Showing papers by "Defence Research and Development Laboratory published in 2009"

Effect of welding parameters on mechanical properties and optimization of pulsed TIG welding of Al-Mg-Si alloy

Abstract: An attempt has been made to study the effect of pulsed TIG welding process parameters on dilution and mechanical properties such as notch tensile strength, hardness, and impact toughness in as-welded condition. Pulsed TIG welds exhibited lower notch tensile strength and impact toughness than the parent metal due to interdendritic network microstructure features. Taguchi method was used to optimize the pulsed TIG welding process parameters of heat-treatable (Al-Mg-Si) aluminum alloy weldments for maximizing the mechanical properties. An inverse relationship has been observed between the notch tensile strength and impact toughness.

Perception of Top Level Knowledge Workers on Productivity Improvement through Tools and Techniques

Abstract: Improving productivity of knowledge workers is one of the major challenges in today’s global environment. Through exploratory research, effort has been made to identify various tools & techniques those can improve productivity of knowledge workers. Through survey, effort has been made to find out perception of top level scientists on - usefulness of various tools & techniques; use of these tools & techniques and encouragement given in organisations for acquiring skill in these; trainings given for these tools & techniques and relative importance given by scientists for these tools & techniques. Questionnaires have been designed and given to select scientists at top level to find out their perception on various aspects indicated above, followed by interview where responses were not adequate or further clarifications were required. Scientists have indicated that most of the identified tools & techniques can improve their productivity and these are used in organisations or scientists are encouraged to acquire skill in the same and majority of them are presently not trained in these tools & techniques. They also indicated the relative importance of various tools & techniques. The extensive use of these tools & techniques and provision of trainings to the scientists in these can improve their productivity.

Comparison of the Radar and Seeker Modes of Pursuer Guidance

Abstract: This paper compares closed-loop performance of seeker-based and radar-based estimators for surface-to-air interception through 6-degree-of-freedom simulation using proportional navigation guidance.Ground radar measurements are evader range, azimuth and elevation angles contaminated by Gaussian noise. Onboard seeker measurements are pursuer-evader relative range, range rate also contaminated by Gaussian noise. The gimbal angles and line-of-sight rates in the gimbal frame,contaminated by time-correlated non-Gaussian noise with realistic numerical values are also available as measurements. In both the applications, extended Kalman filter with Gaussian noise assumption are used for state estimation. For a typical engagement, it is found that,based on Monte Carlo studies, seeker estimator outperforms radar estimator in terms of autopilot demand and reduces the miss distance.Thus, a seeker estimator with white Gaussian assumption is found to be adequate to handle the measurements even in the presence of non-Gaussian correlated noise. This paper uses realistic numerical values of all noise parameters.

Design and Analysis of MEMS-based Microballoon Actuators for Aerodynamic Control of Flight Vehicles

Abstract: The development of microelectromechanical systems (MEMS) technology and the suitability and compatibility of sizes of microactuators with the boundary layer thickness fueled the active flow separation control to gain the air flow momentum for the last few years. The present paper deals with the development of a robust, largedeflection, and large-force MEMS-based microballoon actuator for aerodynamic control of flight vehicles such as projectiles, micro air vehicles, aircrafts, etc. Experiments were carried out on the scaled-up models for different input pressure conditions to study the response of microballoon actuator. To evaluate the performance of the microballoon actuators, simulation studies on MEMS scale models were conducted in the CoventorWare environment. Simulation studies involving static and dynamic analyses have been carried-out on the microballoon actuator models. Various geometric and input parameters influencing the behaviour of the microballoon actuator were investigated. It has been observed that a maximum deflection of 1.2 mm to 1.5 mm can be achieved using microballoon actuators and the maximum operational frequency of 60 Hz to 80 Hz can be used for the operation of microballoon actuators. Also, the sizes of the microballoon actuators designed are compatible and suitable to be used in turbulent boundary layer of aerodynamic flight vehicles. Defence Science Journal, 2009, 59(6), pp.642-649 , DOI:http://dx.doi.org/10.14429/dsj.59.1570

