Showing papers by "Naval Postgraduate School published in 1993"
TL;DR: In this article, a sliding-mode autopilot is designed for the combined steering, diving, and speed control functions of an AUV, assuming decoupled modeling, and the influence of speed, modeling nonlinearity, uncertainty, and disturbances can be effectively compensated.
Abstract: A six-degree-of-freedom model for the maneuvering of an underwater vehicle is used and a sliding-mode autopilot is designed for the combined steering, diving, and speed control functions. In flight control applications of this kind, difficulties arise because the system to be controlled is highly nonlinear and coupled, and there is a good deal of parameter uncertainty and variation with operational conditions. The development of variable-structure control in the form of sliding modes has been shown to provide robustness that is expected to be quite remarkable for AUV autopilot design. It is shown that a multivariable sliding-mode autopilot based on state feedback, designed assuming decoupled modeling, is quite satisfactory for the combined speed, steering, and diving response of a slow AUV. The influence of speed, modeling nonlinearity, uncertainty, and disturbances, can be effectively compensated, even for complex maneuvering. Waypoint acquisition based on line-of-sight guidance is used to achieve path tracking. >
917 citations
738 citations
TL;DR: In this paper, the authors consider a network interdiction problem in which an enemy attempts to maximize flow through a capacitated network while an interdictor tries to minimize this maximum flow by interdicting (stopping flow on) network arcs using limited resources.
537 citations
TL;DR: Before empirical evidence linking software complexity to software maintenance costs is relatively weak, several researchers have noted that such results must be applied cautiously to the large-scale commercial application systems that account for most software maintenance expenditures.
Abstract: While the link between the difficulty in understanding computer software and the cost of maintaining it is appealing, prior empirical evidence linking software complexity to software maintenance costs is relatively weak [21]. Many of the attempts to link software complexity to maintainability are based on experiments involving small pieces of code, or are based on analysis of software written by students. Such evidence is valuable, but several researchers have noted that such results must be applied cautiously to the large-scale commercial application systems that account for most software maintenance expenditures [13,17]
354 citations
TL;DR: An overview of basic models and solution algorithms for the lot streaming problem is presented, including models with continuous and discrete sublot sizes, models with and without intermittent idling of machines, and models with consistent and variable sublots.
Abstract: We present an overview of basic models and solution algorithms for the lot streaming problem. We include models with continuous and discrete sublot sizes, models with and without intermittent idling of machines, and models with consistent and variable sublots. We also introduce a model with limited transporter capacity. First we present solutions for two machines, then generalize to three machines and, where possible, to several machines. We synthesize previous research and introduce several new results.
159 citations
TL;DR: In this article, a longshore current model which includes a modification of the bottom stress term due to the effects of breaking-wave induced turbulence is developed and applied to field data from both barred and planar beaches.
145 citations
TL;DR: The Space ThermoAcoustic Refrigerator (STAR) as mentioned in this paper is a spacequalified thermoacoustic refrigerator that uses resonant high-amplitude sound waves in inert gases to pump heat.
Abstract: A new spacecraft cryocooler which uses resonant high-amplitude sound waves in inert gases to pump heat is described. The phasing of the thermoacoustic cycle is provided by thermal conduction. This "natural" phasing allows the entire refrigerator to operate with only one moving part (the loudspeaker diaphragm). A spacequalified thermoacoustic refrigerator was flown on the Space Shuttle Discovery (STS-42) in January, 1992. It was entirely autonomous, had no sliding seals, required no lubrication, used mostly low-tolerance machined parts, and contained no expensive components. Thermoacoustics is shown to be a competitive candidate for food refrigerator/freezers and commercial/residential air conditioners. The design and performance of the Space ThermoAcoustic Refrigerator (STAR) is described.
141 citations
TL;DR: The implementation of a hierarchical data structure on the world modeled by NPSNET utilizing quadtrees is explored, which requires the use of hierarchical data structures to provide high fidelity in real-time.
