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NASA NTRS1991

The x ray morphology of the relaxed cluster of galaxies A2256. 1: Evidence for a merger event

The rich cluster of galaxies A2256 was studied utilizing the imaging proportional counter (PSPC (Position Sensitive Proportional Counters)) on board the x-ray observatory ROSAT. A2256 is considered to be a relaxed, Comalike cluster which is dynamically well evolved. However, clear evidence for substructure in A2256 was found. The x-ray surface brightness distribution reveals two separate maxima in the center, one of which is coincident with the central cD galaxy while the morphology of the other shows indications that it is merging with the main cluster body. The x-ray temperatures of the two maxima are different; the probable merging object being about a factor of five cooler than the cluster. The previously measured broad velocity distribution supports the idea that a merger in this cluster is being observed.

Briel, U. G.↗

NASA NTRS1993

Symposium on Parallel Computational Methods for Large-scale Structural Analysis and Design, 2nd, Norfolk, VA, US

Computing speed is leaping forward by several orders of magnitude each decade. Engineers and scientists gathered at a NASA Langley symposium to discuss these exciting trends as they apply to parallel computational methods for large-scale structural analysis and design. Among the topics discussed were: large-scale static analysis; dynamic, transient, and thermal analysis; domain decomposition (substructuring); and nonlinear and numerical methods.

Storaasli, Olaf O.↗

NASA NTRS1976

Stiffness coupling application to modal synthesis program, users guide

A FORTRAN IV computer program used to perform modal synthesis of structures by stiffness coupling, using the dynamic transformation method is described. The program was named SCAMP (Stiffness Coupling Approach Modal-Synthesis Program). The program begins with the entry of a substructure's physical mode shapes and eigenvalues or a substructure's mass and stiffness matrix. If the mass and stiffness matrices are entered, the eigen problem for the individual substructure is solved. Provisions are included for a maximum of 20 substructures which are coupled by stiffness matrix springs. Each substructure has a number degrees of freedom (DOF), except that for DOF greater than 100; vector sets having maximum row and column size of 100 were generated prior to entering SCAMP. The substructures are then coupled together via coupling springs, and the dynamic transformation is used to reduce the size of the eigen problem.

Kuhar, E. J.↗

NASA NTRS1972

Synthesis of shuttle vehicle damping using substructure test results

An empirical method is developed for predicting the modal damping of a combined parallel-stage shuttle model by means of damping measurements performed on the individual substructures. Correlations are first determined for each component in terms of damping energy as a function of peak kinetic energy and modal amplitude. The results are then used to predict component damping energies corresponding to the respective kinetic energies and amplitudes that occur for the new modes of the combined system. Modal characteristics for the system, other than damping, are obtained by a real eigenvalue solution of dynamic equations developed by Hurty's procedure of substructures. System equations, which include component modal damping, are also solved by a complex eigenvalue approach for comparison with results of the empirical method.

Kana, D. D.↗

NASA NTRS1990

Behavior of composite/metal aircraft structural elements and components under crash type loads: What are they telling us

Failure behavior results are presented from crash dynamics research using concepts of aircraft elements and substructure not necessarily designed or optimized for energy absorption or crash loading considerations. To achieve desired new designs which incorporate improved energy absorption capabilities often requires an understanding of how more conventional designs behave under crash loadings. Experimental and analytical data are presented which indicate some general trends in the failure behavior of a class of composite structures which include individual fuselage frames, skeleton subfloors with stringers and floor beams but without skin covering, and subfloors with skin added to the frame-stringer arrangement. Although the behavior is complex, a strong similarity in the static and dynamic failure behavior among these structures is illustrated through photographs of the experimental results and through analytical data of generic composite structural models. It is believed that the similarity in behavior is giving the designer and dynamists much information about what to expect in the crash behavior of these structures and can guide designs for improving the energy absorption and crash behavior of such structures.

Carden, Huey D.↗

NASA NTRS1990

Behavior of composite/metal aircraft structural elements and components under crash type loads - What are they telling us?

Carden, Huey D.↗

NASA NTRS1993

Hierarchical Poly Tree Configurations for the Solution of Dynamically Refined Finte Element Models

This paper demonstrates how a multilevel substructuring technique, called the Hierarchical Poly Tree (HPT), can be used to integrate a localized mesh refinement into the original finite element model more efficiently. The optimal HPT configurations for solving isoparametrically square h-, p-, and hp-extensions on single and multiprocessor computers is derived. In addition, the reduced number of stiffness matrix elements that must be stored when employing this type of solution strategy is quantified. Moreover, the HPT inherently provides localize 'error-trapping' and a logical, efficient means with which to isolate physically anomalous and analytically singular behavior.

