Browsing by Author "Mahan, James Robert"
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- Active control of flexural power flow in elastic thin beamsGonidou, Luc-Olivier (Virginia Tech, 1988-02-05)Active control of flexural power flow in infinite, semi-infinite and finite beams by point force inputs has been analytically and experimentally studied. The systems were analyzed by assuming wave solution and then applying various terminating boundary conditions. Optimal control solutions were then obtained using a quadratic Wiener solution. The influence of system parameters such as discontinuity impedance and effects such as near fields, number and location of control actuators and error sensors is investigated and discussed. The mechanisms by which control is achieved are considered. It is demonstrated that the boundary conditions and the system configuration strongly influence the choice of optimal controller format. The experimental work is compared with the theoretical developments and found to be in good agreement. Control was achieved by a LMS Filtered-x algorithm implemented in assembler language on a TMS32020 digital signal processing chip. In general it is demonstrated that the flexural power flow in the beam types considered can be attenuated with a low number of active actuators.
- Active control of sound radiation due to subsonic wave scattering from discontinuities on thin elastic beamsGuigou, Catherine R. J. (Virginia Tech, 1992-07-05)Much progress has been made in recent years in active control of sound radiation from vibrating structures. Reduction of the far-field acoustic radiation can be obtained by directly modifying the response of the structure by applying structural inputs rather than by adding acoustic sources. Discontinuities, which are present in many structures are often important in terms of sound radiation due to wave scattering behavior at their location. In this thesis, an edge or boundary type discontinuity (clamped edge) and a point discontinuity (blocking mass) are analytically studied in terms of sound radiation. When subsonic vibrational waves impinge on these discontinuities, large scattered sound levels are radiated. Active control is then achieved by applying either control forces, which approximate shakers, or pairs of control moments, which approximate piezoelectric actuators, near the discontinuity. Active control of sound radiation from a simply-supported beam is also examined. For a single frequency, the flexural response of the beam subject to an incident wave or an input force (disturbance) and to control forces or control moments is expressed in terms of waves of both propagating and near-field types. The far-field radiated pressure is then evaluated in terms of the structural response, using Rayleigh's formula or a stationary phase approach, depending upon the application. The control force and control moment magnitudes are determined by optimizing a quadratic cost function, which is directly related to the control performance. On determining the optimal control complex amplitudes, these can be resubstituted in the constitutive equations for the system under study and the minimized radiated fields can be evaluated. High attenuation in radiated sound power and radiated acoustic pressure is found to be possible when one or two active control actuators are located near the discontinuity, as is shown to be mostly associated with local changes in beam response near the discontinuity.. The effect of the control actuators on the farfield radiated pressure, the wavenumber spectrum, the flexural displacement and the near-field time averaged intensity and pressure distributions are studied in order to further understand the control mechanisms. The influence of the near-field structural waves is investigated as well. Some experimental results are presented for comparison.
- Active control of sound radiation from fluid loaded platesGu, Yi (Virginia Tech, 1992-10-15)Active control of sound radiation due to subsonic wave scattering from an infinite or a finite fluid-loaded plate excited below the critical frequency is analytically studied. The disturbance is caused by a flexural wave in an infinite plate, or by a point force on a finite plate at subsonic frequencies. The wave scattering is caused by discontinuities on the plate or by the boundary conditions. A feed-forward control approach is applied by implementing either point/line forces or piezoelectric actuators on the plate. The amplitude and phase of control forces are determined by the optimal solution of a cost function which minimizes the far-field radiated acoustic power over a prescribed surface in the half space of the fluid field. The results show that for subsonic excitations, high global reduction in radiated pressure is possible with properly located active control forces. The number and location of control forces employed in order to obtain high control performance are related to the excitation frequency. The far-field sound radiation directivity pattern, the modal amplitudes of the plate vibration, the plate vibration autospectrum in the wave number domain, and the near-field intensity distribution are extensively studied in order to uncover the mechanisms of control.
