Showing 11 results for Amplitude
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Volume 12, Issue 4 (11-2012)
Abstract
Abstract- Low frequencies vibration is known as a method for stress relieving of metals. This paper shows that the high frequency vibration (ultrasonic) is also a promising method for stress relieving. In this paper the effect of parameters including stress relieving time, vibration amplitude, grain size and pre-load on samples are investigated. In order to evaluate the residual stress before and after ultrasonic relieving process Almen test was used. The samples were made according to Almen standard and after heat treatment, were shot peened so that, the compressive and tensional residual stress induced into the samples, then the stress relieved by means of ultrasonic vibration. Results show that the residual stress has decreased about 46 percent for coarse grain samples and 27 percent for fine grain samples. Also it was found that the most effective factor on the stress relieving rate is the grain size and the pre-load has the least effect.
Saeed Shiri, Mojtaba Yazdani, Mohammad Pourgol Mohammad,
Volume 14, Issue 14 (3-2015)
Abstract
Nowadays, composite materials are used in different applications. Some of these applications involve components subject to cyclic loading. Fatigue is the dominant failure mechanism for structures under this type of loading. Hence, proper prediction of fatigue life is essential for safe design and operation of structures, maintenance, repair and replacement of components. Many of the existing models in this field have not assessed the degradation of material properties such as stiffness and strength during fatigue damage. In this paper, a stiffness-based model is initially evaluated for fatigue damage analysis of composite structures. The model is validated with two sets of experimental data. A residual strength model is coupled to the choice model and a modified model is developed. Then, residual fatigue life of fiber reinforced polymeric composites is predicted for three sets of experimental data under two-stage loading. The results demonstrate that the proposed model has an improvement on accuracy in the estimation of residual fatigue lives. For better evaluation of the developed model, experimental results and some existing models are compared with the present study predictions. It is concluded that in most cases, the predicted values by the proposed model is closer to experimental values in comparison with other models.
Mohammad Hasan Javareshkian, Amir Baghri, Ali Esmaeli, Abdolmajid Zamanifard,
Volume 14, Issue 16 (3-2015)
Abstract
In this research, the plunging motion of an airfoil by a numerical method based on finite volume in different Reynolds numbers is simulated and the thickness effect, amplitude and reduced frequency on the aerodynamic coefficients are investigated. In this process, SIMPLEC algorithm, implicit solver, high order scheme and dynamic mesh method is used in unsteady simulation and the flow is supposed viscous, incompressible and laminar. Simulations are in three Reynolds 1000, 11000 and 50000, respectively, in accordance with the flight of the insects, small birds and pigeons are done in two amplitudes and three reduced frequencies. The simulation results are compared with published data to confirm the validity of research. This comparison shows comprisable agreement. Pressure distribution and Vortex shedding around airfoils show that the thickness of the airfoils delays vortex shedding and changes time-averaged thrust coefficient. Reduced frequency and amplitude of oscillation are two important parameters in this simulation, but the reduce frequency is more effective than amplitude. The response surface methodology (RSM) was used to optimize the plunging airfoil. Optimization shows that airfoil with 0.29% thickness, 3.08 reduced frequency and 0.5 dimensionless oscillating amplitude produce maximum trust coefficient.
Mohammad Mahdi Abootorabi Zarchi, Mohammad Reza Razfar, Amir Abdullah,
Volume 15, Issue 5 (7-2015)
Abstract
Reduction of cutting force in a machining process offers several advantages including increase in tool life, and improvement in the quality of the machined surface. One the new techniques for reducing cutting force relates to ultrasonic vibration assisted machining. In the present paper, one-dimensional ultrasonic vibration-assisted side milling process of Al7022 aluminum alloy has been studied. In order to investigate the effect of cutting speed, feed rate, radial depth of cut, and vibration amplitude on three cutting force components and their resultant, a special experimental setup has been designed and established which applies one dimensional ultrasonic vibration to work piece. Applying the ultrasonic vibrations on milling process, affects mostly on feed component of cutting force which is unidirectional with the work piece vibration, and decreases it by 33.5% in average. Decrease in cutting speed and increase in vibration amplitude, results to increase the separation of tool and work piece from each other in a portion of each vibration cycle, and larger decrease of the feed force. The average decrease of the resultant cutting force in ultrasonic-assisted milling process is 10.8%.
