Mesoscale Numerical Model Research Articles

Implementation and calibration of a mesoscale model for amorphous plasticity based on shear transformation dynamics

A mesoscale numerical model based on shear transformation zone (STZ) theory is implemented in a commercial finite element software. The model is designed to predict the (visco)plastic deformation response of amorphous solids at the nano- and microscale. The theoretical framework relies on earlier models developed by Bulatov and Argon (1994a) and of Homer and Schuh (2009). We justify the potential of the computational model by conducting reference calculations for model metallic and polymeric glasses in plane strain compression. Emphasis is placed on the effect of time and space discretisation on the predicted macroscopic response. The dependence of the predicted yield strength upon the values of the fundamental model parameters is analysed via a mean-field approximation. The mean-field approximation is validated based on a series of simulations in model parameter space. We provide guidelines for a straightforward but consistent parameter identification method via the mean-field approximation while starting from experimental data.

A multi-stage mesoscopic numerical approach to simulate the flexural behavior of concrete beams with corroded rebars

Corrosion is the main factor affecting the service performance of reinforced concrete (RC) structures, especially in offshore or coastal areas. In this paper, taking RC beam as the research object, a three-dimensional meso-scale numerical model involving rebar corrosion was established. The corrosion effects on the mechanical behavior of RC beam was explored through a multi-stage analysis method (namely, corrosion induced expansion stage and structural deterioration stage). The non-uniform radial displacement was applied to concrete around the steel to simulate the expansion of rebar corrosion. The cracking process and the damage pattern of concrete caused by corrosion can be obtained. Then, taking this state as the initial condition, the mechanical analysis of corroded RC beam was carried out. The agreement between the numerical and the test results validates the rationality and correctness of the multi-stage analysis model. According to the simulation results, the concrete damage due to corrosion is mainly concentrated in the diagonal of reinforcement and the middle of adjacent reinforcement. The rust expansion pressure increases gradually when the corrosion level increased. For severely corroded beams, the concrete strain no longer conforms to the plane section assumption. In addition, corrosion reduces the bearing capacity and ductility of the beams. The coupling effects of corrosion of tensile and compression bars on the performance of the beam are more serious than that of only corrosion of tensile bars. Based on the data regression, a relationship to evaluate the bearing capacity of beams was established. It indicates that the flexural bearing capacity decreases by about 1.4%, 1.7% annually in the conditions of tensile reinforcement corroded only and both tensile and compressive reinforcement corroded.

Effects of concrete heterogeneity on FRP-concrete bond behaviour: Experimental and mesoscale numerical studies

Extensive experimental and numerical studies have been conducted to understand the bond behaviour of FRP-concrete interfaces with the assumption of homogenous materials. This study is aimed at a better understanding of the effects of concrete heterogeneity on the FRP-concrete bond behaviour, by a combination of experiments and mesoscale numerical modelling. FRP-concrete and FRP-mortar bonded joints were tested using a four-point bending setup. The crack initiation and propagation process with interfacial debonding until failure was accurately captured by the digital image correlation (DIC) technique. The results show that the presence of coarse aggregates in the FRP-concrete joints leads to 19% higher bond strength, but much higher variations in the bond strength and the strain distribution across the width of FRP sheets, than the FRP-mortar joints. Monte Carlo simulations of mesoscale finite element models with random distribution of polygonal aggregates were then carried out for the FRP-concrete bond tests. It is found that the distribution of coarse aggregates significantly affects the overall force–deflection responses as well as the simulated fracture processes and final failure modes that are highly comparable with the DIC observations.

