scholarly journals Comparative Study on the Hydraulic Characteristics of Nature-Like Fishways

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 955
Author(s):  
Tiegang Zheng ◽  
Zhipan Niu ◽  
Shuangke Sun ◽  
Jiayue Shi ◽  
Haitao Liu ◽  
...  
Keyword(s):  
Comparative Study ◽  
Complex Structure ◽  
Design Criterion ◽  
Migratory Fish ◽  
Hydraulic Characteristics ◽  
Mean Flow ◽  
Low Velocity ◽  
Partition Wall ◽  
Flow Information ◽  
Recirculation Area

Due to the complex structure and the multiformity of boulder arrangements, there is currently no perfect design criterion for nature-like fishways. This paper proposes four types of nature-like fishways arranged with an impermeable partition wall (IPW), a semi-permeable partition wall (SPPW) or a fully permeable partition wall (FPPW). The hydraulic characteristics of these fishways were investigated experimentally. The results show that the discharge of the fishway arranged with a FPPW was almost twice that of an IPW fishway, and the discharge of a SPPW fishway was between the two extremes. The mean flow velocity of the FPPW fishway was larger than that of the other schemes. For the fishway arranged with an IPW, the flow information was basically consistent with that of the engineered technical fishway. In the FPPW or SPPW fishway, there was more abundant flow information and no obvious recirculation zones in the fishway pool, and these conditions are suitable for migratory fish moving up- and downstream. Notably, for the fishway arranged with two fish passages, two mainstreams were formed in the pool, which divided the flow pattern of the pool into three flow regions. A weak recirculation area was formed in the low-velocity region, which facilitates swimming for migratory fish. According to this comprehensive comparative study, the SPPW fishway with two fish passages had low discharge, abundant flow information and favorable fish migration characteristics; thus, it is the optimal fishway scheme among those studied in this paper.

Numerical modeling of refraction arrivals in complex areas

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 90-98 ◽  
Author(s):  
N. R. Hill ◽  
P. C. Wuenschel
Keyword(s):  
Numerical Modeling ◽  
Plane Wave ◽  
Complex Structure ◽  
Real Data ◽  
Synthetic Seismograms ◽  
Weak Signal ◽  
Surface Complex ◽  
Low Velocity ◽  
Near Surface ◽  
Plane Wave Field

Use of refracted arrivals to delineate near‐surface complex structure can sometimes be difficult because of rapid lateral changes in the refraction event along the line of control. The interpreter must correlate over zones of interference and zones of weak signal. During correlation it is often difficult to stay on the correct cycle of the waveform. We present a method to model refracted arrivals numerically in an area where these problems occur. The computation combines plane‐wave field decomposition to calculate propagation in complex regions with a WKBJ method to calculate propagation in simple regions. To illustrate the method, we study a case where the near‐surface complex structure is caused by the presence of low‐velocity gaseous mud. The modeling produces synthetic seismograms showing the interference patterns and changes in intensity that are seen in real data. This modeling shows how correlations may be done over difficult areas, particularly where cycle skips can occur.

A Comparative Study of the Variable Screening and Hartree-Fock Models as Means for the Construction of Two-Center Correlation Diagrams

1995 ◽  
Vol 60 (2) ◽  
pp. 161-171 ◽  
Author(s):  
Jan Lörinčík ◽  
Rudolf Polák ◽  
Zdeněk Šroubek ◽  
Ivana Paidarová
Keyword(s):  
Comparative Study ◽  
Low Velocity ◽  
Variable Screening ◽  
Hartree Fock ◽  
Screening Model ◽  
Computing Correlation ◽  
Shell Vacancy

The aim of this work is to test the Variable Screening Model (VSM) [Wille U., Hippler R.: Phys. Rep. 132, 129 (1986)] as a method for computing correlation diagrams of neutral and ionized diatomic quasimolecules by comparing the results with corresponding Hartree-Fock calculations, and to elucidate the specific features of both aforementioned approaches in applications to given purpose. These calculations serve as the first step in the interpretation of inner-shell vacancy production in low-velocity ion-atom collisions inside bombarded solids.

