Dissipation Stage Research Articles

Fog scavenging of particulate matters in air pollution events: Observation and simulation in the Yangtze River Delta, China

Stable atmospheric boundary layer is conducive to the accumulation of atmospheric pollution and the occurrence of fog, and fog has a removal effect on air pollution. In this study, we use the observation and WRF-Chem (Weather Research and Forecasting Model with Chemistry) simulation to analyze the factors affecting the removal efficiency in a continuous fog and haze episode from November 26 to 28, 2018 in Jiangsu Province, such as fog thickness and duration. The results show that the WRF-Chem simulation well reproduces the boundary layer characteristics in the stages of fog formation, development and dissipation. The atmospheric boundary layer provides favorable conditions for the maintenance of fog and air pollution. The inversion layer, with the maximum intensity of 3 °C per 100 m, creates favorable thermal conditions, and the water vapor advection is also conducive to the fog maintenance. The ground observation verifies the wet scavenging of PM2.5 during dense fog events. The scavenging effect is related to the fog duration, and the correlation is positive when the fog is just formed and negative when the fog is dissipating. The PM2.5 concentration decreases from 159 μg m−3 to 38 μg m−3 after the fog lasts for 11 h. The fog has a remarkable scavenging effect on PM2.5 in the vertical direction, due to the deposition effect of fog droplets on the pollutant particles. The PM2.5 concentration on the ground is lower than the vertical average in the fog area, and the scavenging effects during the dense fog periods on November 27 and 28 are 47.7 μg m−3 and 36.1 μg m−3, respectively. The fog duration is mostly concentrated in 3–17 h. When the duration of fog is 4–8 h, the scavenging effect on PM2.5 reaches the strongest, with an average PM2.5 concentration decrease of >70 μg m−3.

Moisture Source for the Precipitation of Tropical Cyclones over the Pacific Ocean through a Lagrangian Approach

Abstract Tropical cyclones (TCs) are an important component of the hydrological cycle at tropical latitudes. In this study, we investigated the origin of precipitation associated with TCs formed from 1980 to 2018 over the Pacific Ocean in three subbasins: the western North Pacific Ocean (WNP), central and east Pacific Ocean (NEPAC), and South Pacific Ocean (SPO) basins. The analysis was performed throughout the TC lifetime during genesis, when they reached the lifetime maximum intensity (LMI), and the dissipation stage. The backward trajectories of all precipitant atmospheric parcels residing over the TC locations from the global outputs of the Lagrangian Flexible Particle (FLEXPART) dispersion model fed by the ERA-Interim dataset were used to identify moisture sources. The South and East China Seas and the western tropical North Pacific Ocean were identified as the principal moisture sources in the WNP basin, while the atmospheric moisture that precipitated mainly came from the eastern tropical North and South Pacific Ocean in the NEPAC basin, followed by the Caribbean Sea. Meanwhile, the Coral Sea, western tropical South Pacific Ocean, and northern Australia are the origins of the moisture in the SPO. The mean moisture uptake per TC was higher during the hurricane category than during any other stage in each basin.

Discrete-continuous coupling simulation and analysis for asphalt pavement dynamic stress responses under a moving wheel load

Asphalt pavement stress responses are analyzed with the layered elastic system under static loads in the most popularly-used design specifications. In reality, however, traffic loads are moving and the pavement layer materials are mainly aggregated. In order to reasonably consider vehicular loads and layer material features, this paper presents a discrete-continuous coupling model for analyzing asphalt pavement dynamic stress responses under moving loads. The numerical model is divided into an asphalt pavement structure and a moving wheel load. Specifically, the wheel load and the asphalt layer under its load were modelled with the discrete element method to simulate the actual vehicle loads and meso-scopic components of the asphalt mixture. In contrast, the remaining parts of the pavement structure were modelled with the finite difference method. The wheel load was set to move on the surface layer of asphalt pavement at a constant speed as the numerical simulation was conducted. The results were analyzed based on special points of dynamic stress curves. The results showed that: different from the static stress responses, in a typical asphalt pavement dynamic stress curve, there existed three stages of stress responses, namely the stress smoothing stage, stress surge stage, and stress dissipation stage, which had significant fluctuations at high levels and asymmetry. Besides, the loading velocity and mixture meso-structure significantly influenced on the dynamic stress responses of asphalt pavement. Especially the average peak stress calculated by the discrete-continuous coupling model, which considered the mixture meso-structure decreased by 10% compared to the finite-difference model.

