Defeaturing CAD models using a geometry-based size field and facet-based reduction operators

We propose a method to automatically defeature a CAD model by detecting irrelevant features using a geometry-based size field and a method to remove the irrelevant features via facet-based operations on a discrete representation. A discrete B-Rep model is first created by obtaining a faceted representation of the CAD entities. The candidate facet entities are then marked for reduction using a geometry-based size field. This is accomplished by estimating local mesh sizes based on geometric criteria. If the field value at a facet entity goes below a user-specified threshold value then it is identified as an irrelevant feature and is marked for reduction. The reduction of marked facet entities is performed using various facet operators. Care is taken to retain a valid geometry and topology of the discrete model throughout the procedure. The original model is not altered as the defeaturing is performed on a separate discrete model. Associativity between the entities of the discrete model and that of original CAD model is maintained in order to decode the attributes and boundary conditions applied on the original CAD entities onto the mesh via the entities of the discrete model. Example models are presented to illustrate the effectiveness of the proposed approach.     

Performance analysis of a generalised radiative heat engine based on new maximum efficient power density approach

Efficient power density (EPD), defined as the ratio of efficient power to the maximum volume of working fluid, is taken as the objective for performance analysis and optimisation of an internally and externally irreversible radiative Carnot heat engine model from the viewpoint of finite-time thermodynamics or entropy generation minimisation. Maximising the value of EPD gives maximum efficient power density (MEPD). Results obtained are compared with those obtained using maximum efficient power (MEP) criteria, maximum power density (MPD) criteria and maximum power (MP) criteria. The results showed that the engine design at MEPD conditions has an advantage of smaller size and is more efficient than those designed at MP, MPD and MEP conditions.     

Low concentration ethanol sensor based on graphene/ZnO nanowires

Metal-oxide based gas sensors are widely used as the gas sensing elements in industrial and residential areas. Many efforts have been made to increase sensitivity and reduce the working temperature of metal-oxide based gas sensors. In this paper, ZnO nanowires (NWs) were successfully grown on graphene (Gr) nanosheets by the hydrothermal method. The synthesized Gr/ZnO NWs nanocomposite were investigated as the sensing material. Not only is the sensor response much higher, it also works in a lower working temperature toward a low concentration of ethanol in comparison with pure ZnO NWs. The optimum working temperature is reduced from 200 °C in pure ZnO NWs to 125 in Gr/ZnO NWs sensor. The maximum response of the Gr/ZnO NWs sensor is 26, which is approximately enhanced twice as much as the pure ZnO NWs sensor. The lower limit of detection (LLOD) of the proposed sensor is as low as 1 ppm ethanol vapor. The sensor was shown a high response, good selectivity, fast response toward ethanol vapor, excellent repeatability, and low sensitivity toward a high relative humidity, as well as remarkable long-term stability.     

Performance evaluation of a MPPT controller with model predictive control for a photovoltaic system

ABSTRACT

Efficiency has been a major factor in the growth of photovoltaic (PV) systems. Different control techniques have been explored to extract maximum power from PV systems under varying environmental conditions. This paper evaluates the performance of a new improved control technique known as model predictive control (MPC) in power extraction from PV systems. Exploiting the ability of MPC to predict future state of controlled variables, MPC has been implemented for tacking of maximum power point (MPP) of a PV system. Application of MPC for maximum power point tracking (MPPT) has been found to result into faster tracking of MPP under continuously varying atmospheric conditions providing an efficient system. It helps in reducing unwanted oscillations with an increase in tracking speed. A detailed step by step process of designing a model predictive controller has been discussed. Here, MPC has been applied in conjunction with conventional perturb and observe (P&O) method for controlling the dc-dc boost converter switching, harvesting maximum power from a PV array. The results of MPC controller has been compared with two widely used conventional methods of MPPT, viz. incremental conductance method and P&O method. The MPC controller scheme has been designed, implemented and tested in MATLAB/Simulink environment and has also been experimentally validated using a laboratory prototype of a PV system.     

