto Tomasicchio ◽  
Daniela Pantusa
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Wave ◽  
Offshore Wind ◽  
Mooring Line ◽  
Ultimate Limit State ◽  
International Electrotechnical Commission ◽  
Wave Loads ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

The design methodology for mooring systems for a spar buoy wind turbine considers the influence of extreme events and wind/wave misalignments occurring in its lifetime. Therefore, the variety of wind and wave directions affects over the seakeeping and as a result the evaluation of the maxima loads acting on the spar-buoy wind turbine. In the present paper, the importance of wind/wave misalignments on the dynamic response of spar-type floating wind turbine [1] is investigated. Based on standards, International Electrotechnical Commission IEC and Det Norske Veritas DNV the design of position moorings should be carried out under extreme wind/wave loads, taking into account their misalignments with respect to the structure. In particular, DNV standard, in ‘Position mooring’ recommendations, specifies in the load cases definition, if site specific data is not available, to consider non-collinear environment to have wave towards the unit’s bow (0°) and wind 30° relative to the waves. In IEC standards, the misalignment of the wind and wave directions shall be considered to design offshore wind turbines and calculate the loads acting on the support structure. Ultimate Limit State (ULS) analyses of the OC3-Hywind spar buoy wind turbine are conducted through FAST code, a certified nonlinear aero-hydro-servo-elastic simulation tool by the National Renewable Energy Laboratory’s (NREL’s). This software was developed for use in the International Energy Agency (IEA) Offshore Code Comparison Collaborative (OC3) project, and supports NREL’s offshore 5-MW baseline turbine. In order to assess the effects of misaligned wind and wave, different wind directions are chosen, maintaining the wave loads perpendicular to the structure. Stochastic, full-fields, turbulence simulator Turbsim is used to simulate the 1-h turbulent wind field. The scope of the work is to investigate the effects of wind/wave misalignments on the station-keeping system of spar buoy wind turbine. Results are presented in terms of global maxima determined through mean up-crossing with moving average, which, then, are modelled by a Weibull distribution. Finally, extreme values are estimated depending on global maxima and fitted on Gumbel distribution. The Most Probable Maximum value of mooring line tensions is found to be influenced by the wind/wave misalignments. The present paper is organized as follows. Section ‘Introduction’, based on a literature study, gives useful information on the previous studies conducted on the wind/wave misalignments effects of floating offshore wind turbines. Section ‘Methodology’ describes the applied methodology and presents the spar buoy wind turbine, the used numerical model and the selected environmental conditions. Results and the corresponding discussion are given in Section ‘Results and discussion’ for each load case corresponding to the codirectional and misaligned wind and wave loads. Results are presented and discussed in time and frequency domains. Finally, in Section ‘Conclusion’ some conclusions are drawn.

Dynamic Response Analysis of the Offshore Wind Turbine Support Structure Under Extreme Conditions

2011 ◽  
Author(s):  
Qian Chen ◽  
Shixiao Fu ◽  
Zaojian Zou
Keyword(s):  
Wind Turbine ◽  
Bending Moment ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Response Analysis ◽  
Extreme Conditions ◽  
Wave Load ◽  
Support Structure ◽  
Environmental Loads ◽  
Vortex Induced Vibrations

Based on modal analysis, the environmental loads of an offshore wind turbine under extreme conditions are analyzed, including the static wind load on the support structure, the static current load and wave load on the foundation. The vortex-induced vibrations caused by wind and current have also been studied. The dynamic displacement and bending moment characteristics of the offshore wind turbine support structure under the extreme conditions have been analyzed.

Submarine Pipeline Installation Joint Industry Project: Global Response Analysis of Pipelines During S-Laying

2006 ◽  
Author(s):  
Enrico Torselletti ◽  
Luigino Vitali ◽  
Roberto Bruschi ◽  
Erik Levold ◽  
Leif Collberg
Keyword(s):  
Water Depth ◽  
Large Diameter ◽  
Bending Moment ◽  
Response Analysis ◽  
Submarine Pipeline ◽  
Safety Level ◽  
Design Guideline ◽  
Load Effect ◽  
Major Vessel ◽  
Load Effects

