Identification of dynamic structures with special attention to damping matrix representation /

"In finite element modeling, damping parameters, structural characteristics of joints, and boundary conditions are very difficult to estimate, causing discrepancy between analytic results and actual measured behavior. Various methods of structural identification were studied and compared in terms of their basic assumptions and advantages. A nonlinear optimization based method was thought to be promising for the identification of structures with highly uncertain structural parameters. An algorithm was developed to construct the damping matrix from experimental data. A computer program was developed for verification of this method. The method appeared to work well for lightly, viscously damped structures."--Report documentation page.Cover title."Final report for period: May 1991 - September 1991.""January 1992.""WL-TR-91-3101."Includes bibliographical references.Section 1. Introduction. -- Section 2. Basic theoretical background. -- Section 3. Review of previous works. -- Section 4. Identification of damping matrix. -- Section 5. Summary and conclusion."In finite element modeling, damping parameters, structural characteristics of joints, and boundary conditions are very difficult to estimate, causing discrepancy between analytic results and actual measured behavior. Various methods of structural identification were studied and compared in terms of their basic assumptions and advantages. A nonlinear optimization based method was thought to be promising for the identification of structures with highly uncertain structural parameters. An algorithm was developed to construct the damping matrix from experimental data. A computer program was developed for verification of this method. The method appeared to work well for lightly, viscously damped structures."--Report documentation page.Research supported by the United States Air Force Flight Dynamics Directorate, and performed CSA Engineering, Inc., Palo Alto, California, Funding numbersMode of access: Internet

Survey of CFD applications for high speed inlets /

A comprehensive review of techniques and methods for applying computational fluid dynamics (CFD) analysis to high speed inlets and related flows is provided via an extensive literature survey of such applications. Topics covered include governing equations, numerical integration schemes, boundary conditions, gridding requirements, and turbulence models. Results of applications from the literature survey shed light on the relative success of the techniques being used throughout the industry. (AN)."Final Report for Period August 1992 - July 1994.""July 1994."Includes bibliographical references (pages 53-55).A comprehensive review of techniques and methods for applying computational fluid dynamics (CFD) analysis to high speed inlets and related flows is provided via an extensive literature survey of such applications. Topics covered include governing equations, numerical integration schemes, boundary conditions, gridding requirements, and turbulence models. Results of applications from the literature survey shed light on the relative success of the techniques being used throughout the industry. (AN).Mode of access: Internet

The effect of pressure gradients on transition zone length in hypersonic boundary layers /

Boundary layer transition was measured in zero, favorable, and adverse pressure gradients at Mach 8 using heat transfer. Models consisted of 7 degrees half angle forecones 0.4826 m long, followed by flared or ogive aft bodies 0.5334 m long. The flares and ogives produced constant pressure gradients. For the cases examined, favorable pressure gradients delay transition and adverse pressure gradients promote transition, but transition zone lengths are shorter in favorable pressure gradient. Results of the effect of adverse pressure gradient on transition zone lengths were inconclusive."Final Report for 06/01/90 - 12/01/93.""December 1993."Includes bibliographical references (pages 31-35).Boundary layer transition was measured in zero, favorable, and adverse pressure gradients at Mach 8 using heat transfer. Models consisted of 7 degrees half angle forecones 0.4826 m long, followed by flared or ogive aft bodies 0.5334 m long. The flares and ogives produced constant pressure gradients. For the cases examined, favorable pressure gradients delay transition and adverse pressure gradients promote transition, but transition zone lengths are shorter in favorable pressure gradient. Results of the effect of adverse pressure gradient on transition zone lengths were inconclusive.Mode of access: Internet

Characteristic based methods for the time-domain Maxwell equations /

Numerical procedures for solving the time-domain Maxwell equations based on the theory of characteristics were successfully developed. Both explicit and implicit methods were formulated by the time-central and spatial-windward algorithm to better describe wave motion. A new trapezoidal consistent implicit scheme was shown to be unconditionally stable for the linear initial value system and was able to generate numerical solutions comparable to those of the established explicit method. The formulation of the three-dimensional system including generalized coordinate system was completed but not explored. The present 2-D results on Cartesian frame demonstrated a potential for numerical efficiency improvement. Time-domain Maxwell equation, Trapezoidal consistent implicit scheme, Cartesian frame."Final Report for Period June 1990 - February 1991.""August 1993."Includes bibliographical references (pages 41-43).Numerical procedures for solving the time-domain Maxwell equations based on the theory of characteristics were successfully developed. Both explicit and implicit methods were formulated by the time-central and spatial-windward algorithm to better describe wave motion. A new trapezoidal consistent implicit scheme was shown to be unconditionally stable for the linear initial value system and was able to generate numerical solutions comparable to those of the established explicit method. The formulation of the three-dimensional system including generalized coordinate system was completed but not explored. The present 2-D results on Cartesian frame demonstrated a potential for numerical efficiency improvement. Time-domain Maxwell equation, Trapezoidal consistent implicit scheme, Cartesian frame.Mode of access: Internet

