Showing papers by "Naval Postgraduate School published in 1996"

A sound type system for secure flow analysis

Abstract: Ensuring secure information flow within programs in the context of multiple sensitivity levels has been widely studied. Especially noteworthy is Denning’s work in secure flow analysis and the lattice model [6][7]. Until now, however, the soundness of Denning’s analysis has not been established satisfactorily. We formulate Denning’s approach as a type system and present a notion of soundness for the system that can be viewed as a form of noninterference. Soundness is established by proving, with respect to a standard programming language semantics, that all well-typed programs have this noninterference property.

The Organizational Construction of Hegemonic Masculinity: The Case of the US Navy

Abstract: This article examines the construction of hegemonic masculinity within the US Navy. Based on life history interviews with 27 male officers, this study explores alternative discourses and identities of officers from three different communities in the Navy: aviation, surface warfare, and the supply corps. Definitions of masculinity are relationally constructed through associations of difference: aviators tend to draw upon themes of autonomy and risk taking; surface warfare officers draw upon themes of perseverance and endurance; and supply officers draw upon themes of technical rationality. Further, these masculinities depend upon various contrasting definitions of femininity. Finally, this article explores a series of contradictions that threaten the secure construction of masculinity within this military culture.

Effect of the dynamic interaction on coordinated control of mobile manipulators

Abstract: A mobile manipulator composed of a manipulator and a mobile platform has a much larger workspace than a fixed-base manipulator due to the mobility provided by the platform. While the on-board manipulator reaches out and performs manipulation tasks, the role of the mobile platform is to position the manipulator in a preferred configuration. In this paper, we study the effect of the dynamic interaction between the manipulator and the mobile platform of a mobile manipulator on the task performance. We consider the task that the end point of the manipulator tracks a desired trajectory in a fixed reference frame. The effect of the dynamic interaction on the tracking performance is examined by comparing four different cases: 1) with full compensation of the dynamic interaction with each other; 2) with the mobile platform compensating the dynamic interaction caused by the manipulator; 3) with the manipulator compensating the dynamic interaction caused by the mobile platform; and 4) without any compensation of the dynamic interaction at all. Simulation results from representative trajectories are presented to illustrate the effect.

Wind vector retrieval using ERS-1 synthetic aperture radar imagery

Abstract: An automated algorithm intended for operational use is developed and tested for estimating wind speed and direction using ERS-1 SAR imagery. The wind direction comes from the orientation of low frequency, linear signatures in the SAR imagery that the authors believe are manifestations of roll vortices within the planetary boundary layer. The wind direction thus has inherently a 180/spl deg/ ambiguity since only a single SAR image is used. Wind speed is estimated by using a new algorithm that utilizes both the estimated wind direction and /spl sigma//sub 0/ values to invert radar cross section models. The authors show that: 1) on average the direction of the roll vortices signatures is approximately 11/spl deg/ to the right of the surface wind direction and can be used to estimate the surface wind direction to within /spl plusmn/19/spl deg/ and 2) utilizing these estimated wind directions from the SAR imagery subsequently improves wind speed estimation, generating errors of approximately /spl plusmn/1.2 m/s, for ERS-1 SAR data collected during the Norwegian Continental Shelf Experiment in 1991.

Thrust Generation due to Airfoil Flapping

Abstract: Thrust generation on a single flapping airfoil and a flapping/stationary airfoil combination in tandem is studied parametrically. A multiblock Navier-Stokes solver is employed to compute unsteady flowfields. The unsteady flowfield around a single flapping airfoil is also computed by an unsteady potential flow code. The numerical solutions predict thrust generation in flapping airfoils and a significant augmentation of thrust in flapping/stationary airfoil combinations in tandem. The propulsive efficiency is found to be a strong function of reduced frequency and the amplitude of the flapping motion. At a flapping amplitude of 0.40 chord lengths and a reduced frequency of 0.10, the propulsive efficiency of a single NACA 0012 airfoil was computed to be more than 70 %. For the airfoil combination in tandem, the propulsive efficiency was augmented more than 40% at a reduced frequency of 0.75 and a flapping amplitude of 0.20 chord lengths when the airfoils are separated by about two chord lengths.

