2018-10-24T06:20:54Z
http://ijstm.shirazu.ac.ir/?_action=export&rf=summon&issue=267
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Design aspects for feed-forward multiple-input active noise controllers
The use of adaptive feed-forward controllers has proven to be a very successful strategy for controlling noise and vibration in a variety of applications. One reason is that the feed-forward controller is an open loop controller, which can be designed to cancel the undesired noise in a position with any accuracy. However, the feed-forward controller requires an input signal, called a reference signal, correlated to the noise source. Consequently, a single reference controller can only reduce noise radiated from a single noise source. In many applications, there is a need to attenuate noise produced by several noise sources. In this paper, three different structures, single, modulating and individual controller, for multiple input feed-forward controllers have been studied and some design aspects are investigated.
Active noise control
feed-forward control
multiple input
adaptive control
LMS
2013
02
16
407
418
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Using interlacing and irregular meshes in plate analysis
This paper investigates the implementation of interlacing and irregular rectangular meshes used in conjunction with the DXDR method and a modified dynamic relaxation method, to study the large deflection elastic plates. Numerical computations are conducted to evaluate the accuracy of solutions with different mesh arrangements. Emphasis is placed on the selection of appropriate interlacing meshes and the ability of rectangular meshes to treat non-rectangular boundary conditions. Numerical examples demonstrate in detail the efficiency, accuracy and stability attainable in solving various engineering problems. It is concluded that both interlacing and irregular meshes are more efficient than the usual rectangular ones to study rectangular, circular and elliptical plates. However, the irregular mesh technique is superior in treating non-rectangular boundaries.
Interlacing method
irregular mesh
large elastic deformation
dynamic relaxation
2013
02
16
419
430
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Three–dimensional axisymmetric vibrations of orthotropic and cross–ply laminated hemispherical shells
Free vibration of orthotropic and cross–ply laminated hemispherical shells using elasticity approach is studied. The Navier type equations are transformed into partial differential equations with constant coefficients in radial direction, assuming that the ratio of the thickness to mean radius of each lamina of the shell is small and hence can be neglected with respect to unity. The partial differential equations are reduced to ordinary differential equations, by applying Galerkin method, using Legendre polynomials along the meridian direction. The resulting ordinery differential equations are solved exactly for each layer. Connecting all of the exact solutions by means of appropriate continuity conditions and by using a method of successive approximation the solution of the problem is achieved. Convergence tests have been carried out to demonstrate the veracity of the approach. Numerical results are presented and compared with the latest results found in the literature.
vibration
cross-ply
laminated
orthotropic
three-dimensional
hemispherical
axisymmetric
2013
02
16
431
440
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Analysis of multi-layered shallow panels under dynamic thermal load based on the theory of elasticity
Three-dimesional thermoelasticity solutions are presented for the dynamic analysis of an axisymmetric cross-ply laminated shallow panel subjected to thermal load. The panel is simply supported at four sides and has a finite length. Three-dimensional equations of motion, which are coupled partial differential equations, are reduced to system of differential equations with constant coefficients by means of the trigonometric function expansion in circumferential and axial directions. The resulting ordinary differential equations are then solved by the Galerkin finite element method. Numerical results show that fiber orientation strongly influences the stresses in a single layer panel. When the fibers are aligned circumferentially, the hoop stress becomes large. This is due to the large difference between the radial and circumferential coefficients of thermal expansion when the fibers are oriented circumferentially. Finally, numerical examples are presented for (0), (0/90) and (0/90/0) degrees of laminations stacking and those are compared with the results found in literature.
Shallow
panel
dynamic elasticity
Composite
Thermoelasticity
2013
02
16
441
454
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Design of fuzzy systems for modelling of explosive cutting process of plates using singular value decomposition
Fuzzy systems are used for modelling of explosive cutting process of plates by shaped charges. The aim of such modelling is to show how the depth of penetration varies with the variation of important parameters. It is also demonstrated that singular value decomposition (SVD) can be effectively used to fine tuning of such fuzzy models in a noniterative process. Such application of SVD will highly improve the performance of fuzzy systems to model the very complex process of explosive cutting of plates by shaped charges.
