scholarly journals A Modeling Study of a Trapped Lee-Wave Event over the Pyrénées

2016 ◽  
Vol 145 (1) ◽  
pp. 75-96 ◽  
Author(s):  
Mireia Udina ◽  
Maria Rosa Soler ◽  
Ona Sol
Keyword(s):  
Numerical Solutions ◽  
Initial Conditions ◽  
Horizontal Wind ◽  
Wave Crest ◽  
Model Parameters ◽  
Mountain Range ◽  
Mountain Waves ◽  
Model Experiments ◽  
Lee Wave ◽  
Wave Event

Abstract A trapped lee-wave mountain event in the southern part of the Pyrénées area is analyzed using the Weather Research and Forecasting (WRF) Model. Model experiments are designed to address the WRF predictability of such an event and to explore the influence of the model parameters in resolving the mountain waves. The results show that the model is able to capture a trapped lee-wave event using the 1-km horizontal grid model outputs. Different initial conditions, the vertical grid resolution, and the resolved topography lead to changes in the wave field distribution and the wave amplitude meaning that an ensemble of different model settings may be able to quantify the uncertainty of the numerical solutions. However, the model experiments do not significantly change the wavelength of the generated mountain waves, which is shorter in the three-dimensional real simulations than the one derived from satellite imagery. Comparison with observational data from the surface stations and a wind profiler upstream of the mountain range shows that the model underestimates the horizontal wind speed and this can be the reason for the underestimation of the wavelength. In addition, the valley circulations and the formation of a rotor near the surface are explored. The formation of a low-level rotor in the model is intermittent and brief, and it interacts with other flows coming from multiple directions. The first strong wave updraft is located over the valley aligned with the highest mountain peaks and strong vorticity is captured from the surface up to the first wave crest.

scholarly journals Vertical mixing in the lower troposphere by mountain waves over Arctic Scandinavia

2011 ◽  
Vol 11 (11) ◽  
pp. 31475-31493 ◽  
Author(s):  
M. Mihalikova ◽  
S. Kirkwood
Keyword(s):  
Vertical Mixing ◽  
Lower Troposphere ◽  
Vertical Gradient ◽  
High Rate ◽  
Occurrence Rate ◽  
Horizontal Wind ◽  
Mountain Range ◽  
Mixing Ratio ◽  
Mountain Waves ◽  
Back Trajectories

Abstract. Measurements made by ozonesondes and by a 52 MHz wind-profiling radar during February and March 1997 are studied. The radar is located at Esrange, near Kiruna in Arctic Sweden, on the eastern flank of the Scandinavian mountains. Daily ozonesondes were launched from the same site. The radar vertical and horizontal wind measurements are used to identify times when mountain waves were present. Mean vertical gradients in ozone mixing ratio in the lower troposphere are determined in conditions with mountain waves present and when they were absent. Back-trajectories were calculated so that only air-masses with their origin to the west of the mountains were included in the final averages. The vertical gradient in ozone mixing ratio is found to be about twice as steep outside wave conditions as it is during mountain waves. This suggests a very high rate of vertical mixing, with an average eddy diffusivity of order 5000 m2 s−1. This is consistent with an earlier estimate of the occurrence rate of complete mixing by wave breaking over the mountain range.

scholarly journals The Intense Lee-Wave Rotor Event of Sierra Rotors IOP 8

2007 ◽  
Vol 64 (12) ◽  
pp. 4178-4201 ◽  
Author(s):  
Vanda Grubišić ◽  
Brian J. Billings
Keyword(s):  
Sierra Nevada ◽  
Large Amplitude ◽  
Forced Flow ◽  
Mountain Range ◽  
Wave Rotor ◽  
Owens Valley ◽  
Mountain Waves ◽  
Downslope Wind ◽  
Lee Wave ◽  
Strong Control

