NORTHWESTERN UNIV EVANSTON IL Dept. of MECHANICAL ENGINEERING
Overview
Works:  15 works in 18 publications in 1 language and 18 library holdings 

Classifications:  TA354.5, 519.534 
Publication Timeline
.
Most widely held works by
NORTHWESTERN UNIV EVANSTON IL Dept. of MECHANICAL ENGINEERING
Optimal control of systems with uncertainty by
W. E Schmitendorf(
Book
)
3 editions published between 1978 and 1980 in English and held by 3 WorldCat member libraries worldwide
The research supported by AFOSR Grant 762923 has led to some significant results which can be used in the design of optimal controllers when disturbances are present. Sufficient conditions which a minmax control must satisfy were developed for systems with disturbances in the state equation or in the measurement of the initial state. From these conditions, constructive techniques were developed which can be used to generate minmax controllers. The second major area of the research was controllability problems. Criteria for determining the controllability properties of constrained systems were derived. The criteria involve finite dimensional optimization problems and are amenable to computer implementation. (Author)
3 editions published between 1978 and 1980 in English and held by 3 WorldCat member libraries worldwide
The research supported by AFOSR Grant 762923 has led to some significant results which can be used in the design of optimal controllers when disturbances are present. Sufficient conditions which a minmax control must satisfy were developed for systems with disturbances in the state equation or in the measurement of the initial state. From these conditions, constructive techniques were developed which can be used to generate minmax controllers. The second major area of the research was controllability problems. Criteria for determining the controllability properties of constrained systems were derived. The criteria involve finite dimensional optimization problems and are amenable to computer implementation. (Author)
Multiple Scale Methods for Stability Analysis of FluidStructure Systems(
)
2 editions published between 1993 and 1994 in English and held by 2 WorldCat member libraries worldwide
Multiple scale methods, which are based on discrete and continuous reproducing kernels, wavelets, and integral window transforms are developed . In this development, a microscope is constructed with a flexible spacetime localized window function which translates and dilates in space and time to cover the entire domain of interest. This microscope can magnify, examine, and record the image of the various scales and frequencies of the response locally within the support of the window function. The degree of magnification will depend on the power of the microscope, a flexible spacescale and timefrequency window function. This complete characterization of the unknown response is performed through the integral window transform. This localization process can be achieved by dilating the flexible multiplescale window function. The zoom in and zoom out capability of the window function is especially useful in examining complex flow phenomena, such as flow induced vibration, dynamic stability of flowstructure interaction, turbulence structures, and high frequency structural dynamics response
2 editions published between 1993 and 1994 in English and held by 2 WorldCat member libraries worldwide
Multiple scale methods, which are based on discrete and continuous reproducing kernels, wavelets, and integral window transforms are developed . In this development, a microscope is constructed with a flexible spacetime localized window function which translates and dilates in space and time to cover the entire domain of interest. This microscope can magnify, examine, and record the image of the various scales and frequencies of the response locally within the support of the window function. The degree of magnification will depend on the power of the microscope, a flexible spacescale and timefrequency window function. This complete characterization of the unknown response is performed through the integral window transform. This localization process can be achieved by dilating the flexible multiplescale window function. The zoom in and zoom out capability of the window function is especially useful in examining complex flow phenomena, such as flow induced vibration, dynamic stability of flowstructure interaction, turbulence structures, and high frequency structural dynamics response
Catalytic Ignition and Combustion of Lean Mixtures(
Book
)
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
Ignition and heat release rates of fuel/oxygen/nitrogen over platinum wires are experimentally studied using microcalorimetry, aiming to gain additional understanding on the complex transport and kinetic processes involved during catalytic oxidation so as to relate the macroscopic observables with the microscopic behavior. The fuels studied are propane, butane, propylene, ethylene, carbon monoxide and hydrogen. Parameters investigated include catalyst surface temperature, fuel and oxygen concentrations, and flow velocity. Results show that for very low Reynolds number flows the flow velocity has negligible influences on the ignition temperature. Its influence on the heat release rates is also negligible but only for the reactions in kinetically controlled regime. Variation of fuel concentration is found to be an important factor in that the ignition temperatures of propane and butane decrease as their concentrations are increased from lean to rich mixtures while the opposite trend is observed for propylene, ethylene, carbon monoxide and hydrogen
