IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

This paper deals with the application of nonparametric system identification to the nonlinear maneuvering of ships using neural network method. The maneuvering equations contain linear as well as nonlinear terms, and one does not attempt to determine the parameters (or hydrodynamic derivatives) associated with nonlinear terms, rather all nonlinear terms are clubbed together to form one unknown time function per equation, which are sought to be represented by neural network coefficients. The time series used in training the network are obtained from simulated data of zigzag and spiral maneuvers. The neural network has one middle or hidden layer of neurons and the Levenberg-Marquardt algorithm is used to obtain the network coefficients. Using the best choices for number of hidden layer neurons, length of training data, convergence tolerance, and so forth, the performances of the proposed neural network models have been investigated and conclusions drawn.

Department of Aerospace Engineering

Department of Ocean Engineering

Journal of Ship Research

System identification for nonlinear maneuvering of ships using neural network

A projectile that passes through a moving shock wave experiences drastic changes in the aerodynamic forces as it moves from a high-pressure region to a low-pressure region. These sudden changes in the forces are attributed to the wave structures produced by the projectile-shock-wave interaction and are responsible for destabilizing the trajectory of the projectile, consequently leading to a loss of projectile stability and control efficiency. A computational study was performed here using a moving-grid method to analyze the effects of the projectile overtaking a moving shock wave on the projectile aerodynamic characteristics. A one-dimensional analysis was also carried out to identify the projectile overtaking criteria. The analytical results show that the projectile overtaking flowflelds can be in a subsonic or supersonic flow regime, based on the relative projectile Mach number. However, it is found that the actual flowflelds in the present computations cannot be distinguished with the relative projectile Mach number only, because the blast-wave strength is diminishing with time and space. The aerodynamic characteristics of the projectile are hardly affected by the overtaking process for smaller blast-wave Mach numbers, as the blast wave will become weak by the time it is overtaken by the projectile. The projectile drag coefficient is more greatly affected by the unsteady flow structures through which the projectile travels in the near field than by the overtaking process. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

World University root node

Journal of Spacecraft and Rockets

Projectile aerodynamics overtaking a shock wave

This paper deals with the application of nonparametric system identification to a nonlinear maneuvering model for large tankers using artificial neural network method. The three coupled maneuvering equations in this model for large tankers contain linear and nonlinear terms and instead of attempting to determine the parameters (i.e. hydrodynamic derivatives) associated with nonlinear terms, all nonlinear terms are clubbed together to form one unknown time function per equation which are sought to be represented by the neural network coefficients. The time series used in training the network are obtained from simulated data of zigzag maneuvers and the proposed method has been applied to these data. The neural network scheme adopted in this work has one middle or hidden layer of neurons and it employs the Levenberg-Marquardt algorithm. Using the best choices for the number of hidden layer neurons, length of training data, convergence tolerance etc., the performance of the proposed neural network model has been investigated and conclusions drawn. © 2008 Elsevier Ltd. All rights reserved.

Applied Ocean Research

System identification for nonlinear maneuvering of large tankers using artificial neural network

A computational fluid dynamics (CFD) method has been applied to simulate unsteady near-field aerodynamics of the projectile which is launched from a ballistic range. A moving coordinate scheme for a multi-domain technique was employed to investigate the unsteady flow with moving boundary. The coordinate system fixed to each moving domain was applied to the multi-domains, and the effect of virtual mass was added in the governing equations for each domain. The unsteady, axi-symmetric Euler equation systems were numerically solved using the third-order Chakravarthy-Osher total variation diminishing scheme, with Monotone Upstream-centered Scheme for Conservation Laws (MUSCL) approach. The present computations were validated with results of some other CFD works and experimental data available. The computed results reasonably capture the major flow features, such as shock waves, blast waves, shear layers, vortical flows, etc which are generated in launching a projectile up to a supersonic speed. The projectile mass, configuration, and the initial conditions behind the projectile have been varied to investigate its effect on the flow field and the unsteady projectile aerodynamics. The unsteady aerodynamics of the projectile is strongly affected by the projectile mass and configuration. The initial conditions behind the projectile have strong influence on the near flow field structures which govern the development of the blast wave along with the projectile motion. © IMechE 2007.

Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering

A study of unsteady projectile aerodynamics using a moving coordinate method

The ballistic range has long been employed in a variety of engineering fields such as high-velocity impact engineering, projectile aerodynamics and aeroballistics, since it can create an extremely high-pressure state in very short time. Since the operation of the ballistic range includes many complicated phenomena, each process should be understood in detail for the performance enhancement of the device. One of the main processes which have significant influence on the device performance is the compression process of the driver gas. Most of the studies available in this field hardly discuss this phenomenon in detail and thus lack a proper understanding of its effect on the whole system performance. In the present study, a computational analysis has been made to investigate the fluid dynamic aspects of the compression process in the pump tube of a ballistic range and to assess how it affects the performance of the ballistic range. The results obtained are validated with the available experimental data. In order to evaluate the system performance, several performance parameters are defined. Effect of a shock tube added in between the pump tube and launch tube on the performance of the ballistic range is also studied analytically. Performance of the ballistic range could be significantly improved by the proper selection of the pump tube and high-pressure tube parameters and the addition of the shock tube. © 2007 Science Press.