Numerical analysis of the mechanical behavior of the impact-damaged RC beams strengthened with CFRP

In many places, the concrete structures suffered from impacted-damage need to be repaired. Herein, a 3-D numerical meso-scale model was established to study the mechanical behavior of the CFRP strengthened impact-damaged RC beams under 4-point loading. The strain rate effect of the strength of both of the concrete and the steel bars and the Young’s modulus of the concrete were taken into account during the impact process. In the next strengthening process, the anisotropic behavior of the CFRP was considered as well. Furthermore, the bond-slip behavior of the longitudinal bars was simulated in this model. The effectivity of the numerical model in simulating the impact behavior of concrete members and the behavior of FRP strengthened damaged RC beam was validated against experiments. Four types of strengthening schemes were designed and then compared in terms of the failure mode, failure process, strain distribution, and three mechanical indexes. It is found that the approach that strengthening the damaged beam only with the bottom FRP sheet should be avoid in practice because of the shear failure of the concrete in the shear span. Interestingly, though the loading capacity of the damaged beam gets the most significant increase by the strengthening with the U-shaped sheet, the scheme is not suggested due to its inferior ductility resulting from the failure on the FRP at the bending-shear section. Furthermore, the influence of the number of the strengthening layer on the mechanical performance of the damaged beams was discussed as well. It is found that the bearing capacity is enhanced with the increase of the strengthening layer while the ductility and the energy dissipation of the specimen decrease at the same time. In present work, four layers of bottom sheet plus average spaced U-strips in shear span is recommended to strengthen the impacted damaged RC beams.

Meso-scale Numerical Modeling of Uni-directional Composite Panel Under Ballistic Impact

Meso-scale Numerical Modeling of Uni-directional Composite Panel Under Ballistic Impact

Bond-slip behavior between concrete and deformed rebar at elevated temperature: Mesoscale simulation and formulation

Fire accidents will cause deterioration of the mechanical properties of steel and concrete, which will affect the bond-slip behavior of the interface between steel and concrete. In this work, in order to further understand the relationship between bonding performance of reinforced concrete and temperature, a central pull-out test by the three-dimensional (3D) mesoscale numerical model was established. The surface shape of deformed rebar and the heterogeneity of concrete were considered in the model. The effectiveness of the mesoscale model was verified against with the available test results. Moreover, the bond failure mechanism between deformed rebar and concrete was discussed. Subsequently, the influence of thickness to diameter ratio, elevated temperature and cooling down on the bonding behavior was discussed using the mesoscale numerical model. The results show that the failure mode and the bond stress-slip curve of the specimen are obviously related to the ratio of thickness to diameter. The bond strength, slip and bond stress-slip curve of the specimen at high temperature are significantly different from those after cooling down according to the experimental and numerical results. The influence of temperature on bond strength is greater than that on slip. Finally, on the basis of the existing theoretical model of bonding behavior at room temperature, a calculation method that can predict the bond stress-slip curve at elevated constant temperature is proposed. The calculation results are compared with the simulation and test results to illustrate the validity of the prediction formula.

Improving the compressive performance of foam concrete with ceramsite: Experimental and meso-scale numerical investigation

As a new composite material by adding ceramsite into foam concrete, lightweight aggregate foam concrete (LWAFC), mainly composed of cement, water, performed foam, and ceramsite, exhibits excellent compressive performance. To facilitate its application in structure protection where energy absorption is concerned, the responses of ceramsite foam concrete were investigated experimentally and numerically with meso-scale model. First, a compression test (loading rate of 5 mm/min) on cubic LWAFC specimens with side length of 100 mm was conducted, in which two different failure modes, namely foam concrete failure and through-ceramsite failure, were observed. Meanwhile, it was found that the compressive strength of LWAFC specimens increased with increasing foam concrete density. Based on synchrotron radiation CT on foam concrete, a two-dimensional meso-scale numerical model with size of 100 × 100 mm was established. The failure mode, compressive strength, plateau stress, and energy absorption capacity of the LWAFC with an averaged loading rate of 1 m/s were systematically investigated. In particular, the underlying mechanism for the two distinctive failure modes was revealed as the strength match between the foam concrete and ceramsite. Subsequently, the performance of LWAFC was significantly improved by reasonably designing the foam concrete and ceramsite with optimized strength match.

