Time-varying Temperature Distribution Research Articles

Numerical Assessment on Time-Varying Temperature Field of Bridge Tower under Solar Radiation

Bridge tower, time-varying temperature field, heat transfer analysis, finite element model. Abstract. Long span suspension bridges are subjected to daily, seasonal and yearly environmental thermal effects induced by solar radiation and ambient air temperature. This paper aims to investigate the temperature distribution of a tower of a long span suspension bridge. Two-dimensional heat transfer models are utilized to determine the time-dependent temperature distribution of the bridge tower of the bridge. The solar radiation model is utilized to examine the time-varying temperature distribution. Finite element models are constructed for the bridge tower to compute the temperature distribution. The numerical models can successfully predict the structural temperature field at different time. The methodology employed in the paper can be applied to other long-span bridges as well.

Thermal imaging technique to characterize laser light reflection from thermoplastics

Characterization of laser light reflection during the laser transmission welding (LTW)33Abbreviations: LTW—laser transmission welding, CB—carbon black, IR—infrared, NPFD—normalized power flux distribution of thermoplastics is especially important for applications in which non-zero laser incidence angles are used. At higher laser incidence angles, reflection increases and has the potential to burn surrounding features of the part to be welded. This study presents and validates a technique for laser reflection measurement. Reflected energy is absorbed by a black plastic plate (containing carbon black, which is the absorber of the reflected energy). The surface temperature of the plate is measured by an infrared (IR) camera. The distribution of reflected power required to generate this temperature profile is estimated using a simple heat transfer model. The technique was validated by irradiating the black plate by the laser directly, while observing the time-varying temperature distribution of the plate by the IR camera. In this case, good agreement was observed between the estimated total power and the actual laser input power. Good agreement also existed between the estimated power distribution and that determined experimentally via a knife edge based beam profiling technique. The thermal imaging technique was subsequently used to measure the magnitude and distribution of laser light reflection from unreinforced nylon 6.

Temperature Variation of Concrete-Steel Deck Plate under Solar Radiation

The analysis of time-varying temperature field of a composite concrete-steel deck plate under strong solar radiation is carried out in this study. By assuming the temperature distribution along the bridge longitudinal direction is basically constant, one typical segment of the deck plate is investigated. Two-dimensional heat transfer models are utilized to determine the time-dependent temperature distribution of deck plate, deck trough and deck pavement of the bridge. A modified solar radiation model is utilized to predict the variation of solar radiation in a whole day. A thermodynamic model is established and a transient heat transfer analysis is conducted to predict the time-varying temperature distribution of the deck plate at different time. The measured ambient temperature data are used as thermal boundary conditions during the numerical analysis. The made observations demonstrate that the simulated temperature variation of the deck plate based on the modified solar radiation model agrees well with measurement results, as compared with those obtained from the traditional solar radiation model..

Simulation on Temperature Distribution of Composite Bridge Deck Plate

The evaluation on time-varying temperature distribution of composite deck plates of long span bridge is carried out in this study through an integration of knowledge in material science and structural analysis. Two-dimensional heat transfer models are utilized to determine the time-dependent temperature distribution of deck plate, deck trough and deck pavement of the bridge. The solar radiation model is utilized to examine the time-varying temperature distribution. Comparison between the analytical results and the field measurement shows similar properties, in terms of temperature distribution within the deck segment. The made observations demonstrate that the simulated temperature variation of the deck plate based on the solar radiation model agrees well with measurement results.

Time-Domain Modelling: Combining ESM and a Finite-Difference Method for Thermoacoustic Devices

Thermoacoustic devices are today mainly simulated using frequency-domain methods. Contrary to frequency-domain methods, time-domain methods may include non-linear effects and time-varying boundary conditions. However, time-domain modelling of thermoacoustic devices is computationally expensive, due to large differences in geometric length scales and time scales. The primary aim of this paper has been to model thermoacoustic devices with computational efficiency by using two different methods. The acoustic field outside the stack, based on the assumption of plane waves, is modelled using the efficient Equivalent Source Method (ESM), whereas the complex acoustic field in the stack is modelled using a finite-difference model. In a previous paper of the authors, ESM and a finite-difference model have been combined to model acoustic wave propagation, though thermal effects and heat flow to the stack plate were excluded. In this paper, however, these effects are included. The performance of the model is studied and compared to linear thermoacoustic theory. The proposed model may provide a useful tool for studying time-varying acoustic fields and temperature distributions in thermoacoustic devices.

