Feasibility Study of Infrared Detection of Defects in Green-State and Sintered PM Compacts

The electric Joule heating of solid materials through direct current excitation can be used to generate a temperature profile throughout a powdermetallic (P/M) compact. When recording the surface temperature distribution with an infrared (IR) camera important information regarding the integrity of the sample can be gained. This research will concentrate on the formulation of a mathematical model capable of predicting the temperature distribution and heat flow behavior in P/M parts and its relations to the supplied current, injection method, geometric shape as well as the thermo-physical properties. This theoretical model will subsequently be employed as a tool to aid in the actual measurements of infrared signatures over the sample surface and their correlation with the detection of surface and subsurface flaws. In this work we will develop the theoretical background of IR testing of green-state and sintered P/M compacts in terms of stating the governing equations and boundary conditions, followed by devising analytical and numerical solutions. Our main emphasis is placed on modeling various flaw sizes and orientations in an effort to determine flaw resolution limits as a function of minimally detectable temperature distributions. Preliminary measurements with controlled and industrial samples have shown that this IR testing methodology can successfully be employed to test both green-state and sintered P/M compacts

Supercomputer implementation of finite element algorithms for high speed compressible flows

Prediction of compressible flow phenomena using the finite element method is of recent origin and considerable interest. Two shock capturing finite element formulations for high speed compressible flows are described. A Taylor-Galerkin formulation uses a Taylor series expansion in time coupled with a Galerkin weighted residual statement. The Taylor-Galerkin algorithms use explicit artificial dissipation, and the performance of three dissipation models are compared. A Petrov-Galerkin algorithm has as its basis the concepts of streamline upwinding. Vectorization strategies are developed to implement the finite element formulations on the NASA Langley VPS-32. The vectorization scheme results in finite element programs that use vectors of length of the order of the number of nodes or elements. The use of the vectorization procedure speeds up processing rates by over two orders of magnitude. The Taylor-Galerkin and Petrov-Galerkin algorithms are evaluated for 2D inviscid flows on criteria such as solution accuracy, shock resolution, computational speed and storage requirements. The convergence rates for both algorithms are enhanced by local time-stepping schemes. Extension of the vectorization procedure for predicting 2D viscous and 3D inviscid flows are demonstrated. Conclusions are drawn regarding the applicability of the finite element procedures for realistic problems that require hundreds of thousands of nodes

Development of an integrated BEM approach for hot fluid structure interaction

A comprehensive boundary element method is presented for transient thermoelastic analysis of hot section Earth-to-Orbit engine components. This time-domain formulation requires discretization of only the surface of the component, and thus provides an attractive alternative to finite element analysis for this class of problems. In addition, steep thermal gradients, which often occur near the surface, can be captured more readily since with a boundary element approach there are no shape functions to constrain the solution in the direction normal to the surface. For example, the circular disc analysis indicates the high level of accuracy that can be obtained. In fact, on the basis of reduced modeling effort and improved accuracy, it appears that the present boundary element method should be the preferred approach for general problems of transient thermoelasticity

Thermo-hydro-mechanical coupling within a geomechanical multiphase model framework with special reference to fractured rock masses in the vicinity of a geological disposal facility for radioactive waste

A novel numerical approach for the modelling of Thermo-Hydro-Mechanical (THM) processes in the vicinity of a Geological Disposal Facility (GDF) for the long-term storage of radioactive waste is presented. This work is based on a dual numerical code framework with a multiphase flow solver for thermo-hydraulic processes and a geo-mechanical solver for mechanical processes in fractured and fracturing rock masses. The method has a unique continuum-discontinuum configuration that allows each of the THM processes to be represented with the most suited formulation, thus improving the accuracy and complexity of the simulations. Thermal processes are implemented within the geo-mechanical solver using both an explicit and an implicit approach, the latter allowing the modelling of temperature over large time scales, an important feature in the context of geological disposal. Moreover, a novel thermal contact approach is presented to investigate the heat transfer between contacting solids and its application to heat transfer across fractures is discussed. Furthermore, a thermo-mechanical coupling formulation is derived in the geo-mechanical solver, enabling thermal expansion and thermally induced fracturing. Then, the THM coupling is finalised using a conservative projection method that enables information exchange between superimposed numerical meshes e.g. heat transfer between the thermo-hydraulic and the thermo-mechanical solvers. Both applications in porous media and with laminar flow are explored. Finally, the THM dual framework is applied to the modelling of thermal spalling occurring in the excavation walls of a deposition hole in a GDF. The potential of the method to offer new predictive capabilities and insights on unexplained experimental observations is demonstrated by considering the concurrence over time of THM factors influencing spalling, especially multi-phase flow in the continuum and explicitly represented fractures in the discontinuum.Open Acces

Thermal Management of E–Motors in Electric Vehicle Application Employing LPTN Model