scholarly journals GIARPS High-resolution Observations of T Tauri stars (GHOsT)

2020 ◽  
Vol 643 ◽  
pp. A32
Author(s):  
M. Gangi ◽  
B. Nisini ◽  
S. Antoniucci ◽  
T. Giannini ◽  
K. Biazzo ◽  
...  
Keyword(s):  
High Resolution ◽  
Complex Structure ◽  
Central Star ◽  
T Tauri Stars ◽  
Resolving Power ◽  
High Resolution Spectroscopy ◽  
Young Stellar Objects ◽  
Clear Correlation ◽  
Low Velocity ◽  
T Tauri

Context. Disk winds play a fundamental role in the evolution of protoplanetary systems. The complex structure and dynamics can be investigated through the emission of atomic and molecular lines detected in high-resolution optical/IR spectra of young stellar objects. Despite their great importance, however, studies connecting the atomic and molecular components are lacking so far. Aims. In the framework of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project, we aim to characterize the atomic and molecular winds in a sample of classical T Tauri stars (CTTs) of the Taurus-Auriga region, focusing on a statistical analysis of the kinematic properties of the [O I] 630 nm and H2 2.12 μm lines and their mutual relationship. Methods. We analyzed the flux calibrated [O I] 630 nm and H2 2.12 μm lines in a sample of 36 CTTs observed at the Telescopio Nazionale Galileo with the HARPS-N spectrograph (resolving power of R = 115 000) and with the GIANO spectrograph (R = 50 000). We decomposed the line profiles into different kinematic Gaussian components and focused on the most frequently detected component, the narrow low-velocity (vp < 20 km s−1) component (NLVC). Results. We found that the H2 line is detected in 17 sources (~50% detection rate), and [O I] is detected in all sources but one. The NLV components of the H2 and [O I] emission are kinematically linked, with a strong correlation between the peak velocities and the full widths at half maximum of the two lines. Assuming that the line width is dominated by Keplerian broadening, we found that the [O I] NVLC originates from a disk region between 0.05 and 20 au and that of H2 in a region from 2 and 20 au. We also found that H2 is never detected in sources where [O I] originates in regions below 1 au, as well as in sources of early (~F-G) spectral type with a luminosity >1 L⊙. Moreover, in seven sources, both H2 and [O I] have clear blueshifted peaks and prominent [O I] high-velocity components. These components have also been detected in sources with no relevant centroid shift. Finally, we did not find any clear correlation between vp of the H2 and [O I] NVLC and the outer disk inclination. This result is in line with previous studies. Conclusions. Our results suggest that molecular and neutral atomic emission in disk winds originate from regions that might overlap, and that the survival of molecular winds in disks strongly depends on the gas exposure to the radiation from the central star. The presence of jets does not necessarily affect the kinematics of the low-velocity winds. Our results demonstrate the potential of wide-band high-resolution spectroscopy in linking tracers of different manifestations of the same phenomenon.

High Resolution Overset Structured Grid RANS Simulations of Flow Past a Surface Mounted Cube Using Eddy Viscosity Closure Models

2018 ◽  
Author(s):  
Marc C. Goldbach ◽  
Mesbah Uddin
Keyword(s):  
Eddy Viscosity ◽  
Complex Structure ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Separated Flow ◽  
Industrial Applications ◽  
Separated Flows ◽  
Transitional Flow ◽  
Stream Velocity ◽  
Mean Flow

While Reynolds-averaged simulatons (RAS) have found success in the evaluation of many canonical shear flows, and moderately separated flows, their application to highly separated flows have shown notable deficiencies. This study aims to investigate these deficiencies in the eddy-viscosity formulation of four commonly used turbulence models under separated flow in an attempt to aid in the improved formulation of such models. Analyses are performed on the flow field around a wall mounted cube at a Reynolds number of 40,000 based on the cube height, h, and free stream velocity, U0. While a common occurrence in industrial applications, this type of flow constitutes a complex structure exhibiting a large separated wake region, high anisotropy, and multiple vortex structures. As well, interactions between vortices developed off of different faces of the cube significantly alter the overall flow characteristics, posing a significant challenge for the commonly used industrial turbulence models. Comparison of mean flow characteristics show remarkable agreement between experimental values and turbulence models which are capable of predicting transitional flow. Evaluation of turbulence parameters show the general underestimation of Reynolds stress for transitional models, while fully turbulent models show this value to be overestimated, resulting in completely disparate representations of mean flow structures between the two classes of models (transitional and fully turbulent).

