Non-Linear Spring and Damping Forces Estimation During Free Vibration

1995 ◽  
Author(s):  
Michael Feldman ◽  
Simon Braun
Keyword(s):  
Free Vibration ◽  
Hilbert Transform ◽  
Time Domain ◽  
Free Vibration Analysis ◽  
Single Degree Of Freedom ◽  
Non Linear ◽  
Linear Spring ◽  
The Time Domain ◽  
The Hilbert Transform ◽  
Vibrating Systems

Abstract A method for dynamic analysis of sophisticated nonlinear single-degree-of-freedom systems, based on the Hilbert transform in the time domain is described. Using the Hilbert transform together with the proposed method for system identification, we obtain both instantaneous modal parameters together with non-linear force characteristics during free vibration analysis under impulse excitation without long resonance testing. Using the Hilbert transform in the time domain is a new method of studying linear and non-linear vibrating systems exposed to impulse or shock inputs.

Decomposition and Analysis of Non-Stationary Dynamic Signals Using the Hilbert Transform

2008 ◽  
Author(s):  
Michael Feldman
Keyword(s):  
Hilbert Transform ◽  
Time Domain ◽  
Instantaneous Frequency ◽  
Decomposition Method ◽  
Initial Signal ◽  
Time Modeling ◽  
Stationary Signals ◽  
A New Technique ◽  
The Time Domain ◽  
The Hilbert Transform

This paper describes a new technique, called the Hilbert Vibration Decomposition method, dedicated to decomposition of non-stationary wideband dynamic signals. Using the Hilbert transform in the time domain, we extract a number of elementary oscillating components of the initial signal, who’s both the instantaneous frequency and envelope can vary in time. Modeling examples of decomposition of non-stationary signals are included.

Numerical Simulation on Mooring Performance of LNG-FPSO System in Realistic Seas

2005 ◽  
Author(s):  
Yoshiyuki Inoue ◽  
Md. Kamruzzaman
Keyword(s):  
Time Domain ◽  
Oil And Gas ◽  
Three Dimensional ◽  
Time Domain Analysis ◽  
Analysis Tool ◽  
Motion Response ◽  
Non Linear ◽  
Floating System ◽  
Exciting Forces ◽  
The Time Domain

The LNG-FPSO concept is receiving much attention in recent years, due to its active usage to exploit oil and gas resources. The FPSO offloads LNG to an LNG carrier that is located close to the FPSO, and during this transfer process two large vessels are in close proximity to each other for daylong periods of time. Due to the presence of neighboring vessel, the motion response of both the vessels will be affected significantly. Hydrodynamic interactions related to wave effects may result in unfavorable responses or the risk of collisions in a multi-body floating system. Not only the motion behavior but also the second order drift forces are influenced by the neighboring structures due to interactions of the waves among the structures. A study is made on the time domain analysis to assess the behavior and the operational capability of the FPSO system moored in the sea having an LNG carrier alongside under environmental conditions such as waves, wind and currents. This paper presents an analysis tool to predict the dynamic motion response and non-linear connecting and mooring forces on a parallel-connected LNG-FPSO system due to non-linear exciting forces of wave, wind and current. Simulation for the mooring performance is also investigated. The three-dimensional source-sink technique has been applied to obtain the radiation forces and the transfer function of wave exciting forces on floating multi-bodies. The hydrodynamic interaction effect between the FPSO and the LNG carrier is included to calculate the hydrodynamic forces. For the simulation of a random sea and also for the generation of time depended wind velocity, a fully probabilistic simulation technique has been applied. Wind and current loads are estimated according to OCIMF. The effects of variations in wave, wind and current loads and direction on the slowly varying oscillations of the LNG and FPSO are also investigated in this paper. Finally, some conclusions are drawn based on the numerical results obtained from the present time domain simulations.

Non-Stationary Response of Non-Linear SDOF Systems by Perturbation of Wavelet Coefficients

2001 ◽  
Author(s):  
Pranesh Chatterjee ◽  
Biswajit Basu
Keyword(s):  
Wavelet Domain ◽  
Wavelet Coefficients ◽  
Algebraic Equations ◽  
Single Degree Of Freedom ◽  
Displacement Response ◽  
Spring Force ◽  
Non Linear ◽  
Linear Spring ◽  
Random Vibration Theory ◽  
Statistical Functionals

Abstract A wavelet based random vibration theory has been developed for the non-stationary seismic response of single degree of freedom (SDOF) systems with cubic type non-linearity in the spring force. The ground motion process has been characterized by statistical functionals of wavelet coefficients. The wavelet transformed coefficient of the displacement response of the oscillator has been perturbed to obtain a series of wavelet domain algebraic equations. The stochastic response of the system has been obtained by using these sets of wavelet domain equations. The root mean square (r.m.s.) displacement response has been obtained in terms of the functionals of the input wavelet coefficients. Parametric variations are carried out to observe the effects of variation of the magnitudes of non-linear spring stiffness on the temporal variation of instantaneous r.m.s. values of oscillator displacements.

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