Circulation in the Alboran Sea as Determined by Quasi-Synoptic Hydrographic Observations. Part I: Three-Dimensional Structure of the Two Anticyclonic Gyres

Abstract: The circulation and dynamics of the Modified Atlantic Water have been studied using data from an intensive field experiment carried out between 22 September and 7 October 1992. Data included 134 CTD casts, ADCP, and satellite imagery. A well-defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern Alboran Sea. Smaller-scale cyclonic eddies were also observed. The front separates the more saline, older modified Atlantic water (S>38) in the northern region from the fresher, more recent modified Atlantic water (S<36.8) in the south. The associated baroclinic jet had a mean transport of 1 Sv and maximum geostrophic velocities of 1.0 ms−1. The three-dimensional structure and spatial scales of both gyres were similar, that is, 90 km long and 220 m deep. In the eastern Alboran, northeast of Oran, the origin of the Algerian Current was also detected with an eastward transport of 1.8 Sv. The general picture can be presented as a structure formed by a wavelike ...

Three-Dimensional Simulations of Overflows on Continental Slopes

Abstract: Three-dimensional features and instabilities of dense overflows from marginal seas onto continental slopes are investigated using a three-dimensional, primitive equation numerical ocean model. The numerical simulations reveal important instability and three-dimensional features of the overflow plumes that have not been included in previous simulations with a one-dimensional streamtube model and a two-dimensional plume model. It is shown that the large primary plume breaks into a number of smaller subplumes on the offshore side of the plume due to instabilities manifested as growing topographic Rossby waves over the slope. The observed high temporal and spatial variabilities in the Denmark Strait overflow could be caused by the inherent dynamic instabilities as revealed by the numerical simulations. The simulations indicate that the initial overflow velocity and width, the properties of the source water, the planetary rotation, and the slope steepness play major roles in determining the scales of ...

Wake Structures Behind Plunging Airfoils: A Comparison of Numerical and Experimental Results

Abstract: Comparisons are made between numerically and experimentally produced wake structures behind airfoils undergoing rapid, oscillatory plunging motions. Numerical simulations are performed using an unsteady panel code. Inviscid, incompressible ows about arbitrary moving airfoils are computed with the unsteady wake approximated by discrete point vortices, tracked using a Lagrangian mesh scheme. Numerically computed results are visualized using an interactive, graphical-animation interface. Experimental data are obtained from a low-speed water tunnel. Two-color dye injection is used to visualize unsteady wake structures, and velocity data are acquired using laser doppler velocimetry. Comparisons of vortex location agree well with linear theory for low amplitude motions. For large amplitude, high frequency motions, results diverge from linear theory, but wakes from the two approaches compare well with each other, including highly non-linear, non-symmetric wakes obtained for high amplitude, high frequency motions. Computed velocity pro les and integrated thrust coe cients for both approaches agree well.

Northwestward-Propagating Wave Patterns over the Tropical Western North Pacific during Summer

Abstract: The possible relationship between northwestward-propagating wave disturbances and tropical cyclones over the tropical western North Pacific during summer is studied using data assimilated by the navy's global model during May–September 1989–91. A multiple-set canonical correlation (MCC) analysis is applied to the 850-hPa meridional (v) component over a core domain covering the western Pacific. The analysis seeks the maximal geometrically averaged correlation between 12 consecutive twice-daily fields. Two MCC components, with a 90° phase difference and comparable variances that combine to nearly one-third of the total variance, describe the northwestward-propagating pattern with a period near 8–9 days. Upstream of this steady northwestward-propagating pattern there is a weaker, westward propagation along 5°N that may be traced back to 170°E. The surface pressure cell advancing east of the Philippines is consistent with low-level winds for a circulation in gradient wind balance. It has a zonal wave...