Ali Jafargholi, Hassan Karimi, Seyed Reza Mousavi Firdeh,
Volume 15, Issue 7 (9-2015)
Abstract
In this paper, the algorithms for low frequency non-linear dynamic modeling and frequency model determining of LPRE is presented. Considerations that facilitate modeling and debugging processes is also investigated. Using of defined algorithms and also presented considerations is considered for a liquid propellant engine with oxidizer and fuel tanks. Describing equations of LPE is classified as many subsystems. Simulation is done in the SIMULINK environment of MATLAB software. Each simulated subsystem show one or more physical subsystem that their interaction is determined in LPE configuration modeling results demonstrate excellent dynamic behavior of LPE. Then SISO engine model in frequency domain is outcome based on resulted non-linear model of LPE using describing function. Frequency response code is developed for derivation of engine frequency model. Adequate frequency interval and input or excited signal amplitude are selected regarding LPE operating modes. In next step, frequency model is derived by stimulation of non-linear dynamic model with sinusoidal inputs includes considered amplitudes and frequencies. This subject is done by integration and engine output obtaining and Furrier integrals calculation at time that output get to steady state. Then system gains and phases calculation is done at the various amplitudes and frequencies for obtaining describing functions models. Frequency model evaluation characterized that can provide more efficient, simple and adequate conditions for analysis of LPE dynamics.
Arash Bakhtiari, Mostafa Zeinoddini, Majid Ehteshami, Vahid Tamimi,
Volume 16, Issue 10 (1-2017)
Abstract
In recent decades, experimental studies of the vortex-induced vibration (VIV) became one of the interesting fields of science. However, variety of assumptions and methods of experiments have led to different results in various researches. Several parameters such as mass ratio, aspect ratio, degrees of freedom, and boundary conditions affect the VIV response of a simple circular cylinder. The current paper reports and discusses the results of in-water VIV experiments on an elastically mounted rigid cylinder with various types of end conditions. This paper focusses on the effects of the end condition by attaching an endplate to a circular cylinder and the results compared with those from a cylinder with no endplate. The Reynolds number ranges from 5.8×103 to 6.6×104. Experimental setup have also been compared and verified with some classical results of VIV. Results of current study was favorably compatible with previous researchers’ results.
The experimental results show that, the end condition noticeably changes the VIV amplitude especially in the lock-in area. Moreover, non-dimensional amplitudes shift to the higher reduced velocities when the endplate is removed. In the frequency responses, the cylinder with no endplate has lower quantities rather than the cylinder with an attached endplate. Evaluation of lift force coefficients also shows a similar pattern of effects on the non-dimensional amplitude. Consequently, the excitation of the structure in the lock-in region increases, when the endplate from the cylinder’s end is removed.
Amir Hosein Taherian, Ehsan Barati,
Volume 17, Issue 11 (1-2018)
Abstract
Fatigue is one of the most important phenomena in the life determination of parts in various industries. The life determination of the part through the test procedures, due to the real loading (spectral loading) is very complicated. Thus, it is necessary to equalize the fatigue real cycle to test cycles applicable in the laboratory. In this paper, by using the available equations in equalization of fatigue cycles, some equations have been studied for the load spectrum. Then the deviation percentage of these equations has been investigated for two very applicable materials in aviation industries (Aluminum 7075-T6 and Steel 4130) by means of block loading spectrum. It has been observed that the errors is very large and not acceptable in some situations. After that, in order to decrease the errors, a new method has been proposed to determine the number of equivalent cycles in fatigue test, considering equalization of the real load and converting it to an applicable load in the laboratory. In this equalization process, constant amplitude loading was obtained for a sample loading block for each of the mentioned materials in such a way that the rate of fatigue damage to be equal to the real loading. Finally, some standard specimens have been tested by fatigue loading and has been observed that the new proposed procedure is capable to predict the fatigue life. The maximum error is equal to 5.5 per cent.
