An introduction to heat transfer

Abstract This paper presents theoretical descriptions of the key phenomena that govern the behaviour of composite framed structures in fire. These descriptions have been developed in parallel with large scale computational work undertaken as a part of a research project (The DETR-PIT Project, Behaviour of steel framed structures under fire conditions) to model the full-scale fire tests on a composite steel framed structure at Cardington (UK). Behaviour of composite structures in fire has long been understood to be dominated by the effects of strength loss caused by thermal degradation, and that large deflections and runaway resulting from the action of imposed loading on a ‘weakened’ structure. Thus ‘strength’ and ‘loads’ are quite generally believed to be the key factors determining structural response (fundamentally no different from ambient behaviour). The new understanding produced from the aforementioned project is that, composite framed structures of the type tested at Cardington possess enormous reserves of strength through adopting large displacement configurations. Furthermore, it is the thermally induced forces and displacements, and not material degradation that govern the structural response in fire. Degradation (such as steel yielding and buckling) can even be helpful in developing the large displacement load carrying modes safely. This, of course, is only true until just before failure when material degradation and loads begin to dominate the behaviour once again. However, because no clear failures of composite structures such as the Cardington frame have been seen, it is not clear how far these structures are from failure in a given fire. This paper attempts to lay down some of the most important and fundamental principles that govern the behaviour of composite frame structures in fire in a simple and comprehensible manner. This is based upon the analysis of the response of single structural elements under a combination of thermal actions and end restraints representing the surrounding structure.

Fundamental principles of structural behaviour under thermal effects (large composite buildings under compartment fires)

Microstructure, mechanical properties and tribological performance of CoCrFeNi high entropy alloy matrix self-lubricating composite

Self-lubricating materials are becoming more widespread in fields like metal forming or power generation due to the inability to use conventional lubricants in high-temperature (HT) applications. I...

Tribological behaviour of self-lubricating materials at high temperatures

Theory of Plasticity

The eddy currents induced in a thrust bearing result not only in a power loss of the system but also in phase lag and a decrease in magnitude of the magnetic force. Therefore, an accurate model including eddy-current effects would be highly beneficial at the design stage. We present a linear model including eddy-current effects for a typical active magnetic thrust bearing (AMTB). We define and calculate the dynamic current stiffness and displacement stiffness using both an analytical method and transient finite element (FE) analysis. We present a simple magnetic circuit model including eddy currents from which the two stiffnesses can be derived analytically. Furthermore, by using a transient analysis of the FE model, flux saturation, leakage, and fringing effects can all be taken into account. We show that the two stiffnesses have the same frequency response characteristics, both in the analytical model and from the results of the linear FE analysis, when the leakage and fringing effects are ignored. Even in the more practical case when the flux saturation, leakage and fringing effects are considered, the two stiffnesses can be considered to have the same frequency response characteristics within the 3 dB bandwidth without introducing much error. The open-loop frequency response of the two stiffnesses derived from the analytical model and the FE model agrees well with the experimental results.

Dynamic Stiffnesses of Active Magnetic Thrust Bearing Including Eddy-Current Effects

Journal misalignment usually exists in journal bearings that affect nearly all the bearings static and dynamic characteristics including minimum oil film thickness, maximum oil film pressure, maximum oil film temperature, oil film stiffness, and damping. The main point in this study is to provide a comprehensive analysis on the oil film pressure, oil film temperature, oil film thickness, load-carrying capacity, oil film stiffness, and damping of journal bearing with different misalignment ratios and appropriately considering the turbulent and thermo effects based on solving the generalized Reynolds equation and energy equation. The results indicate that the oil thermo effects have a significant effect on the lubrication of misaligned journal bearings under large eccentricity ratio. The turbulent will obviously affect the lubrication of misaligned journal bearings when the eccentricity or misalignment ratio is large. In the present design of the journal bearing, the load and speed become higher and higher, and the eccentricity and misalignment ratio are usually large in the operating conditions. Therefore, it is necessary to take the effects of journal misalignment, turbulent, and thermal effect into account in the design and analysis of journal bearings.

Research on the Static and Dynamic Characteristics of Misaligned Journal Bearing Considering the Turbulent and Thermohydrodynamic Effects

Soft magnetic composites (SMCs) can be described as soft magnetic powders covered by electrically insulating layers. In this work, iron powders with high purity and organic-silicon epoxy resin were chosen for good magnetic properties, thermal stability, and mechanical properties, respectively. The effect of amount of resin, different annealing temperatures on the microstructure, and performance of SMCs was investigated. Results show that organic-silicon epoxy resin has excellent properties as dielectric coating materials for coating iron powders and maximum heat-resistant temperature is about 400 ℃. According to magnetic properties and flexural strength analysis, the optimum annealing temperature of organic-silicon epoxy resin-coated composite is 200 ℃. Furthermore, the finite element analysis indicates that the strength of the whole composites is related to the adhesion of resin and iron and the strength of resin itself.

Annealing effects on magnetic properties and strength of organic-silicon epoxy resin-coated soft magnetic composites

A new nonlinear dynamic analysis method of rotor system supported by oil-film journal bearings

This paper presents a totally analytical method to calculate the eddy current loss in a laminated rotor. First, the method derives the analytical field solutions both in the lamination and the air gap with average boundary conditions at the surface of the rotor. The magnetic field can then be determined from the static flux distribution around the pole surface. Then, the method obtains the eddy current induced in the lamination from the field solution in the lamination. Finally, it calculates the rotation loss by integrating resistive power loss over the volume of the lamination and summed in all sheets. The results show good agreement with experimentally measured losses.

Lie Yu

Papers

Dynamic Stiffnesses of Active Magnetic Thrust Bearing Including Eddy-Current Effects

Research on the Static and Dynamic Characteristics of Misaligned Journal Bearing Considering the Turbulent and Thermohydrodynamic Effects

Annealing effects on magnetic properties and strength of organic-silicon epoxy resin-coated soft magnetic composites

A new nonlinear dynamic analysis method of rotor system supported by oil-film journal bearings

Analytical method for eddy current loss in laminated rotors with magnetic bearings