Numerical investigation of solitary wave breaking over a slope based on multi-phase smoothed particle hydrodynamics

This study presents a numerical investigation of the solitary wave breaking over a slope by using the multi-phase smoothed particle hydrodynamics (SPH) method. Four different computational models are proposed to solve the gas-related far-field boundary conditions, and the model with the least disturbance to the internal flow field is selected. Since the artificial viscous coefficient can greatly affect the wave-breaking location, an empirical equation is fitted to quickly determine the optimal value of the artificial viscous coefficient. In addition, the turbulence model and three-dimensional effect on the wave breaking are discussed in this study. The results show that the present two-dimensional multi-phase SPH without a turbulence model can capture the macroscopic characteristics of the flow before the vortices convert to three dimensional flow structures caused by the wave breaking. Then, the processes of shoaling solitary wave breaking with different slopes and relative wave heights are simulated. Compared with the single-phase SPH, the multi-phase SPH is of great help in improving the prediction of wave breaking. A vortex similar to the Rankine Vortex is observed near the wave crest. Its intensity affects the pressure distribution of the gas, and its relative position to the wave crest is relevant to the energy transfer from the water to the gas. During the solitary wave propagating from deep water to shallow water, energy dissipation of gas and water shows four different stages. In the stage of energy dissipation, the gas can absorb the great energy from the water, which effectively dissipates the wave energy.

Comparative analyses of the effects of divergent winds on the kinetic energy budget with the adoptions of two methods during the extratropical transition of Typhoon Rumbia (1818)

Modification of the divergent wind components and domain of interests can result in obvious changes in the kinetic energy (KE) budget of typhoons and other synoptic systems. Before analyzing the effects of divergent winds on the KE budget of Typhoon Rumbia (2018) during its entire life cycle, especially in its extratropical transition (ET) process, a hybrid integral method to partition the horizontal wind fields in a limited domain with high accuracy is adopted, in comparison with the commonly used iterative method under two sets of domains, that is, the typhoon following domain and the outermost domain that covers the entire typhoon track. The relative importance of the divergent and non-divergent winds in the KE budget is investigated in the three stages of the ET process, namely, the pre-development, re-intensification, and dissipation stages. It is found that the divergent winds computed by the iterative method with a lower accuracy result in sizable errors in spatiotemporal variations of the KE of the typhoon during its ET process, which thus leads to obvious forecasting errors.

Disk Dissipation, Giant Planet Formation, and Star Formation Rate Fluctuations in the 3 Myr History of Gould’s Belt

Although episodic star formation (SF) has been suggested for nearby SF regions, a panoramic view of the recent episodic SF history in the solar neighborhood is still missing. By uniformly constraining the slope α of infrared spectral energy distributions (SEDs) of young stellar objects (YSOs) in the 13 largest Gould’s Belt (GB) protoclusters surveyed by the Spitzer Space Telescope, we have constructed a cluster-averaged histogram of α representing the YSO evolution lifetime as a function of the α value. Complementary to the traditional SED classification scheme (0, i, f, ii, and iii) that is based on different α values, a staging scheme (A, B, C, D, and E) of SED evolution is proposed on the basis of the α statistical features that can be better matched to the physical stages of disk dissipation and giant planet formation. This has also allowed us to unravel the fluctuations of SF rate (SFR) in the 3 Myr history of these GB protoclusters. Diverse evolutionary patterns such as single peaks, double peaks, and ongoing acceleration of SFR are revealed. The SFR fluctuations are between 20% and 60% (∼40% on average) and no dependence on the average SFR or the number of SFR episodes is found. However, spatially close protoclusters tend to have similar SFR fluctuation trends, indicating that the driving force of the fluctuations should be at size scales beyond the typical cluster sizes of several parsecs.

