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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1942

Bending with large deflection of a clamped rectangular plate with length-width ratio of 1.5 under normal pressure

The Von Karman equations for a thin flat plate with large deflections are solved for the special case of a plate with clamped edges having a ratio of length to width of 1.5 and loaded by uniform normal pressure. Center deflections, membrane stresses, and extreme-fiber bending stresses are given as a function of pressure for center deflections up to twice the thickness of the plate. For small deflections the results coincide with those obtained by Hencky from the linear theory. The maximum stresses and center deflection at high pressures differ less than 3 percent from those derived by Bostnov for an infinitely long plate with clamped edges. This agreement suggests that clamped plates with a length-to-width ratio greater than 1.5 may be reared as infinitely long plates for purposes of design.

PLATES-BENDING CIRCULAR↗
NASA NTRS1993

Development and comparison of advanced reduced-basis methods for the transient structural analysis of unconstrained structures

The development of two advanced reduced-basis methods, the force derivative method and the Lanczos method, and two widely used modal methods, the mode displacement method and the mode acceleration method, for transient structural analysis of unconstrained structures is presented. Two example structural problems are studied: an undamped, unconstrained beam subject to a uniformly distributed load which varies as a sinusoidal function of time and an undamped high-speed civil transport aircraft subject to a normal wing tip load which varies as a sinusoidal function of time. These example problems are used to verify the methods and to compare the relative effectiveness of each of the four reduced-basis methods for performing transient structural analyses on unconstrained structures. The methods are verified with a solution obtained by integrating directly the full system of equations of motion, and they are compared using the number of basis vectors required to obtain a desired level of accuracy and the associated computational times as comparison criteria.

Mcgowan, David M.↗
NASA NTRS1994

Cargo systems manual: Heat Pipe Performance (HPP) STS-66

The purpose of the cargo systems manual (CSM) is to provide a payload reference document for payload and shuttle flight operations personnel during shuttle mission planning, training, and flight operations. It includes orbiter-to-payload interface information and payload system information (including operationally pertinent payload safety data) that is directly applicable to the Mission Operations Directorate (MOD) role in the payload mission. The primary objectives of the heat pipe performance (HPP) are to obtain quantitative data on the thermal performance of heat pipes in a microgravity environment. This information will increase understanding of the behavior of heat pipes in space and be useful for application to design improvements in heat pipes and associated systems. The purpose of HPP-2 is to establish a complete one-g and zero-g data base for axial groove heat pipes. This data will be used to update and correlate data generated from a heat pipe design computer program called Grooved Analysis Program (GAP). The HPP-2 objectives are to: determine heat transport capacity and conductance for open/closed grooved heat pipes and different Freon volumes (nominal, under, and overcharged) using a uniform heat load; determine heat transport capacity and conductance for single/multiple evaporators using asymmetric heat loads; obtain precise static, spin, and rewicking data points for undercharged pipes; investigate heat flux limits (asymmetric heat loads); and determine effects of positive body force on thermal performance.

Napp, Robert↗
NASA NTRS1995

Predictions of thermal buckling strengths of hypersonic aircraft sandwich panels using minimum potential energy and finite element methods

Thermal buckling characteristics of hypersonic aircraft sandwich panels of various aspect ratios were investigated. The panel is fastened at its four edges to the substructures under four different edge conditions and is subjected to uniform temperature loading. Minimum potential energy theory and finite element methods were used to calculate the panel buckling temperatures. The two methods gave fairly close buckling temperatures. However, the finite element method gave slightly lower buckling temperatures than those given by the minimum potential energy theory. The reasons for this slight discrepancy in eigensolutions are discussed in detail. In addition, the effect of eigenshifting on the eigenvalue convergence rate is discussed.

Ko, William L.↗
NASA NTRS1998

HOTCFGM-1D: A Coupled Higher-Order Theory for Cylindrical Structural Components with Through-Thickness Functionally Graded Microstructures

The objective of this three-year project was to develop and deliver to NASA Lewis one-dimensional and two-dimensional higher-order theories, and related computer codes, for the analysis, optimization and design of cylindrical functionally graded materials/structural components for use in advanced aircraft engines (e.g., combustor linings, rotor disks, heat shields, blisk blades). To satisfy this objective, a quasi one-dimensional version of the higher-order theory, HOTCFGM-1D, and four computer codes based on this theory, for the analysis, design and optimization of cylindrical structural components functionally graded in the radial direction were developed. The theory is applicable to thin multi-phased composite shell/cylinders subjected to macroscopically axisymmetric thermomechanical and inertial loading applied uniformly along the axial direction such that the overall deformation is characterized by a constant average axial strain. The reinforcement phases are uniformly distributed in the axial and circumferential directions, and arbitrarily distributed in the radial direction, thereby allowing functional grading of the internal reinforcement in this direction.

