The applicability and evaluation of a generalized gamma(T) family of flux-based representations a... more The applicability and evaluation of a generalized gamma(T) family of flux-based representations are examined for two different thermal analysis formulations for structures and materials which exhibit no phase change effects. The so-called H-theta and theta forms are demonstrated for numerous test models and linear and higher-order elements. The results show that the theta form with flux-based representations is generally superior to traditional approaches.
International Journal of Heat and Mass Transfer, 2005
... A comparative experimental and numer-ical study on a miniature JouleThomson cooler for stead... more ... A comparative experimental and numer-ical study on a miniature JouleThomson cooler for steady ... Optimization of rib-roughened surface geom-etries was conducted numerically [93]. ... A ground testing facility was described for modeling projectile flight heating upon reentry [117 ...
39th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, 1998
A plausible standardized formal theory of development/evolution of a wide class of computational ... more A plausible standardized formal theory of development/evolution of a wide class of computational algorithms for dynamic analysis is presented. The proposed developments are significantly different from the way traditional modal type and a wide class of step-by-step time integration approaches have been developed and described in the research literature and in standard text books over the years. The theoretical ideas and basis towards the evolution of a generalized methodology and formulations leading to integral operators in time and a wide class of single-step integration operators, multi-step integration operators, and a class of finite element in time integration operators, and their relationships for the resulting solution of dynamic equation systems are particularly addressed. Comparisons are also drawn with those obtained from the original methods of development. Furthermore, a variety of time operators are uniquely identified by discrete numerically assigned [DNA] algorithmic markers which not only serve as a prelude towards plausibly providing a standardized formal forum for selecting and identifying time operators but also permit lucid communication when referring to time operators. Furthermore, a single analysis code which permits a variety of choices to the analyst is now feasible for performing structural dynamic computations.
Computational Fluid and Solid Mechanics 2003, 2003
Publisher Summary This chapter presents a novel primal-dual technique to overcome many computatio... more Publisher Summary This chapter presents a novel primal-dual technique to overcome many computational challenging issues—namely, constraint preservation, preserving order of accuracy of time integration operators, and faster convergence rates of nonlinear iterations for the solution of flexible multibody dynamical differential-algebraic equations index-3 systems. In addition, the proposed technique preserves the underlying properties of time integration operators for ordinary differential equations and eliminates the need for index reduction, constraint stabilization, and regularization techniques. The claims of the proposed technique are illustrated via numerical examples by employing energy-momentum preserving method and stiff integrators, such as dissipative methods, that are part of a unified family of generalized integration operators encompassing LMS methods. Numerous numerical examples are presented by employing nondissipative and dissipative integrators. From the results, it is evident that the present formulation preserves the constraints and order of accuracy of the time-integration scheme eliminating the need for index reduction, constraint stabilization, and regularization techniques.
The present paper describes a Petrov-Galerki n based Least Squares approach for formulating the t... more The present paper describes a Petrov-Galerki n based Least Squares approach for formulating the transient flow/thermal behavior due to solodification processes. Both single and multiple phase change effects are considered in this study. And, emphasis is placed upon comparisons of the present developments with available experimental results and or results published in the literature. An adaptive time stepping strategy is employed for the trapezoidal family of methods. Applications to practical situations where previous studies have been done are presented. The overall developments agree well and validations are presented in this paper.
