scholarly journals Suppress Numerical Oscillations in Transient Mixed Flow Simulations with a Modified HLL Solver

Water ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1245 ◽  
Author(s):  
Zhonghao Mao ◽  
Guanghua Guan ◽  
Zhonghua Yang
Keyword(s):  
Acoustic Wave ◽  
Wave Speed ◽  
Hydraulic Systems ◽  
Simple Method ◽  
Flow Simulations ◽  
Flow Regime Transition ◽  
Pressurized Flows ◽  
Numerical Oscillations ◽  
Two Parameters ◽  
Good Agreement

Transition between free-surface and pressurized flows is a crucial phenomenon in many hydraulic systems. During simulation of such phenomenon, severe numerical oscillations may appear behind filling-bores, causing unphysical pressure variations and computation failure. This paper reviews existing oscillation-suppressing methods, while only one of them can obtain a stable result under a realistic acoustic wave speed. We derive a new oscillation-suppressing method with first-order accuracy. This simple method contains two parameters, Pa and Pb, and their values can be determined easily. It can sufficiently suppress numerical oscillations under an acoustic wave speed of 1000 ms−1. Good agreement is found between simulation results and analytical results or experimental data. This paper can help readers to choose an appropriate oscillation-suppressing method for numerical simulations of flow regime transition under a realistic acoustic wave speed.

scholarly journals Suppress Numerical Oscillations in Transient Mixed Flow Simulations with a Modified HLL Solver

2020 ◽  
Author(s):  
Zhonghao Mao ◽  
Guanghua Guan ◽  
Zhonghua Yang
Keyword(s):  
Water Surface ◽  
Distribution Systems ◽  
Water Distribution ◽  
Hydraulic Systems ◽  
Flow Simulations ◽  
Flow Regime Transition ◽  
Numerical Viscosity ◽  
Pressurized Flows ◽  
Numerical Oscillations ◽  
Good Agreement

Transition between free-surface and pressurized flows is an crucial phenomenon in many hydraulic systems, including water distribution systems, urban drainage systems, etc. During the transition, the force exerted on the structures changes drastically, thus it is meaningful to simulate this process. However, severe numerical oscillations are widely observed behind filling-bores, causing unphysical pressure variations and even computation failure. In this paper, some oscillation-suppressing approaches are reviewed and evaluated on a benchmark model. Then a new oscillation-suppressing approach is proposed to admit numerical viscosity when the water surface is at proximity of conduct roof which has first order accuracy. This approach adds numerical viscosity when water surface is at the proximity of conduct roof. It can sufficiently suppress numerical oscillations under an acoustic wave speed of 1000m/s and is simple to apply. In comparison with two experiments, the simulation results of this method show good agreement and little numerical oscillations. The results in this paper can help readers to choose an appropriate oscillation-suppressing method to improve the robustness and accuracy of flow regime transition simulations.

A Streamline Curvature Method for Calculating S1 Stream Surface Flow

1984 ◽  
Vol 106 (2) ◽  
pp. 306-312
Author(s):  
S. K. Mao ◽  
D. T. Li
Keyword(s):  
Surface Flow ◽  
Approximation Technique ◽  
Flow Section ◽  
Boolean Expression ◽  
Simple Method ◽  
Stream Surface ◽  
Streamline Curvature ◽  
Calculation Results ◽  
Good Agreement ◽  
Streamline Curvature Method

A streamline curvature method for calculating S1 surface flow in turbines is presented. The authors propose a simple method in which a domain of calculation can be changed into an orderly rectangle without making coordinate transformations. Calculation results obtained on subsonic and transonic turbine cascades have been compared with those of experiment and another theory. Good agreement has been found. When calculating blade-to-blade flow velocity at subsonic speed, a function approximation technique can be used in lieu of iteration method in order to reduce calculation time. If the calculated flow section is of a mixed (subsonic-supersonic) flow type, a Boolean expression obtained from the truth table of flow states is proposed to judge the integrated character of the mixed flow section. Similarly, another Boolean expression is used to determine whether there exists a “choking” of the relevant section. Periodical conditions are satisfied by iterating the first-order derivative of stagnation streamline, which is formed simultaneously. It can be proved that the stagnation streamline formed in this way is unique.

scholarly journals Accuracy of Wind Observations from Open-Ocean Buoys: Correction for Flow Distortion

2020 ◽  
Vol 37 (4) ◽  
pp. 687-703 ◽  
Author(s):  
Michael Schlundt ◽  
J. Thomas Farrar ◽  
Sebastien P. Bigorre ◽  
Albert J. Plueddemann ◽  
Robert A. Weller
Keyword(s):  
Flow Distortion ◽  
Error Sources ◽  
Neutral Winds ◽  
Flow Simulations ◽  
Temporal Sampling ◽  
Empirical Correction ◽  
The Individual ◽  
Wind Vane ◽  
Subsequent Comparison ◽  
Good Agreement

