eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
164
171
72441
Simulation of Strap-On Boosters Separation in the Atmosphere
Mostafa Jafari
mostafa.jafari.um@gmail.com
1
Hamid Parhizkar
hparhiz@yahoo.com
2
Sadjad Ghasemlu
sg1352_3@yahoo.com
3
, Shahid Beheshti University
Department of Aerospace Engineering, Amirkabir University
Department of Aerospace Engineering, Amirkabir University
A numerical dynamic-aerodynamic interface for simulating the separation dynamics of constrained strap-on boosters jettisoned in the atmosphere is presented. A 6-DOF multi body dynamic solver ،using Constraint Force Equation Methodology is coupled with a numerical time dependent Euler flow solver. An automatic dynamic mesh updating procedure is employed using smoothing and local remeshing technique in respect of bodies motion during separation. This interface can simulate multi body separation problems such as strap-on boosters separation as a result of full separation mechanisms like springs, thrusters, joints and so on, interaction with aerodynamic effects .The flow solver is validated by the Titan-IV launch vehicle experimental data. The full separation integration is used for a typical launch vehicle with two strap-on boosters using spring ejector mechanism and spherical constraint joints acting in the dense atmosphere. Hence the aim of presented interface is to facilitate integration of complicated separation mechanisms simulation with a full numerical CFD aerodynamic solver.
https://www.ije.ir/article_72441_ed7b4e94eba4514b12231b9911c7d495.pdf
numerical dynamic
aerodynamic interface
strap
on boosters separation
6
DOF multi body dynamic solver
Constraint Force Equation Methodology
numerical time dependent Euler flow solver
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
172
179
72442
Estimation of LOS Rates for Target Tracking Problems using EKF and UKF Algorithms- a Comparative Study
Saeid Niazi
s_niazi@sbu.ac.ir
1
aerospace engineering, shahid beheshti university
One of the most important problem in target tracking is Line Of Sight (LOS) rate estimation for using from PN (proportional navigation) guidance law. This paper deals on estimation of position and LOS rates of target with respect to the pursuer from available noisy RF seeker and tracker measurements. Due to many important for exact estimation on tracking problems must target position and Line Of Sight rates estimated with least error rather than actual values. In this paper extended Kalman filter (EKF) and unscented Kalman filter (UKF) algorithms are used for estimation of target position in three-dimensional (3-D) and LOS rates in elevation and azimuth for seekers and trackers. For comparison of algorithms, model of the system simulated using MATLAB and many tests were carried out. Simulation experiments show that the efficiency of EKF due to least RMSE has better performance. However, the performance of EKF algorithm has been dramatically decreased when initializations (initial state assumption) are not near to real values, which in this condition UKF method provides a more accurate approximation. Numerical results from simulations show that the UKF is robust against uncertainties and has better state estimation accuracy. Therefore, UKF algorithm is appropriate, and it can run on target tracking systems
https://www.ije.ir/article_72442_133ce7f8b6efc89d78002660c021b880.pdf
Estimation
gimbal seeker
line of sight rate
optimal filtering
Extended Kalman Filter
Unscented Kalman filter
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
180
189
72443
Frictional Strain Hardening-softening in Experimental and Numerical Investigation of Arching Effect
Alireza Abbasnejad
abbasnejad_ar@yahoo.com
1
G Moradi
gmoradi@tabrizu.ac.ir
2
Civil Engineering, University of Tabriz
Civil Engineering, University of Tabriz
In the current paper the results of a numerical simulation that were verified by a well instrumented experimental procedure for studying the arching effect over a trapdoor in sand is presented. To simulate this phenomenon with continuum mechanics, the experimental procedure is modeled in ABAQUS code using stress dependent hardening in elastic state and plastic strain dependent frictional hardening-softening with Mohr Coulomb failure criterion applying user sub-routine. The apparatus comprises concentric circular trapdoors with different diameters that can yield downward while stresses and deformations are recorded simultaneously. As the trapdoor starts to yield, the whole soil mass deforms elastically. However, after an immediate specified displacement, depending on the diameter of the trapdoor, the soil mass behaves plastically. This behavior of sand occurs due to the flow phenomenon and continues until the stress on trapdoor is minimized. Then the failure process develops in sand and the measured stress on the trapdoor shows an ascending trend. This indicates gradual separation of the yielding mass from the whole soil body. Finally, the flow process leads to establish a stable vault of sand called arching mechanism or progressive collapse of the soil body.
