Viscous Flow Effects of Passing Ships in Ports

2011 ◽  
Author(s):  
Tim Bunnik ◽  
Serge Toxopeus
Keyword(s):  
Traditional Method ◽  
Diffraction Method ◽  
Potential Method ◽  
Linear Potential ◽  
Improved Method ◽  
Viscous Effects ◽  
Flow Disturbance ◽  
Flow Effects ◽  
Diffraction Effects ◽  
Straight Ahead

This paper presents a method to compute the effect of passing ships on moored ships. The method is in principle based on the method originally developed by Pinkster. He developed a method to quantify these effects based on linear potential flow. The disturbance of the passing vessel on the port geometry and moored ship is analyzed using a double-body flow. The reflection of this disturbance on the geometry of port and moored ship is analyzed using a linear diffraction method. This method has shown to give good results for ships sailing straight ahead, but is expected to be less accurate for passing ships sailing under a drift angle, in which case the viscous wake related to the lift force on the vessel becomes more dominant. Therefore, the method by Pinkster is extended with viscous effects. The disturbance caused by the passing ship on the moored ship and port geometry is computed by a RANS method instead of a potential method (double-body flow). The diffraction effects due to the presence of the moored ship and port geometry is accounted for in the same way as Pinkster did by means of a linear diffraction analysis. A comparison is made with model tests for a ship passing a moored ship along a quay at various drift angles. Results are shown for the traditional method (double-body flow disturbance) and for the considerably improved method (RANS disturbance).

Improved Method Based on Fluid Mechanics Analysis for Buoy Gauge Design and Experimental Research

2012 ◽  
Vol 163 ◽  
pp. 133-137
Author(s):  
Ao Yu Chen ◽  
Xu Dong Pan ◽  
Guang Lin Wang
Keyword(s):  
Fluid Mechanics ◽  
Experimental Research ◽  
Traditional Method ◽  
New Method ◽  
Improved Method ◽  
Advanced Method ◽  
Inner Surface ◽  
Mechanics Analysis ◽  
Linear Property

Traditional method of buoy gauge design is rather complicated, so an advanced method by building and solving fluid mechanics equations is proposed in this paper. The curve of the taper pipe inner surface is calculated, according to different buoy gravity and diameter. In order to examine the effect of this improved method, an experiment is carried out. Results show that linear property of the buoy gauge improved by new method is excellent.

Improved Wavelet Threshold Denoising Method

2014 ◽  
Vol 602-605 ◽  
pp. 3177-3180
Author(s):  
Wei Ping Cui ◽  
Li Juan Du
Keyword(s):  
Traditional Method ◽  
Wavelet Denoising ◽  
Threshold Function ◽  
Signal Denoising ◽  
Improved Method ◽  
Denoising Method ◽  
Comparison And Analysis ◽  
Selection Of

In this paper, through comparison and analysis of various wavelet denoising methods, a new threshold function is constructed, and the selection of threshold is improved. Signal denoising simulation is made by the software MATLAB, the results show that the improved method is superior to the traditional method, and obtain a better denoising effect.

An Improved Method to Extract Crystalline Cellulose from Alternatives Sources

2017 ◽  
Vol 371 ◽  
pp. 128-130
Author(s):  
M. Sánchez ◽  
Mauro Cesar Terence ◽  
Juan Alfredo Guevara Carrió
Keyword(s):  
Diffraction Method ◽  
Crystallinity Index ◽  
Crystalline Cellulose ◽  
Cellulose Crystallinity ◽  
Improved Method ◽  
X Ray Diffraction ◽  
Waste Wood ◽  
X Ray ◽  
Alternative Sources ◽  
High Cellulose

Crystalline cellulose can be obtained from alternative sources like waste wood by hydrolysis with hydrochloric or sulfuric acid. In this study we report a process for producing crystals with high cellulose crystallinity index of approximately 82%. We chose to work with eucalyptus FSC certified as a way to ensure the reproducibility of experiments. Said wood samples were subjected to acid hydrolysis with nitric acid. The resulting mass was dried out and measured by the X-ray diffraction method.

Wave–current effects on large offshore structures

1989 ◽  
Vol 16 (4) ◽  
pp. 543-551 ◽  
Author(s):  
Michael Isaacson ◽  
John Baldwin
Keyword(s):  
Potential Flow ◽  
Offshore Structures ◽  
Wave Forces ◽  
Ocean Engineering ◽  
Viscous Effects ◽  
Offshore Structure ◽  
Time Stepping ◽  
Waves And Currents ◽  
Flow Effects ◽  
Interaction Problem

The various effects that influence loads acting on a large offshore structure due to the combination of waves and currents are reviewed. These may be broadly associated with potential flow effects and viscous effects. The potential flow effects are nonlinear and may generally be investigated by perturbation or time-stepping methods. Viscous effects include the onset of flow separation, which affects the validity of the assumed potential flow, as well as steady and oscillatory forces. The fluid mechanics of the complete wave–current–structure interaction problem are not yet well understood and areas in need of additional research are identified. Key words: currents, drag, drift forces, hydrodynamics, ocean engineering, offshore structures, waves, wave forces.

