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.

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.

NON LINEAR ANALYSIS OF SHIP MOTIONS AND LOADS IN LARGE AMPLITUDE WAVES

2021 ◽  
Vol 153 (A2) ◽  
Author(s):  
G Mortola ◽  
A Incecik ◽  
O Turan ◽  
S.E. Hirdaris
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Large Amplitude ◽  
Linear Time ◽  
Ship Motions ◽  
Wave Loads ◽  
Time Step ◽  
Strip Theory ◽  
Non Linear ◽  
The Time Domain

A non linear time domain formulation for ship motions and wave loads is presented and applied to the S175 containership. The paper describes the mathematical formulations and assumptions, with particular attention to the calculation of the hydrodynamic force in the time domain. In this formulation all the forces involved are non linear and time dependent. Hydrodynamic forces are calculated in the frequency domain and related to the time domain solution for each time step. Restoring and exciting forces are evaluated directly in time domain in a way of the hull wetted surface. The results are compared with linear strip theory and linear three dimensional Green function frequency domain seakeeping methodologies with the intent of validation. The comparison shows a satisfactory agreement in the range of small amplitude motions. A first approach to large amplitude motion analysis displays the importance of incorporating the non linear behaviour of motions and loads in the solution of the seakeeping problem.

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.

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.

Free Surface Effects on Hydrodynamic Analysis of Flapping Foil Thruster in Waves

2013 ◽  
Author(s):  
E. S. Filippas ◽  
K. A. Belibassakis
Keyword(s):  
Free Surface ◽  
Breaking Waves ◽  
Numerical Results ◽  
Operating Conditions ◽  
Oscillatory Motion ◽  
Ship Motions ◽  
Sea Waves ◽  
Thrust Coefficient ◽  
Hydrodynamic Analysis ◽  
Stage Of Development

The analysis of an oscillating wing located beneath the ship’s hull is investigated as an unsteady thruster, augmenting the overall propulsion of the ship and offering dynamic stabilization. The unsteady thruster undergoes a combined oscillatory motion in the presence of waves. For the system in horizontal arrangement the vertical heaving motion is induced by the motion of the ship in waves, essentially ship heave and pitch, while the rotational pitching motion of the flapping propulsor about its pivot axis is set by an active control mechanism. Our method is based on coupling the seakeeping operators associated with the longitudinal and transverse ship motions with the hydrodynamic forces and moments produced by the flapping lifting surfaces, using simplified unsteady lifting line theory. First numerical results presented in Belibassakis & Politis [1],[2] indicate that high levels of efficiency are obtained in sea conditions of moderate and higher severity, under optimal control settings. For the detailed investigation of the effects of the free surface in the present paper a potential-based panel method has been developed for the hydrodynamic analysis of 2D hydrofoil operating beneath the free surface, undergoing heaving and pitching oscillations while moving with constant forward speed. The instantaneous angle of attack is influenced by the foil oscillatory motion and by the incident waves. At a first stage of development we consider moderate submergence and relatively low speeds permitting us to approximately neglect effects due to breaking waves and cavitation. Numerical results are presented concerning the numerical performance of the developed BEM. Also results concerning the thrust coefficient and the efficiency of the system over a range of motion parameters, including reduced frequency, Strouhal number, feathering parameter and compared against other methods. Our analysis indicates that significant efficiency can be obtained under optimal operating conditions. Thus, the present method can serve as a useful tool for assessment and the preliminary design and control of such systems extracting energy from sea waves for marine propulsion.

Analysis of the Draft Influence on the Numerical Resonant Effects in Side-by-Side Offloading Operation

2015 ◽  
Author(s):  
Pasquale Dinoi ◽  
Rafael A. Watai ◽  
Felipe Ruggeri ◽  
Jesus Gómez-Goñi ◽  
Alexandre N. Simos
Keyword(s):  
Time Domain ◽  
Wave Amplitude ◽  
Vertical Plane ◽  
Numerical Results ◽  
Floating Body ◽  
Damping Factor ◽  
Gap Flow ◽  
Resonant Behavior ◽  
Response Amplitude Operators ◽  
The Time Domain

In the last years hydrodynamic interaction between two vessels in side-by-side configuration is one of the hot issues in offshore floating body dynamics. The paper investigates the hydrodynamical aspects of a floating two body system. The topic is geared towards analysing the influence of the vessel’s draft in side-by-side configuration and in head sea condition. The need to solve this problem arises when one wants to study the hydrodynamic variation for the various stages of a offloading process with a defined operational gap. The system is composed of a barge and a prismatic geosim with a fixed gap value and with two barge’s draft values. Regular wave tests have been performed in the model basin of CEHINAV-Technical University of Madrid (UPM). The motion for the geosim was restricted to the surge, heave and pitch motions (just motions on the vertical plane), whereas the barge was kept fixed. The costant gap value is guaranteed during the tests. A numerical model has been created with WAMIT and with an in-house time-domain Rankine Panel Method (TDRPM). In each case the numerical and experimental response amplitude operators (RAOs) are obtained and compared, researching the limitation of the numerical codes for the gap flow modeling. In the past the gap effects on the numerical results have been studied varying the gap value finding resonant behavior in terms of motion and wave amplitude RAOs. Now the draft value contribution on the hydrodynamic effects is investigated. Also in this case the numerical results indicate a resonant behavior in determined frequencies in motion as well as in wave in the gap, that is not found in the tests. In order to overcome this problem, a procedure for introducing an external damping factor that attenuates the wave amplitude along the gap in the time-domain RPM is evaluated based on the experimental data.

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.

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