Showing papers in "Sadhana-academy Proceedings in Engineering Sciences in 1994"

A tutorial survey of reinforcement learning

Abstract: This paper gives a compact, self-contained tutorial survey of reinforcement learning, a tool that is increasingly finding application in the development of intelligent dynamic systems. Research on reinforcement learning during the past decade has led to the development of a variety of useful algorithms. This paper surveys the literature and presents the algorithms in a cohesive framework.

Artificial neural networks for pattern recognition

Abstract: This tutorial article deals with the basics of artificial neural networks (ANN) and their applications in pattern recognition. ANN can be viewed as computing models inspired by the structure and function of the biological neural network. These models are expected to deal with problem solving in a manner different from conventional computing. A distinction is made between pattern and data to emphasize the need for developing pattern processing systems to address pattern recognition tasks. After introducing the basic principles of ANN, some fundamental networks are examined in detail for their ability to solve simple pattern recognition tasks. These fundamental networks together with the principles of ANN will lead to the development of architectures for complex pattern recognition tasks. A few popular architectures are described to illustrate the need to develop an architecture specific to a given pattern recognition problem. Finally several issues that still need to be addressed to solve practical problems using ANN approach are discussed.

Tropical cyclones in the Bay of Bengal and deterministic methods for prediction of their trajectories

Abstract: Based on information about tropical storms and depressions in the Bay of Bengal over a 100-year period (1877–1976), certain climatic characteristics of tropical cyclones are examined. A brief description of climatic parameters, notably the region of their development, direction and nature of movement and percentage of disturbances intensified into severe tropical storms in different seasons of the year, which are explicitly or implicitly related to the formulation of objective methods for forecasting storm tracks, is presented in this work. A brief review of objective methods (numerical and statistical) used for forecasting the tracks of cyclonic storms and the rationale for development of such methods are described. Two numerical methods based on integral and steering flow concepts and four different physical-statistical methods, which take into consideration the influence of both external and internal forces responsible for the movement of tropical cyclones, are developed for forecasting the trajectories of post monsoon cyclonic storms in the Bay of Bengal. Performance of these six objective methods are illustrated through the study of a homogeneous sample of cyclonic storms (14 cases) in the Bay of Bengal during the post monsoon seasons of 1975 and 1976. These results are compared with those obtained from some of the existing methods for forecasting the movement of tropical cyclones in the Bay of Bengal. Finally, the limitations and prospects of objective methods in predicting the tracks of cyclonic storms in the Bay are discussed.

Significance of knowledge sources for a text-to-speech system for Indian languages

Abstract: This paper discusses the significance of segmental and prosodic knowledge sources for developing a text-to-speech system for Indian languages. Acoustic parameters such as linear prediction coefficients, formants, pitch and gain are prestored for the basic speech sound units corresponding to the orthographic characters of Hindi. The parameters are concatenated based on the input text. These parameters are modified by stored knowledge sources corresponding to coarticulation, duration and intonation. The coarticulation rules specify the pattern of joining the basic units. The duration rules modify the inherent duration of the basic units based on the linguistic context in which the units occur. The intonation rules specify the overall pitch contour for the utterance (declination or rising contour), fall-rise patterns, resetting phenomena and inherent fundamental frequency of vowels. Appropriate pauses between syntactic units are specified to enhance intelligibility and naturalness.

On the prediction of storm surges

Abstract: The article provides a review of some recent work on the prediction of storm surges. Beginning with a historical account of major Bay of Bengal cyclones in the last two decades, it provides a description of surge prediction techniques. The assumptions that are made are discussed critically. This is followed by an account of the forcing terms that drive the surge, and the computational procedure for model prediction. A brief comparison is presented between model outputs and the observed peak surge for major storms. Finally, the interactions of the surge with the astronomical tide, and wind-generated waves are discussed. Although the main focus of the article is on storms in the Bay of Bengal there is a brief description of cyclones in the Arabian Sea. The article ends with suggestions for improving surge prediction in the years to come.

