A New Spectral-Finite Volume Approach in Non-Fourier Heat Conduction Problems With Periodic Surface Disturbances

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Masoud Kharati Koopaee ◽  
Amir Omidvar
Keyword(s):  
Temperature Field ◽  
Heat Conduction ◽  
Steady State ◽  
Surface Temperature ◽  
Finite Volume ◽  
Time Domain ◽  
Periodic Surface ◽  
Fourier Heat Conduction ◽  
Finite Volume Approach ◽  
The Time Domain

In this study, a simple spectral-finite volume approach for hyperbolic heat conduction problems under periodic surface temperature is presented. In this approach, by choosing only three frequencies from a continuum frequency spectrum of the periodic temperature field, the time dependent governing equation is transformed into the steady state one in the frequency domain. Then, using the finite volume technique, temperature field in the frequency domain for each wave number is obtained. Finally, by transforming back the result to the time domain, the temperature field in the time domain would be obtained. This new method has been validated against some published results and a good agreement has been found. Despite the simplicity of the present method, it is able to accurately predict the temperature distribution in the periodic steady state portion of non-Fourier heat conduction problems subjected to periodic surface temperature.

A time-domain finite volume approach for prediction of muffler transmission loss including thermal effects

2013 ◽  
Vol 228 (1) ◽  
pp. 108-118 ◽  
Author(s):  
Ling-Kuan Xuan ◽  
Jing-Feng Gong ◽  
Ping-Jian Ming ◽  
Guo-Yong Jin ◽  
Wen-Ping Zhang
Keyword(s):  
Temperature Field ◽  
Finite Volume ◽  
Time Domain ◽  
Thermal Effects ◽  
Sound Speed ◽  
Heterogeneous Media ◽  
Transmission Loss ◽  
Expansion Chamber ◽  
Commercial Code ◽  
Finite Volume Approach

A time-domain finite volume approach is presented for predicting the transmission loss of muffler including thermal effects with non-uniform sound speed field and density field, in which the acoustic wave equation in heterogeneous media is solved by using unstructured finite volume method with the temperature field specified or solved by some commercial code. An improved time-domain impulse method based on the absorbing boundary condition is applied to predict the acoustic attenuation characteristics of mufflers. The approach is validated by numerical simulations of a simple expansion chamber muffler and a complex muffler with five chambers. The predicted results agree well with the corresponding experimental ones and numerical ones obtained by finite element method with commercial code SYSNOISE. The results of both mufflers under different thermal conditions indicate that the temperature distribution has a significant influence on transmission loss. According to the analysis of a complex muffler with ideal medium, it is shown that the variation of working conditions can obviously affect density and sound speed distributions but have little influence on transmission loss. On the other hand, the obtained transmission loss with the solved temperature field deviates much from the one with specified uniform temperature field.

scholarly journals STEADY-STATE ANALYSIS OF NONLINEARLY COUPLED CHUA'S CIRCUITS WITH PERIODIC INPUT

2003 ◽  
Vol 13 (11) ◽  
pp. 3395-3407 ◽  
Author(s):  
F. A. SAVACI ◽  
M. E. YALÇIN ◽  
C. GÜZELIŞ
Keyword(s):  
Steady State ◽  
Time Domain ◽  
Transfer Functions ◽  
Piecewise Linear ◽  
Time Domain Analysis ◽  
Steady State Analysis ◽  
Linear Dynamic Systems ◽  
Periodic Input ◽  
The Time Domain ◽  
State Analysis

In this paper, nonlinearly coupled identical Chua's circuits, when driven by sinusoidal signal have been analyzed in the time-domain by using the steady-state analysis techniques of piecewise-linear dynamic systems. With such techniques, it has become possible to obtain analytical expressions for the transfer functions in terms of the circuit parameters. The proposed system under consideration has also been studied by analog simulations of the overall system on a hardware realization using off-the-shelf components as well as by a time-domain analysis of the synchronization error.

scholarly journals Comparison of observed borehole temperatures in Antarctica with simulations using a forward model driven by climate model outputs covering the past millennium

