scholarly journals On a Three-Dimensional Nonlinear Model of Pacific Equatorial Ocean Dynamics: Velocities and Flow Paths

Oceanography ◽  
2018 ◽  
Vol 31 (3) ◽  
pp. 51-58 ◽  
Author(s):  
Biswajit Basu ◽  
2017 ◽  
Vol 21 (11) ◽  
pp. 5503-5515 ◽  
Author(s):  
Hiroyuki Hirashima ◽  
Francesco Avanzi ◽  
Satoru Yamaguchi

Abstract. The heterogeneous movement of liquid water through the snowpack during precipitation and snowmelt leads to complex liquid water distributions that are important for avalanche and runoff forecasting. We reproduced the formation of capillary barriers and the development of preferential flow through snow using a three-dimensional water transport model, which was then validated using laboratory experiments of liquid water infiltration into layered, initially dry snow. Three-dimensional simulations assumed the same column shape and size, grain size, snow density, and water input rate as the laboratory experiments. Model evaluation focused on the timing of water movement, thickness of the upper layer affected by ponding, water content profiles and wet snow fraction. Simulation results showed that the model reconstructs relevant features of capillary barriers, including ponding in the upper layer, preferential infiltration far from the interface, and the timing of liquid water arrival at the snow base. In contrast, the area of preferential flow paths was usually underestimated and consequently the averaged water content in areas characterized by preferential flow paths was also underestimated. Improving the representation of preferential infiltration into initially dry snow is necessary to reproduce the transition from a dry-snow-dominant condition to a wet-snow-dominant one, especially in long-period simulations.


2012 ◽  
Vol 9 (5) ◽  
pp. 2885-2914 ◽  
Author(s):  
A. Soloviev ◽  
C. Maingot ◽  
S. Matt ◽  
R. E. Dodge ◽  
S. Lehner ◽  
...  

Abstract. This work is aimed at identifying the origin of fine-scale features on the sea surface in synthetic aperture radar (SAR) imagery with the help of in-situ measurements as well as numerical models (presented in a companion paper). We are interested in natural and artificial features starting from the horizontal scale of the upper ocean mixed layer, around 30–50 m. These features are often associated with three-dimensional upper ocean dynamics. We have conducted a number of studies involving in-situ observations in the Straits of Florida during SAR satellite overpass. The data include examples of sharp frontal interfaces, wakes of surface ships, internal wave signatures, as well as slicks of artificial and natural origin. Atmospheric processes, such as squall lines and rain cells, produced prominent signatures on the sea surface. This data has allowed us to test an approach for distinguishing between natural and artificial features and atmospheric influences in SAR images that is based on a co-polarized phase difference filter.


Author(s):  
Ihor Palkov ◽  
Sergii Palkov ◽  
Oleh Ishchenko ◽  
Olena Avdieieva

The paper considers the main principles that are used to develop the flow paths (FP) of the high-pressure cylinders (HPC), intermediate-pressure cylinders (IPC), and low-pressure cylinders (LPC) for the K-1250-6.9/25 turbine unit. It describes approaches to the numerical experiment when designing flow paths, the advantage of which is lower labor, time and financial costs and higher informativeness compared to the physical experiment on flow paths. When designing the flow paths of high- and intermediate-pressure cylinders (HIPC), the numerical experiment is performed using the three-dimensional viscous-flow method. For this purpose, a three-dimensional model of the blade system in the flow path is built, which consists of a large number of finite volumes (elements) in the shape of hexagons, in each of which the integration of the equations of gas dynamics is performed. When developing LPC, the method of parameterization and analytical profiling of the blade crown sections is used, where the profiles are described by the curves of the fourth and fifth orders with the condition of providing the minimum value of the maximum curvature and monotonicity of variation of the three-dimensional blade geometry along height. This method allows obtaining the optimal profiles of the cross sections of the blades, which correspond to the current flow lines to the fullest extent, and minimizing the profile energy losses when the flow flows around the blades.


2021 ◽  
Vol 67 (4 Jul-Aug) ◽  
Author(s):  
Davide Fiscaletti

A nonlinear model of Brownian motion is developed in a three-dimensional quantum vacuum defined by a variable quantum vacuum energy density corresponding to processes of creation/annihilation of virtual particles. In this model, the polarization of the quantum vacuum determined by a perturbative fluctuation of the quantum vacuum energy density associated with a fluctuating viscosity, which mimics the action of dark matter, emerges as the fundamental entity which generates the Brownian motion.


