نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و یکم شماره 2 (بهار و تابستان 1399)

An experiment was conducted to investigate the bag breakup process of round liquid jet injected into an airstream. The liquid jet was visualized using shadowgraph technique and also a high-speed camera was used to observe the formation and breakup of bags in a water jet injected from a 2.83 mm diameter nozzle with air Weber number in the range of 0.1 to 40 and the liquid-to-air momentum ratio from 5 to 30. An analysis of the force balance on bags was conducted and a criterion for bag formation is obtained. In this study, the diameter of the bag ring and the size of the membrane of the bag are calculated. Present results indicate that the normalized ring diameter and the membrane size are constant. Results also show that the membrane of a bag grows more than its ring towards the airstream direction.

In this paper, the effect of notch depth on the fracture toughness (KIC) and the plastic region of the crack tip material using the Charpy V-Notch test (CVN) data extracted from API X65 with different notch depth were conducted and the fracture energy was measured. Also, computer simulation of the experiment with a three-dimensional model was performed based on Gurson's modified damage law in Abaqus software. To obtain KIC values, equations based on the yield stress (σYS) and the failure energy of the Charpy V-Notch test (CVN) obtained from the steel was used. The estimated KIC data and plastic region of the crack tip, decreased with increasing notch depth.

Nowadays, pollution and reduction in fossil resources are major problems for world.The large number of cars which use hydrocarbons fuels is the main factor of this problem. Using of electric vehicles is a suitable solution. One of the most important parameters to calculate for electric vehicles battery is its state of charge. In this paper, a single prismatic cell of lithium ion battery in discharge cycle with electrochemical-thermal has been simulated with 3D CFD. First, numerical results are validated with experimental results of voltage and temperature. Then, the results of the electrical potential distribution in the current collector, state of charge, the lithium ion concentration in electrode, the temperature distribution and generated heat in battery are presented.

In this paper, the symmetric smoothed particle hydrodynamics (SSPH) as a meshless method is explained in detail. Free vibration analysis of bilayer graphenes with interlayer shear effect is modeled. The bilayer graphene is modeled as a sandwich beam with free-clamp end condition. To obtain the governing equations, each graphene layer is modeled based on the Euler-Bernoulli theory and in-plane displacements are also considered in addition to the transverse displacement. It is also assumed that the graphene layers do not have relative displacement during vibration. The results obtained by the sandwich beam model solved by SSPH method, include the first two natural frequencies of the bilayer graphenes. These results are validated by the molecular dynamic and compared with the GDQM results reported in the literature.

In this paper, the dynamic structure of variable pitch quadrotor and the design of a suitable controller based on mathematical modeling have been studied. The fixed pitch quadrotor because of having a simpler dynamic structure than other models has been the focus of scientific studies. This kind of quadrotors, despite their relative simplicity, creates limitations such as shortening the flight time and various maneuvers. In this paper, at first, the characteristics of variable pitch propeller are studied and compared with the fixed pitch propeller for a quadrotor. In continue, a Feedback Linearization Controllerand a Direct Adaptive Feedback Linearization Controller are used to control the Variable-Pitch quadrotor. Ultimately, the results of the proposed control are investigated via MATLAB software simulation. To better evaluate the performance of the designed controllers, the simulation results are compared with PID and Nonlinear Inverse Dynamics (NID) and Sliding Mode and Adaptive Sliding Mode controllers in the mass change condition of the quadrotor.The simulation results show that this adaptive strategy allows the quadrotor to follow variable time attitude and altitude commands more accurately, in the presence of disturbances or parameter uncertainties, compared to non-adaptive feedback linearization controllers. And also it shows that adaptive feedback linearization and adaptive sliding mode controllers have more accurate tracking with less error compared to feedback linearization, sliding mode, PID and NID controllers, respectively.

Spherical robots are the mobile robots with spherical shape equipped to internal drive mechanism that move on the ground due to their external shell rolling. In this research, after modeling of a pendulum type of the spherical robots, dynamic analysis of their model during planar motion on an inclined surface is performed. The motion equations of spherical robot are derived using Lagrange method. Also, a nonlinear controller based on feedback linearization methods is designed. In the following, considering non-confirm initial conditions on trajectory, parametric uncertainty and also disturbance torque on robot, the motion of robot is simulated. The results indicate that the designed controller has proper and resistant performance in tracking selected trajectory for sphere shell rotation during moving on specified inclined surface.

