Description of Continuous Linear Systems in the Time, Operator and Frequency Domain

2018 ◽  
pp. 37-126
Author(s):  
László Keviczky ◽  
Ruth Bars ◽  
Jenő Hetthéssy ◽  
Csilla Bányász
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Time Operator ◽  
Continuous Linear

Time-Domain Nonlinear SSI Analysis of Foundation Sliding Using Frequency-Dependent Foundation Impedance Derived From SASSI

2008 ◽  
Author(s):  
Mansour Tabatabaie ◽  
Thomas Ballard
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Time Domain ◽  
Soil Structure ◽  
Wave Radiation ◽  
Far Field ◽  
Frequency Dependent ◽  
Nonlinear Springs ◽  
Mat Foundation ◽  
The Time Domain

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using the de-convolution method and/or spatially variable ground motions. For structures that exhibit nonlinearities such as potential base sliding and/or uplift, the frequency-domain procedure is not applicable as it is limited to linear systems. For such problems, it is necessary to solve the problem in the time domain using the direct integration method in programs such as ADINA [2]. The authors recently introduced a sub-structuring technique called distributed parameter foundation impedance (DPFI) model that allows the structure to be partitioned from the total SSI system and analyzed in the time domain while the foundation soil is modeled using the frequency-domain procedure [3]. This procedure has been validated for linear systems. In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used to validate two linear time-domain ADINA models: Model 1 consisting of the mat foundation+DPFI derived from the linear SASSI model and Model 2 consisting of the total SSI system (mat foundation plus a soil block). After linear alignment, the nonlinear springs were added to both ADINA models and re-analyzed in time domain. Model 2 provided the target nonlinear solution while Model 1 provided the results using the DPFI+nonlinear springs. By increasing the amplitude of the vibration load, different levels of foundation sliding were simulated. Good agreement between the results of two models in terms of the displacement response of the mat and cyclic force-displacement behavior of the springs validates the accuracy of the procedure presented herein.

Continuous linear systems

2001 ◽  
pp. 73-205
Author(s):  
Branislav Kisačanin ◽  
Gyan C. Agarwal
Keyword(s):  
Linear Systems ◽  
Continuous Linear

Nonfragile filtering for discrete-time linear systems in finite-frequency domain

2013 ◽  
Vol 86 (4) ◽  
pp. 664-673 ◽  
Author(s):  
Da-Wei Ding ◽  
Xiaoli Li ◽  
Youyi Wang
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Discrete Time ◽  
Finite Frequency ◽  
Time Linear

New frequency domain based stability tests for 2D linear systems

2012 ◽  
Author(s):  
Wojciech Paszke ◽  
Eric Rogers ◽  
Paolo Rapisarda ◽  
Krzysztof Galkowski ◽  
Anton Kummert
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Stability Tests

Approximate Solution of Linear Systems with Laplace-like Operators via Cross Approximation in the Frequency Domain

2019 ◽  
Vol 19 (1) ◽  
pp. 137-145 ◽  
Author(s):  
Ekaterina A. Muravleva ◽  
Ivan V. Oseledets
Keyword(s):  
Approximate Solution ◽  
Iterative Method ◽  
Frequency Domain ◽  
Linear Systems ◽  
Stokes Problem ◽  
Inverse Operator ◽  
Low Rank ◽  
Low Rank Approximation ◽  
Rank Approximation ◽  
Reduced Complexity

AbstractIn this paper we propose an efficient algorithm to compute low-rank approximation to the solution of so-called “Laplace-like” linear systems. The idea is to transform the problem into the frequency domain, and then use cross approximation. In this case, we do not need to form explicit approximation to the inverse operator, and can approximate the solution directly, which leads to reduced complexity. We demonstrate that our method is fast and robust by using it as a solver inside Uzawa iterative method for solving the Stokes problem.

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