Thermal Response Of Structure Research Articles

An exact recursion relation solution for the steady-state surface temperature of a general multilayer structure

A recursion relation technique has been used in the past to determine the surface potential from the multilayer electrical Laplace equation. This has provided for a vastly simplified evaluation of the electrical spreading resistance and four-probe resistance. The isomorphism of the multilayer Laplace equation and the multilayer steady-state heat flow equation suggests the possibility of developing a recursion relation applicable to the multilayer thermal problem. This recursive technique is developed and is shown to provide the surface temperature of the multilayer steady-state heat flow equation. For the three-layer case, the thermal recursion relation readily yields the surface results,which are identical with those presented by Kokkas and the TXYZ thermal code. This recursive technique can be used with any number of layers while incurring only a small increase in computation time for each added layer. For the case of complete, uniform top surface coverage by a heat source, the technique gives rise to the generalized one-dimensional thermal resistance result. An example of the use of the new recursive method is provided by the preliminary calculations of the surface temperature of a buried oxide (SOI, SIMOX) structure containing several thicknesses of the surface silicon layers. This new technique should prove useful in the investigation and understanding of the steady-state thermal response of modern multilayer microelectronic structures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experiments to investigate the origin of anomalously elevated unblocking temperatures

A fundamental problem in rock magnetism and paleomagnetism is the physical origin of anomalously elevated unblocking temperatures. To investigate this problem, we have studied viscous remanent magnetization (VRM) acquired at 225°C by 1–2 μm magnetite particles synthesized with the glass‐ceramic method. Experiments were performed with two primary goals: (1) to determine which particular conditions produce anomalously elevated unblocking temperatures, and (2) to compare various observed aspects of viscous behavior to predictions based on two different physical mechanisms that might raise the unblocking temperature: the reduction of magnetic relaxation time by the applied field (the Neel medium‐field mechanism), and directional ordering of defects within domains and domain walls. When compared to model predictions, the present results indicate that neither the Neel medium‐field mechanism nor the directional ordering mechanism satisfactorily accounts for anomalously high unblocking temperatures. Surprisingly, however, the unblocking temperature spectrum of VRM is critically sensitive to a sample's initial state. When samples first are thermally demagnetized from 580°C to 225°C, VRMs acquired subsequently at 225°C exhibit pronounced high‐temperature “tails” extending to 450°C. Yet when samples first are demagnetized in an alternating field at room temperature before acquisition at 225°C, their VRMs unblock by approximately 300°C. Despite these two very different thermal responses, VRM acquisition curves at 225°C are virtually identical for the two initial states. Furthermore, zero‐field storage prior to acquisition suppresses VRM acquisition coefficients by similar amounts for both initial states. Significantly, standard thermal demagnetization to room temperature greatly attenuates the high‐temperature tail of a VRM acquired subsequently at 225°C. We conclude that thermal response of domain structure, as determined by thermomagnetic history, plays a critical role in the thermal unblocking process.

Thermometric design considerations for temperature monitoring in machine tools and CMM structures

Temperature measurement is an essential element in monitoring and studying the thermal deformation response of machine tools and CMM structures. In this context, temperature measurement is required for model verification, for control purposes and for determining the thermal contact resistance and other thermal boundary conditions. In these applications, where heat flux and temperature rise levels are relatively low, a proper thermometric design is a must to ensure accurate and precise results. This paper addresses the problem of thermometric design in the case of temperature measurement inside a solid body and on its surface. Results and recommendations regarding the interactions between neighbouring thermocouples, the effect of the distance between the thermocouple and the contact interface (i.e. the heat input surface), and the effect of heat flow along the thermocouple wires on the measurement error are presented. The issue of the effect of the unknown thickness and thermal conductivity of the surface paint on the uncertainty in surface temperature measurement is also addressed.

Enthalpy-based explicit finite element data parallel formulations for thermal analysis of structures

Data parallel implementations of two explicit finite element representations, namely temperature representations and enthalpy-temperature representations, for evaluating nonlinear transient thermal response of structures are presented. Compared to the temperature representations, enthalpy-temperature representations eliminate assembly operation of the capacitance vector for nonlinear problems. The assembly operation, which involves communications between the processors, is more expensive than computations on data parallel computers. The effectiveness of the enthalpy-temperature representations are investigated on the Connection Machine system CM-5.