The emerging trends in Resin Transfer Molding (RTM) process technology for composites manufacturi... more The emerging trends in Resin Transfer Molding (RTM) process technology for composites manufacturing are its applications in the manufacture of complex thick composite structures. Process modeling simulation tools analyzing the three-dimensional flow of resin impregnating the thick fiber preform are instrumental in process optimizations. The true three-dimensional flow field with multiple flow fronts and the merging and diverging fronts involved in the solution of the time progression of the resin inside a mold cavity pose significant challenges and there is a need for efficient, physically accurate algorithms for process simulation studies. In this paper, a new formulation based on the time dependent conservation of resin mass and a pure finite element method are employed to implicitly solve both for the pressure field and track the flow front progression of the resin inside the mold cavity of three-dimensional thick composites. The numerical developments involving the implicit tracking of resin progression flow fronts provide an accurate representation of the physical problem, do not involve the time step restrictions based on Courant condition as in past explicit finite element-control volume associated formulations. * Graduate Research Assistants t Professor * Research Scientists The discrete time progression of the flow front computed based on the present methodology does not depend on the time step size and the tracked location of the flow front at any discrete time does not depend on the time step size employed to reach that discrete time. The present developments have been validated with simple geometries and then extended to practical applications involving geometrically complex thick composite sections.
... of the individual fibril diameters, it is often not practical, if not impossible, to model th... more ... of the individual fibril diameters, it is often not practical, if not impossible, to model the intricategeometric details of ... There-fore, when dealing with a porous medium, a common practice is to introduce the idea of local volume ... and k is the effective thermal conductivity defined as ...
40th AIAA Aerospace Sciences Meeting & Exhibit, 2002
The resin transfer molding (RTM) manufacturing process consists of either of two considerations; ... more The resin transfer molding (RTM) manufacturing process consists of either of two considerations; the first is the fluid flow analysis through a porous fiber preform where the location of the flow front is of fundamental importance, and the second is combined flow/heat transfer analysis. For preliminary design purposes and the case of relatively large molds, isothermal considerations seem fairly representative of the physical situation. The continuous sensitivity formulations are developed for the process modeling of composites manufactured by RTM to predict, analyze, and the optimize the manufacturing process. Attention is focused here on developments for isothermal flow simulations, and illustrative examples are presented for sensitivity analysis applications which help serve as a design tool in the process modeling stages. n List of Figures Form Approved OMB No. 0704-0188 Public reporting burden for this collection of Information Is estimated to average 1 hour per response, Including the time for reviewing Instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of Information. Send comments regarding this burden estimate or any other aspect of this collection of Information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports,
The applicability and evaluation of a generalized gamma(T) family of flux-based representations a... more The applicability and evaluation of a generalized gamma(T) family of flux-based representations are examined for two different thermal analysis formulations for structures and materials which exhibit no phase change effects. The so-called H-theta and theta forms are demonstrated for numerous test models and linear and higher-order elements. The results show that the theta form with flux-based representations is generally superior to traditional approaches.
International Journal of Heat and Mass Transfer, 2005
... A comparative experimental and numer-ical study on a miniature JouleThomson cooler for stead... more ... A comparative experimental and numer-ical study on a miniature JouleThomson cooler for steady ... Optimization of rib-roughened surface geom-etries was conducted numerically [93]. ... A ground testing facility was described for modeling projectile flight heating upon reentry [117 ...
39th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, 1998
A plausible standardized formal theory of development/evolution of a wide class of computational ... more A plausible standardized formal theory of development/evolution of a wide class of computational algorithms for dynamic analysis is presented. The proposed developments are significantly different from the way traditional modal type and a wide class of step-by-step time integration approaches have been developed and described in the research literature and in standard text books over the years. The theoretical ideas and basis towards the evolution of a generalized methodology and formulations leading to integral operators in time and a wide class of single-step integration operators, multi-step integration operators, and a class of finite element in time integration operators, and their relationships for the resulting solution of dynamic equation systems are particularly addressed. Comparisons are also drawn with those obtained from the original methods of development. Furthermore, a variety of time operators are uniquely identified by discrete numerically assigned [DNA] algorithmic markers which not only serve as a prelude towards plausibly providing a standardized formal forum for selecting and identifying time operators but also permit lucid communication when referring to time operators. Furthermore, a single analysis code which permits a variety of choices to the analyst is now feasible for performing structural dynamic computations.
