2017-09-21T05:57:37Z
http://ijstm.shirazu.ac.ir/?_action=export&rf=summon&issue=352
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
USING ALE-FEM TO SIMULATE THE INSTABILITY OF BEAM-TYPE
NANO-ACTUATOR IN THE PRESENCE OF ELECTROSTATIC
FIELD AND DISPERSION FORCES
Abstract– The ability of mesh design in arbitrary Lagrangian-Eulerian finite element method(ALE-FEM) makes it a generally efficient device for simulating engineering problems. In thispaper, ALE-FEM is used to model the static deflection and instability of beam-type cantilevernano-actuators using plain element. Effects of electrostatic fields are taken into account throughfirst-order fringing field corrected model. In addition, the influence of quantum vacuumfluctuations is considered via attractive Casimir and van der Waals force depending on the rangeof application. The instability parameters, i.e. pull-in voltage and deflection of the nano-actuatorare computed. The obtained results are compared with those reported in literature using numericalmethod as well as Lagrangian FEM. The findings indicate that ALE method can be used as apowerful technique for modeling beam type nano-actuator.
Cantilever nano-actuator
arbitrary Lagrangian-Eulerian finite element method (ALE-FEM)
pull-in
instability
Casimir force
van der Waals force
electrostatic force
2013
04
01
1
9
http://ijstm.shirazu.ac.ir/article_1461_4b333a6d267c7d773744f1c737cab548.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
LATTICE BOLTZMANN SIMULATION OF MAGNETHYDRODYNAMICS
NATURAL CONVECTION FLOW FOR SALT WATER IN
A HORIZONTAL CYLINDRICAL ANNULUS
Natural convection of an electrically conducting fluid under the different directions ofmagnetic field in a horizontal cylindrical annulus is numerically studied using lattice Boltzmannmethod (LBM). The inner and outer cylinders are maintained at uniform temperatures. Detailednumerical results of heat transfer rate, temperature and velocity fields have been presented for saltwater with Pr=13.2, Ra=105 to 106 and Ha=0 to 100 for three directions of magnetic field. Thecomputational results reveal that in horizontal cylindrical annulus the flow and heat transfer aresuppressed more effectively by direction and intensity of magnetic field. It is also found that theflow oscillations can be suppressed effectively by imposing an external horizontal magnetic field.The average Nusselt number increases with rise in radius ratio but decreases with the Hartmannnumber. Furthermore, it can be observed that there is a good agreement between the present resultand those predicted by available benchmark solutions under the limiting conditions.
Hartman number
cylindrical annulus
Magnetic field
Lattice Boltzmann Method
2013
04
01
11
22
http://ijstm.shirazu.ac.ir/article_1462_8ba58e375c89d04cc3fc73efc88d12ae.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
LATTICE BOLTZMANN SIMULATION OF HEAT TRANSFER ENHANCEMENT
DURING MELTING BY USING NANOPARTICLES
This research paper provides a mathematical modeling of heat transfer enhancementduring melting process in a square cavity through dispersion of nanoparticles. The enthalpy-basedlattice Boltzmann method (LBM) with a combination of D2Q9 and D2Q5 lattice models is used tosolve density, velocity and temperature fields. The nano-enhanced phase change material(NEPCM) is composed of a dilute suspension of copper particles in water (ice) and is melted fromthe left. Also, in this study the sub-cooling case is neglected. Conduction heat transfer has beentaken into account in the solid phase as well as natural convection in the liquid phase. Numericalsimulations are performed for various volume fractions of nanoparticles and Rayleigh numbersranging from 104 to 106. The validation of results is carried out by comparing the present results ofnatural convection and convection-dominated melting in a square cavity with those of existingearlier numerical studies. Predicated results illustrate that by suspending the nanoparticles in thefluid the thermal conductivity of NEPCM is increased in comparison with PCM. Also, byenhancing thermal conductivity and decreasing latent heat of fusion higher rates of heat releasecan be obtained.
nanoparticles
Lattice Boltzmann Method
phase change
melting
enthalpy method
2013
04
01
23
37
http://ijstm.shirazu.ac.ir/article_1463_7f10a4afadc7224d16bb86966f855d7c.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
HEAT TRANSFER AUGMENTATION IN PLATE FINNED TUBE HEAT
EXCHANGERS WITH VORTEX GENERATORS: A COMPARISON
OF ROUND AND FLAT TUBES
Heat transfer augmentation and pressure loss penalty caused by vortex generators(VGs) are numerically studied for finned flat/round tube heat exchangers and compared withavailable experimental results. The simulations are performed with the steady three-dimensionalincompressible conditions and a RNG K-ε turbulence model is used. The Reynolds numbers basedon the bulk velocity and the height of channel are selected from 600 to 4050. To compare theeffectiveness of VGs on the round and flat tubes for tube-fin heat exchangers, two differentconfigurations are investigated with two and four delta winglet vortex generators for each tube.The streamlines, vorticity, the averaged Nusselt number, the friction factor and the performancefactor (JF) are provided to evaluate the effectiveness of VGs for the heat exchangers employed. Itis found that the flat tube with VGs provides better thermal performance than the round one,especially at the lower Reynolds numbers.
