Bragg Scattering of Surface Gravity Waves Due to Multiple Bottom Undulations and a Semi-Infinite Floating Flexible Structure

Surface gravity wave interaction with a semi-infinite floating elastic plate in the presence of multiple undulations has been studied under the assumption of linearized water wave theory and small amplitude structural response. The elastic plate is modeled using the Euler-Bernoulli beam equation, whilst the multiple undulations are categorized as an array of submerged trenches or breakwaters. The numerical solution obtained in finite water depth using the boundary element method is validated with the semi-analytic solution obtained under shallow water approximation. Bragg resonance occurs due to the scattering of surface waves by an array of trenches or breakwaters irrespective of the presence of the floating semi-infinite plate. The zero-minima in wave reflection occur when the width of the trench and breakwater is an integer multiple of 0.6 and 0.35 times wavelength, respectively, as the number of trenches or breakwaters increases. In contrast to trenches and breakwaters in isolation, non-zero minima in wave reflection occur in the presence of a semi-infinite plate. Moreover, the number of complete cycles in trenches is less than the number of complete cycles in breakwaters, irrespective of the presence of the floating structure. The frequency of occurrence of zero minimum in wave reflection is reduced in the presence of the semi-infinite plate, and wave reflection increases with an increase in rigidity of the floating plate. Time-dependent simulation of free surface displacement and plate deflection due to multiple undulations of seabed in the presence of the semi-infinite floating plate is demonstrated in different cases.

Equilibrium and oscillations of liquid fuel free surface in coaxial-cylindrical vessels under microgravity conditions

In the absence of significant mass forces, the behavior of liquid fuel under microgravity conditions is determined by surface tension forces, which are intermolecular forces at the interface of two phases. The paper posed and solved the problem of equilibrium and small oscillations of an ideal liquid under microgravity conditions, and also quantified the influence of various parameters: the contact angle α0, the Bond number, the ratio of the radii of the inner and outer walls of the vessel and the depth of the liquid. For the coaxial-cylindrical vessels, there were obtained expressions in the form of a Bessel series for the potential of the fluid velocities and the free surface displacement field. The study relies on the analytical and experimental data available in the literature and proves the reliability of the developed numerical algorithm. Findings of research show that for and r, with the physical state of the wetted surface being unchanged, the shape of the free surface tends to be flat and the contact angle has little effect on the intrinsic vibration frequency of the free surface of the liquid. The results obtained can be used to solve problems of determining the hydrodynamic characteristics of the movement of liquid fuel in outer space.

Performance Assessment of Three Turbulence Models Validated through an Experimental Wave Flume under Different Scenarios of Wave Generation

This study aimed to adjust the turbulence models to the real behavior of the numerical wave flume (NWF) and the future research that will be carried out on it, according to the turbulence model that best adjusts to each particular case study. The k-ε, k-ω and large-eddy simulation (LES) models, using the volume of fluid (VOF) method, were analyzed and compared respectively. The wavemaker theory was followed to faithfully reproduce the waves, which were measured in an experimental wave flume (EWF) and compared with the theory to validate each turbulence model. Besides, reflection was measured with the Mansard and Funke method, which has shown promising results when studying one of the most critical turbulent behaviors in the wave flume, called the breaking of the waves. The free surface displacement obtained with each turbulence model was compared with the recorded signals located at three points of the experimental wave flume, in the time domain of each run, respectively. Finally, the calculated reflection coefficients and the amplitudes of the reflected waves were compared, aiming to have a better understanding of the wave reflection process at the extinction zone. The research showed good agreement between all the experimental signals and the numerical outcomes for all the turbulence models analyzed.

Simulation of Partially Filled Liquid in a Moving Tank

Numerical simulations have been carried out on a rectangular tank filled partially with liquid using volume of fluid technique. The tank has been given to and fro motion in one direction. Numerical simulation has been carried for a two dimensional case having laminar and unsteady flow. The changes in free surface displacement and dynamic pressure at different times has been observed using ANSYS software. The study was conducted for two sec. It was observed that free surface displacement of fluid increases with velocity. Also, with an increase in volume of liquid the sloshing effect decreases.

Accelerated wind conditions: spectral shape evolution and turbulent kinetic energy dissipation from laboratory and field measurements

<div> <div> <div> <p>A determined shape of the energy wave spectrum can be estimated from a given fetch and wind speed. Also, several studies have characterized the balance of the turbulent kinetic energy under the effect of waves and currents under constant wind conditions. However, deeper research is needed in order to characterize the wind-wave generation processes under non-stationary wind conditions. In this way, to be able to determine the uncertainty on not considering accelerated wind events in the air-sea momentum exchange estimations.</p> <p>Periods of accelerated winds were analyzed from experimental and field data. On one hand, several laboratory experiments were carried out in a large wind-wave facility at the Institut Pytheas (Marseille-France). Momentum fluxes were estimated from hot wire anemometry and, the free surface displacement was measured along the wave tank by resistance and capacitance wire probes. Also, the surface drift current was measured from a profiling acoustic velocimeter. During these experiments, the wind speed goes from 2 m/s to reach the maximum wind speed of 13 m/s. A constant wind acceleration characterizes each test. On the other hand, the field data were obtained from an Oceanographic and Marine Meteorology Buoy (BOMM) located in the Gulf of Mexico, from July 2018 to February 2019. The BOMM was equipped with a sonic anemometer, capacitance wires, and an inertial motion unit. Both sets of data are characterized by a high sampling rate that allows us to directly estimate the wind stress over the sea surface. Also, provide us with useful information about the evolution of the wave spectra and enable us to determine the dissipation rate of turbulent kinetic energy. It was observed that the wind acceleration has a direct effect on the momentum transfer efficiency from the wind to the wave field and that the momentum transfer is reduced as wind acceleration increases.</p> </div> </div> </div>

