Search results

Design sensitivities of plates and shells under transient dynamic loads with constraints on displacements and stresses are likely to be highly erroneous if proper care is not taken in selecting appropriate finite element mesh and time step size to be used in the analysis. An accurate value of design derivative is assured if an optimal mesh coupled with a reasonably fine time step size is used. The optimal mesh can be obtained iteratively and a number of examples are solved to demonstrate the importance of controlling discretization errors in space and time.

The problem of structural optimization of trusses subject to stress and frequency constraints is considered from a practical viewpoint. Assuming that the choice of members has to be from a discrete set of available sections, the solution is attempted using a mathematical programming approach and an approximate two‐step procedure involving a continuous variable optimization followed by a discrete programming algorithm. The latter approach is highly promising for problems involving stress and frequency constraints. Detailed results are presented using several benchmark problems.

This paper aims to introduce the quasi impedance source inverter (qZSI)-based static compensator (STATCOM), which is incorporated into the hybrid distributed power generation system for enhancement of power quality. The distributed power generation system includes the photovoltaic (PV), wind energy conversion system (WECS) and battery energy storage system.

The WECS is used by the self-excited induction generator (SEIG) and the flywheel energy storage system (FESS). To regulate its terminal voltage and frequency, the SEIG requires adjustable volt-ampere reactive (VAR). A combination of a STATCOM and a fixed condenser bank usually serves to satisfy the VAR demand. The maximum correntropy criterion-based adaptive filter technique (AFT) is proposed to control the qZSI-STATCOM and to guarantee that the voltage at the SEIG terminal is harmonic-free while providing non-linear three-phase and single-phase loads.

The coordinated operation of the suggested voltage control and flywheel control systems ensures that load voltage and frequency are retained in their respective values at very low harmonic distortions regardless of wind speed and load variation. The simulation and experimental studies are carried out under different load conditions to validate the efficiencies of the PV-assisted STATCOM.

To improve system stability and minimize total costs, extra load current sensors can also be avoided. This paper proposes to control the SEIG terminal voltage and harmonic elimination in the standalone WECS systems using maximum correntropy criterion-based AFT with a fuzzy logic controller.

The structural design problem can be viewed as an iterative design loop with each iteration involving two stages for topology and shape designs with genetic algorithm (GA) as the optimization tool for both.

The topology optimization problem, which is ill posed, is regularized using a constraint on perimeter and solved using GA. The problem is formulated as one of compliance minimization subject to volume constraint for the single loading case. A dual formulation of this has been used for the multiple loading cases resulting in as many behavioral constraints as there are loading cases. The tentative topology given by the topology optimization module is taken and the domain boundary is approximated using straight lines, B‐splines and cubic spline curves and design variables are selected among the boundary defining points. Optimum boundary shape of the problem has been obtained using GA in two different ways: without stress constraints; and with stress constraints.

The proposed two stage strategy has been tested on benchmark structural optimization problems and its performance is found to be extremely good.

The strategy appears to be eminently suitable for implementation in a general purpose FE software as an add‐on module for structural design optimization.

It has been observed that the integrated topology and shape design method is robust and easy to implement in comparison with other techniques. The computing time requirements for the GA does not appear daunting in the present scenario of high performance parallel computing and improved GA techniques.

This paper focuses attention on a three field coupled problem consisting of two cylindrical shells submerged in an acoustic medium. Method of partitioning is used successfully to partition the three fields. It is shown that the two cylinders are coupled by three‐dimensional flow field and bending mode is important. The paper ends with concluding remarks for extending this method for safety analysis of submerged tubes to include non‐linear fluid/structure behaviour.

The problem of optimal design of pressure vessel heads to maximize limit load behaviour is presented. Incremental elasto‐plastic analysis is used and a formulation based on the finite element method is presented whereby an approximate design model is generated which can be optimized via sequential programming. Results are presented for torispherical head shapes and tables are provided in order to evaluate the influence of different geometrical forms on limiting pressure loads. The method is generally applicable and can be applied to the design of components which are required to exhibit limited plastification under increasing load.