Computational Fluid and Solid Mechanics 2003, 2003
Publisher Summary This chapter presents a novel primal-dual technique to overcome many computatio... more Publisher Summary This chapter presents a novel primal-dual technique to overcome many computational challenging issues—namely, constraint preservation, preserving order of accuracy of time integration operators, and faster convergence rates of nonlinear iterations for the solution of flexible multibody dynamical differential-algebraic equations index-3 systems. In addition, the proposed technique preserves the underlying properties of time integration operators for ordinary differential equations and eliminates the need for index reduction, constraint stabilization, and regularization techniques. The claims of the proposed technique are illustrated via numerical examples by employing energy-momentum preserving method and stiff integrators, such as dissipative methods, that are part of a unified family of generalized integration operators encompassing LMS methods. Numerous numerical examples are presented by employing nondissipative and dissipative integrators. From the results, it is evident that the present formulation preserves the constraints and order of accuracy of the time-integration scheme eliminating the need for index reduction, constraint stabilization, and regularization techniques.
The present paper describes a Petrov-Galerki n based Least Squares approach for formulating the t... more The present paper describes a Petrov-Galerki n based Least Squares approach for formulating the transient flow/thermal behavior due to solodification processes. Both single and multiple phase change effects are considered in this study. And, emphasis is placed upon comparisons of the present developments with available experimental results and or results published in the literature. An adaptive time stepping strategy is employed for the trapezoidal family of methods. Applications to practical situations where previous studies have been done are presented. The overall developments agree well and validations are presented in this paper.
The emerging trends in Resin Transfer Molding (RTM) process technology for composites manufacturi... more The emerging trends in Resin Transfer Molding (RTM) process technology for composites manufacturing are its applications in the manufacture of complex thick composite structures. Process modeling simulation tools analyzing the three-dimensional flow of resin impregnating the thick fiber preform are instrumental in process optimizations. The true three-dimensional flow field with multiple flow fronts and the merging and diverging fronts involved in the solution of the time progression of the resin inside a mold cavity pose significant challenges and there is a need for efficient, physically accurate algorithms for process simulation studies. In this paper, a new formulation based on the time dependent conservation of resin mass and a pure finite element method are employed to implicitly solve both for the pressure field and track the flow front progression of the resin inside the mold cavity of three-dimensional thick composites. The numerical developments involving the implicit tracking of resin progression flow fronts provide an accurate representation of the physical problem, do not involve the time step restrictions based on Courant condition as in past explicit finite element-control volume associated formulations. * Graduate Research Assistants t Professor * Research Scientists The discrete time progression of the flow front computed based on the present methodology does not depend on the time step size and the tracked location of the flow front at any discrete time does not depend on the time step size employed to reach that discrete time. The present developments have been validated with simple geometries and then extended to practical applications involving geometrically complex thick composite sections.
... of the individual fibril diameters, it is often not practical, if not impossible, to model th... more ... of the individual fibril diameters, it is often not practical, if not impossible, to model the intricategeometric details of ... There-fore, when dealing with a porous medium, a common practice is to introduce the idea of local volume ... and k is the effective thermal conductivity defined as ...
40th AIAA Aerospace Sciences Meeting & Exhibit, 2002
The resin transfer molding (RTM) manufacturing process consists of either of two considerations; ... more The resin transfer molding (RTM) manufacturing process consists of either of two considerations; the first is the fluid flow analysis through a porous fiber preform where the location of the flow front is of fundamental importance, and the second is combined flow/heat transfer analysis. For preliminary design purposes and the case of relatively large molds, isothermal considerations seem fairly representative of the physical situation. The continuous sensitivity formulations are developed for the process modeling of composites manufactured by RTM to predict, analyze, and the optimize the manufacturing process. Attention is focused here on developments for isothermal flow simulations, and illustrative examples are presented for sensitivity analysis applications which help serve as a design tool in the process modeling stages. n List of Figures Form Approved OMB No. 0704-0188 Public reporting burden for this collection of Information Is estimated to average 1 hour per response, Including the time for reviewing Instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of Information. Send comments regarding this burden estimate or any other aspect of this collection of Information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports,
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