The development of deep water gas fields using trunklines to carry the gas to the markets is sometime limited by the feasibility/economics of the construction phase. In particular there is market for using S-lay vessel in water depth larger than 1000m. The S-lay feasibility depends on the applicable tension at the tensioner which is a function of water depth, stinger length and stinger curvature (for given stinger length by its curvature). This means that, without major vessel up-grading and to avoid too long stingers that are prone to damages caused by environmental loads, the application of larger stinger curvatures than allowed by current regulations/state of the art, is needed. The work presented in this paper is a result of the project “Development of a Design Guideline for Submarine Pipeline Installation” sponsored by STATOIL and HYDRO. The technical activities are performed in co-operation by DNV, STATOIL and SNAMPROGETTI. This paper presents the results of the analysed S-lay scenarios in relation to extended laying ability of medium to large diameter pipelines in order to define the statistical distribution of the relevant load effects, i.e. bending moment and longitudinal strain as per static/functional, dynamic/total, and environmental load effects. The results show that load effects (longitudinal applied strain and bending moment) are strongly influenced by the static setting (applied stinger curvature and axial force at the tensioner in combination with local roller reaction over the stinger). The load effect distributions are the basis for the development of design criteria/safety factors which fulfil a predefined target safety level.

Global Structural Response Analysis of Jack-Up Ship in Transit Condition

2013 ◽  
Vol 344 ◽  
pp. 66-69
Author(s):  
Xiang Zhu ◽  
Yong Sheng Tang ◽  
Yao Zhao ◽  
Heng Kui Ye
Keyword(s):  
Structural Response ◽  
Bending Moment ◽  
Element Model ◽  
Inertia Force ◽  
Response Analysis ◽  
Wave Loads ◽  
Critical Areas ◽  
Hull Structure ◽  
In Transit ◽  
Jack Up

The global structural response of a four-leg jack-up wind turbine installation ship in the transit condition was analyzed in this paper. The finite element model of the hull and legs were established with the Software MSC. PATRAN. On the basis of long-term forecast of the wave loads, the corresponding designed wave parameters are determined with the vertical wave bending moment of the midship cross section served as the main load control parameter. Considering the gravity, hydrostatic pressure, the hydrodynamic loads induced by the wave, inertia force induced by the motion and acceleration of the ship and the wind force on the legs and hull, the direct calculated method was used to evaluate the global structural response of the vessel. The deformation and stress of the hull and legs were calculated and checked. The results showed that the strength of the hull and leg could meet the rules requirements. For the jack-up ship in the transit condition, the critical areas are mainly lower part of legs and the corresponding hull structure.

Extreme Dynamic Structural Response Analysis of Catenary Moored Spar Wind Turbine in Harsh Environmental Conditions

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Madjid Karimirad ◽  
Torgeir Moan
Keyword(s):  
Wind Turbine ◽  
Fatigue Limit ◽  
Limit State ◽  
Structural Response ◽  
Bending Moment ◽  
Response Analysis ◽  
Ultimate Limit State ◽  
Average Wind Speed ◽  
Structural Responses ◽  
H 20

Proper performance of structures requires among other things that their failure probability is sufficiently small. This would imply design for survival in extreme conditions. The failure of a system can occur when the ultimate strength is exceeded (ultimate limit state (ULS)) or fatigue limit (fatigue limit state) is exhausted. The focus in this paper is on the determination of extreme responses for ULS design checks, considering coupled wave and wind induced motion and structural response in harsh condition up to 14.4 m significant wave height and 49 m/s 10 min average wind speed (at the top of the tower, 90 m) for a parked floating wind turbine of a spar type concept. In the survival condition, the wind induced resonant responses (mainly platform pitch resonance) are dominant. Due to the platform resonant motion responses, the structural responses are close to Gaussian, but wide banded. The critical structural responses are determined by coupled aerohydro-elastic time domain simulation. Based on different simulations (20 1 h, 20 2 h, 20 3 h, and 20 5 h), the mean up-crossing rate has been found in order to predict the extreme structural responses. The most probable maximum of the bending moment and the bending moment having an up-crossing rate of 10−4 are found to be close in the present research. The minimum total simulation time in order to get accurate results is highly correlated with the needed up-crossing rate. The 1 h and 2 h raw data cannot provide any information for 10−4 up-crossing rate. Comparison of different simulation periods shows that the 20 1 h simulations can be used in order to investigate the 3 h extreme bending moment if the proper extrapolation of up-crossing rate is used.

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