Mesoscale Interactions Research Articles

Constitutive response of calcium‐silicate‐hydrate layers under combined loading

AbstractCalcium‐silicate‐hydrate (C‐S‐H) is the main hydration product for ordinary Portland cement (OPC) materials that exhibits a layered structure containing interfaces that controls the system response to shear deformation at the nanometer scale. In this work, we used molecular statics simulations to study the mechanical behavior of an atomistic model of C‐S‐H under combined loading conditions that are typical of structural applications of these materials. Combined loading is implemented by first compressing or stretching the atomistic structure to impose an external hydrostatic pressure, and then loading the system through both heterogeneous and homogeneous shear deformation. By utilizing two different shear methodologies, we were able to isolate the interface behavior from the bulk response. Our results show several qualitative similarities with that of macroscale cementitious materials including pressure sensitivity of the maximum shear strength and strength asymmetry in compression and tension. This indicates that the well‐known cohesive‐frictional behavior of cementitious materials is fundamental to interfaces between C‐S‐H grains at the nanoscale. Comparing differences in our results with nanoindentation experiments motivate future investigations of the effect of C‐S‐H particle size and morphology on strength scaling properties at the mesoscale. These mesoscale model interactions should include the normal‐stress or pressure dependency that we observe.

The response of future projections of the North American monsoon when combining dynamical downscaling and bias correction of CCSM4 output

A 20-km regional climate model (RCM) dynamically downscaled the Community Climate System Model version 4 (CCSM4) to compare 32-year historical and future “end-of-the-century” climatologies of the North American Monsoon (NAM). CCSM4 and other phase 5 Coupled Model Intercomparison Project models have indicated a delayed NAM and overall general drying trend. Here, we test the suggested mechanism for this drier NAM where increasing atmospheric static stability and reduced early-season evapotranspiration under global warming will limit early-season convection and compress the mature-season of the NAM. Through our higher resolution RCM, we found the role of accelerated evaporation under a warmer climate is likely understated in coarse resolution models such as CCSM4. Improving the representation of mesoscale interactions associated with the Gulf of California and surrounding topography produced additional surface evaporation, which overwhelmed the convection-suppressing effects of a warmer troposphere. Furthermore, the improved land–sea temperature gradient helped drive stronger southerly winds and greater moisture transport. Finally, we addressed limitations from inherent CCSM4 biases through a form of mean bias correction, which resulted in a more accurate seasonality of the atmospheric thermodynamic profile. After bias correction, greater surface evaporation from average peak GoC SSTs of 32 °C compared to 29 °C from the original CCSM4 led to roughly 50 % larger changes to low-level moist static energy compared to that produced by the downscaled original CCSM4. The increasing destabilization of the NAM environment produced onset dates that were one to 2 weeks earlier in the core of the NAM and northern extent, respectively. Furthermore, a significantly more vigorous NAM signal was produced after bias correction, with >50 mm month−1 increases to the June–September precipitation found along east and west coasts of Mexico and into parts of Texas. A shift towards more extreme daily precipitation was found in both downscaled climatologies, with the bias-corrected climatology containing a much more apparent and extreme shift.

Multi‐scale analysis of acoustic emission signals in dense‐phase pneumatic conveying of pulverized coal at high pressure

Acoustic emission technique in conjunction with multiscale processing method has been utilized to investigate the flow behavior of the dense‐phase pneumatic conveying system at high pressure. A clearly defined classification of microscale, mesoscale, and macroscale signals has been put forward with the aid of wavelet transform and V statistics analysis. The detailed signals d1–d4, d5–d7, d8–d10 were recomposed into the microscale, mesoscale, and macroscale signals, respectively, which represent microscale particle‐wall interactions, mesoscale interaction between gas phase and solid phase (such as bubbles, plugs, dunes), and macroscale flow‐induced pipe vibration. Further analysis shows that as the mass flow rate of pulverized coal increases, the energy fraction (energy of detailed signal divided by the energy of original signal) of microscale signals decreases while that of mesoscale signals increases, which indicates that particles are more likely to move as particle aggregates than individual particles when mass flow rate increases. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2635–2648, 2016

Dissipative Particle Dynamics interaction parameters from ab initio calculations

Dissipative Particle Dynamics (DPD) is a commonly employed coarse-grained method to model complex systems. Presented here is a pragmatic approach to connect atomic-scale information to the meso-scale interactions defined between the DPD particles or beads. Specifically, electronic structure calculations were utilized for the calculation of the DPD pair-wise interaction parameters. An implicit treatment of the electrostatic interactions for charged beads is introduced. The method is successfully applied to derive the parameters for a hydrated perfluorosulfonic acid ionomer with absorbed vanadium cations.