Sonochemical reaction engineering

Abstract: Ultrasound has been widely used by chemists to enhance yields as well as rates of homogeneous as well as heterogeneous chemical reactions. The effect of ultrasound on the course of chemical reactions is mediated through cavitation bubbles it generates. High temperatures and pressures are attained inside the cavitating bubbles when they collapse. The extreme conditions so generated lead to the formation of reactive intermediates, e.g., free radiacls, inside the bubbles, which cause chemical reactions to occur when they enter the surrounding liquid. This is the mechanism through which ultrasound influences the path of homogeneous reactions. The cavitation bubbles collapse asymmetrically in the vicinity of solids, e.g., catalyst particles. Asymmetric collapse lead to formation of high speed microjets. The microjets can enhance transport rates, the increase surface area through pitting as well as particle fragmentation through collisions. Both can alter the rates of heterogeneous reaction rates. It however appears that these effects do not exhaust the scope of the influence of ultrasound on heterogeneous reactions. Modelling and quantitative prediction of the effect of ultrasound on chemical reactions is however at a stage of infancy as the phenomena are complex. Only a few examples of modelling exist in literature. Apart from this, reactor design and scaleup pose significant problems. Thus sonochemical reaction engineering offers large scope for research and development efforts.

Distortion, degeneracy and rezoning in finite elements — A survey

Abstract: The results obtained from finite element analysis are significantly affected by the quality of elements. In certain applications like shape optimization, crash analysis, metal forming, fluid flow analysis, and large displacement analysis, the finite element mesh is systematically updated in an iterative process. In such situations, in spite of an ideal starting mesh, the quality of elements could deteriorate, causing severly distorted elements. In extreme cases, the elements become degenerate and further progress of analysis is restricted. An understanding of the methods of quantifying element distortion helps in identifying ‘bad’ geometry and in deciding when to remesh. Knowledge about geometric configurations which cause degeneracy assists in controlling degeneracy during the analysis. This paper contains a survey of available distortion measures and degeneracy conditions for various elements in two and three dimensions. It is a review of the literature in this field in the last two decades. A brief review of rezoning is also included, since it is one of the more popularly used methods to correct a distorted mesh.

A novel enthalpy formulation for multidimensional solidification and melting of a pure substance

Abstract: This paper presents a new finite-difference formulation of the multidimensional phase change problems involving unique phase change temperature. The solutions obtained with this formulation show that the problem of “waviness” of the temperature histories encountered with the conventional enthalpy formulation is now removed. The formulation derived provides a simple method for “local” tracking of the interface using the enthalpy variable in a novel way. During the solution of the finite-difference equations, the present formulation obviates the need for “book-keeping” of the phase-change nodes, and hence allows solution of the equations by tridiagonal matrix algorithm. It is argued that the benefits of enthalpy formulation can be extended to phase-change problems involving convection by solving the equations of motion on non-staggered grid.

The differentially heated cavity

Abstract: This review discusses recent work dealing with natural convection flow in a differentially heated cavity. The emphasis is placed primarily on work dealing with the non-Boussinesq regime, transitional flow, and turbulent flow. Direction for future work in areas where additional effort is required is also provided.

Flow transitions and pattern selection of the rayleigh-bénard problem in rectangular enclosures

Abstract: In this paper, research efforts in the broad area of flow transitions of Rayleigh-Benard convection in rectangular enclosures with sidewalls are reviewed. Numerical studies are given primary emphasis. However, experimental works that are relevant are described. Our current physical understanding of the transition phenomena as occurring in the Rayleigh-Benard problem is critically reviewed. Two broad categories of transition are discussed. In the former, the transitions are temporal in nature, and mostly confined to small enclosures. In the latter, transitions are a result of change in spatial patterns. This phenomenon, known as pattern selection, is looked into for both small and intermediate enclosures.