AbstractThe comparison of equivalent neutral winds obtained from (i) four WHOI buoys in the subtropics and (ii) scatterometer estimates at those locations reveals a root-mean-square (RMS) difference of 0.56–0.76 m s−1. To investigate this RMS difference, different buoy wind error sources were examined. These buoys are particularly well suited to examine two important sources of buoy wind errors because 1) redundant anemometers and a comparison with numerical flow simulations allow us to quantitatively assess flow distortion errors, and 2) 1-min sampling at the buoys allows us to examine the sensitivity of buoy temporal sampling/averaging in the buoy–scatterometer comparisons. The interanemometer difference varies as a function of wind direction relative to the buoy wind vane and is consistent with the effects of flow distortion expected based on numerical flow simulations. Comparison between the anemometers and scatterometer winds supports the interpretation that the interanemometer disagreement, which can be up to 5% of the wind speed, is due to flow distortion. These insights motivate an empirical correction to the individual anemometer records and subsequent comparison with scatterometer estimates show good agreement.

scholarly journals Theoretical investigation of acoustic wave velocity of aluminum phosphide under pressure

2019 ◽  
Vol 7 (1) ◽  
pp. 3
Author(s):  
Salah Daoud ◽  
Abdelhakim Latreche ◽  
Pawan Kumar Saini
Keyword(s):  
Acoustic Wave ◽  
Wave Velocity ◽  
Elastic Constants ◽  
Structural Parameters ◽  
Theoretical Data ◽  
Aluminum Phosphide ◽  
Semiconducting Material ◽  
Wave Velocities ◽  
Knoop Microhardness ◽  
Good Agreement

The bulk and surface acoustic wave velocities of Aluminum phosphide (AlP) semiconducting material under pressure up to 9.5 GPa were studied. The structural parameters and the elastic constants used in this work are taken from our previous paper published in J. Optoelec-tron. Adv. M. 16, 207 (2014). The results obtained at zero-pressure are analyzed and compared with other data of the literature. In addition, the acoustic Grüneisen parameter and the Vickers and Knoop microhardness are predicted and analyzed in detail. Our calculated results are in good agreement with the experimental and other theoretical data of literature.   

scholarly journals Comparison of GPM Core Observatory and Ground-Based Radar Retrieval of Mass-Weighted Mean Raindrop Diameter at Midlatitude

2018 ◽  
Vol 19 (10) ◽  
pp. 1583-1598 ◽  
Author(s):  
Leo Pio D’Adderio ◽  
Gianfranco Vulpiani ◽  
Federico Porcù ◽  
Ali Tokay ◽  
Robert Meneghini
Keyword(s):  
High Sensitivity ◽  
Sensitivity Study ◽  
Three Dimensions ◽  
Convective Precipitation ◽  
Precipitation Pattern ◽  
Dual Frequency ◽  
Weighted Mean ◽  
Raindrop Size Distribution ◽  
Two Parameters ◽  
Good Agreement

Abstract One of the main goals of the National Aeronautics and Space Administration (NASA) Global Precipitation Measurement (GPM) mission is to retrieve parameters of the raindrop size distribution (DSD) globally. As a standard product of the Dual-Frequency Precipitation Radar (DPR) on board the GPM Core Observatory satellite, the mass-weighted mean diameter Dm and the normalized intercept parameter Nw are estimated in three dimensions at the resolution of the radar. These are two parameters of the three-parameter gamma model DSD adopted by the GPM algorithms. This study investigates the accuracy of the Dm retrieval through a comparative study of C-band ground radars (GRs) and GPM products over Italy. The reliability of the ground reference is tested by using two different approaches to estimate Dm. The results show good agreement between the ground-based and spaceborne-derived Dm, with an absolute bias being generally lower than 0.5 mm over land in stratiform precipitation for the DPR algorithm and the combined DPR–GMI algorithm. For the DPR–GMI algorithm, the good agreement extends to convective precipitation as well. Estimates of Dm from the DPR high-sensitivity (HS) Ka-band data show slightly worse results. A sensitivity study indicates that the accuracy of the Dm estimation is independent of the height above surface (not shown) and the distance from the ground radar. On the other hand, a nonuniform precipitation pattern (interpreted both as high variability and as a patchy spatial distribution) within the DPR footprint is usually associated with a significant error in the DPR-derived estimate of Dm.

