Ayoub Shirvani

Optimization of Partially Textured Parallel Thrust Bearings with Square-Shaped Micro-Dimples

In this study we attempt to find the optimum geometrical parameters of square-shaped micro-dimples imposed on parallel flat bearing surfaces, which give the best tribological performance, including the load capacity and the friction coefficient. An analytical solution of the Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of the number of dimples as well as the dimple length, and the height ratios for a constant dimpled length, it is used to get the optimum value of the parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remains nearly constant.

Optimised textured surfaces with application in piston ring/cylinder liner contact

The application of textured surfaces in tribology has recently gained a huge momentum. In this chapter, a systematic approach to investigate the maximum outcomes from employing such surfaces is introduced with an insight into their application in internal combustion engines. A combination of various affecting parameters on the tribological performance of such surfaces is studied and the optimum results are introduced. The effect of employing such optimised textures in enhancing the lubrication condition in piston ring/cylinder liner contact is also studied.

Hexagonal honeycomb cell optimisation by way of meta-model techniques

This paper presents the result of an optimisation study by linear, quadratic, Kriging and radial basis meta-models in order to augment the crashworthiness characteristic of cellular structures. Thin-walled cellular structures (honeycomb) have the ability to absorb impact energy during crashing, thus it is important to enhance the crushing efficiency and optimise the structural reliability. The optimisation carried out in this study is aimed at maximising the energy absorption characteristics using meta-models while considering some limitation on the maximum force as a constraint. Achieving these characteristics is an important factor in crashworthiness analysis, which minimises the damage in dynamic performance. The objective of using various meta-models is to qualify the meta-model in crashworthiness analysis using different point selection schemes and different number of points. The optimisation is performed in two stages; through experimental design methods in which a set of sampling points is selected from design space and polynomial fitting in order to optimise the objective. It is concluded that D-optimal best suits response surface method for model approximation. Kriging performed best by space filling and the best point selection scheme for radial basis surrogate is latin hypercube design. The results show that for optimising the crashworthiness characteristics of honeycomb, Kriging and quadratic response surface (RS) are best, in terms of accuracy and robustness point of view and the radial basis neural network would be the second best. During this optimisation, the RS was combined with detailed geometrically simplified finite element model of honeycomb cell using ANSYS/LS-DYNA, LS-DYNA and LS-opt packages. Approximated functions combined with the finite element analysis were an effective tool to optimise highly non-linear impact problems. This has led to the development of validated algorithm that enabled the development of the optimised solutions.

Using WPKI for security of web transaction

Today, a web transaction is typically protected by using SSL/TLS. SSL/TLS without compulsion for a clients public key certificate, which is the typical usage, is not able to fulfill the security requirements for web transactions. The main remaining threats for this use are client authentication and non-repudiation. This paper presents a scheme to address SSL/TLS security holes, when it is used for web transaction security. The focus is only on transaction that is carried out by using credit/debit cards. The scheme uses wireless public key infrastructure (WPKI) in the clients mobile phone to generate a digital signature for the client. Thus we obtain client authentication and nonrepudiation. At the same time, no overhead is imposed on the client, there is no need for any change to the actual system when performing the transaction, and no connection, by using the mobile phone, is required to perform the transaction.

A web transaction security scheme based on disposable credit card numbers

Today, an e-commerce transaction is performed by sending the clients credit card details over a SSL/TLS connection. This form of transaction raises many security threats. The most important one is the client authentication. Because the client normally does not have a public key certificate, the clients authentication is achieved only by the credit card details. In addition, these details are stored unencrypted in the merchants database. A Disposable Credit Card Number (DCCN) is a technique to overcome these security threats. This paper presents a scheme for off-line generation of the DCCNs. The scheme uses a pre-shared secret key between the issuer and the client to generate Hashed Message Authentication Code for some selected data from the transaction. The scheme is secure and adds minimum overhead on the issuer and client. Furthermore, the generated DCCN has all the features of classical credit card details.

Comparative study of honeycomb optimization using Kriging and radial basis function

Structural optimization for crashworthiness criteria is of particular significance especially at early stage of design. The comparative study of Kriging and radial basis function network (RBFN) was performed in order to improve the crashworthiness effects of honeycomb. Improving the crashworthiness characteristic of honeycomb was achieved using LS-OPT® and domain reduction strategy. This optimization is performed on the basis of validated numerical simulation to establish the approximated model to illustrate the relationship between the responses and design variables. The results showed that Kriging meta-model is excelled in accuracy, robustness and efficiency compared to radial basis function (RBF) and crashworthiness characteristic of honeycomb is improved by 4%.

An Investigation into Air-Sand-Water Three-Phase Flow through the Sandblasting Nozzle

The numerical analysis of air-sand-water three-phase turbulent flow through converging-diverging nozzle is investigated for employing on sandblasting systems. For this purpose-dispersed flow of air-sand-water by various airs inlet pressures and different mass flow rates of sand particles and water droplets were considered. Two-way turbulence coupling between particles/droplets and airflow as well as interference between the incident streams of particles and rebounded from the wall were applied in the numerical model. In addition, the shock wave, which is produced in supersonic flow at diverging part of nozzle, was considered. In this study the Realizable k-e and Discrete Phase models were utilized for simulating of multi-phase turbulent flow through the converging-diverging nozzle. As review of literature indicates there is not any experimental or analytical data on three-phase flow through the nozzle, consequently for validation of model, the same turbulent and multi-phase models were utilized on air-wat...

Design Attributes for Geometry Optimization Process of Thin Walled Honeycomb Structures

Thin walled cellular structures have the ability to absorb impact energy during crashing thus it is important to enhance the crashing efficiency and optimise the structural reliability. This paper discusses the honeycomb cell configuration optimization procedure. For the design optimization, the response surface method (RSM) is used to formulate the complex design where the energy absorption (EA) representing the structure’s ability of absorbing energy was selected as objective, the Y split side parting length w1 , w2 , and thickness T1 are defined as three design variables, and the maximum crushing force (Max.F) occurs as constraint. During this distinctive optimization, the (RSM) was combined with detailed geometrically simplified finite element (FE) model using ANSYS/LS-DYNA (pre-processor), LS-DYNA (solver) and LS-Opt (optimiser). RSM combined with (FE)model without user intervention, was the effective tool to optimize non-linear impacted cellular structures. Optimal design achieved through LS-OPT is compared to the validated results for accuracy and effectiveness.Copyright

Enhancing the security and efficiency of 3-d secure

Security is a major concern for all involved in E-Commerce and particularly in the case of online transactions using debit/credit card. Following the failure of Secure Electronic Transaction (SET), 3-D Secure is an emerging industry standard for online transaction security. Although 3-D Secure is a well designed protocol, it is still prone to some security problems and excessive numbers of messages which could reduce the speed of transaction. This paper uses a new cryptographic technique based on password only authentication and key exchange to present a new vision for 3-D Secure. The new vision covers the security problems and reduces the number of messages for 3-D Secure. Moreover, the new vision has the development ability to simulate SSL/TLS in its simplicity and at the same time abolishes SSL/TLS security glitches. This simplicity and security are the necessary factors for online transaction protocol to be the future standard.

Optimization of Partially Textured Parallel Thrust Bearings With Square-Shaped Micro-Dimples

In this study we attempt to find the optimum geometrical parameters of square-shape micro-dimples imposed on parallel flat bearing surfaces which give the best tribological performance, including load capacity and friction coefficient. An analytical solution of Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of number of dimples as well as dimple length and height ratios for a constant dimpled length, it is tended to get the optimum value of parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remain nearly constant.