Use Of Mesoscale Models Research Articles

Bridging length scales from micro to mesoscale through rate-dependent traction-separation law predictions

Mesoscale models are useful for modeling dynamic impact on fiber reinforced polymer composites . Mesoscale damage can be modeled using cohesive zones , but determining the governing traction-separation laws is a challenge. We developed finite element models with a stochastic fiber-matrix microstructure embedded within a larger mesoscale continuum to study transverse tension and shear loading of unidirectional S-glass/epoxy composite. We included rate-dependent matrix constitutive behavior and failure and rate-dependent fiber-matrix interface debonding, which are important microscale damage mechanisms that comprise mesoscale fracture. With these multiscale models , we simulated mode I and II crack initiation and propagation. We determined mesoscale, mode I and II, rate-dependent cohesive laws from the models using a domain J-integral approach to calculate the fracture energy as a function of crack opening displacement. We explored the effects of loading rate, matrix failure strain, and fiber-matrix interface debonding properties on the traction laws and crack morphologies. Finally, consistent bridging between length scales is demonstrated by comparing energy dissipation of microstructurally-resolved fracture to mesoscale continuum cohesive zone fracture. This work provides a methodology for determining rate-dependent traction-separation laws, derived from accurate micro-mechanics and experimental input, for bridging lengths scales and use in mesoscale models to evaluate ballistic performance of composites.

Sensitivity Analysis of the WRF Model: Wind-Resource Assessment for Complex Terrain

AbstractWind energy requires accurate forecasts for adequate integration into the electric grid system. In addition, global atmospheric models are not able to simulate local winds in complex terrain, where wind farms are sometimes placed. For this reason, the use of mesoscale models is vital for estimating wind speed at wind turbine hub height. In this regard, the Weather Research and Forecasting (WRF) Model allows a user to apply different initial and boundary conditions as well as physical parameterizations. In this research, a sensitivity analysis of several physical schemes and initial and boundary conditions was performed for the Alaiz mountain range in the northern Iberian Peninsula, where several wind farms are located. Model performance was evaluated under various atmospheric stabilities and wind speeds. For validation purposes, a mast with anemometers installed at 40, 78, 90, and 118 m above ground level was used. The results indicate that performance of the Global Forecast System analysis and European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) as initial and boundary conditions was similar, although each performed better under certain meteorological conditions. With regard to physical schemes, there is no single combination of parameterizations that performs best during all weather conditions. Nevertheless, some combinations have been identified as inefficient, and therefore their use is discouraged. As a result, the validation of an ensemble prediction system composed of the best 12 deterministic simulations shows the most accurate results, obtaining relative errors in wind speed forecasts that are <15%.

Analysis and numerical simulation of an aircraft icing episode near Adolfo Suárez Madrid-Barajas International Airport

Aircraft icing is one of the most dangerous weather phenomena in aviation security. Therefore, avoiding areas with high probability of icing episodes along arrival and departure routes to airports is strongly recommended. Although such icing is common, forecasting and observation are far from perfect. This paper presents an analysis of an aircraft icing and turbulence event including a commercial flight near the Guadarrama Mountains, during the aircraft approach to the airport. No reference to icing or turbulence was made in the pre-flight meteorological information provided to the pilot, highlighting the need for additional tools to predict such risks. For this reason, the icing episode is simulated by means of the Weather Research and Forecasting (WRF) model and analyzed using images from the Meteosat Second Generation (MSG) satellite, with the aim of providing tools for the detection of icing and turbulence in the airport vicinity.The WRF simulation shows alternating updrafts and downdrafts (>2ms−1) on the lee side of the mountain barrier. This is consonant with moderate to strong turbulence experienced by the aircraft on its approach path to the airport and suggests clear air turbulence above the mountain wave cloud top. At the aircraft icing altitude, supercooled liquid water associated with orographic clouds and mountain waves is simulated. Daytime and nighttime MSG images corroborated the simulated mountain waves and associated supercooled liquid water. The results encourage the use of mesoscale models and MSG nowcasting information to minimize aviation risks associated with such meteorological phenomena.

