Intermolecular spectral densities of liquids: A quantitative comparison of time‐domain and frequency‐domain techniques

1996 ◽  
Vol 104 (3) ◽  
pp. 962-966 ◽  
Author(s):  
Peijun Cong ◽  
John D. Simon ◽  
C. Y. She
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Quantitative Comparison ◽  
Spectral Densities ◽  
Frequency Domain Techniques

A Numerical Method for Representing Retardation Functions With Complex Exponentials

2017 ◽  
Author(s):  
Fushun Liu ◽  
Lei Jin ◽  
Jiefeng Chen ◽  
Wei Li
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Added Mass ◽  
Memory Effects ◽  
Floating Structure ◽  
Frequency Dependent ◽  
Laplace Domain ◽  
The Time Domain ◽  
Frequency Domain Techniques

Numerical time- or frequency-domain techniques can be used to analyze motion responses of a floating structure in waves. Time-domain simulations of a linear transient or nonlinear system usually involve a convolution terms and are computationally demanding, and frequency-domain models are usually limited to steady-state responses. Recent research efforts have focused on improving model efficiency by approximating and replacing the convolution term in the time domain simulation. Contrary to existed techniques, this paper will utilize and extend a more novel method to the frequency response estimation of floating structures. This approach represents the convolution terms, which are associated with fluid memory effects, with a series of poles and corresponding residues in Laplace domain, based on the estimated frequency-dependent added mass and damping of the structure. The advantage of this approach is that the frequency-dependent motion equations in the time domain can then be transformed into Laplace domain without requiring Laplace-domain expressions of the added mass and damping. Two examples are employed to investigate the approach: The first is an analytical added mass and damping, which satisfies all the properties of convolution terms in time and frequency domains simultaneously. This demonstrates the accuracy of the new form of the retardation functions; secondly, a numerical six degrees of freedom model is employed to study its application to estimate the response of a floating structure. The key conclusions are: (1) the proposed pole-residue form can be used to consider the fluid memory effects; and (2) responses are in good agreement with traditional frequency-domain techniques.

Reproducibility of Time-domain and Three Different Frequency-domain Techniques for the Analysis of the Signal-Averaged Electrocardiogram

2000 ◽  
Vol 33 (2) ◽  
pp. 99-105 ◽  
Author(s):  
Rafael Vázquez ◽  
Edward B. Caref ◽  
Francisco Torres ◽  
Margarita Reina ◽  
Jose A. Guerrero ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Frequency Domain Techniques
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