Solid finite elements through three decades

Abstract: conventionally, solid finite elements have been looked upon as just generalizations of two-dimensional finite elements. In this article we trace their development starting from the days of their inception. Keeping in tune with our perceptions on developing finite elements, without taking recourse to any extra variational techniques, we discuss a few of the techniques which have been applied to solid finite elements. Finally we critically examine our own work on formulating solid finite elements based on the solutions to the Navier equations.

Computational aircraft dynamics and loads

Abstract: An alternative approach that has the potential to advance classical methods of flight load prediction by combining computational fluid dynamics (CFD), structural flexibility and the interaction of flight control system (FCS) in a multidisciplinary analysis package is described. The method employs the concept of system identification to characterize aircraft dynamics in the state space coordinate system and includes an adaptive control law design methodology. An extended account of the theoretical basis for the new multidisciplinary flight manoeuvre analysis will be presented in one of a seven-volume series on computational mechanics by Argyris and his associates to be published shortly. However, as a precursor to the complete work, a brief account of the theoretical development leading to this loads prediction methodology is included in this paper.

Natural convection of a radiating fluid in a square enclosure with perfectly conducting end walls

Abstract: Combined natural convection and radiation in an asymmetrically heated square enclosure is studied numerically with both adiabatic and perfectly conducting end walls. The momentum and energy equations are solved by a control volume based finite difference algorithm which is coupled with the discrete ordinates method for radiative heat transfer calculations. The changes in the flow patterns and temperature distributions due to the presence of radiation in an enclosure with conducting end walls are compared with those for the case of an enclosure with adiabatic end walls, and significant differences are noted. The flow field is stronger, and the heat input along the hot wall and the end walls are greater for the conducting end wall case. The effects of optical thickness, scattering and wall emissivity on the flow and temperature fields and heat transfer rates are analysed.

Design and analysis trends of helicopter rotor systems

Abstract: To overcome many of the problems associated with conventional articulated rotor systems, new rotor systems are being contemplated. In this paper, the state-of-art technology of advanced rotor systems is assessed. Advanced rotors include hingeless, bearingless, composite, circulation control, tilt and advanced geometry rotors. The paper reviews mathematical modelling, analysis methods, past and recent developments, potential limitations and future research needs in each system. Also, the potential of incorporation of structural optimization methodology and smart structures technology in rotors to improve the efficiency and capabilities of rotorcraft is discussed.

Finite element/finite volume approaches with adaptive time stepping strategies for transient thermal problems

Abstract: Transient thermal analysis of engineering materials and structures by space discretization techniques such as the finite element method (FEM) or finite volume method (FVM) lead to a system of parabolic ordinary differential equations in time. These semidiscrete equations are traditionally solved using the generalized trapezoidal family of time integration algorithms which uses a constant single time step. This single time step is normally selected based on the stability and accuracy criteria of the time integration method employed. For long duration transient analysis and/or when severe time step restrictions as in nonlinear problems prohibit the use of taking a larger time step, a single time stepping strategy for the thermal analysis may not be optimal during the entire temporal analysis. As a consequence, an adaptive time stepping strategy which computes the time step based on the local truncation error with a good global error control may be used to obtain optimal time steps for use during the entire analysis. Such an adaptive time stepping approach is described here. Also proposed is an approach for employing combinedFEM/FVM mesh partitionings to achieve numerically improved physical representations. Adaptive time stepping is employed thoughout to practical linear/nonlinear transient engineering problems for studying their effectiveness in finite element and finite volume thermal analysis simulations.

A fuzzy expert system approach using multiple experts for dynamic follow-up of endemic diseases

Abstract: In this paper, an architecture oflepdiag — a knowledge-based system for on-line diagnosis and for monitoring prognosis of leprosy is presented. The important features oflepdiag that have been detailed are a multiple expert environment, a homeostatic expert containing the model of immune reaction, a performance evaluator that can compare the observed signs and symptoms with those predicted by the homeostatic expert and a prognostic expert which optimizes the management schedule for the patients. The entire systems is built around a fuzzy expert-system building toolfext to deal with the imprecise knowledge.

