Seakeeping Analysis of a SWATH-type Trimaran Using Potential Flow

2015 ◽  
Author(s):  
Adrian S. Onas ◽  
Jaye Falls ◽  
Ivan Stojanovic
Keyword(s):  
Potential Flow ◽  
Transfer Functions ◽  
Numerical Models ◽  
The United States ◽  
Ship Motions ◽  
Naval Academy ◽  
Viscous Effect ◽  
Viscous Effects ◽  
United States Naval Academy ◽  
Institute Of Technology

Potential flow methods tend to over-predict ship motions, especially the lightly damped, viscous effect dominated modes, such as roll. For SWATH ships, it is not uncommon to also over-predict heaving and pitching motions because of the strong viscous effects dominating the energy dissipation mechanism due to significant vortex shedding generated by the submerged hull(s). Care should be taken whenever such viscous effect become a significant part the total damping. Such fact appears to render the potential flow approach less useful when analyzing the restored response of SWATH ships compared to conventional ships, such as monohulls. The Atlantic Center for Innovative Design and Control of Small Ships (ACCeSS), under ONR sponsorship, has been studying a hybrid trimaran hull form with a small waterplane area center hull, so-called the Tri-SWACH. Extensive towing tank testing has been undertaken with the intent to characterize the behavior of the Tri-SWACH and to provide data for the verification and validation of predictive tools. For previous work, the scale models of the Tri-SWACH were identical below the waterline, but lacked any realistic cross-deck structure above the waterline. This setup is ideal to capture the nonlinear ship motion behavior in future studies since the scale and numerical models were made identical above and below the waterline, and include a representative cross-deck. For the current study, the linear transfer functions and short-term statistics are obtained using the potential flow code WASIM, and are partially validated using experimental results obtained from the United States Naval Academy and Stevens Institute of Technology.

scholarly journals 1342. TOSCANA: The Observational Seroepidemiologic Study of COVID-19 at the United States Naval Academy

2021 ◽  
Vol 8 (Supplement_1) ◽  
pp. S758-S759
Author(s):  
Eugene Millar ◽  
Eric Laing ◽  
Adam Saperstein ◽  
Jitu Modi ◽  
Christopher Heaney ◽  
...  
Keyword(s):  
United States ◽  
Risk Factors ◽  
Blood Sample ◽  
Saliva Sample ◽  
The United States ◽  
Pathogen Transmission ◽  
Naval Academy ◽  
United States Naval Academy ◽  
Increased Risk ◽  
Seroepidemiologic Study

Abstract Background University students, including those at military service academies, are at increased risk of acute respiratory infection (ARI), including SAR-CoV-2, due to crowded living conditions, frequent social interaction and other factors that facilitate pathogen transmission. Unlike many universities, the United States Naval Academy (USNA) continued in-person instruction in Fall 2020 in the midst of the COVID-19 pandemic. The Observational Seroepidemiologic Study of COVID-19 at the United States Naval Academy (TOSCANA,) a longitudinal cohort characterizes the burden and risk factors of SARS-CoV-2 in USNA midshipmen. Methods Midshipmen were enrolled August- October 2020. Participants were queried about their ARI risk factors, COVID-19 history, and recent receipt of medical care for any ARI at enrollment, in December 2020 and again in May 2021. Subjects were also asked to provide blood and saliva samples to assess their SARS-CoV-2 serostatus at the same three timepoints. A saliva sample was collected by a subset of subjects in February 2021. Presence of anti-SARS-CoV-2 serum IgG in dried blood spots and saliva was measured by multiplex magnetic microparticle-based immunoassays. Results 181 midshipmen consented to the study and completed the baseline survey (Table 1). 17 (17.5%) of the 97 subjects who submitted baseline blood sample were SARS-CoV-2 seropositive. Only 4 (24%) positive individuals reported having been tested for or diagnosed with COVID-19 prior to arrival at USNA. 121 participants completed the midyear survey, of whom 61 (50%) submitted a blood sample. 16 (26%) of the midyear specimens were SARS-CoV-2 positive. Of these, 3 were new infections. 73 subjects completed the May survey, and 63 (100%) of the submitted blood samples were positive. 83 subjects provided baseline saliva samples, and ~55 submitted saliva at each successive time point. 1 (5%) was positive at enrollment, 9 (17%) were positive at midyear and 47 (96%) were positive in May. Table 1. Key characteristics of TOSCANA participants Conclusion SAR-CoV-2 prevalence in a sample of USNA midshipmen was < 20% at enrollment. A small proportion of subjects seroconverted between the September and December visits. SARS-CoV-2 positivity rose in May, following a COVID-19 outbreak in February and COVID-19 vaccination efforts in March at USNA. Disclosures Jitu Modi, MD, GSK (Speaker’s Bureau)

Numerical Simulation of Short Duration Hydrodynamic Impact

2014 ◽  
Author(s):  
Thomas C. Fu ◽  
Thomas T. O’Shea ◽  
Kyle A. Brucker ◽  
Carolyn Q. Judge ◽  
Christine M. Ikeda ◽  
...  
Keyword(s):  
Short Duration ◽  
Flow Analysis ◽  
The United States ◽  
Detailed Examination ◽  
Naval Academy ◽  
United States Naval Academy ◽  
Calm Water ◽  
Wedge Impact ◽  
Impact Experiments ◽  
Naval Surface Warfare