https://www.ije.ir/article_72443_1f580b2858d122cff4ef29e14fc14986.pdf
Arching Effect
Modified Mohr Coulomb
Frictional hardening
softening
ABAQUS
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
190
197
72444
Approximate Incremental Dynamic Analysis Using Reduction of Ground Motion Records
Hessam Baharmast
hessam.baharmast@yahoo.com
1
Sanaz Razmyan
s.razmyan@qhttc.com
2
Azad - Yazdani
a.yazdani@uok.ac.ir
3
Engineering, University of Kurdistan
Mathematics, Islamic Azad University, Firozkoh Branch
Engineering, University of Kurdistan
Incremental dynamic analysis (IDA) requires the analysis of the non-linear response history of a structure for an ensemble of ground motions, each scaled to multiple levels of intensity and selected to cover the entire range of structural response. Recognizing that IDA of practical structures is computationally demanding, an approximate procedure based on the reduction of the number of ground motions is developed. A methodology based on data envelopment analysis (DEA), mathematical programming that can handle large numbers of variables and relations, is proposed to reduce the number of ground motions needed for the production of a reliable median IDA curve. The IDA curves computed by the exact and approximate procedures for two different sets of ground motions for the 9-storey SAC-Los Angeles building, are presented. The results demonstrate that the approximate procedure, which uses a limited number of input ground motions, is accurate enough for practical application in building evaluation and design.
https://www.ije.ir/article_72444_d1aaa1bdfce2b5df31f96b7a1d307947.pdf
Incremental Dynamic Analysis
Data Envelopment Analysis
Ranking
Ground motion
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
198
204
72445
Dynamic Obstacle Avoidance by Distributed Algorithm based on Reinforcement Learning (RESEARCH NOTE)
Hamidreza Koohi
h.r.koohi@semnan.ac.ir
1
Electrical and computer, semnan univer
In this paper we focus on the application of reinforcement learning to obstacle avoidance in dynamic Environments in wireless sensor networks. A distributed algorithm based on reinforcement learning is developed for sensor networks to guide mobile robot through the dynamic obstacles. The sensor network models the danger of the area under coverage as obstacles, and has the property of adoption of itself against possible changes. The proposed protocol can integrate the reward computation of the sensors with information of the intended place of robot so that it guides the robot step by step through the sensor network by choosing the safest path in dangerous zones. Simulation results show that the mobile robot can get to the target point without colliding with any obstacle after a period of learning.Also we discussed about time propagation between obstacle, goal, and mobile robot information. Experimental results show that our proposed method has the ability of fast adoption in real applications in wireless sensor networks.
https://www.ije.ir/article_72445_720271f9ec6a8633fb60532d77a46bc1.pdf
Reinforcement Learning
Sensor Network
Dynamic Obstacle Avoidance
Robot Navigation
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
205
213
72446
A Novel Objective Function for Directional Overcurrent Relays Coordination
Seyyed Hadi Mousavi Motlagh
hadi_mousavi66@yahoo.com
1
protection and control group, zanjan regional electric company
Directional overcurrent relays (DOCRs) are widely used to protect power systems. For optimal coordination of DOCRs, several techniques have been proposed to solve this problem. A common way of optimal coordination of DOCRs is using evolutionary algorithms such as genetic algorithm (GA). In this paper, a novel strategy for DOCRs coordination is proposed. In the proposed strategy, a new objective function (OF) is introduced. The proposed objective function can removed mis-coordination between paired relays and can result in better coordination. Proposed OF is applied to 6-bus and 30-bus sample networks.
