Mating Analysis and a Typical Floatover Design

2012 ◽  
Author(s):  
Alan M. Wang ◽  
Ruhua Yuan ◽  
Shaohua Zhu ◽  
Min He ◽  
Ju Fan ◽  
...  
Keyword(s):  
Diffraction Analysis ◽  
Shallow Water ◽  
Frequency Domain ◽  
Time Domain ◽  
Bohai Bay ◽  
Hydrodynamic Properties ◽  
Nonlinear Time Domain ◽  
Offshore Operations

This paper presents a typical floatover design in the shallow water and benign environment of Bohai Bay, China and the major floatover installation devices, as well as the nonlinear time-domain mating analysis. The nonlinear mating simulations are performed using SIMO based on the hydrodynamic properties of the floatover barge, obtained by WADAM, from the linear diffraction analysis in frequency domain. The mating analysis yields numerical findings in selecting and designing floatover devices critical to the success of the floatover operations, thus minimizing any potential operation risks and enabling the offshore operations as smoothly and efficiently as possible.

Non-Linear Time and Frequency Domain Methods for Multi-Row Aeromechanical Analysis

2012 ◽  
Author(s):  
M. T. Rahmati ◽  
L. He ◽  
D. X. Wang ◽  
Y. S. Li ◽  
R. G. Wells ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Computational Models ◽  
Linear Time ◽  
Navier Stokes ◽  
Frequency Domain Method ◽  
Domain Method ◽  
Frequency Domain Methods ◽  
Blade Row ◽  
Nonlinear Time Domain

An unsteady Navier-Stokes solution system for aeromechanical analysis of multiple blade row configurations is presented. A distinctive feature of the solver is that unified numerical methods and boundary condition treatments are consistently used for both a nonlinear time-domain solution mode and a frequency-domain one. This not only enables a wider range of physical aeromechanical problems to be tackled, but also provides a consistent basis for validating different computational models, identifying and understanding their relative merits and adequate working ranges. An emphasis of the present work is on a highly efficient frequency-domain method for multi-row aeromechanic analysis. With a new interface treatment, propagations and reflections of pressure waves between adjacent blade rows are modeled within a domain consisting of only a single passage in each blade row. The computational model and methods are firstly described. Then, extensive validations of the frequency-domain method against both experimental data and the nonlinear time-domain solutions are described. Finally the computational analysis and demonstration of the intra-row reflection effects on the rotor aerodynamic damping are presented.

Time Domain Fatigue Analysis of the Pin for Offshore Bridges Considering the Nonlinear Effect of Sliding Connections

2017 ◽  
Author(s):  
Wenbin Dong ◽  
Ingar Scherf ◽  
Gudfinnur Sigurdsson
Keyword(s):  
Fatigue Life ◽  
Friction Coefficient ◽  
Frequency Domain ◽  
Time Domain ◽  
Stochastic Analysis ◽  
Fatigue Analysis ◽  
Fatigue Assessment ◽  
Nonlinear Spring ◽  
Linear Frequency ◽  
Nonlinear Time Domain

A bridge between platforms needs to operate safely and continuously over its lifecycle. This paper focuses on the fatigue assessment of the bridge pin connection due to relative movements between platforms. A nonlinear time domain stochastic fatigue analysis of the pin connection in a bridge in the North Sea using a combined model of the jacket platforms and the interconnecting bridge is presented. The fatigue life is compared to the fatigue life from a linear frequency domain stochastic analysis. The facility has been in operation for more than 40 years and the operator requested an update of the inspection plans for the bridge. An RBI analysis has been done according to [1] based on fatigue results from wind gusts and relative movements. Regarding the fatigue assessment due to relative movements there are uncertainties related to selection of the friction coefficient. It was assessed that a friction coefficient of 0.4 is slightly conservative in this case. The fatigue life of the pin was calculated based on a linear frequency domain stochastic analysis, assuming that the bridge was fixed at both ends and this was considered reasonable conservative for fatigue estimation. Efforts have been made in the study presented here to assess the conservatism through a nonlinear time domain stochastic fatigue analysis. The sliding connections of the bridge are simulated by nonlinear springs. The effects of assuming different friction coefficients and different nonlinear spring models for a certain friction coefficient on the fatigue damage of the pin are investigated by a sensitivity study. The fatigue lives of the pin thus computed for a series of short-term sea states for the different assumptions for the friction coefficient and the nonlinear spring model are then compared to the result from a corresponding frequency domain approach.