Possibilities of the Phase-Contrast X-Ray Method in a Laboratory Astrophysical Experiment on the Study of Plasma Instabilities

In this paper, a computational-theoretical analysis of the possibilities of using the method of phase-contrast X-ray radiography for the study of low-contrast turbulent flows in laser plasma in experiments with astrophysical similarity is carried out. By modeling the passage of hard coherent X-ray radiation through test objects, we studied the parameters of a laboratory experiment that affect the contrast and resolution of the resulting phase-contrast images. The limiting scale for measuring the frequency-spatial spectrum of image power was determined, on which the manifestation of artifacts from the superimposition of diffraction effects from neighboring objects is not yet critical for the correct interpretation of the results. Optimal object-detector distances are found that provide resolution of the power spectrum of a turbulent flow on micron scales. These results are relevant for future laboratory experiments on the development of instabilities in plasma with astrophysical similarity up to the stage of energy dissipation.

ШТОРМОВОЙ ЦИКЛОГЕНЕЗ НАД ЯПОНСКИМ МОРЕМ 16-18 ЯНВАРЯ 2016 Г.: АНАЛИЗ ЭНЕРГИИ И ВЗАИМОДЕЙСТВИЯ ВИХРЕЙ

The paper presents the results of studying the conversion of various types of energy, taking into account the formation and dissipation of a warm core in the central part of cyclones. The contribution of energy types (kinetic, potential, and internal) and their impact on the intensity of the cyclone development were also assessed by the example of the evolution of a mesocyclone. The mesocyclone was generated on the periphery of the main subtropical cyclone in January 2016 over the Sea of Japan and caused heavy precipitation and strong winds on the southern coast of the Primorsky krai. It is shown for each of the two analyzed cyclones that the stage of their deepening is accompanied by the formation of the warm core with a simultaneous decrease in the bulk values of all potential energy indicators for the vortex in the central region. At the stage of dissipation of the warm core, the values of all potential energy indicators increase. A change in water vapor reserves in the central part of both cyclones is similar to a change in internal energy, which is associated with the transformation of water vapor in the atmosphere (forced and free convection).

Multiobjective strict dissipativity via a weighted sum approach

We consider nonlinear model predictive control (MPC) with multiple competing cost functions. This leads to the formulation of multiobjective optimal control problems (MO OCPs). Since the design of MPC algorithms for directly solving multiobjective problems is rather complicated, particularly if terminal conditions shall be avoided, we use an indirect approach via a weighted sum formulation for solving these MO OCPs. This way, for each set of weights we obtain an optimal control problem with a single objective. In economic MPC it is known that strict dissipativity is the key assumption for concluding performance and stability results. We thus investigate under which conditions a convex combination of strictly dissipative stage costs is strictly dissipative again. We first give conditions for problems with linear dynamics and then move on to consider fully nonlinear optimal control problems. We derive both necessary and sufficient conditions on the individual cost functions and on the weights to conclude strict dissipativity and illustrate our findings with numerical examples.

Explicit Thermal Resistance Model of Self-Heating Effects of AlGaN/GaN HEMTs with Linear and Non-Linear Thermal Conductivity

We presented an explicit empirical model of the thermal resistance of AlGaN/GaN high-electron-mobility transistors on three distinct substrates, including sapphire, SiC, and Si. This model considered both a linear and non-linear thermal resistance model of AlGaN/GaN HEMT, the thickness of the host substrate layers, and the gate length and width. The non-linear nature of channel temperature-visible at the high-power dissipation stage-along with linear dependency, was constructed within a single equation. Comparisons with the channel temperature measurement procedure (DC) and charge-control-based device modeling were performed to verify the model's validity, and the results were in favorable agreement with the observed model data, with only a 1.5% error rate compared to the measurement data. An agile expression for the channel temperature is also important for designing power devices and monolithic microwave integrated circuits. The suggested approach provides several techniques for investigation that could otherwise be impractical or unattainable when utilizing time-consuming numerical simulations.

Nondestructive analysis of rolling contact fatigue cracks using induced scanning thermography.

Rolling contact fatigue (RCF) produced by wheel-rail interaction is now considered to be a critical factor that causes failure. Throughout this work, induced scanning thermography (IST) for detecting RCF defects at different depths is investigated. The original thermal sequences could not utilize the features at the heat dissipation stage; thus, a data reconstruction method, including principal component analysis (PCA) and Tucker factorization, was employed to extract the spatial and time patterns. In addition, detectability was evaluated across a range of speed studies. The Tucker-PCA combination algorithms obtained defects with improved quality, showing a clear boundary over the velocity range of 1-4km/h, which dramatically suppressed background noise. A unique gradient response characteristic in the cooling phase was summarized and utilized through experimental verification in order to recognize defect width.

