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Stochastic analysis of an ecosystem of two competing species
Title
Stochastic analysis of an ecosystem of two competing species.
Creator
Cai, Guo-Qiang, Lin, Y. K.
Date Issued
2006-08
PURL
http://purl.flvc.org/fau/fd/FAUIR000098
Format
Citation
Determination of probability density from statistical moments by neural network approach
Title
Determination of probability density from statistical moments by neural network approach.
Creator
Zheng, Zhiyin., Florida Atlantic University, Cai, Guo-Qiang, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
It is known that response probability densities, although important in failure analysis, are seldom achievable for stochastically excited systems except for linear systems under additive excitations of Gaussian processes. Most often, statistical moments are obtainable analytically or experimentally. It is proposed in this thesis to determine the probability density from the known statistical moments using artificial neural networks. A multi-layered feed-forward type of neural networks with...
Show moreIt is known that response probability densities, although important in failure analysis, are seldom achievable for stochastically excited systems except for linear systems under additive excitations of Gaussian processes. Most often, statistical moments are obtainable analytically or experimentally. It is proposed in this thesis to determine the probability density from the known statistical moments using artificial neural networks. A multi-layered feed-forward type of neural networks with error back-propagation training algorithm is proposed for the purpose and the parametric method is adopted for identifying the probability density function. Three examples are given to illustrate the applicability of the approach. All three examples show that the neural network approach gives quite accurate results in comparison with either the exact or simulation ones.
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Date Issued
1996
PURL
http://purl.flvc.org/fcla/dt/15330
Subject Headings
Distribution (Probability theory), Moments method (Statistics), Estimation theory, Structural failures--Investigation, Neural networks (Computer science)
Format
Document (PDF)
Nonlinear stochastic systems
Title
Nonlinear stochastic systems.
Creator
Cai, Guo-Qiang, Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
This thesis is concerned with nonlinear dynamical systems subject to random or combined random and deterministic excitations. To this end, a systematic procedure is first developed to obtain the exact stationary probability density for the response of a nonlinear system under both additive and multiplicative excitations of Gaussian white noises. This procedure is applicable to a class of systems called the class of generalized stationary potential. The basic idea is to separate the...
Show moreThis thesis is concerned with nonlinear dynamical systems subject to random or combined random and deterministic excitations. To this end, a systematic procedure is first developed to obtain the exact stationary probability density for the response of a nonlinear system under both additive and multiplicative excitations of Gaussian white noises. This procedure is applicable to a class of systems called the class of generalized stationary potential. The basic idea is to separate the circulatory probability flow from the noncirculatory flow, thus obtaining two sets of equations for the probability potential. It is shown that previously published exact solutions are special cases of this class. For those nonlinear systems not belonging to the class of generalized stationary potential, an approximate solution technique is developed on the basis of weighted residuals. The original system is replaced by the closest system belonging to the class of generalized stationary potential, in the sense that the statistically weighted residuals are zero for some suitably selected weighting functions. The consistency of the approximation technique is proved in terms of certain statistical moments. The above exact and approximate solution techniques are extended to two types of nonlinear systems: one subjected to non-Gaussian impulsive noise excitations and another subjected to combined harmonic and broad-band random excitations. Approximation procedures are devised to obtain stationary probabilistic solutions for these two types of problems. Monte Carlo simulations are performed to substantiate the accuracy of the approximate solution procedures.
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Date Issued
1992
PURL
http://purl.flvc.org/fcla/dt/12293
Subject Headings
Nonlinear theories, Stochastic systems, Stochastic processes
Format
Document (PDF)
new methodology in accelerated testing of mechanical heart valve prostheses
Title
A new methodology in accelerated testing of mechanical heart valve prostheses.
Creator
Wu, Changfu., Florida Atlantic University, Lin, Y. K., Cai, Guo-Qiang, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
Mechanical heart valve (MHV) prosthesis is used commonly for clinical replacement of a diseased or dysfunctional natural valve. It is expected to operate uninterruptedly in the human chest for at least 10 years. Classified as Class III medical devices, MHVs of a new design are required by the Food and Drug Administration (FDA) to undergo accelerated durability test for up to 600 million cycles, before a pre-market approval (PMA) can be considered. Knowledge of potential damage/failure...
Show moreMechanical heart valve (MHV) prosthesis is used commonly for clinical replacement of a diseased or dysfunctional natural valve. It is expected to operate uninterruptedly in the human chest for at least 10 years. Classified as Class III medical devices, MHVs of a new design are required by the Food and Drug Administration (FDA) to undergo accelerated durability test for up to 600 million cycles, before a pre-market approval (PMA) can be considered. Knowledge of potential damage/failure mechanisms is of practical interest in assessing the results obtained from accelerated testing. During such tests, an MHV is subjected to higher stresses at higher cycling frequency, and to more severe hydrodynamic environment than those under normal physiological conditions. Three primary factors contributable to damage/failure of an MHV are investigated, namely, contact stresses, water hammer effect, and cavitation. Parametric study is conducted on the contact-induced damage, using the model of a ball-indentation test. Four possible modes of contact damage are identified. Schemes for the selection of appropriate coating parameters to minimize contact stresses in a valve component are discussed. Experimental results of dynamic stresses on a leaflet are presented. The water hammer effect at the instant of valve closure is studied. The destructive force of cavitation is investigated, by incorporating bubble dynamics in a damage tolerance analysis. Cavitation is found to have a greater effect on potential valve damage/failure during accelerated testing. A new measure, cavitation impulse (CI), is introduced to quantify the intensity of MHV cavitation. It is defined as the area under the trace of the high-frequency pressure bursts generated by collapses of cavitation bubbles. CI is modeled as a stationary stochastic process with a discrete parameter (beats), the probability structure of which is estimated from the experimental data. Each CI accounts for both the magnitude and the time-duration of the impinging high pressure of cavitation; therefore, it correlates more closely with cavitation damage on MHV components, thus the time-to-failure (life) of an MHV undergoing testing.
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Date Issued
2003
PURL
http://purl.flvc.org/fau/fd/FADT12077
Subject Headings
Heart valve prosthesis, Cavitation, Accelerated life testing
Format
Document (PDF)