Pulsed high-current discharge in water: adiabatic model of expanding plasma channel and acoustic wave

2021 ◽  
Author(s):  
Andrey V. Kozyrev ◽  
Andrey A. Zherlitsyn ◽  
Natalia S. Semeniuk
Keyword(s):  
Acoustic Wave ◽  
Pulsed Power ◽  
High Current ◽  
Number Density ◽  
Pulsed Discharge ◽  
Current Channel ◽  
High Current Discharge ◽  
Isothermal Plasma ◽  
A Current ◽  
Good Agreement

Abstract This paper presents the results of a theoretical and experimental study of the use of a pulsed discharge in water to obtain a strong acoustic wave in a liquid medium. A discharge with a current amplitude of 10 kA, a duration of 400 ns, and an amplitude pulsed power of 280 MW in water at atmospheric pressure created an expanding acoustic wave with an amplitude of more than 100 MPa. To describe the formation of the discharge channel, an isothermal plasma model has been developed, which made it possible to calculate both the expansion dynamics of a high-current channel and the strong acoustic wave generated by it. Our calculations show that the number density of plasma in the channel reaches 10^20 cm^(–3), while the degree of water vapour ionization is about 10%, and the channel wall extends with a velocity of 500 m/s. The calculations for the acoustic wave are in good agreement with measurements

Numerical Modelling of Circulation in Lake Sperillen, Norway

2000 ◽  
Vol 31 (1) ◽  
pp. 57-72 ◽  
Author(s):  
N. R. B. Olsen ◽  
D. K. Lysne
Keyword(s):  
Numerical Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Field Measurements ◽  
Navier Stokes ◽  
Water Current ◽  
Simple Method ◽  
Vertical Temperature Profile ◽  
Navier Stokes Equations ◽  
Good Agreement

A three-dimensional numerical model was used to model water circulation and spatial variation of temperature in Lake Sperillen in Norway. A winter situation was simulated, with thermal stratification and ice cover. The numerical model solved the Navier-Stokes equations on a 3D unstructured non-orthogonal grid with hexahedral cells. The SIMPLE method was used for the pressure coupling and the k-ε model was used to model turbulence, with a modification for density stratification due to the vertical temperature profile. The results were compared with field measurements of the temperature in the lake, indicating the location of the water current. Reasonably good agreement was found.

Molecular Beam Epitaxy of AlN Layers on Si (111)

2008 ◽  
Vol 1068 ◽  
Author(s):  
Jean-Christophe Moreno ◽  
Eric Frayssinet ◽  
Fabrice Semond ◽  
Jean Massies
Keyword(s):  
Molecular Beam Epitaxy ◽  
Acoustic Wave ◽  
Wave Speed ◽  
Molecular Beam ◽  
Bulk Acoustic Wave ◽  
X Ray Diffraction ◽  
High Crystalline Quality ◽  
Force Microscopy ◽  
Atomic Force ◽  
Film Bulk

ABSTRACTIn this work, we present a study of epitaxial Aluminium Nitride (AlN) for thin film bulk acoustic wave (BAW) applications. Molecular beam epitaxy (MBE) was used to perform high crystalline quality AlN thin films growth on different silicon substrate preparations. A morphological study was performed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), while structural properties and acoustic wave speed were respectively assessed by X-ray diffraction and acoustic picoseconds.

scholarly journals Nonlinear run-ups of regular waves on sloping structures

2012 ◽  
Vol 12 (12) ◽  
pp. 3811-3820 ◽  
Author(s):  
T.-W. Hsu ◽  
S.-J. Liang ◽  
B.-D. Young ◽  
S.-H. Ou
Keyword(s):  
Boussinesq Equations ◽  
Irregular Waves ◽  
Coastal Structures ◽  
Regular Waves ◽  
Wave Flume ◽  
Coastal Risk ◽  
Run Up ◽  
Two Parameters ◽  
Prediction Capability ◽  
Good Agreement

Abstract. For coastal risk mapping, it is extremely important to accurately predict wave run-ups since they influence overtopping calculations; however, nonlinear run-ups of regular waves on sloping structures are still not accurately modeled. We report the development of a high-order numerical model for regular waves based on the second-order nonlinear Boussinesq equations (BEs) derived by Wei et al. (1995). We calculated 160 cases of wave run-ups of nonlinear regular waves over various slope structures. Laboratory experiments were conducted in a wave flume for regular waves propagating over three plane slopes: tan α =1/5, 1/4, and 1/3. The numerical results, laboratory observations, as well as previous datasets were in good agreement. We have also proposed an empirical formula of the relative run-up in terms of two parameters: the Iribarren number ξ and sloping structures tan α. The prediction capability of the proposed formula was tested using previous data covering the range ξ ≤ 3 and 1/5 ≤ tan α ≤ 1/2 and found to be acceptable. Our study serves as a stepping stone to investigate run-up predictions for irregular waves and more complex geometries of coastal structures.

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