Ramesh Kolar

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Papers by Ramesh Kolar

I, TITLE Ebcaod SeCitntty oall-ficar-on)

1: PRO~1.C4OGA " ATI]REPOR.T 1 ifE3 R5S WAMO = OaT0cG tc-V ZAT-REPORT f~tc3'!P S 68 wwV... more

Reliability block diagrams

Reliability Block Diagrams 375 Chapter 15 Reliability Block Diagrams RAM Commander's reliability ... more Reliability Block Diagrams 375 Chapter 15 Reliability Block Diagrams RAM Commander's reliability block diagram (RBD) module allows you to quickly and easily define and compute scenarios for reliability, availability and mean time between critical failures (MTBCF). You can use analytic or simulation techniques to evaluate RBDs. Analytical techniques are possible for most configurations. When such analyses are not possible, you can use RAM Commander's built-in Monte Carlo simulation engine to evaluate the RBD scenario. Working with Reliability Block Diagrams RAM Commander displays the RBD in a window. RBDs are graphically composed of the following elements: Parallel section A redundancy section containing n items. Parallel sections fail when all its items fail at the same time. Parallel branch A series of elements in parallel with other elements or a group of elements SubRBD A collapsed representation of an RBD. Regular item Any item with reliability data. k-out-of-n section A parallel section with n items. A k-out-of-n section is functional when k or more of the n elements are operational. The section fails when n-k + 1 items fail at the same time.

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Business Case Analysis of Medium Altitude Global ISR Communications (MAGIC) UAV System

Public reporting burden for this collection of information is estimated to average 1 hour per res... more Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington headquarters Services, Directorate for Information Operations and Reports,

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Dynamic characterization of layered metal-fiber-composites including transverse shear deformation

SPIE Proceedings, 2002

ABSTRACT

Simulation of Thermo Mechanical Behavior of a Ballistic Missile Model

ABSTRACT

Approach to Dynamic Modeling of Aircraft Landing on Moving Ships

This paper presents an application of the dynamic response and load calculations on a tricycle ty... more This paper presents an application of the dynamic response and load calculations on a tricycle type landing gear of an aircraft. The formulation based on the Lagrange's equations of motion treats the aircraft landing on a stationary deck in terms of pitching motion, roll motion, and vertical heaving motion. The landing is simulated as a single point, dual point, and three-point touch down with specified initial conditions. Effect of damping on ensuing motion is discussed. The results for a typical aircraft configuration are presented in the form of state variables and representative dynamic loads are shown in the form of graphs. In order to see the effect of motion of the deck, the equations are modified to include the deck movement into the formulation. Some preliminary results are presented in this case.

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Modal Analysis and Damage Assessment of Cracked Plates

Dynamic characterization of cantilevered cracked plates assumes importance for a variety of appli... more Dynamic characterization of cantilevered cracked plates assumes importance for a variety of applications including aging aerospace, mechanical and ship structural components. In this paper modal characteristics of isotropic plates with damage identified as cracks are investigated. The paper describes results obtained by finite element simulation of cracked plates. The frequency degradation as a function of the crack length is presented for selected aspect ratios. Some damage metrics are developed based on the modal parameters to describe the structural integrity of the plate type structures with root cracks. Frequency response analysis is presented to show the effect of the crack growth on the response of the plates. Some suggestions are developed based on the observations of the simulation for health monitoring of structural components.

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Efficient solution methods for nonlinear finite element analysis [microform] /

ABSTRACT

Reliability Analysis of Unidirectional Composites using Genetic Algorithms

47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<BR> 14th AIAA/ASME/AHS Adaptive Structures Conference<BR> 7th, 2006

ABSTRACT

An Approach for Analysis and Design of Composite Rotor Blades

31st Structures, Structural Dynamics and Materials Conference, 1990

ABSTRACT

<title>Dynamic characteristics of piezoelectric shear deformable composite plates</title>

Smart Structures and Materials 2004: Active Materials: Behavior and Mechanics, 2004

