A Hybrid Data-driven Model of Ship Roll

A hybrid data-driven method, which combines low-fidelity physics with machine learning (ML) to model nonlinear forces and moments at a reduced computational cost, is applied to predict the roll motions of an appended ONR Tumblehome (ONRT) hull in waves. The method is trained using CFD data of unforced roll decay time series--a common data set used in parameter identification for ship roll damping and restoring moments. The trained model is then used to predict wave excited roll responses in a range of wave frequencies and the results are compared to CFD validation data. The predictions show that the method improves predictions of roll responses, especially near the natural frequency

Understanding the effect of cube size on the near wake characteristics in a turbulent boundary layer

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143036/1/6.2017-3640.pd

Hydrodynamic forces in water exit problems

The three-dimensional steady problem of an elongated smooth body moving along the water free surface at a constant speed is considered within the 2D+T approximation. The corresponding unsteady two-dimensional problem describes both the water entry and the subsequent exit of a smooth contour from the water. The shape of the contour varies in time. The present paper is concerned with the exit stage. The draft of the body is small compared with the body length and beam. The hydrodynamic loads during the entry stage are evaluated by the original Wagner model of water impact. The linearized exit model (Korobkin, 2013) is generalized to account for time-dependent acceleration of the body and the body shape which also varies in time. The integral equation with respect to the size of the wetted area of the body is solved numerically. The theoretical predictions of the hydrodynamic forces acting on the body during its exit from the liquid are compared with the numerical results obtained by solving the Navier-Stokes equations. A simplified model of water exit with the body shape approximated by a parabolic contour with a time-dependent radius of curvature is proposed and validated. It is shown that the linearized water-exit model with non-linear correction terms predicts reasonably well the hydrodynamic loads

Wedge impact with the influence of ice

This work presents a canonical study on a wedge entering water near a single piece of ice using computational-fluid-dynamics (CFD) and a Wagner-type theoretical model with corrections for non-linear effects. Calculations for a series of conditions with ice of different sizes and locations relative to the wedge are conducted. The hydrodynamic force due to impact, the pressure distribution on the wedge surface, and the pile-up phenomenon are examined to study the role of ice in the impact process. The theoretical model is shown to be accurate and can serve as a useful method to assess slamming loads under the influence of ice. It is shown that even for the case of a small piece of ice, the slamming force on the wedge can increase by 30%

An adaptive interface compression method for water entry and exit

http://deepblue.lib.umich.edu/bitstream/2027.42/97021/1/Piro13c.pd

CFD-based Design Optimization of Ducted Hydrokinetic Turbines

Hydrokinetic turbines extract kinetic energy from moving water to generate renewable electricity, thus contributing to sustainable energy production and reducing reliance on fossil fuels. It has been hypothesized that a duct can accelerate and condition the fluid flow passing the turbine blades, improving the overall energy extraction efficiency. However, no substantial evidence has been provided so far for hydrokinetic turbines. To investigate this problem, we perform a CFD-based optimization study with a blade-resolved Reynolds-averaged Navier--Stokes (RANS) solver to explore the design of a ducted hydrokinetic turbine that maximizes the efficiency of energy extraction. To handle the high-dimensional design space of the blade and duct geometry, we use a gradient-based optimization approach where the gradients are computed using the adjoint method. The final design is re-evaluated through higher-fidelity unsteady RANS (URANS) simulations. Our optimized ducted turbine achieves an efficiency of about 54% over a range of operating conditions, higher than the typical 46% efficiency of unducted turbines such as the well-known Bahaj model

Impact of source data on the interpretation of contrast-enhanced magnetic resonance angiography of the lower limbs

Background The primary purpose of this study is to examine whether use of source data is effective in increasing the number of arterial segments that can be interpreted from maximum intensity projections of lower limb MR angiograms. Correlation between sites of arterial disease and venous contamination was also measured. Interpretation of source data is performed routinely by radiologists, but the value of this has not been well studied with randomized studies. Results The proportion of segments visible above the knee was 87% using maximal intensity projection alone (MIP) and 88% when the MIP was combined with source data. The proportions were 67% for MIP and 72% for MIP plus source data below the knee. There was substantial agreement between presence of arterial disease and venous contamination in the calf and thigh. Conclusion The use of source data increases the number of assessable segments, but not individuals, by a statistically significant but small amount (1.2%, p <0.05). This study supports the association between arterial disease and venous contamination

Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields: Technical Summary and Data Release

The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained five-band optical-wavelength imaging near the Galactic plane outside of the nominal survey boundaries. These additional data were obtained during commissioning and subsequent testing of the SDSS observing system, and they provide unique wide-area imaging data in regions of high obscuration and star formation, including numerous young stellar objects, Herbig-Haro objects and young star clusters. Because these data are outside the Survey regions in the Galactic caps, they are not part of the standard SDSS data releases. This paper presents imaging data for 832 square degrees of sky (including repeats), in the star-forming regions of Orion, Taurus, and Cygnus. About 470 square degrees are now released to the public, with the remainder to follow at the time of SDSS Data Release 4. The public data in Orion include the star-forming region NGC 2068/NGC 2071/HH24 and a large part of Barnard's loop.Comment: 31 pages, 9 figures (3 missing to save space), accepted by AJ, in press, see http://photo.astro.princeton.edu/oriondatarelease for data and paper with all figure

Periodontal disease adversely affects the survival of patients with end-stage renal disease

Periodontal disease is associated with cardiovascular disease and is thought to accelerate systemic atherosclerosis. Here we examined the relationship between periodontitis and cardiovascular disease mortality in outpatients on hemodialysis using a retrospective analysis of 168 adult patients in New York City and North Carolina. During 18 months of follow-up, cardiovascular disease and all-cause mortality were determined from a centralized dialysis registry. One hundred patients had mild or no periodontal disease but the remaining 68 had moderate-to-severe disease defined as 2 or more teeth with at least 6 mm of inter-proximal attachment loss. At baseline, the proportion of males was significantly lower in the moderate-to-severe group. Compared with mild or no periodontal disease, moderate-to-severe disease was significantly associated with death from cardiovascular causes. Adjustment for age, gender, center and dialysis vintage, smoking status, and history of diabetes mellitus or hypertension did not diminish the strength of this association. Our findings suggest a need for larger studies to confirm this connection, along with intervention trials to determine if treating periodontitis reduces cardiovascular disease mortality in dialysis patients

Surface processes recorded by rocks and soils on Meridiani Planum, Mars: Microscopic Imager observations during Opportunity's first three extended missions

The Microscopic Imager (MI) on the Mars Exploration Rover Opportunity has returned images of Mars with higher resolution than any previous camera system, allowing detailed petrographic and sedimentological studies of the rocks and soils at the Meridiani Planum landing site. Designed to simulate a geologist's hand lens, the MI is mounted on Opportunity's instrument arm and can resolve objects 0.1 mm across or larger. This paper provides an overview of MI operations, data calibration, and analysis of MI data returned during the first 900 sols (Mars days) of the Opportunity landed mission. Analyses of Opportunity MI data have helped to resolve major questions about the origin of observed textures and features. These studies support eolian sediment transport, rather than impact surge processes, as the dominant depositional mechanism for Burns formation strata. MI stereo observations of a rock outcrop near the rim of Erebus Crater support the previous interpretation of similar sedimentary structures in Eagle Crater as being formed by surficial flow of liquid water. Well-sorted spherules dominate ripple surfaces on the Meridiani plains, and the size of spherules between ripples decreases by about 1 mm from north to south along Opportunity's traverse between Endurance and Erebus craters