Scientia Iranica
Volume:24 Issue: 4, 2017

Estimation of physical parameters of a parametrically excited gyroscope is studied in this paper. This estimation is possible by reading the input and output data of the gyroscope. Because of di erent faults in the manufacturing process and tolerances, physical parameters of a gyroscope are not exactly same as the expected values of the manufacturer. Moreover, changing of temperature, humidity, external acceleration, etc. can change the physical parameters of the gyro. Thus, the physical parameters of gyroscope are not xed values and may deviate from the desired designed values. The physical parameters of gyroscope determine the optimal region for working of gyroscope. Thus, if the parameters deviate from the original ones but the excitation frequency is fi xed at its initial value, the sensitivity of the gyroscope will be reduced. The new parameters of the gyroscope can determine the new point of excitation frequency and, because of this, estimation of these parameters should be done to prevent sensitivity reduction. Estimation of these new parameters using the input and output values is studied here.

Surface modi cation has been applied in many ways to enhance exclusive implant product. Electrical Discharge Machine Die Sinker (EDM DS) is a new approach to machine a macro surface on the biomaterial. In this study, investigations of current properties of EDM DS to obtain a new surface in titanium alloy (Ti-6Al-4V) and stainless steel (E-316-L), which placed pit on the material-sized (25 mm) diameter sample with a radius of 6.3 mm, were conducted. All the samples of concave textured circular pits with a fi xed diameter and depth of 0.5 mm were successfully machined. This study revealed that the pits were produced in the concave cup and the lubricant was con ned inside the pits, making easier contact between metal ball and metal concave surface. The results also show that the discharge machine is an attractive machining method for surface modi cation of biomaterial. This paper suggests that concave implant surface embedded with pits will work as a trap for lubricant and wear debris; in addition, it is possible to increase the lifespan of implant structure.

This paper deals with the dynamic response and energy absorption of foam-fi lled aluminum parabolic tubes under axial impact loading. The numerical crush analysis of empty and foam- lled tubes is performed using non-linear nite element techniques. The eff ects of geometrical (wall thickness) and material parameters (foam density and Young's relaxation modulus) on the impact response and energy absorption capacity of foam- filled tube are investigated using numerical models. The results show that the foam properties have signi cant e ect on the crushing behavior, force and impact acceleration magnitude, and energy absorption capacity. Furthermore, there is a critical foam density beyond which the structure loses its energy absorption performance. Experimental results acquired from a test setup are used for validating the Finite-Element Analysis (FEA). There is good agreement between numerical and experimental results.

Annoying vibration waves generated by passing trains highlight the necessity for the assessment of the eff ects of railways on their environment. Dynamics of structures close to railway tracks is amongst such important issues. Contrary to the past studies, this article proposes a modeling method that is totally based on the idea of discrete masses. It considers three major parts as the accomplices causing undesirable oscillations including the track, the ground bed, and the structure in the vicinity of the track. The ground bed is considered as an elastic half space subdivided into discrete masses. It facilitates modeling for the track systems that may include any deliberate discontinuity, such as voids and trenches, in the ground bed that supports the railway track. Such discontinuities arise from engineering perception and are useful in controlling the spread of noise and vibrations. A \MATLAB" based computer program is written to solve the motion equations in the time domain. The proposed method provides flexibility in modeling. Variety of track loading and wave propagation scenarios can be simulated without the need to rebuild the model. This method can be practically used when seeking remedies for controlling the levels of unwanted vibrations in the structures.

In the present study, a combination of Lattice Boltzmann Method (LBM) and Smoothed Pro le Method (SPM) is used to simulate one, two, and many particles motion in a planar channel with two symmetric protuberances. LBM is applied as the fluid flow solver and SPM is used to satisfy the no-slip boundary condition at particles surfaces. Bounceback boundary conditions are used for lower and upper walls while pressure boundary conditions are applied for the fluid inlet and outlet boundaries. Horizontal, vertical, and angular velocities of particles are recorded during the simulation. It is concluded that the combined LBM-SPM can be considered as a good candidate for simulation of particle motion in a channel with stenotic geometry.

In this study, mechanical and microstructural characteristics of AA5XXX aluminum plates connected by MIG welding were investigated. Thus, after several preliminary experiments done to ensure quality requirements of the parameters, specimens in the form of long aluminum plates were welded, and then some of them were spared for the subsequent sub-zero treatment at about 146C for 12 and 24 h, respectively. To investigate the e ect of this super cooling on the welded parts, several tensile, bending, and hardness tests in conjunction with micro-structure examinations were carried out and results were discussed in detail. It was concluded that during sub-zero treatment, microstructure gets fi ner and stabilized, positively a ecting the overall strength of the material. There is no signi cant di erence in the overall strength of the material right after the subzero treatment and that of the specimens rested for one year at room temperature after cryogenics treatments.

In this paper, we study the motion of a cavitation bubble near a concave boundary from a theoretical perspective. To illustrate the e ect of the surface concavity of the boundary, boundary integral and nite di erence methods are utilized to investigate the more detailed process of jet formation. Bubble shapes and its lifetime, movement of the bubble centroid, pressure contours, and velocity vectors are used to demonstrate the numerical results. The velocity of a liquid jet impacting on the far side of the bubble surface tends to increase with decreasing boundary concavity. This result suggests that higher pressures can occur when cavitation bubbles collapse near a concave boundary. With the increase of boundary concavity, the time evolutions of the bubble growth and collapse tend to increase, and the liquid jet is formed later.