Application of Linearized Morison Load in Pipe Lay Stinger Design

2008 ◽  
Author(s):  
Riaan van ‘t Veer
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Current Velocity ◽  
Extreme Values ◽  
Numerical Results ◽  
Analysis Time ◽  
Ship Motions ◽  
Hydrodynamic Analysis ◽  
Response Amplitude Operators ◽  
Nonlinear Time Domain

This paper presents numerical results of ship motions and global stinger loads through a combined hydrodynamic analysis of a pipe lay vessel with submerged stinger. The results of nonlinear time domain simulations are compared to those obtained through linearization of the Morison load on the slender stinger elements. Through linearization, an iterative frequency domain solution scheme is developed reducing analysis time significantly. Response amplitude operators in operating and limiting sea states are shown, including the influence of current velocity. Through nonlinear time domain simulations insight is obtained on the distribution and magnitude of the extreme values.

scholarly journals Comparison of Frequency Domain and Time-Domain Methods for Aeromechanical Analysis

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
M. T. Rahmati
Keyword(s):  
Unsteady Flow ◽  
Frequency Domain ◽  
Time Domain ◽  
Solution Method ◽  
Frequency Domain Method ◽  
Physical Conditioning ◽  
Domain Method ◽  
Frequency Domain Methods ◽  
Phase Solution ◽  
Nonlinear Time Domain

Unsteady flow around an oscillating plate cascade and that through a single compressor rotor subject to vibration have been computationally studied, aimed at examining the predictive ability of two low fidelity frequency methods compared with a high fidelity time-domain solution method for aeroelasticity. The computational solutions demonstrate the capabilities of the frequency domain methods compared with the nonlinear time-domain solution method in capturing small perturbations in the unsteady flow. They also show the great advantage of significant CPU time saving by the frequency methods over the nonlinear time method. Comparisons of two different frequency methods, nonlinear harmonic and phase solution method, show that these methods can produce different results due to the differences in numeric and physical conditioning. The results obtained using phase solutions method are in better agreement with the nonlinear time-domain solution. This is because the same numeric and physical conditioning are used in both the nonlinear time-domain method and phase solution frequency domain method.

Nonlinear Time and Frequency Domain Methods for Multirow Aeromechanical Analysis

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
M. T. Rahmati ◽  
L. He ◽  
D. X. Wang ◽  
Y. S. Li ◽  
R. G. Wells ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Computational Models ◽  
Navier Stokes ◽  
Frequency Domain Method ◽  
Domain Method ◽  
Frequency Domain Methods ◽  
Blade Row ◽  
Consistent Basis ◽  
Nonlinear Time Domain

An unsteady Navier–Stokes solution system for aeromechanical analysis of multiple blade row configurations is presented. A distinctive feature of the solver is that unified numerical methods and boundary condition treatments are consistently used for both a nonlinear time-domain solution mode and a frequency-domain one. This not only enables a wider range of physical aeromechanical problems to be tackled, but also provides a consistent basis for validating different computational models, identifying and understanding their relative merits and adequate working ranges. An emphasis of the present work is on a highly efficient frequency-domain method for multirow aeromechanical analysis. With a new interface treatment, propagations and reflections of pressure waves between adjacent blade rows are modeled within a domain consisting of only a single passage in each blade row. The computational model and methods are firstly described. Then, extensive validations of the frequency-domain method against both experimental data and the nonlinear time-domain solutions are described. Finally, the computational analysis and demonstration of the intrarow reflection effects on the rotor aerodynamic damping are presented.

Controlled-source electromagnetic sounding in shallow water: Principles and applications

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. F21-F32 ◽  
Author(s):  
David Andréis ◽  
Lucy MacGregor
Keyword(s):  
Shallow Water ◽  
Frequency Domain ◽  
Time Domain ◽  
Electromagnetic Sounding ◽  
Analytical Analysis ◽  
Controlled Source ◽  
The Earth ◽  
Higher Dimensional ◽  
Marine Csem ◽  
Water Depths

The marine controlled-source electromagnetic (CSEM) method is being applied to the problem of detecting and characterizing hydrocarbons in a variety of settings. Until recently, its use was confined to deepwater (water depths greater than approximately [Formula: see text]) because of the interaction of signals with the atmosphere in shallower water depths. The purpose of this study was to investigate, using a simple 1D analytical analysis, the physics of CSEM in shallow water. This approach demonstrates that it is difficult to simply decouple signals that have interacted with the earth from those that have interacted with the air using either frequency-domain or time-domain methods. Stepping away from wavelike approaches, which if applied without care can be misleading for the diffusive fields of CSEM, we demonstrate an effective way to mitigate the effect of the air in shallow water surveys by decomposing the EM signal into modes and using only the mode least affected by interaction with the atmosphere. Such decomposition is straightforward in a 1D earth, and we demonstrate that the approach remains valid in higher dimensional structures. We also show that the coupling between signals diffusing through the earth and those that have interacted with air can be used to our advantage in the interpretation of marine CSEM data.

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