A Study of Ecological Water Use Based on the Improved Tennant Method

2010 ◽  
Vol 113-116 ◽  
pp. 1504-1508 ◽  
Author(s):  
Jing Huan Tian ◽  
Ling Yu ◽  
Zhi Hong Zheng
Keyword(s):  
Water Use ◽  
Traditional Method ◽  
Extreme Values ◽  
Mean Value ◽  
Improved Method ◽  
Existing Problems ◽  
Runoff Series ◽  
Tennant Method ◽  
The Mean ◽  
The Impact

To solve the existing problems arose in the Tennant method for estimating ecological water use in river course, a new methodology is proposed to replace the mean value by the median of runoff series in the Tenna nt formula. The motive is to eliminate the impact of some extreme values. Given runoff series of 47 years in Jiaokou reservoir of Zhangxi River, the traditional and the improved method were respectively applied to calculate the ecological water consumption in the river. The results show that the improved Tennant method is more reasonably than the traditional method.

An Improved Method of Short Text Feature Extraction Based on Words Co-Occurrence

2014 ◽  
Vol 519-520 ◽  
pp. 842-845 ◽  
Author(s):  
Li Hong Wang
Keyword(s):  
Feature Extraction ◽  
Chinese Text ◽  
Traditional Method ◽  
Low Frequency ◽  
Text Clustering ◽  
Improved Method ◽  
Short Text ◽  
Text Feature ◽  
Short Text Clustering

In Chinese text clustering, short text is very different from traditional long text, principally in the low frequency of words. As a result, traditional text feature extraction and the method for weight calculating is not directly suitable for short text clustering .To solve the problem of clustering drift in short text segments ,this paper proposes an method for feature extraction through improving the method of weight calculating based on words co-occurrence. Experiments show the method can get better performance in Chinese short-text clustering compared with the traditional method TF-IDF.

Numerical Study on Sea Keeping Performances of Ship by Exact Linear 3-D Potential Method

2007 ◽  
Author(s):  
N. M. Golam Zakaria ◽  
M. S. Baree
Keyword(s):  
Frequency Domain ◽  
Wave Height ◽  
Time Domain ◽  
Domain Analysis ◽  
Potential Method ◽  
Frequency Domain Analysis ◽  
Numerical Calculations ◽  
Irregular Waves ◽  
Linear Potential ◽  
Time Domain Simulation

This paper deals with the numerical calculations of sea-keeping performances of ship in irregular sea condition. Here linear potential theory has been applied for describing the fluid motion and 3-D sink-source technique has been used to determine hydrodynamic forces for surface ship advancing in waves at constant forward speed. Numerical coding based on 3-D potential method has been tested in an extensive manner keeping an eye with the criteria recommended by various ITTC committees [1]. The numerical accuracy of the coding has been examined using some experiment results as well as some other contemporary numerical calculations given by some authors for the case of frequency domain analysis. Taking a typical Panamax Container Vessel and in order to simulate its sea-keeping performances in real sea condition, the frequency domain analysis has been performed. The result is then used for time domain simulation in short crested irregular waves. Unequal frequency spacing has been taken into account to get longer simulation time and also empirical nonlinear roll damping has been taken in the way of time domain simulation. From this time domain simulation, relative wave height has been calculated which could sometimes damage deck equipment as well as posing a risks to personnel in severe sea condition. The effect of speed & wave direction on relative wave height has been considered and finally the numerical results of the maximum and significant values of irregular relative wave heights for these conditions are discussed.

scholarly journals An Improved Method for Pan-Tropical Above-Ground Biomass and Canopy Height Retrieval Using CYGNSS

2021 ◽  
Vol 13 (13) ◽  
pp. 2491
Author(s):  
Fade Chen ◽  
Fei Guo ◽  
Lilong Liu ◽  
Yang Nan
Keyword(s):  
Soil Moisture ◽  
Correlation Coefficient ◽  
Traditional Method ◽  
Satellite System ◽  
Canopy Height ◽  
Above Ground Biomass ◽  
Improved Method ◽  
Ground Biomass ◽  
Artificial Neural Network Ann ◽  
Global Navigation Satellite