Paninian framework and its application toAnusaraka

Abstract: ThePaninian framework proposeskarakas as semanticosyntactic relations that play a crucial role in mediating between surface form and meaning. The framework accounts for theta-role assignment, active passive, and control in a uniform manner. It has been successfully used in building an extremely fast prototype machine-translation system between two Indian languages. The constraint parser and the generator are designed with information theoretic considerations. Paninian framework is particularly suited to free word order languages. As most human languages are relatively word-order free, the Paninian framework should be explored as a serious contender for such languages. Based on the Paninian theory, the concept of language accessor oranusaraka has emerged, which has the potential to overcome the language barrier in India.

Tropical cyclone hazards and warning and disaster mitigation systems in India

Abstract: The main features of a cyclone that cause death and destruction are: (1) Storm surge, a rapid increase in sea level along the coast, primarily caused by the strong surface wind field of the cyclone as it approaches the coast, (2) the violent sustained wind and wind gusts and cyclone-spawned tornadoes, and (3) the heavy rain and consequent flooding. The paper describes the structure of a tropical cyclone of hurricane intensity and its damage potential, cyclone detection, tracking, forecasting and warning systems. It concludes that with over a hundred years of research and operational experience on cyclones available with the meteorological community and with theinsat and cyclone detection radar network, India has now an efficient cyclone warning system. This system would however benefit from further sophistication notably the use of Doppler Radars for cyclone wind field monitoring and an aircraft reconnaissance facility for probing cyclones. Research is needed to develop techniques for better forecasting of the tracks of cyclones more than a day ahead and also their intensity changes.

Buoyant plane plumes from heated horizontal confined wires and cylinders

Abstract: Two-dimensional computations are reported for time-dependent laminar buoyancy-induced flows above a horizontal heated source immersed in an air-filled vessel. Two kinds of heated source were considered: a line heat source, modelled as a heat source term in the energy equation, and a heat-flux cylinder of small diameter. First, comparisons are presented for the results obtained for these two heated sources. Rather large discrepencies between the velocity fields appeared in the conduction regime due to the weak plume motion, while close agreements were found in the boundary layer regime. Nevertheless, same types of bifurcations occur with almost identical frequencies, whatever the Rayleigh number. It is concluded that for dimensions of the enclosures, which largely compared with the cylinder radius, the heat source term model is a promising way to study the behaviour of unsteady plumes owing to its simplicity, flexibility, and low computational costs. Second, transitions to unsteady flows were studied through direct flow simulations for various depths of immersion of a line heat source in the central vertical plane of a vessel. Different routes to chaos were shown to occur according to the aspect ratio of the vessel and the depth of immersion of the line source. Three distinct regimes were detected with different underlying physical mechanisms called natural swaying motion, penetrative convection and Rayleigh-Benard-like convection. The first bifurcations associated with these regimes are supercritical Hopf bifurcation, pitchfork bifurcation and subcritical Hopf bifurcation. Comparisons with experimental results of confined buoyant plumes above heated wires show very good agreement with laminar frequency correlations.

Magneto-visco-elastic surface waves in stressed conducting media

Abstract: The present paper is concerned with magneto-visco-elastic surface waves in conducting media involving time rate of strain and stress of first order, the media being under an initial stress of hydrostatic tension or compression. The theory of magneto-visco-elastic surface waves in a conducting medium involving time rate of strain and stress of first order is derived under an initial stress. The above general theory is then employed to characterise Rayleigh, Love and Stoneley waves. Results obtained in the above cases reduce to well-known classical results when viscosity and magnetic field are absent.