Abstract A large-amplitude lee-wave rotor event observationally documented during Sierra Rotors Project Intensive Observing Period (IOP) 8 on 24–26 March 2004 in the lee of the southern Sierra Nevada is examined. Mountain waves and rotors occurred over Owens Valley in a pre-cold-frontal environment. In this study, the evolution and structure of the observed and numerically simulated mountain waves and rotors during the event on 25 March, in which the horizontal circulation associated with the rotor was observed as an opposing, easterly flow by the mesonetwork of surface stations in Owens Valley, are analyzed. The high-resolution numerical simulations of this case, performed with the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) run with multiple nested-grid domains, the finest grid having 333-m horizontal spacing, reproduced many of the observed features of this event. These include small-amplitude waves above the Sierra ridge decoupled from thermally forced flow within the valley, and a large-amplitude mountain wave, turbulent rotor, and strong westerlies on the Sierra Nevada lee slopes during the period of the observed surface easterly flow. The sequence of the observed and simulated events shows a pronounced diurnal variation with the maximum wave and rotor activity occurring in the early evening hours during both days of IOP 8. The lee-wave response, and thus indirectly the appearance of lee-wave rotor during the core IOP 8 period, is found to be strongly controlled by temporal changes in the upstream ambient wind and stability profiles. The downstream mountain range exerts strong control over the lee-wave horizontal wavelength during the strongest part of this event, thus exhibiting the control over the cross-valley position of the rotor and the degree of strong downslope wind penetration into the valley.

Model Study of Intermediate-Scale Tropical Inertia–Gravity Waves and Comparison to TWP-ICE Campaign Observations

2012 ◽  
Vol 69 (2) ◽  
pp. 591-610 ◽  
Author(s):  
Stephanie Evan ◽  
M. Joan Alexander ◽  
Jimy Dudhia
Keyword(s):  
Initial Conditions ◽  
Deep Convection ◽  
Source Region ◽  
Wave Structure ◽  
Horizontal Resolution ◽  
Radiosonde Data ◽  
Horizontal Wind ◽  
Vertical Resolution ◽  
Wave Event ◽  
Wave Properties

Abstract A 2-day inertia–gravity wave (IGW) was observed in high-resolution radiosonde soundings of horizontal wind and temperature taken during the 2006 Tropical Warm Pool–International Cloud Experiment (TWP-ICE) experiment in the Darwin area. The wave was observed in the stratosphere above Darwin from 28 January to 5 February. A similar wave event is observed in the European Centre for Medium-Range Weather Forecasts (ECMWF) operational data. A comparison between the characteristics of the IGW derived with the ECMWF data to the properties of the wave derived with the radiosonde data shows that the ECMWF data capture similar structure for this 2-day wave event but with a larger vertical wavelength. A reverse ray-tracing method is used to localize the source region. Using ECMWF data to define the atmospheric background conditions and wave properties observed in the soundings, it is found that the 2-day wave event originated from deep convection in the Indonesian region around 20 January. The Weather Research and Forecasting (WRF) modeling system is used to complement the ECMWF data to assess the influence of vertical resolution and initial conditions on the wave structure. The model domain is configured as a tropical channel and the ECMWF analyses provide the north/south boundaries and initial conditions. WRF is used with the same horizontal resolution (40 km) as the operational ECMWF in 2006 while using a finer vertical grid spacing than ECMWF. The model is run from 18 January to 11 February to cover the wave life cycle. Different experiments are also performed to determine the sensitivity of the wave structure to cumulus schemes, initial conditions, and vertical resolution. The 2-day wave properties resulting from the WRF experiments are compared to those retrieved from the radiosonde data and from the ECMWF analyses. It is demonstrated that higher vertical resolution would be required for ECMWF to accurately resolve the vertical structure of the wave and its effect on the middle-atmospheric circulation.

