Papers by Keyword: Transition

Abstract: Combined free and forced convection in a square cavity filled with a viscous fluid characterized by a small Prandtl number is studied numerically. The left wall is moving with a constant velocity v and is maintained at a local cold temperature Tc, while the right wall is fixed and maintained at a local hot temperature Th (Tc <Th). The top and bottom walls of the cavity is assumed to be adiabatic. The governing Navier-Stokes, and energy equations along with appropriate boundary conditions are solved using the finite-volume method. The flow and temperature fields are presented by stream function and isotherms, respectively. The effects of important parameters such as Reynolds number, Prandtl number, and Grashof number on the transition from forced convection to mixed convection are investigated. Results indicate that increasing Reynolds number results to fluid acceleration and, thus, to flow transition. Results also show that Grashof and Prandtl's numbers influenced the conditions for the transition to the mixed convection regime.

Abstract: It is recognized that Change Management is a necessity in the current environment characterized by competitiveness and the desire for continuous innovation [3]. In order to answer these questions, the work begins with a secondary research of the different types of organizational change: change as development, change as transition, change as transformation, and then, by analyzing their particular characteristics, the risks associated with the process of change are identified the possible causes of possible implementation difficulties. Research results show that changing as a transition rarely involves adapting processes, existing tools, but rather replacing them with completely new ones (mergers, assignments, IT & C revolutions, etc.). One of the conclusions of this paper is that the success of a changing company depends not only on the way in which it is carried out, but also on the way it is maintained at the operational level during the change, so a complex management structure is needed. ensure the functionality of the company and supervise the change process.

Abstract: This paper presents the flight dynamics simulation and analysis of a tilt-rotor vertical takeoff and landing (VTOL) aircraft on transition phase, that is conversion from vertical or hover to horizontal or level flight and vice versa. The model of the aircraft is derived from simplified equations of motion comprising the forces and moments working on the aircraft in the airplane's longitudinal plane of motion. This study focuses on the problem of the airplane's dynamic response during conversion phase, which gives an understanding about the flight characteristics of the vehicle. The understanding about the flight dynamics characteristics is important for the control system design phase. Some simulation results are given to provide better visualization about the behaviour of the tilt-rotor. The simulation results show that both transition phases are quite stable, although an improved stability can give better manoeuver and attitude handling. Improvement on the simulation model is also required to provide more accurate and realistic dynamic response of the vehicle.

Abstract: The article deals with results of the implementation of the k-k_L-ω turbulence model for compressible transitional flow into OpenFOAM. This model was firstly proposed by Walters and Leylek [2] and utilizes the approach of the laminar kinetic energy in order to predict the transition between laminar and turbulent flows. The performance of the implemented model has been tested for the case of flow over a flat plate and the flow through VKI and SE 1050 turbine cascades. The properties of the implementation of the model for compressible flow simulations into OpenFOAM are discussed.

Abstract: In order to evaluate the performance of airfoils with computational fluid dynamics (CFD) tools, modelling of transitional region in the boundary layer is very critical. Currently, there are several classes of transition-based turbulence model which are based on different methods. Among these, the k-k_L- ω, which is a three equation turbulence model, is one of the prominent ones which is based on the concept of laminar kinetic energy. This model is phenomenological and has several advantageous features. Over the years, different researchers have attempted to modify the original version which was proposed by Walter and Cokljat in 2008 to enrich the modelling capability. In this article, a modified form of k-k_L-ω transitional turbulence model has been used with the help of OpenFOAM for an investigative CFD analysis of a NACA 4-digit airfoil at range of angles of attack.

Abstract: In this paper we have presented some of the major technical and economic challenges for companies that address mass customization as a new strategy. The need to approach this concept and the increasingly larger trend towards mass customization is due to the demand from individual clients of customized products. The importance of the interaction between customer and manufacturing companies that use or want to introduce mass customization as the new strategy brings the client in the middle of the action from the first stage of the process. Increased efficiency can be achieved when innovative methods and techniques are pursued and implemented. Some of the most important capabilities that companies must posses in order to have complete success in their transition towards mass customization are presented in this paper.

Abstract: IPv4 and IPv6 will coexist for a long time, due to ISPes’ inertia in the transition from IPv4 to IPv6. Domain Name System (DNS) is a very important functional unit in the Internet. This paper describres the hierarchy and operating process of IPv6 DNS, IPv6 DNS resolver, and presents the DNS transition from IPv4 to IPv6 in particular. We suggest two methods to implement DNS service during the transition period: DNS-Application Level Gateway (DNS-ALG) with Network Address Translation-Protocol Translation (NAT-PT), and dual stacks. And we also propose their respective operational principles. This paper is of valuable reference for network engineers to construct DNS in the transition phase.

Abstract: The needs to improve the efficiency of coolants undeniably become one of the concerns in cooling systems technologies nowadays. Nanofluid as coolant is invented and studied where it can provide better option for users due to augmentation in properties. This study provides experimental investigation on Titanium Oxide dispersed in water and ethylene glycol mixture under transition region with Reynolds number range of 2000 < Re <10000. Three volume concentrations are used which are 0.5 %, 1.0 % and 1.5 % for heat transfer experimental investigation under working temperature of 30 °C at constant heat flux of 600 W. The Nusselt number of the nanofluid increase with the increasing of Reynolds number at 1.5 % concentration, slightly higher than based fluid. The finding on the heat transfer coefficient shows enhancement of 2.1 % achieved by Titanium Oxide nanofluid at 1.5 % volume concentration. For 0.5 % and 1.0 % concentration, no enhancement of heat transfer achieved for the fluid flow under transition region at temperature of 30 °C.

Abstract: The paper presents a design of rectangular waveguide-SIW transition, which provides a broadband and low insertion loss performance. The broadband transition is realized by using double-rhombus antenna probe inserted into rectangular metal waveguide. The transition is simulated and measured at 9-20GHz. The measured results show that a good agreement with simulation and an insertion loss less than 2.8 dB and a return loss better than 10 dB are obtained at 10–18.5 GHz for a back-to-back structure.

Abstract: A novel compact Ultra-Wide Band (UWB) microstrip-slotline transition utilizing high impedance chip resistor is proposed and analyzed. The reactance introduced by the microstrip open end and slotline short end, which is the main limitation to the bandwidth in the traditional structures, is minimized in the design. The model is analyzed with the method of equivalent circuits and simulated by the commercial software HFSS. To test the performance of this transition a back-to-back structure is fabricated. The measurement results show that the bandwidth of 45 octaves can be obtained while the insert loss is better than 0.7dB within the band.