Forced vibration and low-velocity impact of laminated composite plates

Abstract: The layerwise theory of Reddy is used to study the low velocity impact response of laminated plates. Forced-vibration analysis is developed by the modal superposition technique. Six different models are introduced for representation of the impact pressure distribution. The first five models, in which the contact area is assumed to be known, result in a nonlinear integral equation similar to the one obtained by Timoshenko in 1913. The resulting nonlinear integral equation is discretised using a time-element scheme. Two different interpolation functions, namely: (i) Lagrangian and (ii) Hermite, are used to express the impact force. The Hermitian polynomial-based representation, obviously more sophisticated, is introduced to verify the Lagrangian-based representation. Due to its modular nature the present numerical technique is preferable to the existing numerical methods in the literature. The final loading model, in which the time dependence of the contact area is taken into account according to the Hertzian contact law, resulted in a relatively more complicated but more realistic, nonlinear integral equation. The analytical developments concerning this model are all new and are reported for the first time in this paper. Also a simple, but accurate, numerical technique is developed for solving our new nonlinear integral equation which results in the time-history of the impact force. Our numerical results are first tested with a series of existing example problems. Then a detailed study concerning all the response quantities, including the in-plane and interlaminar stresses, is carried out for symmetric and antisymmetric cross-ply laminates and important conclusions are reached concerning the usefulness and accuracy of the various plate theories.

PVU and wave-particle splitting schemes for Euler equations of gas dynamics

Abstract: A new way of flux-splitting, termed as the wave-particle splitting is presented for developing upwind methods for solving Euler equations of gas dynamics. Based on this splitting, two new upwind methods termed as Acoustic Flux Vector Splitting (AFVS) and Acoustic Flux Difference Splitting (AFDS) methods are developed. A new Boltzmann scheme, which closely resembles the wave-particle splitting, is developed using the kinetic theory of gases. This method, termed as Peculiar Velocity based Upwind (PVU) method, uses the concept of peculiar velocity for upwinding. A special feature of all these methods is that the unidirectional and multidirectional parts of the flux vector are treated separately. Extensive computations done using these schemes demonstrate the soundness of the ideas.

Detailed study of complex flow fields of aerodynamical configurations by using numerical methods

Abstract: The mathematical physics of fluid flow in a compressible medium, leads to nonlinear partial differential equations or their equivalent integral versions. For the solution of these equations one has generally to resort to numerical methods using mostly finite difference or finite volume schemes, which are well established now. These field methods are very suitable for studying the physical features of complex flows. The present paper gives at first a short sketch of the numerical procedure and thereafter goes into the detailed analysis of the flow fields of delta wings, double-delta wings, delta shaped wing-canard combinations and space vehicles. Further examples include long span wings and wing-bodies at supercritical onflows, flows around propellers and rotors and finally some unsteady flows. The examples cited are selected topics from the extensive studies undertaken in the department of numerical aerodynamics of thedlr in Braunschweig in the course of the last few years.

Understanding design: Artificial intelligence as an explanatory paradigm

Abstract: A substantial part of the intellectual content of what H A Simon called the ‘sciences of the artificial’ is contained in the activity we calldesign. A central aim ofdesign theory is to construct testable, explanatory models of the design process that will serve to enhance our understanding of how artifacts are, or can be, designed. In this paper, we discuss how some of the basic concepts underlying the discipline ofartificial intelligence (ai) can serve to provide anexplanatory paradigm for understanding design. We present an AI-based model of the design process and describe some of the implications of this model for our understanding of design — including that aspect of it we call ‘invention’.

On the boundary-layer control through momentum injection: Studies with applications

Abstract: The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned experimental programme complemented by numerical studies. The moving surface was provided by rotating cylinders located at the leading edge and/or trailing edge as well as top surface of the airfoil. Results suggest that the concept is quite promising, leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of angle of attack. Next, effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of attack, rectangular prisms and three-dimensional models of trucks is assessed through an extensive wind tunnel test-programme. Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motordriven, hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. The momentum injection procedure also proved effective in arresting wind-induced vortex resonance and galloping type of instabilities. A flow visualization study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl choride tracer particles, adds to the wind-tunnel and numerical investigations. It shows, rather dramatically, the effectiveness of the moving surface boundary-layer control (MSBC).