https://www.ije.ir/article_72446_66dfc53d64ed7ff0016c67702e404271.pdf
Relay Coordination
Artificial Algorithms
Objective Function
Relay TMSs
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
214
223
72447
A New Balancing and Ranking Method based on Hesitant Fuzzy Sets for Solving Decision-making Problems under Uncertainty
H. Gitinavard
hossein.gitinavard@yahoo.com
1
S.M. Mousavi
mousavi.sme@gmail.com
2
School of Industrial Engineering , Iran University of Science and Technology
Industrial Engineering Department, Faculty of Engineering, Shahed University
The purpose of this paper is to extend a new balancing and ranking method to handle uncertainty for a multiple attribute analysis under a hesitant fuzzy environment. The presented hesitant fuzzy balancing and ranking (HF-BR) method does not require attributes’ weights through the process of multiple attribute decision making (MADM) under hesitant conditions. For the rating of possible alternatives, firstly, they are defined as hesitant fuzzy terms and then converted into hesitant fuzzy sets. Second, an outranking matrix indicates that a possible alternative overcomes the other alternatives regarding to each chosen attribute. Third, the outranking matrix is triangularized; this means that we prepare provisional order of possible alternatives or implicit preordering under hesitant conditions. Eventually, the empirical order of alternatives goes through variant operations of balancing and screening that needs continuous application of a balancing axiom to the advantages–disadvantages table. It links incompatible attributes with pair-wise comparisons of the possible alternatives for the multiple attribute analysis. Finally, we present an application example for the supplier selection to show the applicability and feasibility of the proposed HF-BR method in the hesitant fuzzy setting.
https://www.ije.ir/article_72447_36ba42180be0be9d1c03f8bd2b9a3960.pdf
Ranking and Balancing Method
Multiple Attribute Decision Making
Advantage and Disadvantage Matrix
Outranking Matrix
Hesitant Fuzzy Set
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
224
233
72448
Estimating the Time of a Step Change in Gamma Regression Profiles Using MLE Approach
Fatemeh Sogandi
f.sogandy@gmail.com
1
Industrial Engineering, Shahed university
Sometimes the quality of a process or product is described by a functional relationship between a response variable and one or more explanatory variables referred to as profile. In most researches in this area the response variable is assumed to be normally distributed; however, occasionally in certain applications, the normality assumption is violated. In these cases the Generalized Linear Models (GLM) such as Gamma regression models are used to characterize the profile. Also, in statistical process control finding the real time of change in process, called as change point, is necessary because it leads to saving time and cost in finding assignable cause(s). Therefore, in this paper we consider Gamma regression profile and use maximum likelihood to estimate the real time of a step change in Phase II. We evaluate accuracy and precision of the proposed change point estimator by simulation. The results show the proposed change point estimator is effective in estimating the real time of step shifts in the process parameters of Gamma regression profiles. Also, a confidence set for the process change point based on the logarithm of the likelihood function is presented. Finally, the performance of the estimator is illustrated through a numerical example.