139 citations
TL;DR: It is shown that the well-known Levinson algorithm for computing the inverse Cholesky factorization of positive definite Toeplitz matrices can be viewed as a special case of a more general process.
136 citations
TL;DR: In this article, the authors report on the results of an empirically based study of passwords characteristics and provide a comparative evaluation on the memorability and users'subjective preferences of the various passwords mechanims, and suggest that cognitive passwords and associative passwords seem the most appropriate for secondary passwords.
Abstract: Various mechanisms for authenticating users of computer-based information systems have been proposed. These include traditional, user-selected passwords, system-generated passwords, passphrases, cognitive passwords and associative passwords. While the mechanisms employed in primary passwords are determined by the operating systems'manufacturers, system designers can select any password mechanism for secondary passwords, to further protect sensitive applications and data files. This paper reports on the results of an empirically based study of passwords characteristics. It provides a comparative evaluation on the memorability and users'subjective preferences of the various passwords mechanims, and suggests that cognitive passwords and associative passwords seem the most appropriate for secondary passwords
134 citations
TL;DR: In this article, a combined observational and numerical modeling approach is used to study the upstream track deflections of westward-moving tropical cyclones approaching the mountainous terrain of Taiwan, where the deflection tend to be larger for weaker and slower-moving storms.
Abstract: A combined observational and numerical modeling approach is used to study the upstream track deflections of westward-moving tropical cyclones approaching the mountainous terrain of Taiwan. Although the standard deviations are large, the mean track deflections are larger and have a different orientation for storms approaching the southern end of the island from those approaching the northern end. The deflections tend to be larger for weaker and slower-moving storms. Two distinct regions of upstream track deflections that are detected in the observations are explored in a sensitivity study with a 45-km horizontal resolution and 16-layer numerical model. As the outer circulation of the tropical cyclone begins to interact with the mountain barrier, the zonal decelerations and southward track deflections are explained by an enhanced blocking and deflection of the environmental flow advecting the cyclone. The larger effect for southern-approaching storms compared to northern storms is because the stron...
TL;DR: In this paper, the authors use a series of monthly IBM product revenues to illustrate the usefulness of seasonal fractionally differenced ARMA models for business forecasting, and compare the resulting model with a specific non-fractional seasonal ARIMA model by looking at each model's forecasts.
01 Jan 1993
TL;DR: Model integration is projected as the springboard for building a theory of models equivalent in power to relational theory in the database community.
Abstract: Model integration extends the scope of model management to include the dimension of manipulation as well. This invariably leads to comparisons with database theory. Model integration is viewed from four perspectives: Organizational, definitional, procedural, and implementational. Strategic modeling is discussed as the organizational motivation for model integration. Schema and process integration are examined as the logical and manipulation counterparts of model integration corresponding to data definition and manipulation, respectively. A model manipulation language based on structured modeling and communicating structured models is suggested which incorporates schema and process integration. The use of object-oriented concepts for designing and implementing integrated modeling environments is discussed. Model integration is projected as the springboard for building a theory of models equivalent in power to relational theory in the database community.
TL;DR: Based on an empirical study in a simulated systems development environment, several major issues that need to be considered in the development of a model of requirements traceability are addressed.
Abstract: In the development of large-scale, real-time, complex computer intensive systems, it is essential to maintain traceability of requirements to various outputs to ensure that the system meets the current set of requirements. Based on an empirical study in a simulated systems development environment, several major issues that need to be considered in the development of a model of requirements traceability are addressed. >
TL;DR: In this paper, a set of kinematical and intrinsic equilibrium equations for plates undergoing large deflection and rotation but with small strain was derived for the case of large deformation and rotation.
Abstract: A set of kinematical and intrinsic equilibrium equations are derived for plates undergoing large deflection and rotation but with small strain
TL;DR: In this paper, a kinematic model is developed for the manipulator, its relationship to the world coordinate frame and the tool, as well as the derivation of the tool pose from experimental measurements.
