Sharif Digital Repository

In [1], an optimal midcourse guidance law for close distances, where the difference of gravity for interceptor and ballistic missile is negligible, was introduced. There, a closed form solution, based on an optimization problem, was found, with very good performance for close distances but degraded performance in real problems with unequal gravity for missile and interceptor. In this paper, the difference of gravity is taken into account by considering a spherical gravity model. A new equation to express the relative motion between missile and interceptor is used to derive a "Near Optimal Guidance Law". The results found using the new derivation are similar to those in [1] but it provides a... 

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating Shkval missile. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is... 

Extensive wind tunnel tests have been conducted to study the unsteady aerodynamic behavior of a standard dynamics model, SDM, oscillating in plunge mode. The unsteady aerodynamic behavior of various missile and aircraft configurations under pitching motion has been studied so far. However up to now, there is little or no result on the plunging behavior of an aircraft or missile as a whole and the present experiments can be considered as one of the first attempts to study the compressible flowfield over an aircraft undergoing plunging motion. The experiments involved measuring the normal force and pitching moment of the model oscillating in plunge at Mach numbers of 0.4, 0.6 and 1.5 and... 

In this paper, a new model-based Fault Detection and Diagnosis (FDD) method for an agile supersonic flight vehicle is presented. A nonlinear model, controlled by a classical closed loop controller and proportional navigation guidance in interception scenario, describes the behavior of the vehicle. The proposed FDD method employs the Inertial Navigation System (INS) data and nonlinear dynamic model of the vehicle to inform fins damage to the controller before leading to an undesired performance or mission failure. Broken, burnt, unactuated or not opened control surfaces cause a drastic change in aerodynamic coefficients and consequently in the dynamic model. Therefore, in addition to the... 

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating Shkval missile. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile's motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is... 

In this study, the guidance and control problem of a single-channel spinning missile is investigated. The missile utilizes a single ON-OFF actuator to drive a pair of control surfaces (e.g. elevators) and consequently to perform all required lateral maneouvers. An approximated linear response of the so-called non-rotating frame to ON-OFF input, applied to the rotating frame, is derived using the multiple-input describing function technique. It is shown that there is a relationship between the response of the non-rotating frame and that of the equivalent non-rotating body. It is also shown that the two-channel flight controller, designed for the equivalent non-rotating body, can be reduced to... 

A new method of integrated guidance and control for homing missiles with actuator fault against manoeuvring targets is proposed. Model of the integrated guidance and control system in the pitch plane with actuator fault and some uncertainty is developed. A control law using combination of adaptive backstepping and sliding mode approaches is designed to achieve interception in the presence of bounded uncertainties and actuator fault. Simulation results show that new approach has better performance than adaptive backstepping and has good performance in the presence of actuator fault  

This paper presents a new method to counter Anti Radiation Missile (ARM) threats, which is effective against advanced ARM. By using random phase and amplitude active decoys in the specified optimum positions and network implementation we show that ARM threats will be removed profoundly. Also, iterative methods are presented to cancel the internal interference effects in the proposed structure  

This paper proposes a supervisory Command to Line-of-Sight (CLOS) guidance law with lead angle. The proposed scheme guarantees the missile to fly within the beam, when there is a beam angle constraint. In this regard a supervisory controller is coupled with a main Sliding Mode Controller (SMC). The supervisory control signal is activated when the beam constraint goes to be violated. First the supervisory controller is designed based on a recent idea on how the states of a nonlinear system with local stable controller can be controlled to stay within the domain of attraction. Then a sliding mode controller is designed, as the main tracking controller, to force the missile to fly along the... 

The comparison of aerodynamic characteristics of circular and noncircular bodies using computational-fluid-dynamics (CFD) code and semi-emperical code was discussed. It was observed that the performance of aerodynamic coefficients was better for squared section body at different angles of attack. It was also observed from the study of the flow physics that the pressure difference between the front and back of the body that produce pressure drag was more in the circular body. Results show that the friction drag is more for the square body than the circular body as the surface area of the square body is large  

The purpose of this work is to decrease coupling effects of a tactical missile by designing a robust autopilot for its roll channel. In tactical STT missiles due to control strategy, in order to execute acceleration commands, roll angular velocity should be kept close to zero. Generally, in the design of autopilot for many of tactical missiles the inter influences of channels is neglected. However, three channels of the missile impact each other in different ways including kinematic, inertia and aerodynamic couplings. Aerodynamic coupling is a dominant in roll channel dynamics appearing as induced and control cross coupling roll moments. In this paper first the coupling terms are modeled... 

This paper is concerned with the problem of guidance filter design for a homing air defense missile using measurements of an on-board pitch-yaw gimballed seeker mechanism. This problem possess a highly nonlinear dynamic which is influenced by various error sources such as seeker's stabilization loop torque disturbances originated from pursuer's accelerations and angular velocities, significant channel couplings, time-delayed and noisy measurements of optical sensor besides the unknown target maneuvers. To handle the inherent nonlinearity of problem a wide variety of assumptions are made in literature to derive simplified engagement kinematics. In present work, performance degradations which... 

The three-dimensional supersonic turbulent flows over wrap-around fin missiles have been computed using the Thin Layer Navier-Stokes (TLNS) equations to reduce the computational efforts compared to those of the Full Navier-Stokes (FNS) equations. In this research, the missile configuration is divided into multi regions to enable fluid flow simulation using Personal Computers (PC). It also makes it possible to use a different number of nodes and distribution of grids in each region to enhance the accuracy. The Thin Layer Navier-Stokes equations in the generalized coordinate system were solved using an efficient, implicit, finite-difference factored algorithm of the Beam and Warming. For the... 

An integrated guidance and control (IGC) is designed in this study for a surface-to-air missile considering burned or broken fin as a fault. The IGC model in the pitch plane is developed with various uncertainties in the presence of fin failure. The considered fault may cause a change in the vehicle’s shape that leads to a change in aerodynamic coefficients and consequently in the model. To identify the new model, aerodynamic coefficients are estimated using an estimator and the result is sent to the controller. Then, an adaptive robust controller is designed using the combination of backstepping and sliding mode scheme to compensate fin failure and changes in the dynamic. The simulation...