https://www.ije.ir/article_72448_4b01a0ceb9fbe2e79465b146c0f07ec5.pdf
Gamma Regression Profile
Change Point Estimation
Maximum Likelihood Estimator (MLE)
Statistical Process Control (SPC)
Phase II
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
234
242
72449
Applications of Impedance Plane and Magnetic Differential Permeability in Microstructural Characterization of AISI D2 Tool Steel
Mehrdad Kashefi
m-kashefi@um.ac.ir
1
Saeed Kahrobaee
saeed.kahrobaee@yahoo.com
2
Materials and Metallurgical Engineering, Ferdowsi University of Mashhad
Materials and Metallurgical Engineering, Ferdowsi University of Mashad
Two nondestructive electromagnetic/magnetic techniques including hysteresis loop and eddy current methodologies have been used to characterize microstructural changes of AISI D2 cold work tool steel as a result of quench and tempering treatments. To measure the fraction retained austenite in quenched microstructure, six specimens were austenitized in the range of 1000-1130 °C. Samples austenitized at 1080 °C were also tempered in the range of 200-650 °C for characterization by eddy current and magnetic hysteresis loop outputs, nondestructively. Impedance point movement and maximum differential permeability were measured as a function of austenitizing/tempering temperature to characterize the microstructural features. The study shows that there are good correlations between microstructural variations detected by destructive methods (hardness, XRD and microscopic observation) and outputs of the nondestructive techniques.
https://www.ije.ir/article_72449_6938c5c2b1e9c107f0a966e20b7a49a3.pdf
Nondestructive method
Microstructural changes
Impedance point
Magnetic differential permeability
Cold work tool steel
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
243
250
72450
Dynamic Behavior Analysis of a Planar Four-bar Linkage with Multiple Clearances Joint
seyyed mojtaba varedi koulaei
varedi@stu.nit.ac.ir
1
Morteza Dardel
dardel@nit.ac.ir
2
Department of Mechanical Engineering, Babol University of Technology
, Babol Noshirvani university of technology
In practice, clearances in the joints are inevitable due to tolerances, and defects arising from design and manufacturing. In the presence of clearance at a joint, a mechanism gains some additional, uncontrollable degrees of freedom which are the source of error. Moreover, joints undergo wear and backlashes and so cannot be used in precision mechanisms. In this study, the dynamic behaviour of a planar mechanism with revolute joints, in the presence of clearances is investigated. A continuous contact force model, based on the elastic Hertz theory together with a dissipative term, is used to evaluate the contact forces. Moreover, using a new contact model the dynamic characteristics of planar mechanical system with multiple revolute joints in the presence of clearance are analyzed. Numerical results for four-bar linkage with one, two and three revolute clearance joints are presented and compared.
https://www.ije.ir/article_72450_6a213c6c4f31431672c4c318550a3c5b.pdf
Dynamic
four
bar linkage
clearance
revolute joint
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
251
260
72451
An Experimental and Theoretical Study of the Effects of Excess Air Ratio and Waste Gate Opening Pressure Threshold on Nox Emission and Performance in a Turbocharged CNG SI Engine
Shahaboddin kharazmi
kharazmi@mech.sharif.edu
1
Center of Excellence for energy convers,Mech. dept, Sharif Univ. of Technology
Turbocharged CNG engines produce high NOx emission due to the fuel type and high combustion temperature. In this research, the effects of lean-burn and waste gate opening pressure threshold on NOx emission are studied theoretically and experimentally at WOT condition as well as 13-mode ECE-R49 test cycle. A code is developed in MATLAB environment for predicting engine NOx and the results are validated with the research experiments. Simulations show that NOx increases by increase of excess air ratio and reaches at most to 2486ppm at excess air ratio of 1.1 and then decreases. It is also experimentally found that changing waste gate opening pressure threshold from 165mmHg to 200 and 265mmHg decreases total bsNOx at a rate of 6% and 12% respectively. Increase of the threshold to 323mmHg increases total bsNOx. Therefore, to minimize the cycle bsNOx, the threshold of 265mmHg is the optimum threshold for the engine between the four pressure thresholds experimented.