Vertical changes of PM2.5 driven by meteorology in the atmospheric boundary layer during a heavy air pollution event in central China

Regional PM2.5 transport is a crucial factor affecting air quality, and the meteorological mechanism in the atmospheric boundary layer (ABL) has not been fully understood over the receptor region in the regional transport of air pollutants. Based on the intensive vertical measurements of air pollutants and meteorology in the ABL during a transport-induced heavy air pollution event in Xiangyang, an urban site over a receptor region in central China, we investigated the meteorological mechanism in vertical PM2.5 changes in the ABL for heavy air pollution over the receptor region. Driven by northerly winds, regional PM2.5 transport was built from upstream northern China to downstream central China, where the observed ABL structures were unstable throughout the air pollution event. We assessed the ABL structures with meteorological and PM2.5 profiles at growth, maintenance, and dissipation stages, and elucidated the mechanism of regional PM2.5 transport inducing air pollution over the receptor region with the contribution of thermal and mechanical factors. The regional PM2.5 transport was concentrated in the upper ABL over the downwind receptor region with high PM2.5 concentrations at altitudes of 600–800 m, where the transported PM2.5 peaks were downwards mixed by vertical wind shear, forming the vertical PM2.5 transport from the upper ABL to near-surface in the growth stage; the weakened winds and less unstable structures in the ABL favored the sustained pollution with slight vertical PM2.5 changes in the maintenance stage, which was dominated by thermal factors with 87 % contribution; the removal of PM2.5 was triggered by increasing winds from the upper ABL, activating the dissipation of heavy PM2.5 pollution with the mechanical effect accounting for 60 % in the dissipation stage. These findings could improve our understanding of ABL's influence on air pollution over the receptor region with implications for the regional transport of air pollutants in environmental changes.

Characterization of Tensile Crack Propagation and Energy Evolution during the Failure of Coal–Rock Samples Containing Holes

The instability and fracturing of gas drainage boreholes are one of the main causes of low drainage efficiency. Based on the rock mass energy principle and the Barenblatt model, the energy evolution of the coal–rock mass around the hole, the conversion characteristics of the dissipated energy Ud, and the propagation pattern of the initial tensile cracks were investigated. The results show that based on the conversion process of the dissipated energy, the failure process of samples containing holes can be divided into an initial dissipation stage, a decelerated dissipation stage, a stable dissipation stage, and an accelerated dissipation stage. The dissipated energy is always greater than the elastic energy during the first half of loading, and it is mainly used for the continuous development and propagation of initial tensile cracks. Then, remote cracks and cracks to the left and right of the hole boundary are generated to inhibit the propagation of the tensile cracks. Later, when the energy storage limit is reached, the elastic strain energy around the hole is released, and the macroscopic failure cracks propagate and coalesce, which causes the stress environment to change and the tensile cracks to reopen and finally propagate. The tensile cracks in the upper and lower ends of the holes undergo an opening–closing–reopening process, and the presence of cohesion c(x) hinders the propagation of the tensile cracks that are formed by the generation and migration of fracture initiation zone, friction zone, and intact zone. The dissipated energy released was related to the different stages of the tensile crack propagation, which could be used for the structure monitoring and flaw predicting of the gas drainage borehole.

Action Law and Deterioration Characteristics of Trigger Cavity of Plasma-Jet-Triggered Air-Gap Switch

