Second Order Loads on LNG Terminals in Multi-Directional Sea in Water of Finite Depth

2007 ◽  
Author(s):  
Fla´via Rezende ◽  
Xin Li ◽  
Xiao-Bo Chen
Keyword(s):  
Near Field ◽  
Low Frequency ◽  
Finite Depth ◽  
Accurate Method ◽  
Second Order ◽  
Wave Loading ◽  
Storage Tanks ◽  
Offshore Area ◽  
Directional Waves ◽  
Poor Convergence

Large LNG terminals are designed to be installed in an offshore area approximate to harbors where the water is of finite depth and waves are multi-directional. The terminal can be of a barge type LNG/FRSU including accommodations, gas preconditioning and liquefied plant, a number of storage tanks and offloading facilities. It serves also as a support to moor a LNG carrier during offloading operations. In the design of such mooring system of LNG/FRSU and LNG carriers in a zone of shallow water, one key issue is the accurate simulation of low-frequency motions of the system to which the second-order wave loading is well known as the main source of excitation. The computation of second-order wave loading in multi-directional waves of finite waterdepth is considered here. New formulations obtained recently in [1] for the computation of second-order loads in mono-directional waves are extended to the case of multi-directional waves. Both the classical near-field formulation and the new middle-field formulation developed in [1] are used and numerical results are compared. Unlike the usual near-field formulation giving results of second-order loads with poor convergence, the middle-field formulation provides an accurate method for the computation of vertical components.

Approximation of Second-Order Low-Frequency Wave Loading in Multi-Directional Waves

2010 ◽  
Author(s):  
Flavia C. Rezende ◽  
Xiao-bo Chen
Keyword(s):  
Low Frequency ◽  
Second Order ◽  
Wave Loads ◽  
Wave Loading ◽  
Frequency Wave ◽  
New Developments ◽  
Directional Waves ◽  
Novel Method ◽  
The Difference ◽  
Accurate Scheme

Further to the studies by Chen & Rezende (OMAE2009) on the quadratic transfer function (QTF) of low-frequency wave loading in which the QTF is developed by the series expansion associated with the difference-frequency up to the order-Δω2, new formulations have been developed in order to take into account the effect of interactions between waves of different headings. It provides a novel method to evaluate the low-frequency second-order wave loads in a more accurate than usual order-Δω approximation (often called Newman approximation) and more efficient way comparing to the computation of complete QTF in multi-directional waves. New developments including numerical results of different components of QTF are presented here. Furthermore, the time-series reconstruction of excitation loads by quadruple sums in the motion simulation of mooring systems is analyzed and a new efficient and accurate scheme using only a triple sum is demonstrated.

Efficient Computations of Second-Order Low-Frequency Wave Load

2009 ◽  
Author(s):  
Xiao-Bo Chen ◽  
Fla´via Rezende
Keyword(s):  
Low Frequency ◽  
Second Order ◽  
Wave Loads ◽  
Wave Loading ◽  
Wave Load ◽  
Frequency Wave ◽  
New Developments ◽  
Novel Method ◽  
The Difference ◽  
New Formulation

As the main source of resonant excitations to most offshore moored systems like floating LNG terminals, the low-frequency wave loading is the critical input to motion simulations which are important for the design. Further to the analysis presented by Chen & Duan (2007) and Chen & Rezende (2008) on the quadratic transfer function (QTF) of low-frequency wave loading, the new formulation of QTF is developed by the series expansion of the second-order wave loading with respect to the difference-frequency upto the order-2. It provides a novel method to evaluate the low-frequency second-order wave loads in a more accurate than usual order-0 approximation (often called Newman approximation) and more efficient way comparing to the computation of complete QTF. New developments including numerical results of different components of QTF are presented here. Furthermore, the time-series reconstruction of excitation loads in the motion simulation of mooring systems is analyzed and a new efficient and accurate scheme is demonstrated.

Finite Depth and Tank Wall Effects Upon First and Second-Order Forces

1991 ◽  
Vol 113 (4) ◽  
pp. 297-305 ◽  
Author(s):  
G. E. Hearn ◽  
S. Y. Liou
Keyword(s):  
Low Frequency ◽  
Open Water ◽  
Finite Depth ◽  
Second Order ◽  
Confined Water ◽  
Rankine Source ◽  
Method Of Solution ◽  
Direct Pressure ◽  
Expansion Matching ◽  
Matching Techniques

This paper presents a hybrid method of solution of the radiation and diffraction fluid-structure interaction problems based upon Rankine source distributions and eigenfunction expansion matching techniques. Using direct pressure integration of the first-order solutions, the second-order drift forces are calculated in “open” water and “confined” water situations with and without forward speed effects included. The method has been developed to provide an alternative way of calculating low-frequency damping coefficients.

Second-Order Wave Loads on a LNG Carrier in Multi-Directional Waves

2008 ◽  
Author(s):  
Mathieu Renaud ◽  
Fla´via Rezende ◽  
Olaf Waals ◽  
Xiao-Bo Chen ◽  
Radboud van Dijk
Keyword(s):  
Low Frequency ◽  
Model Tests ◽  
Second Order ◽  
Wave Loads ◽  
Wave Kinematics ◽  
Directional Waves ◽  
Slow Drift ◽  
Wave Directionality ◽  
Offshore Industry ◽  
Cross Waves

Due to the installation of LNG terminals moored in proximity to the coast, the wave kinematics in shallow water and the consequence on the behavior of those terminals have recently became a major concern of the offshore industry. One key issue is the accurate simulation of the low-frequency motions of LNG carriers, specially the surge, for which the vessel presents low damping, in order to perform the design of the mooring system. The present paper focuses on the effect of wave directionality on second-order slow-drift loads and the related response of the vessel. The paper describes results of model tests in regular cross waves — monochromatic but coming from two directions separated by 90 degrees, as well as bichromatic cross waves. The new “middle field” formulation extended to the case of cross waves, is used to compute the wave drift loads and low-frequency Quadratic Transfer Function (QTF). The results are compared with those from the model tests.