https://www.ije.ir/article_72451_b6b5b5a4445db0c9e58cef5f58f4fe37.pdf
Turbocharged CNG SI engine
NOx emission
ECE
R49 test cycle
Lean
Burn
waste gated turbocharger
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
261
269
72452
Simulation Study: The Role of Area to Volume Ratio and Key Parameters in Cylindrical Micro Combustors
Denny Widhiyanuriawan
denny_malang2000@yahoo.com
1
Slamet Wahyudi
slamet_w72@yahoo.co.id
2
Sudjito Soeparman
sudjitospn@yahoo.com
3
Wirawan Wirawan
wira.polmal@gmail.com
4
Mechanical Engineering, Brawijaya University
Mechanical Engineering, Brawijaya University
Mechanical Engineering, Brawijaya University
Mechainical Engineering, Politeknik Negeri Malang (POLINEMA), Indonesia, http://www.polinema.ac.id
Abstract A new micro combustion concept is described in this work by introducing a new terminology in the micro combustion. The effects of Area to Volume Ratio (AVR) of the micro-combustors were studied to find the best performance of designed micro-combustors. In order to test the feasibility of the designed micro combustors before the actual experiment is conducted, simulation work was performed. There are three key parameters involved in the current study: Area to Volume Ratio (AVR), Flow Velocity of the mixture (U), and Fuel-Air Equivalence Ration (ɸ). Main results of this experiment are images of temperature contour, graphs of temperature distribution profile, and graphs of mean temperature profile. This study found there is a specific range of mixture flow velocity (0.50 – 0.56 m/sec) which result a high and uniform temperature distribution as well as its best mean temperature of micro combustion process. The simulation work could also localized the specific range of AVR-value (1.40 – 2.01) which require further investigation in the future.
https://www.ije.ir/article_72452_13b9ccfb5bad1ab8caf1706f90e8998b.pdf
Premixed micro
Combustion
Micro Combustor
Area to volume ratio
temperature distribution
Numeric simulation
Premixed flame
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
270
276
72453
Application of Thau Observer for Fault Detection of Micro Parallel Plate Capacitor Subjected to Nonlinear Electrostatic Force
Ghader rezazadeh
g.rezazadeh@urmia.ac.ir
1
Hamed Mobki
hamedmobki@live.com
2
mechanical engineering, Urmia university
Mecanical Engineering, Tabriz University
This paper investigates the fault detection of a micro parallel plate capacitor subjected to nonlinear electrostatic force. For this end Thau observer, which has good ability in fault detection of nonlinear system has been presented and governing nonlinear dynamic equation of the capacitor has been presented. Upper and lower threshold for fault detection have been obtained. The robustness of the observer to noise and uncertainty and sensitivity to fault has been investigated. Finally, simulation results for fault detection of the capacitor are presented and the ability of the observer in the vicinity of dynamic pull-in voltage has been checked.
https://www.ije.ir/article_72453_777884716a51bdcae4d6014aa6d125c0.pdf
fault detection
Thau observer
nonlinear force
Micro
parallel plate capacitor
noise and uncertainty
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
277
283
72454
Vibration Characteristics of Heavy Load Rackwith Split-hom together Structure (RESEARCH NOTE)
Yongqiao Wei
659458025@qq.com
1
Ruqiang Mou
rqmouscu@163.com
2
Li Hou
houli@163.com
3
Bo Li
493721805@qq.com
4
School of Mechanical and Manufacturing Engineering, Sichuan University
School of Mechanical and Manufacturing Engineering, Sichuan University
School of Mechanical and Manufacturing Engineering, Sichuan University
School of Mechanical and Manufacturing Engineering, Sichuan University
Split-hom together structure is a new heavy load rack structure, and its reliability needs to be verified. Through analyzing multimodal hom-connection principle from the perspective of bionics and contact mechanics, the article puts forward three kinds of hom-connection methods and establishes the finite element model and mathematical model of the rack. Afterwards, the finite element model and the mathematical model are separately performed modal analysis and numerical simulation. The results of modal analysis show that the two sides` pressure of hom bonding interfaces remain higher than the pressure making sub body slip when the rack has prestress, so the rack is safe. Meanwhile the results of numerical simulation indicate that the displacement and deformation of the rack is consistent with the results of modal analysis when occurring resonance and working in the eccentric loading condition. The results validate the reliability of the design on split-hom together rack.