Modelling behaviour of a partially loaded road tanker with agro-food liquids during the breaking manoeuver

Longitudinal and lateral liquid sloshing in a partially filled tanker affect the braking performance of the tankers. The movement during braking of the liquid load is determined by the change in the position of the centre of gravity of the load inside the vehicle. Becoming an undesirable phenomenon when analyzing the performance of the vehicle braking manoeuver. In this paper modelling of the behaviour of the cross-section circular tank with baffles, partially filled with liquid agro-food products, was performed, which performs a braking manoeuver. Two different fluids have been used to simulate the sloshing effect of agro-food liquid cargo and study the behaviour of the tank. In to order generate the geometric model of the tank was done by using SolidWorks, and simulating the behaviour of the tank and cargo with agro-food products during the ANSYS-CFX braking manoeuver. A sequence of numerical experiments has been carried out to estimate the pressure developed over the tanker wall and the free surface displacement of the fluids for different fill levels. Simulations with the two liquids and the results obtained were compared to be able to analyze the behaviour of the tank partially filled into a braking manoeuver.

Experimental Tests of a 1:16th-Scale Model of the Spar-Buoy OWC in a Large Scale Wave Flume in Regular Waves

This paper presents the experimental tests of a 16th-scale model of the Spar-buoy oscillating water column (OWC) carried out at a large scale wave flume. The model is slack-moored to the flume floor by two mooring lines. The turbine effect is replicated using calibrated orifice plates. The device six degree-of-freedom motion, inner free surface displacement and air chamber pressure are measured. The influence of wave height, turbine damping and mass distribution on the system dynamics is analysed for regular waves. An in-house developed numerical time-domain model is used to simulate the motion and power absorption under the same wave conditions as the physical model tests. The formulation considers linear hydrodynamic forces, viscous drag effects and drift forces. The floater is assumed to oscillate in six degrees of freedom and the OWC can move vertically in the tube. The mooring system is simulated using a quasi-static model. The comparison between experiments and numerical simulations shows a good agreement for wave periods outside the zone where parametric resonance in roll and pitch occurs.

Comparison of Distributions of Wave Heights From Nonlinear Schröedinger Equation Simulations and Laboratory Experiments

Numerical simulations of the nonlinear Schrödinger (NLS) equation are performed by imposing randomly synthesized free surface displacement at the wave maker characterized by the Joint North Sea Wave Project (JONSWAP) spectrum and compared with four different sea states generated in the deepwater wave basin of Marintek. The comparisons show that the numerical simulations have a high degree of agreement with the laboratory experiments although a little overestimation can be observed, especially in the severe sea state. Thus, the simulations still catch the main characteristics of extreme waves and provide an important physical insight into their generation. The coefficient of kurtosis λ40 presents a similar spatial evolution trend with the abnormal wave density, and the nonlinear Gram–Charlier (GC) model is used to predict the wave height distribution. It is demonstrated again that the theoretical approximation based on the GC expansion can describe large wave heights reasonably well in most cases. However, if the sea state is severe, wave breaking can significantly decrease the actual tail of wave height distribution, and discrepancy occurs when comparing with the numerical simulation. Moreover, the number of waves also plays an important role on the prediction of extreme wave height.

How cavity dimension influences in the composite deformation during polymerization shrinkage

PURPOSE: To understand how the dimensions of the cavity made of a rigid substrate influences on displacement of the composite free surface during polymerization shrinkage. MATERIAL AND METHODS: Cylindrical cavities in 4 or 6mm diameter and 1 or 2mm depth were prepared in glass rods. These cavities were restored in bulk (Single Bond + Filtek Z250). Free surface displacement was monitored for 10 minutes with a probe. The data was analyzed 60 seconds and 10 minutes after photo-activation. Results were analyzed using two-way ANOVA/Tukey’s test to evaluate the influence of diameter and depth, and Student’s t-test to compare the periods (α=0.05). RESULTS: The interaction between the factors diameter and depth was statistically significant (p<0.05 for both periods), but Tukey’s test did not revealed this interaction. For the same diameter the higher the cavity depth, the higher was the displacement. Student’s t-test showed that the displacement was significant higher at 10 minutes than at 60 seconds (p<0.05), even though this difference was not so evident numerically. It was not possible to determine any strong correlation with volume neither with C-factor. CONCLUSIONS: The displacement of free surface represents the stress state to which the composite is subjected. The variation in depth of the cavity seems to be a further factor that influences the displacement of free surface, more than variation in diameter.