2018 ◽  
Vol 75 (7) ◽  
pp. 2157-2174 ◽  
Author(s):  
Konstantinos Menelaou ◽  
M. K. Yau ◽  
Tsz-Kin Lai

Abstract It is known that concentric eyewalls can influence tropical cyclone (TC) intensity. However, they can also influence TC track. Observations indicate that TCs with concentric eyewalls are often accompanied by wobbling of the inner eyewall, a motion that gives rise to cycloidal tracks. Currently, there is no general consensus of what might constitute the dominant triggering mechanism of these wobbles. In this paper we revisit the fundamentals. The control case constitutes a TC with symmetric concentric eyewalls embedded in a quiescent environment. Two sets of experiments are conducted: one using a two-dimensional nondivergent nonlinear model and the other using a three-dimensional nonlinear model. It is found that when the system is two-dimensional, no wobbling of the inner eyewall is triggered. On the other hand, when the third dimension is introduced, an amplifying wobble is evident. This result contradicts the previous suggestion that wobbles occur only in asymmetric concentric eyewalls. It also contradicts the suggestion that environmental wind shear can be the main trigger. Examination of the dynamics along with complementary linear eigenmode analysis revealed the triggering mechanism to be the excitation of a three-dimensional exponentially growing azimuthal wavenumber-1 instability. This instability is induced by the coupling of two baroclinic vortex Rossby waves across the moat region. Additional sensitivity analyses involving reasonable modifications to vortex shape parameters, perturbation vertical length scale, and Rossby number reveal that this instability can be systematically the most excited. The growth rates are shown to peak for perturbations characterized by realistic vertical length scales, suggesting that this mechanism can be potentially relevant to actual TCs.


Author(s):  
M. Pau ◽  
F. Cambuli ◽  
N. Mandas

Three dimensional steady multistage calculations, using mixing plane approach, are presented for two different blade geometries in a two stage axial test turbine with shrouded blades. A 3D multiblock Navier-Stokes finite volume solver (TBLOCK) has been used in all the simulations. In order to study shroud leakage flow effects the whole shroud cavity geometry has been modeled, overcoming most of the limitations of simple shroud leakage model in calculating fluid flow over complex geometries. Numerical investigations are mainly focused on assessing the ability of the solver to be used as multistage design tool for modeling leakage-mainstream flow interaction. Several calculations are compared. The first computes the main blade flow path with no modeling of the shroud cavities. The second includes the modeling of the shroud cavities for a zero leakage mass flow rate. Finally a multiblock calculation which models all the leakage flow paths and shroud cavities has been carried out for two different levels of shroud seal clearance. It is found that neglecting shroud leakage significantly alters the computed velocity profiles and loss distributions, for both the computed blade geometries. A numerically predicted shroud leakage offset loss is presented for the two considered blade geometries, focusing on the relative importance of the leakage flow, re-entry mixing losses, and inlet and exit shroud cavity effect. Results demonstrates that full calculation of leakage flow paths and cavities is required to obtain reliable results, indicating the different effects of the leakage-to-mainstream flow interaction on the blade geometries computed. Despite a slight increase in the computational time, multiblock approach in handling leakage flow problem can now-days be used as a practical tool in the blade design process and routine shroud leakage calculations.


2018 ◽  
Vol 245 ◽  
pp. 04004 ◽  
Author(s):  
Aleksandr Drozdov ◽  
Alexey Rekstin

Preliminary design is an important stape in the development of centrifugal compressors and compressor stages. Basically for this purpose, various recommendations on the choice of the flow path dimensions are applied. Researchers of the Research and Development Laboratory “Gas dynamics of turbomachines” prof. Yu.B. Galerkin and A.F. Rekstin analyzed and summarized the dimensions of flow paths of 124 impellers. On the basis of this analysis, formulas were proposed for choosing the flow path dimensions of the centrifugal compressor stages, which were included in the preliminary design program. The formulas used are designed for relative Mach number of 0.7 and isentropic coefficient of 1.4. The correct application of these formulas for other Mach numbers and isentropic coefficient required development of an appropriate approach and algorithm for adjusting the height of the impeller blades at the outlet. Calculations of gas-dynamic characteristics using the Universal Modeling Method showed the need for selecting a coefficient that takes into account the influence of viscosity to obtain the required pressure characteristics of the compressor stage. This problem was also solved in the program of preliminary design. To check the quality of preliminary design, the results were verified using a non-viscous quasi-three-dimensional calculation program. Three stages were designed for parameters different to those used for development of preliminary design formulas. Analysis of the velocity diagrams of the impeller blades and distribution of meridional velocities showed good results of the preliminary design.


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