https://www.ije.ir/article_72454_32f460c22aaed55567bec9033d1f85dc.pdf
Heavy load rack
Prestress
Modal Analysis
numerical simulation
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
284
294
72455
The Effect of Base Position on Maximum Allowable Load of Dual Arm Robots
ABOLFAZL JAVANMARD
abolfazl.javanmard@gmail.com
1
HASHEM GHARIBLU
ghariblu@znu.ac.ir
2
Mechanical Engineering, University of Zanjan
Mechanical Engineering, University of Zanjan
A new computational technique is presented to find the optimal base position of dual arm robots in order to carry maximum allowable load. The maximum allowable load on a desired trajectory is limited by the number of factors such as; actuators torque limits, kinematic constraints, and kinematic redundancy of cooperative manipulators. For a dual arm robot mounted on a rail or table, load workspace (LWS) is introduced as the union of places where the base can locate and robots carry a load on a desired trajectory. It is possible to increase the maximum allowable load by replacing the base of the arms robots in the LWS. By dividing the LWS into grid points, the base position of the rail mounted dual arm robot considered at each point. Using the Newton-Euler formulation and appropriate procedure, maximum allowable load of the robots in all points of the LWS are computed. Then, by iteration a smaller subspace near to optimum base position is selected until maximum allowable load and corresponding base position is found with acceptable precision. Finally, in two different cases the application of the proposed algorithm is presented and verified.
https://www.ije.ir/article_72455_0a2fc03072aaca9aafca04b802d02856.pdf
Dual
arm robot
Base position
Maximum Load
Cooperative
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
290
295
72456
Effect of Activated Flux on Properties of SS 304 Using TIG Welding
Ravi Duhan
ravi88duhan@gmail.com
1
Suraj choudhary
surajchoudhary786@yahoo.co.in
2
Mecanical Engineering, E-Max college of engineering
Mecanical Engineering, Ambala College of Engineering and Applied Research
In this experimental work, Manganese oxide (MnO2), Zinc oxide (ZnO), Iron oxide (Fe2O3) and Magnesium chloride (MgCl2) were used as activating flux to investigate the effects for SS 304 in tungsten inert gas (TIG) welding. Ultimate tensile strength, percentage elongation, Penetration depth and width were studied of material SS 304. The experimental results indicated that the MnO2 and Fe2O3 fluxes increases the weld penetration depth and decrease the weld width but ZnO and MgCl2 fluxes shows a little effect on penetration depth and weld depth to width ratio compared with conventional TIG process. Since the activated TIG welding can increase the ultimate tensile strength and percentage elongation.
https://www.ije.ir/article_72456_0dab76441e91330157a6409d2b2ef412.pdf
Keywords TIG welding
Different Fluxes
tensile strength
Penetration depth
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
296
304
72457
Size Effect on Free Transverse Vibration of Cracked Nano-beams using Couple Stress Theory
Amin Jafari
ytadibeni@yahoo.com
1
Faculty of Engineering, ShahreKord University
In this paper, the transverse vibration of cracked nano-beam has been studied based on modified couple stress theory. Crack is modeled by a rotational spring that creates a discontinuity. Frequency equations of cracked nano-beam with some typical boundary conditions are derived and the frequency parameter for different crack positions, crack parameter and length scale parameters value are calculated. According to the results, it can be found that the effects of the crack parameter and crack location on transverse frequency of the cracked nano-beam are significant. In addition, scale effect parameter is one of the important parameter in nanoscale that must be obtained. Finally, the results of special cases show good agreement with the results available in the literature.