An improved method for retrieving Above-ground Biomass (AGB) and Canopy Height (CH) based on an observable from Cyclone Global Navigation Satellite System (CYGNSS), soil moisture from Soil Moisture Active Passive (SMAP) and location is proposed. The observable derived from CYGNSS is more sensitive to vegetation. The CYGNSS observable, soil moisture and the location are used as the input features of an Artificial Neural Network (ANN) to retrieve AGB and CH. The sensitivity analysis of the CYGNSS observable to target parameters shows that the proposed observable is more sensitive to AGB/CH than the conventional observable. The AGB/CH retrievals of the improved method show that it has better performance than that of the traditional method, especially in the areas with AGB in the range of 0 to100 Mg/ha and CH in the range of 0 to10 m. For AGB retrievals, the root mean square error (RMSE) and correlation coefficient are 64.84 Mg/ha and 0.80 in the range of 0 to 550 Mg/ha. Compared with the traditional method, the RMSE is decreased by 11.63%, while the correlation coefficient is increased by 5.26%. For CH retrievals, the RMSE and correlation coefficient are 5.97 m and 0.83 in the range of 0 to 45 m. The RMSE is decreased by 12.59%, while the correlation coefficient is increased by 5.06%. The analysis of the improved method in different areas shows that the performance of the improved method over the area with high vegetation is better than the area with low vegetation. The results obtained here further strengthens the capability of GNSS-R for global AGB/CH retrievals as well as different land cover areas.

scholarly journals Amplitude Induced Nonlinearity in Piston Mode Resonant Flow: A Fully Viscous Numerical Analysis

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Luca Bonfiglio ◽  
Stefano Brizzolara
Keyword(s):  
Free Surface ◽  
Vortex Shedding ◽  
Potential Flow ◽  
Stokes Equations ◽  
Body Wave ◽  
Oscillation Amplitude ◽  
Computational Technique ◽  
Linear Potential ◽  
Viscous Effects ◽  
Piston Mode

Near field flow characteristics around catamarans close to resonant conditions involve violent viscous flow such as energetic vortex shedding and steep wave making. This paper presents a systematic and comprehensive numerical investigation of these phenomena at various oscillating frequencies and separation distances of twin sections. The numerical model is based on the solution of Navier–Stokes equations assuming laminar-flow conditions with a volume of fluid (VOF) approach which has proven to be particularly effective in predicting strongly nonlinear radiated waves which directly affect the magnitude of the hydrodynamic forces around resonant frequencies. Considered nonlinear effects include wave breaking, vortex shedding and wave-body wave-wave interactions. The method is first validated using available experiments on twin circular sections: the agreement in a very wide frequency range is improved over traditional linear potential flow based solutions. Particular attention is given to the prediction of added mass and damping coefficients at resonant conditions where linear potential flow methods fail, if empirical viscous corrections are not included. The results of the systematic investigation show for the first time how the so-called piston-mode motion characteristics are nonlinearly dependent on the gap width and motion amplitude. At low oscillation amplitudes, flow velocity reduces and so does the energy lost for viscous effects. On the other hand for higher oscillation amplitude, the internal free surface breaks dissipating energy hence reducing the piston mode amplitude. These effects cannot be numerically demonstrated without a computational technique able to capture free surface nonlinearity and viscous effects.

Nonlinear Vibrations of Woven Dacron Aortic Prostheses Conveying Pulsatile Flow

2017 ◽  
Author(s):  
Eleonora Tubaldi ◽  
Marco Amabili ◽  
Michael P. Païdoussis
Keyword(s):  
Pulsatile Flow ◽  
Structural Model ◽  
Stokes Equations ◽  
Orthotropic Shell ◽  
Linear Potential ◽  
Viscous Effects ◽  
Lagrange Equations ◽  
Response Curves ◽  
Flowing Fluid ◽  
Modal Damping

Woven Dacron grafts represent standard implants for replacements of the thoracic aorta in current medical practice. Wide knowledge about the distinctly different mechanical properties of the Dacron implants with respect to the native aorta is available in literature while very little is known about the dynamic behavior of these prostheses. This study addresses the dynamic response to pulsatile physiological blood flow and pressure of woven Dacron grafts currently used in thoracic aortic replacements. The structural model assumes a cylindrical orthotropic shell described by means of the nonlinear Novozhilov shell theory. Residual stresses because of pulsatile physiological pressurization are evaluated and included in the model. The pulsatile flowing fluid is formulated using a hybrid model that contains the unsteady effects obtained from linear potential flow theory and the viscous effects obtained from the unsteady time-averaged Navier–Stokes equations. Physiological waveforms of blood pressure and velocity are approximated with the first eight harmonics of the corresponding Fourier series. Coupled fluid-structure Lagrange equations for a non-material volume with wave propagation in case of pulsatile flow are utilized. Frequency-response curves in the physiological range show the geometrically nonlinear vibration response to pulsatile flow with several superharmonic resonance peaks in the high physiological frequency range. Different values of modal damping are considered; in the limit case of low modal damping values, flow-induced asymmetric vibration of the aortic prosthesis is possible. Finally, in order to reproduce the weave design of the woven Dacron fabrics, geometric imperfections are introduced in the structural model. The numerical natural frequencies of the pressurized prosthesis are compared with the experimental results obtained from the modal analysis of a woven Dacron graft.

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