Shashi Ranjan Kumar

Sliding-Mode Guidance and Control for All-Aspect Interceptors with Terminal Angle Constraints

In this paper, sliding-mode-control-based guidance laws to intercept stationary, constant-velocity, and maneuvering targets at a desired impact angle are proposed. The desired impact angle, which is defined in terms of a desired line-of-sight angle, is achieved in finite time by selecting the missiles lateral acceleration to enforce terminal sliding mode on a switching surface designed using nonlinear engagement dynamics. The conditions for capturability are also presented. In addition, by considering a three-degree-of-freedom linear-interceptor dynamic model and by following the procedure used to design a dynamic sliding-mode controller, the interceptor autopilot is designed as a simple static controller to track the lateral acceleration generated by the guidance law. Numerical simulation results are presented to validate the proposed guidance laws and the autopilot design for different initial engagement geometries and impact angles.

Nonsingular Terminal Sliding Mode Guidance with Impact Angle Constraints

Guidance laws based on a conventional sliding mode ensures only asymptotic convergence. However, convergence to the desired impact angle within a finite time is important in most practical guidance applications. These finite time convergent guidance laws suffer from singularity leading to control saturation. In this paper, guidance laws to intercept targets at a desired impact angle, from any initial heading angle, without exhibiting any singularity, are presented. The desired impact angle, which is defined in terms of a desired line-of-sight angle, is achieved in finite time by selecting the interceptors lateral acceleration to enforce nonsingular terminal sliding mode on a switching surface designed using nonlinear engagement dynamics. Numerical simulation results are presented to validate the proposed guidance laws for different initial engagement geometries and impact angles. Although the guidance laws are designed for constant speed interceptors, its robustness against the time-varying speed of interceptors is also evaluated through extensive simulation results.

Simulation of flow around a row of square cylinders

In this paper, the low-Reynolds number (Re = 80) flow around a row of nine square cylinders placed normal to the oncoming flow is investigated using the latticeBoltzmann method. The effects of the cylinder spacing on the flow are studied for spacing to diameter ratios of 0.3 to 12. No significant interaction between the wakes is observed with spacings greater than six times the diameter. At smaller spacings, the flow regimes as revealed by vorticity field and drag coefficient signal are: synchronized, quasi-periodic and chaotic. These regimes are shown to result from the interaction between primary (vortex shedding) and secondary (cylinder interaction) frequencies; the strength of the latter frequency in turn depends on the cylinder spacing. The secondary frequency is also related to transition between narrow and wide wakes behind a cylinder. The mean drag coefficient and Strouhal number are found to increase rapidly with a decrease in spacing; correlations of these parameters with spacing are proposed. The Strouhal number based on gap velocity becomes approximately constant for a large range of spacings, highlighting the significance of gap velocity for this class of flows. It is also possible to analyse the vortex pattern in the synchronized and quasi-periodic regimes with the help of vorticity dynamics. These results, most of which have been obtained for the first time, are of fundamental significance.

Sliding mode control based guidance law with impact time constraints

In this paper, the sliding mode control based guidance laws to intercept stationary targets at a desired impact time are proposed. Then, it is extended to constant velocity targets using the notion of predicted interception. The desired impact time is achieved by selecting the interceptors lateral acceleration to enforce a sliding mode on a switching surface designed using non-linear engagement dynamics. Numerical simulation results are presented to validate the proposed guidance law for different initial engagement geometries, impact times and salvo attack scenarios.

Non-singular terminal sliding mode guidance and control with terminal angle constraints for non-maneuvering targets

In this paper guidance laws to intercept stationary and constant velocity targets at a desired impact angle, based on sliding mode control theory, are proposed. The desired impact angle, which is defined in terms of a desired line-of-sight (LOS) angle, is achieved in finite time by selecting the missiles lateral acceleration (latax) to enforce non-singular terminal sliding mode on a switching surface designed using this desired LOS angle and based on non-linear engagement dynamics. Numerical simulation results are presented to validate the proposed guidance laws for different initial engagement geometries and impact angles.