- Analysis of a space experimental design for high-Tc superconductive thermal bridgesGarcia, Sandrine L. (Virginia Tech, 1994-12-12)Infrared sensor satellites are used to monitor the conditions in the earth's upper atmosphere. In these systems, the electronic links connecting the cryogenically cooled infrared detectors to the significantly warmer amplification electronics act as thermal bridges and, consequently, the mission lifetimes of the satellites are limited due to cryogenic evaporation. High-temperature superconductor (HTS) materials have been proposed by researchers at the National Aeronautics and Space Administration Langley's Research Center (NASA-LaRC) as an alternative to the currently used manganin wires for electrical connection. The potential for using HTS films as thermal bridges has provided the motivation for the design and the analysis of a spaceflight experiment to evaluate the performance of this superconductive technology in the space environment The initial efforts were focused on the preliminary design of the experimental system which allows for the quantitative comparison of superconductive leads with manganin leads, and on the thermal conduction modeling of the proposed system (Lee, 1994). Most of the HTS materials were indicated to be potential replacements for the manganin wires. In the continuation of this multi-year research, the objectives of this study were to evaluate the sources of heat transfer on the thermal bridges that have been neglected in the preliminary conductive model and then to develop a methodology for the estimation of the thermal conductivities of the HTS thennal bridges in space. The Joule heating created by the electrical current through the manganin wires was incorporated as a volumetric heat source into the manganin conductive model. The radiative heat source on the HTS thermal bridges was determined by performing a separate radiant interchange analysis within a high-Tc superconductor housing area. Both heat sources indicated no significant contribution on the cryogenic heat load, which validates the results obtained in the preliminary conduction model. A methodology was presented for the estimation of the thermal conductivities of the individual HTS thermal bridge materials and the effective thermal conductivities of the composite HTS thermal bridges as functions of temperature. This methodology included a sensitivity analysis and the demonstration of the estimation procedure using simulated data with added random errors. The thermal conductivities could not be estimated as functions of temperature; thus the effective thermal conductivities of the HTS thermal bridges were analyzed as constants.
- Analytical and Experimental Characterization of a Linear-Array Thermopile Scanning Radiometer for Geo-Synchronous Earth Radiation Budget ApplicationsSorensen, Ira Joseph (Virginia Tech, 1998-11-30)The Thermal Radiation Group, a laboratory in the department of Mechanical Engineering at Virginia Polytechnic Institute and State University, is currently working towards the development of a new technology for cavity-based radiometers. The radiometer consists of a 256-element linear-array thermopile detector mounted on the wall of a mirrored wedge-shaped cavity. The objective of this research is to provide analytical and experimental characterization of the proposed radiometer. A dynamic end-to-end opto-electrothermal model is developed to simulate the performance of the radiometer. Experimental results for prototype thermopile detectors are included. Also presented is the concept of the discrete Green's function to characterize the optical scattering of radiant energy in the cavity, along with a data-processing algorithm to correct for the scattering. Finally, a parametric study of the sensitivity of the discrete Green's function to uncertainties in the surface properties of the cavity is presented.
