An Advanced Numerical Model for Assessing 3-D Wind Fields

2007 ◽  
Author(s):  
Darrell W. Pepper ◽  
Xiuling Wang
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Element Model ◽  
Integral Function ◽  
Wind Fields ◽  
Local Flow ◽  
Irregular Terrain ◽  
Topographic Features ◽  
Element Size ◽  
The Difference

An h-adaptive mass consistent finite element model (FEM) is developed for constructing 3-D wind fields over irregular terrain. The h-adaptive FEM allows the element size to be changed dynamically according to local flow and topographic features. The mesh is refined and unrefined to satisfy preset error criteria. Localized high resolution wind fields can be constructed. The FEM model uses a variational method in an integral function that minimizes the variance of the difference between the observed and analyzed variable. Simulation results are presented for constructing 3-D wind fields for two regions in Nevada. The method appears promising for accurately depicting large scale wind fields, especially where high resolution is needed to capture rapidly changing flows associated with local topographic features.

scholarly journals Multi-scale snowdrift-permitting modelling of mountain snowpack

2020 ◽  
Author(s):  
Vincent Vionnet ◽  
Christopher B. Marsh ◽  
Brian Menounos ◽  
Simon Gascoin ◽  
Nicholas E. Wayand ◽  
...  
Keyword(s):  
High Resolution ◽  
Snow Depth ◽  
Large Scale ◽  
Small Scale ◽  
Topographic Effects ◽  
Blowing Snow ◽  
Wind Fields ◽  
Canopy Interception ◽  
Multi Scale ◽  
Temporal And Spatial

Abstract. The interaction of mountain terrain with meteorological processes causes substantial temporal and spatial variability in snow accumulation and ablation. Processes impacted by complex terrain include large-scale orographic enhancement of snowfall, small-scale processes such as gravitational and wind-induced transport of snow, and variability in the radiative balance such as through terrain shadowing. In this study, a multi-scale modeling approach is proposed to simulate the temporal and spatial evolution of high mountain snowpacks using the Canadian Hydrological Model (CHM), a multi-scale, spatially distributed modelling framework. CHM permits a variable spatial resolution by using the efficient terrain representation by unstructured triangular meshes. The model simulates processes such as radiation shadowing and irradiance to slopes, blowing snow redistribution and sublimation, avalanching, forest canopy interception and sublimation and snowpack melt. Short-term, km-scale atmospheric forecasts from Environment and Climate Change Canada's Global Environmental Multiscale Model through its High Resolution Deterministic Prediction System (HRDPS) drive CHM, and were downscaled to the unstructured mesh scale using process-based procedures. In particular, a new wind downscaling strategy combines meso-scale HRDPS outputs and micro-scale pre-computed wind fields to allow for blowing snow calculations. HRDPS-CHM was applied to simulate snow conditions down to 50-m resolution during winter 2017/2018 in a domain around the Kananaskis Valley (~1000 km2) in the Canadian Rockies. Simulations were evaluated using high-resolution airborne Light Detection and Ranging (LiDAR) snow depth data and snow persistence indexes derived from remotely sensed imagery. Results included model falsifications and showed that both blowing snow and gravitational snow redistribution need to be simulated to capture the snowpack variability and the evolution of snow depth and persistence with elevation across the region. Accumulation of wind-blown snow on leeward slopes and associated snow-cover persistence were underestimated in a CHM simulation driven by wind fields that did not capture leeside flow recirculation and associated wind speed decreases. A terrain-based metric helped to identify these lee-side areas and improved the wind field and the associated snow redistribution. An overestimation of snow redistribution from windward to leeward slopes and subsequent avalanching was still found. The results of this study highlight the need for further improvements of snowdrift-permitting models for large-scale applications, in particular the representation of subgrid topographic effects on snow transport.