1 edition published in 1984 in English and held by 1 WorldCat member library worldwide
Ignition and heat release rates of fuel/oxygen/nitrogen over platinum wires are experimentally studied using microcalorimetry, aiming to gain additional understanding on the complex transport and kinetic processes involved during catalytic oxidation so as to relate the macroscopic observables with the microscopic behavior. The fuels studied are propane, butane, propylene, ethylene, carbon monoxide and hydrogen. Parameters investigated include catalyst surface temperature, fuel and oxygen concentrations, and flow velocity. Results show that for very low Reynolds number flows the flow velocity has negligible influences on the ignition temperature. Its influence on the heat release rates is also negligible but only for the reactions in kinetically controlled regime. Variation of fuel concentration is found to be an important factor in that the ignition temperatures of propane and butane decrease as their concentrations are increased from lean to rich mixtures while the opposite trend is observed for propylene, ethylene, carbon monoxide and hydrogen
Multiple Scale Reproducing Kernel Methods for Compressible FlowStructure Systems(
)
1 edition published in 1996 in English and held by 1 WorldCat member library worldwide
Multiple temporal and spatial scale methods were developed and employed for the study of structural dynamics system in which the response is characterized by multiplespatial and multipletime scales. The following fundamental research topics were addressed: (1) development of multiple scale Reproducing Kernel Particle Methods, which can provide accurate mesh free interpolation functions and possess superior convergence rate for compressible flowstructure interaction problems; (2) incorporation of multiresolution analysis concepts into RKPM so that the response can be separated into multiple frequency/wave number bands for a better representation of the computed physics; (3) incorporation of (1) and (2) via a 2D pilot computer code; and (4) application of the multiplescale computer code to study nonlinear compressible flow and large deformation structural phenomena
1 edition published in 1996 in English and held by 1 WorldCat member library worldwide
Multiple temporal and spatial scale methods were developed and employed for the study of structural dynamics system in which the response is characterized by multiplespatial and multipletime scales. The following fundamental research topics were addressed: (1) development of multiple scale Reproducing Kernel Particle Methods, which can provide accurate mesh free interpolation functions and possess superior convergence rate for compressible flowstructure interaction problems; (2) incorporation of multiresolution analysis concepts into RKPM so that the response can be separated into multiple frequency/wave number bands for a better representation of the computed physics; (3) incorporation of (1) and (2) via a 2D pilot computer code; and (4) application of the multiplescale computer code to study nonlinear compressible flow and large deformation structural phenomena
Combustion and MicroExplosion of Water/Oil Emulsions in High Pressure Environments(
Book
)
1 edition published in 1985 in English and held by 1 WorldCat member library worldwide
Water/oil emulsions hold potential for soot reduction, multifuel capability, and selfextinguishment upon spillage and incendiary ignition. In view of the fact that most of the fundamental research performed so far were in the normal atmosphere although the potential applications of water/oil emulsions are in such highpressure combustors as diesel engines and gas turbines, this program was initiated to study the combustion characteristics of water/oil emulsions droplets in a hightemperature, highpressure, convective environment such that useful guidelines can be identified for emulsion formulation and engine design. Of particular interest is the exploration of the phenomenon of microexplosion which may be responsible for much of the potential benefits of emulsion utilization
1 edition published in 1985 in English and held by 1 WorldCat member library worldwide
Water/oil emulsions hold potential for soot reduction, multifuel capability, and selfextinguishment upon spillage and incendiary ignition. In view of the fact that most of the fundamental research performed so far were in the normal atmosphere although the potential applications of water/oil emulsions are in such highpressure combustors as diesel engines and gas turbines, this program was initiated to study the combustion characteristics of water/oil emulsions droplets in a hightemperature, highpressure, convective environment such that useful guidelines can be identified for emulsion formulation and engine design. Of particular interest is the exploration of the phenomenon of microexplosion which may be responsible for much of the potential benefits of emulsion utilization
Organic Azides as Jet Fuel Additives(