In this paper, the effects of tripwire in upstream of flow over a circular cylinder in a 2D channel and Re=100 has been investigated. The dimensions of the channel are 20D×50D. The distance between cylinder and wire is considered from 1.5D to 6D, and the relative size of wire is considered from 0.1D to 0.9D. The governing equations are continuity, momentum, and energy for 2D, incompressible, unsteady and vicious conditions. The no-slip condition for both cylinder wall, constant temperature for cylinder, and adiabatic wall for wire have been considered in this paper. The followed equations have been solved by the back-ward differentiate method and the CFD software - COMSOL MULTYPHISIC. The results show that the higher diameter of the wire and horizontal and vertical distances of the wire causes a higher decrease in values of cylinder’s drag and heat transfer. At all, It is found that existing of wire in upstream, decreases the drag and heat transfer of the cylinder but oscillating wire with the amplitude of 0.25D and relative distance and diameters of 3D and.3D causes increasing in discussed parameters relative to the stationary state of them.

The reduction of electronic devices’s input power and the requirement to portable energy sources have attracted many researchers. Hence, the estimation of electrical output and modeling of piezoelectric beams have became so important. Along this efforts, dynamic stiffness method for a uniform cantilever beam with a tip mass is developed in this research and the result of this method is compared with result of analytical modal analysis method that the differences between dynamic stiffness method and analystical modal analysis method with five mode is very small. Also the dynamic stiffness matrix is developed for a two segmented beam with a tip mass. The effects of the tip mass relocating on electrical outputs and system is explored that the relocating of the tip mass from the base to the tip causes the reduction in first natural frequency of system, although the effects of this relocating on second natural frequency is alternative. Moreover, a place is proposed for the tip mass to harvest the maximum energy.

The initial processes that take place in the operating facilities of the pressure reduction station on natural gas do not remove all its pollutants, whether moisture or solid particles. Under such conditions, corrosion in pipelines, blockage of instrumentation equipment, and destruction of valves and regulators will be intensified, so it is necessary at distribution and pressure reduction stations to prevent gas pressure drop and damage to pipeline equipment, processes to separate solid particles. And liquefied droplets of natural gas. This report first defines natural gas flow erosion and then briefly describes the flow erosion using the Discrete Phase Method DPM and the Eulerian-Lagrangian biphasic flow, or the discrete phase abbreviated simulation using Ansys Fluent 2019R1 software. The gas-solid in the elbow deals with the welding of this elbow joint. This report describes the discrete and continuous phase flow equations. In this regard, to consider the perturbation effects of the energy-perturbation loss model (Realizable k- ), to model the behavior of particles in the vicinity of the wall and also the scattering of particles due to perturbation in the fluid phase is modeled using random tracing model. . The boundary conditions of solid particles colliding with the wall and the steps of numerical solution of the equations in the discrete phase method are explained and the present effect investigates the erosive corrosion. The results show that even in slow currents with low Reynolds number, the gas-solid fluid is heterogeneous, and increasing the diameter of the solid particles increases the heterogeneity of the gas-solid flow and ultimately causes more abrasion corrosion at the weld roughness.

of combustion .In this research was conducted to study the addition of aluminum oxide nanoparticles to fuel on performance and emissions of a CI engine done. Simulation of engine combustion carried out by AVL-Fire.  In this study, in order to calculate the quantity of quality the mixing of fuel and air a modified parameter called the homogeneity factor, was used. Thus, in addition to check the quality of fuel and air mixing, the compression ignition process is also studied. According to the results obtained in this study, by adding Nano-particles of alumina to fuel, specific fuel consumption reduces. Also, the average engine exhaust emissions such as NOx and soot are reduced. These results indicate that the addition of alumina nanoparticles to fuel causes increasing the homogeneity factor of mixing of fuel and air inside the combustion chamber.

Study of vortex shedding and flow downstream of a square bluff body can be used to a vortex flowmeter. In this paper, flow velocity, turbulence intensity and vortex shedding from a 15 mm square bluff body have been investigated experimentally using hot-wire anemometer. Results show that flow angle has little effect on flow velocity distribution and turbulence intensity. However, variations of Strouhal  number (St) with respect to the flow angle is large, so that Strouhal number at flow angle of 12° has the maximum value of 0.176 and at angle of 43°, it has the minimum value of 0.129. If the probe is placed in the region x/a=2.5 and 2.2≤y/a≤6, the velocity will be equal to the free stream velocity and the vortices will be measureable.