2020 ◽  
Author(s):  
Zhiqiang Lyu ◽  
Anais J. Orsi ◽  
Hugues Goosse
Keyword(s):  
Surface Temperature ◽  
Antarctic Peninsula ◽  
Time Domain ◽  
Climate Model ◽  
Forward Model ◽  
Model Data ◽  
West Antarctica ◽  
Data Comparison ◽  
Borehole Temperature ◽  
The Time Domain

Abstract. The reconstructed surface temperature series from boreholes in Antarctica have significantly contributed to our understanding of centennial and multi-decadal temperature changes and thus provides us a good way to evaluate the climate model ability to reproduce low-frequency climate variability. However, up to now, there were no systematic model-data comparisons based on temperature from boreholes at regional or local scale in Antarctica. Here, we discuss two different ways to perform such a comparison using boreholes measurements and the corresponding reconstructions of surface temperature at West Antarctic Ice Sheet (WAIS), Larissa, Mill Island and Styx in Antarctica. The standard approach is to compare climate model outputs at the grid point closest to each site with the reconstructions in the time domain derived from the direct borehole temperature observations. Although some characteristics of the reconstructions, for instance the non-uniform smoothing, limit to some extent the model-data comparison, several robust features can be evaluated. In addition, a more direct model-data comparison based on the temperature measured in the boreholes is conducted using a forward model that simulates explicitly the subsurface temperature profiles when driven with climate model outputs. This comparison in the depth domain provides many consistent signals with those in the time domain, but also suggest some information that we cannot extract from the comparison in the time domain. The major results from these comparisons are used to define some metrics derived from the borehole temperature data for future model-data comparison, and demonstrate the spatial representativity of the sites chosen for the metrics. The long term cooling trend in West Antarctica from 1000 to 1600 CE (−1.0 °C) is generally reproduced by the models, but often with a weaker amplitude. The 19th century cooling in the Antarctic Peninsula (−0.94 °C) is not reproduced by any of the models, which tend to show warming instead. The trend over the last 50 years is generally well reproduced in West Antarctica and at Larissa (Antarctic Peninsula), but overestimated at other sites. The wide range of simulated trends indicates the importance of internal variability on the observed trends, and show the value of model-data comparison to investigate the response to forcings.

scholarly journals Steady state signatures in the time domain for nonintrusive appliance identification

2015 ◽  
Vol 35 (1Sup) ◽  
pp. 58-64
Author(s):  
Yulieth Jimenez ◽  
Cesar Duarte ◽  
Johann Petit ◽  
Jan Meyer ◽  
Peter Schegner ◽  
...  
Keyword(s):  
Steady State ◽  
Time Domain ◽  
Energy Savings ◽  
Single Point ◽  
Impact Factors ◽  
Font Size ◽  
Electrical Measurements ◽  
Stroke Width ◽  
Load Monitoring ◽  
The Time Domain

<p class="Abstractandkeywordscontent"><span lang="ES-CO"><span><span><span style="font-family: OptimaLTStd-DemiBold; font-size: 10pt; color: #231f20; font-style: normal; font-variant: normal;"><span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">Smart Grid paradigm promotes advanced load monitoring applications to support demand side management and energy savings. Recently, considerable attention has been paid to Non-Intrusive Load Monitoring to estimate the individual operation and power consumption of the residential appliances, from single point electrical measurements. This approach takes advantage of signal processing<span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"> in order to reduce the hardware effort associated to systems with multiple dedicated sensors. Discriminative characteristics of the <span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">appliances, namely load signatures, could be extracted from the transient or steady state electrical signals. In this paper the effect of <span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">impact factors that can affect the steady state load signatures under realistic conditions are investigated: the voltage supply distortion, <span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">the network impedance and the sampling frequency of the metering equipment. For this purpose, electrical measurements of several <span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">residential appliances were acquired and processed to obtain some indices in the time domain. Results include the comparison of<br /><span style="font-family: OptimaLTStd; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">distinct scenarios, and the evaluation of the suitability and discrimination capacity of the steady state information.</span></span></span></span></span></span></span><br style="font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" /><br class="Apple-interchange-newline" /></span></span></span></span></p>

scholarly journals Time-resolving the COVID-19 outbreak using frequency domain analysis