Substructure Analysis of a Flexible System Contact-Impact Event

2004 ◽  
Vol 126 (1) ◽  
pp. 126-131 ◽  
Author(s):  
Anping Guo ◽  
Steve Batzer
Keyword(s):  
Impact Analysis ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Time History ◽  
Dynamic Responses ◽  
Computational Time ◽  
Stress Wave Propagation ◽  
Model Parameters ◽  
Flexible System ◽  
Contact Impact

In this paper, the application of the substructure methodology to contact-impact analysis of flexible multibody systems is validated. Various impact model parameters that affect the model’s accuracy are presented. A contact-impact system is used that consists of a flexible cantilever bar longitudinally struck at its free end by a rigid body moving at a finite velocity. First, a dynamic model using the substructure method is established. Second, the initial conditions of the system’s dynamic responses during contact-impact are derived. Finally, a numeric contact-impact simulation is performed. The excellent agreement between the numeric solutions to both the substructure model and the analytical solutions demonstrates that the substructure model can successfully describe stress wave propagation within flexible bodies during contact-impact. The method can also clearly display the contact force time history and deformation distribution along the bar during contact-impact time and correctly predict the displacement of the contact surface of the flexible bar and the contact duration of the two bodies. It is shown that a larger substructure number will improve the accuracy of the numerical solutions, but an excessive number will lower the model’s accuracy since increasingly fine substructures increase the number of modal coordinates and lead to more serious computational round off errors and longer computational time.

scholarly journals E–ε Model of Spray-Laden Near-Sea Atmospheric Layer in High Wind Conditions

2014 ◽  
Vol 44 (2) ◽  
pp. 742-763 ◽  
Author(s):  
Yevgenii Rastigejev ◽  
Sergey A. Suslov
Keyword(s):  
Turbulent Flow ◽  
Drag Coefficient ◽  
Turbulent Mixing ◽  
Numerical Solutions ◽  
Turbulent Energy ◽  
Wave Crest ◽  
Mixing Length ◽  
High Wind ◽  
Close Proximity ◽  
Ocean Spray

Abstract In-depth understanding and accurate modeling of the interaction between ocean spray and a turbulent flow under high wind conditions is essential for improving the intensity forecasts of hurricanes and severe storms. Here, the authors consider the E–ε closure for a turbulent flow model that accounts for the effects of the variation of turbulent energy and turbulent mixing length caused by spray stratification. The obtained analytical and numerical solutions show significant differences between the current E–ε model and the lower-order turbulent kinetic energy (TKE) model considered previously. It is shown that the reduction of turbulent energy and mixing length above the wave crest level, where the spray droplets are generated, that is not accounted for by the TKE model results in a significant suppression of turbulent mixing in this near-wave layer. In turn, suppression of turbulence causes an acceleration of flow and a reduction of the drag coefficient that is qualitatively consistent with field observations if spray is fine (even if its concentration is low) or if droplets are large but their concentration is sufficiently high. In the latter case, spray inertia may become important. This effect is subsequently examined. It is shown that spray inertia leads to the reduction of wind velocity in the close proximity of the wave surface relative to the reference logarithmic profile. However, at higher altitudes the suppression of flow turbulence by the spray still results in the wind acceleration and the reduction of the local drag coefficient.

Kinetic Model of Adiabatic Temperature Rise of Mass Concrete

2021 ◽  
Vol 13 (5) ◽  
pp. 771-780
Author(s):  
Shou-Kai Chen ◽  
Bo-Wen Xu
Keyword(s):  
Temperature Field ◽  
Temperature Rise ◽  
Initial Conditions ◽  
Dynamic Change ◽  
Adiabatic Temperature ◽  
Model Parameters ◽  
Hydration Reaction ◽  
Mass Concrete ◽  
Adiabatic Temperature Rise ◽  
Proposed Model