Ab initio modelling of the early stages of precipitation in Al-6000 alloys

Age hardening induced by the formation of (semi)-coherent precipitate phases is crucial for the processing and final properties of the widely used Al-6000 alloys. Early stages of precipitation are particularly important from the fundamental and technological side, but are still far from being fully understood. Here, an analysis of the energetics of nanometric precipitates of the meta-stable β″ phases is performed, identifying the bulk, elastic strain and interface energies that contribute to the stability of a nucleating cluster. Results show that needle-shape precipitates are unstable to growth even at the smallest size β″ formula unit, i.e. there is no energy barrier to growth. The small differences between different compositions points toward the need for the study of possible precipitate/matrix interface reconstruction. A classical semi-quantitative nucleation theory approach including elastic strain energy captures the trends in precipitate energy versus size and composition. This validates the use of mesoscale models to assess stability and interactions of precipitates. Studies of smaller 3D clusters also show stability relative to the solid solution state, indicating that the early stages of precipitation may be diffusion-limited. Overall, these results demonstrate the important interplay among composition-dependent bulk, interface, and elastic strain energies in determining nanoscale precipitate stability and growth.

Exploration of the impact of nearby sources on urban atmospheric inversions using large eddy simulation

The Indianapolis Flux Experiment (INFLUX) aims to quantify and improve the effectiveness of inferring greenhouse gas (GHG) source strengths from downstream concentration measurements in urban environments. Mesoscale models such as the Weather Research and Forecasting (WRF) model can provide realistic depictions of planetary boundary layer (PBL) structure and flow fields at horizontal grid lengths (Δx) down to a few km. Nevertheless, a number of potential sources of error exist in the use of mesoscale models for urban inversions, including accurate representation of the dispersion of GHGs by turbulence close to a point source. Here we evaluate the predictive skill of a 1-km chemistry-adapted WRF (WRF-Chem) simulation of daytime CO2 transport from an Indianapolis power plant for a single INFLUX case (28 September 2013). We compare the simulated plume release on domains at different resolutions, as well as on a domain run in large eddy simulation (LES) mode, enabling us to study the impact of both spatial resolution and parameterization of PBL turbulence on the transport of CO2. Sensitivity tests demonstrate that much of the difference between 1-km mesoscale and 111-m LES plumes, including substantially lower maximum concentrations in the mesoscale simulation, is due to the different horizontal resolutions. However, resolution is insufficient to account for the slower rate of ascent of the LES plume with downwind distance, which results in much higher surface concentrations for the LES plume in the near-field but a near absence of tracer aloft. Physics sensitivity experiments and theoretical analytical models demonstrate that this effect is an inherent problem with the parameterization of turbulent transport in the mesoscale PBL scheme. A simple transformation is proposed that may be applied to mesoscale model concentration footprints to correct for their near-field biases. Implications for longer-term source inversion are discussed.

Meteorología mesoescalar en Marte

The revitalizing of Mars exploration in the early 1990s combined with the maturation of terrestrial mesoscale modeling codes provided fertile ground for the application of suitably modified models to the atmosphere of Mars. The use of mesoscale models, particular for Mars, has become an integral part of interpreting the data returned from missions and providing constraints and bounds on environmental conditions in support of mission planning and operations. Mesoscale models are ideal tools for greatly minimize risk during entry, descent, and landing phases. Slope winds, dust injection processes and atmospheric volatiles transport are the main Mars mesoscale circulations that affect the atmospheric structure and dynamics. In this article is also included as an example the meteorological simulation of Gale Crater environment, in which the Mars Science Laboratory (MSL) Rover Curiosity landed in August 2012, with the spanish weather station Rover Environmental Monitoring Station (REMS) aboard. The observational data record provides sufficient means against which to evaluate mesoscale model. Meteorological interpretations show a dynamically complex environment. Local, regional and synoptic scales all interact in nonlinear ways to produce the observed weather. Two different atmospheric periods could be distinguished inside the crater: semi-isolated period during most of the martian year (Ls 0, 90 and 180) and mixing period during the summer (Ls 270). During the semi-isolated period, warm air from south overrides the crater creating a very stable boundary layer. Crater air mass is generally much colder than outside the crater forcing downslope flows, thermodynamically driven, to not scour crater and hence decreasing mixing level in this period. Ls 270 was shown to be an anomalous season when air within and outside the crater was well mixed by strong, flushing, northerly flow and large amplitude breaking mountain waves. At other seasons, the air in the crater was more isolated form the surrounding environment.