The electric motor is at the center focus as an alternative to the internal combustion engine for automotive applications since it does not produce greenhouse gas emissions and can contribute significantly to the reduction of fossil fuel consumption globally. As extensive research works are being done on electric vehicles at present, thermal analysis of traction motor is increasingly becoming the key design factor to produce electric motors with high power and torque capabilities in order to satisfy electric vehicle driving requirements. Motor losses cause active heat generation in the motor components and excessive temperature rise affects the electromagnetic performance of the traction motor. High torque and power requirements based on the driving conditions under urban and highway drive conditions demand high capacity motor cooling system in order to keep the temperature within the safe limit. Hence, it is critical to develop and design a temperature prediction tool to dynamically estimate the winding and magnet temperature and regulate cooling to remove excessive heat from the motor. Conventional thermal modeling of motors includes analytical and numerical modeling. Analytical modeling is done by using Lumped Parameter Thermal Network (LPTN) which is analogous to electric circuit and a fast method for predicting temperature. It uses heat transfer equations involving thermal resistances and thermal capacitances to analytically determine temperature at different nodes. Numerical modeling is done in two ways–Finite Element Analysis and Computational Fluid Dynamics. Numerical modeling can produce more accurate results, but it requires more computational time. Since the temperature of motor components has to be predicted very quickly, i.e. during driving, LPTN is more effective because LPTN can quickly predict temperature based on the heat transfer equations. This thesis proposes an LPTN model that predicts motor temperature and regulates the required coolant flow rate simultaneously. Thus, it is able to dynamically predict the temperature. MATLAB Simulink has been used for simulation of the LPTN model for a laboratory PMSM prototype. The thermal resistances in the thermal network model have been obtained from the motor geometrical parameters. The electromagnetic loss data with respect to torque and speed were taken as input, and thus the temperature results of motor components have been found. The future work will be to implement this model into full scale prototype of the motor

Analysis of Transient Heat conduction in Different Geometries

Present work deals with the analytical solution of unsteady state one-dimensional heat conduction problems. An improved lumped parameter model has been adopted to predict the variation of temperature field in a long slab and cylinder. Polynomial approximation method is used to solve the transient conduction equations for both the slab and tube geometry. A variety of models including boundary heat flux for both slabs and tube and, heat generation in both slab and tube has been analyzed. Furthermore, for both slab and cylindrical geometry, a number of guess temperature profiles have been assumed to obtain a generalized solution. Based on the analysis, a modified Biot number has been proposed that predicts the temperature variation irrespective the geometry of the problem. In all the cases, a closed form solution is obtained between temperature, Biot number, heat source parameter and time. The result of the present analysis has been compared with earlier numerical and analytical results. A good agreement has been obtained between the present prediction and the available results

Disaggregation process for dynamic multidimensional heat flux in building simulation

Heat transfer across envelopes (façade, roof, glazed areas) represents a big share of the energy flow within the heat balance of buildings. This paper focuses on areas of the envelope where multi-dimensional heat transfer occurs. These areas are commonly defined as thermal bridges, due to a localized reduction of thermal resistance of constructions in these places. This paper reviews common standardized methods to assess heat transfer in buildings, under various modelling assumptions: one-dimensional, multi-dimensional, steady state and dynamic. Within presently developed modelling and assessment methods, a need for improvement has been identified over existing methods for the thermal assessment of multi-dimensional heat transfer under dynamic conditions. A phasorial approach to differential heat transfer in thermal bridges has been developed, which serves as the dynamic extension of steady-state thermal bridge coefficients. This formulation is applied to the junction of a masonry wall with a concrete slab

Lattice Element Method and its application to Multiphysics

In this thesis, a Lattice element modelling method is developed and is applied to model the loose and cemented, natural and artificial, granular matters subject to thermo-hydro-mechanical coupled loading conditions. In lattice element method, the lattice nodes which can be considered as the centres of the unit cells, are connected by cohesive links, such as spring beams that can carry normal and shear forces, bending and torsion moment. For the heat transfer due to conduction, the cohesive links are also used to carry heat as 1D pipes, and the physical properties of these rods are computed based on the Hertz contact model. The hydro part is included with the pore network modelling scheme. The voids are inscribed with the pore nodes and connected with throats, and then the meso level flow equation is solved. The Euler-Bernoulli and Timoshenko beams are chosen as the cohesive links or the lattice elements, while the latter should be used when beam elements are short and deep. This property becomes interesting in modelling auxetic materials. The model is applied to study benchmarks in geotechnical engineering. For heat transfer in the dry and full range of saturation, and fractures in the cemented granular media.How through porous media failure behaviours of rocks at high temperature and pressure and granular composites subjected to coupled Thermo hydro Mechanical loads. The model is further extended to capture the wave motion in the heterogeneous granular matter, and a few case studies for the wavefield modification with existing cracks are presented. The developed method is capable of capturing the complex interaction of crack wave interaction with relative ease and at a substantially less computational cost

Transient Analysis of Thermal Bending and Vibration of Steam Turbine Rotor

Rotor-bearing systems often exhibit nonlinear behavior due to hydrodynamic effects and external forces. Finite element methods based on linear analysis are commonly used for rotor dynamic analyses, where nonlinear bearing/damping forces are linearized into equivalent stiffness and damping coefficients. However, this method may not accurately describe strongly nonlinear systems. Engineers use transient analysis and nonlinear models to improve rotor behavior analysis. This study investigates the effects of transient-thermal bending and vibration on a high-pressure steam turbine rotor using the finite element method. A scaled rotor-shaft was used to study thermal bending and vibrations caused by steam heat. The design of the shaft was based on an existing power station high-pressure turbine rotor. Numerical modal analyses were performed using ANSYS software to obtain a partial level of integrity between the numerical model and the analytical model. Natural frequencies were compared between the experimental, numerical, and analytical results, which showed good correlations