scholarly journals WAVE-CURRENT INTERACTION OVER SEABEDS WITH DIFFERENT ROUGHNESS: A STATISTICAL ANALYSIS

2017 ◽  
pp. 16
Author(s):  
Carla Faraci ◽  
Pietro Scandura ◽  
Enrico Foti
Keyword(s):  
Gaussian Distribution ◽  
Current Velocity ◽  
Mass Conservation ◽  
Distribution Functions ◽  
Wave Velocities ◽  
Velocity Statistics ◽  
Steady Current ◽  
Wave Effects ◽  
Current Interaction ◽  
Rippled Bed

Wave-current flow over seabeds covered with different roughness has been studied in order to deepen the knowledge on the statistical properties of the near-bed velocity. The results of three different experimental campaigns performed in the presence of a sandy bed, a gravel bed and a rippled bed, carried out superimposing a steady current onto an orthogonal wave, have been analysed. The statistics of the current velocity, including the wave effects on the steady current have been investigated. It has been observed that in the absence of waves, the fluctuations of the near-bed velocities closely follow a Gaussian distribution. When waves are also present, in order to obtain consistent near-bed velocity statistics, it is necessary to decouple the velocity events in the current direction by taking into account the sign of the wave velocities. In the latter case, the nature of the distribution functions is influenced by the mass conservation principle. A Gaussian distribution well describes the turbulent fluctuations obtained by removing the phase averaged velocity from the current velocity.

A Semi Submersible in Combined Extreme Waves and Current: Comparison of Model Tests and Existing Software

2007 ◽  
Author(s):  
Anne Katrine Bratland ◽  
Sverre Haver ◽  
Carl Trygve Stansberg ◽  
Fuwei Zhang ◽  
Joachim Allers ◽  
...  
Keyword(s):  
Production Systems ◽  
Dynamic Loads ◽  
Test Results ◽  
Sea Waves ◽  
Extreme Waves ◽  
Calculation Methods ◽  
Steady Current ◽  
Current Interaction ◽  
Extreme North ◽  
Mean Current

Floating production systems are often exposed to combined waves and current. Normally, the effects from a steady current are neglected in the calculation methods for dynamic loads and motions. In some parts of the world the current velocities can be so large that neglecting wave-current interaction effects is questionable. Computer programs that handle wave-current interaction have been available for decades. However, so far very little results have been documented which validate the theories. Model test results for a semi submersible in extreme North Sea waves are presented, with and without current. The comparison with wave-current interaction computer models shows that the effect is generally over-estimated for the present case with a mean current velocity equal to 1.3 m/sec.

Comparative Study of Probability Distribution Functions of Wind Power Variation

2014 ◽  
Vol 953-954 ◽  
pp. 414-418
Author(s):  
An Jue Dai ◽  
Qian Wang ◽  
Yan Nan Zhou
Keyword(s):  
Distribution Function ◽  
Probability Distribution ◽  
Wind Power ◽  
Gaussian Distribution ◽  
Gaussian Mixture ◽  
Second Order ◽  
Distribution Functions ◽  
Normal Distribution Function ◽  
One Dimensional ◽  
Power Variation

This work focuses on the probability distribution function of wind power variation. After analyzing the characters of the power fluctuation data, normal distribution function, t location-scale distribution function and mixed second-order one-dimensional Gaussian distribution function are chosen to describe the wind power variation. Then K-S test(Kolmogorov-Smirnov) test and Pearson product-moment correlation coefficient are used to evaluate the fitting effect of the three distribution functions respectively, which indicates that the mixed second-order one-dimensional Gaussian distribution is the most appropriate one. At last, the factors affecting the parameters of Gaussian mixture distribution and to what degree they can achieve are investigated.

Wind and wave effects on surface currents in the Mediterranean Sea

2020 ◽  
Author(s):  
Verónica Morales Márquez ◽  
Ismael Hernández Carrasco ◽  
Vincent Rossi ◽  
Alejandro Orfila
Keyword(s):  
Mediterranean Sea ◽  
Current Velocity ◽  
Wave Interaction ◽  
Surface Currents ◽  
Mixing Properties ◽  
Wave Effects ◽  
The Mediterranean ◽  
Transport And Mixing ◽  
Lagrangian Motion ◽  
Transported Material

<p>The knowledge of Lagrangian motion is of a great importance due to their impact on the properties of transported material like the Essential Ocean Variables (phytoplankton, temperature, pCO2, etc), or other material like plastics debris, oil spill pollution, etc. In this study we analyze the influence of the wind and waves in the transport and mixing properties at the upper layers of the Mediterranean Sea. In this context, we propose a new approach for current velocity where we take into account the wind-wave interaction and the variability that it inserts into the current velocity through Ekman and Stokes components.</p><p><br>Surface currents, Ekman, Stokes, Lyapunov exponent</p>

Numerical Investigation of Collision-Induced Breakup of Raindrops. Part II: Parameterizations of Coalescence Efficiencies and Fragment Size Distributions

2010 ◽  
Vol 67 (3) ◽  
pp. 576-588 ◽  
Author(s):  
Winfried Straub ◽  
Klaus Dieter Beheng ◽  
Axel Seifert ◽  
Jan Schlottke ◽  
Bernhard Weigand
Keyword(s):  
Fragment Size ◽  
Mass Conservation ◽  
Distribution Functions ◽  
Size Distributions ◽  
Independent State ◽  
Peak Structure ◽  
Binary Collisions ◽  
The One ◽  
Physical Quantities ◽  
Second Peak

