The Application of Response Based Design in the Verification of the Banff Riser System

2002 ◽  
Author(s):  
David McCann ◽  
Keith Anderson ◽  
Thomas S. Taylor ◽  
Patrick O’Brien
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Design Methodology ◽  
Linear Time ◽  
Frequency Content ◽  
Method Of Solution ◽  
Stochastic Techniques ◽  
Computationally Expensive ◽  
Frequency Domain Approach ◽  
Dynamic Frequency

This paper details work that was conducted during the retrieval and subsequent re-installation of the Banff riser system between September 2000 and March 2001. Originally, deterministic methods were used to design the riser system. It is demonstrated that these methods may not be conservative when compared against stochastic techniques. To ensure a conservative design methodology it is necessary to fully account for the inherent dynamic frequency content of the riser. This is usually achieved using non-linear time domain irregular sea techniques. Time domain irregular sea analysis is computationally expensive in terms of resources and time. This paper presents the results of an alternative method of solution based on the frequency domain approach. Excellent agreement between the results of the time and frequency domain is observed.

Robust Nondiagonal Controller Design for Uncertain Multivariable Regulating Systems

1997 ◽  
Vol 119 (1) ◽  
pp. 80-85 ◽  
Author(s):  
M. A. Franchek ◽  
P. Herman ◽  
O. D. I. Nwokah
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Design Methodology ◽  
Controller Design ◽  
Parametric Uncertainty ◽  
Specific Class ◽  
Loop Design ◽  
Hard Time ◽  
System Integrity ◽  
Frequency Domain Approach

Presented in this paper is a robust controller design methodology for a class of uncertain, multivariable, regulating systems required to maintain a prespecified operating condition within hard time domain tolerances despite a vector of step disturbances. The design methodology is a frequency domain approach and is based on sequential loop design where a Gauss elimination technique facilitates the various design steps. The specific class of systems addressed are those which can be modeled as square, multivariable systems with parametric uncertainty. One restriction imposed is that the system and its inverse are stable for all plant parameter combinations. The key features of this design methodology include (i) the design of a fully populated controller matrix, (ii) the ability to design for system integrity, and (iii) the direct enforcement of hard time domain tolerances through frequency domain amplitude inequalities.

A Frequency Domain Analysis of Learning Control

1994 ◽  
Vol 116 (4) ◽  
pp. 781-786 ◽  
Author(s):  
C. J. Goh
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Linear Time ◽  
Planning Horizon ◽  
Time Domain Analysis ◽  
Learning Control ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Convergence Criterion ◽  
The Time Domain

The convergence of learning control is traditionally analyzed in the time domain. This is because a finite planning horizon is often assumed and the analysis in time domain can be extended to time-varying and nonlinear systems. For linear time-invariant (LTI) systems with infinite planning horizon, however, we show that simple frequency domain techniques can be used to quickly derive several interesting results not amenable to time-domain analysis, such as predicting the rate of convergence or the design of optimum learning control law. We explain a paradox arising from applying the finite time convergence criterion to the infinite time learning control problem, and propose the use of current error feedback for controlling possibly unstable systems.

Efficient Dynamic Analysis of a Combined Spar System via a Frequency Domain Approach

2005 ◽  
Author(s):  
Pol D. Spanos ◽  
Rupak Ghosh ◽  
Lyle D. Finn ◽  
Fikry Botros ◽  
John Halkyard
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Alternative Methods ◽  
Design Parameters ◽  
Combined System ◽  
Frequency Dependent ◽  
Equivalent Linear ◽  
Frequency Domain Approach

