IFC
text
article
2014
per
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
0
0
http://mme.modares.ac.ir/article_11108_5593f2c7536066e616b8a931dbf5434f.pdf
Application of crossentropy method in multi limitstate reliability analysis
mahdi
fakoor
University of Tehran
author
Parviz
Mohammadzadeh
دانشگاه تهران
author
Mahdi
Bajellan
دانشگاه تهران
author
text
article
2014
per
This paper is focused upon the development of an efficient multi limitstate reliability analysis method based on extended crossentropy. In order to achieve a reliable state in the modern critical structural designs, it is necessary to utilize an efficient reliability analysis method to estimate the probability of failure. Reliability analysis of such designs is faced with several challenges, such as rarity of the probability of failure and multiplicity of limitstate functions. To address these issues, in this research an importance sampling (IS)based method is developed which uses crossentropy (CE) method to reduce sampling variance, and leads to a fast and accurate reliability analysis method. The main advantage of this method is the ability to perform reliability estimation (especially for rare events) without the most probable failure point (MPP) calculation. The proposed method is demonstrated on several test problems and the results are compared together. Results obtained show that method introduced in this paper provides an effective way of improving reliability analysis of multi limitstate functions. In addition, using the proposed method, prevents the mistake of overdesigning while retains usability of the method.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
1
6
http://mme.modares.ac.ir/article_10857_e96a7518733aab8684ec49e352ada094.pdf
Vibrational Study of laminated composite plates reinforced by carbon nanotubes
Esmail
Asadi
دانشگاه صنعتی مالک اشتر
author
Mahmood
Farhadi Nia
دانشگاه صنعتی مالک اشتر  تهران
author
text
article
2014
per
In this paper, the influence of carbon nanotubes on vibrational properties of laminated composite plates is studied theoretically and experimentally. The plates are made of glass/epoxy composite. Multi walled and single walled carbon nanotubes in different weight percentages are added to these composites. At first, carbon nanotubes are dispersed in the epoxy resin via ultrasonic procedure. Then the composite plates are made by hand layup and vacuum bagging methods in a mould manufactured for this research. Mechanical properties of the fiber composite reinforced by carbon nanotubes calculated using modified HalphinTsai equations. Next composite plates are modeled in ABAQUS software and frequency analysis is done. Also vibrational properties of structure are obtained by experimental modal analysis in fixed boundary condition. Experimental results showed 210% increase in damping for samples which have 0.5 weight percent of single walled carbon nanotubes (in comparison with plane glass/epoxy composite plates). Also a good agreement was observed between obtained natural frequencies from finite element analyses and experimental tests.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
7
16
http://mme.modares.ac.ir/article_10858_7a28f7db9fe0ca77c34edd638750d35c.pdf
The microstructure and mechanical properties of friction stir welded 7075T6 aluminum alloy by the use of Design of Experiment
Amirhossein
Lotfi
دانشگاه صنعتی بابل
author
salman
nourouzi
Babol University of Technology
author
text
article
2014
per
The 7075T6 aluminum alloy is one of the strongest aluminum alloys that possess excellent combination of mechanical properties such as high strength to weight ratio, good corrosion resistance and thermal conductivity but they generally present low weldability by traditional fusion welding process. Friction stir welding is a new solid state process that is function of different process parameters. In the current study, to investigate the effect of some of the main welding process parameters such as rotational speed, traverse speed and tool shoulder diameter properly, a Design of Experiment (DOE) was used with a Response Surface Methodology (RSM) approach to find the best process settings and achieve optimal performance. Results showed that to achieve sound highgrade joints parameters should be optimized. When improper welding parameters are used, problems such as defect formation, precipitates dissolution and grain growth can deteriorate the mechanical properties of the joint. So, of the twenty joints fabricated using various welding parameters, the joint fabricated at a rotational speed of 1050 rpm, welding speed of 100 mm/min and shoulder diameter of 14 mm exhibited superior metallurgical and mechanical properties in comparison to other fabricated joints.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
17
26