- An Application of Wavelet Techniques to Bi-directionality in the Monte Carlo Ray Trace EnvironmentSmith, Dwight Eldridge (Virginia Tech, 2002-12-16)This dissertation presents three different aspects of the incorporation of directionality into the Monte Carlo ray-trace (MCRT) environment: (1) the development of a methodology for using directional surface optical data, (2) the measurement of the bi-directional reflectivity functions for two different surfaces, and (3) MCRT simulations performed using these directional data sets. The methodology presented is based upon a rigorous analytical formulation and is capable of performing simulations of radiation exchange involving directional emission, absorption and reflection given the bi-directional reflectivity functions (BDRF) of the participating surfaces. A wavelet compression technique is presented for the management of extremely large directional data sets. The BDRFs of two different surfaces were acquired using a Surface Optics Corporation model SOC-250 bi-directional reflectometer. These data were processed according to the methodology presented and an MCRT code was used to simulate the action of the SOC-250 in measuring radiant energy reflected from the surfaces of the two samples when illuminated by the source of the SOC-250. Another MCRT code was used to simulate the radiant energy reflected into a plane at the exit of an open-ended rectangular box when the entrance to the box is illuminated by source of the SOC-250. The RMS error between the MCRT simulations of sampling using the SOC-250 and the measured data were determined and then divided by the mean BDRF level of the measured data (RMS/mean[rho]) to provide an estimate of convergence. The RMS/mean[rho] was observed to fall from as much as 138 to 0.84 for the aluminum substrate coated with Krylon Shortcuts Hunter Green Satin aerosol paint as the number of energy bundles emitted in the MCRT simulation went from 103 to 106 at an incident zenith angle of 40 deg. The RMS/mean[rho] was observed to fall from as much as 2.2 to 0.2 for the Norton (150 Fine grit) all-purpose sandpaper coated with Krylon Shortcuts Hunter Green Satin aerosol paint as the number of energy bundles emitted in the MCRT simulation went from 103 to 106 at an incident zenith angle of 40 deg.
- Bidirectional Reflectance Measurements of Low-Reflectivity Optical Coating Z302Shirsekar, Deepali (Virginia Tech, 2019-02-05)Black coatings essentially absorb incident light at all wavelengths from all directions. They are used when minimal reflection or maximum absorption is desired and therefore are effective in applications that require control of stray light. Our motivation stems from the use of black coating Lord Aeroglaze® Z302 in aerospace and remote sensing applications and the desire to support the development of bidirectional spectral models that can be used successfully to predict the performance of optical instruments such as telescopes. The bidirectional reflectance distribution function (BRDF) is an indispensable parameter in the optical characterization of such coatings. The current effort involves investigation of the BRDF of the commercial black coating Aeroglaze® Z302. An automated goniometer reflectometer has been designed, fabricated and successfully used for performing the BRDF measurements of Z302 at visible and ultraviolet wavelengths and at both polarizations. The current contribution involves study of Z302 samples prepared at different thicknesses and by different methods, which provides insight about influence of surface roughness on BRDF of Z302.
- Characterization of Pyranometer Thermal Offset and Correction of Historiacal DataCarnicero Dominguez, Bernardo Antonio (Virginia Tech, 2001-06-15)The Eppley Precision Pyranometer (PSP) is a radiometer used in networks around the world to measure downwelling and upwelling diffuse and total hemispherical broadband solar irradiances. PSP's present an offset in the signal, called thermal offset, produced by a radiation heat exchange between the glass dome, which defines the spectral throughput and the detector. This offset can reach up to 15\% of the total value of the signal when measuring diffuse irradiance under clear sky conditions. The thermal offset is characterized by monitoring the temperature gradient between the dome and detector using thermistors at key locations. The temperatures are acquired by using thermistors. Relationships between the thermal offset and the temperature gradient are established using nighttime data and subsequently used to estimate the offset during daytime. To correct historical data the thermal offset is related to other variables such as the output of a Precision Infrared Pyrgeometer (PIR) or the fraction of cloud cover in the sky. The use of thermistors is a very reliable method to estimate and correct the thermal offset. The relationships between the offset and the IR output and between the offset and the cloud cover fraction provide good estimates of the thermal offset in historical data sets, reducing it 60% to 100% depending on the instrument and the relationship used.
