نشریه مهندسی مکانیک ایران
سال بیستم شماره 1 (پیاپی 50، بهار 1397)

This study proposes a micromechanical algorithm for analysis and homogenization of heterogeneous brain tissue. The presented method has led to the development of a 3D cell model for homogenization of disordered part of brain matter. The structural complexity of neuron has modeled with low level of simplification in order to achieve more accurate results. In the homogenization process the constituents of brain, neuron and extracellular cell matrix, are assumed to have an elastic behavior. The proposed model is studied in some micromechanical aspects and results indicate the model simulates the tissue behavior reasonably. Results show that because of low length to diameter ratio (aspect ratio) in the cell body, increase in number of neurons in the representative volume element has low effect on improvement of tissue mechanical properties, such as elastic modulus, and the properties are close to the prediction of lower bound or Reuss model. Investigation of stress fields caused by compression load on the representative volume element, as the part of brain tissue, announce that the maximum stress is located in the neuron and specially at the junction of neurites (axon and dendrites) and soma and also along the neurites.

In the present research, behavior of a sandwich plate with point supports subjected to an eccentric low-velocity impact is investigated. In this regard, time histories of the contact force and lateral deflection of a sandwich plate with simply supported edges are compared with those of a plate resting on point supports. This comparison has not been accomplished so far, even for the single-layer isotropic plates. Other novelty consists of proposing a semi-analytical solution in conjunction with a new energy formulation to consider the spatial dependency and using a numerical time integration method, implicitly. The governing equations of motions are found based on extremizing the total potential energy, including work of the inertia forces, employing Ritz technique and reduced to quasi-static one through a novel approach. In contrast to the available researches, influence of the lower layer on the stiffness of the contact region is incorporated. Verification of the results has been accomplished based on results of ABAQUS computer code. In the results section, the significant effects of the point supports (in comparison to the complete edge support), initial velocity of the indenter, and the aspect ratio of the plate on time histories of the contact force and lateral deflection of the plate are investigated.

Appropriate control of the vehicle longitudinal dynamic requires accurate and real-time knowledge of the parameters affecting the dynamics of the vehicle. The main contribution of this paper is in developing an estimator called short-time linear quadratic form (STLQF) which is a new parameter estimation technique to simultaneously estimate the time-varying parameters that affect on vehicle longitudinal dynamics with a low latency. These parameters are the vehicle mass, time varying road slope angle and overall aerodynamic drag coefficient of the vehicle in real time. Next, the efficiency of STLQF algorithm is shown by comparing the results of STLQF technique in an experimental test against the recursive least squares (RLS) parameter estimation method. The results of implementing STLQF parameter estimation algorithm, showes the better performance of STLQF estimator compared with RLS algorithm. In the end, the STLQF estimator is simulated in hardware in the loop configuration using an AVR microcontroller in order to rapid prototype of the STLQF method by minimum cost and high accuracy in the least possible time.

Incremental sheet metal forming is one of methods more innovation in science and industrial zone. The purpose of this research is the study of influence of factors such as tool diameter, step down, rotation speed and feed rate on metallurgical properties of explosive-welded Al/Cu/Al multilayer. In order to this purpose, a sample of explosive-welded Al/Cu/Al multilayer was produced. Then, a statistical model (RSM) was used for the experimental plan (with these variables) to determine the runs of experiment (or selected points). Next, forces and times values of sheet metal forming were measured. The experimental results showed that force and time forming of Al/Cu/Al multilayer is highly sensitive to factors like step down and feed rate. Also the most effective coefficient on the incremental forming is belonged to step down factor that showed it is very important in machining parameters. Finally, by using coefficient estimates of (RSM) model, relation between input variables and response was obtained. Finally, this model was predicted the optimum design points of machining parameters.

The easiest method of communication between humans and machines is through speech and one of the essentials aspects of this relationship, is perception of humanistic sentiments by machine. As a result, getting speech’s patterns and creating a system based on this model has been a challenge for researchers in recent years. Although the emotion shown in speech could ranges in a very divergent spectrum, because of pander to accent, culture and environment, but a fixed patterns could be found in feelings of people’s speech. In this paper, a new algorithm to detect emotion in human voice is presented. In proposed algorithm, features are extracted from the audio signal, inspired by human hearing. And then the optimal features are chosen from the extracted features with the aim of increasing the speed and accuracy of diagnosis with an intelligent method. In addition, classifying is done by combining a set classifiers subsequently, patterns of anger, joy, fear, boredom, disgust and sadness is distinguished by the designed intelligent system. Results of the simulations of the implemented algorithm is presented with two databases, Farsi and Germany and then compared with the outcomes of other algorithms with the same databases. Results indicate that the proposed algorithm could predict emotions of anger, joy, fears, boredom, disgust and sadness with good accuracy. This algorithm could be used in designing control systems and robot guidance. In addition, emotion recognition system could be utilized in psychology, medicine, and behavioral science and security applications such as polygraph.

