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At least 217 records · Page 12

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Advanced Manufacturing of the SLS Block 1B Payload Adapter: Engineering Development Unit

The Payload Adapter (PLA) for the Space Launch System Block 1B configuration (SLS B1B) is a structural frustum that interfaces with the Exploration Upper Stage (EUS) and the Universal Stage Adapter (USA) or the cargo fairing at the aft end and interfaces with the primary or co-manifested payload at the forward end. The primary structure is composed of a single piece aluminum forward ring, a segmented aluminum aft ring, eight carbon composite sandwich panels, and composite bonded longitudinal joints. The PLA is designed and fabricated in-house at MSFC. Development and flight article builds are joint efforts between the Materials & Processes Laboratory (EM), the Spacecraft & Vehicle Systems Department (EV), the Space Systems Department (ES), and the Test Laboratory (ET). The large-scale manufacturing efforts associated with this task include the fabrication of pathfinder panels; the fabrication and assembly of a full-scale Manufacturing Demonstration Article (MDA); the fabrication, assembly, and test of an Engineering Demonstration Unit (EDU); the fabrication, assembly, and test of a qualification Article; and the fabrication, assembly, and proof test of subsequent flight articles. The PLA team recently completed assembly of the EDU. The final assembly included the instillation of the co-manifested secondary payload, NEST, and the instillation and tensioning of the Payload Separation System (PSS). This poster will detail the assembly process which includes: (1) composite panel to ring assembly, (2) adhesive bonding for the longitudinal joints, and (3) instillation of the NEST and PSS. The PLA EDU is prepared to undergo modal and static load testing.

Monique Wallace↗

NASA NTRS2014

Elastomeric Structural Attachment Concepts for Aircraft Flap Noise Reduction - Challenges and Approaches to Hyperelastic Structural Modeling and Analysis

Airframe noise is a significant part of the overall noise of transport aircraft during the approach and landing phases of flight. Airframe noise reduction is currently emphasized under the Environmentally Responsible Aviation (ERA) and Fixed Wing (FW) Project goals of NASA. A promising concept for trailing-edge-flap noise reduction is a flexible structural element or link that connects the side edges of the deployable flap to the adjacent main-wing structure. The proposed solution is distinguished by minimization of the span-wise extent of the structural link, thereby minimizing the aerodynamic load on the link structure at the expense of increased deformation requirement. Development of such a flexible structural link necessitated application of hyperelastic materials, atypical structural configurations and novel interface hardware. The resulting highly-deformable structural concept was termed the FLEXible Side Edge Link (FLEXSEL) concept. Prediction of atypical elastomeric deformation responses from detailed structural analysis was essential for evaluating feasible concepts that met the design constraints. The focus of this paper is to describe the many challenges encountered with hyperelastic finite element modeling and the nonlinear structural analysis of evolving FLEXSEL concepts. Detailed herein is the nonlinear analysis of FLEXSEL concepts that emerged during the project which include solid-section, foamcore, hollow, extended-span and pre-stressed concepts. Coupon-level analysis performed on elastomeric interface joints, which form a part of the FLEXSEL topology development, are also presented.

Sreekantamurthy, Thammaiah↗

NASA NTRS1985

Large scale structural synthesis

A general purpose optimization program is coupled to a large scale finite element program to provide an efficient tool for structural synthesis. The resulting interface program may be used to design structures for minimum weight, subject to constraints on stress, displacement, and vibration frequencies. A variety of state-of-the-art techniques are employed, including design variable linking, constraint deletion, reciprocal variables, and formal approximations. The capability is demonstrated with the design of a gear housing using 30 design variables and over 5000 nonlinear inequality constraints. The finite element model consists of over 1600 elements and 7000 displacement degrees of freedom. The design required six detailed finite element analyses and approximately one hour on a Cray-1s supercomputer. It is concluded that structures of practical size and complexity can be efficiently designed using numerical optimization.

Vanderplaats, G. N.↗

NASA NTRS1996

Flexibility and Performance of Parallel File Systems

As we gain experience with parallel file systems, it becomes increasingly clear that a single solution does not suit all applications. For example, it appears to be impossible to find a single appropriate interface, caching policy, file structure, or disk-management strategy. Furthermore, the proliferation of file-system interfaces and abstractions make applications difficult to port. We propose that the traditional functionality of parallel file systems be separated into two components: a fixed core that is standard on all platforms, encapsulating only primitive abstractions and interfaces, and a set of high-level libraries to provide a variety of abstractions and application-programmer interfaces (API's). We present our current and next-generation file systems as examples of this structure. Their features, such as a three-dimensional file structure, strided read and write interfaces, and I/O-node programs, are specifically designed with the flexibility and performance necessary to support a wide range of applications.