- A computer-aided software engineering toolkit for the integration of CAD/CAM application software in a network environmentGrieshaber, Michele Marie (Virginia Tech, 1991-11-21)Much progress has been made in recent years in the development of Computer-Aided Design and Computer-Aided Manufacturing (CAD/CAM) tools for engineering design, analysis, and manufacturing. Unfortunately, most of these CAD/CAM applications were constructed independently and without standardization. In essence, they automate a single aspect of design, analysis, or manufacturing and cannot be combined to form a cohesive environment, since integration among applications was not addressed during the design phase of CAD/CAM application software creation. In view of this problem, a novel approach is suggested for software integration of applications in a network environment. The distributed integration solution described in this dissertation employs a new "integration client/server" relationship, where the integration server is the core of the system, providing functions to translate or transform data between applications. The integration client consists of an interface with the server, a CAD/CAM application, and a user interface with the integrated system called the GRIM (GRaphical Interface Manager). There is only one integration server in the system, but there may be an unlimited number of clients. The solution created for distributed integration is implemented in a Computer-Aided Software Engineering (CASE) workbench, geared specifically toward the generation of integration systems. This workbench is known as the CAD/CAM CASE Workbench, and includes an integration solution as well as standard CASE tools. The integration solution contains several tools which will aid a system designer in generating integration systems for CAD/CAM applications. Included is the distributed integration solution described in this dissertation. The distributed integration solution is designed to facilitate the semi-automatic generation of an integration system. It consists of an integration server at the center of the integration system which manages the exchange of data among the integration clients. The integration clients are the CAD/CAM applications in the context of the integration system. To use the distributed integration solution, the integration system designer will customize portions of the structure charts, data dictionary, and module specifications contained in the workbench according to the needs of the applications programs and generate C-source code defining the integration system. Using the distributed integration solution, the user will be able to effect data requests for applications, using the GRIM to interact with the system. All data exchanges are request driven. In addition to the distributed integration solution, this research includes a prototype integrated system which allows data to be requested from one application, and translated to a second for display and manipulation. The prototype was tested in a distributed environment and the results are described.
- A Coupled Heat Transfer and Electromagnetic Model for Simulating Microwave Heating of Thin Dielectric Materials in a Resonant CavityMcConnell, Brian Gregory (Virginia Tech, 1999-12-09)Microwave heating is an emerging but still underutilized tool in modern industrial applications. The task of designing microwave applicators for heating industrial materials with temperature-dependent properties is challenging, and trial-and-error system prototyping is an expensive and wasteful means to accomplish this goal. The purpose of this work is to combine existing heat transfer and electromagnetic models to provide a complete simulation for heating dielectric materials in a resonant microwave cavity. The numerical simulation is validated by comparison to several independent sets of experimental data. The ultimate goal is to provide a research tool that will facilitate the industrial microwave applicator design process. With a complete, accurate, and user-friendly numerical simulation, parameters affecting the temperature distribution in stationary and moving process materials can be studied to optimize the results before the first prototype is made. This work also explores the sources of power loss in a microwave system and develops means for quantifying these power losses.
- Creation and Experimental Validation of a Numerical Model of a Michelson InterferometerStancil, Maurice Marcus (Virginia Tech, 2017-02-07)The study whose results are presented here was carried out in support of an ongoing larger effort to investigate and understand the impact of coherence and polarization on the performance of instruments intended to monitor the Earth's radiant energy budget. The visibility of fringes produced by a Michelson interferometer is known to be sensitive to the degree to which the incident light beam is monochromatic. Therefore, the Michelson interferometer has significant potential as a tool for quantifying the degree of temporal coherence of a quasi-monochromatic light beam. Simulation of the performance of an optical instrument using the Monte-Carlo ray-trace (MCRT) method has been shown to be an efficient method for transferring knowledge of the coherence state of a beam of light from one instrument to another. The goal of the effort reported here is to create and experimentally validate an MCRT model for the optical performance of a Michelson interferometer. The effort is motivated by the need to consolidate the knowledge and skills of the investigator in the realm of physical optics, and by the need to make a useful analytical tool available to other investigators in the larger effort.