2020 ◽  
Author(s):  
Keno L. Krewer ◽  
Mischa Bonn
Keyword(s):  
Steady State ◽  
Severe Acute Respiratory Syndrome ◽  
Spectral Density ◽  
Frequency Domain ◽  
Time Domain ◽  
Case Fatality ◽  
Frequency Domain Analysis ◽  
Time Domain Data ◽  
Current Outbreak ◽  
The Time Domain

AbstractDifficulties assessing and predicting the current outbreak of the severe acute respiratory syndrome coronavirus 2 can be traced, in part, to the limitations of a static description of a dynamic system. Fourier transforming the time-domain data of infections and fatalities into the frequency domain makes the dynamics easily accessible. Defining a quantity like the “case fatality” as a spectral density allows a more sensible comparison between different countries and demographics during an ongoing outbreak. Such a case fatality informs not only how many of the confirmed cases end up as fatalities, but also when. For COVID-19, knowing this time and using the entire case fatality spectrum allows determining that an outbreak had entered a steady-state (most likely its end) about 14 days before this is obvious from time-domain data. The lag between confirmations and deaths also helps to estimate the effectiveness of contact management: The larger the lag, the less time the average confirmed person had to infect people before quarantine.

Mesoscopic Heat Conduction and Onset of Periodicity

2003 ◽  
Author(s):  
Kal Renganathan Sharma
Keyword(s):  
Heat Flux ◽  
Heat Conduction ◽  
Time Domain ◽  
Heat Conduction Equation ◽  
Higher Order ◽  
Heat Propagation ◽  
Conduction Equation ◽  
Transient Temperature ◽  
Higher Order Terms ◽  
Fourier Heat Conduction

Mesoscopic approach deals with study that considers temporal fluctuations which is often averaged out in a macroscopic approach without going into the molecular or microscopic approach. Transient heat conduction cannot be fully described by Fourier representation. The non-Fourier effects or finite speed of heat propagation effect is accounted for by some investigators using the Cattaneo and Vernotte non-Fourier heat conduction equation: q=−k∂T/∂x−τr∂q/∂t(1) A generalized expression to account for the non-Fourier or thermal inertia effects suggested by Sharma (5) as: q=−k∂T/∂x−τr∂q/∂t−τr2/2!∂2q/∂t2−τr3/3!∂3q/∂t3−…(2) This was obtained by a Taylor series expansion in time domain. Manifestation of higher order terms in the modified Fourier’w law as periodicity in the time domain is considered in this study. When a CWT is maintained at one end of a medium of length L where L is the distance from the isothermal wall beyond which there is no appreciable temperature change from the initial condition during the duration of the study the transient temperature profile is obtained by the method of Laplace transforms. The space averaged heat flux is obtained and upon inversion from Laplace domain found to be a constant for the the case obeying Fourier’s law; 1 − exp(−τ) using the Cattaneo and Vernotte non-Fourier heat conduction equation, and upon introduction of the second derivative in time of the heat flux the expression becomes, 1 − exp(−τ)(Sin(τ) + Cos(τ)). Thus the periodicity in time domain is lost when the higher order terms in the generalized Fourier expression is neglected.

scholarly journals The Dependence of Temperature Profiles in Ice Sheets on Longitudinal Variations in Velocity and Surface Temperature

1978 ◽  
Vol 20 (82) ◽  
pp. 31-39 ◽  
Author(s):  
A. S. Jones
Keyword(s):  
Temperature Field ◽  
Steady State ◽  
Surface Temperature ◽  
Radial Flow ◽  
Ice Sheets ◽  
Temperature Profiles ◽  
Flow Lines ◽  
Temperature Variations ◽  
Longitudinal Variations ◽  
Surface Ice

Abstract Formulae for calculating temperature profiles in steady-state ice sheets are derived in terms of the horizontal and vertical velocities of the surface ice, and of the variation in surface temperature along the flow lines. Two models are considered: parallel flow and radial flow. In each case the result consists of a “stationary” term (equivalent to Robin's equation), a term dependent on the horizontal velocity, and a term arising from the temperature variations. This last term produces reversals in the temperature field such as are measured in practice.

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