Modelling of turbulent flames with transported probability density function and rate-controlled constrained equilibrium methods

In this study, turbulent diffusion flames have been modelled using the Transported Probability Density Function (PDF) method and chemistry reduction with the Rate-Controlled Constrained Equilibrium (RCCE). RCCE is a systematic method of chemistry reduction which is employed to simulate the evolution of the chemical composition with a reduced number of species. It is based on the principle of chemical time-scale separation and is formulated in a generalised and systematic manner that allows a reduced mechanism to be derived given a set of constraint species. The transported scalar PDF method was coupled with RANS turbulence modelling and this PDF-RANS methodology was exploited to simulate several turbulent diffusion flames with detailed and RCCE-reduced chemistry. The phenomena of extinction and reignition, soot formation and thermal radiation in these flames are explored. Sandia Flames D, E and F have been simulated with both the detailed GRI-3.0 mechanism and RCCE reduced mechanisms. Scatter plots show that PDF methods with simple mixing models are able to reproduce different degrees of local extinction in Sandia piloted flames. The PDF-RCCE results are compared with PDF simulations with the detailed mechanism and with measurements of Sandia flames. The RCCE method predicted the three flames with the same level of accuracy of the detailed mechanism. The methodology has also been applied to sooting flames with radiative heat transfer. Semi-empirical soot model and Optically-thin radiation model have been combined with the PDF-RCCE method to compute these flames. Methane flames measured by Brooks and Moss [26] have been predicted using several RCCE mechanisms with good agreement with measurements. The propane flame with preheated air [162] has also been simulated with the PDF-RCCE methodology. Gaseous species profiles of the propane flame compare reasonably with measurements but soot and temperature predictions in this flame were weak and improvements are still needed.Open Acces

Absense of slow transients, and the effect of imperfect vertical alignment, in turbulent Rayleigh-Benard convection

We report experimental results for the influence of a tilt angle beta relative to gravity on turbulent Rayleigh-Benard convection of cylindrical samples. The measurements were made at Rayleigh numbers R up to 10^11 with two samples of height L equal to the diameter D (aspect ratio Gamma = D/L = 1). The fluid was water with a Prandtl number sigma = 4.38. In contrast to the experiences reported by Chilla et. al. (2004) for a similar sample but with Gamma = 0.5 (D = 0.5 and L = 1.0 m), we found no long relaxation times. For R = 9.4 times 10^10 we measured the Nusselt number N as a function of tilt angle beta and obtained a small beta dependence about a factor of 50 smaller than the result found by Chilla et. al. (2004) for their Gamma = 0.5 sample. We measured side-wall temperatures at eight equally spaced azimuthal locations on the horizontal mid-plane of the sample and used their cross-correlation functions to find the turn-over time of the large-scale circulation (LSC). The resulting Reynolds numbers R_e^cc were found to increase with beta. An important conclusion is that the increase of R_e^cc with beta of the LSC does not significantly influence the heat transport. Over the range 10^9 < R < 10^11 the enhancement of R_e^cc at constant beta due to the tilt could be described by a power law of R with an exponent of -1/6, consistent with a simple model that balances the additional buoyancy due to the tilt angle by the shear stress across the boundary layers. Even a small tilt angle dramatically suppressed the azimuthal meandering and the sudden reorientations characteristic of the LSC in a sample with beta = 0. The azimuthal mean of the temperature at the horizontal mid-plane within our resolution was independent of beta.Comment: 32 pages, 17 figures. Under consideration for publication in J. Fluid Mec

Path planning algorithm for a car like robot based on Coronoi Diagram Method

The purpose of this study is to develop an efficient offline path planning algorithm that is capable of finding optimal collision-free paths from a starting point to a goal point. The algorithm is based on Voronoi diagram method for the environment representation combined with Dijkstra’s algorithm to find the shortest path. Since Voronoi diagram path exhibits sharp corners and redundant turns, path tracking was applied considering the robot’s kinematic constraints. The results has shown that the Voronoi diagram path planning method recorded fast computational time as it provides simpler, faster and efficient path finding. The final path, after considering robot’s kinematic constraints, provides shorter path length and smoother compared to the original one. The final path can be tuned to the desired path by tuning the parameter setting; velocity, v and minimum turning radius, Rmin. In comparison with the Cell Decomposition method, it shows that Voronoi diagram has a faster computation time. This leads to the reduced cost in terms of time. The findings of this research have shown that Voronoi Diagram and Dijkstra’s Algorithm are a good combination in the path planning problem in terms of finding a safe and shortest path

Programmable logic controller based variable speed drives for educational trainer

The PLC based motor control system is the key area of concerned to relate PLC to the real industrial environment. However, there is no PLC based industrial motor control trainer available in the Automation lab of Politeknik Kota Kinabalu for the practical purposes. This has initiated the need to develop a research and product on the title of “Programmable Logic Controller Based Variable Speed Drives For Educational Trainer”. This research focused on VSD controlled by PLC conventional programming and Fuzzy Logic based PLC programming. A prototype “Two Conveyors Packaging System” has been constructed. This application is to synchronize two conveyors so that parts and packaging boxes are positioned correctly, regardless of the part and package box positions and the speed of conveyor. Several PLC programs were developed individually for sectionals of the prototype application; the input devices photoelectric part sensors (P004A), motor encoders E1 and E2 (P004B) and output device is VSD for box conveyor M2 (P004E). All these programs can work independently; subsequently to be combined to control the whole prototype application with additional PLC program on conventional basis, and fuzzy logic basis (P004C and P004D). These step by step programming methods contributed to the 10 experiments procedures to achieve the objective to construct the educational trainer procedures. As a conclusion, this research has achieved the objectives to construct the educational trainer procedures to implement PLC conventional and fuzzy logic based programming to control a motor driven by VSD, based on the concept of Prototype Two Conveyor Packaging System

