Numerical Simulations of Violent Free Surface by a Coupled Level-Set and Volume-of-Fluid Method

This study contributes to the development of a Coupled Level-Set and Volume- Of-Fluid (CLSVOF) method capable of capturing interface between two immiscible fluids in overset grid system. The present CLSVOF interface-capturing method is employed in conjunction with the Finite-Analytical Navier-Stokes (FANS) method for time-domain simulations of violent free surface flow problems. In this method, immiscible two-phase flow is modeled as a single continuum with variable fluid properties across the interface. The interface is captured by a level set function which is corrected to ensure mass conservation under the framework of a volume of fluid function. The interface is propagated by the evolution of the level set and volume of fluid functions in time. In addition, the conservation equations for mass and momentum are solved in the transformed domain for the dynamics of the fluid flow. Moreover, a chimera domain decomposition approach is implemented using overset grid systems, including embedding, overlapping, and matching grids for accurate resolutions of all varieties of free surface flow problems

Computational Fluid Dynamics Simulation of Green Water Around a Two-dimensional Platform

An interface-preserving level set method is incorporated into the Reynolds-Averaged Navier-Stokes (RANS) numerical method to simulate the application of the green water phenomena around a platform and the breaking wave above the deck. In the present study, this method is used to evaluate the laminar in two dimension plane with fixed orthogonal grids. In this method, it is assumed that the free surface is modeled as immiscible two-phase flow (air and water). A level set function can present the individual fluids, and the interface between two-phase is represented by the zero level set. In addition, the level set evolution equation is coupled with the conservation equations for mass and momentum, which will be solved in the transformed plane. For different purposes, there are several block domains in the application grid. Chimera domain decomposition technique is employed to handle such embedding, overlapping, or matching grids. Several simple test cases were performed to demonstrate the feasibility of this method. The comparisons between the ENO scheme and the WENO scheme will be illustrated in the Zalesak's disk case and will further prove that the WENO scheme is superior to the ENO scheme. The propagation of continuous wave case will validate some properties of wave and determine the importance of some parameters in code. Moreover, the method will be applied in simulation of green water around a two dimensional platform. By configuring different deck heights, some distinct phenomena can be represented. Lastly, it is crucial to observe the green water phenomena around the platform deck by applying the velocity-extrapolation routine

Atmospheric Stability and Gravity Wave Dissipation in the Mesopause Region

High-resolution temperature profile data collected at the Urbana Atmospheric Observatory (40ºN, 88ºW) and Starfire Optical Range, NM (35ºN, 106.5ºW) with a Na lidar are used to assess the stability of the mesopause region between 80 and 105 km. The mean diurnal and annual temperature profiles demonstrate that in the absence of gravity wave and tidal perturbations, the background atmosphere is statically stable throughout the day and year. Thin layers of instability can be generated only when the combined perturbations associated with tides and gravity waves induce large vertical shears in the horizontal wind and temperature profiles. There is a region of reduced stability below the mesopause between 80 and 90 km where the temperature lapse rate is large and the buoyancy parameter N2 is low. The vertical heat flux is maximum in this region which suggests that this is also a region of significant wave dissipation. There is also a region of enhanced stability above 95 km in the lower thermosphere where N2 is large. There appears to be little wave dissipation above 95 km because the temperature variance increases rapidly with increasing altitude in this region and the vertical heat flux is zero

Measurements of Atmospheric Stability in the Mesopause Region at Starfire Optical Range, NM

The structure and seasonal variations of static (convective) and dynamic (shear) instabilities in the mesopause region (80–105 km) are examined using high-resolution wind and temperature data obtained with a Na lidar at the Starfire Optical Range, NM. The probabilities of static and dynamic instability are sensitive functions of N2/S2, where N is the buoyancy frequency and S is the total vertical shear in the horizontal winds. The mesopause region is most stable in summer when the mesopause is low, N is large and S is small. Monthly mean N2/S2 varies from a maximum value of about 1.06 in mid-summer to a minimum of 0.68 in January. The annual mean values of N and S are, respectively, 0.021 s−1 and 23 ms−1 km−1. The probabilities of static and dynamic instabilities are maximum in mid-winter when they average about 10% and 12%, respectively, and are minimum in summer when they average about 7% and 5%, respectively. The observations are generally consistent with theoretical predictions based on Gaussian models for the temperature and wind fluctuations induced by gravity waves. They also show that statically unstable conditions are generally preceded by dynamically unstable conditions. The instability probabilities vary considerably from night to night and the structure of the unstable regions are significantly influenced by atmospheric tides. Tides alone are usually not strong enough to induce instability but they can establish the environment for instabilities to develop. As the tidal temperature perturbations propagate downward, they reduce the stability on the topside of the positive temperature perturbation. Instabilities are then induced as gravity waves propagate through this layer of reduced static stability

Mesospheric Temperature Variability and Seasonal Characteristics Over the Andes

The Utah State University CEDAR Mesospheric Temperature Mapper (MTM) is a high-quality CCD imager capable of remote sensing faint optical emissions from the night sky to determine mesospheric temperature and its variability at an altitude of ~87 km. The MTM was operated at the new Andes Lidar Observatory (ALO)located at Cerro Pachon, Chile (30.2° S, 70.7° W) since August 2009 to investigate the seasonal characteristic of the mesopause at mid-latitudes. Measurement were made alongside a powerful lidar capable of height sounding the mesosphere. In this study, the MTM data have been analyzed to determine night to night variability and seasonal characteristics in the OH mesospheric intensity and temperature induced by acoustic-gravity waves and atmospheric tides

The First Ten Months of Investigation of Gravity Waves and Temperature Variability Over the Andes

The Andes region is an excellent natural laboratory for investigating gravity wave influences on the Upper Mesospheric and Lower Thermospheric (MLT) dynamics. The instrument suite that comprised the very successful Maui-MALT program was recently re-located to a new Andes Lidar Observatory (ALO) located at Cerro Pachon, Chile to obtain in-depth seasonal measurements of MLT dynamics over the Andes mountains. As part of the instrument set the Utah State University CEDAR Mesospheric Temperature Mapper (MTM) has operated continuously since August 2009 measuring the near infrared OH(6,2) band and the O2(0,1) Atmospheric band intensity and temperature perturbations. This poster focuses on an analysis of nightly OH temperatures and the observed variability, as well as selected gravity wave events illustrating the high wave activity and its diversity