An H-Adaptive Finite Element Model for Constructing 3-D Wind Fields

2004 ◽  
Author(s):  
Xiuling Wang ◽  
Darrell W. Pepper ◽  
Yitung Chen ◽  
Hsuan-Tsung Hsieh
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Wind Field ◽  
Compressible Flows ◽  
Element Model ◽  
Computational Time ◽  
Individual Element ◽  
Adaptive Finite Element ◽  
Wind Fields ◽  
Irregular Terrain

Calculating wind velocities accurately and efficiently is the key to successfully assessing wind fields over irregular terrain. In the finite element method, decreasing individual element size (increasing the mesh density) and increasing shape function interpolation order are known to improve accuracy. However, computational speed is typically impaired, along with tremendous increases in computational storage. This problem becomes acutely obvious when dealing with atmospheric flows. An h-adaptation scheme, which allows one to start with a coarse mesh that ultimately refines in high gradients regions, can obtain high accuracy at reduced computational time and storage. H-adaptation schemes have been shown to be very effective in compressible flows for capturing shocks [1], but have found limited use in atmospheric wind field simulations [2]. In this paper, an h-adaptive finite element model has been developed that refines and unrefines element regions based upon velocity gradients. An objective analysis technique is applied to generate a mass consistent 3-D flow field utilizing sparse meteorological data. Results obtained from the PSU/NCAR MM5 atmospheric model are used to establish the initial velocity field in lieu of available meteorological tower data. Wind field estimations for the northwest area of Nevada are currently being examined as potential locations for wind turbines.

The Design of Ultra-Large Hydraulic-Balance Oil Tank With Double-Shell

2011 ◽  
Author(s):  
Guowei Cao ◽  
Zhiping Chen ◽  
Wenjing Guo
Keyword(s):  
Large Scale ◽  
Element Model ◽  
Working Principle ◽  
Oil Tank ◽  
The Difference ◽  
Rational Construction ◽  
Oil Tanks ◽  
The Cost ◽  
The Finite Element Model ◽  
Hydraulic Balance

Large-scale oil tanks are being studied all along because they have a series of advantages. For example, they can reduce the cost of manufacturing and management of the facilities, and save land. So the volume of oil tanks becomes larger and larger during their development. However, without on-site heat treatment, the thickness of the shell of traditional oil tanks is restricted to 200,000 m3. In this paper, a new structure named Ultra-large Hydraulic-Balance oil tank with double-shell was put forward. With the method of hydraulic-balance, oil tanks of this structure could be larger than 200,000 m3. Besides expounding the working principle in detail, a 200,000 m3 oil tank with double-shell was also designed in the paper according to API 650, and the finite element model was used to analyze the stress including intensity and distribution of both shells in order to test and verify its security. Furthermore, its economy was analyzed by comparing with traditional oil tanks. Finally, the problem caused by the difference of liquid lever as well as was discussed. Results show that Ultra-large Hydraulic-Balance oil tank with double-shell owned advantages including rational construction, economy and easy manufacturing.

The role of small-scale topographic features on inundation dynamics: potential impacts on large-scale investigations

2021 ◽  
Author(s):  
Alessio Domeneghetti ◽  
Antonio Leonardi ◽  
Oliver E. J. Wing ◽  
Francesca Carisi ◽  
Armando Brath
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Hydraulic Modeling ◽  
Data Availability ◽  
Small Scale ◽  
Topographic Features ◽  
Capacity Data ◽  
The Impact ◽  
Flood Prone Areas

<p>The execution of large-scale (i.e., continental or global) hydraulic modeling is nowadays a reality thanks to the increasing computational capacity, data availability, as well as understanding of essential physical dynamics. Such achievements are typically associated to a compromise in terms of model resolutions (the finer being of few tens of meters, with a coarsened representation of the terrain) and, thus, accuracy on representing the topographic peculiarities of the flood-prone areas. Nevertheless, the experience gained observing the dynamics of past inundations highlights the role of small-scale topographic features (e.g., minor embankments, road deck, railways, etc.) in driving the flow paths. Recent advances on automated identification of flood defense from high resolution digital elevation model paved the way to include hydraulically relevant features (e.g., main levees) while preserving the model resolution suitable for large-scale applications (Wing et al, 2020). <br>The present study extends this approach to flood-prone areas by investigating how the automatic detection of minor topographic discontinuities can enhance the estimation of flood dynamics of large-scale models. Taking advantage of high-resolution topographic data (i.e., 1-2 m) the approach automatically detects hydraulically relevant features and preserves their height while coarsening the resolution of the terrain used into the hydraulic model. The impact of such approach on the inundation dynamic is tested referring to three different case-studies that recently experienced riverine flooding: Secchia and Enza rivers (2014, 2017, respectively; Italy), Des Moines (Iowa, USA). The results confirm the relevance of small-scale topographic features, which, when considered, ensure a high correspondence to observations and local models. The element of strength of the presented approach is that such performances are ensured without requiring the adoption of high grid resolutions, and thus, not affecting the overall computational costs.</p>