https://www.ije.ir/article_72457_fde5c95065f3919d992175c1e30e01bf.pdf
Cracked nano
Beam
frequency parameter
couple stress theory
size effect parameter
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
305
313
72458
Numerical Study on Improvement of Hydrofoil Performance using Vortex Generators (RESEARCH NOTE)
Hassan Ghassemi
gasemi@aut.ac.ir
1
Mohammad Javad Ketabdari
ketabdar@aut.ac.ir
2
Arash Ashrafi
arashonline65@aut.ac.ir
3
Marine Engineering Department, Amirkabir University of Technology
Marine Engineering Department, Amirkabir University of Technology
Marine Engineering Department, Amirkabir University of Technology
In this paper the effects of rigid triangular passive vortex generators on a hydrofoil were investigated numerically. In the first step using the Finite Volume Method the bare hydrofoil were modeled and the results of lift and drag coefficients were validated using experimental data. In the next step the hydrofoil armed with vortex generators was modeled and its effect on the hydrofoil performance was examined. In the next step by introducing a source term into the momentum equation the vortex generators effect was considered. However their geometry was completely removed. The results showed that this can significantly decrease the computational memory and calculation time. The results also revealed that the use of vortex generators can delay the stall conditions by increase the stall angle leading to a higher lift coefficient in new stall angle and decreasing the drag coefficient. In a case study on NACA 0012 section profile results showed that the use of vortex generators increases the stall angle by 4 degrees and the lift coefficient at this point by 37%.
https://www.ije.ir/article_72458_e753c516acd9dc55726e5b2e34580a9c.pdf
Hydrofoil
Drag Reduction
Vortex Generators
finite volume method
Source Term
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
314
320
72459
Investigation of Thermoelastic Damping in the Longitudinal Vibration of a Micro Beam
Ghader rezazadeh
g.rezazadeh@urmia.ac.ir
1
rasoul shabani
r.shabani@urmia.ac.ir
2
Saber Najafi
me_sn66@yahoo.com
3
Mohammad Maroofi
m.e_marofi@yahoo.com
4
mechanical engineering, Urmia university
mechanical engineering, Urmia university
Mechanical Engineering, Urmia University
Mechanical Engineering, Urmia University
In the design of high Quality factor (Q) micro or nano beam resonators, different dissipation mechanisms may have damaging effects on the quality factor. One of the major dissipation mechanisms is the thermoelastic damping (TED) that needs an accurate consideration for prediction. In this paper, thermoelastic damping of the longitudinal vibration of a homogeneous micro beam with both ends clamped have been investigated. A Galerkin method has been used to analyze thermoelastic damping for the first mode of vibration of the micro beam. Then the quality factor and longitudinal vibrations frequency are obtained. Changing of Quality factor versus geometrical properties and ambient temperature for different materials are plotted.
https://www.ije.ir/article_72459_954b519704e89b8ca237af12a718b90b.pdf
Quality factor
Thermoelastic damping
Longitudinal vibrations
Coupled Equations
Galerkin method
Natural frequency
eng
Materials and Energy Research Center
International Journal of Engineering
1025-2495
1735-9244
2015-02-01
28
2
321
329
72460
A Simple Method for Modeling Open Cracked Beam
Mohammad Hassan Ghasemi
mhghasemi@nit.ac.ir
1
Amar Mofid Nakhaei
a.nakhaei@stu.nit.ac.ir
2
Morteza Dardel
dardel@nit.ac.ir
3
Mechanical Engineering, Babol Noshirvani University of Technology
Department of solid Mechanics, Babol Noshirvani University of Technology
, Babol Noshirvani university of technology
Abstract A simple method is proposed to model the open cracked beam structures. In this method, crack is modeled as a beam element. Hence cracked beam can be assumed to be a beam with stepped cross sections, and problem of determining natural frequency and mode shape of cracked beam, can be solved as determining these characteristics for a beam with different length and cross section. With this work, it is not necessary to model crack as lumped flexibility model in according to fracture mechanics and related sciences to obtain crack stiffness, and use this spring model of crack for further analysis.
https://www.ije.ir/article_72460_b7dd26cc5cb531ab3709e88fe2b81136.pdf
Keywords Crack
lumped stiffness model
step beam
Natural frequency
Mode shape