نشریه علوم کاربردی و محاسباتی در مکانیک
سال بیست و نهم شماره 2 (بهار و تابستان 1397)

Introduction: The main objective of this study is a parametric investigation of twin spool unmixed flow turbofan engines for 6-person light aircraft. Obtaining the engine performance curves and mathematical modeling of the off-design function of the engine by using the Serial Nested Loops method is studied. Despite the complexity of mathematical modeling, the performance of offdesign turbofan engine is investigated and Twin Spool modeling of unmixed flow is presented. The design choices for specific fuel consumption and specific thrust are examined. The performance parameters of the turbofan engine with constant geometry contain thrust, specific fuel consumption, engine intake air, component efficiency, component pressure ratio, turbine inlet and outlet temperature. For cycles, the static or flight performance is analyzed and the performance matching of each engine component is determined.  Engine Modeling To facilitate the simulation of the turbofan engine performance, the engine is numbered according to the location of the main components of the engine, Discussion of Result : simulated model and GSP (Gas Turbine Simulation Program) software is compared. As seen on the right side of figure, the matching error has a high error in the low period. However, as the RPM increases, the error is reduced until the error rate reaches less than 20% in over than 90% RPM. It indicates that the simulated model in the high RPM has an acceptable accuracy. At the design point, the error is minimum but as the RPM decreases or increases, the error increases which is due to the application of the scale method. In this study, it is indicated that the cycles with intermediate-stage combustion chambers at higher speeds perform better than those of conventional cycles. In turbofan engine, the cycles with the secondary combustion chamber have a higher specific thrust and lower specific fuel consumption and lower pollution compared to ordinary cycles. By increasing their fan pressure ratio, the specific thrust ascends and specific fuel consumption descends. In fact, the cycles can support engines that have high bypass ratio and can increase their efficiency. Generally, the cycles with less input temperature in high pressure turbine can reduce the specific fuel consumption of the cycle. It is found that due to the unavailability of the curve of the engine's characteristics, using the scaling method is proper for estimating functional curves. In this method, constant coefficients of the design point of the engine are analyzed and the obtained curves are closer to each other and the error in simulation results is reduced.

In the present study the heat transfer of nanofluid flow inside a channel with different arrangements of nanoparticles injection (dispersive elements) is investigated. In the heat transfer phenomena, nanoparticles presence in the fluid flow is known as one of the most important factor for the thermal dispersion. In this work, the distribution of dispersive elements or nanoparticles in the channel is considered to be uniformly distributed in the central region and near the walls. The validation of results is verified by the analytical solution for a simple state of the problem and also by comparison with previous published papers. The presence of the nanoparticels in the center region, increase the Nusselt number and heat transfer characteristics with an ascending form. For the boundary arrangement, increasing the thickness of injected nanoparticles lead to an ascending-descending behavior for Nusselt number. Therefore in this distribution, the optimum thickness for dispersive elements is obtained. Also it can be seen that the presence of the nanoparticels with parabolic distribution increase the Nusselt number with a univocal form. For the exponential arrangement, especially for large values of dispersive coefficient, increasing the Nusselt number has a nonlinear behavior that is the most important distinction of these two distribution functions.

In this study, a linear parabolic trough concentrating photovoltaic/thermal system has been simulated and the effects of using Al2O3/ethylene glycol-water 50:50 nanofluid with different nanoparticle shapes including platelet, cylindrical, blade and brick shapes from energy and exergy standpoints in the laminar and turbulent regimes have been numerically investigated. The proposed model has been validated using existing experimental results where good agreement was observed. The results indicated that using nanoparticles of cylindrical shape in laminar regime and brick-shaped one in turbulent regime lead to the best system performance compared to others. In addition, applying nanofluid in laminar regime is more effective compared to turbulent regime

