Computational Methods in Engineering

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This paper is about discrete sensitivity analysis. A triangular bending element with constant moment and six degrees of freedom is used. The required derivatives for sensitivity analysis are calculated explicitly. These formulations, finite element method and sequential linear programming are utilized to find shape optimization of plate bending structures. The numerical examples, which show the ability of the derivatives, are presented.

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In this research the microorganism was initially isolated and selected after evaluation based on COD reduction of cheese whey and biomass production. The selected microorganism was identified as Trichosporon sp. The cultivation conditions of the microorganism were optimized under batch: temperature 30˚C initial pH = 6 aeration speed = 2 ν.ν.m and agitation rate: 800 rpm. Under these conditions, the specific growth rate and biomass doubling time were measured as 0.59 h-1 and 1.16 h, respectively. The COD reduction and biomass production under optimized batch conditions after 24 hours were obtained as 52% and 8.73 g L-1, respectively. The optimized conditions under continuous cultivation were: temperature, 30˚C agitation rate, 800 rpm aeration speed, 2 ν.ν.m dilution rate, 0.42 h-1 pH in fermentor, 4-5. Under these conditions the biomass production, COD reduction and productivity were obtained as: 8.17 g L-1, 53.21%, and 3.4 g L-1 h-1 respectively. The nutritional value of biomass was evaluated for crude protein, nucleic acid, fat, ass and moisture content. According to the results, the single cell protein obtained in this research is suitable and valuable for animal and poultry feed.

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Observations of the Caspian Sea during August-September 1995 are used to develop a three-dimensional numerical model to be used in calculating temperature and current. The model has variable grid resolution and horizontal smoothing that filters out small scale vertical motion. Data from the meteorological buoy network on the Caspian Sea are combined with routine observations at first-order synoptic station around the lake to obtain hourly values of wind stress and pressure fields. The hydrodynamic model of the Caspian Sea has 6 vertical levels and a uniform horizontal grid size of 50 km. The model is driven with surface fluxes of heat and momentum derived from observed meteorological data. The model was able to reproduce all the basic features of the thermal structure in the Caspian Sea and larger-scale circulation patterns tended to be anticyclone, with anticyclone circulation within each sub-basin. The results matched observation data. Keywords: Circulation, Temperature, Numerical model, Vorticity, wind stress

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Titanium is a highly reactive metal so that a thin layer of oxide forms on its surface whenever exposed to the air or other environments containing oxygen. This layer increases the corrosion resistance of titanium. The oxide film is electrochemically formed through anodizing. In this study, anodizing of titanium was performed in phosphate-base solutions such as H3Po4, NaH2Po4, and Na2Hpo4 at 9.75Ma/cm2 and 35ºC under galvanostatic conditions. The Potential-Time curves in the above solutions show that the anodic films formed on titanium are compact and their thickness depends on the solution type and concentration. The SEM and XRD techniques show that these layers are amorphous. In this paper, the effect of electrolyte concentration, composition and resistivity on breakdown voltage have been discussed in terms of Ikonopisov electron avalanche breakdown model. This model shows that the major factor contributing to the decrease in breakdown voltage is the increased electrolyte concentration leading to increased primary electronic current.

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In this paper, a numerical scheme is proposed for the multi-fluid compressible flows. This method is applied to the problem of underwater explosion. The proposed scheme is basically the extension of Godunov method in gas dynamic problems to the multifluid environments and is second-order accurate in space. In this method, also, the problem of artificial mixing of two different phases on Eulerian grids is prevented by a front tracking technique. The numerical results of this study are in very good agreement with previous numerical and exprimental results

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There are a number of parameters influencing the dynamic and seismic response of bridges. Of these, two important parameters warranting special notice include: the properties of the neoperenes in the state of connection between girders and columns and the shear stiffness of underlying soil in the level of bridge substructure’s connectivity to the ground. In this paper, the effects of these two parameters on the dynamic and seismic response of Ghadir Bridge in Isfahan are investigated. The main conclusions drawn from these investigations include: the sensitivity of the bridge’s lateral modes of vibration to the horizontal shear stiffness of the neoperenes and the substantial effects of the soil’s shear rigidity on the longitudinal modes. Based on the findings, it is recommended tha a thorough geotechnical site investigation of the soil be conducted and the properties of the underlying soil be accurately established in order to correctly identify the dynamic behaviour of a bridge.

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Considering the vulnerability of double-layer grid space structures to progressive collapse phenomenon, it is necessary to pay special attention to this phenomenon in the design process. Alternate path method is one of the most appropriate and accepted methods for progressive collapse resistant design of structures. Alternate Path Method permits local failure to occur but provides alternate paths around the damaged area so that the structure is able to absorb the applied loads without overall collapse. Following the sudden initial local failure event, severe dynamic effects may arise which should be taken into account in determining the realistic collapse behavior of the structure. In this paper, a new methodology based on alternate path method is presented to apply dynamic effects of initial local failure. The method is called nonlinear dynamic alternate path method. Due to its capability to take account of dynamic nature of the failure, this method can be used to evaluate realistic collapse behavior of the structure and to investigate the vulnerability of the structure to progressive collapse phenomenon.

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An intensive experimental investigation was conducted to study the effect of vertical tail, single and twin (with different cant angles) on the flow field and the corresponding aerodynamic forces and moments of a model of a fighter A/C. Aerodynamic forces under different flight conditions and different vertical tail settings were measured in a supersonic wind tunnel. Furthermore, effects of vertical tail on the model wake at subsonic speed were investigated. In addition to the force and pressure measurements, schlieren system was used to visualize the shock formation and movement oat various locations on the model. The results show existence of a pair of symmetric vortices for the model equipped with a 22 degree vertical tail cant angle. The vortices burst symmetrically at moderate angle of attack. The drag coefficient increases with increasing cant angle at low to moderate alpha and decreases when alpha is further increased.

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In this paper, the problem of batch scheduling in a flexible flow shop environment is studied. It is assumed that machines in some stages are able to process a number of jobs simultaneously. The applications of this problem can be found in various industries including spring and wire manufacturing and in auto industry. A mixed integer programming formulation of the problem is presented and it is shown that the problem is NP-Hard. Three heuristics will then be developed to solve the problem and a lower bound is also developed for evaluating the performance of the proposed heuristics. Results show that heuristic H3 gives better results compared to the others.

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In this paper, two suboptimum detectors are proposed for coherent radar signal detection in K-distributed clutter. Assuming certain values for several initial moments of clutter amplitude, the characteristic function of the clutter amplitude is approximated by a limited series. Using the Pade approximation, it is then converted to a rational fraction. Thus, the pdf of the clutter amplitude is obtained as a sum of simple exponential functions. Using such a pdf, we develop the suboptimum detectors PGLR and PAALR, which are simplified forms of the GLR and AALR. Computer simulations show that the suggested detectors have appropriate performance compared to OLD, GLR and AALR detectors.