Abstract: The work reported in this article addresses the kinematic calibration of a robot manipulator using a coordinate measuring machine (CMM) which is able to obtain the full pose of the end-effector. A kinematic model is developed for the manipulator, its relationship to the world coordinate frame and the tool. The derivation of the tool pose from experimental measurements is discussed, as is the identification methodology. A complete simulation of the experiment is performed, allowing the observation strategy to be defined. The experimental work is described together with the parameter identification and accuracy verification. The principal conclusion is that the method is able to calibrate the robot successfully, with a resulting accuracy approaching that of its repeatability.
TL;DR: In this paper, numerical model simulations of west-moving tropical cyclones approaching and crossing the Taiwan orography are shown to contain many of the observed surface features, such as deformation of the inner-core circulation, surface pressure and surface wind centers becoming decoupled and may be dissipated at different rates.
Abstract: Numerical model simulations of west-moving tropical cyclones approaching and crossing the Taiwan orography are shown to contain many of the observed surface features. Vortices tend to track continuously around the northern end of the island due to the deflection of the deep-layer mean flow, and the vortex circulation is modified less because the higher winds to the right of the center do not have a strong interaction with the barrier. Discontinuous tracks predominate for vortices approaching the central southern portions of the Taiwan orography. Severe distortions of the inner-core circulation occur, and the surface pressure and surface wind centers become decoupled and may be dissipated at different rates. Numerical sensitivity studies demonstrate that more intense and rapidly moving vortices are more like to cross directly over the barrier and thus maintain a continuous track. In one special case of a weak but fast-moving vortex approaching the southern end, the model simulates the existence of...
TL;DR: Developers should include cognitive feedback as an integral part of the GDSS at ever level and the human-computer interaction should be designed so there is an intuitive and effective transaction across the components of feedback at all levels.
Abstract: Cognitive feedback in group decision making is information that provides decision makers with a better understanding of their own decision processes and that of the other group members. It appears to be an effective aid in group decision making. Although it has been suggested as a potential feature of group decision support systems (GDSS), little research has examined its use and impact. This article investigates the effect of computer generated cognitive feedback in computer-supported group decision processes. It views group decision making as a combination of individual and collective activity. The article tests whether cognitive feedback can enhance control over the individual and collective decision making processes and can facilitate the process of convergence among group members. In a laboratory experiment with groups of three decision makers, 15 groups received online cognitive feedback and 15 groups did not. Users receiving cognitive feedback maintained a higher level of control over the decision-making process as their decision strategies converged. This research indicates that (1) developers should include cognitive feedback as an integral part of the GDSS at ever level, and (2) they should design the human-computer interaction so there is an intuitive and effective transaction across the components of feedback at all levels. Researchers should extend the concepts explored here to other models of conflict that deal with ill-structured decisions, as well as study the impact of cognitive feedback over time. Finally, researchers trying to enhance the capabilities of GDSS should continue examining how to take advantage of the differences between individual, interpersonal, and collective decision making.
TL;DR: A combination of satellite imagery, shipboard profiles, drifter tracks, and moored current observations reveals that an anticyclonic eddy off the coast of northern California transported plumes of suspended sediments from the continental shelf into the deep ocean in 1988, providing direct evidence that eddies export sediment from continental shelves.
Abstract: A combination of satellite imagery, shipboard profiles, drifter tracks, and moored current observations reveals that an anticyclonic eddy off the coast of northern California transported plumes of suspended sediments from the continental shelf into the deep ocean. The horizontal scale of the eddy was about 90 kilometers, and the eddy remained over the continental shelf and slope for about 2 months during the summer of 1988. The total mass of sediments transported by the eddy was of order 105 metric tons. Mesoscale eddies are recurrent features in this region and occur frequently in eastern boundary currents. These results provide direct evidence that eddies export sediments from continental shelves.