Tube-fin heat exchanger
heat transfer enhancement
flat tube
round tube
vortex generator
2013
04
01
39
51
http://ijstm.shirazu.ac.ir/article_1464_f3f420db43e120a106217f05dfe02272.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
ASYMPTOTIC STABILIZATION OF COMPOSITE PLATES
UNDER FLUID LOADING
This paper presents a solution to the boundary stabilization of a vibrating compositeplate under fluid loading. The fluid is considered to be compressible, barotropic and inviscid. Alinear control law is constructed to suppress the composite plate vibration. The control forces andmoments consist of feedbacks of the velocity and normal derivative of the velocity at theboundaries of the composite plate. The novel features of the proposed method are that (1) itasymptotically stabilizes vibrations of a composite plate in contact with fluid (the fluid has a freesurface) via boundary control and without truncation of the model; and (2) the stabilization of boththe composite plate vibrations and fluid motion are simultaneously achieved by using only a linearfeedback from the composite plate boundaries.
Semigroups of operators
LaSalle invariant set theorem
asymptotic stabilization
symmetric angle-ply
composite plate
compressible Newtonain Barotropic fluid
2013
04
01
53
62
http://ijstm.shirazu.ac.ir/article_1465_c01b3940575daeff9d80939c14c8bf0e.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
EXPERIMENTAL AND NUMERICAL STUDY OF A TURBULENT AXISYMMETRIC
JET IMPINGING ONTO A CIRCULAR CYLINDER IN OFFSET
AND NON-OFFSET SITUATIONS
In this study, an experimental and numerical analysis is done to study the flowcharacteristics of an offset and non-offset axisymmetric jet impingement on a circular cylinder.The purpose of this study is investigation of the behavior of the cutting gas jets and finding theoptimum distance between nozzle and cylinder to achieve maximum cutting performance. Finitevolume approach is used to solve the governing equations for a turbulent, incompressible jetnumerically. According to the literature the suitable turbulence model for this purpose is realizablek-ε. Velocity and pressure fields around the cylinder and pressure and shear stress distribution onthe cylinder surface are determined for various cases. Also, some experiments are done to validaterepeatability of experiments and numerical results. Comparisons between numerical results andexperimental measurements validate the accuracy of numerical results. Also, results show that ifthe horizontal distance between the nozzle outlet and the stagnation point of cylinder is 2.5D, theshear stress on the cylinder surface has maximum value. Therefore in this situation jet has amaximum performance in cutting procedure.
impinging jet
axisymmetric jet
offset/non-offset impinging
circular cylinder
2013
04
01
63
70
http://ijstm.shirazu.ac.ir/article_1466_809eaf8b5ff3419a3f2810aae4c21a00.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
SIMULATION OF LAMINAR MIXED CONVECTION RECESS FLOW
COMBINED WITH RADIATION HEAT TRANSFER
In the current work, two-dimensional simulations are presented for incompressiblelaminar mixed convection flow of a radiating gas over a recess including two backward andforward facing steps in a vertical duct. The continuity, momentum and energy equations for fluidflow are solved by the computational fluid dynamic (CFD) techniques. The fluid is treated as agray, absorbing, emitting and scattering medium. For computation of the radiative term in theenergy equation, the radiative transfer equation (RTE) is solved numerically by the discreteordinates method (DOM). The effects of Grashof number, radiation-conduction parameter andoptical thickness on heat transfer behavior of the system are studied.
Laminar mixed convection flow
recess
radiation
DOM
2013
04
01
71
75
http://ijstm.shirazu.ac.ir/article_1467_7acf1baec66d5c04fc122ee8b37e4ea0.pdf
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2013
37
1
VIBRATION CHARACTERISTICS OF CONTINUOUSLY
VARIABLE TRANSMISSION PUSH BELTS
A CVT push-belt, composed of 12 layers of bands and a number of segments, ismodeled for vibration analysis. Predefined compression and tension loads are applied to segmentsand bands respectively. Continuous and discrete beams composed of segments are used toinvestigate contact properties between segments. Three models of band contacts have beenestablished based on complexity and various modeling approaches in ABAQUS. Contacts betweenbands are modeled by a frictionless contact between shell elements tied together in the first modeland in the second model. To improve the accuracy, a composite shell with special interface layersis utilized as third model. By using the segment models, it has been concluded that a group ofsegments can be considered as a continuous beam at high compression loads and as individualrigid masses in low compression loads. The results of composite shell model show betterprediction of the vibration properties of bands pack model. Separate cases of loading areconsidered for tension and compression spans.
CVT
push-belt
vibration
finite element
contact modeling
2013
04
01
77
82
http://ijstm.shirazu.ac.ir/article_1468_ce5b9cded07edc5c7f603fec85e9b8c6.pdf