- Design and analysis of radiometric instruments using high-level numerical models and genetic algorithmsSorensen, Ira Joseph (Virginia Tech, 2002-11-15)A primary objective of the effort reported here is to develop a radiometric instrument modeling environment to provide complete end-to-end numerical models of radiometric instruments, integrating the optical, electro-thermal, and electronic systems. The modeling environment consists of a Monte Carlo ray-trace (MCRT) model of the optical system coupled to a transient, three-dimensional finite-difference electrothermal model of the detector assembly with an analytic model of the signal-conditioning circuitry. The environment provides a complete simulation of the dynamic optical and electrothermal behavior of the instrument. The modeling environment is used to create an end-to-end model of the CERES scanning radiometer, and its performance is compared to the performance of an operational CERES total channel as a benchmark. A further objective of this effort is to formulate an efficient design environment for radiometric instruments. To this end, the modeling environment is then combined with evolutionary search algorithms known as genetic algorithms (GA's) to develop a methodology for optimal instrument design using high-level radiometric instrument models. GA's are applied to the design of the optical system and detector system separately and to both as an aggregate function with positive results.
- Development of a CAD system for automated conceptual design of supersonic aitcraftWampler, Steven Glenn (Virginia Tech, 1988-05-03)Development of a conceptual aircraft design system based on ACSYNT, an aircraft synthesis program written by the NASA Ames Research Center; is discussed. The system, named ACSYNT/VPI, was written using the PHIGS graphics standard for machine independence and designed based on top·down principles and standards. A functional description of ACSYNT is presented as well as detailed software requirements for ACSYNT/VPI. The software's design is covered in depth including design philosophies and software functional specifications. Program output and design results are presented in conjunction with project recommendations. The appendices include supporting design and development information.
- Development of a Thermal Management Methodology for a Front-End DPS Power SupplySewall, Evan Andrew (Virginia Tech, 2002-10-11)Thermal management is a rapidly growing field in power electronics today. As power supply systems are designed with higher power density levels, keeping component temperatures within suitable ranges of their maximum operating limits becomes an increasingly challenging task. This project focuses on thermal management at the system level, using a 1.2 kW front-end power converter as a subject for case study. The establishment of a methodology for using the computer code I-deas to computationally simulate the thermal performance of component temperatures within the system was the primary goal. A series of four benchmarking studies was used to verify the computational predictions. The first test compares predictions of a real system with thermocouple measurements, and the second compares computational predictions with infrared camera and thermocouple measurements on a component mounted to a heat sink. The third experiment involves using flow visualization to verify the presence of vortices in the flow field, and the fourth is a comparison of computational temperature predictions of a DC heater in a controlled flow environment. A radiation study using the Monte Carlo ray-trace method for radiation heat transfer resulted in the reduction of some component temperature predictions of significant components. This radiation study focused on an aspect of heat transfer that is often ignored in power electronics. A component rearrangement study was performed to establish a set of guidelines for component placement in future electronic systems. This was done through the use of a test matrix in which the converter layout was varied a number of different ways in order to help determine thermal effects. Based on the options explored and the electrical constraints on the circuit, an optimum circuit layout was suggested for maximum thermal performance. This project provides a foundation for the thermal management of power electronics at the system level. The use of I-deas as a computational modeling tool was explored, and comparison of the code with experimental measurements helped to explore the accuracy of I-deas as a system level thermal modeling tool.
- Development of an infrared gaseous radiation band model based on NASA SP-3080 for computational fluid dynamic code validation applicationsNelson, Edward L. (Virginia Tech, 1992-08-01)The increased use of infrared imaging as a flow visualization technique and as a validation technique for computational fluid dynamics (CFD) codes has led to an in-depth study of infrared band models. The ability to create fast and accurate images of airframe and plume infrared emissions often depends on the complexity of the band model. An infrared band model code has been created based largely on the band model published in NASA SP-3080, Handbook of Infrared Radiation from Combustion Gases. Improvements to the NASA SP-3080 model using the N I RA T AM data files have been made. The model and its theoretical basis are thoroughly described. Results are presented and are compared with results from the band models contained in SCORPIO and LOIR.