Impact time guidance for large heading errors using sliding mode control

In this paper, sliding mode control-based impact time guidance laws are proposed. Even for large heading angle errors and negative initial closing speeds, the desired impact time is achieved by enforcing a sliding mode on a switching surface designed by using the concepts of collision course and estimated time-to-go. Unlike existing guidance laws, the proposed guidance strategy achieves impact time successfully even when the estimated interception time is greater than the desired impact time. Simulation results are also presented.

A methodology and algorithms for efficient interprocess communication synthesis from system description in SDL

This paper discusses a methodology and algorithms for efficient hardware synthesis of inter-process communication in systems described in SDL. The basic idea of our approach is to implement an SDL process by two hardware blocks, namely Computation Block and Communication Block. The Computation Block implements the data computation functions of the process as an Extended FSM (EFSM). The Communication Block implements the communication of the process with other processes. We give an algorithm to classify the communication requirements of the process and have an efficient implementation for it. Our scheme also has a supervisor block for every SDL block to manage interprocess communication. Our methodology supports multiple instances of the processes and dynamic processes. In our scheme, a single copy of hardware (Compute block) is shared among multiple copies of a process within a block which leads to efficient hardware implementation.

Impact Time and Angle Control Guidance

In this paper, a guidance strategy, which extends the existing impact angle control guidance laws to cater to the impact time constraints as well, is proposed. This guidance scheme is based on switching between sliding mode control based impact time control guidance law and the impact angle control guidance laws. Unlike the usual impact time guidance laws, the proposed guidance law also takes into account the requirement of the curvature of the trajectory toward the interception point due to the an impact angle requirement. The impact time guidance law is derived using a switching surface based on nonlinear engagement dynamics and time-to-go. In the first step, the guidance law corrects for the impact time and then in the second step, the impact angle control guidance achieves the impact angle requirements along with the interception. Initially stationary targets are considered, and later the same guidance scheme is extended to a constant velocity target using the notion of predicted interception. Numerical simulation results are presented to validate the proposed guidance law for different initial engagement geometries, impact times, and angles scenarios. By controlling both the impact time and angle, simulation results are presented to evaluate the performance for different salvo attack scenarios.

Three dimensional impact angle constrained guidance law using sliding mode control

In this paper, three dimensional impact angle control guidance laws are proposed for stationary targets. Unlike the usual approach of decoupling the engagement dynamics into two mutually orthogonal 2-dimensional planes, the guidance laws are derived using the coupled dynamics. These guidance laws are designed using principles of conventional as well as nonsingular terminal sliding mode control theory. The guidance law based on nonsingular terminal sliding mode guarantees finite time convergence of interceptor to the desired impact angle. In order to derive the guidance laws, multi-dimension switching surfaces are used. The stability of the system, with selected switching surfaces, is demonstrated using Lyapunov stability theory. Numerical simulation results are presented to validate the proposed guidance law.

Three-dimensional impact angle guidance with coupled engagement dynamics

This paper proposes three-dimensional impact angle control guidance laws based on a sliding mode control technique. Unlike the usual approach of decoupling the engagement dynamics into two mutually orthogonal two-dimensional planes, the guidance laws are derived using coupled engagement dynamics. By using this approach, the control effort required to achieve the objective reduces and the performance of the guidance law is improved. The derivations of guidance laws are done using both conventional as well as nonsingular terminal sliding mode control, which guarantees asymptotic and finite time convergence, respectively, to the desired impact angle. In order to derive the guidance laws, multi-dimensional switching surfaces are used. The stability of the system, with selected switching surfaces, is demonstrated using Lyapunov stability theory. Numerical simulation results are presented to validate the proposed guidance laws for constant speed, as well as a realistic interceptor model with given aerodynamic properties. The simulations show the advantage of using coupled dynamics. The robustness of the proposed guidance laws, with respect to the interceptor’s system lag, is also investigated.