Underfill flow simulation based on lattice Boltzmann method

Underfill process is carried out mainly to prevent interconnection failures caused by the mismatch of CTE between the die and the substrate in flip chip encapsulation. Owing to troubles in calculating the capillary force, i.e., result-based and interface reconstruction, the underfill flow cannot be well characterized by current simulation methods. In this paper, we present a mesoscale underfill simulation method based on three-dimensional LBM (lattice Boltzmann method) with D3Q19 velocity set and LBGK (lattice-Bhatnagar–Gross–Krook) evolution model. In this method, the GIPM (generalized interparticle-potential model) is first proposed to model the capillary flow, which can solve the fluid–fluid interaction and the solid–fluid interaction in a unified manner. A geometric model for underfill simulation is then developed. The solid wall is divided into three parts, i.e., the substrate, the die and the solder bump, and each part is allowed to have a different wettability by assigning a mesoscale interaction parameter. For verification purpose, three underfill cases, which are different in wall wettability, are examined. In each case, besides the experimental results, we also present numerical results predicted by a VOF multiphase method with CSF capillary model. The results show that the proposed method has a good performance in the underfill simulation.

Observation- and numerical-analysis-based dynamics of the Uttarkashi cloudburst

Abstract. A Himalayan cloudburst event, which occurred on 3 August 2012 in the Uttarkashi (30.73° N, 78.45° E) region of Uttarakhand, India, was analyzed. The near-surface atmospheric variables were analyzed to study the formation, evolution, and triggering mechanisms of this cloudburst. In order to improve upon the understanding provided by the observations, numerical simulations were performed using the Weather Research and Forecasting (WRF) model, configured with a single domain at 18 km resolution. The model was tuned using variation of different parameterizations (convective, microphysical, boundary layer, radiation, and land surface), and different model options (number of vertical levels, and spin-up time), which resulted in a combination of parameters and options that best reproduced the observed diurnal characteristics of the near-surface atmospheric variables. Our study demonstrates the ability of WRF in forecasting precipitation, and resolving synoptic-scale and mesoscale interactions. In order to better understand the cloudburst, we configured WRF with multiply nested two-way-interacting domains (18, 6, 2 km) centered on the location of interest, and simulated the event with the best configuration derived earlier. The results indicate that two mesoscale convective systems originating from Madhya Pradesh and Tibet interacted over Uttarkashi and, under orographic uplifting and in the presence of favorable moisture condition, resulted in this cloudburst event.

Two-scale models of polycrystals: Independence of the loading process image of a representative macrovolume

The paper considers variants of constructing the process image introduced by A.A. Ilyushin for loading of a representative macrovolume of polycrystalline metal with high displacement gradients. Analysis is performed to clarify whether the loading process image in the variants under study depends on the rigid rotation imposed on the entire representative volume (or on the choice of a reference frame). It is found that with high displacement gradients, the loading process image is rather difficult to construct. Possible ways of decomposing the motion into quasi-rigid and strain-induced motions are investigated. The behavior of the representative macrovolume is described using a two-scale model based on the physical theory of elasto-viscoplasticity. The motion of rigid coordinate systems descriptive of quasi-rigid motion is defined by a specific hypothesis of motion decomposition on the macro-scale. The hypotheses under consideration are the following: (i) the whole motion of the representative volume is strain-induced motion; (ii) the motion is decomposed into strain-induced motion and quasi-rigid motion whose spin is determined by averaging mesoscale spins calculated from a certain general lattice rotation model; and (iii) the quasi-rigid and strain-induced motions are defined respectively by the antisymmetric and symmetric parts of the macroscale displacement velocity gradient. It is shown that with the first hypothesis, the loading process image depends on the rigid rotation imposed on the representative volume as a whole; with the other two hypotheses, the process image does not depend on the choice of the reference frame. At the same time, the third hypothesis makes it impossible to determine the lattice rotations independently of macroscale kinematic relations which, in fact, are determined by micro- and mesoscale physical interactions.