http://mme.modares.ac.ir/article_10851_8002ac8ec35d3d53cadfdce55b764950.pdf
Experimental Investigation of Slug Initiation Dependency to Upstream Conditions of Two Phases in Long Horizontal Channels in TwoFluid Flow
Pouyan
Adibi
دانشجو دکتری
author
mohamadreza
ansari

author
text
article
2014
per
Abstract In this paper, the effect of gas and liquid inlet velocities and for the first time the effect of liquid hold up on slug initiation position are studied experimentally. Empirical correlations are also presented based on the obtained results. The tests are conducted for three liquid hold ups (0.25, 0.50 and 0.75) in a long horizontal channel made of Plexiglas with dimensions of 510 cm2 and 36m length in Multiphase Flow Lab. of Tarbiat Modares University. The superficial liquid and air velocities rated as to 0.110.56 m/s and 1.8813 m/s, respectively. The obtained results show that as αl=0.25, slug initiation position is increasing monotonically with Usl and Usg. During αl=0.50, slug initiation position is increasing with Usl and Usg but the slope is smoother than αl=0.25. For αl=0.75, slug initiation position is decreasing monotonically with Usl and Usg. In the case of equal void fraction of phases, slugs are generated weakly (low pressure). However, for the unequal void fraction of phases strong slugs (high pressure) are formed.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
27
35
http://mme.modares.ac.ir/article_10852_adea3592fab83dc077d93f4742f0f186.pdf
Investigation of the Stability of Electro Hydraulic Servo System using Fuzzy Intelligent Controller
Abdulah
Akbari
هیات علمی
author
Amir Reza
Zare Bidaki
استاد مدعو دانشگاه آزاد
author
Amir Reza
Hosseini
استاد مدعو دانشگاه آزاد
author
Mahdi
Aliyari
استادیار دانشگاه خواجه نصیرالدین طوسی
author
text
article
2014
per
Electro hydraulic servo systems (EHSS) are widely used in all aspects of industry, due to their ability to handle large torque loads and quick response. According to the wide range of use, the desired control objectives for EHSS are: velocity, force/torque and position control. Existing approaches for control of electro hydraulic servo systems are in the presence of external noises, internal friction and nonlinearity in the model behavior which is considered as uncertainty parameters. In this paper fuzzy intelligent controller by using parallel distributed compensator (PDC) method based on TakagiSugeno is used. The controller is designed for a high level performance (velocity control) which could reach the main control goals. The concluding results of this approach best fit the other researches data.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
36
42
http://mme.modares.ac.ir/article_10849_7b1f51a14ec4b125d9c431af006fd596.pdf
Experimental Study of Turbulent Layers with Different Obstacles to Stimulate Optimal Point Augmentation in Heat Transfer Coefficient
Mohsen
Kahrom
استاد دانشگاه فردوسی مشهد
author
Saeid
Vahidifar
دانشجوی دکتری  گروه مهندسی مکانیک  دانشگاه فردوسی مشهد.
author
text
article
2014
per
Experimental evaluation of overall convection heat transfer coefficient of a rectangular bar in the vicinity of a flat plate is investigated. A quad of rectangular shape and later a quad with the cause of optimal heat transfer are placed at the near and the inside of a turbulent boundary layer over a flat plate. The overall convection heat transfer coefficient of the flat plate are measured and compared to the case similar to a single flat plate. A low speed wind tunnel is employed to maintain main flow field at the requested speed and special electrical circuit is prepared to provide heat and measure heat losses from the flat plate. Conclusion is made that when the obstacle closes to the flat plate, the total convective heat transfer coefficient increases to a maximum and then reduces again by moving towards the plate. Distance from the flat in which the maximum heat transfer coefficient occurs is reported.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
43
50
http://mme.modares.ac.ir/article_10854_c161d1d6125521dab6ab314a14d9cbd7.pdf
Drag Reduction in a HighSpeed Planing Hull Using Tunnels
Abdorreza
Yousefi
دانشگاه صنعتی نوشیروانی بابل
author
Rouzbeh
Shafeghat
عضو هیات علمی دانشگاه صنعتی نوشیروانی بابل
author
Mostafa
Mohebi
دانشگاه صنعتی شریف
author
Abbas
Ramiar
دانشگاه صنعتی نوشیروانی بابل
author
text
article
2014
per