The response of a combined Spar/ risers/mooring lines system is conventionally determined by conducting nonlinear time domain analysis. The system nonlinearity is introduced by the mooring nonlinear force, the friction between the buoyancy-can and the preloaded compliant guide, and the quadratic model of the fluid related damping. Obviously, during the design process, it is important to understand the sensitivity of the Spar responses to various parameters. To a great extent, these objectives cannot be readily achieved by using time domain analysis since, in this context, elements with frequency dependent representation such as the added masses and supplementary damping must be incorporated in the analysis; this may require the use of elaborate convolution techniques. This attribute of the time domain solution combined with the necessity of running a significant number of simulations makes it desirable to develop alternative methods of analysis. In the present paper, a frequency domain approach based on the method of the statistical linearization is used for conducting readily a parametric study of the combined Spar system. This method allows one to account by an equivalent linear damping and an equivalent linear stiffness for the mooring nonlinearity, friction nonlinearity, and the damping nonlinearity of the system. Further, frequency dependent inertia and radiation damping terms in the equations of motion are accommodated. This formulation leads to a mathematical model for the combined system, which involves five-by-five mass, damping and stiffness matrices. In the solution procedure, the equivalent parameters of the linear system are refined in an iterative manner, and by relying on an optimization criterion. This procedure is used to assess the sensitivity of representative Spar system responses to various design parameters. Further, the effect of various design parameters on the combined system response is examined. The environmental loadings considered are of the JONSWAP format of a 100-yr hurricane in the Gulf of Mexico.

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.

scholarly journals Frequency–time analysis, low-rank reconstruction and denoising of turbulent flows using SPOD

2021 ◽  
Vol 926 ◽  
Author(s):  
Akhil Nekkanti ◽  
Oliver T. Schmidt
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Large Scale ◽  
Time Series Data ◽  
High Energy ◽  
Turbulent Jet ◽  
Low Rank ◽  
Series Data ◽  
Time Analysis ◽  
Frequency Domain Approach

Four different applications of spectral proper orthogonal decomposition (SPOD) are demonstrated on large-eddy simulation data of a turbulent jet. These are: low-rank reconstruction, denoising, frequency–time analysis and prewhitening. We demonstrate SPOD-based flow-field reconstruction using direct inversion of the SPOD algorithm (frequency-domain approach) and propose an alternative approach based on projection of the time series data onto the modes (time-domain approach). We further present a SPOD-based denoising strategy that is based on hard thresholding of the SPOD eigenvalues. The proposed strategy achieves significant noise reduction while facilitating drastic data compression. In contrast to standard methods of frequency–time analysis such as wavelet transform, a proposed SPOD-based approach yields a spectrogram that characterises the temporal evolution of spatially coherent flow structures. A convolution-based strategy is proposed to compute the time-continuous expansion coefficients. When applied to the turbulent jet data, SPOD-based frequency–time analysis reveals that the intermittent occurrence of large-scale coherent structures is directly associated with high-energy events. This work suggests that the time-domain approach is preferable for low-rank reconstruction of individual snapshots, and the frequency-domain approach for denoising and frequency–time analysis.

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.

A Comparison of Methods for the Coupled Analysis of Floating Structures

2007 ◽  
Author(s):  
Ying Min Low ◽  
Robin S. Langley
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
High Frequency ◽  
Geometric Nonlinearity ◽  
Low Frequency ◽  
Alternative Methods ◽  
Coupled Analysis ◽  
Intermediate Water ◽  
Low Frequency Motion ◽  
Frequency Domain Approach

The dynamic analysis of a deepwater floating platform and the associated mooring/riser system should ideally be fully coupled to ensure a reliable response prediction. It is generally held that a time domain analysis is the only means of capturing the various coupling and nonlinear effects accurately. However, in recent work it has been found that for an ultra-deepwater floating system (2000m water depth), the highly efficient frequency domain approach can provide highly accurate response predictions. One reason for this is the accuracy of the drag linearization procedure over both first and second order motions, another reason is the minimal geometric nonlinearity displayed by the mooring lines in deepwater. In this paper, the aim is to develop an efficient analysis method for intermediate water depths, where both mooring/vessel coupling and geometric nonlinearity are of importance. It is found that the standard frequency domain approach is not so accurate for this case and two alternative methods are investigated. In the first, an enhanced frequency domain approach is adopted, in which line nonlinearities are linearized in a systematic way. In the second, a hybrid approach is adopted in which the low frequency motion is solved in the time domain while the high frequency motion is solved in the frequency domain; the two analyses are coupled by the fact that (i) the low frequency motion affects the mooring line geometry for the high frequency motion, and (ii) the high frequency motion affects the drag forces which damp the low frequency motion. The accuracy and efficiency of each of the methods are systematically compared.

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