Heats of sublimation of nitramines based on simple parameters

In this work, a simple procedure is introduced to determine heats of sublimation of nitramines as an important class of explosives. Molecular weight and one structural parameter of nitramines would be needed in the new method. Calculated heats of sublimation for well-known explosives such as HMX [1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane], RDX [1,3,5-trinitro-1,3,5-triazacyclohexane] and TETRYL [1-(methylnitramino)-2,4,6-trinitrobenzene] as well as new nitramines CL-20 [2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane] and TNAZ [1,3,3-trinitroazatidine] show good agreement with experimental data. R-squared value or the coefficient of determination of new correlation is 0.945. The root-mean-square deviation (RMS) from experiment for the predicted heats of sublimation by new method is 10.10 kJ/mol.     

Predictive compression of animated 3D models by optimized weighted blending of key‐frames

Efficient compression techniques are required for animated mesh sequences with fixed connectivity and time‐varying geometry. In this paper, we propose a key‐frame‐based technique for three‐dimensional dynamic mesh compression. First, key‐frames are extracted from the animated sequence. Extracted key‐frames are then linearly combined using blending weights to predict the vertex locations of the other frames. These blending weights play a key role in the proposed algorithm because the prediction performance and the required number of key‐frames greatly depend on these weights. We present a novel method in order to compute the optimum blending weight that makes it possible to predict location of the vertices of the non‐key frames with the minimum number of key‐frames. The residual prediction errors are finally quantized and encoded using Huffman coding and another heuristic method. Experimental results on different test sequences with various sizes, topologies, and geometries demonstrate the privileged performance of the proposed method compared with the previous techniques. Copyright © 2015 John Wiley & Sons, Ltd.     

Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082

This paper describes a three-dimensional numerical model based on finite volume method to simulate heat transfer and fluid flow in laser–tungsten inert gas (TIG) hybrid welding process. To simplify the model and reduce the calculation time, keyhole dynamics are not considered; instead, a new modified volumetric heat source model is presented for the laser source to take into account the effect of the keyhole on the heat transfer into the workpiece. Due to the presence of arc current, an appropriate electromagnetic model based on the Maxwell equations are also solved to calculate electromagnetic forces in the weld pool. The results of computer simulation, including temperature, current density, electromagnetic, and melted material velocity field, are presented here. Furthermore, several dimensionless numbers are employed to recognize the importance of fluid flow driving forces in the weld pool. It is deduced that the fluid flow has an important effect on the weld pool shape. It is also founded that among the driving forces, Marangoni force is dominant fluid force in the weld pool. Besides, calculated results of hybrid welding process are compared with those of TIG and laser welding processes. The weld pool depth is relatively the same, but the width of the weld pool is highly larger in hybrid welding than lone laser welding. Eventually, the presented model is validated by comparison between calculated and experimental weld pool shape. It is founded that there is a good agreement as the capability of this model can be proved.     

An analysis of carbone monoxide distribution in large tunnel fires

Fire events and the related toxicants such as CO are responsible for many fatalities in the current century. These hazardous events are much more dangerous when they occur in enclosed spaces. In the present study, a theoretical relation is developed for horizontal distribution of CO in a large tunnel fire. Then, the developed criterion is used to study the effect of some rudimentary parameters such as the heat release rate (HRR) of fire and tunnel’s aspect ratio (AR) on CO and temperature stratification. Theoretical results of various heat release rates and aspect ratios for horizontal distribution of CO are compared with numerical results using fire dynamics simulator (FDS5.5). It is found that big fires have higher rates of CO concentration decay in comparison to the smaller ones due to higher air entrainment into the travelling plume. It is indicated that the smoke travelling at higher values of tunnel AR, dilutes faster. Moreover, using FDS5.5, the relevant variations in temperature and CO concentration are discussed for tunnel angles ranging from ?20° to 20°.     

Identifying a simplified model for heavy duty gas turbine

A dynamic model was developed for long-term simulation of a heavy duty gas turbine. The model includes the essential control algorithm of the gas turbine as well as the most common outputs and other important intermediate variables. Control algorithm details, such as wind up protection and load limiter algorithm which have large effect on gas turbine transient behavior, are included. The model parameters are identified by applying genetic algorithm and least squares algorithm on regular operational data from a real plant to better match the model response to the real plant. The simulation results have been validated with real plant data and shown to have valid accuracy for many engineering applications.     

Experimental study and numerical modeling of arc and weld pool in stationary GTA welding of pure aluminum

In this study, a 2D mathematical model was developed for both arc and weld pool in stationary GTA welding. In arc model, current continuity equation has been solved in both arc and cathode regions without any assumption of fixed current density on the cathode surface which was essential in most previous works. The results of arc model were presented for both copper and aluminum anodes to investigate the effect of anode material on arc properties. It was seen that aluminum anode has lower maximum anode current density and heat flux but the distributions are wider than copper anode. Furthermore, shear stress on anode surface is higher in the case of aluminum anode. Also, calculated results of this study were compared with other available theoretical and experimental results. It has been shown that the agreement between calculated and experimental results was fairly good. The necessary information to simulate the weld pool, including the anode current density and heat flux to the workpiece were taken from the arc model. In this model, due to high thermal conductivity of pure aluminum, fluid flow into the weld pool was ignored. Effects of arc variables, i.e., arc length, applied current and welding time on the shape and size of the weld pool were investigated as well. In order to check the validity of the weld pool model, a comparison between calculated results and the results of our experimental tests was conducted. Generally, these comparisons reveal an acceptable agreement between calculated results and experimental data.     

Supplier selection using revised multi-segment goal programming model

Selecting the best supplier has been turned into a strategic subject in the competitive market, in the recent years. Supplier selection is one of the significant multiple criteria decision-making problems, which is studied in this paper. This research applies the multi-segment goal programming formulation, which considers different positions in the goal programming. This new kind of goal programming is revised in this investigation. The advantage of the proposed method is that it allows decision makers to set multiple aspiration levels for the coefficient of variables. Hence, the decision makers obtain more revenue and match with the reality of their problems. Unlike the multi-segment goal programming proposed in the literature, the revised formulation is linearized in the current study. The supplier selection problem is solved by this new formulation in a special circumstance. Finally, some concluding notes are remarked.     

Robust control of speed and temperature in a power plant gas turbine

In this paper, an H(∞) robust controller has been designed for an identified model of MONTAZER GHAEM power plant gas turbine (GE9001E). In design phase, a linear model (ARX model) which is obtained using real data has been applied. Since the turbine has been used in a combined cycle power plant, its speed and also the exhaust gas temperature should be adjusted simultaneously by controlling fuel signals and compressor inlet guide vane (IGV) position. Considering the limitations on the system inputs, the aim of the control is to maintain the turbine speed and the exhaust gas temperature within desired interval under uncertainties and load demand disturbances. Simulation results of applying the proposed robust controller on the nonlinear model of the system (NARX model), fairly fulfilled the predefined aims. Simulations also show the improvement in the performance compared to MPC and PID controllers for the same conditions.