Abstract Forward speed is perhaps the most important parameter in the design of a planing hull. The speed strongly influences the drag and thus the energy supplied by the engine of the ship. Employment of an appropriate drag reduction strategy plays an important role in the design of these hulls. The flow around a Cougar highspeed planing hull was numerically simulated and the results were compared against experiments available in the literature. To reduce the total drag, two tunnels were introduced at the bottom section of the original Cougar hull. The weight and center of gravity of both hulls remained the same. An unstructured mesh was generated in the computational domain around the hull and a ReNormalization Group Kε formulation was used to model the turbulence. To capture the freesurface of the flow around the hull, the volume of fluid model was applied. The drag forces of both the original and modified Cougar hulls were obtained for various forward speeds, corresponding to the original hull length based Froude numbers ranging from 1.00 to 5.62. The results show reduction in total drag for the modified hull at the forward speed of 60 knot.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
51
59
http://mme.modares.ac.ir/article_10853_cde1caa253a2dbb3f28075ec6b393056.pdf
Numerical and experimental investigations on buckling and control amount of energy absorption of stainless steel 304L shells with various shapes under axial loading
Mahmoud
Shariati
دانشگاه شاهرود
author
Mohamad
Davarpanah
دانشگاه صنعتی شاهرود
author
Hamid
Chavoshan
دانشگاه صنعتی شاهرود
author
Hamidreza
Allahbakhshy
دانشگاه صنعتی شاهرود
author
text
article
2014
per
In this paper, buckling and energy absorption behavior of stainless steel semisphere, cylindrical and conical shells under axial loading are studied. Every shell with the same mass and different shapes with and without groove is designed. In this paper the effect of shape, thickness, height, groove of shells and distance between grooves, on buckling and energy absorption were investigated. In experimental test, Samples had same mass and thickness and also grooves had same depth and distance. Experimental tests were performed by a servohydraulic INSTRON 8802 machine. Numerical analysis is carried out by ABAQUS software and is validated with experimental results.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
60
68
http://mme.modares.ac.ir/article_10855_4f3cb8aab42d1c12a6b12c8bae628311.pdf
Numerical study of effective techniques to increase mixed convection heat transfer rate within the enclosure subjected to magnetic field
Masoud
Kharati
استادیار دانشگاه صنعتی شیراز
author
Iman
Jelodari
دانشگاه صنعتی شیراز
author
text
article
2014
per
In this research, two effective techniques to increase mixed convection heat transfer rate within an enclosure subjected to a transverse magnetic field are studied. In order to increase the heat transfer rate, the addition of Al2O3 nanoparticles is concerned as the first strategy and the change in magnetic field inclination angle is considered as the second. In this study, the left and right sides of the enclosure are kept at constant temperature while the top and bottom walls are adiabatic. In this work, the results are obtained with an inhouse finite volume code. To validate the code, the results of the present code are compared to that of an existing correlation as well as those of previous works and good agreements are observed. In the present work, Richardson number varies from Ri=0.05 to Ri=50. Results show that the addition of solid particles may increase or decrease the heat transfer rate whereas the increase in magnetic field inclination angle mostly leads to increase in the heat transfer rate.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
69
77
http://mme.modares.ac.ir/article_10856_76d1a9e9fb9f9ecae8426ba07eb90892.pdf
Acoustic emission based study to monitor the initiation and growth of delamination in composite materials
parinaz
belalpour dastjerdi
دانشجو
author
Mohammad
Fotouhi
دانشجو
author
Sakine
Fotouhi
دانشجو
author
Mahdi
Ahmadi
هیئت علمی
author
text
article
2014
per
Delamination is one of the main defects in composite materials. Studying the initiation and propagation of delamination is useful for the design and production of high quality resistant materials. Therefore understanding the behavior of delamination damage and having enough knowledge about that will be helpful. In this study, generated acoustic emission signals from two types of glass/epoxy composite specimens at different layups, [0,90]5s and [0]10, is recorded. After that signals were analyzed by applying strain energy function. The results indicate that specimens at different layups have different stiffness behavior toward damage initiation and growth. Using strain energy function method initiation and growth of delamination can be evaluated. The obtained results provide useful information for the design and production of high quality resistant composite materials.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
78
84
http://mme.modares.ac.ir/article_10869_b37d4aee9eb064b6f9fa0cd0d97e81a7.pdf
Study of vortical structures in a microfiberinduced dragreduced turbulent channel flow using DNS
Amin
Moosaie
Department of Mechanical Engineering
Engineering Faculty
Yasouj University
author