Land Surface Heterogeneity Signature in Tornado Climatology? An Illustrative Analysis over Indiana, 1950–2012*

Abstract Land surface heterogeneity affects mesoscale interactions, including the evolution of severe convection. However, its contribution to tornadogenesis is not well known. Indiana is selected as an example to present an assessment of documented tornadoes and land surface heterogeneity to better understand the spatial distribution of tornadoes. This assessment is developed using a GIS framework taking data from 1950 to 2012 and investigates the following topics: temporal analysis, effect of ENSO, antecedent rainfall linkages, population density, land use/land cover, and topography, placing them in the context of land surface heterogeneity. Spatial analysis of tornado touchdown locations reveals several spatial relationships with regard to cities, population density, land-use classification, and topography. A total of 61% of F0–F5 tornadoes and 43% of F0–F5 tornadoes in Indiana have touched down within 1 km of urban land use and land area classified as forest, respectively, suggesting the possible role of land-use surface roughness on tornado occurrences. The correlation of tornado touchdown points to population density suggests a moderate to strong relationship. A temporal analysis of tornado days shows favored time of day, months, seasons, and active tornado years. Tornado days for 1950–2012 are compared to antecedent rainfall and ENSO phases, which both show no discernible relationship with the average number of annual tornado days. Analysis of tornado touchdowns and topography does not indicate any strong relationship between tornado touchdowns and elevation. Results suggest a possible signature of land surface heterogeneity—particularly that around urban and forested land cover—in tornado climatology.

Crop Wind Energy Experiment (CWEX): Observations of Surface-Layer, Boundary Layer, and Mesoscale Interactions with a Wind Farm

Perturbations of mean and turbulent wind characteristics by large wind turbines modify fluxes between the vegetated surface and the lower boundary layer. While simulations have suggested that wind farms could significantly change surface fluxes of heat, momentum, momentum, moisture, and CO2 over hundreds of square kilometers, little observational evidence exists to test these predictions. Quantifying the influences of the “turbine layer” is necessary to quantify how surface fluxes are modified and to better forecast energy production by a wind farm. Changes in fluxes are particularly important in regions of intensely managed agriculture where crop growth and yield are highly dependent on subtle changes in moisture, heat, and CO2. Furthermore, speculations abound about the possible mesoscale consequences of boundary layer changes that are produced by wind farms. To address the lack of observations to answer these questions, we developed the Crop Wind Energy Experiment (CWEX) as a multiagency, multiuniversity field program in central Iowa. Throughout the summer of 2010, surface fluxes were documented within a wind farm test site and a 2-week deployment of a vertically pointing lidar quantified wind profiles. In 2011, we expanded measurements at the site by deploying six flux stations and two wind-profiling lidars to document turbine wakes. The results provide valuable insights into the exchanges over a surface that has been modified by wind turbines and a basis for a more comprehensive measurement program planned for the summer in 2014.

Coarse-Graining Approach to Infer Mesoscale Interaction Potentials from Atomistic Interactions for Aggregating Systems

A coarse-graining (CG) approach is developed to infer mesoscale interaction potentials in aggregating systems, resulting in an improved potential of mean force for Langevin dynamics (LD) and Browni...

CWEX: Crop/Wind-energy EXperiment: Observations of surface-layer, boundary-layer and mesoscale interactions with a wind farm

CWEX: Crop/Wind-energy EXperiment: Observations of surface-layer, boundary-layer and mesoscale interactions with a wind farm

