Scientia Iranica
Volume:21 Issue: 6, 2014

In this paper, modeling and control of a rotary missile which uses the proportional navigation law is purposed, applying Quantitative Feedback Theory (QFT) technique. Dynamics of missile are highly uncertain; thus application of robust control methods for high precise control of missiles is inevitable. In the modeling section, a new coordinate system has been introduced which simplifies the analysis of rotary missile’s dynamics equations. In the controlling part,applicationofQFTmethod leads to the design of robust PID controller for highly uncertain dynamics of missile. Since the missile’s dynamics have multivariable nonlinear transfer functions, in order to apply QFT technique, these functions are converted to a family of linear time invariant processes with uncertainty. Next, in the loop shaping phase, an optimal robust PID controller for thelinear process is designed. Lastly, analysis of design procedure shows that robust PID controller is superior to the commonly used PID scheme and multiple sliding surface schemes in terms of both tracking accuracy and robustness.

This paper focuses on a theoretical analysis of an AFM based nano-manipulation in liquid environment. To achievethis goal, major forces in liquid environment were reviewed and the of manipulation processes was modelled by introducing the effect of intermolecular forces and hydrodynamic forces. Dynamic behaviour of pushing a gold nanoparticle of 50-nm radius on a silicon substrate at a velocity of 100 nm/s was investigated. A virtual reality user interface was also implemented and evaluated in liquid environment so that the users can get a senseof forces. The results show that, in comparison to air, the required forces and time are increased by 2 and 6.5%, for sliding and 2 and 4.3% for rolling in liquid environment. Furthermore for various submerged lengths of the cantilever in water, forces and time value are varied 8 and 10.5% respectively.Based on the simulation a result, sliding occurs in nominal values and critical forces and manipulation time in liquid environment increases over the values. For biologicalmanipulation purposes liquid environment is superior in comparison to air and the obtained results are verified by existing experimental.

In this article, a forced reduced-order modeling approach, suitable for active optimal control of fluid dynamical systems based on the Proper Orthogonal Decomposition and perturbation method on the Reynolds-Averaged Navier-Stokes equations is presented. Numerical simulation of turbulent flow equations is too costly for the purpose of optimization and control of unsteady flows. As a result, POD/Galerkin projection and perturbation method on the RANS equations is considered. Using perturbation method, the controlling parameter shows up explicitly in the forced reduced-order system. The feedback control of the controlling parameter is one of the objectives of this study. With the perturbation method, the effect of the controller is sensed by fluid flow in each time step. The effectiveness of this method has been shown on optimal control of re-circulation problem for the turbulent flow over step with blowing/suction controlling jets. Actuators are positioned at two different locations—blowing/suction jets at the foot and edge of the step and blowing/suction jets at the wall of the step. Results show that perturbation method is fast and accurate in estimating the re-circulated turbulent flow over step. It is concluded that blowing/suction jets at the wall of the step are more efficient in mitigating flow separation.

This paper presents vibration and buckling analysis of functionally gradedbeams with different boundary conditions, using reproducing kernel particle method(RKPM). Vibration of simple Euler–Bernoullibeam using RKPM is already developed and reported in the literature. Modeling of FGM beams using theoretical method or finite element technique is not evolved with accurate results for power law form of FGM with large power of “n” value so far. Accuracy of the RKPM results is very good and is not sensitive to n value. System of equations of motion is derived using Lagrange’s method under the assumption of Euler–Bernoulli beam theory. Boundary conditions of the beam are taken into account using Lagrange multipliers. It is assumed that material properties of the beam vary continuously in the thickness direction according to the power-law form. RKPM is implemented to obtain the equation of motion and consequently natural frequencies and buckling loads of the FGM beam are evaluated. Results are verified for special cases reported in the literature. Considering the displacement of the neutral axis, buckling loads with respect to length and material distribution are evaluated. For the special case of homogenous beam, RKPM matches theoretical evaluation with less than one percent error.

In recent years, the positioning of cylindrical nanoparticles, like CNTs and nanowires, by means of Atomic Force Microscope (AFM) nanorobots has been investigated widely. Despite this growing scienti c interest, no one has studied 3D model simulations of di erent modes (sliding, rolling and rotation). Previous work has only focused on twodimensional simulations, which often cannot be extended to the manipulation of cylindrical particles. The aim of this study is to present a 3D model for the positioning of cylindrical nanoparticles. In order to validate the results, 2D and 3D simulations have been compared. Moreover, the ndings show that both simulations act similarly with a gradual decrease in the e ects of 3D parameters. We have developed a 3D kinematic model, which makes it possible to predict the positioning process from the moment the tip of the cantilever touches the particle to when the particle reaches the desired point. These simulations also determine the displacements of the particle and cantilever during the time when the particle is stuck into the substrate. In response to real-time monitoring limitations, the introduced kinematic simulation is able to predict the motion behavior of a cylindrical nanoparticle during the manipulation process.

Synchronization of two chaotic systems has been used in secure communications. In this paper, synchronization of two identical 4D Lu hyper-chaotic systems is used to identify the drive system. Parameters in both drive and response systems are unknown and the systems are synchronized by applying one state feedback controller. Since the goal here is to identify the parameters of the drive system, an adaptive method is used. The stability of the closed-loop system with the controller and convergence of parameters is studied using the Lyapunov theorem. In order to improve the speed of convergence in one parameter, a fractional adaptation law is used and the stability with the fractional law is shown. Finally, the results of both integer and fractional methods are compared.