- Dynamic Electrothermal Model of a Sputtered Thermopile Thermal Radiation Detector for Earth Radiation Budget ApplicationsWeckmann, Stephanie (Virginia Tech, 1997-08-28)The Clouds and the Earth's Radiant Energy System (CERES) is a program sponsored by the National Aeronautics and Space Administration (NASA) aimed at evaluating the global energy balance. Current scanning radiometers used for CERES consist of thin-film thermistor bolometers viewing the Earth through a Cassegrain telescope. The Thermal Radiation Group, a laboratory in the Department of Mechanical Engineering at Virginia Polytechnic Institute and State University, is currently studying a new sensor concept to replace the current bolometer: a thermopile thermal radiation detector. This next-generation detector would consist of a thermal sensor array made of thermocouple junction pairs, or thermopiles. The objective of the current research is to perform a thermal analysis of the thermopile. Numerical thermal models are particularly suited to solve problems for which temperature is the dominant mechanism of the operation of the device (through the thermoelectric effect), as well as for complex geometries composed of numerous different materials. Feasibility and design specifications are studied by developing a dynamic electrothermal model of the thermopile using the finite element method. A commercial finite element-modeling package, ALGOR, is used.
- An end-to-end model of the Earth Radiation Budget Experiment (ERBE) Earth-viewing nonscanning radiometric channelsPriestly, Kory James (Virginia Tech, 1993-10-01)The Earth Radiation Budget Experiment (ERBE) active-cavity radiometers are used to measure the incoming solar, reflected solar, and emitted longwave radiation from the Earth and its atmosphere. The radiometers are carried by the National Aeronautics and Space Administration's Earth Radiation Budget Satellite (ERBS) and the National Oceanic and Atmospheric Administration's NOAA-9 and NOAA-10 spacecraft. Four Earth-viewing nonscanning active-cavity radiometers are carried by each platform. Two of the radiometers are sensitive to radiation in the spectral range from 0.2 to 50 μm, while the other two radiometers are sensitive to radiation in the spectral range from 0.2 to 5.0 μm. Each set of radiometers comes in a wide-field-of-view (WFOV) and a medium-field-of-view (MFOV) configuration. The cavities of the shortwave (visible) radiometers are covered with a Suprasil® hemispherical dome to filter out the incoming longwave radiation. Knowledge of the optical and physical properties of the radiometers allows their responses to be predicted using a low-order physical model. A high-level, dynamic electrothermal end-to-end model which accurately predicts the radiometers dynamic output has also been completed. This latter model is used to numerically simulate the calibration procedures of the actual instruments. With calibration of the end-to-end model complete, a simulation of a phenomena referred to as the "solar blip" is conducted to investigate the instruments' responses to steep transient events. The solar blip event occurs when direct solar radiation is briefly incident to the active-cavity radiometric channels as the spacecraft passes into and out of the Earth's shadow.
- Estimation of thermal properties in a medium with conduction and radiation heat transferGuynn, Jerome Hamilton (Virginia Tech, 1996-07-05)The simultaneous estimation of multi-mode heat transfer properties, conductive and radiative, is investigated for materials that include significant heat transfer by radiation. The focus is on insulative type materials with a relatively large optical thickness. Two basic models were developed for the combined conduction and radiation heat transfer: a diffusion solution and a more exact absorbing and isotropically scattering solution. Both solutions were written for one-dimensional heat transfer in gray, isotropically scattering materials. Different experimental setups were compared through a sensitivity analysis of the parameters to determine the best experiment for estimating the properties. An experiment was performed to collect real data to verify estimation procedures. The material used for the experiment was Styrofoam and the experiment consisted of a heat flux supplied by a thin film heater on one boundary and a constant temperature on the other boundary. The thermal capacitance of the heater proved to have an effect on the temperature measurements at the heated surface and had to be incorporated into the model. The estimation procedure involved the use of two methods, the modified Box Kanemasu algorithm and a genetic algorithm. Difficulties were encountered in simultaneously estimating all the properties due to correlation between the thermal conductivity and the radiation parameters, as well as some correlation between the heat capacity of the Styrofoam and the heat capacity of the heater. However, the genetic algorithm did provide fairly narrow and well-defined property ranges and confirmed that radiation transfer was significant in the Styrofoam.