Gute, G. D.↗

NASA NTRS1970

Nonlinear damping in structures

Experimental results prove the feasibility of substructure testing to measure local damping properties directly. Dynamic responses of a structure can be predicted quantitatively, and specimens are less costly and more easily tested with better controlled tests and environments.

Chang, C. S.↗

NASA NTRS1990

Failure behavior of generic metallic and composite aircraft structural components under crash loads

Failure behavior results are presented from crash dynamics research using concepts of aircraft elements and substructure not necessarily designed or optimized for energy absorption or crash loading considerations. To achieve desired new designs incorporating improved energy absorption capabilities often requires an understanding of how more conventional designs behave under crash loadings. Experimental and analytical data are presented which indicate some general trends in the failure behavior of a class of composite structures including individual fuselage frames, skeleton subfloors with stringers and floor beams without skin covering, and subfloors with skin added to the frame-stringer arrangement. Although the behavior is complex, a strong similarity in the static/dynamic failure behavior among these structures is illustrated through photographs of the experimental results and through analytical data of generic composite structural models.

Carden, Huey D.↗

NASA NTRS1995

The spatial distribution, kinematics, and dynamics of the galaxies in the region of Abell 2634 and 2666

A total of 663 galaxies with known redshifts in a 12 deg x 12 deg field centered on A2634, including 211 new measurements, are used to study in detail the structure of the region. In it we find six main galaxy concentrations: the nearby clusters A2634 and A2666, two groups in the vicinity of A2634, and two distant clusters at approximately 18,000 (A2622) and approximately 37,000 km/s seen in projection near the core of A2634. For A2634, the most richly sampled of those concentrations, we are able to apply strict cluster membership criteria. Two samples - one containing 200 galaxies within 2 deg from the cluster center and a second, magnitude-limited, of 118 galaxies within the central half degree - are used to examine the structure, kinematics, dynamics, and morphological segregation of the cluster. We show that early type galaxies appear to be a relaxed system, while the spiral population eschews the center of the cluster and exhibits both a multimodal velocity distribution and a much larger velocity dispersion that the ellipticals. We propose that the spiral galaxies of A2634 represent a dynamically young cluster population. For the galaxy component of A2634, we find no evidence of significant substructure in the central regions. We also conclude that the adoption of lenient membership criteria that ignore the dynamical complexity of A2634 are unlikely to be responsible for the conflicting results reported on the motion of this cluster with respect ot the CMB. The kinematical and dynamical analysis is extended to A2634's close companion, A2666, and the two distant background clusters.

Scodeggio, Marco↗

NASA NTRS1971

Dynamic analysis of large structures by modal synthesis techniques.

Several criteria that may be used to evaluate the merits of some of the existing techniques for the dynamic analysis of large structures which involve division into substructures or components are examined. These techniques make use of component displacement modes to synthetize global systems of generalized coordinates and, for that reason, they have come to be known as modal synthesis or component mode methods. Two techniques have been found to be particularly useful - i.e., the modal synthesis method with fixed attachment modes, and the modal synthesis method with free attachment modes. These two methods are treated in detail, and general flow charts are presented for guidance in computer programming.

Hurty, W. C.↗

NASA NTRS1990

Unique failure behavior of metal/composite aircraft structural components under crash type loads

Failure behavior results are presented on some of the crash dynamics research conducted with concepts of aircraft elements and substructure which have not necessarily been designed or optimized for energy absorption or crash loading considerations. To achieve desired new designs which incorporate improved energy absorption capabilities often requires an understanding of how more conventional designs behave under crash type loadings. Experimental and analytical data are presented which indicate some general trends in the failure behavior of a class of composite structures which include individual fuselage frames, skeleton subfloors with stringers and floor beams but without skin covering, and subfloors with skin added to the frame-stringer arrangement. Although the behavior is complex, a strong similarity in the static/dynamic failure behavior among these structures is illustrated through photographs of the experimental results and through analytical data of generic composite structural models. It is believed that the thread of similarity in behavior is telling the designer and dynamists a great deal about what to expect in the crash behavior of these structures and can guide designs for improving the energy absorption and crash behavior of such structures.

Carden, Huey D.↗

NASA NTRS1991

The X-ray morphology of the relaxed cluster of galaxies A2256. I - Evidence for a merger event

The rich cluster of galaxies A2256 are studied by utilizing the imaging proportional counter on board the X-ray observatory ROSAT. A2256 is considered to be a relaxed Coma-like cluster which is dynamically well evolved. Cleara evidence, however, is found for substructure in A2256. The X-ray surface brightness distribution reveals two separate maxima in the center; one of which is coincident with the central cD galaxy while the morphology of the other shows indications that it is merging with the main cluster body. The X-ray temperatures of the two maxima are different; the probable merging object being about a factor of five cooler than the cluster. The previously measured broad velocity distribution supports the idea that a merger is occurring in this cluster.