Kotz, David↗

NASA NTRS1995

A two dimensional interface element for coupling of independently modeled three dimensional finite element meshes and extensions to dynamic and non-linear regimes

The work reported here pertains only to the first year of research for a three year proposal period. As a prelude to this two dimensional interface element, the one dimensional element was tested and errors were discovered in the code for built-up structures and curved interfaces. These errors were corrected and the benchmark Boeing composite crown panel was analyzed successfully. A study of various splines led to the conclusion that cubic B-splines best suit this interface element application. A least squares approach combined with cubic B-splines was constructed to make a smooth function from the noisy data obtained with random error in the coordinate data points of the Boeing crown panel analysis. Preliminary investigations for the formulation of discontinuous 2-D shell and 3-D solid elements were conducted.

Aminpour, Mohammad↗

NASA NTRS1972

A plausible energy source and structure for quasi-stellar objects

If a collision of two large, massive, fast gas clouds occurs, their kinetic energy is converted to radiation in a pair of shock fronts at their interface. The resulting structure is described, and the relevance of this as a radiation source for quasi-stellar objects is considered.

Daltabuit, E.↗

NASA NTRS2006

Recent Results from Epitaxial Growth on Step Free 4H-SiC Mesas

This paper updates recent progress made in growth, characterization, and understanding of high quality homoepitaxial and heteroepitaxial films grown on step-free 4H-SiC mesas. First, we report initial achievement of step-free 4H-SiC surfaces with carbon-face surface polarity. Next, we will describe further observations of how step-free 4H-SiC thin lateral cantilever evolution is significantly impacted by crystal faceting behavior that imposes non-uniform film thickness on cantilever undersides. Finally, recent investigations of in-plane lattice constant mismatch strain relief mechanisms observed for heteroepitaxial growth of 3C-SiC as well as 2H-AlN/GaN heterofilms on step-free 4H-SiC mesas will be reviewed. In both cases, the complete elimination of atomic heterointerface steps on the mesa structure enables uniquely well-ordered misfit dislocation arrays to form near the heterointerfaces with remarkable lack of dislocations threading vertically into the heteroepilayers. In the case of 3C-SiC heterofilms, it has been proposed that dislocation half-loops nucleate at mesa edges and glide laterally along the step-free 3C/4H interfaces. In contrast, 3C-SiC and 2H-AlN/GaN heterofilms grown on 4H-SiC mesas with steps exhibit highly disordered interface misfit dislocation structure coupled with 100X greater density of dislocations threading through the thickness of the heteroepilayers. These results indicate that the presence of steps at the heteroepitaxial interface (i.e., on the initial heteroepitaxial nucleation surface) plays a highly important role in the defect structure, quality, and relaxation mechanisms of single-crystal heteroepitaxial films.

Neudeck, Philip G.↗

NASA NTRS1974

Mechanics of load transfer at the interface

The mechanism of load transfer from matrix to fiber though the interface and, as a consequence, the effects of the interface on composite structural integrity are discussed. Specifically, the present work deals with the role of interfacial bonding in composite strength, the dependence of fracture surface on interface bond strength, and methods of measuring and predicting the stress at the interface, the microresidual stress, and load condition effects on the interface bond. The possibility of designing composites with specified bond properties is examined. Many of these effects are illustrated graphically to indicate general trends and to illustrate significant points. The discussion is based on theoretical considerations and is supplemented with pertinent experimental data.

Chamis, C. C.↗

NASA NTRS1989

NASA standard GAS Can satellite

The Get-Away Special canister (GAS Can) satellite is a small, (150 lb) low-cost satellite making it possible for commercial and scientific institutions to conduct experiments in space on an economical and short-term basis. The current model is called Xsat (Exceptional Satellite) and is designed to be launched from a GAS canister on the STS Orbiter; also provided is a low-cost automated PC-operated ground station for commercial, scientific, and government users. The Xsat structure is diagrammed, and details such as payload interface, weight restrictions, and structural loads are described in detail, pointing out that Xsat has a maximum payload weight of 50 lbs, and has a natural vibration frequency of around 45 Hz, with a minimum requiremet of 35 Hz. Thermal designs, power system, electronics, computer design and bus system, and satellite operations are all outlined.

Cudmore, Patrick H.↗

NASA NTRS2000

Finite Element Model Development For Aircraft Fuselage Structures

Buehrle, Ralph D.↗

NASA NTRS2000

Finite Element Model Development and Validation for Aircraft Fuselage Structures

The ability to extend the valid frequency range for finite element based structural dynamic predictions using detailed models of the structural components and attachment interfaces is examined for several stiffened aircraft fuselage structures. This extended dynamic prediction capability is needed for the integration of mid-frequency noise control technology. Beam, plate and solid element models of the stiffener components are evaluated. Attachment models between the stiffener and panel skin range from a line along the rivets of the physical structure to a constraint over the entire contact surface. The finite element models are validated using experimental modal analysis results. The increased frequency range results in a corresponding increase in the number of modes, modal density and spatial resolution requirements. In this study, conventional modal tests using accelerometers are complemented with Scanning Laser Doppler Velocimetry and Electro-Optic Holography measurements to further resolve the spatial response characteristics. Whenever possible, component and subassembly modal tests are used to validate the finite element models at lower levels of assembly. Normal mode predictions for different finite element representations of components and assemblies are compared with experimental results to assess the most accurate techniques for modeling aircraft fuselage type structures.