Tip Leakage Behavior and Large Coherent Perturbation Analysis of an Axial-radial Combined Compressor with Outlet Distortion

2021 ◽  
Author(s):  
Li Fu ◽  
Ce Yang ◽  
Chenxing Hu ◽  
Xin Shi
Keyword(s):  
Transient Flow ◽  
Flow Instability ◽  
Complex Structure ◽  
Potential Effect ◽  
Structure Design ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Compact Structure ◽  
Tip Leakage ◽  
Flow Unsteadiness

Abstract Increasing performance requirements and compact structure design promote the generation of axial-radial combined compressors. However, its complex structure and asymmetrical outlet boundary cause difficulty to get an in-depth comprehension of the flow unsteadiness associated with spike-stall. In this work, unsteady full-annular simulations of an axial-radial combined compressor coupled with performance experiment validations were carried out. Based on the overall understanding of outlet distortion on each component, the general feature of tip leakage flow with asymmetrical outlet boundary was extracted. The temporal and spatial development of large coherent perturbations was revealed by the decomposition and reconstruction of the transient flow data with the DMD approach. The results demonstrate that the outlet distortion can propagate reversely to the compressor inlet and the degree of distortion decreases gradually, which leads to the highest possibility for radial rotor to suffer from flow unsteadiness. In the circumferential location with distortion affected, the leakage momentum of the adjacent blade LE is enhanced by the secondary leakage, inducing the expansion of TLV and causing flow instability. Besides organized perturbation structures related to mean flow and BPF, two large low-frequency stall perturbations approximately one-third and three-fourth RF was captured by the DMD method, which is caused by volute potential effect and stator/rotor interference, respectively. The former occurs in the radial rotor and decays during its propagation, while the latter always exists owing to the multiple rotor/stator or stator/rotor interference in the axial-radial combined compressor.

scholarly journals Comparative Study of Lattice Boltzmann Models for Complex Fractal Geometry

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6779
Author(s):  
Dong Zhang ◽  
Enzhi Wang ◽  
Xiaoli Liu
Keyword(s):  
Standard Model ◽  
Convergence Rate ◽  
Comparative Study ◽  
Incompressible Flow ◽  
Lattice Boltzmann ◽  
Fractal Geometry ◽  
Complex Structure ◽  
Structural Complexity ◽  
Grid Resolution ◽  
Lattice Boltzmann Models

A standard model, one of the lattice Boltzmann models for incompressible flow, is broadly applied in mesoscopic fluid with obvious compressible error. To eliminate the compressible effect and the limits in 2D problems, three different models (He-Luo model, Guo’s model, and Zhang’s model) have been proposed and tested by some benchmark questions. However, the numerical accuracy of models adopted in complex geometry and the effect of structural complexity are rarely studied. In this paper, a 2D dimensionless steady flow model is proposed and constructed by fractal geometry with different structural complexity. Poiseuille flow is first simulated to verify the code and shows good agreements with the theoretical solution, supporting further the comparative study on four models to investigate the effect of structural complexity and grid resolution, with reference results obtained by the finite element method (FEM). The work confirms the latter proposed models and effectively reduces compressible error in contrast to the standard model; however, the compressible effect still cannot be ignored in Zhang’s model. The results show that structural error has an approximately negative exponential relationship with grid resolution but an approximately linear relationship with structural complexity. The comparison also demonstrates that the He-Luo model and Guo’s model have a good performance in accuracy and stability, but the convergence rate is lower, while Zhang’s model has an advantage in the convergence rate but the computational stability is poor. The study is significant as it provides guidance and suggestions for adopting LBM to simulate incompressible flow in a complex structure.

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