Abstract Results of numerically investigated binary collisions of 32 drop pairs presented in Part I of this study are used to parameterize coalescence efficiencies and size distributions of breakup fragments of large raindrops. In contrast to the well-known results of Low and List, it is shown that coalescence efficiencies Ec can be described best by means of the Weber number We yielding Ec = exp(−1.15We). The fragment size distributions gained from our numerical investigations were parameterized by fitting normal, lognormal, and delta distributions and relating the parameters of the distribution functions to physical quantities relevant for the breakup event. Thus, this parameterization has formally a substantial similarity to the one of Low and List, although no reference is made to breakup modes such as filament, disk, and sheet. Additionally, mass conservation is guaranteed in the present approach. The parameterizations from Low and List, as well as the new parameterizations, are applied to compute a stationary size distribution (SSD) from solving the kinetic coagulation–breakup equation until a time-independent state is reached. Although with the parameterizations of Low and List, the SSD shows an often-reported three-peak structure, with the new parameterizations the second peak vanishes completely.

System-Based Modelling of KCS Manoeuvring in Calm Water, Current and Waves

2020 ◽  
Author(s):  
Yuting Jin ◽  
Lucas J. Yiew ◽  
Allan R. Magee ◽  
Yingying Zheng
Keyword(s):  
Water Current ◽  
Flow Solver ◽  
Wave Drift ◽  
Future State ◽  
Steady Current ◽  
Mmg Model ◽  
Calm Water ◽  
Wave Effects ◽  
Object Of Study ◽  
Water Speed

Abstract Maritime autonomous surface ships (MASS) require accurate future state projection to initiate collision-avoidance manoeuvres. Forecasts of the vessels’ trajectories and motions are fundamentally based on the mathematical manoeuvring model, which is an essential component of their hydrodynamic digital twin nowadays. Using the benchmark container ship KCS as an object of study, this paper adopts a 4-DOF modular-type manoeuvring (MMG) model to predict the vessel trajectories in calm water and under the presence of steady current and regular waves. The current effects are treated as additional ship over water speed, while the wave effects are considered by superimposing the second-order mean wave drift loads to the calm water hull hydrodynamics. The wave drift loads are solved using the potential flow solver WASIM, which is based on Rankine panel method. The computed vessel trajectories and motions are compared with available literature results and show good correlation.

Bimodal distribution of the solar wind using data from ACE spacecraft.

2020 ◽  
Author(s):  
Carlos Larrodera ◽  
Consuelo Cid
Keyword(s):  
Solar Wind ◽  
Gaussian Distribution ◽  
Bimodal Distribution ◽  
Distribution Functions ◽  
Solar Cycles ◽  
Proton Temperature ◽  
Gaussian Distribution Function ◽  
Transient Events ◽  
Solar Wind Parameters ◽  
Using Data

<p>The main goal of this work is to separate the behavior of the two types of quiet solar wind at 1 AU: fast and slow.<br>Our approach is a bi-Gaussian distribution function, formed by the addition of two Gaussian distribution functions, where each one represents one type of wind. We check our approach by fitting the bi-Gaussian to data from ACE spacecraft. We use level 2 data measured during solar cycles 23 and 24 of different solar wind parameters, including proton speed, proton temperature, density and magnetic field. Our results show that the approach is fine and only transient events departs from the proposed function. Moreover, we can show bi modal behavior of the solar wind at 1 AU, not only for the proton speed, but also for the other analyzed parameters. We also check the solar cycle dependence of the different fitting parameters.</p>

scholarly journals Analysis of Cohesive Microsized Particle Packing Structure Using History-Dependent Contact Models

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Raihan Tayeb ◽  
Xin Dou ◽  
Yijin Mao ◽  
Yuwen Zhang
Keyword(s):  
Particle Size ◽  
Coordination Number ◽  
Gaussian Distribution ◽  
Packing Density ◽  
Mean Value ◽  
Distribution Functions ◽  
Particle Packing ◽  
Size Distributions ◽  
Packing Structure ◽  
Contact Models

Granular packing structures of cohesive microsized particles with different sizes and size distributions, including monosized, uniform, and Gaussian distribution, are investigated by using two different history dependent contact models with discrete element method (DEM). The simulation is carried out in the framework of liggghts, which is a DEM simulation package extended based on branch of granular package of widely used open-source code LAMMPS. Contact force caused by translation and rotation, frictional and damping forces due to collision with other particles or container boundaries, cohesive force, van der Waals force, and gravity is considered. The radial distribution functions (RDFs), force distributions, porosities, and coordination numbers under cohesive and noncohesive conditions are reported. The results indicate that particle size and size distributions have great influences on the packing density for particle packing under cohesive effect: particles with Gaussian distribution have the lowest packing density, followed by the particles with uniform distribution; the particles with monosized distribution have the highest packing density. It is also found that cohesive effect to the system does not significantly affect the coordination number that mainly depends on the particle size and size distribution. Although the magnitude of net force distribution is different, the results for porosity, coordination number, and mean value of magnitude of net force do not vary significantly between the two contact models.

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