Pindera, Marek-Jerzy↗
NASA NTRS2004

Thermal Buckling Analysis of Rectangular Panels Subjected to Humped Temperature Profile Heating

This research investigates thermal buckling characteristics of rectangular panels subjected to different types of humped temperature profile heating. Minimum potential energy and finite-element methods are used to calculate the panel buckling temperatures. The two methods give fairly close thermal buckling solutions. 'Buckling temperature magnification factor of the first kind, eta' is established for the fixed panel edges to scale up the buckling solution of uniform temperature loading case to give the buckling solution of the humped temperature profile loading cases. Also, 'buckling temperature magnification factor of the second kind, xi' is established for the free panel edges to scale up the buckling solution of humped temperature profile loading cases with unheated boundary heat sinks to give the buckling solutions when the boundary heat sinks are heated up.

Ko, William I.↗
NASA NTRS2005

Finite Element Analysis of Adaptive-Stiffening and Shape-Control SMA Hybrid Composites

The usage of shape memory materials has extended rapidly to many fields, including medical devices, actuators, composites, structures and MEMS devices. For these various applications, shape memory alloys (SMAs) are available in various forms: bulk, wire, ribbon, thin film, and porous. In this work, the focus is on SMA hybrid composites with adaptive-stiffening or morphing functions. These composites are created by using SMA ribbons or wires embedded in a polymeric based composite panel/beam. Adaptive stiffening or morphing is activated via selective resistance heating or uniform thermal loads. To simulate the thermomechanical behavior of these composites, a SMA model was implemented using ABAQUS user element interface and finite element simulations of the systems were studied. Several examples are presented which show that the implemented model can be a very useful design and simulation tool for SMA hybrid composites.

Gao, Xiu-Jie↗
NASA NTRS2005

Finite Element Analysis of Adaptive-Stiffening and Shape-Control SMA Hybrid Composites

Shape memory alloy hybrid composites with adaptive-stiffening or morphing functions are simulated using finite element analysis. The composite structure is a laminated fiber-polymer composite beam with embedded SMA ribbons at various positions with respect to the neutral axis of the beam. Adaptive stiffening or morphing is activated via selective resistance heating of the SMA ribbons or uniform thermal loads on the beam. The thermomechanical behavior of these composites was simulated in ABAQUS using user-defined SMA elements. The examples demonstrate the usefulness of the methods for the design and simulation of SMA hybrid composites. Keywords: shape memory alloys, Nitinol, ABAQUS, finite element analysis, post-buckling control, shape control, deflection control, adaptive stiffening, morphing, constitutive modeling, user element

Gao, Xiujie↗
NASA NTRS1998

Analysis and Testing of Plates with Piezoelectric Sensors and Actuators

Piezoelectric material inherently possesses coupling between electrostatics and structural dynamics. Utilizing linear piezoelectric theory results in an intrinsically coupled pair of piezoelectric constitutive equations. One equation describes the direct piezoelectric effect where strains produce an electric field and the other describes the converse effect where an applied electrical field produces strain. The purpose of this study is to compare finite element analysis and experiments of a thin plate with bonded piezoelectric material. Since an isotropic plate in combination with a thin piezoelectric layer constitutes a special case of a laminated composite, the classical laminated plate theory is used in the formulation to accommodated generic laminated composite panels with multiple bonded and embedded piezoelectric layers. Additionally, the von Karman large deflection plate theory is incorporated. The formulation results in laminate constitutive equations that are amiable to the inclusion of the piezoelectric constitutive equations yielding in a fully electro-mechanically coupled composite laminate. Using the finite element formulation, the governing differential equations of motion of a composite laminate with embedded piezoelectric layers are derived. The finite element model not only considers structural degrees of freedom (d.o.f.) but an additional electrical d.o.f. for each piezoelectric layer. Comparison between experiment and numerical prediction is performed by first treating the piezoelectric as a sensor and then again treating it as an actuator. To assess the piezoelectric layer as a sensor, various uniformly distributed pressure loads were simulated in the analysis and the corresponding generated voltages were calculated using both linear and nonlinear finite element analyses. Experiments were carried out by applying the same uniformly distributed loads and measuring the resulting generated voltages and corresponding maximum plate deflections. It is found that a highly nonlinear relationship exists between maximum deflection and voltage versus pressure loading. In order to assess comparisons of predicted and measured piezoelectric actuation, sinusoidal excitation voltages are simulated/applied and maximum deflections are calculated/measured. The maximum deflection as a function of time was determined using the linear finite elements analysis. Good correlation between prediction and measurement was achieved in all cases.