TL;DR: In this article, the nonlinear dynamic response of a cylinder subjected to a side-on, far-field underwater explosion was studied using both numerical and experimental techniques, and the results indicated that the dynamic motion of the cylinder has an accordion mode, a breathing mode and a whipping mode.
01 Aug 1993
TL;DR: A trajectory planning scheme for a 6-DOF space robot is developed in which nonholonomic redundancy for avoiding joint limits and obstacles is utilized.
Abstract: Nonholonomic redundancy is an intrinsic property of nonholonomic mechanical systems. A free-flying space robot is a nonholonomic mechanical system, and exhibits the presence of nonholonomic redundancy even in the absence of ordinary kinematic redundancy. Like ordinary kinematic redundancy, nonholonomic redundancy can also be utilized while planning trajectories for the system. In the paper, a trajectory planning scheme for a 6-DOF space robot is developed in which nonholonomic redundancy for avoiding joint limits and obstacles is utilized. >
TL;DR: A real-time decision support system which uses optimization methods, simulation, and the judgement of the decision maker for operational assignment of units to tasks and for tactical allocation of Units to task requirements is introduced.
Abstract: We introduce a real-time decision support system which uses optimization methods, simulation, and the judgement of the decision maker for operational assignment of units to tasks and for tactical allocation of units to task requirements. The system, named ARES for the Greek god of war, accommodates a high degree of detail in the logistics of unit movements during operations, yet separates the assignment and allocation activities in a fashion which naturally accommodates human intervention and judgement—ARES is designed to assist the decision maker, not to replace him. ARES is demonstrated with a hypothetical scenario constructed for 14 Engineering Battalions of the Hellenic Army which are assigned 20 tasks employing 25 resource types in repairing major damage to public works following a great earthquake. (This hypothetical data was prepared prior to the earthquake in Kalamata near Athens on 13 September, 1986, and exhibits uncanny, but coincidental, resemblance to that real situation.) ARES is designed for use in real time, and quick data preparation is aided by the provision from published sources of standard data for many foreseeable tasks; this data can be quickly accessed via visual icons on a computer screen and customized for the actual work at hand. © 1993 John Wiley & Sons, Inc.
TL;DR: It is shown that significantly improved reliability predictions can be obtained by using a subset of the failure data, and the US Space Shuttle on-board software is used as an example.
Abstract: The possibility of obtaining more accurate predictions of future failures by excluding or giving lower weight to the earlier failure counts is suggested. Although data aging techniques such as moving average and exponential smoothing are frequently used in other fields, such as inventory control, the author did not find use of data aging in the various models surveyed. A model that includes the concept of selecting a subset of the failure data is the Schneidewind nonhomogeneous Poisson process (NHPP) software reliability model. In order to use the concept of data aging, there must be a criterion for determining the optimal value of the starting failure count interval. Four criteria for identifying the optimal starting interval for estimating model parameters are evaluated The first two criteria treat the failure count interval index as a parameter by substituting model functions for data vectors and optimizing on functions obtained from maximum likelihood estimation techniques. The third uses weighted least squares to maintain constant variance in the presence of the decreasing failure rate assumed by the model. The fourth criterion is the familiar mean square error. It is shown that significantly improved reliability predictions can be obtained by using a subset of the failure data. The US Space Shuttle on-board software is used as an example. >
TL;DR: In this paper, a 20-year dataset from 22 surface stations is used to describe the effects of the Taiwan terrain on the surface structure of typhoon circulation, and empirical orthogonal function analysis on the pressure field is employed to identify the primary structure modes.