Thermally induced bending vibrations of a flexible rolled-up solar array

An analytical approach for determining the thermal-structural response of a flexible rolled-up solar array due to a sudden increase in external heating is developed. Two analyses are presented: 1) an uncoupled thermal-structural analysis that assumes the heating and temperature gradients are not affected by thermally induced motions, and 2) a coupled thermal-structural analysis that includes the effects of structural deformations on heating and temperature gradients. The analytical methods identify key parameters for understanding the static and dynamic response. A stability criterion given in nondimensional parameters establishes the conditions for thermal flutter. Key parameters for thermal flutter include the ratio of thermal and structural response times, the solar inclination angle, and the system damping. Numerical calculations are presented for the solar arrays on the Hubble Space Telescope. Unstable oscillations are possible but are unlikely to have practical importance.

Analysis of Interaction of Disruption Induced Runaway Electrons with Plasma Facing Components in Next Generation Tokamaks

Runaway electrons which are accelerated during plasma disruptions may cause damage to the plasma facing components when their energy is deposited locally. In order to assess the possible damage of plasma facing components and the associated damage thresholds in a next generation tokamak, analyses have been carried out. The energy deposition by 100 and 300 MeV electrons in component materials has been calculated using a Monte Carlo code. The effect of parametric changes of carbon armor thickness, electron energy and angle of incidence has been evaluated. Subsequently the thermal response of divertor structures with carbon armor and with bare tungsten, and of a first wall structure has been analyzed and thresholds for thermally induced component damage were derived. The damage threshold under 100 MeV electron impact on a divertor structure with 10 mm carbon coverage and dispersion strengthened copper cooling tubes is about 60 MJ/m2 of incident energy, that for a divertor structure with molybdenum coolant tubes is about 115 MJ/m2, whereas the damage threshold for melting of the bare tungsten divertor is only about 30 MJ/m2. Damage of the first wall structure would occur above 180 MJ/m2. For 300 MeV electron incidence the damage thresholds are 13 to 47% lower than the values for 100 MeV.

A finite element spectral method with application to the thermoelastic analysis of space structures

AbstractA combined spectral finite element method is devised for use in finding the thermal and thermoelastic dynamic response of truss structures to time‐periodic loading. The thermal problem is strongly non‐linear due to the presence of heat radiation. The problems considered are typical in the analysis of space structures. In the method proposed, the spatial domain is first discretized using a consistent finite element formulation. Then the resulting semi‐discrete equations in time are solved analytically by using a spectral method that is symbolically coded. Some numerical examples are presented which demonstrate the performance of the method and its ability to identify some key characteristics in space structure problems.

A unified finite element modeling/analysis approach for thermal-structural response in layered composites

A computational finite element modeling/analysis approach for unified thermal-structural response in layered composites is described. Basic concepts of the methodology including the characteristic features of the formulations are presented in technical detail. First, layered thermal finite elements capable of handling varying thermophysical layer properties are described for thermal modeling/analysis. Next, layered structural finite elements which use concepts of substitute shape functions are described for effectively modeling bending and plane stress or plane strain type problems. Finally, unified thermostructural formulations for combined thermal-structural modeling/analysis are described. Results demonstrate that the layered thermal elements can be effectively interfaced with the layered structural elements for unified analysis and the models predict good agreement for thermal, structural, and combined thermal-structural responses, respectively, with relatively reduced model sizes.

Self-shadowing effects on the thermal-structural response of orbiting trusses

An investigation of self-shadowing effects on the thermal-structural response of orbiting trusses is described. The shadowing, heating, thermal and structural analyses are summarized. The significance of shadowing on the thermal-structural behavior of a single member and a beam constructed from truss members is described. For the trusses considered, the study shows that member self-shadowing effects significantly alter the behavior and must be included to predict the thermal-structural response correctly.

On the methodologies of stress analysis of composite structures

Abstract The rapidly increasing technological importance of composite materials and composite structures is leading to the development of new, more advanced models of their actual response to mechanical and thermal loads. This in turn results in the development of new experimental and analytical methods for determination of the mechanical and thermal responses of such structures and materials to various loads. In this respect the reliability and the predictive power of various methods and techniques of stress analysis become very important since all the analytical, experimental and numerical methods used for the determination, prediction and optimization of the actual mechanical responses of composite structures and materials are based on the concepts of strain and stress. Because of the inherently three-dimensional stress and strain states in composite materials and structures and the wide use of viscoelastic polymers as the matrix and some reinforcing fiber materials, a more rigorous type of modelling than had been common in the past is needed of all the involved physical phenomena which influence the strain and stress states at the local and global levels. Also, a more rigorous analysis of practical consequences of the physical and mathematical simplifications is required to assure reliability and accuracy of various methods of stress analysis. The influence of the above-mentioned factors on the reliability and applicability of analytical and experimental procedures is illustrated by examples of actual material responses. Part 2 of this paper presents theories and techniques of three new methods of strain/stress analysis which have been developed on the basis of comprehensive physical models of involved phenomena: the isodyne, strain gradient and thermoelastic effect methods. Presented examples illustrate the efficacy of these methods.