The kernel/nucleolus of a standard tree game

Abstract: In this paper we characterize the nucleolus (which coincides with the kernel) of a tree enterprise. We also provide a new algorithm to compute it, which sheds light on its structure. We show that in particular cases, including a chain enterprise one can compute the nucleolus in O(n) operations, wheren is the number of vertices in the tree.

The Antarctic zone flux experiment

Abstract: In winter the eastern Weddell Sea in the Atlantic sector of the Southern Ocean hosts some of the most dynamic air–ice–sea interactions found on earth. Sea ice in the region is kept relatively thin by heat flux from below, maintained by upper-ocean stirring associated with the passage of intense, fast-moving cyclones. Ocean stratification is so weak that the possibility of deep convection exists, and indeed, satellite imagery from the Weddell Sea in the 1970s shows a large expanse of open water (the Weddell Polynya) that persisted through several seasons and may have significantly altered global deep-water production. Understanding what environmental conditions could again trigger widespread oceanic overturn may thus be an important key in determining the role of high latitudes in deep-ocean ventilation and global atmospheric warming. During the Antarctic Zone Flux Experiment in July and August 1994, response of the upper ocean and its ice cover to a series of storms was measured at two drifting stations s...

Transformation of a Large Monsoon Depression to a Tropical Storm during TCM-93

Abstract: Data obtained during two aircraft observing periods (AOP) from the TCM-93 mini field experiment are used to describe the transformation between 5° and 10°N of a large depression in the western North Pacific monsoon trough into a tropical cyclone over a 36-h period. The transformation is defined to occur in three stages. Although a large mesoscale convective system (MCS) was present along the eastern periphery of the monsoon depression during the preorganization stage characterized by observations from the first AOP, the overall convective organization of the broad circulation is weak. The structure of the MCS provided a midlevel subsynoptic contribution to the vorticity of the monsoon depression and contributed to a shift in the center of the monsoon depression circulation between 800 and 600 mb toward the MCS location. However, the presence of unsaturated downdrafts associated with the MCS perturbed the low-level thermodynamic conditions and contributed to the rapid decay of the MCS. Slow intens...

A Comparison of Directional Buoy and Fixed Platform Measurements Of Pacific Swell

Abstract: The performance of the Datawell Directional Waverider and the National Data Buoy Center (NDBC) 3-m discus buoy, widely used to measure the directional properties of surface gravity waves, are evaluated through comparisons to an array of six pressure transducers mounted 14 m below the sea surface on a platform in 200-m depth. Each buoy was deployed for several months within a few kilometers of the platform. The accuracy of the platform ground-truth array was verified by close agreement of wavenumber estimates with the theoretical linear dispersion relation for surface gravity waves. Buoy and array estimates of wave energy and directional parameters, based on integration of the directional moments across the frequency band of energetic swell (0.06–0.14 Hz), are compared for a wide range of wave conditions. Wave energy and mean propagation direction estimates from both buoys agree well with the platform results. However, the Datawell buoy provides significantly better estimates of directional spread...

Vertical Wind Shear Influences on Tropical Cyclone Formation and Intensification during TCM-92 and TCM-93

Abstract: Vertical wind shears between 200 and 850 mb are calculated from operational analyses and special interactive analyses for Tropical Storm Steve during the Tropical Cyclone Motion (TCM-93) field experiment and for Typhoon Omar at the end of the TCM-92 experiment. The operational Fleet Numerical Meteorology and Oceanography Center (FNMOC) analyses have strong 200-mb winds crossing over the intensifying storms, which leads to vertical wind shears exceeding the 12.5 m s−1 threshold value believed to prevent tropical cyclone intensification. Interactive analyses are produced with the multiquadric interpolation technique that blends composited cloud-drift winds and aircraft reports between 1800 and 0000 UTC and between 0600 and 1200 UTC, sets of synthetic observations to represent missing or mislocated tropical circulations, and the FNMOC analyses that are used as a first-guess field. These interactive analyses indicate that the high winds at 200 mb associated with low-latitude circulations such as mons...