Buehrle, Ralph D.↗

NASA NTRS1991

Compressive testing of filament-wound cylinders

An experimental investigation has been conducted on the compressive buckling and failure of filament-wound circular cylinders. This investigation identifies one of the relationships between structural performance and scale, as well as some of the causes of reduced structural performance in large-scale structures. It is hypothesized that this effect is related to two conditions: first, the number of fiber tow undulations; and second, the percentage of weak interfaces within the structure. The effect of winding pattern and the resulting location of the fiber undulations were studied by varying the winding parameters. Three types of cylinders were manufactured from Amoco T650-35/1908 graphite/epoxy preimpregnated tow with different winding sequences (0/+/-60)s, (+/-30/90)s, and (90/+/-30)s. The (90/+/-30)s cylinders were manufactured with two different winding patterns (distributed and classical) and radius-to-thickness ratios (15 and 55). All cylinders were loaded in compression to failure. Comparisons of the compressive strength and failure modes demonstrate the relationship between the winding parameters, scale, and structural performance of filament-wound composite cylinders.

Jensen, David W.↗

NASA NTRS1990

Employment of CB models for non-linear dynamic analysis

The non-linear dynamic analysis of large structures is always very time, effort and CPU consuming. Whenever possible the reduction of the size of the mathematical model involved is of main importance to speed up the computational procedures. Such reduction can be performed for the part of the structure which perform linearly. Most of the time, the classical Guyan reduction process is used. For non-linear dynamic process where the non-linearity is present at interfaces between different structures, Craig-Bampton models can provide a very rich information, and allow easy selection of the relevant modes with respect to the phenomenon driving the non-linearity. The paper presents the employment of Craig-Bampton models combined with Newmark direct integration for solving non-linear friction problems appearing at the interface between the Hubble Space Telescope and its solar arrays during in-orbit maneuvers. Theory, implementation in the FEM code ASKA, and practical results are shown.

Klein, M. R. M.↗

NASA NTRS1981

The SMART MIL-STD-1553 bus adapter hardware manual

The SMART Multiplexer Interface Adapter, (SMIA) a complete system interface for message structure of the MIL-STD-1553, is described. It provides buffering and storage for transmitted and received data and handles all the necessary handshaking to interface between parallel 8-bit data bus and a MIL-STD serial bit stream. The bus adapter is configured as either a bus controller of a remote terminal interface. It is coupled directly to the multiplex bus, or stub coupled through an additional isolation transformer located at the connection point. Fault isolation resistors provide short circuit protection.

Ton, T. T.↗

NASA NTRS2004

High temperature seal for large structural movements

A high temperature sealing system is operative to seal an interface between adjacent hot structures and to minimize parasitic flow between such structures that move relative to one another in-plane or out-of-plane. The sealing system may be used to seal thrust-directing ramp structures of a reusable launch vehicle and includes a channel and a plurality of movable segmented sealing elements. Adjacent ramp structures include edge walls which extend within the channel. The sealing elements are positioned along the sides of the channel and are biased to engage with the inner surfaces of the ramp structures. The segmented sealing elements are movable to correspond to the contour of the thrust-directing ramp structures. The sealing system is operative to prevent high temperature thrust gases that flow along the ramp structures from infiltrating into the interior of the vehicle.

Steinetz, Bruce M.↗

NASA NTRS1987

Integrated Analysis Capability Program

Integrated Analysis Capability (IAC) software system provides highly effective, interactive analysis tool for integrated design of large structures. Developed to serve as interface for programs from fields of structures, thermodynamics, controls, and system dynamics with executive system and data base to yield highly-efficient multidisciplinary system. Written in FORTRAN 77.

Frisch, Harold P.↗

NASA NTRS1991

Conservative multizonal interface algorithm for the 3-D Navier-Stokes equations

A conservative zonal interface algorithm using features of both structured and unstructured mesh CFD technology is presented. The flow solver within each of the zones is based on structured mesh CFD technology. The interface algorithm was implemented into two three-dimensional Navier-Stokes finite volume codes and was found to yield good results.

Klopfer, G. H.↗

NASA NTRS1993

A flux-limited treatment for the conductive evaporation of spherical interstellar gas clouds

In this work, we present and analyze a new analytic solution for the saturated (flux-limited) thermal evaporation of a spherical cloud. This work is distinguished from earlier analytic studies by allowing the thermal conductivity to change continuously from a diffusive to a saturated form, in a manner usually employed only in numerical calculations. This closed form solution will be of interest as a computational benchmark. Using our calculated temperature profiles and mass-loss rates, we model the thermal evaporation of such a cloud under typical interstellar medium (ISM) conditions, with some restrictions. We examine the ionization structure of the cloud-ISM interface and evaluate column densities of carbon, nitrogen, oxygen, neon, and silicon ions toward the cloud. In accord with other investigations, we find that ionization equilibrium is far from satisfied under the assumed conditions. Since the inclusion of saturation effects in the heat flux narrows the thermal interface relative to its classical structure, we also find that saturation effects tend to lower predicted column densities.

Dalton, William W.↗