Bevan, Jeffrey S.↗
NASA NTRS2006

Dynamic Snap-Through of Thin-Walled Structures by a Reduced Order Method

The goal of this investigation is to further develop nonlinear modal numerical simulation methods for application to geometrically nonlinear response of structures exposed to combined high intensity random pressure fluctuations and thermal loadings. The study is conducted on a flat aluminum beam, which permits a comparison of results obtained by a reduced-order analysis with those obtained from a numerically intensive simulation in physical degrees-of-freedom. A uniformly distributed thermal loading is first applied to investigate the dynamic instability associated with thermal buckling. A uniformly distributed random loading is added to investigate the combined thermal-acoustic response. In the latter case, three types of response characteristics are considered, namely: (i) small amplitude vibration around one of the two stable buckling equilibrium positions, (ii) intermittent snap-through response between the two equilibrium positions, and (iii) persistent snap-through response between the two equilibrium positions. For the reduced order analysis, four categories of modal basis functions are identified including those having symmetric transverse (ST), anti-symmetric transverse (AT), symmetric in-plane (SI), and anti-symmetric in-plane (AI) displacements. The effect of basis selection on the quality of results is investigated for the dynamic thermal buckling and combined thermal-acoustic response. It is found that despite symmetric geometry, loading, and boundary conditions, the AT and SI modes must be included in the basis as they participate in the snap-through behavior.

Przekop, Adam↗
NASA NTRS2007

Dynamic Snap-Through of Thermally Buckled Structures by a Reduced Order Method

The goal of this investigation is to further develop nonlinear modal numerical simulation methods for application to geometrically nonlinear response of structures exposed to combined high intensity random pressure fluctuations and thermal loadings. The study is conducted on a flat aluminum beam, which permits a comparison of results obtained by a reduced-order analysis with those obtained from a numerically intensive simulation in physical degrees-of-freedom. A uniformly distributed thermal loading is first applied to investigate the dynamic instability associated with thermal buckling. A uniformly distributed random loading is added to investigate the combined thermal-acoustic response. In the latter case, three types of response characteristics are considered, namely: (i) small amplitude vibration around one of the two stable buckling equilibrium positions, (ii) intermittent snap-through response between the two equilibrium positions, and (iii) persistent snap-through response between the two equilibrium positions. For the reduced-order analysis, four categories of modal basis functions are identified including those having symmetric transverse, anti-symmetric transverse, symmetric in-plane, and anti-symmetric in-plane displacements. The effect of basis selection on the quality of results is investigated for the dynamic thermal buckling and combined thermal-acoustic response. It is found that despite symmetric geometry, loading, and boundary conditions, the anti-symmetric transverse and symmetric in-plane modes must be included in the basis as they participate in the snap-through behavior.

Przekop, Adam↗
NASA NTRS1991

Improved compression buckling for rectangular composite plates by stiffness tailoring

Buckling resistance is often a controlling criterion in the design of structural elements. Design concepts that lead to increased buckling loads (or strains) can directly lower the structural cost and/or weight by a number of means. This study quantifies the improvements that can be achieved in compression buckling loads of rectangular composite plates by using a simple stiffness tailoring concept. The approach is to position the unidirectional lamina through the thickness and over the planform of the plate so that the buckling load is increased with no loss in in-plane stiffness or increase in weight. Finite element analyses have been used to determine the effects of tailoring on the buckling load of plates with various boundary conditions, aspect ratios, thicknesses, and membrane stiffnesses. Increases in buckling loads (or strains) of nearly 200 percent over the uniform plate buckling loads are shown possible with this tailoring concept.