Meso-scale modeling of concrete cracking induced by 3D corrosion expansion of helical strands

A meso-scale numerical model is established to simulate concrete cracking induced by the three-dimensional (3D) corrosion expansion of helical strands in the present study. A 3D corrosion expansion model is proposed to consider the longitudinal helix shape and transverse flower-like shape of the strand. The concrete in the model is considered as a three-phase composite material consisting of a mortar matrix, aggregate, and interfacial transition zones (ITZ) between the mortar matrix and aggregate. The rationality of the proposed model is validated, and the effects of the space helix structure and the lay length of the strand on corrosion-induced cracking are discussed. The results indicate that considering the space helix structure of a strand can effectively improve the prediction accuracy of strand corrosion-induced concrete cracking. The change in strand lay length has little effect on the critical corrosion loss of the initial damage occurrence. The critical corrosion loss at cover cracking increases with increasing strand lay length, whereas the corrosion-induced crack width decreases with increasing strand lay length.

Assessing the Risks of Vessel Icing and Aviation Hazards during Downslope Windstorms in the Russian Arctic

Downslope windstorms are known sources of hazardous weather, such as severe gusty winds, rapid temperature changes, ship icing, strong turbulence and others, posing a great danger to people and infrastructure. This paper investigates the risks of ship icing and aviation hazards (rapid changes in the angle of attack and gust load factor) during downslope windstorms in five regions in the Russian Arctic based on observational data, reanalysis, and mesoscale numerical modeling. The highest frequency of ship icing was found during downslope windstorms downstream from Svalbard and Novaya Zemlya. Icing is rare during Tiksi and Wrangel Island downslope windstorms due to almost permanent sea ice cover during the cold season, while icing is absent during very warm Pevek downslope windstorm even in the ice-free conditions. Conditions for heavy icing are rather frequent (up to 5% of cases in winter) during Novaya Zemlya downslope windstorms and less frequent (up to 0.5% in spring) during Svalbard windstorm. The presence of downslope windstorms in those regions causes an increase in the maximum icing rate by about 2 times. Strong aviation turbulence hazardous for light aircraft is typical for all considered regions with downslope windstorms; it is observed mainly at an altitude of 1 to 4 km above the surface. Hazardous turbulence for jet aircraft like Boeing 737 on its cruising flight levels was found on Svalbard and in Tiksi region in 10–15% of cases during strong downslope windstorms.

Modelling of atmospheric optical turbulence with the Weather Research and Forecasting model at the Ali observatory, Tibet

ABSTRACT In this study, we make use of a meso-scale numerical model to obtain the parameters of atmospheric optical turbulence at the Ali observatory above the Tibetan Plateau. These parameters are essential for ground-based optical observations and some adaptive optics techniques. We present the characterization of the vertical distributions of atmospheric optical turbulence Cn2 and the main integral parameters, such as coherence time τ0, isoplanatic angle θ0 and seeing ε0 derived from Cn2. Meanwhile, the measurement of Cn2 obtained with a radiosonde instrument is used to quantify the model performance on reconstructing the optical turbulence above the site. This shows a high level of agreement and provides a reliable tool for astronomical site testing. The results presented in this paper demonstrate the good behaviour of the atmospheric optical turbulence condition at Ali, particularly during the summer half of the year. We find yearly median values of seeing ε0 = 0.47 arcsec, isoplanatic angle θ0 = 4.35 arcsec and atmospheric coherence time τ0 = 5.52 ms in 2016, and we also provide independent confirmation of the potential of the Ali site in adaptive optics. Moreover, it has been proven that meso-scale models can provide reliable estimations of atmospheric optical turbulence conditions above an astronomical site on the Tibetan Plateau.

Comparison of rainfall microphysics characteristics derived by numerical weather prediction modelling and dual‐frequency precipitation radar

AbstractThe understanding of large‐scale rainfall microphysical characteristics plays a significant role in meteorology, hydrology and natural hazards managements. Traditional instruments for estimating raindrop size distribution (DSD), including disdrometers and ground dual‐polarization radars, are available only in limited areas. However, the development of space‐based radars and mesoscale numerical weather prediction models would allow for DSD estimation on a large scale. This study investigated the performance of the weather research and forecasting (WRF) model and the global precipitation measurement mission (GPM) dual‐frequency precipitation radar for DSD retrieval under different conditions. The DSD parameters (Dm and Nw), rain rate (R), rainfall kinetic energy (KE) and radar reflectivity (Z) were estimated in Chilbolton, United Kingdom, by using long‐term disdrometer observations for validation. The rainfall kinetic energy–rain rate (KE–R) and radar reflectivity–rain rate (Z–R) relationships were explored using a disdrometer, the WRF model and GPM. It was found that the DSD parameter distribution trends of the three approaches are similar although the WRF model has larger Dm and smaller Nw values. In terms of the rainfall microphysical relationship, GPM performs better when both Ku‐ and Ka‐band precipitation radars (KuPR and KaPR) observe precipitation simultaneously (R > 0.5 mm h−1), while the WRF model shows high accuracy in light rain (R < 0.5 mm h−1). The fusion of GPM and WRF model is recommended for the improved understanding of rainfall microphysical characteristics in ungauged areas.

