2018-01-16T13:09:46Z
http://ijstm.shirazu.ac.ir/?_action=export&rf=summon&issue=265
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
Comparison of different control strategies on a vehicle using sliding mode control
In this study, the vibration control of a half vehicle model with a passenger seat using a sliding mode control is considered. Three cases are taken into account as the control strategies. First, the model having passive suspensions with an active passenger seat is studied. Then active suspensions and passive seat combination is examined. In the last case, both the passenger seat and suspensions are active. Pitch motions of the vehicle body and bounce motions of the passenger in the three cases due to road input, which is a commonly used speed bump to slow down the vehicles at junctions in some countries, are simulated and the results are compared in order to select the combination which provides the best ride comfort
Active passenger seat
active suspensions
control strategy
Sliding mode control
2013
02
16
413
422
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
A biomechanical model to analyze normal, degenerated, and fused cervical spines using IAR’s concept
During voluntary flexion/extension of the head-neck system, the cervical spine undergoes a stepwise motion from upper to lower regions with a specific pattern. The motion of each vertebra is composed of a translation and rotation with respect to lower vertebrae, which may be considered as an absolute rotation about an axis called instantaneous axis of rotation (IAR). The location of this axis is different between normal and degenerated spines. A biomechanical computer model of the head and cervical vertebrae, including eight separate rigid links and nine spinal muscles as actuating elements was developed to evaluate and compare inter-segmental force-moments and muscle forces in normal, degenerated, and fused situations. Kinematics data were used as the input to our model and the joint reaction forces and moments and muscle forces were analyzed as model output in solving an inverse dynamic problem. As a result, significant differences were noticed among these three situations which are thoroughly discussed in this paper.
Cervical spines
degenerated
fused
Normal
dynamics modeling
2013
02
16
423
433
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
Performance comparison between planing monohull and catamran at high Froude numbers
Conventional ships have been used for many years with usual body forms. But recent developments in high speed crafts have created many different alternatives. Therefore the selection of hull type becomes an important issue in the preliminary design stage. This selection should be based on performance comparisons and also other parameters such as building costs and so on. Since planing monohulls and catamarans are very popular types of high speed crafts, in this paper their behaviors from resistance at high speeds are compared. The results may prove useful for designers at conceptual or preliminary design stages.
High speed crafts
planning monohull
planning catamaran
2013
02
16
435
441
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
The LES and DNS simulations of heat transfer and fluid flow in a plate-fin heat exchanger with vortex generators
Unsteady three-dimensional DNS and LES simulations for resolutions up to about 1.2 million points were performed to investigate the fluid flow and heat transfer in a plate-fin heat exchanger with vortex generators. The Prandtl and Reynolds numbers are 0.71 and 2000, respectively. An incompressible finite volume code, based on a fractional step technique with a non-staggered grid arrangement and a multigrid pressure Poisson solver, was used. From these simulations, the heat transfer and fluid flow were studied using instantaneous and time-averaged quantities such as the contours of velocity components, pressure, vorticity, turbulent stresses, temperature fluctuations and Nusselt number. This study shows that the temperature fluctuations, the turbulent kinetic energy, and the unsteadiness effects are stronger in the regions where the longitudinal vortices are more active. In this study, the effects of spatial resolution and the angle of incidence of the vortex generators are also investigated. A comparison between DNS and LES simulations for the present study shows that the predicted structures of fluid flow and temperature fields are similar for both methods.
heat transfer enhancement
vortex generators
large eddy simulation (LES)
direct numerical simulation (DNS)
2013
02
16
443
452
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
Stagnation flow and heat transfer on a moving cylinder with transpiration and high Reynolds numbers consideration
High-Reynolds-number unsteady viscous flow and heat transfer in the vicinity of an axisymmetric stagnation point of an infinite moving cylinder with time-dependent axial velocity and with uniform transpiration, , is investigated. The impinging free stream is steady and with a strain rate . An exact solution of the Navier-Stokes equations and energy equation is derived in this problem. The general self-similar solution is obtained when the axial velocity of the cylinder and its wall temperature or its wall heat flux vary as certain functions. These solutions are presented for special cases when the time-dependent axial velocity of the cylinder and its wall temperature or heat flux are certain functions of time. All the solutions above are presented for Reynolds numbers, , ranging from 0.1 to 1000 and different values of dimensionless transpiration rate, , where is cylinder radius and is kinematic viscosity of the fluid. Shear stresses corresponding to all the cases increase with the Reynolds number and decrease with the increase of suction rate. Using an inner-outer expansion, uniformly valid solutions of the equations in the case of high Reynolds numbers are obtained.