The adiabatic temperature rise model of mass concrete is very important for temperature field simulation, same to crack resistance capacity and temperature control of concrete structures. In this research, a thermal kinetics analysis was performed to study the exothermic hydration reaction process of concrete, and an adiabatic temperature rise model was proposed. The proposed model considers influencing factors, including initial temperature, temperature history, activation energy, and the completion degree of adiabatic temperature rise and is theoretically mature and definitive in physical meaning. It was performed on different initial temperatures for adiabatic temperature rise test; the data were employed in a regression analysis of the model parameters and initial conditions. The same function was applied to describe the dynamic change of the adiabatic temperature rise rates for different initial temperatures and different temperature changing processes and subsequently employed in a finite element analysis of the concrete temperature field. The test results indicated that the proposed model adequately fits the data of the adiabatic temperature rise test, which included different initial temperatures, and accurately predicts the changing pattern of adiabatic temperature rise of concrete at different initial temperatures. Compared with the results using the traditional age-based adiabatic temperature rise model, the results of a calculation example revealed that the simulated calculation results using the proposed model can accurately reflect the temperature change pattern of concrete in heat dissipation conditions.

Frequency of Mountain Waves Over Kanto Area Revealed by Imaging Observations of OH Airglow

2021 ◽  
Author(s):  
Satoshi Ishii ◽  
Yoshihiro Tomikawa ◽  
Masahiro Okuda ◽  
Hidehiko Suzuki
Keyword(s):  
Spatial Scales ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Leeward Side ◽  
Mountainous Areas ◽  
Wind Fields ◽  
Mountain Waves ◽  
The World ◽  
Geostationary Meteorological Satellite ◽  
Good Proxy

Abstract Imaging observations of OH airglow were conducted at Meiji University, Japan (IN, mE), from May 2018 to December 2019. Mountainous areas, including Mt. Fuji, are located to the west of the imager, and westerly winds are dominant in the lower atmosphere throughout the year. Mountain waves (MWs) are generated on the leeward sides of mountains and occasionally propagate to the upper atmosphere. However, during the observation period (about 1 year and 8 months), only four possible MW events were identified. Based on previous reports, this incidence is considerably lower than expected. There are two possible reasons for the low incidence of MW events: (1) The frequency of MW excitation is small in the lower layers of the atmosphere, and/or (2) MWs do not propagate easily to the upper mesosphere due to background wind conditions. This study verified the likelihood of the former case. Under over-mountain airflow conditions, wavy clouds are often generated on the leeward side. Since over-mountain airflow is essential for the excitation of MWs, the frequency of wavy clouds in the lower atmosphere can be regarded as a measure of the occurrence of MWs. The frequency and spatial distribution of MWs around Japan were investigated by detecting the wavy clouds from color images taken by the Himawari-8 geostationary meteorological satellite (GSM-8) for one year in 2018. The wavy clouds were detected on more than 70 days a year around the Tohoku region, but just 20 days a year around Mt. Fuji. This suggests that few MWs are generated around Mt. Fuji. The differences between these two regions were examined focusing on the relationship between the local topography and dominant horizontal wind fields in the lower atmosphere. Specifically, the findings showed that the angle between the dominant horizontal wind direction and the orientation of the mountain ridge is a good proxy of the occurrence of wavy clouds, i.e., excitation of MWs in mountainous areas. We have also applied this proxy to topography in other areas of the world to investigate areas where MWs would be occurring frequently. Finally, we discuss the likelihood of "MW hotspots" at various spatial scales in the world.

Oscillatory flow past a circular cylinder in a rotating frame

1997 ◽  
Vol 345 ◽  
pp. 101-131
Author(s):  
M. D. KUNKA ◽  
M. R. FOSTER
Keyword(s):  
Circular Cylinder ◽  
Steady Flow ◽  
Stagnation Point ◽  
Oscillatory Flow ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Temporal Integration ◽  
Oncoming Flow ◽  
Flow Past ◽  
Rear Stagnation Point