The switch-type controllable metal oxide arrester (CMOA) is a flexible method to depress deeply switching overvoltage of transmission system, and the switching time of the fast bypass switch in CMOA is less than 1 ms with the meet of engineering. The plasma-jet-triggered air-gap switch (PTAS) has obvious advantages for the above switch. However, the cumulative effect of increasing the trigger discharge times is prone to trigger failure of the PTAS. In this article, a platform about trigger lifetime of PTAS is established to study the action law and degradation characteristics. The results show that the plasma jet process is divided into three stages: rapid growth stage, stable development stage, and dissipation and decline stage. The peak plasma jet velocity is up to 1.7 km/s, and the shock pressure can reach 5 MPa. With the increase of trigger discharge times, the surface discharge channel of PTAS trigger cavity gradually degrades due to the arc ablation cumulative effect, the surface roughness and nozzle diameter increase, the plasma jet characteristic parameters decrease, and plasma jet ability is weakened. The ablation degradation of trigger cavity surface is characterized by “pore size increasing, pore connection, and gully penetration.” The plasma jet characteristics are consistent with three types of the trigger cavity insulating materials, namely, Poly tetra fluoroethylen (PTFE), PTFE +0.5% Cu powder, and PTFE +0.2% MoS2. The decay rate of plasma jet parameters for +0.5% Cu powder is the fastest. Adding 0.2% MoS2, the ac ablation ability is strengthened. However, the trigger discharge lifetimes of both +0.5% Cu powder and +0.2% MoS2 are lower than that of PTFE. PTFE has obvious advantages in gas-producing performance and ablation resistance ability. The research results provide theoretical guidance for improving the trigger performance of PTAS.

Singularities in turbulent flows: How to observe them?

The existence and relevance of finite time singularities of the fluid equations are outstanding problems in turbulent flows at high Reynolds number. Their existence is based on recent analytical studies of the time dependent equations for inviscid flow and it explains well the long known observation of intermittency there. The analysis of hot wire records of a turbulent flow in the wind tunnel of Modane is in fair agreement with this existence of finite time singularities passing by the point of recording. This analysis relies on the behavior of the structure functions of the Eulerian acceleration at increasing exponents. It is completed by the analysis of Lagrangian data coming from a von Karman experiment. A particular choice of multi-correlation functions of the acceleration, called test functions, makes them sensitive to the irreversible character of the dynamics, which is shown to be effective at short time only, that we interpret as a signature of the presence of singular events developing a very large acceleration on a very short time scale before they disappear. This time is of the order of the Kolmogorov dissipation time. Differently the test functions built on the velocity correlation functions display a much longer irreversible signal which we associate to the energy transfer occurring before the dissipation stage inside the isolated spots where singularities are formed.

The Effect of Sea Surface Temperature on Relative Humidity and Atmospheric Visibility of a Winter Sea Fog Event over the Yellow-Bohai Sea

Sea fog is one of the main types of dangerous weather affecting offshore operations. The sea surface temperature (SST) has an important influence on the water vapor content and intensity of sea fog. In order to study the impact of SST on local relative humidity and atmospheric visibility, a sea fog episode that occurred over the Yellow Sea and Bohai Sea on 21 January 2013 was investigated through observational data, reanalysis data, and Weather Research and Forecasting (WRF) simulation. The results show that the influence of SST on the distribution of sea fog with different properties is inconsistent. Based on the time-varying equation of relative humidity, the changes in the advection, radiation, and turbulence effects on the relative humidity with respect to SST are explored through control and sensitivity experiments. The results show that the advection effect plays a decisive role in the generation and dissipation stages of sea fog. The increase (decrease) in SST weakens (strengthens) the radiative cooling and relative humidity. The contribution magnitude of advection effect to relative humidity is 10−5, while those of radiation and turbulence are 10−6 and 10−7, respectively. The atmospheric visibilities in the Bohai Sea and northern Yellow Sea decrease with increasing SST, which are mainly affected by the positive turbulence effect; whereas the atmospheric visibility in the central and southern Yellow Sea increases with SST, which is mainly influenced by the combined effects of U-direction advection, radiation, and turbulence. The stability related to boundary layer height plays an important role in water vapor condensation.

Inherent Stochastic Robustness of Model Predictive Control to Large and Infrequent Disturbances

We introduce a new class of large, infrequent disturbances to complement the small, persistent disturbances typically considered in robustness analysis. This new class of disturbances includes discrete disturbances that become pertinent when considering discrete actuators and production scheduling in control problems. To properly account for the infrequent nature of these disturbances, we define a stochastic form of robustness. Under suitable assumptions, we prove that certain closed-loop systems subject to large, infrequent disturbances admit an SISS-Lyapunov function and are robust in this stochastic context. We apply these results to economic model predictive control (MPC) with a strictly dissipative nominal system and stage cost, which includes tracking MPC as a special case, and prove that economic MPC is robust to large, infrequent disturbances. Without dissipativity assumptions, we define and establish robust asymptotic performance for economic MPC. We present a simple tracking problem to illustrate the results of this work, and a production scheduling (economic MPC) problem, to demonstrate the relevance of this analysis to practical applications.

