Rab Nawaz

Scattering of a fluid-structure coupled wave at a flanged junction between two flexible waveguides

The scattering of a fluid-structure coupled wave at a flanged junction between two flexible waveguides is investigated. The flange is assumed to be rigid on one side and soft on the other; this enables a solution to be formulated using mode-matching. It is shown that both the choice of the edge conditions imposed on the plates at the junction and the choice of incident forcing significantly affect the transmission of energy along the duct. In particular, the edge conditions crucially affect the transmission of structure-borne vibration but have little effect on fluid-borne noise. Given the singular nature of the velocity field at the flange tip, particular attention is paid to the validity of the mode-matching method. It is demonstrated that the velocity field can be accurately reconstructed by incorporating the Lanczos filter into the truncated modal expansions. The mode-matching method is thus confirmed as an viable tool for this class of problem.

Numerical study of a thin film flow of fourth grade fluid

Purpose – The purpose of this paper is to study the thin film flow of a fourth grade fluid subject to slip conditions in order to understand its velocity profile. Design/methodology/approach – An exact expression for flow velocity is derived in terms of hyperbolic sine functions. The practical usage of the exact flow velocity is restrictive as it involves very complicated integrals. Therefore, an approximate solution is also derived using a Galerkin finite element method and numerical error analysis is performed. Findings – The behavior of fluid velocity with respect to various flow parameters is discussed. The results are not restrictive to small values of flow parameters unlike those obtained earlier using homotopy analysis method and homotopy perturbation method. Originality/value – An approximate solution based on finite element technique is derived.

Acoustic Scattering in Flexible Waveguide Involving Step Discontinuity

In this paper, the propagation and scattering of acoustic waves in a flexible wave-guide involving step discontinuity at an interface is considered. The emerging boundary value problem is non-Sturm-Liouville and is solved by employing a hybrid mode-matching technique. The physical scattering process and attenuation of duct modes versus frequency regime and change of height is studied. Moreover, the mode-matching solution is validated through a series of numerical experiments by testifying the power conservation identity and matching interface conditions.

Parametric Quantification of Low GWP Refrigerant for Thermosyphon Driven Solar Water Heating System

Abstract Modern lifestyle, growing industrial and economy thrive on energy which is getting expensive over time. Natural convection based systems are getting attraction for their promising heat transfer efficiency and zero energy utilization. Refrigerants having ozone depletion potential (ODP) and high Global Warming Potential (GWP) have been banned or under time bared permission under the Montreal (1987) and Kyoto (1997) protocols. To retrofit and modify existing cooling and heating systems, various natural and synthetic refrigerants are being investigated worldwide. We have devolved a Refrigerant Parametric Quantification (RPQ) method for the choice of optimal refrigerant for thermosyphon driven solar water heaters. A set of 29 refrigerants are simulated Using REFPROP under various temperature and pressure conditions. The optimal parameters of thermosyphon system are identified from governing equations, international environmental and safety protocols. The proposed RPQ method shows most appropriate refrigerant for given temperature range. In the second part, a glass evacuated tube collector is designed; fabricated and tested employing the best refrigerant emerged from a simulation study.

Beaconless multihop routing protocol for wireless sensor networks

Routing is a major challenge in sensor networks, due to constrained resources of energy, processing power, and memory. This proves that there is an urgent need to design energy efficient routing protocols for sensor networks for prolonging network lifetime. This paper presents a new beaconless multihop routing algorithm (BMR) for wireless sensor networks which is light weight, energy efficient and makes routing decisions based on residual energy of nodes. Additionally BMR is a non-positioned beaconless routing protocol which eliminates the overhead of control messages exchanged during network setup in cluster based routing protocols. The proposed protocol first divides the whole network into different zones using message passing techniques by Base Station (BS) and performs energy efficient location base routing without taking any assumption of location services. A simulation-based evaluation is conducted to compare the performance of BMR against energy efficient protocol with static clustering for wireless sensor networks (EEPSC). Simulation results show that BMR performs better than EEPSC in terms of network lifetime and energy consumption minimization.

A note on elastic noise source localization

The problem of reconstructing the spatial support of ambient noise sources from elastic wavefield boundary measurements using cross-correlation techniques is dealt with. It is demystified that the cross-correlation-based standard source localization functional in elastic media does not provide optimal refocusing due to different pressure and shear wave speeds. Then, a weighted functional is proposed to rectify the coupling artifacts. A numerical experiment is presented to substantiate the appositeness of the proposed functional.

Numerical study of two dimensional unsteady flow of an anomalous Maxwell fluid

Purpose – The purpose of this paper is to undertake an unsteady flow problem of an anomalous Maxwell fluid. The flow takes place between two side walls over a plate perpendicular to them and is driven by a sudden pressure force with constant gradient. Design/methodology/approach – A finite element method is invoked and is blended with a finite difference method for left Caputo fractional time derivatives in order to study the anomalous dynamics of the fluid. Findings – A numerical scheme for the constitutive equations of the prescribed flow in order to approximate the velocity field is designed. The graphical results to draw different physical conclusions on the flow problem are also presented. Originality/value – A rigorous mathematical exposition of the numerical scheme is provided and the results are valid for large values of the parameters.

Magnetohydrodynamic (MHD) flow analysis of second grade fluids in a porous medium with prescribed vorticity

Steady and unsteady flow of a second grade MHD fluid in a porous medium with Hall current effects is studied. Assuming an a priori known vorticity proportional to the stream function up to an additive uniform stream, exact solutions for velocity field are obtained corresponding to different choices of pertinent flow parameters. Graphical results are presented to depict the influence of pertinent flow parameters on the considered MHD flow.

An intermediate range solution to a diffraction problem with impedance conditions

An intermediate range solution for the problem of plane wave diffraction by a finite plate with impedance boundaries is presented. Initially, the problem is expressed in terms of two Wiener–Hopf equations with the help of Fourier transform and the boundary conditions in the transformed domain. The consideration of the intermediate range approximation in terms of source position renders integrals that are generally elusive to tackle because of the presence of branch points. These integrals are evaluated by invoking a modified stationary phase method, thereby a field valid over an intermediate range is calculated. The graphical analysis is preformed for various parameters of physical interest for both intermediate and far-field solutions.

Electromagnetic Time Reversal Algorithms and Source Localization in Lossy Dielectric Media

The problem of reconstructing the spatial support of an extended radiating electric current source density in a lossy dielectric medium from transient boundary measurements of the electric fields is studied. A time reversal algorithm is proposed to localize a source density from loss-less wave-held measurements. Further, in order to recover source densities in a lossy medium, we first build attenuation operators thereby relating loss-less waves with lossy ones. Then based on asymptotic expansions of attenuation operators with respect to attenuation parameter, we propose two time reversal strategies for localization. The losses in electromagnetic wave propagation are incorporated using the Debyes complex permittivity, which is well-adopted for low frequencies (radio and microwave) associated with polarization in dielectrics.