text
article
2014
per
In this study, using the results of a DNS of dragreduced turbulent channel flow, vortical flow structures especially in the nearwall region are investigated. For this purpose, a Lagrangian MonteCarlo method has been used to simulate the spatial orientation of fibers. Namely, the flow field is treated in an Eulerian manner whereas the fiber dynamics is described by a Lagrangian point of view. This method yields the exact solution of the governing equations. Vorticity fluctuations in the channel are studied and it turns out that the level of these fluctuations decreases in the dragreduced flow. The reason for this reduction is explained using the reduction in velocity gradient fluctuations. Also, the distribution of the angle between the vorticity axis and the wall is studied and it turns out that horseshoe vortices exist in both flows. However, in the dragreduced flow, they are formed farther away from the wall which indicates a weakening of sweep and ejection mechanism in the vicinity of the wall. This weakening leads to drag reduction. Also, the orientation of vortices in the dragreduced flow is well ordered.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
85
93
http://mme.modares.ac.ir/article_10868_6f87f3ae866dabfad2ead8ce912662d4.pdf
Dynamics of lean hydrogen/air flame regimes in micro scale combustion
Alireza
Alipoor
دانشگاه تربیت مدرس
author
Kiumars
Mazaheri
Tarbiat Modares University
author
Ali
Shamoonipour
دنشگاه تربیت مدرس
author
text
article
2014
per
In the present work, the dynamics of lean (ϕ =0.5) premixed hydrogen/air flames in a micro channel with prescribed wall temperature is studied. The investigation is carried out using the low Mach formulation of NavierStokes equations with detailed chemistry and molecular transport for different inflow velocity. Ignitionextinction repetitive, steady symmetry flame and asymmetric flame are observed as the inlet velocity increased. Close to lower flammability limit, ignitionextinction repetitive flame was observed duo to imbalance between chemical time scale and residence time scale. In this regime, the reacting flow is affected by high wall temperature and the extinction occurred by the flow temperature. Upon increasing the inlet velocity, symmetric flame can be observed due to the balance between time scales. It is observed that further increasing the inlet velocity would cause symmetry flame to become unstable because of presence of some perturbations in flow field. Based on the obtained results, it is suggested that the perturbations are created by preferential diffusion of species.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
94
102
http://mme.modares.ac.ir/article_10859_09e4cf7d8fdbef3a8008e697e557773c.pdf
Mechanical and thermal properties of nanocomposites based on polypropylene/linear low density polyethylene/titanium dioxide
Faramarz
Ashenai
استادیار دانشگاه تربیت دبیر شهید رجایی، دانشکده مهندسی مکانیک
author
Ismail
Ghasemi
پژوهشکده پلیمر و پتروشیمی
author
Sajjade
Daneshpayeh
دانشگاه تربیت دبیر شهید رجایی
author
text
article
2014
per
Abstract In this study, mechanical and thermal properties of nanocomposites based on polypropylene/ linear low density polyethylene/ nano titanium dioxide (PP/LLDPE/Tio2) were studied. The samples were produced using a corotating twin screw extruder including 0,2,4 Wt.% of nano particles, 20,40,60 Wt.% of LLDPE and styreneethylenebutylenestyrene(SEBS) as comptabilizer. Tensile properties (modulus, tensile strength and elongation at break), impact resistance and thermal properties (meltingand crystallization temperatures) were evaluated. The results showed that modulus was increased by 9% with addition of nano particles in comparison to PP/LLDPE. In addition, impact resistance was increased and tensile strength and elongation at break were decreased. Melting and crystallization temperatures of PP were increased less or more while, these temperatures for LLDPE did not show meaningful differences.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
103
109
http://mme.modares.ac.ir/article_10870_d24143e880d3fa5c1b8f12ab32d0e003.pdf
The effect of damping ratio and balls mass on the stability of automatic ball balancer and determining their optimum values
Mousa
Rezaee
Associate Professor  University of Tabriz
author
Reza
Fathi
دانشگاه تبریز
author
text
article
2014
per