Using multiple searchers in constrained‐path, moving‐target search problems

Abstract: The search theory open literature has paid little, if any, attention to the multiple-searcher, moving-target search problem. We develop an optimal branch-and-bound procedure and six heuristics for solving constrained-path problems with multiple searchers. Our optimal procedure outperforms existing approaches when used with only a single searcher. For more than one searcher, the time needed to guarantee an optimal solution is prohibitive. Our heuristics represent a wide variety of approaches: One solves partial problems optimally, two use paths based on maximizing the expected number of detections, two are genetic algorithm implementations, and one is local search with random restarts. A heuristic based on the expected number of detections obtains solutions within 2% of the best known for each one-, two-, and three-searcher test problem considered. For one- and two-searcher problems, the same heuristic's solution time is less than that of other heuristics. For three-searcher problems, a genetic algorithm implementation obtains the best-known solution in as little as 20% of other heuristic solution times.

Natural-language retrieval of images based on descriptive captions

Abstract: We describe a prototype intelligent information retrieval system that uses natural-language understanding to efficiently locate captioned data. Multimedia data generally require captions to explain their features and significance. Such descriptive captions often rely on long nominal compounds (strings of consecutive nouns) which create problems of disambiguating word sence. In our system, captions and user queries are parsed and interpreted to produce a logical form using a detailed theory of the meaning of nominal compounds. A fine-grain match can then compare the logical form of the query to the logical forms for each caption. To improve system efficiency, we first perform a coarse-grain match with index files, using nouns and verbs extracted from the query. Our experiments with randomly selected queries and captions from an existing image library show an increase of 30% in precision and 50% in recall over the keyphrase approach currently used. Our processing times have a median of seven seconds as compared to eight minutes for the existing system, and our system is much easier to use.

Discrete-event simulation on the World Wide Web using Java

Abstract: This paper introduces Simkit, a small set of Java classes for creating discrete event simulation models. Simkit may be used to either implement stand-alone models or Web page applets. Exploiting network capabilities of Java, the lingua franca of the World Wide Web (WWW), Simkit models can easily be implemented as applets and executed in a Web browser. Java's graphical capabilities enable the rapid development of intuitive user interfaces. Java's use of in terpreted bytecodes, while imposing a performance penalty, enable development of platform-independent models. The language's inherent internet-awareness make other possibilities, such as distributed simulation, much easier to implement.

Lot Splitting in Stochastic Flow Shop and Job Shop Environments

Abstract: In recent years many firms have been implementing small lot size production. Lot splitting breaks large orders into smaller transfer lots and offers the ability to move parts more quickly through the production process. This paper extends the deterministic studies by investigating various lot splitting policies in both stochastic job shop and stochastic flow shop settings using performance measures of mean flow time and the standard deviation of flow time. Using a computer simulation experiment, we found that in stochastic dynamic job shops, the number of lot splits is more important than the exact form of splitting. However, when optimal job sizes are determined for each scenario, we found a few circumstances where the implementation of a small initial split, called a “flag,” can provide measurable improvement in flow time performance. Interestingly, the vast majority of previous research indicates that methods other than equal lot splitting typically improves makespan performance. The earlier research, however, has been set in the static, deterministic flow shop environment. Thus, our results are of practical interest since they show that the specific method of lot splitting is important in only a small set of realistic environments while the choice of an appropriate number of splits is typically more important.

Integrated aircraft-controller design using linear matrix inequalities

Abstract: A new methodology is presented for solving the problem of optimizing the aircraft parameters, such as the size of its control surfaces, while meeting openand closed-loop static and dynamic performance requirements. The approach proposed involves rewriting these requirements as linear matrix inequalities and solving a related constrained optimization problem for which efficient numerical solutions are available.

