28,973 research outputs found
Heat flux evaluation in high temperature ring-on-ring contacts
A comprehensive methodology to investigate heat flux in a ring-on-ring tribometer is presented. Thermal fluxes under high contact pressures and temperature differences were evaluated through an experimental campaign and by a numerical procedure of inverse analysis applied to surface temperature measurements. An approximation of a two-dimensional time-dependent analytical solution for the temperature distribution was first developed and subsequently adapted to mimic the specific testing configuration characteristics; the problem was finally simplified to enable further inverse analysis. Experiments were performed using an innovative high temperature ring-on-ring tribometer. The evaluated contact heat transfer rates were reported as a function of normal load and temperature difference between the discs under steady-state conditions; the results reported here show that, in the present test configuration, the temperature difference has stronger influence than the applied load in terms of heat transfer induced by contact
Inverse Design Based on Nonlinear Thermoelastic Material Models Applied to Injection Molding
This paper describes an inverse shape design method for thermoelastic bodies.
With a known equilibrium shape as input, the focus of this paper is the
determination of the corresponding initial shape of a body undergoing thermal
expansion or contraction, as well as nonlinear elastic deformations. A
distinguishing feature of the described method lies in its capability to
approximately prescribe an initial heterogeneous temperature distribution as
well as an initial stress field even though the initial shape is unknown. At
the core of the method, there is a system of nonlinear partial differential
equations. They are discretized and solved with the finite element method or
isogeometric analysis. In order to better integrate the method with
application-oriented simulations, an iterative procedure is described that
allows fine-tuning of the results. The method was motivated by an inverse
cavity design problem in injection molding applications. Its use in this field
is specifically highlighted, but the general description is kept independent of
the application to simplify its adaptation to a wider range of use cases.Comment: 22 pages, 13 figure
Heat transport and phonon localization in mass-disordered harmonic crystals
We investigate the steady state heat current in two and three dimensional
disordered harmonic crystals in a slab geometry, connected at the boundaries to
stochastic white noise heat baths at different temperatures.The disorder causes
short wavelength phonon modes to be localized so the heat current in this
system is carried by the extended phonon modes which can be either diffusive or
ballistic. Using ideas both from localization theory and from kinetic theory we
estimate the contribution of various modes to the heat current and from this we
obtain the asymptotic system size dependence of the current. These estimates
are compared with results obtained from a numerical evaluation of an exact
formula for the current, given in terms of a frequency transmission function,
as well as from direct nonequilibrium simulations. These yield a strong
dependence of the heat flux on boundary conditions. Our analytical arguments
show that for realistic boundary conditions the conductivity is finite in three
dimensions but we are not able to verify this numerically, except in the case
where the system is subjected to an external pinning potential. This case is
closely related to the problem of localization of electrons in a random
potential and here we numerically verify that the pinned three dimensional
system satisfies Fourier's law while the two dimensional system is a heat
insulator. We also investigate the inverse participation ratio of different
normal modes.Comment: 30 pages, 28 figures (Revised and improved version
Study of laser heated propulsion devices. Part 1: Evaluation of laser devices, fuels and energy coupling mechanisms
Closed cycle, CW waveform and short wavelength laser devices are desirable characteristics for laser propulsion. The choice of specific wavelengths for hydrogen fuel affects the operational conditions under which a laser supported absorption (LSA) wave is initiated and maintained. The mechanisms of initiating and maintaining LSA waves depend on the wavelength of the laser. Consequently, the shape and size of the hot core plasma is also dependent on wavelength and pressure. Detailed modeling of these mechanisms must be performed before their actual significance can be ascertained. Inverse bremsstrahlung absorption mechanism is the dominant mechanism for coupling energy into the plasma, but other mechanisms which are wavelength dependent can dictate the LSA wave plasma initiation and maintenance conditions. Multiphoton mechanisms become important at visible or shorter wavelengths. These are important mechanisms in creating the initial H2 gas breakdown and supplying the precursor electrons required to sustain the plasma
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