The Effect of Aircushion Division on the Motions of Large Floating Structures

2007 ◽  
Author(s):  
J. L. F. van Kessel ◽  
J. A. Pinkster
Keyword(s):  
Water Surface ◽  
Three Dimensional ◽  
Potential Method ◽  
Wave Fields ◽  
Floating Structures ◽  
Different Types ◽  
The Mean ◽  
Motion Characteristics ◽  
The Stability ◽  
Drift Forces

The effect of aircushion division on the motions of large floating structures is studied by means of calculations based on a linear three-dimensional potential method. A linear adiabatic law is used to describe the air pressures inside the cushions. The water surface within the aircushions and the mean wetted surface are modelled by panel distributions representing oscillating sources. The behaviour of different types of aircushion supported structures is described and compared with that of a rectangular barge having the same dimensions. Successively, the aircushion theory, motion characteristics, wave frequency forces and moments, mean second order drift forces and surrounding wave fields are discussed. The results show that aircushions significantly influence the stability and behaviour of large floating structures.

Numerical and Experimental Study on Aircushion Supported Structures

2008 ◽  
Author(s):  
J. L. F. van Kessel
Keyword(s):  
Water Surface ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Potential Method ◽  
Model Tests ◽  
Numerical Calculations ◽  
Floating Structures ◽  
University Of Technology ◽  
The Mean ◽  
Very Large Floating Structures

The use of aircushions for very large floating structures has been investigated in recent years at Delft University of Technology. Model tests were performed to validate the results of numerical calculations based on a linear three-dimensional potential method. A linear adiabatic law was used in the numerical approach to describe the air pressures inside the cushions. It is assumed that air cannot escape from the cavity underneath the structure. The water surface within the aircushions and the mean wetted surface are modelled by panel distributions representing oscillating sources. Experimental results and numerical calculations of two configurations of aircushion supported structures at zero speed are presented in this paper. The results show that model tests of different aircushion supported structures can be well predicted by means of 3D diffraction calculations.

The Effect of Aircushion Division on the Structural Loads of Large Floating Offshore Structures

2007 ◽  
Author(s):  
J. L. F. van Kessel ◽  
J. A. Pinkster
Keyword(s):  
Water Surface ◽  
Three Dimensional ◽  
Potential Method ◽  
Offshore Structures ◽  
Bending Moments ◽  
Shear Forces ◽  
Floating Structures ◽  
The Mean ◽  
Wave Induced

The effect of aircushion division on the structural loads of large floating offshore structures is described and compared with that of a rectangular barge having the same dimensions. Calculations are based on a linear three-dimensional potential method using a linear adiabatic law for the air pressures inside the cushions. The water surface within the aircushions and the mean wetted surface are modelled by panel distributions representing oscillating sources. In the presented cases the structural loads include the wave induced bending moments and shear forces along the length of the structure. Aircushions significantly influence the behaviour of large floating structures in waves and consequently reduce the bending moments. The internal loads of different configurations of aircushion supported structures are described and compared with those of a rectangular barge having the same dimensions. The significant reduction of the bending moments shows that aircushion support can be of interest for large floating structures.

scholarly journals Experimental Study on 2D Motion Characteristics of Submerged Floating Tunnel in Waves

2020 ◽  
Vol 8 (2) ◽  
pp. 123 ◽  
Author(s):  
Zhiwen Yang ◽  
Jinzhao Li ◽  
Huaqing Zhang ◽  
Chunguang Yuan ◽  
Hua Yang
Keyword(s):  
Wave Height ◽  
Water Surface ◽  
Weight Ratio ◽  
Mooring Line ◽  
Natural Period ◽  
Main Challenge ◽  
Line Angle ◽  
Submerged Floating Tunnel ◽  
Motion Characteristics ◽  
The Stability

Submerged floating tunnel (SFT) is a new type of transportation infrastructure for crossing sea straits in relatively deeper water. Compared with the fixed tunnel, the main challenge in designing a SFT is the stability maintaining in a complex hydrodynamic environment, especially for the wave-induced dynamic load. In this study, a series of systematic experiments were conducted to investigate the 2D motion characteristics (i.e., heave, sway and roll) of the SFT exposed to regular waves. The movement of the SFT model is measured by the image processing method which is a noncontact measurement. The experimental observation of SFT motion during the process of wave and SFT interaction is described in detail, and the influence of several governing parameters is thoroughly analyzed, including the wave height and period, submergence depth, buoyancy to weight ratio (BWR), and the mooring line angle. The results show that the motion amplitudes of SFT increase with the wave height increasing. The effect of wave period is related to the natural period of the structure. The sway, heave and roll of the SFT submerged beneath the water surface are much smaller than that of the SFT on the water surface. With the increase of BWR, the motion of SFT decreases. The motion amplitude increases with mooring line angle increasing. Finally, empirical equations are proposed to estimate the motion characteristics of the SFT.