Stagnation flow
moving cylider
heat transfer
transpiration
high Reynolds numbers
2013
02
16
453
466
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
3D thermo-viscoplastic modeling of welds: effect of piece-wise welding on thermo-mechanical response of thick plate weldments
The effect of piece-wise welding on thermal and mechanical response of thick plate weldments is studied by the use of a 3-D thermo-viscoplastic model. Anand’s viscoplastic model is used to simulate the rate dependent plastic deformation of welded materials. Modeling of the welded region in the present study has been done by the use of the “isothermal melting pool” approach. The temperature dependency of thermal and mechanical properties of material is considered in analysis and the effect of welder characteristics such as welding speed and welding lag between sequences are introduced into the model. In addition, the element Rebirth technique (ERT) is incorporated into the model to introduce the effect of material of welds that added to the weldments during the welding. The model was compared with the results of two analytical and experimental works. The results of the present model are feasible and clearly show the relation between the order of joining blocks and distribution of thermal loads. They also demonstrate the role of this kind of welding sequence on the formation of residual stresses and distortion in thick plate weldments.
Thick plates
piece-wise welding
block welding sequence
3D thermo-viscoplastic
Anand viscoplastic
2013
02
16
467
478
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
On stability of the column with a step change in a cross section
Stability of an elastic column with a changeable cross section loaded by a concentrated force of arbitrary intensity is studied. It is assumed that the column is fixed to a rigid circular plate that is positioned on a homogeneous, isotropic, linearly elastic half-space. The constitutive equation of a column allows effects of axial compressibility and shear stresses. The bifurcation points of the full nonlinear system are determined by the eigenvalues of the linearized equations. It is shown that different types of bifurcations dependent on values of parameters can occur. The post critical shape of the column is determined by numerical integration of the system of equilibrium equations.
Critical load
Stability
Bifurcation
postcritical shape
2013
02
16
479
488
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
Generalized line-of-sight guidance with lead angle
A generalized three-dimensional line-of-sight guidance with a lead angle (GLOS) is presented for maneuvering targets. In the proposed guidance law, we define a desired line-of-sight (LOS) from the tracker by taking the target future maneuvers into account. Because of the limitation of the tracker field-of-view (FOV), the lead angles in the azimuth and elevation channels must be fractions of the azimuth and elevation angles for straight collision trajectory. Simulation results show that GLOS has better performance, i.e., lower miss distance and total control effort, than the conventional LOS guidance with lead a angle.
Three-point guidance
line-of-sight trajectory
lead angle
2013
02
16
489
493
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
Pressure-based compressible calculation method utilizing normalized variable diagram scheme
A pressure-based implicit procedure to solve the Euler and Navier-Stokes equations on a nonorthogonal mesh with collocated finite-volume formulation is described. The boundedness criteria for this procedure are determined from the NVD method, and are applied to the convected quantities. The procedure incorporates the eddy viscosity turbulence model. The algorithm is tested for several inviscid flows at different Mach numbers ranging from subsonic to supersonic on a bump in channel geometry where the results are compared with other existing numerical solutions. The method is then validated against experimental data for the case of turbulent transonic flow through a gas turbine rotor blade cascade. The comparisons presented show that the quality of the resolution of the SBIC scheme for steady state flows is remarkable.
internal flow
normalized variable diagram
SBIC
pressure-based
finite-volume
2013
02
16
495
500
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
An analysis of shear correction factors in a thermoplastic composite cantilever beam
In the present study, an analysis of shear correction factors is carried out for a homogeneous polyethylene thermoplastic cantilever beam which is reinforced by steel fibers with a rectangular cross-section. An applied shear force produces extension-shear coupling which has not been considered in previous out-of-plane shear deformation studies of beams. The shear correction factor is defined taking into account the coupling effect. Normal and shear stress distributions, as well as shear strain cross section of the rectangular solid beam are obtained analytically. The variation of shear correction factors versus ply angle for the composite beam is also presented.
Thermoplastic composite
shear correction factor
stress and strain analysis
2013
02
16
501
504
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2004
28
4
The improvement of combustion process and reduction of unburned hydrocarbon emission in a two-stroke motorcycle
In desert areas in which there are few asphalt roads, heavy vehicles can not commute easily. Two-stroke motorcycles are lighter and have higher output power in comparison with similar four-stroke ones. In the present project, a two-stroke motorcycle that is used in Iran and is the most powerful has been improved. Its engine is cooled with air and its average fuel (premixed petrol and oil or pet-oil) consumption is 5 liters per hour. The timing ignition in the base engine is constant for all conditions. Then, the effect of the improvement parameter of ignition timing is carefully examined and automatically tuned in terms of engine speed. This modification has been achieved by using a mechanical tuning system based on the governor timing method. Finally, the major emission pollutants’ parameters in modified and base engines are compared according to ECE regulation No.40. In this effort the following useful results are achieved:
a) The fuel consumption has been reduced to 3.5 liters per hour.
b) The UHC emission is reduced by 30 percent with the base engine.
c) The movement acceleration from rest condition to 60 kilometers per hour has been vvviremarkably increased in comparison with the base engine.
combustion
modification
motorcycle
pollutants
two-stroke
2013
02
16
505
508