Naval Postgraduate School

About: Naval Postgraduate School is a education organization based out in Monterey, California, United States. It is known for research contribution in the topics: Tropical cyclone & Boundary layer. The organization has 5246 authors who have published 11614 publications receiving 298300 citations. The organization is also known as: NPS & U.S. Naval Postgraduate School.

Structure of transitionally rough and fully rough turbulent boundary layers

Abstract: Structural characteristics of transitionally rough and fully rough turbulent boundary layers are presented. These were measured in flows at different roughness Reynolds numbers developing over uniform spheres roughness. Inner regions of the longitudinal component of normal Reynolds stress profiles and log regions of mean profiles continuously change in the transitionally rough regime, as the roughness Reynolds number, Rek, varies. These properties asymptotically approach fully rough behaviour as Rek increases, and smooth behaviour at low Rek Profiles of other Reynolds-stress tensor components, turbulence kinetic energy, turbulence-kinetic-energy production, and the turbulence-kinetic-energy dissipation are also given, along with appropriate scaling variables. Fully rough, one-dimensional spectra of longitudinal velocity fluctuations from boundary-layer inner regions are similar to smooth-wall results for k1 y > 0.2 when non-dimensionalized using distance from the wall y as the lengthscale, and (τ/ρ)½ as the velocity scale, where τ is local shear stress, ρ is static density, and k1 is one-dimensional wavenumber in the flow direction.

An annual cycle of Arctic surface cloud forcing at SHEBA

Abstract: [1] Wepresentananalysisofsurfacefluxesandcloudforcingfromdataobtainedduringthe Surface Heat Budget of the Arctic Ocean (SHEBA) experiment, conducted in the Beaufort and Chuchki Seas and the Arctic Ocean from November 1997 to October 1998 The measurements used as part of this study include fluxes from optical radiometer sets, turbulent fluxes from an instrumented tower, cloud fraction from a depolarization lidar and ceilometer, and atmospheric temperature and humidity profiles from radiosondes Clear-sky radiative fluxes were modeled in order to estimate the cloud radiative forcing since direct observation of fluxes in cloud-free conditions created large statistical sampling errors This was particularly true during summer when cloud fractions were typically very high A yearlong data set of measurements, obtained on a multiyear ice floe at the SHEBA camp, was processed in 20-day blocks to produce the annual evolution of the surface cloud forcing components: upward, downward, and net longwave and shortwave radiative fluxes and turbulent (sensible and latent heat) fluxes We found that clouds act to warm the Arctic surface for most of the annual cycle with a brief period of cooling in the middle of summer Our best estimates for the annual average surface cloud forcings are � 10 W m � 2 for shortwave, 38Wm � 2 for longwave,and � 6Wm � 2 forturbulentfluxes Totalcloudforcing (the sum of all components) is about 30 W m � 2 for the fall, winter, and spring, dipping to a minimum of � 4Wm � 2 in early July We compare the results of this study with satellite, model, and drifting station data INDEX TERMS: 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 3349 Meteorology and Atmospheric Dynamics: Polar meteorology; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3394 Meteorology and Atmospheric Dynamics: Instruments and techniques; KEYWORDS: remote sensing, atmospheric radiation, polar meteorology, clouds, forcing

Software complexity and maintenance costs

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]

Analysis of the Intel Pentium's ability to support a secure virtual machine monitor

Abstract: A virtual machine monitor (VMM) allows multiple operating systems to run concurrently on virtual machines (VMs) on a single hardware platform. Each VM can be treated as an independent operating system platform. A secure VMM would enforce an overarching security policy on its VMs. The potential benefits of a secure VMM for PCs include: a more secure environment, familiar COTS operating systems and applications, and enormous savings resulting from the elimination of the need for separate platforms when both high assurance policy enforcement, and COTS software are required. This paper addresses the problem of implementing secure VMMs on the Intel Pentium architecture. The requirements for various types of VMMs are reviewed. We report an analysis of the virtualizability of all of the approximately 250 instructions of the Intel Pentium platform and address its ability to support a VMM. Current "virtualization" techniques for the Intel Pentium architecture are examined and several security problems are identified. An approach to providing a virtualizable hardware base for a highly secure VMM is discussed.

Morphodynamic modeling of an embayed beach under wave group forcing

Abstract: [1] The morphodynamic response of the nearshore zone of an embayed beach induced by wave groups is examined with a numerical model. The model utilizes the nonlinear shallow water equations to phase resolve the mean and infragravity motions in combination with an advection-diffusion equation for the sediment transport. The sediment transport associated with the short-wave asymmetry is accounted for by means of a time-integrated contribution of the wave nonlinearity using stream function theory. The two-dimensional (2-D) computations consider wave group energy made up of directionally spread, short waves with a zero mean approach angle with respect to the shore normal, incident on an initially alongshore uniform barred beach. Prior to the 2-D computations, the model is calibrated with prototype flume measurements of waves, currents, and bed level changes during erosive and accretive conditions. The most prominent feature of the 2-D model computations is the development of an alongshore quasi-periodic bathymetry of shoals cut by rip channels. Without directional spreading, the smallest alongshore separation of the rip channels is obtained, and the beach response is self-organizing in nature. Introducing a small amount of directional spreading (less than 2°) results in a strong increase in the alongshore length scales as the beach response changes from self-organizing to being quasi-forced. A further increase in directional spreading leads again to smaller length scales. The hypothesized correlation between the observed rip spacing and wave group forced edge waves over the initially alongshore uniform bathymetry is not found. However, there is a correlation between the alongshore length scales of the wave group-induced quasi-steady flow circulations and the eventual alongshore spacing of the rip channels. This suggests that the scouring associated with the quasi-steady flow induced by the initial wave groups triggers the development of rip channels via a positive feedback mechanism in which the small scour holes start attracting more and more discharge.