Validação da assimilação de dados na inferência da refletividade de um radar com o sistema MM5

Em certas ocasiões o Estado do Rio Grande do Sul é assolado por sistemas meteorológico com manifestações atmosféricas atípicas e que se enquadram entre os fenômenos de mesoescala. A impossibilidade dos modelos globais simularem adequadamente diversos efeitos localizados, que ocorrem nas mais variadas regiões do globo, associada ao rápido aumento dos recursos computacionais, vem facilitando e induzindo, cada vez mais, o emprego de modelos de mesoescala para melhorar os conhecimentos sobre eventos anômalos e severos e até mesmo para utilização como ferramenta operacional em alguns centros de previsão do tempo. Para se avaliar a destreza de um modelo de mesoescala em prover previsões de precipitação, em escala espacial e temporal compatível com àquelas de um radar meteorológico Doppler, é implantado todo o sistema de modelagem de mesoescala, que constitui o MM5 na exploração da ocorrência de um evento relativamente severo de precipitação, ocorrido na região próxima da cidade de Canguçu/RS, no dia 11 de janeiro de 2008. O evento foi arbitrariamente selecionado para avaliação do modelo em inferir a refletividade do radar meteorológico instalado na cidade de Canguçu/RS, processando-se com e sem a assimilação de dados convencionais; bem como para abordar a análise da situação termo-hidrodinâmica e sinótica.

Multiscale Modelling of Plastic Deformation of Polycrystals: Implementation of Texture-Based Anisotropy in Engineering Applications (FE Codes for Forming, Prediction of Forming Limit Curves)

Finite element models for metal forming are used to design and optimise industrial forming processes. The limit strain in sheet metal forming can be predicted for monotonic loading or strain paths with changes. Models like these should be as accurate as possible in order to be useful, and hence take the texture, microstructure and substructure (dislocation patterns) into account. To achieve this, a hierarchical type of modelling is proposed in order to maintain the balance between calculation speed (required for engineering applications) and accuracy. In that case, FE models to be used at the engineering length scale work with an analytical constitutive model, the parameters of which are identified using results of multilevel models (meso-scale with an homogenisation procedure). The analytical model to be used at macro-scale will be discussed, as well as the identifications procedure. The later make use of meso-scale models. Finally an example will be given (formability of a sheet material).

A parameterization of wave stress in the planetary boundary layer for use in mesoscale models

Abstract A parameterization of gravity wave stress generated by subgrid-scale topography is described and tested in a one-dimensional version of the Advanced Regional Prediction System (ARPS) model. It is argued that in the planetary boundary layer (PBL) where wave reflections occur, the so-called WKB method for evaluating wave stress may not be applicable. Gravity waves launched by a subgrid-scale Gaussian ridge are calculated on line using a linear wave model. The total flow is constrained to be convectively stable by using a terrain-height adjustment to decrease wave amplitudes and thereby prevent wave overturning. In this method when the waves grow large enough to overturn, the wave amplitudes are decreased by decreasing the maximum height of the terrain obstacle, H. At each time step, the ARPS model flow is modified by the divergence of the wave stress. The effects of wave-stress divergence on turbulence parameterization is examined using three turbulence closure schemes, K-theory with constant eddy diffusivity, the Smagorinsky closure, and the turbulence-kinetic energy closure. Also, the effects of vertical grid spacing are tested using spacings of 10, 20, 50 and 100 m . The model is initialized with a hyperbolic-tangent wind profile and constant Brunt–Vaisala frequency. It is shown that wave-stress divergence can lead to elevated layers of turbulence and diffusion where they would not occur in the absence of the wave-stress parameterization. It is also shown that if the vertical grid spacing is too great, then the effects of wave breaking are not fully realized.

