Influences of a Varying Sill at the Seabed on Two-Dimensional Radiation of Linear Water Waves by a Rectangular Buoy

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Xiaolei Liu ◽  
Xuefeng Wang ◽  
Shengwen Xu ◽  
Aibing Ding
Keyword(s):  
Water Waves ◽  
Hydrodynamic Characteristics ◽  
Published Data ◽  
Two Dimensional ◽  
Matching Method ◽  
Mass Coefficient ◽  
Added Mass Coefficient ◽  
The Right ◽  
Interaction Problem ◽  
Linear Water Waves

Abstract The presence of a sill alters the traditional flat seabed conditions, imposing significant effects on hydrodynamic characteristics of the wave–body interaction problem. Eigenfunction matching method (EMM), which is a typical analytical method, is employed to precisely evaluate these effects on two-dimensional radiation of linear water waves by a rectangular buoy. The agreement with the published data and numerical results by the boundary element method (BEM) indicates the correctness of the present EMM. Four aspects involving varying height of the sill, varying width of the sill, varying water depth of the right semi-infinite subdomain, and varying relative positions between the buoy and the sill are considered. Analytical results show that among all the hydrodynamic coefficients, the added mass coefficient of heave is affected most by the varying sill.

Approximations to wave trapping by topography

1996 ◽  
Vol 325 ◽  
pp. 357-376 ◽  
Author(s):  
P. G. Chamberlain ◽  
D. Porter
Keyword(s):  
Water Waves ◽  
Two Dimensional ◽  
Trapped Modes ◽  
Wave Trapping ◽  
Mild Slope Equation ◽  
Precise Shape ◽  
Different Depths ◽  
Linear Water Waves ◽  
Local Irregularity

The trapping of linear water waves over two-dimensional topography is investigated by using the mild-slope approximation. Two types of bed profile are considered: a local irregularity in a horizontal bed and a shelf joining two horizontal bed sections at different depths. A number of results are derived concerning the existence of trapped modes and their multiplicity. It is found, for example, that the maximum number of modes which can exist depends only on the gross properties of the topography and not on its precise shape. A range of problems is solved numerically, to inform and illustrate the analysis, using both the mild-slope equation and the recently derived modified mild-slope equation.

Hydrodynamic Design of a Morphic Autonomous Underwater Vehicle Using Neural Networks

2019 ◽  
Author(s):  
Quentin Becker ◽  
Mohammad-Reza Alam ◽  
Alexandre Immas
Keyword(s):  
Autonomous Underwater Vehicle ◽  
Autonomous Underwater Vehicles ◽  
Added Mass ◽  
Training Dataset ◽  
Hydrodynamic Coefficient ◽  
Optimal Velocity ◽  
Mass Coefficient ◽  
Added Mass Coefficient ◽  
Reliability And Robustness ◽  
The Right

Abstract With the advent of Artificial Intelligence and new manufacturing techniques, Autonomous Underwater Vehicles (AUVs) have started to prevail over their manned version in terms of cost efficiency when it comes to accomplish tasks in ocean exploration, offshore platform and ship maintenance or other military missions. As progress has been made over the past years, autonomy remains a topical issue for the untethered AUVs. Drawing its inspiration from nature, this paper aims at minimizing the energy consumed by the device on a specific mission by allowing its shape, parameterized with Bezier curves, to morph throughout time. The framework is restricted to one dimensional trajectories only. A first step consisting of finding the optimal velocity and shapes added mass coefficient in surge as functions of time for a given mission is presented. Then a way of determining the succession of shapes the AUV must take so that it has the right added mass coefficient at any time is proved and used. This last part is made computationally affordable by using a Neural Network instead of a Boundary Element Method to evaluate the hydrodynamic coefficient in surge of the shape. Outliers detection and elimination are being performed on the training dataset to increase the predictive model reliability and robustness.

