نشریه مهندسی مکانیک مدرس
سال چهاردهم شماره 1 (فروردین 1393)

Friction is an inevitable issue in most of mechanical servo systems. Friction has a counter-effect on the dynamic performance of servo mechanisms and needs to be considered in the design process. Particularly، in high-performance motion systems، friction can severely deteriorate performance and can cause tracking errors، longer settling time and limit cycles. In this paper، a new method is presented based on the adaptive fuzzy sliding mode control strategy for position control of mechanical systems. The first order dynamic LuGre model is used for the design of friction observer. Unlike previous papers، the control input and friction are applied to the system with non-equal gains. An adaptive law is employed for the estimation of the ratio between the gains of input and friction terms. Various uncertainties on parameters of friction also are considered and an appropriate control strategy is designed to tackle these uncertainties.

In rocket systems، the re-entry speed to atmosphere is very high which leads to compression of air molecules and appearance of strong bow shock waves in the leading edge; consequently، this yields aerodynamic heating. Using ablating-dispensing materials on the leading edge surfaces، it is important to accurately determine heat flux on these moving boundaries. Measuring heat flux directly is very difficult or impossible in some situations. In the present study، the online Kalman filtering is used to determine heat flux accurately. Since the heat flux is estimated in online (non-iterative) fashion، the optimum location of temperature sensors can be effectively determined. In addition، the results of this study can be used to design heat flux sensors. In this paper، the optimum locations of three temperature sensors are calculated on the basis that the disturbances occur due to burning of sensors are reduced. More robust solutions are obtained for heat flux on the ablating surfaces.

Buckling and vibration characteristics of thin symmetrically laminated elliptical composite plates under initial in-plane edge loads and resting on Winkler-type elastic foundation are presented based on the classical laminated plate theory. The governing equations are obtained from the variational approach and solved by the Ritz method. Extensive numerical data are provided for the first three natural frequencies as a function of in-plane load for various classical edge conditions (free، clamped and simply supported). Moreover، the effects of fiber orientation on the natural frequencies and buckling loads of laminated angle-ply plates with stacking sequence of [(β /-β / β /-β)]s، are studied for chosen foundation parameter. Also، selected deformation mode shapes are illustrated. The accuracy of calculations is checked by performing good convergence studies، and the correctness of results is established by comparison with the existing results in the literature as well as FEM data.

In the present paper، power transmission interaction of multilayered sound isolation panels consists of porous، solid materials and air gaps using Transfer Matrix Method (TMM) has been considered. Considering the theories related to acoustical behavior of multilayered panel lined with poroelastic materials، detail explanation of Transmission Loss (TL) of a panel via TMM has been presented. Calculation of TL for a specified panel via TMM has been compared to existed experimental data in the literature and excellent agreement is observed. Next، based on this verified model، a multi-objective optimization of multilayered panel has been conducted using NSGA-II to maximize TL of panel while the panel weight is kept to a minimum. Results of two-objective optimization reveals، if the designer target is to achieve a specific average TL in the frequency band of 10 to 500 Hz، for a panel with constant width، selecting a panel with lower layers (three layers) can bring lower weight. But، if a higher average TL in the same frequency band is desired، a panel with more layers (six layers) has much better conditions in terms of weight.

In the paper، a three-axis power transmission system is modeled mathematically and simulated by software. In mathematically method، a system consisting of three flexible shafts with different rotation axis which connected through two universal joints is investigated via a three degree-of-freedom model. The stability is analyzed by means of a monodromy matrix technique. This is verified by comparing the results with dynamic analytical software AdamsView simulation and the results of the previous research. Then، the effects of rotational velocity، non-aligned angles، shaft''s properties (stiffness and damping) on the stability are investigated. Finally، the stability charts constructed on various parameters is presented. It is observed that decreasing shaft stiffness and universal joint angle due to more stability، while decreasing shaft damping has the opposite effect.

Dynamic response of fully-clamped laminated plate subjected to small mass and low-velocity impact studied in this paper by using the suitable Algebraic Polynomials and Galerkin method. The first-order deformation theory as well as the displacement filed is used to solve the governing equations of the composite plate analytically. The interaction between the impactor and the target are considered in the impact analysis. This interaction is modeled with the help of a two degrees-of-freedom system، consisting of springs-masses. The results indicated that some of parameters like mass and velocity of the impactor in a constant impact energy level، mass of the plate (target)، increasing the length-to-width ratio of the plate (a/b ratio) and orientation of composite fibers of plate are important factors affecting the impact process and the design of structures.