Book
)
1 edition published in 1985 in English and held by 1 WorldCat member library worldwide
Under the sponsored program and experimental investigation has been conducted on the vaporization and combustion characteristics of freelyfalling droplets of organic azides in hot oxidizing or inert environments. The droplets of organic azides in hot oxidizing or inert environments. The droplet burning rate and the state of microexplosion have been measured. Results show that, compared with the conventional hydrocarbon fuels, droplets of azido fuels burn faster and microexplode earlier in the droplet lifetime. The effect is especially strong for diazido nalkanes whose gasification rates can be several hundred percent of the corresponding nalkanes. Such strong responses are postulated to be caused by dissociative gasification with very low heat of gasification
1 edition published in 1985 in English and held by 1 WorldCat member library worldwide
Under the sponsored program and experimental investigation has been conducted on the vaporization and combustion characteristics of freelyfalling droplets of organic azides in hot oxidizing or inert environments. The droplets of organic azides in hot oxidizing or inert environments. The droplet burning rate and the state of microexplosion have been measured. Results show that, compared with the conventional hydrocarbon fuels, droplets of azido fuels burn faster and microexplode earlier in the droplet lifetime. The effect is especially strong for diazido nalkanes whose gasification rates can be several hundred percent of the corresponding nalkanes. Such strong responses are postulated to be caused by dissociative gasification with very low heat of gasification
Gridless Computational Methods for Penetration Mechanics(
)
1 edition published in 1999 in English and held by 1 WorldCat member library worldwide
Efficient and accurate gridless methods were developed for the simulation of the nonlinear response of solids. Such methods are of potential usefulness in penetration mechanics because they facilitate the modeling of phenomena which involves the creation of new surfaces, such as penetration and fracture, and problems involving high gradients, such as shear bands. Two approaches, moving least mean square interpolants and kernel functions similar to smooth particle hydrodynamics (SPH), have been explored. A correction function was developed and convergence of the corrected approximation was proven for linear problems. Several different approaches were also taken to extending these methods to problems involving large deformations of solids. These methods have been applied to problems involving shear banding and moving cracks. Computations were compared to the Kalthoff experiments and good agreement was achieved with experimental fracture paths. These studies entailed the development of contactimpact algorithms, but within the framework of methodologies based on moving least squares and kernel function interpolants
1 edition published in 1999 in English and held by 1 WorldCat member library worldwide
Efficient and accurate gridless methods were developed for the simulation of the nonlinear response of solids. Such methods are of potential usefulness in penetration mechanics because they facilitate the modeling of phenomena which involves the creation of new surfaces, such as penetration and fracture, and problems involving high gradients, such as shear bands. Two approaches, moving least mean square interpolants and kernel functions similar to smooth particle hydrodynamics (SPH), have been explored. A correction function was developed and convergence of the corrected approximation was proven for linear problems. Several different approaches were also taken to extending these methods to problems involving large deformations of solids. These methods have been applied to problems involving shear banding and moving cracks. Computations were compared to the Kalthoff experiments and good agreement was achieved with experimental fracture paths. These studies entailed the development of contactimpact algorithms, but within the framework of methodologies based on moving least squares and kernel function interpolants
Finite element technology for penetration problems by
Ted Belytschko(
)
1 edition published in 1994 in English and held by 1 WorldCat member library worldwide
Finite element methods for penetration mechanics are developed. A pinball contactimpact algorithm which is easily vectorizable has been implemented on partitioned memory SIMD computers. The pinball algorithm is further extended to problems with friction and erosion; Lagrange and augmented Lagrange multiplier methods, and its convergence have also been studied. Multiplequadrature elements with hourglass control and physical stabilization and multitime step integration have also been studied. Numerical results of the multiplequadrature elements with stabilization showed that simple stabilization forces can be obtained which are convergent and based on physical parameters. The implementation of this algorithm on massively parallel machines has also been investigated. (AN)
1 edition published in 1994 in English and held by 1 WorldCat member library worldwide