Experimental Investigation on Hydrodynamics of a Fish Cage Floater-net System in Oscillatory and Steady Flows by Forced Oscillation Tests

2014 ◽  
Vol 58 (01) ◽  
pp. 20-29
Author(s):  
Shixiao Fu ◽  
Yuwang Xu ◽  
Ke Hu ◽  
Qian Zhong ◽  
Runpei Li
Keyword(s):  
Drag Coefficient ◽  
Drag Force ◽  
Oscillatory Flow ◽  
Forced Oscillation ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Steady Flows ◽  
Steady Current ◽  
Mass Coefficient ◽  
Added Mass Coefficient

In this article, the hydrodynamic characteristics of a floater-net system in oscillatory and steady flows are investigated through forced oscillation experiments in a towing tank. The effects of Keulegan-Carpenter number, Reynolds number, and reduced velocity are studied. Also, hydrodynamic forces on the floater and net are compared in detail to analyze their respective contributions to the total drag force. The results indicate that in oscillatory flow, the added mass coefficient of the floater is larger than that of the floater-net system, whereas the drag coefficient is smaller. The proportion of the drag force exerted on the floating cylinder reaches its maximum in oscillatory flow and its minimum in steady current flow. In addition, the reduced velocity has a very clear influence on the hydrodynamic performance of the floater-net system; specifically, the drag coefficient in oscillatory flow becomes smaller as reduced velocity increases.

scholarly journals Radiation of water waves by a heaving submerged horizontal disc

1997 ◽  
Vol 337 ◽  
pp. 365-379 ◽  
Author(s):  
P. A. MARTIN ◽  
L. FARINA
Keyword(s):  
Integral Equation ◽  
Free Surface ◽  
Water Waves ◽  
Numerical Solutions ◽  
Boundary Integral ◽  
Fredholm Integral Equations ◽  
Mass Coefficient ◽  
Added Mass Coefficient ◽  
Thin Rigid Plate ◽  
Hypersingular Boundary Integral Equation

A thin rigid plate is submerged beneath the free surface of deep water. The plate performs small-amplitude oscillations. The problem of calculating the radiated waves can be reduced to solving a hypersingular boundary integral equation. In the special case of a horizontal circular plate, this equation can be reduced further to one-dimensional Fredholm integral equations of the second kind. If the plate is heaving, the problem becomes axisymmetric, and the resulting integral equation has a very simple structure; it is a generalization of Love's integral equation for the electrostatic field of a parallel-plate capacitor. Numerical solutions of the new integral equation are presented. It is found that the added-mass coefficient becomes negative for a range of frequencies when the disc is sufficiently close to the free surface.

It is better an approximate answer to the right question than the exact answer to the wrong question : the case of the psychometric analysis of the ASQ:SE

2020 ◽  
Author(s):  
Luis Anunciacao ◽  
janet squires ◽  
J. Landeira-Fernandez
Keyword(s):  
Internal Structure ◽  
Statistical Methods ◽  
Principal Component ◽  
Psychological Theory ◽  
Published Data ◽  
Multivariate Statistical ◽  
Exact Answer ◽  
Wide Range ◽  
Ages And Stages Questionnaire ◽  
The Right

One of the main activities in psychometrics is to analyze the internal structure of a test. Multivariate statistical methods, including Exploratory Factor analysis (EFA) and Principal Component Analysis (PCA) are frequently used to do this, but the growth of Network Analysis (NA) places this method as a promising candidate. The results obtained by these methods are of valuable interest, as they not only produce evidence to explore if the test is measuring its intended construct, but also to deal with the substantive theory that motivated the test development. However, these different statistical methods come up with different answers, providing the basis for different analytical and theoretical strategies when one needs to choose a solution. In this study, we took advantage of a large volume of published data (n = 22,331) obtained by the Ages and Stages Questionnaire Social-Emotional (ASQ:SE), and formed a subset of 500 children to present and discuss alternative psychometric solutions to its internal structure, and also to its subjacent theory. The analyses were based on a polychoric matrix, the number of factors to retain followed several well-known rules of thumb, and a wide range of exploratory methods was fitted to the data, including EFA, PCA, and NA. The statistical outcomes were divergent, varying from 1 to 6 domains, allowing a flexible interpretation of the results. We argue that the use of statistical methods in the absence of a well-grounded psychological theory has limited applications, despite its appeal. All data and codes are available at https://osf.io/z6gwv/.