Abstract: The island of Taiwan is situated in the main path of western North Pacific typhoons. Its dominant central mountain range (CMR), with a hoizontal scale comparable to the radius of a typhoon, often produces significant distortions in the typhoon circulation. A 20-year dataset from 22 surface stations is used to describe the effects of the Taiwan terrain on the surface structure of typhoons. Empirical orthogonal function analysis on the pressure field is used to identify the primary structure modes. The first mode is a uniform-sign anomaly pattern portraying the decrease in pressure as a typhoon is approaching. The second mode represents the strong terrain-induced west-east pressure gradient that is normal to the main axis of the CMR. The third mode results mainly from the west-cast pressure gradient arising from the relative location of the typhoon center to the east or west of Taiwan, but it also contains a weak south-north pressure gradient that can he attributed to the terrain. A regression tech...
01 Oct 1993
TL;DR: It is shown that if there exists sufficient dynamical coupling between the set of actuated and unactuated joints it is possible to converge all the manipulator joints to their desired values.
Abstract: Underactuated mechanisms will provide low-cost automation, easily overcome actuator failures, and be particularly useful for space applications because of their reduced mass and lower power consumption. In space underactuation can be effectively introduced in robot manipulators. Such mechanisms will however be difficult to control because of the fewer number of actuators in the system. It is shown that when the actuated joints do not have brakes, it is possible to bring the system to a complete rest and converge the actuated joints to their desired values, provided the system maintains zero momentum and none of the unactuated joints are cyclic coordinates. To converge both the actuated and the unactuated joints to their desired set of values, it is assumed that the number of actuated joints is more than the number of unactuated joints, and the unactuated joints have brakes. It is shown that if there exists sufficient dynamical coupling between the set of actuated and unactuated joints it is possible to converge all the manipulator joints to their desired values. >
TL;DR: The heuristics deployed to cope with the problems of poor estimation and poor visibility that hamper software project planning and control are investigated, and the implications for software project management are examined.
Abstract: Software project management is becoming an increasingly critical task in many organizations. While the macro-level aspects of project planning and control have been addressed extensively, there is a serious lack of research on the micro-empirical analysis of individual decision making behavior. The heuristics deployed to cope with the problems of poor estimation and poor visibility that hamper software project planning and control are investigated, and the implications for software project management are examined. A laboratory experiment in which subjects managed a simulated software development project is reviewed. The subjects were given project status information at different stages of the lifecycle and had to assess software productivity in order to dynamically readjust project plans. A conservative anchoring and adjustment heuristic is shown to explain the subjects' decisions quite well. Implications for software project planning and control are presented. >
TL;DR: The development of software required to support large scale, networked, multiparty virtual environments is discussed by describing how a real system, the NPSNET virtual world, is being constructed.
Abstract: The first phase of virtual world development has focused on the novel hardware 3-D input and 3-D output and the graphics demo. The second phase of virtual worlds development will be to focus in on the more significant part of the problem, the software bed underlying “real” applications. The focus of this paper is on the software required to support large scale, networked, multiparty virtual environments. We discuss navigation virtual camera view point control and its coupling to real-time, hidden surface elimination, interaction software for constructing a dialogue from the inputs read from our devices and for applying that dialogue to display changes, communication software for passing changes in the world model to other players on the network, and software for allowing the entry of previously undescribed players into the system, autonomy software for playing autonomous agents in our virtual world against interactive players, scripting software for recording, playing back, and multitracking previous play against live or autonomous players, with autonomy provided for departures from the recorded script, and hypermedia integration software for integrating hypermedia data-audio, compressed video, with embedded links-into our geometrically described virtual world. All of this software serves as the base for the fully detailed, fully interactive, seamless environment of the third phase of virtual world development. We discuss the development of such software by describing how a real system, the NPSNET virtual world, is being constructed.
TL;DR: Engineering notes as mentioned in this paper are short manuscripts describing new developments or important results of a preliminary nature, which cannot exceed 6 manuscript pages and 3 figures; a page of text may be substituted for a figure and vice versa.
Abstract: ENGINEERING NOTES are short manuscripts describing new developments or important results of a preliminary nature. These Notes cannot exceed 6 manuscript pages and 3 figures; a page of text may be substituted for a figure and vice versa. After informal review by the editors, they may be published within a few months of the date of receipt. Style requirements are the same as for regular contributions (see inside back cover).