- Experimental Design for Estimating Electro-Thermophysical Properties of a Thermopile Thermal Radiation DetectorBarreto, Joel (Virginia Tech, 1998-07-16)As the Earth's atmosphere evolves due to human activity, today's modern industrial society relies significantly on the scientific community to foresee possible atmospheric complications such as the celebrated greenhouse effect. Scientists, in turn, rely on accurate measurements of the Earth Radiation Budget (ERB) in order to quantify changes in the atmosphere. The Thermal Radiation Group (TRG), a laboratory in the Department of Mechanical Engineering at Virginia Polytechnic Institute and State University, has been at the edge of technology designing and modeling ERB instruments. TRG is currently developing a new generation of thermoelectric detectors for ERB applications. These detectors consist of an array of thermocouple junction pairs that are based on a new thermopile technology using materials whose electro-thermophysical properties are not completely characterized. The objective of this investigation is to design experiments aimed at determining the electro-thermophysical properties of the detector materials. These properties are the thermal conductivity and diffusivity of the materials and the Seebeck coefficient of the thermocouple junctions. Knowledge of these properties will provide fundamental information needed for the development of optimally designed detectors that rigorously meet required design specifications.
- Experimental Design Optimization and Thermophysical Parameter Estimation of Composite Materials Using Genetic AlgorithmsGarcia, Sandrine (Virginia Tech, 1999-06-04)Thermophysical characterization of anisotropic composite materials is extremely important in the control of today fabrication processes and in the prediction of structure failure due to thermal stresses. Accuracy in the estimation of the thermal properties can be improved if the experiments are designed carefully. However, on one hand, the typically used parametric study for the design optimization is tedious and time intensive. On the other hand, commonly used gradient-based estimation methods show instabilities resulting in nonconvergence when used with models that contain correlated or nearly correlated parameters. The objectives of this research were to develop systematic and reliable methodologies for both Experimental Design Optimization (EDO) used for the determination of thermal properties, and Simultaneous Parameter Estimation (SPE). Because of their advantageous features, Genetic Algorithms (GAs) were investigated for use as a strategy for both EDO and SPE. The EDO and SPE approaches used involved the maximization of an optimality criterion associated with the sensitivity matrix of the unknown parameters, and the minimization of the ordinary least squares error, respectively. Two versions of a general-purpose genetic-based program were developed: one is designed for the analysis of any EDO / SPE problems for which a mathematical model can be provided, while the other incorporates a control-volume finite difference scheme allowing for the practical analysis of complex problems. The former version was used to illustrate the genetic performance on the optimization of a difficult mathematical test function. Two test cases previously solved in the literature were first analyzed to demonstrate and assess the GA-based {EDO/SPE} methodology. These problems included the optimization of one and two dimensional designs for the estimation at ambient temperature of two and three thermal properties, respectively (effective thermal conductivity parallel and perpendicular to the fibers plane and effective volumetric heat capacity), of anisotropic carbon/epoxy composite materials. The two dimensional case was further investigated to evaluate the effects of the optimality criterion used for the experimental design on the accuracy of the estimated properties. The general-purpose GA-based program was then successively applied to three advanced studies involving the thermal characterization of carbon/epoxy anisotropic composites. These studies included the SPE of successively three, seven and nine thermophysical parameters, with for the latter case, a two dimensional EDO with seven experimental key parameters. In two of the three studies, the parameters were defined to represent the dependence of the thermal properties with temperature. Finally, the kinetic characterization of the curing of three thermosetting materials (an epoxy, a polyester and a rubber compound) was accomplished resulting in the SPE of six kinetic parameters. Overall, the GA method was found to perform extremely well despite the high degree of correlation and low sensitivity of many parameters in all cases studied. This work therefore validates the use of GAs for the thermophysical characterization of anisotropic composite materials. The significance in using such algorithms is not only the solution to ill-conditioned problems but also, a drastically cost savings in both experimental and time expenses as they allow for the EDO and SPE of several parameters at once.
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