جستجوی مقالات مرتبط با کلیدواژه « four » در نشریات گروه « مکانیک »

In this study, hydrodynamic behavior of four-sided wind tower attached to parlor and courtyard of a scaled model form existing historical house with wind incident angel as variable was numerically investigated. Hazire-ei house wind tower, which has six channels with rectangular cross section, integrated with parlor and courtyard is considered among the most typical ones in the vernacular architecture of Yazd city. This article seeks to investigate the performance of four-sided wind tower regarding suction and supply amount of air and the way it was used as a vernacular solution for natural ventilation in order to provide engineers with design guidelines for contemporary use. Numerical study was conducted on a 1:25 scaled model and for 13 wind incident angels with 15 degrees intervals and interested parameters are mass flow rate and flow direction in each channel. A structured mesh was generated and ANSYS Fluent software was used for numerical simulation. Numerical modeling results were validated against experimental tests conducted on the same scaled model and good agreement was observed. Results indicate that in 68.5% of incident angels, four-sided wind tower acts as sucking the air out of building and in other incident angels with approximately equal amount of supply and extract rate, it operates as an air exchange unit. Accordingly it can be concluded that putting aside stack effects, four-sided wind towers in dry regions of Iran are mostly employed for heat dissipation elements rather than inducing outdoor cool breezes.

In this investigation, kinked crack path of friction stir Cu-Al7075-T6 alloy welded joints in four-point bending test conditions has been studied as well as the fatigue lifetime of the welded joints, numerically and experimentally. To do so, four-point bending and fatigue tests of welded specimens have been carried out and the experimental fatigue test data and the kinked crack angles in bending tests have been extracted. Maximum Tangential Stress (MTS) and (KII)min criteria have been used for estimating the kinked crack angles, and Paris law has been applied to predict fatigue crack propagation life of the welded specimens. Functionally graded materials concept has been employed for determining mechanical properties of different regions of welded joints. To do so, the mechanical properties of the weld region such as Young's Modulus and Poisson's ratio have been considered to be linear functions of the positions of the weld region points. It has been shown that, when the original notch is close to the material with the higher fracture toughness (Copper), the kinked crack angle becomes smaller. The results show good agreement between the experimental data and numerical estimations.

In this paper; reduced order modeling (ROM) of unsteady two-phase flows is performed based upon two-fluid models and a proper-orthogonal decomposition (POD) method. The four-equation two-phase flow model is used as a mathematical model to describe physics of the problem. After presenting the governing equations, direct numerical solution of the problem is introduced using AUSMDV* method. Then, the POD method is introduced as a mathematical tool to reduce computational time of the transient problems. In the present research, an equation free/Galerkine free POD method is used for ROM of the unsteady two-phase flows. In this approach, the singular value decomposition (SVD) method is used to compute the base vectors of the reduced space. A shock tube and water-air separation two-phase problems are solved using the present ROM method. Results show that this approach can reduce computational time of unsteady simulations about 35%. Reduction of the computational time directly depends on the size of the computational gird. The results also indicate that application of POD method on the fine grids is more efficient than on the coarse grids.

In this paper, in order to separate images in four spectral bands (from blue to near infrared) in multispectral cameras, four-color separation prism advantages are reviewed. Then, while description of ray tracing of four-color separation prism, main design parameters and principles are mentioned. After that, design of a four-color separation prism model that attached to detector (CCD) by using the Zemax software are described, also spot diagrams, ray tracing and aberration graphs are analyzed. Finally, while expression four-color separation prism characteristics that yield from programming with Zemax software, including weight, length of the optical path and thickness of equivalent blade, its specifications in remote sensing satellite multispectral cameras are explained.

In this paper، a novel four-variable refined theory of plate، called RPT، has been proposed for free vibration of composite laminated plates، using a hyperbolic sine function، for calculating out-of-plane shear strains. It is one of the properties of this theory that the boundary condition of zero shear stress is satisfied over upper layer and under lower layer of plate، with no reference to Timoshenko shape factor. In contrast to other higher-order shear deformation theories، in RPT theory، equations of motion are coupled dynamically only in inertial terms، while elastic energy terms are not coupled for the variables used. From this viewpoint، RPT theory is similar to classical plate theory (CLPT). Some of the objectives of this paper are the investigation of effect of influential parameters on fundamental frequency، such as modulus ratio، angle of plies، and plate length-to-thickness ratio. The results of this proposed version of RPT are compared and validated with those of first-order shear deformation theory (FSDT)، higher-order shear deformation theory (HSDT)، and the original version of RPT.

In the present study, effects of different percentages of ethanol as a gasoline additive on high temperature oxidation behavior of cylinder head and valve alloys were investigated. A single-cylinder four-stroke engine was used to simulate the hot chamber of cylinder environment. Samples were located within the exhaust pipe and were deposited with ethanol blended gasoline combustion gases under certain operating cycles. Then in order to evaluate the oxide layer, the cross-section of samples were observed by scanning electron microscopy (SEM) and to determine the amount of oxygen, the surface of samples were analyzed by energy dispersive X-ray (EDX) technique. The obtained results exhibited that, thickness of oxide film was increased by increasing of the ethanol percentages and engine operating cycles. The most porous film was belonged to steel in 15% ethanol-containing fuel with 60 operating cycles. Metal loss in steel specimens was significantly more due to linear behavior of steel oxidation.

Four-roll bending process is usually used for manufacturing of seamed thick-walled and thin-walled cylinders. Due to complexity of this process, the analytical solution of plate bending in this process has not been developed completely. The existence of friction and multi-step processing makes it more difficult. Investigation of four-roll bending process using analytical and numerical methods is the main aim of current research. At first, using plate deformation theories, an analytical solution for four-roll bending process is extracted. By decomposing the deformation to elastic and elasto-plastic, the required bending moment is calculated. Considering the distribution of bending moment along the plate, the radius of bending is calculated considering spring back effects. The four-roll bending process is simulated by the finite element method. The simulation results show that the level of strain is less than the critical value and hence there are no damaged parts in the plate during process. Besides, bending radius of the plate after spring back is calculated and compared with the analytical values. Finally, for validation of analytical and numerical results, some experiments were conducted on aluminum. Results of this research show that both analytical and numerical methods are proper techniques for predicting plate behavior during four-roll bending.