Interactive 3D visualization for wireless sensor networks

Wireless sensor networks open up a new realm of ubiquitous computing applications based on distributed large-scale data collection by embedded sensor nodes that are wirelessly connected and seamlessly integrated within the environment. 3D visualization of sensory data is a challenging issue, however, due to the large number of sensors used in typical deployments, continuous data streams, and constantly varying network topology. This paper describes a practical approach for interactive 3D visualization of wireless sensor network data. A regular 3D grid is reconstructed using scattered sensor data points and used to generate view-dependent 2D slices that are consequently rendered with commodity graphics hardware leading to smooth visualization over space and time. Furthermore, the use of efficient space partitioning data structures and the independent processing of sensor data points facilitates interactive rendering for large number of sensors while accommodating constantly changing network topology. The practical value of the proposed method is demonstrated and results obtained for visualizing time-varying temperature distributions in an urban area are presented.

Thermal stability analysis of high temperature superconducting magnet coils under overcurrent pulses

This paper presents some numerical simulation results of thermal behavior on the high temperature superconducting (HTS) magnet coils wounded by Bi2223/Ag multifilamentary tapes subjected to an overcurrent pulse using the finite element method (FEM). The analytical results show that the time-varying spatial temperature distribution of the HTS magnet coils under the condition of different overcurrent pulses has an important influence on its stability estimation, and the temperature dependence of minimum propagation current plays a key role in the stability analysis of the HTS magnet. Through the FEM analysis, the permitted duration time of 5-multiple overcurrent pulse has been obtained for the HTS magnet under the various operating conditions and cooling conditions. In this paper, an analytical method for determining the stability of the HTS magnet coils subjected to an overcurrent pulse has been proposed and a stability criterion has been presented. The critical current and minimum propagation current can be chosen as the restrictive condition of operating current in the HTS magnet coils subjected to an overcurrent pulse.

Development and Evaluation of a High-Resolution Turbine Pyrometer System

Optical pyrometers provide many advantages over intrusive measuring techniques in determining the spatial and time varying temperature distribution of fast rotating components in gas turbines. This paper describes the development and evaluation of a versatile high-resolution pyrometer system and its application to radial turbine rotor temperature mapping as has been done in a R&D project at the Technical University Berlin under funding from Siemens Power Generation (KWU). The development goal was a pyrometer system with a temporal resolution of 1 μs, a minimum field of view of 1 mm, and a measurement range from 600 to 1500°C. A prototype of the pyrometer system has been built and tested at the small gas turbine test facility of the Technical University Berlin. The system yielded excellent results with respect to measurement uncertainty, resolution, and reliability. Finally, measurement results obtained with the new system on a radial turbine rotor and on a heavy duty industrial gas turbine are compared with measurements conducted with a commercially available turbine pyrometer system.

In Vivo Results with a New Device for Ultrasonic Monitoring of Pig Skin Cryosurgery: The Echographic Cryoprobe

One of the main difficulties encountered in cryosurgery is the uncertainty in the extent and depth of the tissue effectively treated during the freezing process. The objective of this study was to evaluate in vivo ultrasonic control of skin cryosurgery using a new echographic cryoprobe. An echographic cryoprobe, developed specifically for dermatology applications, combines a high-frequency (20 MHz) miniature ultrasonic transducer and a N2O-driven closed cryoprobe. Knowledge of the ultrasound velocity of frozen skin is a prerequisite for monitoring the iceball formation kinetics. Therefore, in a first study, we estimated the ultrasound velocity of frozen skin specimens. In a second step, the operation of the echographic cryoprobe was assessed, under in vivo conditions similar to those used in human therapeutics, on normal skin of three female "Large-White" pigs under anesthesia. The mean value of ultrasound velocity of frozen skin obtained by pooling the data from all the skin specimens included in this study was 2865 +/- 170 m per s. The average rates of growth (10(-2) mm per s) of the iceballs were found to be 12.2 +/- 1.0 (pig 1), 9.0 +/- 1.0 (pig 2), and 8.4 +/- 0.9 (pig 3). The echographic cryoprobe had a built-in high-frequency ultrasonic transducer that served two functions. It enabled in vivo real-time monitoring of depth penetration of the iceball and it gave important feedback to the operator or to the console relating to the rate of growth of the iceball. Automatic (i.e., operator-independent) detection of the echo signal from the freezing front and calculation of the depth penetration of the iceball was possible.