Fuzzy systems
explosive cutting process
SVD
2013
02
16
455
464
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Control-volume finite-element method for the solution of 2d euler equations on unstructured moving grids
In this paper, Euler equations are solved to simulate compressible flow on unstructured moving grids. Solution domain is discretized using control-volume finite-element method. This method is benefited from the power of finite element in discretizing solution domain, and the capability of finite volume in conserving physical quantities. For the evaluation of flux vector components at the control-volume surfaces, we employed the flux-difference scheme of Roe, modified for moving grids. Geometric conservation laws are implemented carefully to prevent solution errors produced by grid movement. To demonstrate the accuracy of the algorithm in solving fluid flow problems on moving grids, a number of test problems have been carried out.
Euler equations
unstructured mesh
moving grid
geometric-conservation-laws
2013
02
16
465
476
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Simulation of srm internal ballistics with inner/outer burning surfaces
In this paper, internal ballistics of solid rocket motors (SRM), in which the grain is burned from inside (inner burning surface) or from both inside and outside (inner and outer burning surfaces), is numerically simulated. The solution domain includes two passages and a converging-diverging nozzle. It is discretized using a control-volume finite-element method. Governing equations of the quasi one-dimensional Euler flow are integrated over each control volume. The flux-vector components are related to the nodal values using a physical influence scheme. Erosive burning is incorporated in the flowfield calculation using a quasi-steady model. In cases with inner and outer burning surfaces, the resulting system of equations deviates from a block tri-diagonal one. Therefore, special care is needed for the efficient solution of this system of equations. To evaluate performance of the present algorithm, transient flow fields of several SRMs with different burning surfaces are simulated, and the results compared with the experimental data and numerical results. The excellent agreement observed in all cases validates the algorithm and approves its accuracy. For SRMs with inner and outer burning surfaces, possibility of their modeling with an equivalent motor is also investigated. In addition, a SRM with area transition along the grain is simulated to demonstrate the general capability of the present code.
Internal ballistics
solid rocket motor
erosive burning
Euler equations
2013
02
16
477
486
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Numerical analysis of 2d high speed flow of real gases on an adaptive unstructured grid
The 2D hypersonic real gas flow has been analyzed on an adaptive unstructured grid using Roe's Flux Difference Splitting and AUSM schemes. In high temperature and hypersonic regime, the flow is extremely compressible and ideal gas assumption is not valid. In fact in these flows, due to changes in the flow properties, composition of fluid elements will also change.
<span style="font-size: x-small;">To solve steady and unsteady 2D Euler equations for real gases, assumption of a general equation of state for real gases in equilibrium is considered. We use an unstructured Delaunay triangulation and adapt it in high gradient areas. Results are compared with known numerical and exact solutions. The scheme is convergent, and provides accurate results with fairly small number of cells due to adaptation and application of the algorithm to one dimensional shock tube and blunt body problem shows its quality and robustness. </span>
Real gas
unstructured grid
Roe method
adaptive mesh
hypersonic
2013
02
16
487
496
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Temporal and spatial behaviors of discharge in nitrogen gas between two parallel-plane electrodes
In this article, a full temporal and spatial description of discharge for pure nitrogen gas in a nearly uniform electric field is reported. Results of simulation given provide a full understanding of the discharge at different stages of the ionization process. Effects of the primary energetic electrons and the secondary electrons are clearly shown at each stage of the ionization growth being followed in the discharge gap. Presented are the local electric field distribution and temporal behavior of the streamers at each point of the discharge medium along with the secondary processes affecting ionization growth.
Discharge
current
spark gap
breakdown
ionization
2013
02
16
497
506
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
The measurement of oxidant/fuel ratio in injector plate of
liquid propellant rocket engine before combustion, with an experimental method and its comparison with a theoretical method
Mixture ratio (oxidant/ fuel) in combustion chamber has influence on combustion and thermodynamic properties as thrust and impulse; therefore, calculation of this parameter in the injector plate of liquid propellant rockets is very important. We have proposed an experimental method in which water and oil (simulating oxidant and fuel) passed from injection plate enter in elemental vessels. A computer code based on existent theoretical methods is developed and its results are compared with experimental results.