scholarly journals Refining IKONOS DEM for Dehradun Region Using Photogrammetry Based DEM Editing Methods, Orthoimage Generation and Quality Assessment of Cartosat-1 DEM

2020 ◽  
Vol 5 (1) ◽  
pp. 3
Author(s):  
Ashutosh Bhardwaj ◽  
Kamal Jain ◽  
Rajat Subhra Chatterjee
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Digital Terrain Model ◽  
Optimal Number ◽  
Mean Difference ◽  
Surface Model ◽  
Difference Image ◽  
Polynomial Coefficients ◽  
Rational Polynomial ◽  
The Difference

The correct representation of the topography of terrain is an important requirement to generate photogrammetric products such as orthoimages and maps from high-resolution (HR) or very high-resolution (VHR) satellite datasets. The refining of the digital elevation model (DEM) for the generation of an orthoimage is a vital step with a direct effect on the final accuracy achieved in the orthoimages. The refined DEM has potential applications in various domains of earth sciences such as geomorphological analysis, flood inundation mapping, hydrological analysis, large-scale mapping in an urban environment, etc., impacting the resulting output accuracy. Manual editing is done in the presented study for the automatically generated DEM from IKONOS data consequent to the satellite triangulation with a root mean square error (RMSE) of 0.46, using the rational function model (RFM) and an optimal number of ground control points (GCPs). The RFM includes the rational polynomial coefficients (RPCs) to build the relation between image space and ground space. The automatically generated DEM initially represents the digital surface model (DSM), which is used to generate a digital terrain model (DTM) in this study for improving orthoimages for an area of approximately 100 km2. DSM frequently has errors due to mass points in hanging (floating) or digging, which need correction while generating DTM. The DTM assists in the removal of the geometric effects (errors) of ground relief present in the DEM (i.e., DSM here) while generating the orthoimages and thus improves the quality of orthoimages, especially in areas such as Dehradun that have highly undulating terrain with a large number of natural drainages. The difference image of reference, i.e., edited IKONOS DEM (now representing DTM) and automatically generated IKONOS DEM, i.e., DSM, has a mean difference of 1.421 m. The difference DEM (dDEM) for the reference IKONOS DEM and generated Cartosat-1 DEM at a 10 m posting interval (referred to as Carto10 DEM) results in a mean difference of 8.74 m.

Constructing 3-D Wind Fields for Nellis Dunes in Nevada

2008 ◽  
Author(s):  
Xiuling Wang ◽  
Darrell W. Pepper ◽  
Brenda Buck ◽  
Dirk Goossens
Keyword(s):  
Element Model ◽  
Posteriori Error ◽  
Large Element ◽  
Error Estimator ◽  
Small Element ◽  
Computational Domain ◽  
Wind Fields ◽  
Adaptive Procedure ◽  
Irregular Terrain ◽  
L2 Norm

An h-adaptive, mass consistent finite element model (FEM) is used to construct 3-D wind fields over irregular terrain utilizing sparse meteorological tower data. The element size in the computational domain is dynamically controlled by a–posteriori error estimator based on the L2 norm. In the h-adaptive FEM algorithm, large element sizes are typically associated with computational regions where the flow is smooth and small errors; small element sizes are attributed to fast changing flow regions and large errors. The adaptive procedure uses mesh refinement/unrefinement to satisfy error criteria. The application of a mass consistent approach essentially poses a least-squares problem in the computational domain. Preliminary results are obtained for constructing 3-D wind fields for Nellis Dunes in Nevada.

