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A finite element method based on the Eulerian velocity correction method has been used to analyse the laminar natural convection in an annular cavity. Unsteady, incompressible, axisymmetric Navier‐Stokes equations have been made use of. Different radius ratios of the annular cavity have been considered to investigate the effect of the radius of curvature on the heat transfer coefficient.

With the current COVID-19 outbreak, the majority of the higher educational institutes (HEI) are conducting online examinations to assess their students, where both teachers and students are facing various constraints. Under these circumstances, it is very important to understand the perspectives of teachers and students towards online examinations in higher education institutions and the factors affecting their perspectives.

This study has been conducted with the mentioned objective through online survey responses and rigorous statistical analysis of the data. The data analysis has been performed and presented using self-explanatory bar graphs, partial least squares structural equation modeling (PLS-SEM) and sentiment analysis.

While the students responded diversely for items in one of the constructs: scope for malpractice, the teachers agreed with the items, indicating that the online exams are not sufficiently effective in dealing with cheating and malpractice. Few more issues related to Internet connections, short time duration for uploading answer scripts are identified as problems and need attention while framing the rules to conduct the online examinations in future.

A new questionnaire was drafted to measure the effect of different constructs. An attempt is made to understand the perspectives of both the teachers and the students towards online examinations with respect to each of these considered constructs with a rigorous statistical analysis.

This paper aims to numerically analyse natural convection of yield stress fluids in rectangular cross-sectional cylindrical annular enclosures. The laminar steady-state simulations have been conducted for a range of different values of normalised internal radius (r_i/L 1/8 to 16, where L is the difference between outer and inner radii); aspect ratio (AR = H/L from 1/8 to 8 where H is the enclosure height); and nominal Rayleigh number (Ra from 10³ to 10⁶) for a single representative value of Prandtl number (Pr is 500).

The Bingham model has been used to mimic the yield stress fluid motion, and numerical simulations have been conducted for both constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions for the vertical side walls. The conservation equations of mass, momentum and energy have been solved in a coupled manner using the finite volume method where a second-order central differencing scheme is used for the diffusive terms and a second-order up-wind scheme is used for the convective terms. The well-known semi-implicit method for pressure-linked equations algorithm is used for the coupling of the pressure and velocity.

It is found that the mean Nusselt number based on the inner periphery Nu¯_i increases (decreases) with an increase in Ra (Bn) due to augmented buoyancy (viscous) forces irrespective of the boundary condition. The ratio of convective to diffusive thermal transport increases with increasing r_i/L for both Newtonian (i.e. Bn = 0) and Bingham fluids regardless of the boundary condition. Moreover, the mean Nusselt number Nu¯_i normalised by the corresponding Nusselt number due to pure conductive transport (i.e. Nu¯_i/(Nu¯_i)_cond) shows a non-monotonic trend with increasing AR in the CWT configuration for a given set of values of Ra, Pr, L_i for both Newtonian (i.e. Bn = 0) and Bingham fluids, whereas Nu¯_i/(Nu¯_i)_cond increases monotonically with increasing AR in the CWHF configuration. The influences of convective thermal transport strengthen while thermal diffusive transport weakens with increasing AR, and these competing effects are responsible for the non-monotonic Nu¯_i/(Nu¯_i)_cond variation with AR in the CWT configuration.

Detailed scaling analysis is utilised to explain the observed influences of Ra, BN, r_i/L and AR, which along with the simulation data has been used to propose correlations for Nu¯_i.

Presents a numerical study on heat transfer by natural convection in porous media in vertical enclosures with side wall heating. The model for porous media includes inertia terms and also the Brinkman extension in addition to the Darcy resistance term. A semi‐implicit finite element scheme based on operator splitting method is adopted for solving the time‐dependent system of equations. The first half of the investigations is confined to the low permeability regime where Darcy law holds good. Presents the results for annular and rectangular cavities and proposes correlations for two types of boundary conditions, namely constant wall temperature case and uniform wall heat flux case. In the second half of the investigations, the scheme is applied in a high permeability regime, where the validity of Darcy law becomes questionable. Employs plane rectangular cavities with the two types of boundary conditions mentioned earlier. Highlights the influence of Rayleigh number (Ra) and Darcy number (Da) as separate parameters and proposes correlations for a square cavity for the first time in terms of Ra and Da as separate parameters. Discusses a qualitative study of the effect of aspect ratio on heat transfer as the permeability changes.