Farm to farm wake interaction in WRF: impact on power production

This work focuses on the study of interactions between neighboring wind farms through a mesoscale numerical modelling approach. High resolution simulations with three wind farm parameterizations (WFP, EWP and IAWFP), implemented on the WRF model, over a set of “real world” neighboring onshore wind farms are performed. The sensitivity of the three parameterizations to wake development is analyzed. The older version of the WFP is also included to account for differences between versions in terms of wake length and intensity, and TKE production and advection. Finally, the impacts of upstream wind farms are studied through a series of simulations where they are “disabled” and the increases in power at downstream farms are quantified. These results and the adopted methodology have direct application and are highly relevant for the feasibility assessment of new wind farms in the shadow of other existing ones.

Applying urban climate model in prediction mode\u2014evaluation of MUKLIMO_3 model performance for Austrian cities based on the summer period of 2019

Extreme heat events are natural hazards affecting many regions of the world. This study uses an example of the six largest cities in Austria to demonstrate the potential of urban climate model simulations applied in prediction mode providing detailed information on thermal conditions. For this purpose, the urban climate model MUKLIMO_3 of the German Meteorological Service (DWD) coupled with the hydrostatic numerical weather prediction model, ALARO, is used to simulate the development of the urban heat island (UHI) in Austrian cities for the summer period of 2019 with a horizontal resolution of 100 m. In addition to the evaluation of UHI predicting skills, other relevant variables, such as humidity and wind characteristics on hourly basis, are also analysed in this paper. Model evaluation confirmed that the MUKLIMO_3 microscale model had the capacity to simulate the main thermal spatiotemporal patterns in urban areas; however, a strong dependence on the input data from the mesoscale model was found. Our results showed large benefit in prediction of maximum air temperatures in urban areas, while the relative humidity predictions of MUKLIMO_3 appear to be much less plausible and show large variety of model prediction skills. Urban climate model simulations using real atmospheric conditions can facilitate better quantification and understanding of day-to-day intra-urban variations in microclimate as well as provide a basis for evaluation of the microclimate prediction skills of mesoscale numerical models with urban extensions.

The Potential Impact of Assimilating Synthetic Microwave Radiances Onboard a Future Geostationary Satellite on the Prediction of Typhoon Lekima Using the WRF Model

Geostationary meteorological satellites can provide continuous observations of high-impact weather events with a high temporal and spatial resolution. Sounding the atmosphere using a microwave instrument onboard a geostationary satellite has aroused great study interests for years, as it would increase the observational efficiency as well as provide a new perspective in the microwave spectrum to the measuring capability for the current observational system. In this study, the capability of assimilating future geostationary microwave sounder (GEOMS) radiances was developed in the Weather Research and Forecasting (WRF) model’s data assimilation (WRFDA) system. To investigate if these frequently updated and widely distributed microwave radiances would be beneficial for typhoon prediction, observational system simulation experiments (OSSEs) using synthetic microwave radiances were conducted using the mesoscale numerical model WRF and the advanced hybrid ensemble–variational data assimilation method for the Lekima typhoon that occurred in early August 2019. The results show that general positive forecast impacts were achieved in the OSSEs due to the assimilation of GEOMS radiances: errors of analyses and forecasts in terms of wind, humidity, and temperature were both reduced after assimilating GEOMS radiances when verified against ERA-5 data. The track and intensity predictions of Lekima were also improved before 68 h compared to the best track data in this study. In addition, rainfall forecast improvements were also found due to the assimilation impact of GEOMS radiances. In general, microwave observations from geostationary satellites provide the possibility of frequently assimilating wide-ranging microwave information into a regional model in a finer resolution, which can potentially help improve numerical weather prediction (NWP).