Finite element methods for penetration mechanics are developed. A pinball contactimpact algorithm which is easily vectorizable has been implemented on partitioned memory SIMD computers. The pinball algorithm is further extended to problems with friction and erosion; Lagrange and augmented Lagrange multiplier methods, and its convergence have also been studied. Multiplequadrature elements with hourglass control and physical stabilization and multitime step integration have also been studied. Numerical results of the multiplequadrature elements with stabilization showed that simple stabilization forces can be obtained which are convergent and based on physical parameters. The implementation of this algorithm on massively parallel machines has also been investigated. (AN)
Technical Report on Atomistic and Dislocation Dynamic Modeling of Plasticity in Polycrystalline Metals(
)
1 edition published in 2005 in English and held by 1 WorldCat member library worldwide
In this effort we have studied in atomic detail the structure / property relationship of geometrically realistic metallic nanowires. It has been shown that surface roughness can greatly affect defect nucleation as nucleation from the surface dominates. Twin boundaries were introduced and were found not to be favored as sites for defect nucleation but do lead to deformation hardening as they are efficient obstacles against dislocation propagation. The details of heterogeneous dislocation nucleation have been studied in depth showing the initial state of local stress determining the strength of the defect is very complex having many sometimes competing components. Three point bending tests performed by simulated nanoindentation experiments yield qualitative results very similar to recent atomic force microscopy investigations. Preliminary results subject to complex states of bending stress show the possible roles pressure may play in dislocation nucleation as well as propagation. Region of high hydrostatic stress appear to prohibit dislocation nucleation and propagation. Currently we are refining our simulation methods to include accurate force measurements from our simulated nanoindenter for direct comparison with current experimental efforts
1 edition published in 2005 in English and held by 1 WorldCat member library worldwide
In this effort we have studied in atomic detail the structure / property relationship of geometrically realistic metallic nanowires. It has been shown that surface roughness can greatly affect defect nucleation as nucleation from the surface dominates. Twin boundaries were introduced and were found not to be favored as sites for defect nucleation but do lead to deformation hardening as they are efficient obstacles against dislocation propagation. The details of heterogeneous dislocation nucleation have been studied in depth showing the initial state of local stress determining the strength of the defect is very complex having many sometimes competing components. Three point bending tests performed by simulated nanoindentation experiments yield qualitative results very similar to recent atomic force microscopy investigations. Preliminary results subject to complex states of bending stress show the possible roles pressure may play in dislocation nucleation as well as propagation. Region of high hydrostatic stress appear to prohibit dislocation nucleation and propagation. Currently we are refining our simulation methods to include accurate force measurements from our simulated nanoindenter for direct comparison with current experimental efforts
An Investigation on High Temperature Behavior of Laminate and Nanostructured Composite Materials(
)
1 edition published in 2001 in English and held by 1 WorldCat member library worldwide
A novel highstrainrate and high temperature experimental setup was developed to investigate failure of advanced materials. Experiments were performed on preheated Ti6Al4V specimens, at temperatures in the range 25550 deg C, to determine the role of thermal activation on dynamic stress induced inelasticity and damage. Interferometric techniques were employed to record the free surface velocity of the target plates. The experimental results show that thermal activation overcomes the role of rate dependence in the material constitutive behavior. The Hugoniot Elastic Limit (HEL) and spall strength of Ti6Al4V significantly decrease with temperature despite of the high strain rates, about 10(exp 5)/s, used in the tests. Microscopy studies, performed on recovered samples, show that temperature substantially reduces the strain inhomogeneity leading to microvoid formation and that a change in void nucleation site occurs. A completely reversible shockinduced phase transformation alpha right arrow omega be present in the tested Ti6Al4V. Evidence of this phase transformation is observed in the velocity histories upon unloading of the first compressive pulse. The phase transformation is controlled by a combination of thermal and Stress driven mechanisms. Two oiler activities were completed under this grant, the development of software for finite element analysis of failure in brittle and layered materials, and the development of dynamic fracture experiments with full field measurements by means of speckle techniques. The new software accounts for crack initiation and propagation, finite deformation and surface roughness effects