For the rst time, the problem of impulsive oblique stagnation-point flow on a vertical cylinder along with mixed convection heat transfer due to buoyancy forces has been solved in this study. The uid at rest with uniform temperature, T1, around the cylinder starts flowing towards it at strength rate of k, and the cylinder temperature rises to Tw at t = 0, simultaneously. The governing equations induced by the impinging flow on the constant-temperature vertical cylinder at any obliqueness angle, , have been reduced to ODEs by using similarity transformations, and then they have been solved numerically. Considering a sample case of incompressible flow with Re = 1 and Pr = 0:7, the results of Nusselt number and similarity functions of velocity and temperature distributions have been obtained for di erent values of time and angle, . At the initial instants of time, the Nusselt number, regardless of 's magnitude, has large values; for example Nu = 5:1 at  = 0:01. As time passes, the value of the Nusselt number reduces intensely within a short period of time (until   0:4), and then it changes with a moderate reduction rate, such that in the steady-state situation, its value reaches 0.67, 0.61, and 0.51 for obliqueness angles = 10, 30, 60.

The prediction of deposition eciency of submicron particles in the pulmonary alveoli has received special attention due to its importance for drug delivery systems and for assessing air pollutants health risks. In this work, the pulmonary alveoli of a healthy human are idealized by a three-dimensional honeycomb-like con guration and a fluid-structure interaction analysis is performed. In contrast to previous works in which the inlet ow rate is prede ned, in this model, a negative pressure is imposed on the outside surface of the alveolus which causes air to flow in and out of the alveolus. The resulting flow patterns con rmed that there was no circulation in the terminal alveolus. The predicted alveolar air flow was used to calculate the trajectories of submicron particles using the Lagrangian approach. Our ndings suggest that an accurate simulation requires including at least ten breathing cycles, considering a parabolic radial distribution of injected particles and continuous injection. The presented results show high deposition eciency for submicron sizes in the alveolar region if these particles can reach the alveolar region. Therefore, the vesicles technology in which particle agglomerates would be released after the vesicle reaching the alveoli is suggested for targeted drug delivery to the alveolar region.

Quality problems in the polymer composite products are mainly attributed to design flaws, material inconsistencies, defects in manufacturing process, unquali ed manpower, use of primitive technology, and defective machines. The purpose of this research is to develop a generic framework of quality for polymer composite manufacturing, which is validated and optimized through determining flexure properties by Taguchi method. To test the proposed framework, 27 polymer composite laminates were produced according to Taguchi L27 orthogonal array by varying thirteen key process parameters including laminate's thickness, weight, ber pattern, matrix, core type, resin and hardener mixing time, viscosity, layup pattern, tooling, cure, temperature, labour and process techniques. Flexure strength was de ned as quality characteristic, and accordingly, e ffects of the selected parameters on exural properties were studied through three-point bending test. Results of the study reveal that ber pattern, cure, tooling type, and layup pattern are the most signi cant variables influencing flexure stress, whereas ber pattern, matrix, resin hardening mixing time, and process techniques have signi cant e ffect on flexure strain. The optimized levels of each control parameter for exure stress and strain were obtained, and results were validated through predictive analysis. Findings of this study and the proposed framework are useful for polymer composite application in aviation, mechanical, sports, automobile, and civil industries.

In this paper, based on the modi ed couple stress theory, the size-dependent dynamic behavior of circular rings on elastic foundation is investigated. The ring is modeled by Euler-Bernoulli and Timoshenko beam theories, and Hamilton's principle is utilized to derive the equations of motion and boundary conditions. The formulation derived is a general form of the equation of motion of circular rings and can be reduced to the classical form by eliminating the size-dependent terms. On this basis, the size-dependent natural frequencies of a circular ring are calculated based on the non-classical Euler-Bernoulli and Timoshenko beam theories. The ndings are compared with classical beam theories. Response of the micro-ring under application of static and dynamic loads is investigatedand compared with the classical theories. Results show that when the thickness of the ring is in the order of the length scale of the ring material, the natural frequencies evaluated using the modi ed couple stress are considerably more than those predicted based on the classical beam theories, while the defection and natural frequencies of the classical and non-classical beam theories approach one another for the rings with thickness much larger than the material length scale.

The article deals with a sophisticated approach to the study of basic kinetic dynamic process in metal production. It is concerned with three agendas: study of reduction reactions of iron oxides and carbon as reducing agents with secondary created oxides; study of the e ect of catalyst occurrence on the reaction space; study of the eff ect of variable temperature and pressure gradients on the processes. The main experiments were carried out in the newly established Laboratory for Research on High Temperaturev Properties equipped with testing setup and upgraded with interpretive model system, enabling a generalization of experimentally obtained information to theoretical conclusions about processing of non-standard alternative and waste materials.

SPH method is one of the most used numerical mesh-free methods in CFD simulations which can easily model problems with free surfaces. Considering the importance of surface tension in most engineering applications and the capability of SPH method in simulating free surfaces, a single-phase method for implementing surface tension is introduced in this study. Unlike time-consuming multi-phase simulations, this method does not need to model the second lighter fluid, which reduces the CPU-time and memory requirements substantially. Mirror imaginary particles are used near the free surface to obtain surface properties such as surface normal vector and curvature, which are required in surface tension calculation. The advantages of using these imaginary particles are explained qualitatively through the use of some examples of droplet dynamics. This method is applied to several benchmark problems in surface tension simulations, and acceptable results are obtained.