Layered composites have attracted attention for their high specific stiffness, high specific stre... more Layered composites have attracted attention for their high specific stiffness, high specific strength, and application specific tailoring of their properties. It is also recognized that layered composites are prone to delamination failure in addition to other failure modes. Consideration of transverse shear on the deformation behavior of the composites is an important aspect in the study of delamination mode failure of such plates. In this paper, we consider the effects of including the transverse shear deformation on the vibration characteristics of layered piezoelectric composites. The formulation is based on the Raleigh-Ritz method using the beam characteristic functions. MATLAB based symbollic math tool box is used in evaluating th eintegrals resulting from the Raleigh Ritz approach. Various commonly occuring boundary conditions are discussed. Results are provided showing the effects of the shear deformation on the dynamics of layered laminated composites. The effects of laminate thickness, fiber orientation, and the plate aspect ratios on the free vibration characteristics of the composite laminates are given to demonstrate the methodology described.

Numerical simulation of inflatable membrane structures

SPIE Proceedings, 2001

Inflatable structures are effective in space applications, as they are weight, volume and cost co... more Inflatable structures are effective in space applications, as they are weight, volume and cost competitive. For certain space applications, higher gains are obtained for the antennas by increasing their size. Higher gains often result in increased data throughput. These and other advantages lead to inflatable structures being considered increasingly for building large space structures. However, large inflatable structures are prone to surface errors arising from environmental factors, among others. The degradation in the performance may be reduced by active and passive control of the shape of the antennas by using appropriate sensors. In this context, piezoelectric films are used for the active and passive control. In this paper, we discuss both experimental and numerical approaches exploring piezoelectric film. In order to explore the applications of piezoelectric films, a circular diaphragm is subjected to varying pressures and displacements are measured using laser instrumentation. The effects of applying voltage on the shape of the piezoelectric film subjected to pressurization are studied. The piezoelectric film is modeled as a large displacement/large rotation geometrically nonlinear membrane undergoing small strains. This paper presents experience gained in modeling the piezoelectric film subjected to both thermal and pressure loads. The numerical results are presented in the form of graphs. The response is studied for applied steady-state temperatures for various pressurization levels. Certain thermo-structural instabilities were encountered in the modeling and the paper presents procedures used in circumventing such instabilities for the piezoelectric type of thin inflatable membranes. Introduction: Inflatable structures are increasingly being considered for space applications as they are lightweight and cost competitive when compared with conventional metal structures. When used as antennas in communications satellites, the inflatable structures yield high gains and high data throughput. Typical

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Application of Two Chaos Methods to Higher Harmonic Control Data

Journal of the American Helicopter Society, 1993

This paper presents two new data analysis methods which will reduce H i~h e r Harmonic Control (H... more This paper presents two new data analysis methods which will reduce H i~h e r Harmonic Control (HHC) night test reouirements. HHC is an active svstem which suuuresses helieouter vibrations. These methods. orieinallv. .. ... used in the \tudy of C~D D S , are the I'oinciarc srctiun iand the Van d~r 1' 01 plane. Using flight test data iturn a \lrl)nnnrll D4,sgla% OII-f,,\ IIII(' lest 3irrr;afl. 1hr.s~ rnrthn~lPsh,,w lhc libllnsing: I) the linlitv 111 IIIIC rihrution reduction; 2) determination of HHC controller type; and 3) that the HHC controller transfer matrix is predictable and repeatahlc when defined in the "Rotor Time Domain.'' (This domain is a concept introduced in this uauer. These benefits do not require an HHC equiu~ed helieader, althouda they do require an instrumentation

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Elastoacoustic response of laminated plates

The Journal of the Acoustical Society of America, 2005

The application of composite materials in the aerospace and naval structures has increased enormo... more The application of composite materials in the aerospace and naval structures has increased enormously due to high specific strength and specific stiffness afforded by these materials. In this paper a formulation is developed based on Hamilton’s Principle and laminated composite plate theory to study the elasto-acoustical response of composite plates under heavy fluid loadings. The formulation starts by using Hamilton’s principle in conjunction with shear deformable theory of laminated composite plates. The acoustic pressure described by wave equation is computed similar to Sandman and Nelisse. Using the Rayleigh Ritz method and symbolic mathematics for evaluation of integrals, the formulation provides efficient approach for the problem defined. Typical results include radiation impedance as a function of driving frequency, vibroacoustic indicators such as radiated sound power and mean square velocity for a model problem. Such results are very important in studying constrained layer ...