Persistent Increases in Nighttime Heat Stress From Urban Expansion Despite Heat Island Mitigation

AbstractUrban areas generally have higher near‐surface air temperature and lower air humidity than rural areas. Little is known about how heat stress, the combined effect of high air temperature and high humidity on human physiology, will be affected by future urban land expansion. Here we use a mesoscale numerical weather prediction model to examine the effects of urban land expansion from 2000 to 2050 on heat stress (measured as wet‐bulb globe temperature, WBGT) in the urban areas of China, India, and Nigeria, which are projected to account for one‐third of global urban population growth through 2050. Our results show that urban expansion slightly reduces heat stress during the day (∼0.2°C) but substantially intensifies it at night, by ∼1°C on average and by up to 2–3°C in five mega‐urban regions (MURs). These effects exist with or without climate change induced by rising concentrations of greenhouse gases (GHGs). Installing cool roofs—an urban heat island mitigation measures—can reduce the daytime WBGT by 0.5–1°C, partially offsetting the heat stress conditions caused by GHG‐induced climate change. However, even with cool roofs, the nighttime WBGTs are higher by 0.3–0.9°C over the whole countries studied, and by 1–2°C in the MURs under the urban expansion scenario, compared to the situation in which urban areas remain unchanged. These results show that future urban expansion and heat island mitigation can result in potential daytime benefits but also persistent nighttime risks.

Mesoscale Prediction in the Antarctic Using Cycled Ensemble Data Assimilation

AbstractDue in part to sparse conventional observation coverage in the Antarctic region, atmospheric studies in this part of the globe often rely more heavily on numerical models. Model representation of atmospheric processes in the Antarctic remains inferior to representation in the Northern Hemisphere midlatitudes. Poor representation may be related to inaccurate model analyses that do not optimally utilize the limited observation network. Here, the ensemble Kalman filter (EnKF) data assimilation (DA) technique is employed in lieu of variational DA techniques to investigate impacts on model analysis accuracy. This DA technique [provided by the Data Assimilation Research Testbed (DART)] is coupled with a polar-modified, mesoscale numerical model that together compose Antarctic-DART (A-DART). A-DART is cycled with DA and run over a 1-month period, assimilating only conventional observations. Results show relatively good agreement between A-DART and observations. Comparison with radiosonde temperature and geostationary satellite wind observations shows large differences between RMSE and ensemble spread in the upper troposphere. The analysis increment shows large values in the eastern Atlantic–western Indian Oceans associated with geostationary satellite wind observations. Further evaluation determines that geostationary satellite wind observations may be biased in this region. Overall, this baseline demonstration of ensemble-based modeling applied in the Antarctic produced short-term forecasts that were competitive with two operational modeling systems while assimilating on the O(106) fewer observations. A-DART is capable of assimilating additional observations for a variety of applications. This study highlights the capability of applying this ensemble-based DA technique for process and forecast studies in an observation-sparse region.

A Simulated Radar Reflectivity Calculation Method in Numerical Weather Prediction Models

AbstractThe simulated radar reflectivity used by current mesoscale numerical weather prediction models can reflect the grid precipitation but cannot reflect the subgrid precipitation generated by a cumulus parameterization scheme. To solve this problem, this study developed a new simulated radar reflectivity calculation method to obtain the new radar reflectivity corresponding to the subgrid-scale and grid-scale precipitation based on the mesoscale Global/Regional Assimilation and Prediction System (GRAPES) model of the China Meteorological Administration. Based on this new method, two 15-day forecast experiments were carried out for two different time periods (11–25 April 2019 and 1–15 August 2019), and the radar reflectivity products obtained by the new method and previous method were compared. The results show that the radar reflectivity obtained by the new simulated radar reflectivity calculation method gives a clear indication of the subgrid-scale precipitation in the model. Verification results show that the threat scores of the improved experiments are better than those of the control experiments in general and that the reliability of the simulated radar reflectivity for the indication of precipitation is improved. It is concluded that the new simulated radar reflectivity calculation method is effective and significantly improves the reflectivity products. This method has good prospects for providing more information about forecasting precipitation and convective activity in operational models.