Biggers, Sherrill B.↗
NASA NTRS2007

Stress Analysis of Composite Cylindrical Shells with an Elliptical Cutout

A special-purpose, semi-analytical solution method for determining the stress and deformation fields in a thin laminated-composite cylindrical shell with an elliptical cutout is presented. The analysis includes the effects of cutout size, shape, and orientation; non-uniform wall thickness; oval-cross-section eccentricity; and loading conditions. The loading conditions include uniform tension, uniform torsion, and pure bending. The analysis approach is based on the principle of stationary potential energy and uses Lagrange multipliers to relax the kinematic admissibility requirements on the displacement representations through the use of idealized elastic edge restraints. Specifying appropriate stiffness values for the elastic extensional and rotational edge restraints (springs) allows the imposition of the kinematic boundary conditions in an indirect manner, which enables the use of a broader set of functions for representing the displacement fields. Selected results of parametric studies are presented for several geometric parameters that demonstrate that analysis approach is a powerful means for developing design criteria for laminated-composite shells.

Oterkus, E.↗
DOE OSTI2026

Electrocoagulation in Water Treatment: Targeted Contaminant Removal and Laboratory Best Practices

Electrocoagulation for water treatment offers many advantages over traditional treatment technologies, including improved energy efficiency and modularity. One challenge with electrocoagulation is the lack of standardization in the methodology and reporting. This review provides a novel contribution by examining the past literature using a uniform metric (charge loading) as a basis for comparison, highlighting the importance of uniform reporting practices in this field. Furthermore, this review provides practical guidance for experimentalists in standardizing the electrocoagulation design and operating procedures. First, we present a comprehensive overview of contaminant-specific electrocoagulation as an electrochemical treatment technology for processing industrial, municipal, and agricultural water, with a focus on aluminum and iron electrocoagulation. We detail the fundamental mechanisms that allow for constituent removal during pretreatment. Specifically, we highlight electrocoagulation’s potential for organics, metalloids, microbes, and hardness remediation, examining the optimal removal conditions in terms of charge loading and current density. We conclude this work with some experimental best practices for lab-scale electrocoagulation experiments.

aluminum↗
NASA NTRS1980

Deflections of beam columns on multiple supports

Lateral deflections of beam columns on multiple equally spaced supports are calculated using the STAGS nonlinear structural analysis computer program. Three lateral loadings are considered, uniform, linear, and uniform over only the center bay. Two types of boundary conditions are considered at the end supports, clamped, and simple support. The effect of an initial sinusoidal imperfection are considered. Deflections in the center and end bays of the beam columns are presented as a function of applied axial compressive load. As the number of bays becomes large, the effect of boundary conditions on the deflections in the center bays diminishes. For cases involving a uniform or linearly varying load, imperfections can have a much larger effect on deflections in the center bays than can lateral pressure.

Stroud, W. J.↗
NASA NTRS1980

Stress intensity factors and COD in an orthotropic strip

The elasticity problem for an orthotropic strip or a beam with an internal or an edge crack under general loading conditions is considered. The numerical results are given for four basic loading conditions, namely, uniform tension, pure bending, three point bending, and concentrated surface shear loading. For the strip with an edge crack additional results regarding the crack opening displacements are obtained by using the plastic strip model. A critical quantity which is tabulated is the maximum compressive stress in the plane of the crack. It is shown that this stress may easily exceed the yield limit in compression and hence may severely limit the range of application of the plasticity results.

Kaya, A. C.↗
NASA NTRS1994

Shear buckling response of tailored composite plates

This Note evaluates the piecewise-uniform approach to tailoring as a mean of improving the shear buckling loads of composite plates. This design approach is referred to herein as stiffness tailoring or, more simply, as tailoring. The primary objectives are to determine the tailoring patterns and the degree of concentration of the material used to achieve the tailoring in each pattern that maximize the shear buckling load and to quantify the maximum relative improvement that can be achieved in the buckling load compared to uniform plates.

Biggers, Sherrill B.↗
NASA NTRS1984

Dugdale plastic zone size and CTOD equations for the compact specimen

With the aim of applying the Dugdale model to the compact specimen, the equations for stress intensity factor and crack surface displacement are obtained for a pair of pin loads and a uniform stress acting on a segment of the crack surface. The plastic zone size is calculated from the 'finiteness' condition of Dugdale, and the results agree well with collocation results from Terada (1983). The load that causes incipient yielding at the compression point of the compact specimen is calculated from a finite element strip yield analysis for an elastic-perfectly plastic material. The crack tip opening displacement for the compact specimen is calculated by adding the displacement at the tip of the physical crack length due to the pin load and due to the uniform stress. The results are within 1.5 percent of current collocation results.

Newman, J. C., Jr.↗