scholarly journals The Dependence of ITCZ Structure on Model Resolution and Dynamical Core in Aquaplanet Simulations

2014 ◽  
Vol 27 (6) ◽  
pp. 2375-2385 ◽  
Author(s):  
Kiranmayi Landu ◽  
L. Ruby Leung ◽  
Samson Hagos ◽  
V. Vinoj ◽  
Sara A. Rauscher ◽  
...  
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Convective Available Potential Energy ◽  
Specific Humidity ◽  
Tropospheric Temperature ◽  
Dynamical Core ◽  
Community Atmosphere Model ◽  
Double Itcz ◽  
Lateral Extent ◽  
The Difference

Abstract Aquaplanet simulations using the Community Atmosphere Model, version 4 (CAM4), with the Model for Prediction Across Scales–Atmosphere (MPAS-A) and High-Order Method Modeling Environment (HOMME) dynamical cores and using zonally symmetric sea surface temperature (SST) structure are studied to understand the dependence of the intertropical convergence zone (ITCZ) structure on resolution and dynamical core. While all resolutions in HOMME and the low-resolution MPAS-A simulations give a single equatorial peak in zonal mean precipitation, the high-resolution MPAS-A simulations give a double ITCZ with precipitation peaking around 2°–3° on either side of the equator. This study reveals that the structure of ITCZ is dependent on the feedbacks between convection and large-scale circulation. It is shown that the difference in specific humidity between HOMME and MPAS-A can lead to different latitudinal distributions of the convective available potential energy (CAPE) by influencing latent heat release by clouds and the upper-tropospheric temperature. With lower specific humidity, the high-resolution MPAS-A simulation has CAPE increasing away from the equator that enhances convection away from the equator and, through a positive feedback on the circulation, results in a double ITCZ structure. In addition, it is shown that the dominance of antisymmetric waves in the model is not enough to cause double ITCZ, and the lateral extent of equatorial waves does not play an important role in determining the width of the ITCZ but rather the latter may influence the former.

Numerical Investigation on the Strain Evolution of Ti-6Al-4V Alloy during Multi-directional Forging at Elevated Temperatures

2018 ◽  
Vol 37 (6) ◽  
pp. 571-580 ◽  
Author(s):  
Chenkan Yan ◽  
Jun Shen ◽  
Peng Lin
Keyword(s):  
Friction Coefficient ◽  
Large Scale ◽  
Elevated Temperatures ◽  
Effective Strain ◽  
Element Model ◽  
Strain Evolution ◽  
Compression Strain ◽  
Individual Strain ◽  
Metal Materials ◽  
The Difference

AbstractMulti-directional forging (MDF) is one of the most promising severe plastic deformation (SPD) methods used in fabricating large-scale bulk metal materials with ultra-fine grains (UFG). A finite element model for MDF is developed to investigate the strain evolution of Ti-6Al-4V alloy subjected to MDF. Results show that the billet subjected to MDF can be divided into four individual strain zones in terms of the equivalence of effective strain evolution, and that the strain increment in each individual strain zone varies from pass to pass. The deviation between the maximum and the minimum strain increases with the increase of passes and friction coefficient. The effective strain linearly decreases from the core to the exterior of the billet in all three directions after the MDF process. With the increase of the passes and friction coefficient, the gradient of the effective strain in the billet increases in all three directions due to the difference of deformability in different individual strain zones. For the definite friction coefficient, the average and maximum effective strains are in proportion to the accumulative compression strain.

scholarly journals Multi-scale snowdrift-permitting modelling of mountain snowpack

2021 ◽  
Vol 15 (2) ◽  
pp. 743-769
Author(s):  
Vincent Vionnet ◽  
Christopher B. Marsh ◽  
Brian Menounos ◽  
Simon Gascoin ◽  
Nicholas E. Wayand ◽  
...  
Keyword(s):  
High Resolution ◽  
Snow Depth ◽  
Large Scale ◽  
Small Scale ◽  
Topographic Effects ◽  
Prediction System ◽  
Wind Fields ◽  
Multi Scale ◽  
Temporal And Spatial ◽  
Snow Transport