In this paper an innovative vibration rotary tool was designed and manufactured. Vibration turning tool is a compound of turning rotary tool and ultrasonic assistant turning. In this tool، an ultrasonic wave generator with power equal to 20 KHz transducer that has a rotational motion during the process was used. For tool vibration، a stainless horn with resonance frequency equal to 20618 Hz، were designed and manufactured. Round insert with 10 millimeter diameter were used. One of the most important key points in this setup is that the simultaneous rotation and vibration has to be achieved. For rotational motion a motor power and a rack and pinion were used. Also a structure with ability to mount on turning machine were designed and manufactured. Cutting force and surface roughness for each experiment were measured and compared with data collected from conventional rotary tool on 7075 aluminum material. Results shows that ultrasonic vibration cause decreasing in cutting tools and surface roughness، tremendously.

In this study، an analytical solution is presented to calculate interlaminar stresses in long symmetric cross-ply composite laminates subjected to uniform axial strain and thermal loading. At first، the most general form of layerwise-based displacement field is extracted by a successive integration of elastic strain–displacement relations and imposing the physical restrictions based on deformation patterns of these laminates. The equilibrium equations are then derived by using the principle of minimum total potential energy and solved analytically in order to obtain three-dimensional stress field in the laminated plate. Finally، various numerical examples are investigated in order to validate the efficiency and accuracy of the layerwise theory in predicting the interlaminar stresses. For the assessment of the accuracy of the proposed method، the interlaminar stresses are also calculated within the framework of a 3D finite element analysis using the Abaqus software. The corresponding numerical results are in good agreement with those obtained through the layerwise theory. All results indicate that the presented approaches have a good prediction capability of interlaminar stresses in interior regions of the laminate and theirs high stress concentration near its free edges that can cause delamination failure.

This paper presents the experimental study on vibration characteristics of polymeric nanocomposites containing 1 weight percentage of mesoporous silica (MCM-41)، Hydroxy Apatite (HA)، the composite of MCM-41 and HA (MH) and carbon nanotube (CNT) as a fillers. Experimental results show that damping ratio and natural frequency increase in the neat PP، CNT/ PP، HA/ PP، MCM-41/ PP nanocomposites and MH/ PP hybrid nanocomposite specimens، respectively. In order to introduce the effect of foam agent in the vibration absorbing properties، foam agent is added to CNT/ PP and MH/ PP nanocomposits. The results show that foamed specimens have more damping capacity and lower natural frequency than unfoamed specimens. The maximum value of increasing the damping ratio and natural frequency of the MH/ PP hybrid nanocomposite than neat PP is 55. 02 % and 34. 05%، respectively. So، MH/ PP hybrid nanocomposite that is studied in this paper for the first time، can remove the reduction of unwanted vibrations of structures problems.

In this paper، multi-objective optimization of sandwich panels with open and prismatic core has been studied. Naming these panels is based on the number of corrugations (n) of the core. The panel is considered as a heat exchanger that is loaded under longitudinal loading simultaneously. Multi-objective particle swarm optimization (MOPSO) is used by considering weight and heat transfer index as objective function. Optimization is carried out so that the panel has minimum weight and maximum heat transfer index simultaneously، moreover it will not suffer from yielding and buckling in face and core plates. The results showed that two panels، i. e. n=1 and n=7 are very suitable in one-objective and two-objective optimizations. Also، maximum of heat transfer index obtained by a certain panel is nearly the same in various loadings. Pareto diagrams achieved out of two-objective optimization have two separate areas where in one area weight increase may cause an intense increase in heat transfer index and in another area this index remains almost constant. The diagrams are helpful in selecting suitable panel and its geometric dimensions based on significance of each objective functions. Comparing the results indicate efficiency of PSO method in one-objective and two-objective optimization of the panels.

Using of minimum quantity of lubricant in near dry machining is one the new method in machining processes that causes improvement of process. In this study، the role of near dry lubrication is investigated on tool wear in turning of Monel K500. The used tools are consisted of simple and viper ceramic tools. After preparation of process on lathe machine، the designed experiments are done. During the experiments force، surface roughness and tool wear are measured. The obtained results confirm that near dry lubrication causes the reduction of tool wear considerably. Also، viper ceramic tool has less tool wear rather than simple ceramic tool.

Single point incremental forming is a sheet metal forming process that has more flexibility than another methods. This process don''t require to die and could formed various shape white use the simple tool and CNC machine. In this paper the influence of process parameters on the forces and dimensional accuracy and thickness distribution in single point incremental forming is investigated. These parameters include the feed rate، tool rotation، vertical step، movement strategy of tool and lubrication. Beginning with the design and construction of the fixture and clamping it on the dynamometer and create of tool (tungsten carbide)، the preparation process was done on a CNC milling machine. Then، the experimental tests were carried out on Aluminum alloy sheets (Al-1200) with creation of pyramid frustum; after the measuring of force in different directions، the influence of parameters on the forming force was investigated. Also parts were measured with CMM devices and compared. The results showed that with increasing the feed rate، the vertical force decreases and with increasing tool rotation speed، horizontal force decreases. The use of lubricant، is effective on the improvement of process.