An analytical model of the atmospheric entry of large meteors and its application to the Tunguska Event

The atmospheric entry of a meteor is quite complex, with the body losing kinetic energy both from atmospheric drag and from mass loss due to aerodynamic heating. Moreover, high pressures on the windward side of the body result in enormous compressive stresses which may exceed the yield strength of the material and cause rapid fragmentation of the meteor. While ablative mass loss is not important for extremely large objects, it must be accurately estimated to correctly predict the trajectories of objects that are several tens of meters in diameter. The current paper describes a computer model which performs calculations of shock layer conditions, accounting for the time varying temperature distribution, radiative cooling of the shocked gases, and blockage of surface heating by ablation products. Application of the model to the well‐known Tunguska Event indicates that the responsible bolide was probably a carbonaceous chondrite, although a stony asteroid or a cometary body cannot be conclusively ruled out.

Measurement of time varying temperature fields using visible imaging CCD cameras

A method for measuring time-varying surface temperature distributions using high frame rate visible imaging CCD cameras is described. The technique is based on an ad hoc model relating measured radiance to local surface temperature. This approach is based on the fairly non-restrictive assumptions that atmospheric scattering and absorption, and secondary emission and reflection are negligible. In order to assess performance, both concurrent and non-concurrent calibration and measurement, performed under dynamic thermal conditions, are examined. It is found that measurement accuracy is comparable to the theoretical accuracy predicted for infrared-based systems. In addition, performance tests indicate that in our experimental system, real-time calibration can be achieved while real-time whole-field temperature measurements require relatively course spatial resolution. The principal advantages of the proposed method are its simplicity and low cost. In addition, since independent temperature measurements are used for calibration, emissivity remains unspecified, so that a potentially significant source of error is eliminated.

A finite element model for radiofrequency ablation of the myocardium.

A finite element model was developed to simulate the temperature distributions produced by radiofrequency catheter ablation. This model incorporated blood, myocardium and torso tissues. The Laplace equation was solved to determine the steady-state electric field. The heat generation in the tissues was then computed from the power density distribution and the bioheat equation was solved to determine the time-varying temperature distribution, taking into account the convective energy exchange at the blood-myocardium and torso-air interfaces. This model was used to predict the lesion depth and to evaluate the effects of electrode location, changes of the electrical and thermal conductivities, and the electrode radius on the thermally induced damage to the myocardium. Temperature distributions induced by radiofrequency ablation were found to be: i) not very sensitive to the reference electrode location, ii) more sensitive to electrical conductivity changes than to thermal conductivity changes, and iii) larger electrodes allow a current distribution at higher level of power with reducing the chance of impedance rise.

The Incremental Strain Growth of an Elastic-Plastic Body Loaded in Excess of the Shakedown Limit

This paper considers the problem of a body composed of an elastic/perfectly plastic solid that is subjected to constant applied load P and a time-varying cyclic temperature distribution, characterized by a maximum thermoelastic stress σt. For sufficiently large P and σt, in excess of the shakedown limit, the body will begin to suffer incremental growth. A linearized theory is used to obtain a relationship between the increase in displacement Δu per cycle and the increase in ΔP and Δσt, above the shakedown limit. From the result, a simple lower bound is derived for Bree-type problems, which for kinematically determinate structures shows that for moderate thermal loading the displacement increment per cycle is four times the elastic displacement of the body if it were subjected only to the increase ΔP. From a practical point of view the analysis indicates that ratchet rates are always high, in the sense that only a small increase of load above shakedown will produce substantial ratcheting within relatively few cycles.

Transient deformation of liquid surfaces by laser-induced thermocapillarity

Heavy hydrocarbons are irradiated with a Gaussian laser beam. The time-varying temperature distribution induced in the fluid gives rise to a surface-tension distribution. The later gives rise in turn to an accompanying liquid flow and surface-height distribution. In this paper, the time-varying shape of the induced depression is calculated as a function of the power distribution in the laser beam and of the thermal and mechanical properties of the material. The intensity distribution in the laser beam reflected from the depression is also calculated. Good agreement is found with previous experimental results.

Temperature Variations in Deep Reservoirs

A mathematical model is developed to study the thermal behavior of freshwater impoundments. The model is formulated to simulate thermal stratification, turnover, hypolimnetic behavior, and epilimnetic behavior. Inputs to the model include meteorological data so that an energy budget relation is included. Output from the model includes the time-varying temperature distribution for the impoundment. A 315-day simulation is made of the thermal distributions in the TVA's Fontana Reservoir using the model. The results of the simulation show excellent comparison between predicted and measured quantities.