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.

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.

Application of a Boundary Element Method for Wave-Body Interaction Problems Considering the Non-Linear Water Surface

2017 ◽  
Author(s):  
Daniel Ferreira González ◽  
Jonas Bechthold ◽  
Moustafa Abdel-Maksoud
Keyword(s):  
Water Surface ◽  
Three Dimensional ◽  
Free Water ◽  
Numerical Approach ◽  
Panel Method ◽  
The Body ◽  
Time Step ◽  
Non Linear ◽  
Wigley Hull ◽  
Tank Test

In this paper an existing time domain panel method, which was originally developed for propeller flow simulations, is extended by implementing the mixed Eulerian-Lagrangian approach for the computation of the non-linear free water surface. The three-dimensional panel method uses a constant source and doublet density distribution on each panel and a Dirichlet boundary condition to solve the velocity potential in every time step. Additionally, a formulation for the acceleration potential is included in order to determine the hydrodynamic forces accurately. The paper gives an overview on the governing equations and introduces the numerical approach. Validation results of the developed method are presented for the wave resistance of a submerged spheroid and a wigley hull. Additionally, the wave diffraction due to a surface piercing cylinder in regular waves is validated regarding the forces and the water surface elevation around the body. Here, the computations are compared with other numerical methods as well as tank test results. Apart from this, the paper deals with an application example showing simulations of an artificial service vessel catamaran in waves. The forces on the hull with and without forward speed are presented. The paper concludes with a discussion of the presented results and a brief outlook on further work.

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.

Validation of a New Hydroelastic Code for Flexible Floating Structures Moored in Waves

2009 ◽  
Author(s):  
J. L. F. van Kessel
Keyword(s):  
Wave Spectrum ◽  
Three Dimensional ◽  
Numerical Results ◽  
Floating Bodies ◽  
Hydrodynamic Analysis ◽  
Floating Structures ◽  
University Of Technology ◽  
Deformable Bodies ◽  
Elastic Modes ◽  
Experimental Values

Natural periods of elastic modes can be in the range of the wave spectrum for relatively long and slender floating bodies. As a result elastic body deformations such as vertical bending, horizontal bending and torsion may be significant and need to be taken into account in the hydrodynamic analysis of very large floating structures. The behavior of flexible floating bodies in waves has been studied at Delft University of Technology. For this purpose the existing linear three dimensional diffraction code DELFRAC was modified to take into account the fluid-structure interaction of deformable bodies at zero forward speed in waves. This paper focuses on the validation of the new hydroelastic code for flexible floating structures moored in waves. Numerical results are validated by model experiments of a flexible barge in waves from different headings. In addition, the obtained results are compared with results from other existing hydroelastic programs. In general it is shown that numerical results show good agreement with experimental values.

Electron Holographic Nano-Characterization of Gold Catalyst at Interface

2002 ◽  
Vol 727 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
M. Okumura ◽  
M. Haruta ◽  
K. Tanaka
Keyword(s):  
Contact Angle ◽  
Titanium Oxide ◽  
Gold Catalyst ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Electron Holography ◽  
Gold Particles ◽  
Oxide Support ◽  
The Mean ◽  
A Charge

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”

Modeling and Assessment of the Produced Water Discharges from Offshore Petroleum Platforms

2007 ◽  
Vol 42 (4) ◽  
pp. 303-310 ◽  
Author(s):  
Zhi Chen ◽  
Lin Zhao ◽  
Kenneth Lee ◽  
Charles Hannath
Keyword(s):  
Random Walk ◽  
Produced Water ◽  
Model Development ◽  
Three Dimensional ◽  
Monitoring Program ◽  
Ecological Monitoring ◽  
Numerical Approach ◽  
Ocean Model ◽  
Scale Model ◽  
Water Stream

Abstract There has been a growing interest in assessing the risks to the marine environment from produced water discharges. This study describes the development of a numerical approach, POM-RW, based on an integration of the Princeton Ocean Model (POM) and a Random Walk (RW) simulation of pollutant transport. Specifically, the POM is employed to simulate local ocean currents. It provides three-dimensional hydrodynamic input to a Random Walk model focused on the dispersion of toxic components within the produced water stream on a regional spatial scale. Model development and field validation of the predicted current field and pollutant concentrations were conducted in conjunction with a water quality and ecological monitoring program for an offshore facility located on the Grand Banks of Canada. Results indicate that the POM-RW approach is useful to address environmental risks associated with the produced water discharges.