Because of the importance of oscillatory components in the oncoming flow at certain oceanic topographic features, we investigate the oscillatory flow past a circular cylinder in an homogeneous rotating fluid. When the oncoming flow is non-reversing, and for relatively low-frequency oscillations, the modifications to the equivalent steady flow arise principally in the ‘quarter layer’ on the surface of the cylinder. An incipient-separation criterion is found as a limitation on the magnitude of the Rossby number, as in the steady-flow case. We present exact solutions for a number of asymptotic cases, at both large frequency and small nonlinearity. We also report numerical solutions of the nonlinear quarter-layer equation for a range of parameters, obtained by a temporal integration. Near the rear stagnation point of the cylinder, we find a generalized velocity ‘plateau’ similar to that of the steady-flow problem, in which all harmonics of the free-stream oscillation may be present. Further, we determine that, for certain initial conditions, the boundary-layer flow develops a finite-time singularity in the neighbourhood of the rear stagnation point.

scholarly journals Elasto-plastic-adhesive DEM model for simulating hillslope debris flows: cross comparison with field experiments

2018 ◽  
Author(s):  
Adel Albaba ◽  
Massimiliano Schwarz ◽  
Corinna Wendeler ◽  
Bernard Loup ◽  
Luuk Dorren
Keyword(s):  
Numerical Model ◽  
Flow Velocity ◽  
Debris Flows ◽  
Field Experiments ◽  
Initial Conditions ◽  
Experimental Tests ◽  
Height Velocity ◽  
Model Parameters ◽  
Fine Content ◽  
Adhesive Model

Abstract. This paper presents a Discrete Element-based elasto-plastic-adhesive model which is adapted and tested for producing hillslope debris flows. The numerical model produces three phases of particle contacts: elastic, plastic and adhesion. The model capabilities of simulating different types of cohesive granular flows were tested with different ranges of flow velocities and heights. The basic model parameters, being the basal friction (ϕb) and normal restitution coefficient (ϵn), were calibrated using field experiments of hillslope debris flows impacting two sensors. Simulations of 50 m3 of material were carried out on a channelized surface that is 41 m long and 8 m wide. The calibration process was based on measurements of flow height, flow velocity and the pressure applied to a sensor. Results of the numerical model matched well those of the field data in terms of pressure and flow velocity while less agreement was observed for flow height. Those discrepancies in results were due in part to the deposition of material in the field test which are not reproducible in the model. A parametric study was conducted to further investigate that effect of model parameters and inclination angle on flow height, velocity and pressure. Results of best-fit model parameters against selected experimental tests suggested that a link might exist between the model parameters ϕb and ϵn and the initial conditions of the tested granular material (bulk density and water and fine contents). The good performance of the model against the full-scale field experiments encourages further investigation by conducting lab-scale experiments with detailed variation of water and fine content to better understand their link to the model's parameters.

Key words: Nonlinear Differential-Difference Equations; Exp-Function Method; N-Soliton Solutions

2010 ◽  
Vol 65 (11) ◽  
pp. 935-949 ◽  
Author(s):  
Mehdi Dehghan ◽  
Jalil Manafian ◽  
Abbas Saadatmandi
Keyword(s):  
Partial Differential Equations ◽  
Differential Equations ◽  
Homotopy Analysis Method ◽  
Fractional Derivatives ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Analysis Method ◽  
Partial Differential ◽  
Integer Order ◽  
Homotopy Analysis

In this paper, the homotopy analysis method is applied to solve linear fractional problems. Based on this method, a scheme is developed to obtain approximation solution of fractional wave, Burgers, Korteweg-de Vries (KdV), KdV-Burgers, and Klein-Gordon equations with initial conditions, which are introduced by replacing some integer-order time derivatives by fractional derivatives. The fractional derivatives are described in the Caputo sense. So the homotopy analysis method for partial differential equations of integer order is directly extended to derive explicit and numerical solutions of the fractional partial differential equations. The solutions are calculated in the form of convergent series with easily computable components. The results of applying this procedure to the studied cases show the high accuracy and efficiency of the new technique.

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