Rotating unbalance is a major cause of vibration in rotating machinery. One of the new methods used to control and reduce the unbalance is use of automatic dynamic ball balancer. In previous researches comprehensive studies have been done on the dynamic behavior and stability of automatic ball balancer, however there is no research has been done on determining the optimum values of the system parameters. Harmful forces caused by the unbalance in the system causes unwanted vibration and malfunctions of the system, therefore reducing the time of balancing is necessary. In this study, the effect of damping ratio and the mass of balls of the automatic dynamic ball balancer on the stability and the balance of system have been investigated. Moreover, for the first time the optimum values of these parameters to minimize the balance time are obtained. The results show that the optimal choice of the system parameters reduces the balance time considerably.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
110
118
http://mme.modares.ac.ir/article_10873_2e3c49b8f6643e4ec8630c4328126e75.pdf
3D Analysis of the Boundary Layer on Wind Turbine Blades
Hossein
HafiziRad
دانشجوی کارشناسی ارشد مهندسی مکانیک، دانشگاه شهید چمران
شرکت طراحی و ساخت توربینهای بادی آترین نقش جهان، شهرک علمی و تحقیقاتی اصفهان
author
Morteza
BehbahaniNejad
Shahid Chamran University of Ahvaz
author
Seyed Saied
Bahrainian
دانشیار مهندسی مکانیک،دانشگاه شهید چمران
author
Pouya
Tabibi
دانشجوی کارشناسی ارشد مهندسی مکانیک، دانشگاه شهید چمران
شرکت طراحی و ساخت توربینهای بادی آترین نقش جهان، شهرک علمی و تحقیقاتی اصفهان
author
text
article
2014
per
In this paper, threedimensional boundary layer flows on wind turbine blades as well as separation event have been studied. At first, boundary layer and threedimensional momentum integral equations were obtained for incompressible flow considering rotation effects. Next, the effects of pitch angle and the angle between the flow direction and rotation vector on the Coriolis terms were applied using geometry factor definition and Blade Element Momentum (BEM) theory. Then, the integral parameters and effective geometry factors on separation positions and stall structure were investigated for a rotating blade. The obtained results show that rotational ratio, aspect ratio and radial position are three basic parameters for separation occurrence and separation and stall can be delayed via controlling them. Moreover, the results show that the area near the root is strongly influenced by rotational effects. In addition, it is concluded that the centrifugal pumping due to rotation decreases the boundary layer thickness and delays separation especially in the near root region and increases the blade aerodynamic coefficients.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
119
128
http://mme.modares.ac.ir/article_10871_81f5216c171ce58ba153838cb4d91295.pdf
Geometrical modeling of closedcell metal foams using Stochastic cells generation
Mohammad
Hoseinpour
عضو هیئت علمی دانشگاه شهید رجایی
author
Masoud
Abbaszadeh
ارومیه، دانشجوی کارشناسی ارشد مهندسی مکانیک، دانشگاه صنعتی ارومیه
author
Iraj
Mirzaee
ارومیه، استاد گروه تبدیل انرژی، دانشگاه صنعتی ارومیه
author
text
article
2014
per
Metal foams are a new class of materials which are used excessively in recent decade for their good physical and mechanical properties such as low density yet high strength, as well as their good thermal properties which turned them to a good thermal insulator. The main characteristic of the foams is the existence of pores in them which are distributed randomly. Because of the importance of these materials in engineering and other applications, there has been given importance to modeling of them. In this article, a new method has presented for modeling of closedcell foams and a program has written in macro environment of CATIA software in Visual Basic language which made the modeling of metallic foams with controllable pore size and density possible. In continue, the effect of the pore size and the number of the holes on the relative density of the foams has studied. Comparing the properties of the modeled foams using the presented algorithm and real foams has shown a good agreement. The modeled foams have the ability to get into the finiteelement software.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
129
135
http://mme.modares.ac.ir/article_10860_45617fc4024f05f4b428d74c93bd58d9.pdf
Computational Analysis of Stepped Tip Gap Casing Effect on Performance of a Centrifugal Compressor
reza
taghavi zenouz
دانشگاه علم و صنعت ایران
author
Ehsan
Solki
دانشگاه علم و صنعت ایران
author
Hadi
Afshari
دانشگاه علم و صنعت ایران
author
text
article
2014
per
In this article, one of the new casing treatment methods for improving of compressor performance have been investigated. Stepped tip gap is one of the appropriate methods of casing treatment that its functionality in axial compressors have been proved lately. In the present study, for the first time, effects of stepped tip gap on stall margin improvement of a centrifugal compressor have been evaluated numerically. Simulation has been done using Fluent software and kε turbulence modeling. To find the optimum geometry of stepped tip gap, seven casing geometries with one untreated smooth wall were considered. Results of velocity contours and streamlines patterns on various azimuthal and meridional planes showed that by using casing with stepped tip gap, tip leakage flow has been weaken and flow blockage in compressor main passage has been reduced. Hence, stepped tip gap extends the stable operating range of compressor and delays the occurrence of stall phenomenon. Results of present research, shows that by using stepped tip gap with optimum size, stall margin of the proposed compressor was improved by 7.38%.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