One of the fundamental problems of Electrical Discharge Machining (EDM) process is tool electrode wear. In this study، ultra fine grains (UFG) structure of pure copper was used to improve performance and also increase the electrical wear resistance of tool electrode. Equal Channel Angular Pressing (ECAP) was used to reduce the crystal size of pure copper. Samples were processed through ECAP die up to 8 passes، and then used as electrode in EDM process. The effect of electrodes grain size، discharge current، and machining time on the metal removal of the work piece and electrical wear of the electrodes were investigated. In addition، the microstructure، and electrical conductivity of copper tool electrodes were examined. By applying the ECAP on pure copper a fine، approximately 50-200 nm grain size، microstructure was obtained after 8 passes. The results show that for finer crystalline structure of copper electrodes، electrical wear decreases but material removal rate is somehow constant.

The near dry EDM process uses a mixture of a liquid and a gas as dielectric medium. In this study، near dry EDM process at three levels of discharge energy and with two brass and copper electrode was studied to investigate the effects of tool material on machining performance. Also، the Taguchi method of design of experiments technique was employed to study the effects of nonelectrical parameters such as tool rotational speed، liquid flow rate، gas pressure and also discharge energy on material removal rate (MRR)، electrode wear ratio (TWR) and surface roughness (SR) and also the analysis of variance (ANOVA) was employed to find the most important factors effecting MRR، TWR and SR. The results showed that copper electrode has higher MRR and lower TWR as compared to brass electrode. Also the analysis of main effect plots obtained by Taguchi method indicated that MRR and SR is enhanced by increasing water flow rate and discharge energy and also increasing gas pressure leads to lower TWR. The ANOVA results showed that discharge energy is the most important factor influencing MRR، TWR and SR.

The effect of bubbles on frictional drag reduction has been studied experimentally using a vertical Taylor-Couette system. Air bubbles are injected into water flow at the bottom of the system. The flow between cylinders is a fully turbulent flow and Taylor vortices are formed in annulus gap. In these experiments، the variations range of rotational Reynolds number is 5000<=Re_w<=70000. The variations of drag reduction in the presence of bubbles have been investigated by measuring the exerted torque on the inner cylinder. The results show that increasing rotational Reynolds number up to a certain amount leads to enhancement of bubbles effects on drag reduction while the effects are inversed for higher rotational Reynolds number. In this work، the acquired maximum drag reduction is about 5%.

In this study، the shrinkage behavior of knitted fabrics during drying is studied. To this end، a model is presented to predict the knitted fabric length changes during the drying process. In order to model the shrinkage behavior، a 1DOF model consisting of a mass، a linear spring and a linear dashpot was used. Considering that the fabric is wet، mass is time dependent and Three-order Straight Forward Expansion method is used to solve nonlinear equations of motion. The results of the model were compared with the experimental results of five samples with different courses density. The results show that the proposed model is capable to predict the length changes of the center of the mass during the process of drying and after that. Error rate is about ten percent for the samples with less Loop length. But by increasing the length of the loop، error rates increases.

This paper presents a research into the progress of modeling of N-viscoelastic robotic manipulators. The governing equations of the system is obtained by using Gibbs-Appell (G-A) formulation and Assumed Mode Method (AMM). When the beam is short in length direction، shear deformation is a factor that may have substantial effects on the dynamics of the system. So، in modeling the assumption of Timoshenko Beam Theory (TBT) and its associated mode shapes has been considered. Although considering the effects of damping in continuous systems makes the formulations more complex، two important damping mechanisms، namely، Kelvin-Voigt damping as internal damping and the viscous air damping as external damping have been considered. Finally، to validate the proposed formulation a comparative assessment between the results achieved from experiment and simulation is presented in time domain.

Analytical solution for the dynamic stability analysis of functionally graded piezoelectric materials (FGPM) circular plates has been presented based on Love-Kirchhoff hypothesis and the Sander’s non-linear strain-displacement relation. The FGPM plate assumed to be gradded across the thickness. The material properties of the FGPM plate assumed to vary continuously through the thickness of the plate according to a power law distribution of the volume fraction of the constituent materials. The plates are subjected to a radial loading and electric field in the normal direction. Bolotin’s method has been employed to obtain the dynamic instability regions. The effect of plate parameters such as thickness–radius ratios، power index، as well as electric field and state loads on instability behavior of the plate is comprehensively investigated. The functionally graded composite material plays a significant role in changing the unstable regions and the buckling loads.