Multiscale models for synoptic–mesoscale interactions in the ocean

Multiscale analysis is used to derive two sets of coupled models, each based on the same distinguished limit, to represent the interaction of the midlatitude oceanic synoptic scale—where coherent features such as jets and rings form—and the mesoscale, defined by the internal deformation scale. The synoptic scale and mesoscale overlap at low and mid latitudes, and are hence synonymous in much of the oceanographic literature; at higher latitudes the synoptic scale can be an order of magnitude larger than the deformation scale, which motivates our asymptotic approach and our nonstandard terminology. In the first model the synoptic dynamics are described by ‘Large Amplitude Geostrophic’ (LAG) equations while the eddy dynamics are quasigeostrophic. This model has order one isopycnal variation on the synoptic scale; the synoptic dynamics respond to an eddy momentum flux while the eddy dynamics respond to the baroclinically unstable synoptic density gradient. The second model assumes small isopycnal variation on the synoptic scale, but allows for a planetary scale background density gradient that may be fixed or evolved on a slower time scale. Here the large-scale equations are just the barotropic quasigeostrophic equations, and the mesoscale is modeled by the baroclinic quasigeostrophic equations. The synoptic dynamics now respond to both eddy momentum and buoyancy fluxes, but the small-scale eddy dynamics are simply advected by the synoptic-scale flow—there is no baroclinic production term in the eddy equations. The energy budget is closed by deriving an equation for the slow evolution of the eddy energy, which ensures that energy gained or lost by the synoptic-scale flow is reflected in a corresponding loss or gain by the eddies. This latter model, aided by the eddy energy equation—a key result of this paper—provides a conceptual basis through which to understand the classic baroclinic turbulence cycle.

Mesoscale bio-physical interactions between the Agulhas Current and the Agulhas Bank, South Africa

The Agulhas Current on the east coast of South Africa is a major western boundary current that exchanges heat and salt between the Indian and South Atlantic Oceans. The current retroflects as it deflects away from the African continent at the southern tip of the Agulhas Bank, a biologically productive extension of the continental shelf south of the South African coast. The less energetic Benguela Current borders the Agulhas Bank to the west. Little is known about mesoscale interactions between the Agulhas Current and the shelf waters of the Agulhas Bank or how these processes influence the biology of the bank. In this study, physical and biological data collected during a dedicated cruise in September 2010 allowed the identification of several mesoscale features that indicate a strong effect of the current on the bank, including a Natal Pulse that forced the Agulhas Current onto the Agulhas Bank. While on the bank itself, the current entrained particles that were then transported offshore. We also found evidence of upwelling on the southeast edge of the Agulhas Bank, which is thought to be a source of water for a cold ridge that characterizes the eastern region of the bank. Large fluctuations of the thermocline, consistent with internal waves, were observed inshore of the Agulhas Current, with high phytoplankton concentrations at their crests. We suggest that this is a physical effect, with doming of the waves concentrating plankton at their crests, thereby creating episodic biological hotspots.

Storms, shoreface morphodynamics, sand supply, and the accretion and erosion of coastal dune barriers in the southern North Sea

The coast of the southern North Sea is bound by dune barriers that have developed adjacent to a shallow storm- and tide-dominated shoreface comprising numerous shore-parallel to sub-shore-parallel tidal sand banks. The banks evolve under the joint control of tide-, wave- and wind-induced shore-parallel currents, which tend to ‘stretch’ them, eventually leading to bank division, and to shoaling and breaking storm waves, which tend to drive them ashore. The banks, thus, modulate the delivery of storm wave energy to the coast, redirect currents alongshore and are the sand sources for the accretion of coastal dunes. Foredune accretion occurs where major sand banks have migrated shoreward over the last centuries to be finally driven ashore and weld under the impact of storm waves. Morphological changes in the bank field can impact on shoreline stability through dissipation or enhanced shoreward transmission of storm wave energy and effects on radiation stress, particularly when waves are breaking over the banks. Where banks are close to the shore, mitigation of offshore sediment transport, especially during storms, can occur because of gradients in radiation stress generated by the complex 3D bank structure. These macro-scale mechanisms involve embedded meso-scale interactions that revolve around the mobility of sand waves, mobility of beach bars and troughs and foredune mobility, and micro-scale processes of bedform mobility in the subaqueous and intertidal domains, and of swash and aeolian beach–dune sand transport. These embedded interactions and the morphodynamic feedback loops illustrate the importance of synchroneity of sand transport from shoreface to dune on this coast.Large stretches of the foredunes show either signs of stability, or mild but chronic erosion. Furthermore, a demonstrated lack of a clear relationship occurs between storminess and coastal response over the second half of the 20th century. The present situation may be indicative of conditions of rather limited sand supply from offshore, notwithstanding the abundance of sand on the nearby shallow shoreface, except in areas where a nearshore storm-driven tidal sand bank has become shore-attached. Apart from the important influence of shoreface sand banks and of wave–bank interactions, foredune accretion and erosion also depend on various context controls that include individual storm characteristics, wind speed and incidence relative to the shore, tidal stage during storms, and direct human intervention on the shore through foredune and beach management. The bewildering variability inherent in these intricately related parameters may also explain the poor relationship between storminess and barrier shoreline change and will still continue to render unpredictable the response of shores to individual storms.