136
144
http://mme.modares.ac.ir/article_10872_a277f0a75c8ac6b9ee3fc9abfad401d1.pdf
Energy and exergy analysis of Organic Rankine Cycle with using twocomponent working fluid in specified heat source conditions
mahmood
chahartaghi
Assistant Professor
author
mahdi
Babaei
Shahrood University of Technology
author
text
article
2014
per
Waste heat recovery plays an important role in energy resource management. Low grade waste heat could be recovered by Organic Rankine Cycle (ORC). This is the same as the Rankine cycle and an organic fluid is used as working fluid. In this work the effects of using twocomponent mixtures with different temperature glides during phase change, on performance of Organic Rankine Cycle are studied. Four twocomponent mixtures are selected: npentane/nbutane, isopentane/isobutene, npentane/isobutene and isopentane/nbutane. In this study for more reasonable comparison of thermal recovery the inlet and outlet temperatures of heat source heat carrier fluid and its mass flow rate are considered to be constant. Results show that in the use of twocomponent mixtures in comparison with pure fluids, approximately 9% increase in energetic and exergetic efficiencies for simple configuration and 14% in configuration with the internal heat exchanger can be achieved with respect to the temperature glide match in the condenser and evaporator.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
145
156
http://mme.modares.ac.ir/article_10875_3e7bf6aa59abfb9a1a881231d0823e0d.pdf
A new method for selection of reference coordinates in operational modal testing of structures
Hoda
Sarparast
دانشگاه سمنان
author
Mohammad Reza
Ashory
Semnan University
author
Mohammad Mahdi
Khatybi
دانشگاه سمنان
author
text
article
2014
per
One of the drawbacks of the operational modal analysis techniques is that there is no possibility of measurement of the responses in all required points, which is attributed to the limitations of either the number of accelerometers or the number of measurement channels. To overcome this shortcoming, an experiment should be performed in different steps and relations between these steps of the experiment are determined by selection of some specific points as reference points. Existing techniques use the correlation between measurement points to determine the reference points in which an increase in the environmental noise leads to the incapability of the method. In this paper, a new index for selection of reference points is introduced which is more efficient in the noisy environments. To evaluate the proposed method numerically, a comparison has been drawn between the results of this method and correlation approaches using a FE model of a beam. To validate the method, an experiment has been conducted on a steel plate. Obtained results from numerical and experimental cases show that the proposed index is more capable in reference point selection and calculation of the modal parameters of the structures comparing to the results of correlation method.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
157
166
http://mme.modares.ac.ir/article_10874_cbc784c02b14186d92c73a2c07841ddf.pdf
Evaluation of Thermal and Moisture Inertia Effects in Clothing and Gagge’s Model Modification for Body Thermal Sensation and Physiological Responses Estimation
Amir
Omidvar
استادیار دانشگاه صنعتی شیراز
author
Babak
afra
دانشگاه صنعتی شیراز
author
text
article
2014
per
Up to now, lots of thermal comfort models have been introduced to predict human being’s body thermal response to the changes in personal and environmental conditions. Among them, Gagge’s model because of its ability in estimating body physiological responses and thermal sensation in transient conditions has turned to one of the most used thermal comfort models. Although, this model uses transient mechanisms to determine body core and skin temperatures, but yet, simplified assumptions including steady heat and moisture transfer through clothing and disregarding thermal and mass inertia in the clothing is used in its structure. This study, by investigating various mechanisms of heat and moisture transfer in the clothing (steady heat and mass transfer, transient heat transfersteady mass transfer, transient heat transfersemi transient mass transfer) tries to compare upcoming results of these models with those of experiments. It was declared that considering transient heat transfer along with semi transient mass transfer in the clothing have positive effects on the results.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