Unsteady Navier-Stokes solutions for a low aspect ratio delta wing /

A numerical investigation of the flow field about a 76-degree leading edge sweep delta wing at 20.5 degree angle of attack is presented. The computational results are obtained using a Beam-Warming algorithm with a Newton-like subiteration procedure. For M = 0.2 and Re = 900,000 an unsteady flow field is obtained which is shown to be physical in nature. The unsteady behaviour is a result of the existence of small-scale vortical structures that are associated with a Kelvin-Helmholtz type instability of the shear layer emanating form the leading edge of the delta wing. The computed results show qualitative agreement with other experimental and numerical findings."Final report for the period September 1989 - September 1990.""December 1990."Includes bibliographical references (pages 12-13).A numerical investigation of the flow field about a 76-degree leading edge sweep delta wing at 20.5 degree angle of attack is presented. The computational results are obtained using a Beam-Warming algorithm with a Newton-like subiteration procedure. For M = 0.2 and Re = 900,000 an unsteady flow field is obtained which is shown to be physical in nature. The unsteady behaviour is a result of the existence of small-scale vortical structures that are associated with a Kelvin-Helmholtz type instability of the shear layer emanating form the leading edge of the delta wing. The computed results show qualitative agreement with other experimental and numerical findings.Mode of access: Internet

Lift and pitching moment Induced on jet STOVL by the ground vortex : data report /

The data obtained during an investigation of the effects of the ground vortex on a generic wing-body configuration are presented in this report. Circular, rectangular and thrust reverser jets were tested. The tests were conducted in the 14 by 22 foot tunnel at the NASA Langley Research Center. The tests covered a range of heights above the ground, forward velocities, and ground belt speeds."Final Report for Period May 1990 - May 1993.""June 1993."Includes bibliographical references (page 8).The data obtained during an investigation of the effects of the ground vortex on a generic wing-body configuration are presented in this report. Circular, rectangular and thrust reverser jets were tested. The tests were conducted in the 14 by 22 foot tunnel at the NASA Langley Research Center. The tests covered a range of heights above the ground, forward velocities, and ground belt speeds.Research supported by the United States Air Force Flight Dynamics Directorate, and performed by KSA Technology, columbus, Ohio, under Contract No.Mode of access: Internet

Method for transition prediction in high-speed boundary layers /

The parabolized stability equations (PSE) are a new and more reliable approach to analyzing the stability of streamwise varying flows such as boundary layers. This approach has been previously validated for idealized incompressible flows. Here, the PSE are formulated for highly compressible flows in general curvilinear coordinates to permit the analysis of high-speed boundary-layer flows over fairly general bodies. Vigorous numerical studies are carried out to study convergence and accuracy of the linear-stability code LSH, and the linear/ nonlinear PSE code, PSH. Physical interfaces are set up to analyze the M=8 boundary layer over a blunt cone calculated by using a thin-layer Navier Stokes (TNLS) code, and the flow over a sharp cone at angle of attack calculated using the AFWAL Parabolized Navier-Stokes (PNS) code'. While stability and transition studies at high speeds are far from routine, the method developed here is the best tool available to research the physical processes in high-speed boundary layers. Parabolized stability equations, Compressible flows, High-speed boundary layers, General bodies."Final Report for 09/27/90 - 09/27/93.""September 1993."Includes bibliographical references (pages 81-82).The parabolized stability equations (PSE) are a new and more reliable approach to analyzing the stability of streamwise varying flows such as boundary layers. This approach has been previously validated for idealized incompressible flows. Here, the PSE are formulated for highly compressible flows in general curvilinear coordinates to permit the analysis of high-speed boundary-layer flows over fairly general bodies. Vigorous numerical studies are carried out to study convergence and accuracy of the linear-stability code LSH, and the linear/ nonlinear PSE code, PSH. Physical interfaces are set up to analyze the M=8 boundary layer over a blunt cone calculated by using a thin-layer Navier Stokes (TNLS) code, and the flow over a sharp cone at angle of attack calculated using the AFWAL Parabolized Navier-Stokes (PNS) code'. While stability and transition studies at high speeds are far from routine, the method developed here is the best tool available to research the physical processes in high-speed boundary layers. Parabolized stability equations, Compressible flows, High-speed boundary layers, General bodies.Research supported by the United States Air Force Flight Dynamics Directorate, and performed by Dynaflow, Inc., Columbus, Ohio, under Contract No.Mode of access: Internet

Proceedings of Damping '89 : 8-10 February 1989, West Palm Beach, Florida : final report for period Feb. 86 to Feb. 89 /