Radar Analysis on the Interaction between Southwesterly Monsoonal Flow and Circulation Associated with Typhoon Morakot (2009)

This study investigates the mesoscale interaction of typhoon circulation and southwesterly flow during the passage of Typhoon Morakot (2009) over Taiwan using radar observations. Single Doppler radar analysis characterized typhoon features with remarkably distant rainbands, and identified the strong southwesterly monsoonal flow with a maximum speed of more than 45 m s-1 in the southern flank of distant rainbands. Dual-Doppler synthesized winds elucidated a confluent mechanism on the northern side of the rainbands with a maximum convergence over 1.5 × 10-3 s-1. Velocity azimuth display (VAD) winds showed the intensification of southwesterly flow at low levels. The southwesterly monsoonal flow initiated about 6 hrs before typhoon landfall, and then became prominently involved with typhoon circulation. Also, the radial component with respect to the typhoon center was enhanced and became comparable with the tangential one (～30 m s-1) about 7.5 hrs after landfall. The variation in intensity of radial components can be regarded as a unique precursor for the extension of influence of the southwesterly monsoonal flow onto the typhoon circulation. Furthermore, the strong convergence showed that the interaction between the southwesterly flow and typhoon circulation might contribute to the development of rainbands, as well as the intensification of the inward radial flow embedded within typhoon.

Implementation and evaluation of aerosol and cloud microphysics in a regional climate model

[1] A new aerosol modeling framework is presented within the regional climate model COSMO-CLM. The model accounts for the microphysical interactions of internally and externally mixed aerosol particles. Sulfate, black carbon, particulate organic matter, sea salt, and mineral dust are considered. The model is applied over Europe at a horizontal resolution of 50 km. The lateral boundary conditions are given by the ERA-Interim reanalysis for the meteorological fields and by a global ECHAM5-HAM simulation for the aerosols. Present-day AeroCom emissions are used for the evaluation period from 1997 to 2003. The model largely reproduces the annual mean pattern of the aerosol optical depth derived from satellite data over Europe (model and observed domain mean is 0.17, but it is 0.37 with standard model version). The annual cycle is overestimated in COSMO-CLM in some regions due to strong dust transport across the Mediterranean in late spring. Day-to-day variability in aerosol optical depth and the Angstrom exponent is also captured by the model. The corresponding correlations of the daily mean time series between measurements from AERONET stations and the model range from 0.17 to 0.74. In comparison with the standard model version, which does not account for aerosol transport and indirect aerosol effects and uses an outdated aerosol climatology, the mid-European summer cold bias disappears with the new framework. The new framework allows studies of mesoscale interactions between aerosols, clouds, precipitation, and radiation on climatological time scales due to the advanced physical representation of the underlying processes.

Mesoscale Simulation of Tropical Cyclones in the South Pacific: Climatology and Interannual Variability

Abstract The Weather Research and Forecast model at ⅓° resolution is used to simulate the statistics of tropical cyclone (TC) activity in the present climate of the South Pacific. In addition to the large-scale conditions, the model is shown to reproduce a wide range of mesoscale convective systems. Tropical cyclones grow from the most intense of these systems formed along the South Pacific convergence zone (SPCZ) and sometimes develop into hurricanes. The three-dimensional structure of simulated tropical cyclones is in excellent agreement with dropsondes and satellite observations. The mean seasonal and spatial distributions of TC genesis and occurrence are also in good agreement with the Joint Typhoon Warning Center (JTWC) data. It is noted, however, that the spatial pattern of TC activity is shifted to the northeast because of a similar bias in the environmental forcing. Over the whole genesis area, 8.2 ± 3.5 cyclones are produced seasonally in the model, compared with 6.6 ± 3.0 in the JTWC data. Part of the interannual variability is associated with El Niño–Southern Oscillation (ENSO). ENSO-driven displacement of the SPCZ position produces a dipole pattern of correlation and results in a weaker correlation when the opposing correlations of the dipole are amalgamated over the entire South Pacific region. As a result, environmentally forced variability at the regional scale is relatively weak, that is, of comparable order to stochastic variability (±1.7 cyclones yr−1), which is estimated from a 10-yr climatological simulation. Stochastic variability appears essentially related to mesoscale interactions, which also affect TC tracks and the resulting occurrence.