The survey of Sub-Saharan countries shows that after nearly two decades of stagnation, growth is reviving and is likely to receive additional momentum with the pursuit and judicious implementation of further fiscal adjustment efforts. The impact of economic stagnation on the financial management systems is evident in that they continue to be under severe strain despite a series of efforts aimed at their improvement. Lack of accountability and chronically ineffective control of expenditures are two of the major problem areas that need to be addressed. Among other areas that need to be addressed on a priority basis are the revamping of budgetary processes, including the development of a macroeconomic framework and forging more enduring links between planning and budgeting and improved management of foreign aid.

Contact problems are among the most difficult ones in mechanics. Due to its practical importance, the problem has been receiving extensive research work over the years. The finite element method has been widely used to solve contact problems with various grades of complexity. Great progress has been made on both theoretical studies and engineering applications. This paper reviews some of the main developments in contact theories and finite element solution techniques for static contact problems. Classical and variational formulations of the problem are first given and then finite element solution techniques are reviewed. Available constraint methods, friction laws and contact searching algorithms are also briefly described. At the end of the paper, a bibliography is included, listing about seven hundred papers which are related to static contact problems and have been published in various journals and conference proceedings from 1976.

The purpose of this paper is to investigate plasma treatment for Tencel microfibre fabrics for possible improvement in various functional properties.

The plasma treated and untreated fabrics were dyed using reactive dyes and evaluated for comfort properties such as wicking, water vapour permeability and air permeability.

The various comfort properties of plasma treated and an untreated Tencel microfibre fabric have been studied. The wicking results showed a significant reduction in wicking time for plasma treated fabrics compared to untreated fabrics. The test results for water vapour permeability show no significant difference between plasma treated and untreated fabrics. The plasma treated samples show higher air permeability than untreated samples. In the wetting test, it is clearly seen that the plasma treated samples absorbed the water at a faster rate.

This research investigates plasma treatment for Tencel microfibre fabrics for possible improvement in various functional properties.

The information security policy document of an organization needs to be translated into controls and procedures at the implementation level. The technical and business personnel in‐charge of implementing the controls and procedures need to consider a large number of security‐related statements from a heterogeneous pool of security documentation and decide on the implementation plan. The purpose of this paper is to propose an approach to analyze a set of security statements to establish an implicit hierarchy and relative importance among them.

A set of statements relevant to e‐mail service security is chosen from the classified documentation of an IT firm. The authors contacted the technical person who was the owner of this service to obtain a one‐on‐one comparison between the policies. These policies and their inter‐relationships are represented as a graph. Centrality measures based on the in and out degrees of a node are used to calculate the relative importance of a policy. The authors present an improved approach based on DEMATEL, which considers the level of influence of one policy on another.

Security statements fall into different categories based on their relative intensity and nature. They could be of high importance or low on one axis and of driving or receiving nature on the other. The driver policies are the action items that could be implemented to satisfy a large number of other security requirements. The policies that are predominantly receiver in nature, for their fulfillment, need many other requirements to be satisfied.

The intense driver policies are the ones to be considered for immediate implementation so as to achieve maximum benefits. If such an action item cannot be implemented at the level of consideration, it needs to be communicated to the appropriate level where it could be addressed effectively. An orphaned policy statement can indicate to a high‐level requirement left without any action plan or an unnecessary control. Establishing clear linkages between the implemented controls and the organization's security policy document could be very effective in convincing the employees to adhere to security practices.

Analyzing a set of informal security statements to identify the linkages between them is a novel idea. While other works establish the need for translating the security policy to lower levels of implementation, the authors propose an approach to identify the existence or absence of an effective translation. The graph representation with associated centrality measures, and the application of DEMATEL technique to deduce the nature and intensity of security statements are not yet found in literature.