Principles For Calculation Of Load-bearing And Deformation Behaviour Of Composite Structural Elements Under Fire Action

The fire behaviour of composite steel-concrete members was especially investigated by testing as well as by using calculation models for the temperature rise and the load-bearing capacity including deformations and restraints. This combined procedure resulted in well designed members within a comparatively short period. The thermal and structural responses of composite structures are studied theoretically-numerically. Analytical models for determining thermal material properties for concrete and steel are described. Temperature-dependent stress-strain relationships for concrete and structural steel are presented. Finally the application of the analytical models in a computer program is shown.

Thermal-structural analysis of large space structures - An assessment of recent advances

Recent advances in modeling, analyzing, and understanding the thermal-structural responses of large space structures are reviewed, and uncertainties in the thermal-structural analysis are identified. Typical heat-load, thermal, and structural analyses requirements for large space structures are discussed using a design for a future large spacecraft as an example. The current status of heating, thermal, and structural analyses is then reviewed, and computer programs used in research and design are discussed. The need to develop efficient methods for integrating the interdisciplinary analyses is emphasized.

Thermal response of process equipment to hydrocarbon fires. Relatively small fires in a process plant can cause equipment failure and initiate a much more dangerous situation

Requirements for active fire-fighting equipment such as fixed and portable powder extinguishers, foam generators, water guns, and deluge systems, are given in various codes and standards. However, very little is to be found about fire design conditions and passive fire protection. For safety verification of process plants and for designing adequate passive fire protection it is necessary to know the total incident heat fluxes which can occur under realistic conditions and the effects that such heat fluxes may have on process equipment and structures. During the last few years, Det Norske Veritas has been invloved in investigations aimed at estimating realistic fire loads from different types of hydrocarbon fires and the thermal response of process equipment and structures exposed to such fires. These investigations are still in progress and are especially focused on the conditions on off-shore oil and gas production platforms. However, many fire problems will be the same in the land-based process industry. The present paper concentrates on the thermal response of pipes and vessels exposed to a severe hydrocarbon fire with a defined thermal load. (JMT)

Differences in the thermal behaviour of myocardial membranes relative to hibernation

1. 1. Phase transitions and changes in the molecular ordering of membrane lipids were detected by differential scanning calorimetry (DSC) and spin labelling using myocardial membranes from summer-active and winter-hibernating ground squirrels ( Spermophilus richardsonii), dog ( Canis familiaris) and trout ( Salmo gairdnei). 2. 2. Two phase transitions, one at 26°C and the other at 15°C, were detected by DSC in the membranes from the dog, whereas only one transition was found in the membranes from the ground squirrel. This was at 26°C in membranes from summer-active animals but was at 16°C in membranes from winter-hibernating squirrels. No transition was detected in membranes from cold water, adapted trout. 3. 3. Spin labelling showed changes in lipid ordering at about the same temperature as the thermal transitions detected by DSC except in the membranes from the dog where only the transition at 26°C was observed. 4. 4. The membrane lipids from the winter-hibernating squirrel contained a higher proportion of unsaturated fatty acids than those of the summer-active squirrel. 5. 5. The transition at 15°C in membranes from dog correlates with the reported temperature for the loss of cardiac function during hypothermia and suggests a causal relationship between the thermal response of membrane lipid structure and cardiac function. 6. 6. The absence of a transition at 15°C in the membranes of the summer-active ground squirrel is consistent with the ability of this animal to maintain rhythmic heart beat at tissue temperatures near 0°C.

Limiter materials response for long duration plasma burns

Limiter designs are presented that provide plasma position control during long duration plasma burns and absorb the energy released during a plasma disruption. Thermal-structural responses of low Z materials are examined and specific materials are recommended.

Modelled thermal response of structures in fire environments

A computation technique based on the finite element method is presented for the non-linear thermal response of structures submitted to fire environments. The incremental equations which result from the associated non-linear heat transfer problem are solved by a non-iterative solution technique based on the concept of ‘tangential’ conductivity. Computational efficiency is illustrated by comparison with experimental results recorded during fire tests of concrete structural elements.