Three-dimensional meso-scale modelling of failure of steel fiber reinforced concrete at room and elevated temperatures

Steel fiber reinforced concrete (SFRC) is composed of coarse aggregate particles, mortar matrix, fibers, pores and microcracks from the viewpoint of meso-scale. To reflect the mesoscopic characteristics more realistically, a three-dimensional meso-scale model for SFRC was established. In the model, the fibers were explicitly modelled while the concrete matrix was regarded as a tri-phase composite consisting of aggregate, mortar matrix and the interface transition zones (ITZs) between them. Based on the idea of classical random aggregate model for plain concrete, a programme was designed to randomly distribute aggregate particles and steel fibers. The meso-scale numerical model was verified by the good agreement between simulation results and the available test results. The dynamic failure behavior of SFRC at room and elevated temperatures was investigated by utilizing the simulation method. The simulation results indicate that for fiber content no larger than 2% volume, the influence of steel fiber on thermal conduction of SFRC can be ignored. Compared with that of plain concrete, strain rate effect on compressive strength of SFRC is weaker and it would be further decreased under high temperatures. The improvement of SFRC performance induced by steel fiber increases for higher fiber volume fraction whilst decreases with respect to strain rates, regardless of temperature. When the fiber amount is identical, the dynamic compressive strength of SFRC decreases slightly in the case of larger fiber diameter or smaller fiber length.

Honeycomb core failure mechanism of CFRP/Nomex sandwich panel under multi-angle impact of hail ice

The rudder of an airplane is fabricated as a sandwich panel and can potentially be damaged by hail ice. The dynamic responses of a CFRP/Nomex sandwich panel with barely any visible core damage under multi-angle impact of an ice sphere at various velocities are researched experimentally and by using numerical simulations at the mesoscale. The results show that the honeycomb core represents three types of failure modes: wrinkling, fracture of cell walls, and debonding of cell walls at the interface of two-glued-paper-walls (TGPW) due to resin failure. These failure modes exist at specific impact velocities and angles. This paper proposes a mesoscale numerical modeling method of a honeycomb structure to represent the debonding failure at the TGPW interface. In addition, the mechanical properties of these failures are revealed, as the wrinkling of the cell walls are caused by buckling and the fracture of the cell walls and debonding of the TGPW interface are caused by out-plane and in-plane shearing of cell walls. The results showed that the relationship between the denting and impact kinetic energy under multi-angle impact is linear with respect to the impact angle. The effects of impact angles on the contacting forces on a rigid wall and sandwich panel are presented as the amount of peak impact forces affected by the target material type. However, the intensity of the peak impact forces is rarely affected by the type of the target material. The peak impact force of nonvertical impact is greater than that of the normal impact when the normal components of the impact velocities are the same. This is because the impact angle affects the distribution of ice scatter fragments during the impact, and this generates different pressure distributions on the face sheet of the panel.

Numerical analysis of axial compressive behavior of RC short columns subjected to non-uniform fire: A meso-scale study

The bearing capacity and durability of reinforced concrete (RC) structures can be affected by fire. In this study, a three-dimensional (3D) meso-scale simulation model for RC short column subjected to axial compression after exposure to fire was established. The degradation effect of mechanical properties of steel bars and concrete materials after high temperature was taken into account. The bond-slip behavior between longitudinal steel bars and concrete was also considered in the model. Based on the present simulation method, the failure mode and failure mechanism of the RC short columns were investigated. Moreover, the effects of fire scenario and fire duration on the axial compression performance of RC short columns were further investigated. It is found that the meso-scale numerical model can effectively simulate the mechanical behavior of RC short columns under axial load. Moreover, with the increase of fired surfaces and fire duration, the peak bearing capacity, axial compression stiffness and ductility decrease. The mechanical properties of short columns decrease more quickly under non-uniform fire. By comparing the theoretical value with the numerical simulation value of Nut/Nu, it is found that the theoretical value is conservative.