1 edition published in 2001 in English and held by 1 WorldCat member library worldwide
A novel highstrainrate and high temperature experimental setup was developed to investigate failure of advanced materials. Experiments were performed on preheated Ti6Al4V specimens, at temperatures in the range 25550 deg C, to determine the role of thermal activation on dynamic stress induced inelasticity and damage. Interferometric techniques were employed to record the free surface velocity of the target plates. The experimental results show that thermal activation overcomes the role of rate dependence in the material constitutive behavior. The Hugoniot Elastic Limit (HEL) and spall strength of Ti6Al4V significantly decrease with temperature despite of the high strain rates, about 10(exp 5)/s, used in the tests. Microscopy studies, performed on recovered samples, show that temperature substantially reduces the strain inhomogeneity leading to microvoid formation and that a change in void nucleation site occurs. A completely reversible shockinduced phase transformation alpha right arrow omega be present in the tested Ti6Al4V. Evidence of this phase transformation is observed in the velocity histories upon unloading of the first compressive pulse. The phase transformation is controlled by a combination of thermal and Stress driven mechanisms. Two oiler activities were completed under this grant, the development of software for finite element analysis of failure in brittle and layered materials, and the development of dynamic fracture experiments with full field measurements by means of speckle techniques. The new software accounts for crack initiation and propagation, finite deformation and surface roughness effects
Monte Carlo Reliability Analysis(
Book
)
1 edition published in 1989 in English and held by 1 WorldCat member library worldwide
The research resulted in major improvements in Markov models to be used in Monte Carlo modeling of reliability problems. These include a number of component dependency models and modeling of unrevealed failures. A new sampling technique, the method of selftransitions, is developed for treating time dependent failure rates, and non Markovian generalizations are made to model replacement of ageing parts and asgoodasnew repair. Keywords: Reliability: Monte Carlo simulation
1 edition published in 1989 in English and held by 1 WorldCat member library worldwide
The research resulted in major improvements in Markov models to be used in Monte Carlo modeling of reliability problems. These include a number of component dependency models and modeling of unrevealed failures. A new sampling technique, the method of selftransitions, is developed for treating time dependent failure rates, and non Markovian generalizations are made to model replacement of ageing parts and asgoodasnew repair. Keywords: Reliability: Monte Carlo simulation
Failure Prediction of Underwater Structures  Subdomain Decomposition and Meshfree Methods(
)
1 edition published in 2003 in English and held by 1 WorldCat member library worldwide
Meshfree methods for fracture have been extended by considering more general classes of basis functions. These methods do not require any elements, and boundaries and interfaces, such as cracks, are easy to propagate in the model since it does not involve remeshing. The versatility of these methods has been enhanced by developing new vector level set methods. The method has been applied to a variety of crack growth problems in two dimensions including problems involving welds and fillets. Comparisons with experiments show excellent agreement. Domain decomposition methods, whereby a fine scale model can be linked with a coarse scale model were developed. These methods are useful when a part of a ship where severe damage is expected must be modeled by a refined mesh for accuracy and linked to a coarser mesh of the remainder of the ship
1 edition published in 2003 in English and held by 1 WorldCat member library worldwide
Meshfree methods for fracture have been extended by considering more general classes of basis functions. These methods do not require any elements, and boundaries and interfaces, such as cracks, are easy to propagate in the model since it does not involve remeshing. The versatility of these methods has been enhanced by developing new vector level set methods. The method has been applied to a variety of crack growth problems in two dimensions including problems involving welds and fillets. Comparisons with experiments show excellent agreement. Domain decomposition methods, whereby a fine scale model can be linked with a coarse scale model were developed. These methods are useful when a part of a ship where severe damage is expected must be modeled by a refined mesh for accuracy and linked to a coarser mesh of the remainder of the ship
Minmax Control of Systems with Uncertainty in the Initial State and in the State Equations by
W. E Schmitendorf(
Book
)
1 edition published in 1976 in English and held by 1 WorldCat member library worldwide
This paper investigates optimal control problems where there is uncertainty in the initial state measurement or where there are uncertain parameters in the state equations. It is assumed that nature will choose the uncertainty to maximize the cost which the controller is attempting to minimize. Thus a minmax control is sought. Sufficient conditions for a control to be a minmax control are presented. These conditions suggest methods for finding the minmax control and such techniques are described. The application of these methods is illustrated by example problems