In this research, modeling and vibrations analysis of the wind turbine blades and tower is studied. Modeling of each wind turbine blade is considered to be as elastic beam with rotational speed, and wind turbine tower is modeled as an Euler-Bernoulli elastic beam. Vibrations of blades and tower is considered in plane of rotation of blades. The equations of motion of the wind turbine are derived by Lagrangian approach and then numerically are solved. For the numerical solution, a limited number of elements are considered for the blades and the tower and then the natural frequencies of 2.5 MW SAMEN wind turbines is investigated by using its technical specifications. The effect of varying the length of the tower and the total mass of hub and nacelle on the natural frequencies is investigated, and the effect of varying the length of the blade on the natural frequencies of the blade is also investigated. Finally, the sensitivity analysis of the wind turbine natural frequencies with respect to different system parameters are presented.

In the present article, a global-local theory with three-dimensional elasticity corrections is employed to trace the local and instantaneous variations of various displacement and stress components of sandwich and composite plates. The governing equations are extracted based on Hamilton principle. One of the key features of the proposed theory is incorporation of the transverse flexibility of the core; a fact that is crucial when studying behaviors of thick or soft core sandwich plates. Since the transverse shear stresses are extracted based on the 3D elasticity theory, the interlaminar continuity condition of the transverse shear stresses is met. The verification results show that the presented finite element formulation is efficient and leads to accurate results, even for thick or soft core sandwich plates. A comprehensive parametric study is accomplished to evaluate effects of different parameters such as stiffness of the core material and boundary conditions. Finally, the obtained results verified by the available results existed in the literature.

In this study, dynamic instability and nonlinear behavior of sigmoidal-functionally Graded piezoelectric (S-FGP) plates resting on linear elastic foundation under parametric harmonic piezoelectric excitation is investigated. Based on Modified FSDT, applying Hamilton’s principle, the governing nonlinear coupled partial differential equations are derived. By considering six vibration modes, the Galerkin’s procedure is used to reduce the equations of motion to nonlinear Mathieu equations, and dynamic instability of the problem in absence/presence of the Rayleigh's proportional damping model and foundation is analyzed. In the absence of foundation, the validity of the modeling for analyzing the maximum nonlinear deflection and the modified shear correction factors are accomplished by comparing the results with those of the literature. It is shown that as the parameters of the foundation increase, the piezoelectric instability occurs at higher excitation frequencies and increasing the damping makes the region of the instability to be shrunk. By applying the perturbation method, steady-state response equations are derived and the parametric resonance of the system under the piezoelectric excitation is analyzed. Then, the conditions of existence and stability of trivial/nontrivial solutions are discussed. Moreover, the effects of the system parameters, including excitation frequency, amplitude of harmonic excitation voltage, foundation parameters and damping, on the nonlinear dynamics of the S-FGP plate are studied and it is shown that the presence of the damping/foundation has a considerable influence on the resonance characteristic curves.

Energy absorbents are very common in different industries. As can be inferred, they absorb energy when it is necessary in order to prevent possible damages, those could endanger sensitive components. In this study energy absorb er applicable in an automotive bumper system is investigated. It is focused on thin-walled tubular absorbents in axial crushing mode. In this kind of absorb er, tube’s wall buckles locally and deformation in form of sequential folds holds energy and absorbs counterpart external energy. One method to further control energy absorption is to introduce circumferential patterns on tube’s wall. This pattern can dictate the evolution of folds within crushing distance. Here, the effect of pattern’s parameter, like geometry, wave length and depth on energy absorbing behavior of aluminum thin-walled tubes is studied. Energy absorption in static axial crushing is simulated using Finite Element Method. Different pattern’s geometry, like linear, circular and sinusoidal patterns were generated and results were compared with plain tube, that with no pattern. The effect of introducing patterns on different energy absorption characteristics namely, first force pick, mean crushing force, crushing force efficiency, energy absorbed, specific energy absorbed and crushing mode are explored. Findings show that patterns are very influential on energy absorbing behavior of thin-walled tubes. Results show acceptable combination of pattern’s parameters in each set of pattern’s geometry; even though circular pattern yields more desirable outputs.

A wheelchair model has been designed to resist the turning over of the user by applying a spatial 3-RRS mechanism as the Seat on a standard electric wheelchair. The result is a self-balancing robotic wheelchair with the capability to cope with several road conditions. The 3-RRS platform model has been analyzed and then controlling parameters has been reached. By using the parameters two models of the Wheelchair has been mechanically, software and hardware designed, built and tested. To design and implement Robot controller for better mutual cooperation with environment and to better analyze environmental factors on stability, it is needed to build the robot and wheelchair models with Rapid Prototyping methods and correct problems and optimize it before mass production. Two types of wheels (two wheel wheelchair and continuous track) have been inserted. The wheel chair with continuous track showed good result on several road conditions including roll, pitch and combined conditions.