Time Domain Identification of Input Forces in Vibration Testing of Flight Vehicle Structures

Abstract: The paper investigates the problem of determining the input that is to be given to a flight vehicle structure, using the measurement of acceleration responses of the structure, based on a time domain system identification procedure The proposed technique uses the Kalman filter to obtain both the system dynamics and the input force estimates. A realistic model of the vibration exciter is also included in the overall modal formulation and a general algorithm for this purpose is evolved, which is applicable to multi-point vibration testing strategy. A uniform beam with an exciter at its mid-point is chosen as a problem representing the flight vehicle structure undergoing vibration testing. Extensive MATLAB ®

Design of Packaging for Microballoon Actuators and Feasibility of their Integration within Aerodynamic Flight Vehicle

Abstract: The microballoon actuators are used for the active flow control in turbulent boundary layer for aerodynamic control of flight vehicles. The packaging, interfacing, and integration of the microballoon actuators within the flight vehicle play a key role for functioning of the microballoon actuators during the flight conditions. This paper addresses the design and analysis of packaging and integration aspects and associated issues. The use of microballoon actuators on the control surfaces and nose cone of flight vehicles has the positive influence of delaying the flow separation from the aerodynamic surface. This results in enhancing aerodynamic effectiveness and lift as well as reduction of drag. A typical control surface is configured with eight microballoon actuators symmetric wrt the hinge line of the control surface and embedded within the control surface. Provision of the Pneumatic feed line system for inflation and deflation of the microballoons within the control surface has been made. The nose cone has been designed to have 32 such actuators at the circular periphery. The design is found to be completely feasible for the incorporation of microballoon actuators, both in the nose cone and in the control surface. Defence Science Journal, 2009, 59(5), pp.485-493 , DOI:http://dx.doi.org/10.14429/dsj.59.1549

Software Reliability through Theorem Proving

Abstract: Improving software reliability of mission-critical systems is widely recognised as one of the major challenges. Early detection of errors in software requirements, designs and implementation, need rigorous verification and validation techniques. Several techniques comprising static and dynamic testing approaches are used to improve reliability of mission critical software; however it is hard to balance development time and budget with software reliability. Particularly using dynamic testing techniques, it is hard to ensure software reliability, as exhaustive testing is not possible. On the other hand, formal verification techniques utilise mathematical logic to prove correctness of the software based on given specifications, which in turn improves the reliability of the software. Theorem proving is a powerful formal verification technique that enhances the software reliability for missioncritical aerospace applications. This paper discusses the issues related to software reliability and theorem proving used to enhance software reliability through formal verification technique, based on the experiences with STeP tool, using the conventional and internationally accepted methodologies, models, theorem proving techniques available in the tool without proposing a new model. Defence Science Journal, 2009, 59(3), pp.314-317 , DOI:http://dx.doi.org/10.14429/dsj.59.1527

Semi-active vibration isolation using a near-zero-spring-rate device: steady state analysis of a single-degree-of-freedom model

Abstract: A vibration isolator is described which incorporates a near-zero-spring-rate device within its operating range. The device is an assembly of a vertical spring in parallel with two inclined springs. A low spring rate is achieved by combining the equivalent stiffness in the vertical direction of the inclined springs with the stiffness of the vertical central spring. It is shown that there is a relation between the geometry and the stiffness of the individual springs that results in a low spring rate. Computer simulation studies of a single-degree-of-freedom model for harmonic base input show that the performance of the proposed scheme is superior to that of the passive schemes with linear springs and skyhook damping configuration. The response curves show that, for small to large amplitudes of base disturbance, the system goes into resonance at low frequencies of excitation. Thus, it is possible to achieve very good isolation over a wide low-frequency band. Also, the damper force requirements for the proposed scheme are much lower than for the damper force of a skyhook configuration or a conventional linear spring with a semi-active damper.