A Finite-Depth Unified Theory for the Linear and Second-Order Problems of Slender Ships

1998 ◽  
Vol 42 (04) ◽  
pp. 297-309 ◽  
Author(s):  
Yonghwan Kim ◽  
Paul D. Sclavounos
Keyword(s):  
Integral Equation ◽  
Near Field ◽  
Finite Depth ◽  
Theoretical Background ◽  
Second Order ◽  
Design Tool ◽  
Unified Theory ◽  
Slender Body Theory ◽  
Strip Theory ◽  
Drift Forces

In this paper an extension of the unified slender-body theory is introduced to solve the finite-depth seakeeping problem of a slender ship. The far-and near-field behaviors of the velocity potential in finite depth are introduced, and a new kernel of the integral equation is derived for the heave and pitch motions of a slender ship at zero speed. The kernel of the integral equation is expressed in a series form which makes the integral equation easy to solve. Based on the present theoretical background, computations were carried out, and the hydrodynamic coefficients and motion RAOs were obtained. The computational results are compared with WAMIT, and a nice agreement is shown. The present method is extended to the computation of the second-order mean drift forces and moment in infinite and finite depth. Motion RAOs of sway, roll and yaw are obtained using strip theory, and the drift forces using the far-field momentum equations. The results show favorable agreement with WAMIT. Using the drift forces, the wave drift damping matrix is obtained for infinite depth. Aranha's formula is applied, and the damping coefficients are compared with the existing data. The present study shows that unified theory is an efficient and accurate design tool for slender ships.

scholarly journals Occluded Grape Cluster Detection and Vine Canopy Visualisation Using an Ultrasonic Phased Array

Sensors ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 2182
Author(s):  
Baden Parr ◽  
Mathew Legg ◽  
Stuart Bradley ◽  
Fakhrul Alam
Keyword(s):  
Near Field ◽  
Low Frequency ◽  
Volume Estimation ◽  
Yield Estimation ◽  
3D Scan ◽  
Management Processes ◽  
Canopy Volume ◽  
Ultrasonic Phased Array ◽  
Added Benefit ◽  
Grape Yield

Grape yield estimation has traditionally been performed using manual techniques. However, these tend to be labour intensive and can be inaccurate. Computer vision techniques have therefore been developed for automated grape yield estimation. However, errors occur when grapes are occluded by leaves, other bunches, etc. Synthetic aperture radar has been investigated to allow imaging through leaves to detect occluded grapes. However, such equipment can be expensive. This paper investigates the potential for using ultrasound to image through leaves and identify occluded grapes. A highly directional low frequency ultrasonic array composed of ultrasonic air-coupled transducers and microphones is used to image grapes through leaves. A fan is used to help differentiate between ultrasonic reflections from grapes and leaves. Improved resolution and detail are achieved with chirp excitation waveforms and near-field focusing of the array. The overestimation in grape volume estimation using ultrasound reduced from 222% to 112% compared to the 3D scan obtained using photogrammetry or from 56% to 2.5% compared to a convex hull of this 3D scan. This also has the added benefit of producing more accurate canopy volume estimations which are important for common precision viticulture management processes such as variable rate applications.

Hydrodynamic Noise and Radiated Mechanism of 3D Cavity

2012 ◽  
Vol 217-219 ◽  
pp. 2590-2593 ◽  
Author(s):  
Yu Wang ◽  
Bai Zhou Li
Keyword(s):  
Sound Pressure ◽  
Near Field ◽  
Low Frequency ◽  
Dipole Source ◽  
Fluctuating Pressure ◽  
Common Structure ◽  
Hydrodynamic Noise ◽  
Near Field Sound ◽  
Equivalent Sources ◽  
Field Sound

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

Ground Attenuation Factor Based on Measurements

2021 ◽  
Vol 263 (3) ◽  
pp. 3436-3447
Author(s):  
Dan Lin ◽  
Andrew Eng
Keyword(s):  
Near Field ◽  
Attenuation Factor ◽  
Measurement Data ◽  
Low Frequency ◽  
Sound Sources ◽  
Frequency Sound ◽  
Sound Levels ◽  
Different Types ◽  
Noise Measurements ◽  
Field Sound

Assumptions made on the ground types between sound sources and receivers can significantly impact the accuracy of environmental outdoor noise prediction. A guideline is provided in ISO 9613-2 and the value of ground factor ranges from 0 to 1, depending on the coverage of porous ground. For example, a ground absorption factor of 1 is suggested for grass ground covers. However, it is unclear if the suggested values are validated. The purpose of this study is to determine the sound absorption of different types of ground by measurements. Field noise measurements were made using an omnidirectional loudspeaker and two microphones on three different types of ground in a quiet neighborhood. One microphone was located 3ft from the loudspeaker to record near field sound levels in 1/3 and 1 octave bands every second. The other microphone was located a few hundred feet away to record far field sound in the same fashion as the near field microphone. The types of ground tested were concrete, grass, and grass with trees. Based on the measurement data, it was found that grass and trees absorb high frequency sound well and a ground factor of 1 may be used for 500Hz and up when using ISO 9613-2 methodology. However, at lower frequencies (125 Hz octave band and below), grassy ground reflects sound the same as concrete surfaces. Trees absorb more low frequency sound than grass, but less than ISO 9613-2 suggested.

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