Clinical Case: Complications after Endovascular Treatment of Intracranial Aneurysm in a Patient after Subarachnoid Hemorrhage

2020 ◽  
Vol 8 (1) ◽  
pp. 9-15
Author(s):  
Petrov Nikolay ◽  
◽  
Marinova R. ◽  
Odiseeva Ev.
Keyword(s):  
Intracranial Aneurysm ◽  
Endovascular Treatment ◽  
Clinical Case ◽  
Endovascular Coiling ◽  
Published Data ◽  
Military Medical Academy ◽  
Life Threatening ◽  
Arachnoid Hemorrhage ◽  
The Right ◽  
Brain Artery

Abstract: Intracranial aneurysm is one of the most common neurovascular complications. During the recent years the accepted treatment of enraptured cranial aneurysm is noninvasive endovascular coiling. This technique is modern but it is not without complications which can be serious and life-threatening. A clinical case of a patient admitted to the ICU of Military Medical Academy - Sofia with sub arachnoid hemorrhage is described. After a positive clinical course, the check-up magnetic resonance showed intracranial aneurism of the right carotid artery. The patient underwent angiographic endovascular treatment. Vasospasm of the middle and right brain artery and thrombosis were detected during the procedure. Attempt of thromboaspiration was made without success. This article reviews published data on broad-spectrum researches concerning complications of endovascular coiling of intracranial aneurysms and the ways to prevent and reduce them.

Recognition of human kidney ultrasonic organ images by two-dimensional dp matching method

1986 ◽  
Vol 17 (8) ◽  
pp. 50-59 ◽  
Author(s):  
Hiromitsu Yamada ◽  
Kazuhiko Yamamoto ◽  
Masahiko Matsuura
Keyword(s):  
Human Kidney ◽  
Two Dimensional ◽  
Matching Method

scholarly journals On local and integrated stress-tensor commutators

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Mert Besken ◽  
Jan de Boer ◽  
Grégoire Mathys
Keyword(s):  
Stress Tensor ◽  
Free Field ◽  
Virasoro Algebra ◽  
Light Sheet ◽  
Operator Product ◽  
Local Form ◽  
Two Dimensional ◽  
Conformal Embedding ◽  
General Aspects ◽  
The Right

Abstract We discuss some general aspects of commutators of local operators in Lorentzian CFTs, which can be obtained from a suitable analytic continuation of the Euclidean operator product expansion (OPE). Commutators only make sense as distributions, and care has to be taken to extract the right distribution from the OPE. We provide explicit computations in two and four-dimensional CFTs, focusing mainly on commutators of components of the stress-tensor. We rederive several familiar results, such as the canonical commutation relations of free field theory, the local form of the Poincaré algebra, and the Virasoro algebra of two-dimensional CFT. We then consider commutators of light-ray operators built from the stress-tensor. Using simplifying features of the light sheet limit in four-dimensional CFT we provide a direct computation of the BMS algebra formed by a specific set of light-ray operators in theories with no light scalar conformal primaries. In four-dimensional CFT we define a new infinite set of light-ray operators constructed from the stress-tensor, which all have well-defined matrix elements. These are a direct generalization of the two-dimensional Virasoro light-ray operators that are obtained from a conformal embedding of Minkowski space in the Lorentzian cylinder. They obey Hermiticity conditions similar to their two-dimensional analogues, and also share the property that a semi-infinite subset annihilates the vacuum.

scholarly journals New exact relations for steady irrotational two-dimensional gravity and capillary surface waves

2017 ◽  
Vol 376 (2111) ◽  
pp. 20170220 ◽  
Author(s):  
Didier Clamond
Keyword(s):  
Free Surface ◽  
Gravity Waves ◽  
Water Waves ◽  
Two Dimensional ◽  
Physical Plane ◽  
Theme Issue ◽  
Nonlinear Water Waves ◽  
Dimensional Gravity ◽  
Irrotational Motion ◽  
Exact Relations

Steady two-dimensional surface capillary–gravity waves in irrotational motion are considered on constant depth. By exploiting the holomorphic properties in the physical plane and introducing some transformations of the boundary conditions at the free surface, new exact relations and equations for the free surface only are derived. In particular, a physical plane counterpart of the Babenko equation is obtained. This article is part of the theme issue ‘Nonlinear water waves’.

Sign in / Sign up

Export Citation Format

Share Document