TL;DR: In this article, a boundary-layer model is proposed to predict dynamic characteristics of liquid motion in partially filled tanks of a spinning spacecraft, and the solution is obtained by solving three boundary-value problems: an inviscid fluid problem, a boundary layer problem, and a viscous correction problem.
Abstract: This paper presents a boundary-layer model to predict dynamic characteristics of liquid motion in partially filled tanks of a spinning spacecraft. The solution is obtained by solving three boundary-value problems: an inviscid fluid problem, a boundary-layer problem, and a viscous correction problem. The boundary-layer solution is obtained analytically, and the solutions to inviscid and viscous correction problems are obtained by using finite element methods. The model has been used to predict liquid natural frequencies, mode shapes, damping ratios, and nutation time constants for a spinning spacecraft. The results show that liquid motion in general will contain significant circulatory motion due to Coriolis forces except in the first azimuth and first elevation modes. Therefore, only these two modes can be represented accurately by equivalent pendulum models. The analytical results predict a sharp drop in nutation time constants for certain spacecraft inertia ratios and tank fill fractions. This phenomenon was also present during on-orbit liquid slosh tests and ground air-bearing tests. I. Introduction A RECENT trend in geosynchronou s spacecraft design is to use liquid apogee motors, which results in liquid constituting almost half of the spacecraft mass during transfer orbit. In these spacecraft, liquid motion significantly influences the spacecraft attitude stability and control. LEAS AT, a geosynchronous spacecraft with liquid apogee motor, launched in September 1984, experienced attitude control motion instability1 during the pre-apogee injection phase, immediately following the activation of despin control. The instability was found to be the result of interaction between liquid lateral sloshing modes and the attitude control. This experience demonstrated that the analysis of dynamic interaction between liquid slosh motion and attitude control is critical in the attitude control design of these spacecraft. To perform this analysis, accurate determination of liquid dynamic characteristics, such as natural frequencies, mode shapes, damping, and modal masses becomes important. Accurate prediction of liquid dynamic characteristics is, however, a difficult problem because of the complexity of the hydrodynamical equations of motion. Several investigators have analyzed the fluid motion in rotating containers. Greenspan2 analyzed the transient motion during spin up of an arbitrarily shaped container filled with viscous imcompressible fluid. Stewartson3 developed a stability criterion for a spinning top containing fluid. This stability criterion was corrected by Wedemeyer 4 by considering fluid viscosity. Nayfeh and Meirovitch5 analyzed a spinning rigid body with a spherical cavity partially filled with liquid. Viscous effects are considered only for a boundary layer near the wetted surface. Hendricks and Morton6 analyzed the stability of a rotor partially filled with a viscous incompressible fluid. Stergiopoulous and Aldridge7 studied inertial waves in a partially filled cylindrical cavity during spin up. Pfeiffer8 introduced the concept of homogeneous vorticity to the problem of partially filled containers. El-Raheb and Wagner9 developed a finite element model based on a homogeneous vorticity as
TL;DR: A hybrid continuous software estimation model supporting adaptive, corrective, and perfective estimation activities is described and an implementation using constructive cost model (Cocomo) and the system dynamics (SD) simulator is presented.
Abstract: A hybrid continuous software estimation model supporting adaptive, corrective, and perfective estimation activities is described. The adaptive activity accommodates new system or user requirements or reflects new organizational realities. Corrective maintenance remedies an error detected in the software product, and perfective maintenance eliminates processing inefficiencies and enhances performance of the overall software system. An implementation using constructive cost model (Cocomo) and the system dynamics (SD) simulator is presented. Three examples are presented that demonstrate how the model can be used: before the project starts to adapt the Cocomo estimates to organizational realities, during software development to correct initial assumptions about sizing, and after project completion to perfect model estimates. >