Impact of satellite observed microwave SST on the simulation of tropical cyclones

The impact of realistic representation of sea surface temperature (SST) on the numerical simulation of track and intensity of tropical cyclones formed over the north Indian Ocean is studied using the Weather Research and Forecast (WRF) model. We have selected two intense tropical cyclones formed over the Bay of Bengal for studying the SST impact. Two different sets of SSTs were used in this study: one from TRMM Microwave Imager (TMI) satellite and other is the weekly averaged Reynold's SST analysis from National Center for Environmental Prediction (NCEP). WRF simulations were conducted using the Reynold's and TMI SST as model boundary condition for the two cyclone cases selected. The TMI SST which has a better temporal and spatial resolution showed sharper gradient when compared to the Reynold's SST. The use of TMI SST improved the WRF cyclone intensity prediction when compared to that using Reynold's SST for both the cases studied. The improvements in intensity were mainly due to the improved prediction of surface latent and sensible heat fluxes. The use of TMI SST in place of Reynold's SST improved cyclone track prediction for Orissa super cyclone but slightly degraded track prediction for cyclone Mala. The present modeling study supports the well established notion that the horizontal SST gradient is one of the major driving forces for the intensification and movement of tropical cyclones over the Indian Ocean.

Doubly spectral stochastic finite element method (DSSFEM) for random field problems

Uncertainties in complex dynamic systems play an important role in the prediction of a dynamic response in the mid- and high-frequency ranges. For distributed parameter systems, parametric uncertainties can be represented by random fields leading to stochastic partial differential equations. Over the past two decades, the spectral stochastic finite-element method has been developed to discretize the random fields and solve such problems. On the other hand, for deterministic distributed parameter linear dynamic systems, the spectral finite-element method has been developed to efficiently solve the problem in the frequency domain. In spite of the fact that both approaches use spectral decomposition (one for the random fields and the other for the dynamic displacement fields), very little overlap between them has been reported in literature. In this paper, these two spectral techniques are unified with the aim that the unified approach would outperform any of the spectral methods considered on their own. An exponential autocorrelation function for the random fields, a frequency-dependent stochastic element stiffness, and mass matrices are derived for the axial and bending vibration of rods. Closed-form exact expressions are derived by using the Karhunen-Loève expansion. Numerical examples are given to illustrate the unified spectral approach.

Numerical modeling of the contaminant Transport through stratified soil

The transport processes of the dissolved chemicals in stratified or layered soils have been studied for several decades. In case of the solute transport through stratified layers, interface condition plays an important role in determining appropriate transport parameters. First‐ type and third‐ type interface conditions are generally used in the literature. A first‐type interface condition will result in a continuous concentration profile across the interface at the expense of solute mass balance. On the other hand, a discontinuity in concentration develops when a third‐ type interface condition is used. To overcome this problem, a combined first‐ and third‐ type condition at the interface has been widely employed which yields second‐ type condition. This results in a similar break‐through curve irrespective of the layering order, which is non‐physical. In this work, an interface condition is proposed which satisfies the mass balance implicitly and brings the distinction between the breakthrough curves for different layering sequence corroborating with the experimental observations. This is in disagreement with the earlier work by H. M. Selim and co‐workers but, well agreement with the hypothetical result by Bosma and van der Zee; and Van der Zee.

Stress-Strain Prediction of Jointed Rocks using Artificial Neural Networks

The applicability of Artificial Neural Networks for predicting the stress-strain response of jointed rocks at varied confining pressures, strength properties and joint properties (frequency, orientation and strength of joints) has been studied in the present paper. The database is formed from the triaxial compression tests on different jointed rocks with different confining pressures and different joint properties reported by various researchers. This input data covers a wide range of rock strengths, varying from very soft to very hard. The network was trained using a 3 layered network with feed forward back propagation algorithm. About 85% of the data was used for training and remaining15% for testing the predicting capabilities of the network. Results from the analyses were very encouraging and demonstrated that the neural network approach is efficient in capturing the complex stress-strain behaviour of jointed rocks. A single neural network is demonstrated to be capable of predicting the stress-strain response of different rocks, whose intact strength vary from 11.32 MPa to 123 MPa and spacing of joints vary from 10 cm to 100 cm for confining pressures ranging from 0 to 13.8 MPa.