"November 1989."Cover title.Includes bibliographical references.Mode of access: Internet

Integrated passive and active control of structures /

A combination of passive damping and active control is needed on practical structures where sufficient modal damping is not achievable with passive damping alone. The modal theories for structural equations in state space are reviewed and some eigenvector relationship are presented which are not available elsewhere, for use later in the report. Methods for determining sensitivities of eigenvalues land eigenvectors to plant matrix and control inputs are summarized and numerical examples are presented. Procedures are developed for optimizing passive damping through use of the sensitivities of the eigenproperties, for free vibration and forced, random vibrations. Frequency- dependent behavior of viscoelastic damping material by curve-fitting is discussed, which is then used in an overdamped mini-oscillator technique for analysis of an example ten-bar truss. Two approaches are presented for designing the combination of passive viscous damping and full state feedback control. The first is iterative and makes use of eigenvalue sensitivities. The second is based on a perturbation formulation, where the desired changes in eigenvalues and eigenvectors are specified and the corresponding changes in the closed loop characteristic matrix in state space are predicted. Restrictions on the choice of eigenvalues and eigenvectors are discussed in light of related literature on eigenstructure assignment. Fortran computer programs, one coupled with the constrained function minimization program CONMIN, have been written for each type of problem. Space structures, Passive damping, Active control, Analysis, Numerical examples."Final Report for Period May 1990 - May 1993.""December 1993."Includes bibliographical references (pages 91-93).A combination of passive damping and active control is needed on practical structures where sufficient modal damping is not achievable with passive damping alone. The modal theories for structural equations in state space are reviewed and some eigenvector relationship are presented which are not available elsewhere, for use later in the report. Methods for determining sensitivities of eigenvalues land eigenvectors to plant matrix and control inputs are summarized and numerical examples are presented. Procedures are developed for optimizing passive damping through use of the sensitivities of the eigenproperties, for free vibration and forced, random vibrations. Frequency- dependent behavior of viscoelastic damping material by curve-fitting is discussed, which is then used in an overdamped mini-oscillator technique for analysis of an example ten-bar truss. Two approaches are presented for designing the combination of passive viscous damping and full state feedback control. The first is iterative and makes use of eigenvalue sensitivities. The second is based on a perturbation formulation, where the desired changes in eigenvalues and eigenvectors are specified and the corresponding changes in the closed loop characteristic matrix in state space are predicted. Restrictions on the choice of eigenvalues and eigenvectors are discussed in light of related literature on eigenstructure assignment. Fortran computer programs, one coupled with the constrained function minimization program CONMIN, have been written for each type of problem. Space structures, Passive damping, Active control, Analysis, Numerical examples.Research supported by the United States Air Force Flight Dynamics Directorate, and performed by Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park, Pennsylvania, under Contract No.Mode of access: Internet

Portable coupled field CAD /

Coyote Systems has developed a coupled CAD tool for Microelectromechanical Systems (MEMS), called AutoMEMS, which accurately simulates the coupled fields in large, realistic MEMS devices with minimal user input. AutoMEMS generates a three dimensional (3D) solid model from a user-supplied two dimensional device layout. A device mesh is then created from the 3D solid model which can be automatically and adaptively refined for accurate results. Simulations are the conducted utilizing a fast Boundary Element Method (BEM). The resulting cross-capacitances and electrostatic forces can be automatically extracted. The final version of AutoMEMS was developed in a C++ environment using gnu-style tools and high-speed portable OpenGL graphics which allows it to run on Linux and Unix platforms. Two particular examples used to demonstrate the functionality of AutoMEMS were of a micromirror and Analog Devices ADXL76 accelerometer. Thus, an effective and easy-to-use MEMS simulation tool was developed and demonstrated."Coyote Systems, San Francisco, California.""Final Report for period November 1996 to September 1999.""August 2000."Coyote Systems has developed a coupled CAD tool for Microelectromechanical Systems (MEMS), called AutoMEMS, which accurately simulates the coupled fields in large, realistic MEMS devices with minimal user input. AutoMEMS generates a three dimensional (3D) solid model from a user-supplied two dimensional device layout. A device mesh is then created from the 3D solid model which can be automatically and adaptively refined for accurate results. Simulations are the conducted utilizing a fast Boundary Element Method (BEM). The resulting cross-capacitances and electrostatic forces can be automatically extracted. The final version of AutoMEMS was developed in a C++ environment using gnu-style tools and high-speed portable OpenGL graphics which allows it to run on Linux and Unix platforms. Two particular examples used to demonstrate the functionality of AutoMEMS were of a micromirror and Analog Devices ADXL76 accelerometer. Thus, an effective and easy-to-use MEMS simulation tool was developed and demonstrated.United States Air Force Contract No.Mode of access: Internet