Numerical simulations of wedge impact experiments, undertaken by the Naval Surface Warfare Center, Carderock Division, NSWCCD, and more recently by the United States Naval Academy, USNA, Hydromechanics Laboratory, were performed using the computational fluid dynamics code Numerical Flow Analysis, NFA, to assess its capabilities in simulating the short duration hydrodynamic loading associated with free-surface impact. NSWCCD performed experiments using drop heights of 15.24 cm (6 in) and 25.4 cm (10 in), while the Naval Academy used drop heights of: 7.94, 12.7, 15.88, 25.4, 31.75, 38.1, and 50.8 cm (3.125, 5.0, 6.25, 10.0, 12.5, 15.0, and 20.0 in), measured from the keel of the wedge to the calm water surface. Simulations and comparisons were made at heights of 15.24 cm (6 in) and 25.4 cm (10 in) with the NSWCCD data, and 12.5 inches for the USNA data providing for a detailed examination of NFA’s ability to simulate and predict short duration hydrodynamic impacts.

Unsteady Viscous CFD Simulations of KCS Behaviour and Performance in Head Seas

2018 ◽  
Author(s):  
LiXiang Guo ◽  
JiaWei Yu ◽  
JiaJun Chen ◽  
KaiJun Jiang ◽  
DaKui Feng
Keyword(s):  
Degrees Of Freedom ◽  
Transfer Functions ◽  
Resistance Coefficient ◽  
Full Scale ◽  
Body Motion ◽  
Ship Motions ◽  
Added Resistance ◽  
Viscous Effects ◽  
Head Waves ◽  
And Performance

It is critical to be able to estimate a ship’s response to waves, since the added resistance and loss of speed may cause delays or course alterations, with consequent financial repercussions. Traditional methods for the study of ship motions are based on potential flow theory without viscous effects. Results of scaling model are used to predict full-scale of response to waves. Scale effect results in differences between the full-scale prediction and reality. The key objective of this study is to perform a fully nonlinear unsteady RANS simulation to predict the ship motions and added resistance of a full-scale KRISO Container Ship. The analyses are performed at design speeds in head waves, using in house computational fluid dynamics (CFD) to solve RANS equation coupled with two degrees of freedom (2DOF) solid body motion equations including heave and pitch. RANS equations are solved by finite difference method and PISO arithmetic. Computations have used structured grid with overset technology. Simulation results show that the total resistance coefficient in calm water at service speed is predicted by 4 .68% error compared to the related towing tank results. The ship motions demonstrated that the current in house CFD model predicts the heave and pitch transfer functions within a reasonable range of the EFD data, respectively.

Web-Based Data Analysis and Feedback for General Chemistry Laboratory: Improving Analysis with Timely, Distance Feedback

2002 ◽  
Vol 760 ◽  
Author(s):  
Joseph F. Lomax ◽  
Debra K. Dillner ◽  
Melonie A. Teichert
Keyword(s):  
General Chemistry ◽  
Data Analysis ◽  
The United States ◽  
Chemistry Laboratory ◽  
Naval Academy ◽  
Immediate Feedback ◽  
Web Based ◽  
United States Naval Academy ◽  
General Chemistry Laboratory ◽  
Typical Experiment

ABSTRACTIn a general chemistry course, while the hands-on experience of the laboratory is important, the goals of the laboratory are not fulfilled until the calculations and analysis are complete. Quite often students are capable of following laboratory instructions and generating excellent data, only to fail in the data analysis, which rarely occurs in the confines of the laboratory or the presence of the instructor. All too often, students are unable to learn important information from the interpretation of experimental results and draw correct conclusions because they make calculational errors, which are most often discovered by the instructor in the grading process. There is an opportunity for distance learning to help bridge the gap between collection of data and its correct analysis. At the United States Naval Academy (USNA), we have developed a Web-based system where the students input their data and calculational results into a web form with immediate feedback. The students are then allowed to correct their errors and resubmit. This system has been in successful use for 5 years. A description of a typical experiment will be discussed along with an assessment of student and faculty satisfaction with the program.

Rankine Source Method for Seakeeping Predictions

2012 ◽  
Author(s):  
Heinrich Söding ◽  
Alexander von Graefe ◽  
Ould el Moctar ◽  
Vladimir Shigunov
Keyword(s):  
Steady Flow ◽  
Potential Flow ◽  
Transfer Functions ◽  
Stokes Equations ◽  
Computational Time ◽  
Ship Motions ◽  
Periodic Flow ◽  
Source Method ◽  
Rankine Source ◽  
Rankine Source Method

Model tests are usually used for the traditional seakeeping predictions (transfer functions of ship motions and loads in regular waves). Experience shows that numerical solution of Reynolds-averaged Navier-Stokes equations (RANSE) can provide accurate results for this task, however, such computations require too much computational time for the required large number of the loading conditions, ship speeds and wave directions and periods. Traditionally, potential flow methods are used for such computations at early design stages. Although potential flow methods can produce results very quickly for large number of conditions, viscosity effects (most important for the roll motion) have to be taken into account using measurements or RANSE computations. Rankine source method, applied to seakeeping problems perhaps for the first time by Yeung [1] to oscillating ship sections, is increasingly used in practical seakeeping analysis. This paper presents a three-dimensional Rankine source code GL Rankine. Patch method is used instead of the usual collocation method to satisfy boundary conditions on the solid body surface. Periodic flow due to waves is linearized with respect to wave and motion amplitude, taking into account interactions between the nonlinear steady flow and periodic flow due to waves and ship motions. The steady flow solution accounts for the nonlinear free-surface conditions, ship wave and dynamic squat. The paper shows results of the method for ship motions in waves in comparison with model measurements and RANSE simulations.

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