Approach for analysis and design of composite rotor blades

Journal of Aircraft, 1992

The developments in tilt rotor technology allow rotor blades to have different twist and rpm requ... more The developments in tilt rotor technology allow rotor blades to have different twist and rpm requirements in hover and in forward flight to optimize for operational conditions. The available twist of the rotor blade for different flight regimes bears on the performance of the flight. This article presents a detailed analysis of a typical rotor blade, the focus being the static response in the presence of extension-twist coupling induced due to asymmetric stacking sequence of laminas. The baseline rotor blade is modeled as a D-shaped spar using discrete Kirchoff theory-based finite elements. A method is proposed to derive six configurations of blade starting from a base rotor blade made of three laminated shells. The effects of varying rpm and lay-ups for the six configurations are presented as carpet plots in terms of the available tip twist angle. Such plots may be used in the rotor blade design trade-off studies.

Application of chaos methods to helicopter vibration reduction using higher harmonic control

APPLICATION OF CHAOS-METHODS TO HELICOPTER VIBPAT10, REDUCTION USING HIGHER HARMO1NIC CONTROL Sar... more

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On the Application of Bezier Curves and B-Splines for Finite Element Mesh Generation

On a Probabilistic Strain-based Fatigue Life Estimation

44th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, 2003

Probabilistic approaches in the design and analysis of aerospace vehicle have been attracting att... more Probabilistic approaches in the design and analysis of aerospace vehicle have been attracting attention in recent times. In particular, the fatigue life prediction and risk assessment of structural components is of importance in the aging aircraft. In this paper, we discuss the application of Monte Carlo simulation technique for determination of fatigue material constants to be used in the strain-based approach to fatigue. Service loadings on many components of structures are exposed to occasional severe events that are evaluated by strain-based approach. The strain-based approach considers the total strain as comprised of elastic and plastic strains. The deterministic relation based on the relationship between these two strain componets and the number of cycles for failure consists of four fatigue constants. In this paper, we have developed a method to generate life prediction of components. Using experimental data reported on a selected aluminum alloy, several probability density functions are fit to the data. Details of the goodness-of-fit are presented for different distributions. Monte Carlo simulation is used to vary the mean value of the fatigue parameters to develop a strain-life band. The strain range is covered in three segments, the low-cycle, high cycle, and transient regions. Graphs showing the total strain versus number of reversals to failure are shown. The simulated strain-life band using the proposed approach encompasses the entire test data and thus is a useful tool for probabilistic fatigue life estimation. *Presently at NAVAIR, Patuxent River, MD

I, TITLE Ebcaod SeCitntty oall-ficar-on)

1: PRO~1.C4OGA " ATI]REPOR.T 1 ifE3 R5S WAMO = OaT0cG tc-V ZAT-REPORT f~tc3'!P S 68 wwV... more

Reliability block diagrams

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Business Case Analysis of Medium Altitude Global ISR Communications (MAGIC) UAV System

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Dynamic characterization of layered metal-fiber-composites including transverse shear deformation

SPIE Proceedings, 2002

ABSTRACT

Simulation of Thermo Mechanical Behavior of a Ballistic Missile Model

ABSTRACT

Approach to Dynamic Modeling of Aircraft Landing on Moving Ships

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Modal Analysis and Damage Assessment of Cracked Plates

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Efficient solution methods for nonlinear finite element analysis [microform] /

ABSTRACT

Reliability Analysis of Unidirectional Composites using Genetic Algorithms

47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference<BR> 14th AIAA/ASME/AHS Adaptive Structures Conference<BR> 7th, 2006

ABSTRACT