A Shallow-Convection Parameterization for Mesoscale Models. Part I: Submodel Description and Preliminary Applications

Abstract A shallow-convection parameterization suitable for both marine and continental regimes is developed for use in mesoscale models. The scheme is closely associated with boundary layer turbulence processes and can transition to either a deep-convection scheme in conditionally unstable environments or to an explicit (resolved scale) moisture scheme in moist stable environments. The shallow-convection mass-closure assumption uses a hybrid formulation based on boundary layer turbulent kinetic energy (TKE) and convective available potential energy (CAPE), while the convective trigger is primarily a function of boundary layer TKE. Secondary subgrid clouds having nearly neutral buoyancy can form as shallow-convective updrafts detrain mass to their environment. Called neutrally buoyant clouds (NBCs), these can be dissipated through lateral and vertical mixing, light precipitation, ice-crystal settling, and cloud-top entrainment instability (CTEI). The shallow-convection scheme is developed and demonstrated...

Evaluation of model‐simulated upper troposphere humidity using 6.7 μm satellite observations

Use of mesoscale models to simulate details of upper tropospheric relative humidity (UTRH) fields represents an important step toward understanding the evolution of small‐scale water vapor structures that are responsible for cirrus growth and dissipation. Because mesoscale model UTRH simulations require initialization and verification and since radiosonde measurements of relative humidity are unreliable in the upper troposphere, we use GOES 6.7 μm water vapor observations to validate the Pennsylvania State University/National Center for Atmospheric Research nonhydrostatic mesoscale model (MM5) simulations of UTRH. To accomplish this task, MM5 temperature and moisture profiles are used in a forward calculation of the clear‐sky 6.7 μm brightness temperature (T6.7), which is converted into UTRH. A statistical analysis is done to evaluate MM5 simulations of T6.7 and UTRH against the GOES 7 observations. For the simulations, an average correlation coefficient of 0.80 was found with a dry bias of 1.6 K. In terms of UTRH, the average correlation coefficient was 0.65 with a dry bias of 3.3%. We also found that MM5 fails to simulate accurately extrema in the UTRH field.

The effect of cloud cover on surface net radiation: Simple formulae for use in mesoscale models

The effect of cloud cover on surface net radiation is parameterised into simple formulae, which have been fitted to calculated results from a detailed radiation model for various single-layer cloud types. The detailed model uses cloud optical depth information from satellite data analysis as input. The formulae use functional forms based on some of those reported in the literature. The proposed formulae have been shown to compare well to results from the detailed model for various combinations of cloud at different height levels in the atmosphere. By analysis of optical depth variations throughout the world, the proposed formulae have been shown to be valid for any location, except perhaps near the poles.

The Representation of Convection in Mesoscale Models. Part I: Scheme Fabrication and Calibration

Abstract Currently, there is no adequate cumulus parameterization suitable for use in mesoscale models having horizontal resolutions between 5 and 50 kilometers. Based on the similarity of the temporal and spatial evolution of the vertical variances between a CCOPE supercell and a generic tropical squall line as explicitly simulated by the Regional Atmospheric Modeling System developed at Colorado State University, a convective parameterization scheme is developed that represents microscale turbulence with a modified second-order closure scheme and cumulus draft-scale eddies with a convective adjustment scheme. The microscale turbulence scheme is based upon the Mellor and Yamada 2.5-level closure modified to predict solely on w′ w′ and includes Zeman and Lumley's formulation for the buoyancy-driven mixed layer to close the pressure term and the eddy transport term. If deep convection is indicated, the microscale turbulence scheme includes contributions from cumulus draft-scale fluxes determined from a clo...