Finite element analysis of internal flows with heat transfer

Abstract: This paper presents a finite element-based model for the prediction of 2-D and 3-D internal flow problems. The Eulerian velocity correction method is used which can render a fast finite element code comparable with the finite difference methods. Nine different models for turbulent flows are incorporated in the code. A modified wall function approach for solving the energy equation with high Reynolds number models is presented for the first time. This is an extension of the wall function approach of Benim and Zinser and the method is insensitive to initial approximation. The performance of the nine turbulent models is evaluated by solving flow through pipes. The code is used to predict various internal flows such as flow in the diffuser and flow in a ribbed channel. The same Eulerian velocity correction method is extended to predict the 3-D laminar flows in various ducts. The steady state results have been compared with benchmark solutions and the agreement appears to be good.

Managing interprocessor delays in distributed recursive algorithms

Abstract: For a class of distributed recursive algorithms, it is shown that a stochastic approximation-like tapering stepsize routine suppresses the effects of interprocessor delays

Computational study of transport processes in a single-screw extruder for non-newtonian chemically reactive materials

Abstract: A numerical study of the transport phenomena arising in a single-screw extruder channel is carried out. A non-Newtonian fluid is considered, using a power law model for the variable viscosity. Chemical reaction kinetics are also included. Finite difference computations are carried out to solve the governing set of partial differential equations for the velocity, temperature and species concentration fields, over a wide range of governing parameters for the case of a tapered screw channel.

Interaction between a buoyancy-driven flow and an array of annular cavities

Abstract: A numerical study is performed to investigate the interaction between a buoyancy-induced flow and an array of annular cavities. The buoyant flow is generated in a vertical annular enclosure with a centrally-positioned finned inner cylinder. Heat is generated within the inner cylinder, and it is convected through the inter-fin cavities and annular enclosure to the outside environment. The results indicate the presence of a twin recirculating bubble in each cavity. At higher Ra, the main flow enters the cavities and removes the recirculating flow. These observations are more pronounced at higher Pr. For more slender and deeper cavities, the recirculating bubbles closer to the finned wall collapse and split into two bubbles. The presence of cavities create a nearly uniform high-temperature zone adjacent to the finned wall. As the fin length is reduced and the cavities become more shallow, this zone shrinks and the main buoyancy-driven flow maintains a closer thermal communication with the finned wall.

A prototype expert system for interpretation of remote sensing image data

Abstract: Automated image interpretation systems of remotely sensed images are of great help in the present scenario of growing applications. In this paper, we have critically studied visual interpretation processes for urban land cover and land use information. It is observed that the core activity of interpretation can be described as plausible combinations of pieces of evidential information from various sources such as images, collateral data, experiential knowledge and pragmatics. Interpretation keys for the interpretation of standard false colour composites are considered to be tone/colour, pattern, texture, size, shape, association, relief and season. These interpretation keys encompass the spectral, spatial and temporal knowledge required for image interpretation. Our focus is on a knowledge-based approach for interpretation of standard false colour composites (fcc). Basic information required for a knowledge-based approach is of four types viz., spectral, spatial, temporal and heuristic. Generic classes and subclasses of image objects are identified for the land use/land cover theme. Logical image objects are conceptualised as region/area, line and point objects. An object-oriented approach for the representation of spectral and spatial knowledge has been adopted. Heuristic information is stored in rules. The Dempster-Shafer theory of evidence is used to combine evidence from various interpretation keys for identification of generic class and subclass of a logical image object. Analysis of some Indian Remote Sensing Satellite images has been done using various basic probability assignments in combination with learning. Explanation facility is provided by tracing the rules fired in the sequence.