The slippery path to productivity improvement

Abstract: Productivity tools simply aren't delivering increased productivity even when a project is managed "by the book". It is demonstrated that there may be more systemic, albeit counterintuitive, causes for the "productivity paradox". Specifically, the productivity potential of software engineering tools may be squandered not because organizations fail to institute the necessary managerial practices but because the software development environment is a complex social system that causes such practices to have unintended consequences. To support this view, the author uses a system dynamics microworld of the software development process to simulate the long term productivity trend in a a hypothetical project environment managed "by-the-book". The microworld lets the project team examine possible causes one by one through controlled experimentation and hence allows them to discern true causal relationships in a failed project. The results indicate productivity erosion was unintentionally accelerated by perfectly "good" planning and control practices.

Measurements with reticulated vitreous carbon stacks in thermoacoustic prime movers and refrigerators

Abstract: Reticulated vitreous carbon has been successfully used as a stack material in thermoacoustic prime movers and refrigerators. It is a rigid glassy carbon material, with a porous spongelike structure. Test results indicate peak pressure amplitudes of up to 32% in a prime mover, and refrigeration performance comparable to that of a traditional plastic roll stack.

Autonomous underwater vehicles: Hybrid control of mission and motion

Abstract: This paper provides an experimental implementation and verification of a hybrid (mixed discrete state/ continuous state) controller for semi-autonomous and autonomous underwater vehicles in which the missions imply multiple task robot behavior. An overview of some of the missions being considered for this rapidly developing technology is mentioned including environmental monitoring, underwater inspection, geological survey as well as military missions in mine countermeasures.

Environmental Conditions Prior to Formation of a Midget Tropical Cyclone during TCM-93

Abstract: During a 10-day period in the Tropical Cyclone Motion (TCM-93) field experiment over the tropical western North Pacific, tropical cyclone formation occurred in association with persistent deep convection that was observed over low-level, north-oriented confluent flow between a large monsoon gyre to the west of a strong subtropical ridge. The convection was also modulated by a strong diurnal cycle with a convective maximum just before dawn and a convective minimum during the late afternoon. Observations from two aircraft observing periods (A0Ps) during two consecutive daytime periods identified three distinct mesoscale convective vortices (MCVS) in the persistent deep convection. During the initial AOP (AOP-1A), a well-defined mesoscale circulation at 500 mb was located directly above the strong low-level, south-southwesterly confluent flow. However, reduction in convection and associated midlevel forcing during the convective minimum period contributed to the decay of the MCV before it could pene...

Oscillating Flow About Two and Three-Dimensional Bilge Keels

Abstract: The paper describes an experimental investigation of the damping provided by bilge keels in an oscillating flow (in a large U- shaped water tunnel). Rectangular and square flat plates were placed adjacent to a solid boundary (with no gap) in order to simulate flow about bilge keels. The single free edge of the rectangular plate and the three free edges of the square plates were bevelled to 60-degree angles so as to form sharp edges with included angles of about 60 degrees. For comparison, another sharp-edged rectangular plate was tested without the wall proximity effects. All plates were held normal to the direction of the ambient flow. The Fourier-averaged drag and inertia coefficients were then calculated as a function of a suitable Keulegan-Carpenter through the use of the instantaneous force acting on each plate.

Multiple tone interference of frequency-hopped noncoherent MFSK signals transmitted over Ricean fading channels

Abstract: This paper investigates the performance degradation resulting from multitone interference of orthogonal, frequency-hopped, noncoherent M-ary frequency-shift keyed receivers (FH/MFSK) where the effect of thermal and other wideband noise is not neglected. The multiple, equal power jamming tones are assumed to correspond to some or all of the possible FH M-ary orthogonal signaling tones. Furthermore, the channel is modeled as a Ricean fading channel; and both the signaling tones and the multiple interference tones are assumed to be affected by channel fading. It is also assumed that channel fading need not necessarily affect the signaling tones and the interference tones in the same-way. When the information signal power exceeds the power of the individual interference tones, poorer overall system performance is obtained when the multiple interfering tones experience fading. This trend is accentuated as M increases. When the information signal experiences fading, the effect of fading multiple interference tones on overall system performance lessens, and for a Rayleigh-faded information signal, fading of the multiple interference tones has no effect on overall system performance regardless of M.