Abstract. The interaction of mountain terrain with meteorological processes causes substantial temporal and spatial variability in snow accumulation and ablation. Processes impacted by complex terrain include large-scale orographic enhancement of snowfall, small-scale processes such as gravitational and wind-induced transport of snow, and variability in the radiative balance such as through terrain shadowing. In this study, a multi-scale modelling approach is proposed to simulate the temporal and spatial evolution of high-mountain snowpacks. The multi-scale approach combines atmospheric data from a numerical weather prediction system at the kilometre scale with process-based downscaling techniques to drive the Canadian Hydrological Model (CHM) at spatial resolutions allowing for explicit snow redistribution modelling. CHM permits a variable spatial resolution by using the efficient terrain representation by unstructured triangular meshes. The model simulates processes such as radiation shadowing and irradiance to slopes, blowing-snow transport (saltation and suspension) and sublimation, avalanching, forest canopy interception and sublimation, and snowpack melt. Short-term, kilometre-scale atmospheric forecasts from Environment and Climate Change Canada's Global Environmental Multiscale Model through its High Resolution Deterministic Prediction System (HRDPS) drive CHM and are downscaled to the unstructured mesh scale. In particular, a new wind-downscaling strategy uses pre-computed wind fields from a mass-conserving wind model at 50 m resolution to perturb the mesoscale HRDPS wind and to account for the influence of topographic features on wind direction and speed. HRDPS-CHM was applied to simulate snow conditions down to 50 m resolution during winter 2017/2018 in a domain around the Kananaskis Valley (∼1000 km2) in the Canadian Rockies. Simulations were evaluated using high-resolution airborne light detection and ranging (lidar) snow depth data and snow persistence indexes derived from remotely sensed imagery. Results included model falsifications and showed that both wind-induced and gravitational snow redistribution need to be simulated to capture the snowpack variability and the evolution of snow depth and persistence with elevation across the region. Accumulation of windblown snow on leeward slopes and associated snow cover persistence were underestimated in a CHM simulation driven by wind fields that did not capture lee-side flow recirculation and associated wind speed decreases. A terrain-based metric helped to identify these lee-side areas and improved the wind field and the associated snow redistribution. An overestimation of snow redistribution from windward to leeward slopes and subsequent avalanching was still found. The results of this study highlight the need for further improvements of snowdrift-permitting models for large-scale applications, in particular the representation of subgrid topographic effects on snow transport.

An Improved Mass Consistent Model for Three-Dimensional Wind Field Construction

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Xiuling Wang ◽  
Yanlei Liu ◽  
Bin Chen ◽  
Darrell Pepper
Keyword(s):  
Three Dimensional ◽  
Element Model ◽  
Wind Fields ◽  
Irregular Terrain ◽  
Consistent Model ◽  
Digital Elevation ◽  
Terrain Following ◽  
Elevation Data ◽  
Digital Elevation Data ◽  
Improved Model

An improved diagnostic mass-consistent finite element model (FEM) has been developed to construct 3D wind fields over irregular terrain. Instead of using constant Gauss precision moduli over the whole domain in the existing mass-consistent models, the improved mass-consistent model adopts different Gauss precision moduli based on the terrain topography gradient associated with atmospheric boundary conditions. These terrain sensitive moduli resolve wind flows over large topographical obstacles more accurately than constant Gauss precision moduli. In this study, a terrain following mesh generator is developed based on digital elevation data from the U.S. Geological Survey, and the data linked to the modified mass-consistent FEM model. The improved model is validated and verified using a benchmark study for flow over a semicylinder. The model is then used to re-examine 3D wind fields previously simulated for the Nellis Dunes area near Las Vegas, NV. Results show that the improved mass consistent modeling system shows better agreement with the recorded meteorological tower data than the previous results obtained using constant moduli.

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