مجله مکانیک سازه ها و شاره ها
سال دوم شماره 1 (بهار 1391)

Wood plastic composites are ideal in many applications such as furniture، components and automotive industry. However، most polymers especially thermoplastics are non-polar (hydrophobic) substances which are not compatible with polar (hydrophilic) wood fibers. This results in a poor adhesion between polymers and wood fiber. The aim of this study is to improve the adhesion properties by chemically modifying the wood fiber surface to enhance its miscibility within the plastic matrix. This was achieved by using toluene diisocyanate (TDI) linker to couple the wood fiber with either cetyl alcohol to form core-shell like structures. To investigate the effect of modification، composites containing 30% wt of wood was prepared. The effect of modification in three levels (0%، 10% and 20%) was studied on physical-mechanical properties of WPC such as: tensile properties and water absorption. Torque rheometry diagram and Scanning electron microscopy (SEM) were studied. The data showed an increase in the modulus، strength، yield stress and a decrease in the water absorption with increase of wood fiber modification while there is no considerable change in the elongation-at-yield. SEM spectra showed that the modification improve the interfacial adhesion between two phases in WPC.

In frame structures، the maximum bending moment in a given flexural structure always has an importance in estimating both the structural stiffness and strength performance. It is of particular interest to designers to develop an appropriate procedure to minimize the maximum moment through an optimal design of the structure. For this purpose، this paper presents a heuristic optimization algorithm، called the simulated annealing، for minimization of the maximum bending moment by virtue of the structural shape optimization. Simulated annealing is a novel meta-heuristic optimization algorithm، is powerful، efficient and is very simple to solve the combinatorial shape optimization problems. In this paper،at first maximum bending moment in frame structure by using finite element method is investigated and then simulated annealing algorithm is applied to minimize the maximal bending moment. Numerical examples are provided to demonstrate the applicability and capability of the present method. The results indicate the effectiveness of the proposed algorithm and its ability to find optimal shape of structure for minimizing the maximum bending moment problem.

Under various loads، pre-existing cracks (flaws) in rock propagate and leads to crack coalescence and failure. In this paper، crack propagation and coalescence mechanism in rock-like materials (gypsum specimens)، containing two inclined and open flaws (pre-existing cracks) under uniaxial compressive loads are experimentally investigated. The cubic specimens are prepared from the mixture of gypsum and water and the flaws are created by inserting steel shims into modeling material in the mould template. A set of specimens containing two inclined flaws with the fix length of 15 mm، inclination of 45 degree and connection line of 20 mm with various bridge angle of 45، 60، 75، 90، 105 and 120 degrees are subjected to compressive loads and the mechanical behavior of them are monitored. The bridge angle has important role and controls the propagation and coalescence pattern. For different bridge angles، four coalescence modes including shear، shear-tension، tension - shear and tension mode were observed. With the increase of bridge angle، the corresponding coalescence stress increases.

In this paper، we develop a numerical solution of flow for an annular gas turbine combustor. Three dimensional flow fields are considered for whole space from the compressor outlet up to turbine inlet including the inside and outside of the combustion chamber. Previous work has examined different parts of the combustor separately، using boundary conditions obtained from one-dimensional correlations. These correlations obtained with simplifications that often generate error. In this paper، the application of whole space of the combustor implies that no boundary conditions for the air inlet holes to the combustor were required. Comparison of the present numerical solution results with the experimental results indicates consistency between this study and the rest of the existent literature. We then examine the whole coupled system of an applied annular combustion chamber، simulated altogether and simultaneously. A 60 degree section of the annular combustion chamber was selected; including diffuser، swirls، liner، fuel pipes، strut and side channels and the quality of flow field was analyzed.

Heat transfer and fluid flow in a porous medium over a stretching flat surface with internal heat generation and suction/injection have been investigated using a two-temperature model of heat transfer. On assuming non Darcy flow، similarity solutions are obtained for the governing steady laminar boundary layer equations. The surface is maintained at a non uniform temperature. The coupled momentum and energy equations for both fluid and solid phases are obtained and then transformed to the similarity format. The system of governing equations along with the related boundary conditions have been solved using the classical fourth-order Runge–Kutta method allied with the shooting technique. The resulting velocity and temperature distributions are shown for different values of parameters entering into the problem. Also، the values of the local surface heat flux for both solid and fluid phases and critical values of the Prandtl number are reported as a function of the permeability parameter.

In this work، the performance of a flat plate solar collector operating in conjunction with a closed-loop pulsating heat pipe (CLPHP) is experimentally investigated. All the experiments are carried out at the Yazd، Iran. The experimental setup consists of a flat plate solar collector، pulsating heat pipe and a tank. The evaporator of the pulsating heat pipe is located inside the flat plate collector. In order to investigate the effect of the evaporator length on the efficiency of the system، three collectors are manufactured، which are different in the lengths of their evaporating section. Moreover، the effects of filling ratio of the pulsating heat pipe، inclination angle and flow rate are investigated for each collector separately. Although the increment in length of the evaporator negatively affects the convectional heat transfer، results do not show remarkable deterioration in the performance of flat plate solar collector. The optimum value for filling ratio of the pulsating heat pipe in all of three devices is measured as 30%، regardless of evaporator length. Finally، varying the inclination angle demonstrated that at angles between 0° and 20° degrees، the heat pipes exhibit unfavorable performance، while for angles between 30° and 50° degrees، the performances are favorable and almost similar. At the angle of 60 degrees، the performance is reduced due to excessive decrease in solar radiation.

The goal of a present study is to investigate the vortex characteristicsproduced in neighbor wall of canal with gradual expansion in 2D state and expansion ratio is 1:3. In present research theNewtonian fluid flow through canal assume laminar and it is investigated four angles 30، 45، 60 and 90 degree. Discretization of governing equations is performed using finite volume method and for couple of velocity and pressure parameters used the PISO algorithm on a staggered mesh. In all old researches vortexes length investigated for sudden expansion. The main innovation of current study is Investigated and reported regular and classified resultsfor every vortex length، maximum height and length of maximum height، start point and end point for length of vortexes in angles of 30، 45 and 60 degree in the range of Reynolds number in tables. the streamline and contour of velocity for flow through canal is investigated and plotted for various Reynolds number.

In this paper، experimental study of air force effect in harsh environmental condition on standard cables and wires which are recognized as electrical conductors in electricity transmission lines and/or as supporting devices for radio antennas، has been carried out. For this، four different types of cables including 20 & 63 KV، the wire for posts supporting and covered cable with distinct diameter and roughness corresponding to each one. Experiments have been conducted in wind tunnel and measurements have been performed using hot wire anemometer. The velocities employed in this study are 17 and 24 meters per second representing the one in the severe wind and storm. The aim of the survey is actually consideration of mean velocity، drag coefficient and other cables characteristics in a stormy condition. Increasing turbulence and momentum of flow causes that the separated flow from the model surface stick again to it. According to the results، typically in all models except the covered cable، the drag coefficient below the velocity of is less than 17 m/s. It is conclusively correct to say that 20 KV pattern could be used in the corresponding velocities.