On the stability of parallel flows with parallel magnetic fields

1966 ◽  
Vol 293 (1434) ◽  
pp. 342-358 ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Parallel Magnetic Field ◽  
Parallel Flows ◽  
The Mean ◽  
The Stability ◽  
The Magnetic Field ◽  
Parallel Magnetic Fields

The first part of the paper is a physical discussion of the way in which a magnetic field affects the stability of a fluid in motion. Particular emphasis is given to how the magnetic field affects the interaction of the disturbance with the mean motion. The second part is an analysis of the stability of plane parallel flows of fluids with finite viscosity and conductivity under the action of uniform parallel magnetic fields. We show that, in general, three-dimensional disturbances are the most unstable, thus disagreeing with the conclusion of Michael (1953) and Stuart (1954). We show how results obtained for two-dimensional disturbances can be used to calculate the most unstable three-dimensional disturbances and thence we prove that a parallel magnetic field can never completely stabilize a parallel flow.

scholarly journals Ethyl 2-(2-methyl-4-nitro-1H-imidazol-1-yl)acetate

IUCrData ◽  
2016 ◽  
Vol 1 (4) ◽  
Author(s):  
Yassine Hakmaoui ◽  
El Mostapha Rakib ◽  
Souad Mojahidi ◽  
Mohamed Saadi ◽  
Lahcen El Ammari
Keyword(s):  
Hydrogen Bonds ◽  
Title Compound ◽  
Crystal Packing ◽  
Three Dimensional ◽  
Imidazole Ring ◽  
Compound C ◽  
Dimensional Network ◽  
The Mean ◽  
Packing Arrangement ◽  
The Stability

In the title compound, C8H11N3O4, the imidazole ring and the nitro group are nearly coplanar, with the largest deviation from the mean plane being 0.119 (2) Å. The mean plane through the acetate group is approximately perpendicular to the imidazole ring, subtending a dihedral angle of 75.71 (13)°. In the crystal, molecules are linked by weak C—H...O and very weak C—H...N hydrogen bonds, forming a three-dimensional network. There is also a weak C—H...π(imidazole) interaction, which contributes to the stability of the crystal packing arrangement.

On transition of the pulsatile pipe flow

1986 ◽  
Vol 170 ◽  
pp. 169-197 ◽  
Author(s):  
J. C. Stettler ◽  
A. K. M. Fazle Hussain
Keyword(s):  
Steady Flow ◽  
Pipe Flow ◽  
Three Dimensional ◽  
Building Blocks ◽  
Rate Of Change ◽  
Turbulent Pipe Flow ◽  
Dimensional Parameter ◽  
Pipe Length ◽  
The Mean ◽  
The Stability

Transition in a pipe flow with a superimposed sinusoidal modulation has been studied in a straight circular water pipe using laser-Doppler anemometer (LDA) techniques. This study has determined the stability–transition boundary in the three-dimensional parameter space defined by the mean and modulation Reynolds numbers Rem, Remω and the frequency parameter λ. Furthermore, it documents the mean passage frequency Fp of ‘turbulent plugs’ as functions of Rem’ Remω and λ. This study also delineates the conditions when plugs occur randomly in time (as in the steady flow) or phase-locked with the excitation. The periodic flow requires a new definition of the transitional Reynolds number Rer, identified on the basis of the rate of change of Fp with Rem. The extent of increase or decrease in Rer from the corresponding steady flow value depends on λ and Remω. At any Rem and Remω, maximum stabilization occurs at λ ≈ 5. With increasing Remω, the ‘stabilization bandwidth’ of modulation frequencies increases and then abruptly decreases after levelling off. The maximum stabilization bandwidth depends strongly on Rem, decreasing with increasing Rem. Previously reported observations of turbulence during deceleration, followed by a relaminarization during acceleration, can be explained in terms of a new phenomenon: namely, periodic modulation produces longitudinally periodic cells of turbulent fluid ‘plugs’ which differ in structural details from ‘puffs’ or ‘slugs’ in steady transitional pipe flows and are called patches. The length of a patch could be increased continuously from zero to the entire pipe length by increasing Rem. This tends to question the concept that all turbulent plugs (and even the fully-turbulent pipe flow) consists of many identical elementary plugs as basic ‘building blocks’.

BORDER COLLISION BIFURCATIONS IN THREE-DIMENSIONAL PIECEWISE SMOOTH SYSTEMS

2008 ◽  
Vol 18 (02) ◽  
pp. 577-586 ◽  
Author(s):  
INDRAVA ROY ◽  
A. R. ROY
Keyword(s):  
Three Dimensional ◽  
Piecewise Smooth ◽  
Smooth Maps ◽  
Research Fields ◽  
Border Collision Bifurcations ◽  
Period 2 ◽  
Wide Range ◽  
Different Types ◽  
Piecewise Smooth Maps ◽  
The Stability

Piecewise smooth maps have been a focus of study for scientists in a wide range of research fields. These maps show qualitatively different types of bifurcations than those exhibited by generic smooth maps. We present a theoretical framework for analyzing three-dimensional piecewise smooth maps by deriving a suitable normal form and then finding the stability criteria for periodic orbits. We also show by numerical simulation different types of border collision bifurcations that can occur in such a map. We have also been able to observe a border collision bifurcation from a period-2 to a quasiperiodic orbit.