Derecho and MCS Development, Evolution, and Multiscale Interactions during 3–5 July 2003

Abstract From 3 to 5 July 2003 during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX), multiple mesoscale convective systems (MCSs 1 and 2) and derechos (derechos AN, AS, A, BW, and BE) progressed across a preferred upper Midwest corridor. The derechos evolved in a favorable synoptic-scale environment. However, the environmental details associated with each derecho, such as the characteristics of the initial surface boundary, the formation position relative to the upper-level jet stream, the presence of an upper-level mesoscale disturbance, and the CAPE/shear environment varied from derecho to derecho. The MCSs and derechos composed three distinct convective episodes. Multiple mesoscale interactions between the MCSs and derechos and the environment altered the character and longevity of these episodes. The first convective episode consisted of derecho A, which formed from merging derechos AN and AS (northern and southern systems, respectively). The ∼200-hPa-deep cold pool associated with derecho A decreased surface potential temperatures by 4–8 K. MCS 1 dissipated upon entering this cold pool and an inertia–gravity wave was emitted that helped to spawn MCS 2. This inertia–gravity wave connected MCSs 1 and 2 into a compound convective episode. As derecho BW (western system) approached a strong surface boundary across Iowa created by the cold pools of derecho A and MCS 1, derecho BE (eastern system) formed. The remnants of derecho BW merged with derecho BE creating another compound convective episode. The upscale effects resulting from this active convective period directly affected subsequent convective development. Upper-level diabatic heating associated with derecho A resulted in NCEP GFS 66-h negative 1000–500-hPa thickness errors of 4–8 dam (forecast too cold) and negative 200-hPa wind errors of 10–20 m s−1 (forecast too weak). The resulting stronger than forecast 200-hPa jet stream likely increased synoptic-scale forcing for the formation and evolution of derecho BW.

Mesoscale air-sea interaction during the passage of a typhoon over the Yellow and East China Seas

In order to best capture the mutual forcing and feedback process to improve the accuracy of modeling of the mesoscale process, we developed the two-way coupling model MCM (Mesoscale Coupled Model) based on two independent models, the atmospheric model MM5v3 and the ocean model ECOM-si, using a flux coupler designed with the concurrent process communication technique. We selected Typhoon Winnie (9711) passing over the Yellow and East China Seas (YECS) to test the performance of the coupling model, and analyzed the quantitative impacts on atmospheric and oceanic variations. The results show that the simulated air-sea heat and momentum exchanges strongly affect circulation in both the atmosphere and the ocean. When mesoscale air-sea interaction is considered, the results for the atmosphere and ocean improved considerably. In terms of atmosphere, the air-sea interaction updates the distribution of elements (e.g., wind, heat flux, relative humidity and temperature) in the vertical and horizontal fields. The forecast result of typhoon intensity becomes more realistic, with decreases in central pressure error of 3.4 hPa at 30 hr and 9 hPa at 60 hr. A strong wind drives the cyclonic ocean current in the upper layer and induces horizontal transport and vertical mixing. All of these processes directly influence the Sea Surface Temperature (SST), which decreases over a large area, particularly near the typhoon center, and can reach 5°C. Finally, we discuss a possible negative feedback mechanism.

Salt-induced lipid transfer between colloidal supported lipid bilayers

We show that a coordinated interplay between mesoscale colloidal interactions and molecular-scale membrane perturbations affords a novel material platform to controllably recapitulate membrane interactions, such as during fusion and vesicle-based drug delivery. Specifically, a simple modulation of ionic strength is used to alter electrostatically determined colloidal interactions, producing conditions for pre-fusion contact between two independent colloidal and/or planar supported lipid bilayers. The same process also perturbs the membrane at the molecular level, reproducing conditions needed for subsequent fusion steps. We envisage that this platform will yield insights relevant to optimal design and implementation of lipid-coated inorganic constructs used for therapeutic drug delivery and sensing.