Preparation of Iron Ore Micro-pellets and Their Effect on Sinter Bed Permeability

At present around 6–7% of iron ore slimes, out of total production, are being generated and accumulated at iron ore mine sites of National Mineral Development Corporation Limited, India. The accumulated slimes of finer size and relatively inferior grade should be utilized in an economical way for sustainable mining. These slimes can be agglomerated into micro-pellets for subsequent use in sinter making through hybrid pellet sintering method. However, the micro-pellets of sufficient size and strength are required for hybrid sinter making. The green properties of the micro-pellets depend upon various parameters such as surface area, moisture, binder, etc. In this study, iron ore slimes were beneficiated through gravity, and magnetic separation and concentrate of grade 65% Fe (Total) was obtained. Since the concentrate obtained had low surface area (700–900 cm²/grams) rendering it unsuitable for micro-pellet making, it was further subjected to grinding in a ball mill. The requirement of surface area for producing an optimum quality of green micro-pellets was established. The resultant micro-pellets were further used in studying sinter bed properties. The effect of moisture and size of micro-pellets on permeability of sinter bed were examined. The results confirmed that the addition of micro-pellets to the sinter mix improved the permeability of the sinter bed. The sinter bed with highest permeability of JPU 25.25 and void fraction of 36.27% was achieved with micro-pellets of size 3–6 mm at 7% moisture level. Mean granule size of sinter mix was also studied with respect to moisture content and size of the micro-pellets.     

Latest Results from the Damavand Tokamak Experiments

Damavand is a small tokamak (a = 7 cm, R = 36 cm) with an elongated plasma cross section (k 2) and a poloidal divertor. Its passive coils within the vacuum chamber provide the plasma formation at the torus center and act as a passive stabilizer for the plasma current. The experimental measurements presented here are the latest results related to the Damavand discharge main behavior with graphite limiters (before the device modification) during the ohmic heating phase. In this respect, we have evaluated some of the characteristic parameters such as edge safety factor (q_a 3.1), energy confinement (_E = 0.4 ms), electron temperature (T_e = 161 eV), and so on, during normal operation of the plasma current. The assessment of disruption phase of the plasma current has been considered by estimating the characteristic parameters of thermal and current quenches to be about 6 eV and 6 MA/s, respectively. Here, also we have monitored the evolution of the line emission of impurity (C, O) ions in the central deuterium plasma. The relative density of carbon and oxygen impurity levels has been estimated to be 2.6 and 1.4%, respectively. It is concluded that the impurity radiation loss is much higher during disruption phase of plasma current.     

Orthogonal relations for reasoning about posets

In large distributed systems, event abstraction becomes an important issue in order to represent interactions and reason at the right level of abstraction. Abstract events are collections of more elementary events, which provide a view of the system execution at an appropriate level of granularity. Understanding how two abstract events relate to each other is a fundamental problem for knowledge representation and reasoning in a complex system. In this paper, we study how two abstract events in a distributed system are related to each other in terms of the more elementary causality relation. Specifically, we analyze the ways in which two abstract events can be related to each other orthogonally, that is, identify all the possible mutually independent relations by which two such events could be related to each other. © 2002 Wiley Periodicals, Inc.     

Investigation of Plasma Facing Components in Plasma Focus Operation

Both aspects of the plasma–wall interactions, counter effect of plasma and materials, have been considered in our experiments. The AEOI plasma focus, Dena, has Filippov-type electrodes. The experimental results verify that neutron production increases using tungsten as an anode insert material, compared to the copper one. The experiments show decrement of the hardness of Aluminum targets outward the sides, from 135 to 78 in Vickers scale. The sputtering yield is about 0.0065 for deuteron energy of 50 keV.     

Selecting an Optimal Tool Sequence for 2.5D Pocket Machining while Considering Tool Holder Collisions

Milling using a sequence of tools has become very attractive with the advent of rapid tool change mechanisms in modern CNC machines. However, the commercial CAM systems used to generate G&M code rely on experienced process planners to select a good tool sequence. When a tool sequence is selected and tool paths are generated, NC-verify systems are used to check the tool paths for tool holder collisions. If tool holder collisions are detected, the part has to be re-planned ab-initio. In this paper, we describe a method to select an optimal tool sequence by formulating the problem under certain assumptions as the shortest path solution to a single source directed acyclic graph. Also described is a method to incorporate tool holder solution in the context of selecting an optimal tool sequence. Examples have been worked out to illustrate the workings of the algorithm. Received: February 2005 / Accepted: September 2005