Modelling accurately the transient behaviour of natural convection flow in enclosures been a challenging task because of a variety of numerical errors which have limited achieving the higher order temporal accuracy. A fourth-order accurate finite difference method in both space and time is proposed to overcome these numerical errors and accurately model the transient behaviour of natural convection flow in enclosures using vorticity–streamfunction formulation.

Fourth-order wide stencil formula with appropriate one-sided difference extrapolation technique near the boundary is used for spatial discretisation, and classical fourth-order Runge–Kutta scheme is applied for transient term discretisation. The proposed method is applied on two transient case studies, i.e. convection–diffusion of a Gaussian Pulse and Taylor Vortex flow having analytical solution.

Error magnitude comparison and rate of convergence analysis of the proposed method with these analytical solutions establish fourth-order accuracy and prove the ability of the proposed method to truly capture the transient behaviour of incompressible flow. Also, to test the transient natural convection flow behaviour, the algorithm is tested on differentially heated square cavity at high Rayleigh number in the range of 10³-10⁸, followed by studying the transient periodic behaviour in a differentially heated vertical cavity of aspect ratio 8:1. An excellent comparison is obtained with standard benchmark results.

The developed method is applied on 2D enclosures; however, the present methodology can be extended to 3D enclosures using velocity–vorticity formulations which shall be explored in future.

The proposed methodology to achieve fourth-order accurate transient simulation of natural convection flows is novel, to the best of the authors’ knowledge. Stable fourth-order vorticity boundary conditions are derived for boundary and external boundary regions. The selected case studies for comparison demonstrate not only the fourth-order accuracy but also the considerable reduction in error magnitude by increasing the temporal accuracy. Also, this study provides novel benchmark results at five different locations within the differentially heated vertical cavity of aspect ratio 8:1 for future comparison studies.

The transient natural convective flow and heat transfer in a combined vertical and horizontal enclosure have been studied. The Galerkin’s finite element method coupled with Eulerian velocity correction scheme for pressure prediction has been employed. A detailed parametric study has been undertaken for evaluating the effects of Rayleigh number (Ra), width ratio (WR), and prescribed boundary conditions. The results indicate that the flow and isothermal patterns are strongly dependent on Ra and WR. Comparison with the results of vertical and horizontal enclosures indicates that the flow and heat transfer phenomena inside complex shaped cavities may be approximated in terms of the processes within vertical or horizontal sub‐domains. This appears to be reasonably valid if opposite walls of the enclosure are parallel. It is also observed that for certain types of boundary conditions, steady solutions do not exist at high Rayleigh numbers.

Inferences concerning analysis, explanation, prediction, problem‐solving, policy formulation and decision‐making are systematically derived by means of a social cybernetic methodology. The basis of the methodology lies in the construction of a multi‐feedback loop model of the social phenomenon/situation investigated. Salient variables of the system are then identified as those located at the intersection of several feedback cycles. They represent analogs of Ashby's “essential variables”. Their measurement in terms of a scale of “regulatedness” or viability (λ), permits an estimation of time‐varying states of the system's “health” and defines the specific goals of a problem solution. The λ ‐ equivalence of salient variables in terms of Wiener's Principle of Entrainment of Frequencies, yields verifiable predictive inferences. Their hierarchic disaggregation generates a “morphological map” of the problem/phenomenon. This map shows the micro‐level requirements of policies and/or problem‐solving. Maximisation of the viability of decision alternatives provides a logically simple approach to multi‐criteria/attribute decision‐making.

While multinational companies develop meta-level policies to address grand sustainability challenges and CEOs are increasingly showing their social activism, the hard work of concretely defending communities’ rights and the environment from business exploitation is often left to powerless individuals, known as human rights defenders (here defenders), who face severe risks for their advocacy. According to some statistics, between 2015 and 2022, defenders worldwide have been subject to over 4,000 attacks, including killings, tortures, and intimidation. In this chapter, the authors discuss the relevance of defenders to the promotion of the sustainable development goal (SDG) agenda and develop a conceptual model to predict CEOs’ reactions to defenders.