To build trust with employee and gain their loyalty as the key to success

Employees are your most valuable assets. Organisations are highly dependent on employees' loyalty and expect their trust in the organization as a key ingredient factor. A successful company needs employees trust and who are loyal to what it stands for and to what it’s trying to achieve. Therefore, to ensure the sustainability and competitive advantage of an organization in facing the challenge of success, it is advised that employers examine several approaches that can be taken to win loyalty and build their trust and see the benefits and significant impact on the organization in the future. it is a step forward in creating organizational solutions and success

Conceptual design and multidisciplinary optimisation of power device for solar powered aircraft

Solar-powered aircraft is propelled by a photovoltaic cell that converts solar energy into electrical energy. The extra energy is stored in a rechargeable battery for later use when solar energy is not available. The performance of solar-powered aircraft is limited to solar radiation availability, low efficiency of the photovoltaic cell, and low energy density of the rechargeable battery. The research aims to improve the power device sizing, reduce the aircraft's mass, and improve the flight duration for sustainable flight operations for solar-powered aircraft (CLOUD 1). This was achieved using a multidisciplinary optimisation tool, a commercial package ModeFrontier software. Photovoltaic Geographic information system (PVGIS) software was used to obtain a solar radiation model for Malaysia. The model was used to develop both the energy balance and mission path for Malaysia to facilitate the availability and utilisation of solar energy for successful flight operations. Airfoil analysis was conducted. WE.3.55.9.3 airfoil was the best-chosen airfoil used for the wing design, while the empennage design, NACA 0008, was the most suitable. Hence, the latter was used for horizontal and vertical tail design with XFLR5 v6 software's aid. A novel methodology for the power device sizing was developed on MS Excel with 435.48Wh, 540.96Wh, 32, and 70 as the total required electrical energy, available solar energy, number of solar cells required, and the number of batteries required, respectively. The optimisation strategy embraced ModeFrontier software with the goal set to; minimise total electrical energy required, minimise the total mass, and maximise the available solar energy. The optimisation results show that available solar energy was 283.56Wh, the total electrical power required was 228.32Wh, the number of solar cells was 16, and the number of batteries was 36. The total mass of the aircraft was 2.05 Kg, respectively. The optimisation results achieved 53%, 51%, and 26% reductions in the number of solar cells, the number of batteries, and the aircraft's mass. Also, the flight duration was improved by 33%. The optimal configuration was used to design the solar-powered aircraft (CLOUD I)

The SCC and the SICSA multi-core challenge

Two phases of the SICSA Multi-core Challenge have gone past. The first challenge was to produce concordances of books for sequences of words up to length N; and the second to simulate the motion of N celestial bodies under gravity. We took both challenges on the SCC, using C and the Linux Shell. This paper is an account of the experiences gained. It also gives a shorter account of the performance of other systems on the same set of problems, as they provide benchmarks against which the SCC performance can be compared with

The Rate-Controlled Constrained-Equilibrium Approach to Far-From-Local-Equilibrium Thermodynamics

The Rate-Controlled Constrained-Equilibrium (RCCE) method for the description of the time-dependent behavior of dynamical systems in non-equilibrium states is a general, effective, physically based method for model order reduction that was originally developed in the framework of thermodynamics and chemical kinetics. A generalized mathematical formulation is presented here that allows including nonlinear constraints in non-local equilibrium systems characterized by the existence of a non-increasing Lyapunov functional under the system’s internal dynamics. The generalized formulation of RCCE enables to clarify the essentials of the method and the built-in general feature of thermodynamic consistency in the chemical kinetics context. In this paper, we work out the details of the method in a generalized mathematical-physics framework, but for definiteness we detail its well-known implementation in the traditional chemical kinetics framework. We detail proofs and spell out explicit functional dependences so as to bring out and clarify each underlying assumption of the method. In the standard context of chemical kinetics of ideal gas mixtures, we discuss the relations between the validity of the detailed balance condition off-equilibrium and the thermodynamic consistency of the method. We also discuss two examples of RCCE gas-phase combustion calculations to emphasize the constraint-dependent performance of the RCCE method.Fondazione Cariplo (grant 2008-2290)United States. Army Research Office (grant number W911NF-08-1-0444

Comparison Between RCCE and Shock Tube Ignition Delay Times at Low Temperatures

The rate-controlled constrained-equilibrium (RCCE) method is a reduction technique based on local maximization of entropy or minimization of a relevant free energy at any time during the nonequilibrium evolution of the system subject to a set of kinetic constraints. In this paper, RCCE has been used to predict ignition delay times of low temperatures methane/air mixtures in shock tube. A new thermodynamic model along with RCCE kinetics has been developed to model thermodynamic states of the mixture in the shock tube. Results are in excellent agreement with experimental measurements