Briel, U. G.↗

NASA NTRS1991

Parallel Methods on Large-Scale Structural Analysis and Physics Applications; Symposium, Hampton, VA, Feb. 5, 6, 1991, Selected Papers

Recent advances in parallel methods and algorithms integrated into large-scale codes are presented. Consideration is given to problem decomposition (substructuring), efficient matrix solution algorithms for shared memory architectures, dynamic and transient analysis algorithms for shared memory architectures, and algorithms for distributed and massively parallel architectures. Particular attention is given to partitioning of unstructured problems for parallel processing, parallel-vector computation for linear-structural analysis and nonlinear unconstraint optimization problems, a parallel-vector equation solver for unsymmetric matrices on supercomputers, parallel nonlinear finite element dynamic response, multigrid algorithms for solving structural mechanics problems on supercomputers, structural analysis on massively parallel computers, explicit finite element methods with contact-impact on SIMD computers, and the impact of mapping and sparsity on parallelized finite element method modules.

Storaasli, Olaf O.↗

NASA NTRS1991

An overview of the crash dynamics failure behavior of metal and composite aircraft structures

An overview of failure behavior results is presented from some of the crash dynamics research conducted with concepts of aircraft elements and substructure not necessarily designed or optimized for energy absorption or crash loading considerations. Experimental and analytical data are presented that indicate some general trends in the failure behavior of a class of composite structures that includes fuselage panels, individual fuselage sections, fuselage frames, skeleton subfloors with stringers and floor beams without skin covering, and subfloors with skin added to the frame stringer structure. Although the behavior is complex, a strong similarity in the static/dynamic failure behavior among these structures is illustrated through photographs of the experimental results and through analytical data of generic composite structural models.

Carden, Huey D.↗

NASA NTRS1995

Hubble Space Telescope imaging of a radio-quiet galaxy at redshift z = 3.4

We have observed with the Wide Field/Planetary Camera (WF/PC) on the Hubble Space Telescope (HST) a radio-quiet Ly alpha-emitting galaxy at redshift z = 3.428 (G2 below). The images probe the rest-frame UV light around 1250 A with an angular resolution of approx. = 0.1 sec, corresponding to 1.4 h(exp -1, sub 50) kpc at redshift z = 3.4 (in this Letter we use q(sub 0) = 0 and H(sub 0) = 50 h(exp -1, sub 50) km/s/Mpc). The light profile of the central approx. 10h(exp -1, sub 50) kpc region is well fitted by an r(exp 1/4) law with r(sub e) approx. = 1.3 h(exp -1, sub 50) kpc, suggesting a dynamically relaxed state. The outer regions are characterized by the presence of substructures, such as an elongated formation and low surface brightness nebulosities. The isophotal analysis shows no evidence of an active galactic nuclei (AGN)-like unresolved source in the center. The structural properties of G2 are consistent with a dynamically hot stellar system observed during an early phase of star formation, very likely the progenitor of an elliptical or the bulge of a spiral galaxy.

Giavalisco, Mauro↗

NASA NTRS1984

When clusters are superclusters

Recent research on substructure in clusters and superclusters of galaxies is critically surveyed, with an emphasis on the distinction (based on physical size and dynamic state) between the two classes of structures. The cosmological and large-scale structural implications of substructure in rich clusters are analyzed, using N-body-simulation results, and illustrated for the clusters A98 and A548. Consideration is also given to gravitational lensing of distant quasars by intervening clusters and the interpretation of the matter distribution on scales larger than about 5 Mpc. It is determined that A98 and A548 are superclusters.

Geller, M. J.↗

NASA NTRS1978

Structural Dynamics, Stability, and Control of Helicopters

The dynamic synthesis of gyroscopic structures consisting of point-connected substructures is investigated. The objective is to develop a mathematical model capable of an adequate simulation of the modal characteristics of a helicopter using a minimum number of degrees of freedom. The basic approach is to regard the helicopter structure as an assemblage of flexible substructures. The variational equations for the perturbed motion about certain equilibrium solutions are derived. The discretized variational equations can be conveniently exhibited in matrix form, and a great deal of information about the system modal characteristics can be extracted from the coefficient matrices. The derivation of the variational equations requires a monumental amount of algebraic operations. To automate this task a symbolic manipulation program on a digital computer is developed.

Meirovitch, L.↗