The Influence of Blade Wakes on the Performance of Interturbine Diffusers

1996 ◽  
Vol 118 (2) ◽  
pp. 347-352 ◽  
Author(s):  
R. G. Dominy ◽  
D. A. Kirkham
Keyword(s):  
Performance Modeling ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Two Dimensional ◽  
Correct Performance ◽  
Analysis Methods ◽  
Flow Factor ◽  
The Mean ◽  
Lp Turbine

Interturbine diffusers provide continuity between HP and LP turbines while diffusing the flow upstream of the LP turbine. Increasing the mean turbine diameter offers the potential advantage of reducing the flow factor in the following stages, leading to increased efficiency. The flows associated with these interturbine diffusers differ from those in simple annular diffusers both as a consequence of their high-curvature S-shaped geometry and of the presence of wakes created by the upstream turbine. It is shown that even the simplest two-dimensional wakes result in significantly modified flows through such ducts. These introduce strong secondary flows demonstrating that fully three-dimensional, viscous analysis methods are essential for correct performance modeling.

scholarly journals Proximity of the middle meningeal artery and maxillary artery to the mandibular head and mandibular neck as revealed by three-dimensional time-of-flight magnetic resonance angiography

2021 ◽  
Author(s):  
Daphne Schönegg ◽  
Raphael Ferrari ◽  
Julian Ebner ◽  
Michael Blumer ◽  
Martin Lanzer ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Angiography ◽  
Three Dimensional ◽  
Time Of Flight ◽  
Middle Meningeal Artery ◽  
Individual Variability ◽  
Maxillary Artery ◽  
Condylar Process ◽  
The Mean ◽  
Meningeal Artery

Abstract Purpose The close topographic relationship between vascular and osseous structures in the condylar and subcondylar region and marked variability in the arterial course has been revealed by both imaging and cadaveric studies. This study aimed to verify the previously published information in a large sample and to determine a safe surgical region. Methods We analyzed the three-dimensional time-of-flight magnetic resonance angiography images of 300 individuals. Results The mean distance between the middle meningeal artery and the apex of the condyle or the most medial point of the condyle was 18.8 mm (range: 11.2–25.9 mm) or 14.5 mm (range: 8.8–22.9 mm) respectively. The course of the maxillary artery relative to the lateral pterygoid muscle was medial in 45.7% of cases and lateral in 54.3%. An asymmetric course was evident in 66 patients (22%). The mean distance between the maxillary artery and condylar process at the deepest point of the mandibular notch was 6.2 mm in sides exhibiting a medial course (range: 3.7–9.8 mm) and 6.6 mm in sides exhibiting a lateral course (range: 3.9–10.4 mm). The distances were significantly influenced by age, gender, and the course of the maxillary artery. Conclusion Our study emphasizes the marked inter- and intra-individual variability of the maxillary and middle meningeal arterial courses. We confirmed the proximity of the arteries to the condylar process. Extensive surgical experience and thorough preparation for each individual case are essential to prevent iatrogenic vascular injury.

Simulation of small-angle scattering curves by numerical Fourier transformation

2007 ◽  
Vol 40 (1) ◽  
pp. 16-25 ◽  
Author(s):  
Klaus Schmidt-Rohr
Keyword(s):  
Form Factor ◽  
Small Angle ◽  
Fourier Transformation ◽  
Three Dimensional ◽  
Power Laws ◽  
Numerical Approach ◽  
Peak Position ◽  
Two Dimensions ◽  
Correlation Peak ◽  
Scattering Intensity

A simple numerical approach for calculating theq-dependence of the scattering intensity in small-angle X-ray or neutron scattering (SAXS/SANS) is discussed. For a user-defined scattering density on a lattice, the scattering intensityI(q) (qis the modulus of the scattering vector) is calculated by three-dimensional (or two-dimensional) numerical Fourier transformation and spherical summation inqspace, with a simple smoothing algorithm. An exact and simple correction for continuous rather than discrete (lattice-point) scattering density is described. Applications to relatively densely packed particles in solids (e.g.nanocomposites) are shown, where correlation effects make single-particle (pure form-factor) calculations invalid. The algorithm can be applied to particles of any shape that can be defined on the chosen cubic lattice and with any size distribution, while those features pose difficulties to a traditional treatment in terms of form and structure factors. For particles of identical but potentially complex shapes, numerical calculation of the form factor is described. Long parallel rods and platelets of various cross-section shapes are particularly convenient to treat, since the calculation is reduced to two dimensions. The method is used to demonstrate that the scattering intensity from `randomly' parallel-packed long cylinders is not described by simple 1/qand 1/q4power laws, but at cylinder volume fractions of more than ∼25% includes a correlation peak. The simulations highlight that the traditional evaluation of the peak position overestimates the cylinder thickness by a factor of ∼1.5. It is also shown that a mix of various relatively densely packed long boards can produceI(q) ≃ 1/q, usually observed for rod-shaped particles, without a correlation peak.

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