Mixture ratio
liquid propellant rocket engine
injector plate
injection system
2013
02
16
507
517
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Thermohydrodynamic behavior of journal bearings running under different steady conditions
In most previous investigations, journal bearing performance characteristics have been analyzed using different simplified assumptions. The purpose of this study is to eliminate most of those assumptions, using computational fluid dynamics (CFD) techniques to solve the exact governing equations. The bearing has a finite length and operates under incompressible laminar flow and steady conditions. Numerical solutions of the full three-dimensional Navier-Stokes equations, coupled with the energy equation in the lubricant field and the heat conduction equations in the bearing and the shaft are obtained. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid and the governing equations are transformed for use in the computational domain. Discretized forms of the transformed equations are obtained by control volume method and solved by SIMPLE algorithm. Cavitation effects are also considered by introducing an appropriate three-dimensional cavitation model. In order to study the effect of main parameters on thermohydrodynamic behavior of journal bearings, solutions are obtained for different values of the eccentricity and radial clearance and also for different values of the rotational speed of the shaft. To validate the computational results, comparison with the experimental data of other investigators is made, and reasonable agreement is obtained.
Journal bearing
thermohydrodynamic
cavitation
Laminar flow
steady conditions
conformal mapping
2013
02
16
515
532
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Reynolds number influence on the jet flow field of a long neck circular nozzle
Near field circular jet is studied experimentally at discharge Reynolds number range of 21000 to 100000. The effect of Reynolds number on the initial boundary layer mean velocity profile is negligible, but is significant on the exit turbulent velocity profile, extend of the partial self-reservation zone, spread of the shear layer and the viscous shear stress. With decrease Reynolds number the entrainment rate decreased.
laminar
transition
turbulent
entrainment
viscous
momentum
significant
2013
02
16
533
540
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Experimental and computational studies of soot emission in a gas fuelled swirl stabilized combustor
The present study is concerned with measuring and simulating soot and flame structure of a non-premixed gas fired swirl stabilized combustor incorporating a two-step soot model. Soot mass fractions have been measured by gravimetric method. Fluent CFD software has been employed for numerical predictions and the effect of two combustion models on flame structure and soot production are investigated. Both finite rate model with eddy-dissipation concept and flamelet approaches are employed to model the combustion process and the accuracy of each model is compared with the experimental data. In terms of turbulence modeling, the full Reynolds stress transport model is employed to calculate the turbulent characteristics of highly swirling flow. Measurements and computations are performed for different cases by varying the equivalence ratio, the inlet air temperature and the combustor wall temperature. The numerical predictions and experimental measurements show that soot generation strongly depends on the equivalence ratio and the inlet air temperature, as well as it is also affected by the combustor wall temperature. The numerical results show the significant influence of combustion models on soot formation/oxidation, when investigating the non-premixed natural gas/air flame. The comparison of calculated results against the experimental measurements for rich combustion reveals the superiority of flamelet model over the finite rate model.
Soot formation
Flamelet model
finite rate model
2013
02
16
541
554
Iranian Journal of Science and Technology Transactions of Mechanical Engineering
2228-6187
2228-6187
2002
26
3
Time optimal control of robotic manipulator with bounded control input and jerk constraint
In this paper, the time-optimal control for point-to-point motion of robotic manipulators, with fixed initial and final states, bounded control inputs and jerk constraint for entire path is presented.
<span style="font-size: x-small;">First, the jerk constraint with respect to state variables is derived. Afterwards the dynamic equations of robotic manipulator in state space form and jerk constraints discretized by forward difference technique. Thus the time-optimal control problem is formulated as a constrained parameter optimization problem. The MATLAB optimization toolbox is used to obtain the solution of the constrained parameter optimization problem. The proposed method can help us to implement the time-optimal control problem with bounded inputs and jerk constraint. Finally, the above-mentioned method is implemented for a 2R planar robotic manipulator. Simulation results show a smooth trajectory for robot motion when the jerk is limited, which can effectively reduce mechanical wear at joints</span>
2013
02
16
555
562