Department Of Chemistry

Journal of Thermal Science

Computational analysis of the compressible flow driven by a piston in a ballistic range

The ballistic range has long been employed in a variety of engineering fields such as high-velocity impact engineering, projectile aerodynamics, and aeroballistics, since it can create an extremely high-pressure state in a very short time. Of many different types of ballistic ranges developed to date, a two-stage light-gas gun is being employed most extensively. Since the operation of the ballistic range involves many complicated gas dynamic processes, optimization of various design parameters of the ballistic range is important for the durability of its components. In the present study, a theoretical analysis has been carried out to investigate various unsteady processes involved in the operation of the ballistic range and to assess the performance of the ballistic range. The results obtained are validated with the available experimental data. A shock tube is added in between the pump tube and launch tube and its effect on the performance of the ballistic range is quantified using the present theoretical analysis. Several methods are employed to define the ballistic efficiency. The effect of ratio of pump tube area to launch tube area on the performance is also investigated. A significant performance enhancement is obtained in the ballistic range with the addition of a shock tube. © IMechE 2007.

Performance analysis and enhancement of the ballistic range

A computational fluid dynamics method has been applied to simulate the unsteady aerodynamics of the projectile launched from a ballistic range. A moving coordinate scheme for a multi-domain technique was employed to investigate the unsteady flow with moving boundary. The coordinate system fixed to each moving domain was applied to the multi-domains, and the effect of virtual mass was added in the governing equations for each domain. The unsteady, axisymmetric Euler equation systems were numerically solved using the third order Chakravarthy-Osher total variation diminishing scheme, with MUSCL approach. The projectile mass and configuration effects on the unsteady aerodynamics were investigated based on the computational results. The present computations were validated with results of some other CFD works available. The computed results reasonably capture the major flow features, such as shock waves, blast waves, shear layers, vertical flows, etc. which are generated in launching a projectile up to a supersonic speed. The present computational method properly predicts the velocity, acceleration and drag histories of the projectile.

Journal of Mechanical Science and Technology

On the near-field aerodynamics of a projectile launched from a ballistic range

The ballistic range has long been employed in a variety of engineering fields such as high-velocity impact engineering, projectile aerodynamics, creation of new materials, etc, since it can create an extremely high-pressure state in very short time. Of many different types of ballistic ranges developed to date, two-stage light gas gun is being employed most extensively. In the present study, a theoretical work has been made to develop a new type of ballistic range which can easily simulate a flying projectile. The present ballistic range consists of high-pressure tube, piston, pump tube, shock tube and launch tube. The effect of adding a shock tube in between the pump tube and launch tube is investigated. This improvement is identified as the reduction in pressures in the high pressure tube and pump tube while maintaining the projectile velocity. Equations of motions of piston and projectile are solved using Runge-Kutta methods. Dependence of projectile velocity on various design factors such as high pressure tube pressure, piston mass, projectile mass, area ratio of pump tube to launch tube and type of driver gas in the pump tube are also analyzed. Effect of various gas combinations is also investigated. Calculations show that projectile velocities of the order 8 km/sec could be achieved with the present ballistic range.

A theoretical study for the design of a new ballistic range

The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length. © 2006 Science Press.

Optimization study of a Coanda ejector

When a gas is introduced at high velocity through a nozzle into a packed bed, it creates a raceway in the packed bed. It has been found that the raceway size is larger when it is formed by decreasing the gas velocity from its highest value than when it is formed by increasing the gas velocity. This phenomenon is known as raceway hysteresis. A hypothesis has been proposed to explain the hysteresis phenomenon based on a force-balance approach which includes frictional, bed-weight, and pressure forces. According to this hypothesis, the frictional force acts in different directions when the raceway is expanding and contracting. In this article, the entire packed bed has been divided into radial and Cartesian co-ordinate systems, and the forces acting on the raceway have been solved analytically for a simplified one-dimensional case. Based on the force-balance approach, a general equation has been obtained to predict the diameter of the raceway for increasing and decreasing velocities. A reasonable agreement has been found between the theoretical predictions and experimental observations. The model has also been compared with published experimental and plant data. The hysteresis mechanism in the packed beds can be described reasonably by taking into consideration the direction of frictional forces for the increasing- and decreasing-velocity cases. The effects of the particle-shape factor and void fraction on the raceway hysteresis are examined.

Department of Metallurgical and Materials Engineering

Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science

Mechanics of raceway hysteresis in a packed bed

It has been reported in the literature that raceway measurement made during the decreasing gas velocity is relevant to operating blast furnaces. However, no raceway correlation is available for decreasing gas velocity and none of the available correlations either in increasing or decreasing gas velocity take care of frictional properties of the material. Therefore, a systematic experimental study has been carried out on raceway hysteresis. Based on experimental data and using dimensional analysis, two raceway correlations, one each for increasing and decreasing gas velocity, have been developed. Results of these correlations have been compared with the data obtained from literature on the cold models and plant data along with some experimental data. A good agreement exists between the correlations and other data.