In this research، grey cast iron scraps were recycled into powders and were then used in combination with iron powder for producing iron based powder metallurgy parts. Design of experiments was conducted by response surface method for both the green and sintered parts. For the green properties، the parameters cast iron powder percentage and compaction pressure، and for the sintered parts، the mentioned parameters in addition to sintering temperature and sintering time were selected each in five levels as the input process parameters. Transverse rupture strength and elastic modulus were measured as the responses. Regression analysis and analysis of variance were used to investigate the effect of input parameters، develop the mathematical models and evaluate the validity of the models. Scanning electron microscopy and optical microscopy micrographs were provided to better understanding. The obtained results، in addition to determine the effects of the input parameters، demonstrated the adequate mechanical properties of the produced parts in industrial scales and the validity of the proposed models. Also، the proposed method demonstrated its good capability for estimation of elastic modulus of powder metallurgy parts.

Heat pipe is an effective device for heat transferring. Using nanofluid as working fluid can significantly increase heat pipe thermal performance. But rate of the performance improvement, is dependent on parameters of the suspended nanoparticles in nanofluid. In this article, for the first time by considering nanoparticle volume fractions and diameters as design variables and the difference between the wall temperature of evaporator and condenser and liquid pressure drop as objective functions, the heat pipe performance has optimized. The used heat pipe is a cylindrical heat pipe with nanofluid as working fluid. Heat pipe thermal performance while using nanofluid has modeled by CFD method and then GEvoM has used to relate between design variables and objective functions. Using the modified NSGAII approach, pareto front has plotted and the values of recommended optimum points has obtained by mapping method. Recommended design points unveil interesting and important optimal design principles that would not have been obtained without the use of a multi-objective optimization approach.

A buoyant under influence of sea waves and wind excitation experiences unwanted linear and rotational motions. These motions may affect proper performance of high precision equipment placed on the buoyant. Stable platform is one of the solutions employed for decreasing amplitude of the sea induced motions. Design of an optimal fuzzy controller for a tripod stable platform installed on the deck of a medium boat is considered in this paper. For this purpose, a fuzzy controller is proposed for the stable platform control. Furthermore, a 3D virtual model of the boat and the stable platform is developed and the fuzzy controller is applied to the virtual prototype using the co-simulation technique of MATLAB and ADAMS software. The fuzzy controller is then optimized using the genetic algorithm (GA). Moreover, a linear quadratic regulator (LQR) is designed for the stable platform control. The controllers are then applied to the virtual prototype and their performance in the presence of sea wave excitations is examined. Simulation results reveal that the tripod stable platform controlled with the optimal fuzzy controller can reduce pitch and roll motions up to 90 percent and reduce heave motion up to 55 percent.

This paper presents the first and third order shear deformation plate theory and von Karman theories to solve Thermo-elastic problems of functionally graded hollow rotating disk. The material properties of the disk are assumed to be graded in the direction of the thickness by a power law distribution of volume fractions of the constituents. New set of equilibrium equations with small and large deflections are developed. Using small deflection theory an exact solution for displacement field is given. Solutions are obtained in series form in case of large deflection. Numerical results are presented for various percentages of ceramic-metal volume fractions and have been compared with those obtained using first-and third-order shear deformation plate theories. Also the results are verified with ABAQUS soft, simulink method and the known data in the literature.

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.

Vibration control of large flexible structures in new dynamic systems has significantly encountered with many challenges. In this area, there are several approaches of vibration control implemented on complicated dynamic systems in which the change of vibrational characteristics with the time of process leads to performance violation. In this paper, regarding the estimation of undesired vibration frequency of a flexible structure, input control of the dynamic system is reconstructed. In this regards, the input of the dynamic system is made to minimize the magnitude of the vibration. This strategy in which the control input is constructed by means of undesired vibration frequencies is similar to use of anti-viruses in medicinal approaches. The proposed control strategy is implemented on yaw channel of a flexible sounding rocket in order to reduce the destructive effects of bending vibration. The system responses show the effects of the vibration on the yaw channel of the system are significantly decreased.

This paper presents an experimental study on the mold design and the effect of processing parameters on the expansion of foam injection molded parts. Limitation in foam expansion is a primary challenge in foam injection molding process. In this study a novel approach in mold design is introduced to take advantages of concepts such as counter-pressure and mold opening to further extend the expansion range. A modular sheet mold with a rectangular cavity and a fan gate was designed and manufactured. The mold includes a main cavity, the thickness of which could be varied, connected to an overflow channel via a secondary gate, the size of which was also varied in this research. The investigated parameters were part thickness, secondary gate width. Full factorial test experiments were carried out in this research work. The results indicated the high effectiveness of the proposed approach in further reducing the foamed part weight. For the parts with a larger thickness, a noticeable decrease in bulk density and an increase in cell population density along with an improvement in cellular structure uniformity were observed.