A high order accurate mixed finite element-differential quadrature method is proposed to study the dynamics of axially moving orthotropic rectangular plates subjected to linearly varying inplane stresses. The finite element method (FEM) with higher order interpolation functions is first used to discretize the spatial partial derivatives with respect to a co-ordinate direction of the plate. The differential quadrature method (DQM) is then employed to discretize the resulting system of ordinary differential equations. Linearly varying uniform and non-uniform distributed load conditions are considered on two-opposite edges of the plate. Comparisons are made with existing numerical and analytical solutions in the literature. It is revealed that the proposed mixed method is highly accurate and efficient. Finally, the dimensionless complex frequencies of the axially moving orthotropic plate with different boundary conditions under the linearly varying inplane stresses are calculated by the proposed mixed method. The curves for the real and imaginary parts of the first three dimensionless complex frequencies versus the dimensionless axially moving speed are obtained. The effects of material properties of the plate, variation of inplane stresses, and the dimensionless moving speed on the stability of the orthotropic plate are investigated.

Metallic foams are a class of lightweight materials that show high potentials for diff erent industrial applications such as automotive and aerospace engineering. However, many factors have prevented metallic foams from being fully utilized in industrial applications. One main factor is that the influences of the porous structure on the mechanical properties of metallic foams are not well known yet. In this paper, a nite element model was used to analyze monodisperse closed cell aluminum foam in order to determine the relationship between its elastic modulus, porosity and pore diameter. A nonlinear relationship was found between the foams porosity, pore diameter and modulus of elasticity. In this regard, an empirical equation was developed and implemented for the prediction of modulus of elasticity versus porosity and pore diameter. Comparing experimental and analytical approaches by other researchers with those obtained in this research shows that agreement exists within 1 to 3 percent. Therefore, this model could be further used for other porous structures. It was also found that a similar empirical equation with new coecients can also be used to predict the modulus of elasticity of cast iron and steel foams.

The purpose of this paper is using the proposed two step method to impose essential boundary conditions for improving the accuracy of solution field. In the proposed approach, imposing essential boundary conditions in transient heat flow within two-dimensional region is extended in two steps. The essential boundary conditions are defined on Dirichlet boundary as determined temperatures and independent of time. In the first step, Dirichlet boundary conditions are weakly built into the variational formulation, choosing weight function, appropriately. In the second step, with fixed condition, the system of equations is appropriately adjusted. For investigation of the efficiency of the proposed approach, several 2D numerical examples have been performed. The results demonstrate significant improvement in accuracy and rate of convergence in comparison with direct imposition of essential boundary condition.

In this paper, the problem of optimal tracking control for a container ship is addressed. The multi-input–multi-output nonlinear model of the S175 container ship is well established in the literature and represents a challenging problem for control design, where the design requirement is to follow a commanded maneuver at a desired speed. To satisfy the constraints on the states and the control inputs of the vessel nonlinear dynamics and minimize the heading error, a nonlinear optimal controller is formed. To solve the resulted nonlinear constrained optimal control problem, the Gauss Pseudospectral Method (GPM) is used to transcribe the optimal control problem into a Nonlinear Programming Problem (NLP) by discretization of states and controls. The resulted NLP is then solved by a well-developed algorithm known as SNOPT. The results for course-keeping and course-changing autopilots illustrate the effectiveness of the proposed approach to deal with the vessel tracking control.

In this paper, a novel inverse design algorithm called as Ball Spine algorithm is developed to design the blade to blade flow passage of axial-flow compressors. The algorithm considers the blade surfaces as a set of virtual balls that move freely along the specified directions, called ‘spines’. To start the solution an initial guess for the blade geometry is required. Then the blade-to-blade flow field is solved using an in-house inviscid solver. Comparing the computed pressure distribution (CPD) with the target pressure distribution (TPD) over the blade surfaces, gives guidelines in differential movements for the balls to obtain a modified geometry. For the modified geometry, new grids are automatically generated by an algebraic-elliptic grid-generator. The sequence is repeated until the target pressure is met. An error parameter, ∆PD, indicating the difference between CPD and TPD along the suction and pressure surfaces is computed while the blade geometry evolves toward the target geometry. For the initial guess, ∆PD is obtained as 13700 Pa, while after 100 generations, ∆PD is reduced to 222 Pa.

The aim of this paper is to determinate the local convective heat transfer coefficient slot jet impingement by using Inverse Heat Conduction Methods. Sequential specification function method and conjugate gradient method are used to solve the Inverse Heat Conduction Problem (IHCP) and estimate the space-variable convective heat transfer coefficient. This paper proposes a procedure to smooth the temperature data by Mollification method prior to utilizing the inverse method. The measured transient temperature data may be obtained from locations inside the body or on its inactive boundaries. The uncertainties in the estimated in heat transfer coefficient are calculated using Bias and Variance errors. The obtained results show that Mollifying measured data causes an increase in the accuracy and the stability of the estimation.