Mesoscale models and their application to air quality studies

The use of mesoscale models in conjunction with air quality models enables better prediction of pollution transport and dispersion in the atmosphere. The accuracy of the prediction depends upon the physical processes included in the models, on the mathematical representation, and on the initial meteorological and other external data. In most situations large power plants are located near the coast or in hilly terrain. Under these situations the meteorological fields which are relevant to air quality studies change tremendously with time and space (both vertically and horizontally). So far most of the air quality studies and consequently the decisions regarding sitting and management of power plants in coastal or hilly sites are made according to simple Gaussian models which are based on limited observational data, and, therefore, are of doubtful meanings. To obtain better prediction of pollutant concentration dense meteorological observations have to be made. Since such observations are very expensive, it is unrealistic to require them. A reliable mesoscal model, however, can supply the necessary meteorological fields with relatively little expenses with any needed resolution, providing that appropriate computers are available. Model results can be very useful in prediction of maximum concentration that can be expected from routine simultaneous release from several sources during critical weather conditions. Since the late seventies, with the huge development of large computers, it has been made possible also to carry out three-dimensional simulations. Lately with the development of advanced microcomputers and appropriate software it is even possible to perform two- and even three-dimensional experiments on such computers within a reasonable time frame.

The use of mesoscale models on air-pollution studies in industrial installations

This paper discusses the combined use of a mesoscale numerical model and a Lagrangian particle dispersion model in order to derive useful conclusions on the possible environmental impacts in the area around the site of a new industrial installation or in larger areas. This procedure is recommended for cases with complicated flow patterns over irregular terrain or for areas near coastlines. In such cases the dispersion and transport of pollutants could not be achieved with the classical Gaussian models because they are not able to handle important local features accurately. Local circulations such as sea-land breezes or slope flows can influence the dispersion and transport of pollutants in different ways. The results presented in this paper are part of a detailed study for the possible environmental impacts in the Eastern Corinthian Gulf in Greece where an alumina plant will be built. Experimental data, a synoptic classification scheme, and model simulations will help to take all the appropriate measurements during the design of the plant in order to minimize the environmental impacts during its operation.

Mesoscale atmospheric modeling

This review summarizes the current status of the numerical modeling of mesoscale atmospheric phenomena. The numerical characteristics of these limited-area models are discussed, with special emphasis given to those aspects of the modeling problem that are unique to the mesoscale, such as the lateral boundary conditions and specialized parameterizations of mesoscale physical processes. The problem of defining the initial conditions for mesoscale models is emphasized because the lack of complete data sets on this scale makes the process difficult. Objective analysis and both static and dynamic initialization procedures are considered, with special attention given to the implications of the irregular availability of the data in both time and space. The predictability of mesoscale phenomena using models is discussed because the effects of the lateral boundary conditions of the limited-area domains, the often-strong local forcing, and other factors cause the problem to be distinct from the large scale. These factors are discussed, as well as the way the model's predictive skill compares with the skill derived from the use of simple extrapolation techniques. Four representative examples are provided that illustrate recent applications of mesoscale models to a variety of metereological situations. A simulation of thermally forced flow in vicinity of a complex coastline with nearby high topographic elevations is summarized first. In another study, a mesoscale model is used to investigate the influence of islands with elevated terrain on the propagation of tropical cyclones. Two other investigations that are summarized used mesoscale models with real data to simulate a mesoscale convective system and a maritime cyclone. These four investigations served to enhance our understanding of the physical processes as well as the mesoscale modeling techniques required for production of adequate forecasts. This assessment of the current state of mesoscale atmospheric modeling represents a modestly optimistic view of the future. New data sources and computing hardware will allow accelerated progress in removing some of the obstacles to productive operational use of mesoscale models. However, continuing research will be needed in critical areas such as the parameterization of the important physical processes.