167
175
http://mme.modares.ac.ir/article_10877_20a5c4661d9a44ec00c5e38d0c06abe4.pdf
Dynamic modeling, simulation and control of a quadrotor using MEMS sensors’ experimental data
ehsan
davoodi
sahand university of technology
author
Mhadi
Rezaei
sahand university of technology
author
text
article
2014
per
This paper presents the inverted PID control of a quadrotor based on the experimentally measured sensors and actuators’ specifications. The main goal is the control and closed loop simulation of a quadrotor using inverted PID algorithm. First, a nonlinear model of quadrotor is derived using NewtonEuler equations. To have a more realistic simulation a setup were designed and developed to measure the sensors noise performance as well as the actuators’ dynamics. The setup involves a platform that two brushless motors mounted at the ends and rotates on a shaft. The platform attitude is measured using the MEMS sensors attached to it. A Kalman filter was used to reduce the sensors noises effect. Results demonstrate good performance for Kalman filter and the controller.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
176
184
http://mme.modares.ac.ir/article_10916_df7ef08fac8615e02d1339d58cf24796.pdf
Proposition of obliqueable ring installation at crown of the hellertype cooling tower for reduction of throttling effect in windy condition
Saeid Reza
Sabbagh Yazdi
استاد دانشکده عمران/ دانشگاه صنعتی خواجه نصیرالدین طوسی
author
Saeid
Gharehjanloo
دانشجوی کارشناسی ارشد/دانشگاه خواجه نصیرالدین طوسی
author
text
article
2014
per
The heller type dry cooling tower performance is significantly affected by unfavorable wind effects. During recent years, many modifications including the application of new equipment, using new materials, modification of tower's geometry, etc., have been proposed to optimize heller cooling towers performance. In this study, a crown supplement is proposed to reduce the throttling effect of deflected plume. Two alternatives of the elastic ring with 5% and 10% of the cooling tower height are considered. In order to investigate the effect of proposed crown supplement computational modeling is used utilizing ANSYS commercial software. For this purpose, a numerical model was utilized and the results were verified by comparing pressure at trunk of towers with VGB code. The thermal buoyancy phenomenon helps airflow to move upward. Assuming that thermal buoyancy will help to the results, in present work this phenomenon is not considered. The computational results present better performance by increasing 9 to 12.6 percent of air volume flow through the tower compared to the usual condition.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
185
193
http://mme.modares.ac.ir/article_10917_733721d396e2bb261e403a2e560f3c59.pdf
Node enrichmentmoving error estimate and adaptive refinement in Mixed Discrete Least Squares Meshless method for solution of elasticity problems
saeb
faraji
Iran University of Science & Technology (IUST)
author
Mohammad
Afshar
Iran University of Science & Technology (IUST)
author
text
article
2014
per
In this paper a node enrichmentmoving error estimate and adaptive refinement procedure in Mixed Discrete Least Squares Meshless (MDLSM) method is suggested to improve the solution of elasticity problems. The suggested method uses of two node enrichment and node moving refinement procedures simultaneity. The voronoi diagram is used to locate the position of new added nodes in enrichment step. The errors of new added nodes, after each enrichment procedure, are calculated via interpolation rather than the error of simulation nodes to reduce the computational effort. So, the additional simulation effort saves and the steps of suggested method and conventional enrichment procedure are same. Completing the enrichment step, a node moving procedure is used to improve the solutions and solving the nodes excessive vicinity problem that is happened in conventional node enrichment procedure, especially with irregular node distribution. The node enrichmentmoving method is continued to obtain the desirable accuracy. The proposed method is used to solve several examples and the results are presented and compared with those of conventional node enrichment procedure and analytical exact solutions. The results show superior efficiency, effectiveness and accuracy of the proposed method compared to conventional node enrichment method.
Modares Mechanical Engineering
Tarbiat Modares University
10275940
14
v.
3
no.
2014
194
202
http://mme.modares.ac.ir/article_10918_b6c79b58df3246803733a7c361b698c4.pdf