Granulometry and Stability of Aggregates in Different Land Uses in the Santa Catarina Plateau of Southern, Brazil

2019 ◽  
pp. 1-6
Author(s):  
Kristiana Fiorentin dos Santos ◽  
Fabrício Tondello Barbosa ◽  
Ildegardis Bertol ◽  
Romeu De Souza Werner ◽  
Neuro Hilton Wolschick ◽  
...  
Keyword(s):  
Land Use ◽  
Sample Survey ◽  
Land Uses ◽  
Southern Brazil ◽  
Santa Catarina ◽  
Land Use Types ◽  
Different Types ◽  
The Mean ◽  
The Stability ◽  
Definition Of

The aim of the present work was to determine the granulometry and stability of aggregates in different types of land use in the Santa Catarina Plateau of southern, Brazil. The research was conducted on Capão Alto, Santa Catarina, Brazil. The land use types selected were natural forest (NF), stands pine (SP), crop-livestock integration (CLI), and burned natural rangeland (BR). The definition of the collection points in the field was performed by means of a random sample survey, with nine sampling points by type of use. The stability of aggregates in water, expressed by the mean geometric diameter of aggregates (MGD), was performed after separation of the larger aggregates in smaller aggregates by a set of sieves with 8 and 4.76 mm. Subsequently, these aggregates were fractionated by means of a set of sieves of 4.76; 2.00; 1.00; and 0.25 mm by means of shaking submerged in water. The levels of sand, silt and clay presented differences between the types of land use. MGD ranges from 4.43 to 5.70 mm in NF; from 4.06 to 5.81 mm in SP; from 3.00 to 5,45 mm in CLI; e 4.35 to 5.57 mm in BR. In general, the results showed that MGD varied little in the different types of use, and in all treatments there was a trend of decreasing soil MGD with increasing depth.

scholarly journals Occurrence of extreme waves in three-dimensional mechanically generated wave fields propagating over an oblique current

2011 ◽  
Vol 11 (3) ◽  
pp. 895-903 ◽  
Author(s):  
A. Toffoli ◽  
L. Cavaleri ◽  
A. V. Babanin ◽  
M. Benoit ◽  
E. M. Bitner-Gregersen ◽  
...  
Keyword(s):  
Modulational Instability ◽  
Three Dimensional ◽  
Wave Direction ◽  
Subsequent Increase ◽  
Wave Fields ◽  
Wave Trains ◽  
Directional Wave ◽  
The Mean ◽  
Wave Maker ◽  
Non Gaussian

Abstract. Laboratory experiments were performed to study the dynamics of three- dimensional mechanically generated waves propagating over an oblique current in partial opposition. The flow velocity varied along the mean wave direction of propagation with an increasing trend between the wave-maker and the centre of the tank. Tests with regular wave packets traversing the area of positive current gradient showed that the concurrent increase of wave steepness triggered modulational instability on otherwise stable wave trains and hence induced the development of very large amplitude waves. In random directional wave fields, the presence of the oblique current resulted in a weak reinforcement of wave instability with a subsequent increase of the probability of occurrence of extreme events. This seems to partially compensate the suppression of strongly non-Gaussian properties due to directional energy distribution.

Drogue-cluster and dye-dispersion measurements

1987 ◽  
Vol 14 (3) ◽  
pp. 320-326 ◽  
Author(s):  
Merv D. Palmer ◽  
Rob Jarvis ◽  
Larry Thompson
Keyword(s):  
Water Surface ◽  
Center Of Mass ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Dispersion Data ◽  
Batch Release ◽  
Surface Dispersion ◽  
The Mean ◽  
The Difference ◽  
Lagrangian Data

Near the water surface, dispersion and transport were extensively measured in the coastal regions of Lake Ontario using dye patches and clusters of water sail and surface drogues. The measurements were carried out for 6–8 h. Each method produced different measurements of dispersion magnitudes with the largest dilution occurring for the dye, followed by sail drogue clusters (40% of the dye's value) and then surface drogue clusters (25% of the dye's value). Both the sail and surface drogues measured the two-dimensional dispersion. The mean surface dispersion was about 50% less than the dispersion 1.5 m below the water surface. The dilution characteristics decreased as the water surface was approached. The sail dispersion was about half of the dye-dispersion data. It was not known how much of the difference was attributable to the dye being three-dimensional and affected by dispersion in the vertical direction; consequently, as time progressed, the dye patch was measuring dispersion at greater depth than the water sail drogues, which were set for a depth 1.5 m below the water surface. The statistical increase of the variance with time was computed for each method of measuring dispersion, and the results were compared. A method for predicting dilution envelopes for a location using the path lines of the drogue-cluster centroids or center of mass of the dye patch was developed for both a batch release and a continuous discharge. These dilution envelopes are based entirely on Lagrangian data for both the velocity and dispersion estimates. Key words: lake, dispersion, drogue clusters, dye, surface streaking.

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