In this paper the steady state radial stagnation point flow impinging on an infinite cylinder has been investigated. The impinging free stream is steady with a constant strain rate kand axis is rotating with constant angular velocity. Similarity solution of the Navier-Stokes and energy equations is presented in this research. A reduced from of these equations are obtained by using appropriate transformations introduced in this study. For all Reynolds numbers, as the particle fraction increases, fluid velocity component in radial and axial directions and axial component of shear-stresses decrease and in the contrary the angular component of shear stress and velocity field and Nusselt number increase

In thisarticle, an inverse algorithm based on the conjugate gradient method is applied to estimate the unknown location and time-wise varying strength of the point and distributed heat source in functionally graded rectangular plate from the knowledge of temperature measurements taken from the boundaries of plate. It is assumed that no prior information is available on the functional form of timewise variation of the heat source strength so estimation process starts with an arbitrary initial guess. The conjugate gradient method is employed for optimization process and the finite element method is applied to solve the governing differential equations. Results show that the estimation of location and strength of point heat source can be obtained with any arbitrary initial guesses .

he purpose of this paper is to consider the ring systems in the context of a modified gravity theory.
In fact, the gravitational stability of a ring system consisted of N particle with the same mass m rotating around a massive object at the center is studied. After finding the equation of motion and considering the dynamics of the system in the equilibrium state, perturbative analysis is used in order to find the linearized version of the equations of motion. Finally using the Fourier analysis, the dispersion relation of the system is derived. At the end, using the observational values of the free parameters of the above mentioned theory and also the dispersion equation the stability criterion of the system for several cases is derived. Finally, the results have been compared with the corresponding results in Newtonian gravity

In this study, ten novel quadrilateral Kirchhoff’s bending plate elements based on the Trefftz displacement functions and satisfying equilibrium equation are suggested. First, the most suitable arrangement of degrees of freedom and nodes are achieved
by benefiting from previous researches. Afterwards, using the symmetry of terms, ten elements with different interpolation functions for the two top arrangements will be introduced. Numerical tests reveal that the correct choice of the interpolation’s terms from the incomplete Trefftz functions leads to more efficient elements with lower degrees of freedom and higher order than the complete elements. Since the Trefftz functions meet the equilibrium conditions, the force responses of the most cases have a higher accuracy than the displacement responses

Bent pipes have been widely used in industrial usage. In this work different materials have been used as mandrel and it is realized that a bunch of flexible wire is more preferable to optimize bending parameters. This way doesn’t need laborious adjustments and because common flexible wires have plastic deformation even during excessive bending angles, they can be used so many times and also they are easy to remove after bending process . Cross section distortion, cracking at the extrados, wrinkling at the intrados, spring back phenomenon and wall thickness change are issues associated with pipe bending. In this work the effect of flexible wires on bending parameters has been analyzed and the results are confirmed with finite element simulation

In the present study, the effect of tooth profile modifications on the static transmission error is investigated. The most important factor for investigating noise between two gears is the transmission error. First, the static transmission error is analytically calculated by estimating tooth compliance. The compliance of gear is calculated considering tooth as cantilever beam deflection; rigid body tooth rotation at its base and Hertzian contact. After estimating the static transmission error, tooth profile is modified in four ways: tip relief on the gear teeth only, tip and root relief on the gear teeth only, tip relief on both the gear and pinion teeth and tip and root relief on both the gear and pinion teeth. The results indicate the tip and root relief on both the gear and pinion tooth is the best way for transmission error reduction

In this paper, an approach for reducing the shaking force of a spherical parallel robot using extra mechanisms is proposed. The proposed method vanishes the Coriolis acceleration terms due to moving the slider links on each branch from force balancing equation. For this purpose, two links are added to each branch of the manipulator as an extra linkage mechanism. Next, three weights are added to each branch of the robot for reducing the applied shaking forces on the base platform. Finally, the dynamic numerical simulations is performed using ADAMS software. The results show a reduction in the applied shaking forces on the base as much as 98%, 79% and 99.4% along the X, Y and Z axes, respectively