Numerical Study Of Heat Transfer From Pin Fin Heat Sink Using Steady And Pulsated Impinging Jets

The work reported in this thesis is an attempt to enhance heat transfer in electronic devices with the use of impinging air jets on pin-finned heat sinks. The cooling per-formance of electronic devices has attracted increased attention owing to the demand of compact size, higher power densities and demands on system performance and re-liability. Although the technology of cooling has greatly advanced, the main cause of malfunction of the electronic devices remains overheating. The problem arises due to restriction of space and also due to high heat dissipation rates, which have increased from a fraction of a W/cm2to 100s of W /cm2. Although several researchers have at-tempted to address this at the design stage, unfortunately the speed of invention of cooling mechanism has not kept pace with the ever-increasing requirement of heat re- moval from electronic chips. As a result, efficient cooling of electronic chip remains a challenge in thermal engineering. Heat transfer can be enhanced by several ways like air cooling, liquid cooling, phase change cooling etc. However, in certain applications due to limitations on cost and weight, eg. air borne application, air cooling is imperative. The heat transfer can be increased by two ways. First, increasing the heat transfer coefficient (forced convec- tion), and second, increasing the surface area of heat transfer (finned heat sinks). From previous literature it was established that for a given volumetric air flow rate, jet im-pingement is the best option for enhancing heat transfer coefficient and for a given volume of heat sink material pin-finned heat sinks are the best option because of their high surface area to volume ratio. There are certain applications where very high jet velocities cannot be used because of limitations of noise and presence of delicate components. This process can further be improved by pulsating the jet. A steady jet often stabilizes the boundary layer on the surface to be cooled. Enhancement in the convective heat transfer can be achieved if the boundary layer is broken. Disruptions in the boundary layer can be caused by pulsating the impinging jet, i.e., making the jet unsteady. Besides, the pulsations lead to chaotic mixing, i.e., the fluid particles no more follow well defined streamlines but move unpredictably through the stagnation region. Thus the flow mimics turbulence at low Reynolds number. The pulsation should be done in such a way that the boundary layer can be disturbed periodically and yet adequate coolant is made available. So, that there is not much variation in temperature during one pulse cycle. From previous literature it was found that square waveform is most effective in enhancing heat transfer. In the present study the combined effect of pin-finned heat sink and impinging slot jet, both steady and unsteady, has been investigated for both laminar and turbulent flows. The effect of fin height and height of impingement has been studied. The jets have been pulsated in square waveform to study the effect of frequency and duty cycle. This thesis attempts to increase our understanding of the slot jet impingement on pin-finned heat sinks through numerical investigations. A systematic study is carried out using the finite-volume code FLUENT (Version 6.2) to solve the thermal and flow fields. The standard k-ε model for turbulence equations and two layer zonal model in wall function are used in the problem Pressure-velocity coupling is handled using the SIMPLE algorithm with a staggered grid. The parameters that affect the heat transfer coefficient are: height of the fins, total height of impingement, jet exit Reynolds number, frequency of the jet and duty cycle (percentage time the jet is flowing during one complete cycle of the pulse). From the studies carried out it was found that: a) beyond a certain height of the fin the rate of enhancement of heat transfer becomes very low with further increase in height, b) the heat transfer enhancement is much more sensitive to any changes at low Reynolds number than compared to high Reynolds number, c) for a given total height of impingement the use of fins and pulsated jet, increases the effective heat transfer coefficient by almost 200% for the same average Reynolds number, d) for all the cases it was observed that the optimum frequency of impingement is around 50 − 100 Hz and optimum duty cycle around 25-33.33%, e) in the case of turbulent jets the enhancement in heat transfer due to pulsations is very less compared to the enhancement in case of laminar jets.