M. Mousazadeh, K. Jahani, S.s. Samadani Aghdam,
Volume 19, Issue 9 (9-2019)
Abstract
In this paper, the effects of particles size of Magnetorheological Carbonyl iron powder on damping force and energy dissipation capacity for a Magnetorheological double ended type damper is investigated experimentally. Despite of the considerable researches on the effects of particles size on the viscosity of Magnetorheological fluids, sedimentation of fluids and electromagnetic field intensity in damper, there is no a published work about the effects of iron particles size on the damping force amplitude and energy dissipation capacity of double-ended Magnetorheological damper. Therefore, in the present research, two different Magnetorheological fluids were prepared with the same volumetric percentage of % 35 from two different sizes of Iron particles i.e. 40 µm and 63µm and filled into a double ended type damper. The double-ended damper had three electric coils and was tested in different frequencies, different electric currents and 15 mm displacement stroke. The effects of Magnetorheological fluid particles on produced damping force and energy dissipation capacity were analyzed by extracting force-displacement and force-time curves from experiments. The results showed that the maximum amplitude of damping force is increased with increasing the applied electric current on the damper and the amount of this force for fluid with 63µm particles size is slightly higher than that for the fluid with 40µm particles size. However, the energy dissipation capacity of the investigated damper in all excitation frequencies with the all applied electrical currents for fluid with 63µm particles size was considerably higher than that for fluid with 40µm particles size.
S. Shirzadi, E. Badri-Kouhi , S. Adibnazari ,
Volume 19, Issue 10 (10-2019)
Abstract
Turbine blades are exposed to mechanical and thermal stresses due to their operation in critical conditions that lead to various damages such as fatigue and wear. These factors reduce the blades life cycle by accelerating the cracking process. In this paper, the effects of three geometric parameters including the contact length, the contact angle, and the surface friction coefficient on relative slip amplitude and contact pressure values in the turbine blade root were investigated using a two-dimensional finite element model. Comparing the results of the analysis with the actual blade damages by use of scanning electron microscopy shows acceptable consistency between predicted damage site and the actual blade damages. The results of the blade analysis indicate that by moving from the top of the contact edge to the bottom, the contact pressure increases gradually and its maximum occurs near the lower edge of the contact. According to the results, the prescribed increments in the coefficient of friction, the contact angle, and the length of contact, respectively decrease the slip amplitude by 26%, 19%, and 10% and also decrease the contact pressures by 35%, 15%, and 5%. In addition, increasing contact angle and coefficient of friction increase the opening region length at the upper edge on both sides of the blade root. While increasing the contact length has no considerable effect on the length of this region.
S. Ardeshiri, S.h. Mousavizadegan, S. Kheradmad,
Volume 20, Issue 1 (1-2020)
Abstract
Hydrodynamic coefficients have primary importance in determining the maneuvering characteristic of a marine vehicle. The use of computational fluid dynamics (CFD) methods due to the lower cost of these methods compared to laboratory methods in determination of hydrodynamic coefficients have always been considered. Validation of the CFD methods and enhancing their accuracy are the major topics in the application of CFD for the underwater vehicle. The hydrodynamic coefficients of an elliptical-shape underwater vehicle and the effect of motion amplitude and velocity parameters have been investigated by the STAR-CCM+ software and through dynamic overset meshing. The results of the simulations have been compared and analyzed and the error reduction criteria have been presented considering the amplitude dimensions and velocity values in the simulation. In addition, an innovative method for simultaneous calculation of hydrodynamic coefficients of surge motion has been presented which shows good accuracy by comparing the results with theoretical and laboratory data.
Razieh Abedini, Faezeh Najafi, Mohammad Passandideh-Fard, Amir Abdolah, Ali Faezian,
Volume 23, Issue 8 (8-2023)
Abstract
In this article, the numerical and experimental investigation of the effect of ultrasonic waves on the heat transfer rate with an increase of the wave amplitude is discussed. Numerical modeling determines the possibility of the investigation of the ultrasonic wave’s effects on fluid flow distribution and heat transfer. For this purpose, a cylindrical tank is considered inside which a spiral heater is placed at a fixed height in the water. In addition, ultrasonic transducers are considered as circular plates under the bottom of the tank. In order to simulate, the ANSYS Fluent software is used and the modeling is accomplished in two stages before and after ultrasonic excitation. To validate the numerical results, they are compared with those of the experiments. For this purpose, an experimental setup is prepared witch consists two coaxial cylinders, a spiral heater kept at a certain height in the water, and five transducers attached to the bottom of the tank. Both experimental and numerical results show that the convection heat transfer coefficient increases with the use of ultrasonic waves with a discrepancy of nearly 4% between the results. By increasing the heat transfer coefficient, the heater surface temperature decreases. The discrepancy between the measured and calculated temperature is about 5%. The velocity and temperature distributions obtained from the numerical results show that using ultrasonic waves enhance the fluid flow mixing which in turn increases the convection heat transfer. The higher the amplitude of the ultrasonic wave, the higher the heat transfer coefficient will result.