1 edition published in 1976 in English and held by 1 WorldCat member library worldwide
This paper investigates optimal control problems where there is uncertainty in the initial state measurement or where there are uncertain parameters in the state equations. It is assumed that nature will choose the uncertainty to maximize the cost which the controller is attempting to minimize. Thus a minmax control is sought. Sufficient conditions for a control to be a minmax control are presented. These conditions suggest methods for finding the minmax control and such techniques are described. The application of these methods is illustrated by example problems
Learning Combinatorial Map Information from Permutations of Landmarks(
Book
)
1 edition published in 2010 in English and held by 1 WorldCat member library worldwide
This paper considers a robot that moves in the plane and is only able to sense the cyclic order of landmarks with respect to its current position. No metric information is available regarding the robot or landmark positions; moreover, the robot does not have a compass or odometers (i.e., knowledge of coordinates). We carefully study the information space of the robot, and establish its capabilities in terms of mapping the environment and accomplishing tasks, such as navigation and patrolling. When the robot moves exclusively inside the convex hull of the set of landmarks, the information space can be succinctly characterized as an order type, which provides information powerful enough to determine which points lie inside the convex hulls of subsets of landmarks. Additionally, if the robot is allowed to move outside the convex hull of the set of landmarks, the information space is described with a swap cell decomposition, which is an aspect graph in which each aspect is a cyclic permutation of landmarks. We show how to construct such decomposition through its dual, using two kinds of feedback motion commands based on the landmarks sensed
1 edition published in 2010 in English and held by 1 WorldCat member library worldwide
This paper considers a robot that moves in the plane and is only able to sense the cyclic order of landmarks with respect to its current position. No metric information is available regarding the robot or landmark positions; moreover, the robot does not have a compass or odometers (i.e., knowledge of coordinates). We carefully study the information space of the robot, and establish its capabilities in terms of mapping the environment and accomplishing tasks, such as navigation and patrolling. When the robot moves exclusively inside the convex hull of the set of landmarks, the information space can be succinctly characterized as an order type, which provides information powerful enough to determine which points lie inside the convex hulls of subsets of landmarks. Additionally, if the robot is allowed to move outside the convex hull of the set of landmarks, the information space is described with a swap cell decomposition, which is an aspect graph in which each aspect is a cyclic permutation of landmarks. We show how to construct such decomposition through its dual, using two kinds of feedback motion commands based on the landmarks sensed
Combustion characteristics of sprays by S. H Sohrab(
Book
)
1 edition published in 1989 in English and held by 1 WorldCat member library worldwide
This report provides a general description of the results of research studies aimed at providing a basic understanding of turbulent spray combustion. The environment in a liquid rocket engine can lead to complex flow/flame/droplet interactions which can substantially modify the droplet evaporation and combustion processes which can affect the stability characteristics of the rocket engine. The various studies conducted during this research project were: spray combustion in stagnationpoint flow, thermodiffusive flame instabilities, the influence of vorticity on flame stability/stabilization, nonplanar flame configurations. Areas of future research are presented along with a discussion as to how the results of the investigation can be applied to liquid rocket engine combustion. (kt)
1 edition published in 1989 in English and held by 1 WorldCat member library worldwide
This report provides a general description of the results of research studies aimed at providing a basic understanding of turbulent spray combustion. The environment in a liquid rocket engine can lead to complex flow/flame/droplet interactions which can substantially modify the droplet evaporation and combustion processes which can affect the stability characteristics of the rocket engine. The various studies conducted during this research project were: spray combustion in stagnationpoint flow, thermodiffusive flame instabilities, the influence of vorticity on flame stability/stabilization, nonplanar flame configurations. Areas of future research are presented along with a discussion as to how the results of the investigation can be applied to liquid rocket engine combustion. (kt)
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