Experimental and Numerical Investigation of Energy Evolution Characteristic of Granite considering the Loading Rate Effect

In order to investigate the loading rate effect of energy evolution in granite, the indoor physical simulation test of single face fast unloading-three directions and five faces stress-vertical continuous loading under different loading rates was conducted using a new true triaxial rockbursttest system. The energy accumulation-dissipation-release characteristics in the process of rock deformation and failure were revealed. Based on the three-dimensional discrete element theory and the polycrystalline modeling technique (randomly generated Voronoi mineral grains), the entire process of rockburst inoculation-occurrence-development, as well as the energy evolution characteristics under true triaxial single face unloading conditions, were studied. The test results indicate that the energy transport and conversion of rock samples under different loading rates exhibit distinct stage characteristics. It can be divided into the initial energy accumulation stage, steady energy accumulation stage, rapid energy dissipation stage, and rapid energy release stage. With a rise in loading rate, the specimen in the process of energy accumulation is accompanied by energy dissipation, more external input energy, and elastic strain energy release amount into the kinetic energy of fragments, resulting in the rockburst phenomenon. As the loading rate increases, the elastic strain energy conversion rate (Ue/U) falls, while the dissipative energy conversion rate (Ud/U) increases. The higher the elastic strain energy conversion rate and the lower the dissipative energy conversion rate, the more serious the rockburst occurs. Numerical simulation results show that the entire process of rockburst inoculation-occurrence-development is successfully simulated using the crystal scale fine model (CSFM) considering the grain mineral composition. The ejection failure process can be divided into four stages, including grains ejection, rock spalling into plates, rock shearing into fragments, and rock fragments ejection. The relationships between the peak strength, elastic strain energy of rock samples, and loading rates are obtained, which is consistent with the laboratory test results. The high rate linear growth of kinetic energy evolution between the two inflection points can provide precursor information for rockburst prediction.

Programmable Electronic Load Prototype for the Power Quality Analysis of an Experimental Microgrid

Microgrids have been widely adopted in many countries because they provide more reliable electricity service to those users connected to the power grid. These systems comprise various power sources, energy storage devices, and loads. However, detailed studies require considering linear and nonlinear loads, which are now used in this type of network. In addition, experimental tests require devices that emulate loads, represent different topologies, and construct assemblies for better identification, validation, and theoretical approximations of the power grid. Therefore, this paper presents a programmable electronic load to emulate linear and nonlinear loads of a microgrid, based on the control of a single-phase voltage source converter that considers rectification and power dissipation stages. Furthermore, a control stage allows power consumption variations, controlling the current demanded by the load, according to the reference current waveform programmed through a user interface. A synchronous reference frame phase-locked loop is implemented on a microcontroller. Thus, the programmable electronic load enables studying power quality in microgrids. Finally, the operation of the programmable electronic load is validated through experimental and simulation tests, considering different case studies.

A multi-scale insight into gas transport in a deep Cenozoic clay

The migration of gases is crucial to ensure the long-term feasibility of argillaceous formations for the deep disposal of radioactive waste. This paper presents an experimental investigation with a multi-scale perspective on the response to gas transport of initially saturated Boom Clay (Belgium). Gas injection tests have been performed under oedometer conditions at different controlled-volume rates, constant total vertical stress and different sample orientations (flow orthogonal or parallel to bedding planes). The results confirm soil expansion and consequent degradation during injection that has a significant impact on the aperture of localised gas pathways (fissures) and increases intrinsic permeability during the gas pressure dissipation stage. The analyses with complementary techniques (mercury intrusion porosimetry, field-emission scanning electron microscopy and X-ray micro-tomography) confirm the opening of fissures with different apertures and separations at the microstructural scale. Large-aperture fissures develop along the weaker bedding planes. These techniques allow the volume of fissures to be quantified, which does not significantly depend on gas flow direction, as also measured in the isotropic response of the gas effective permeability. A scalar damage variable derived from the fissured fraction has been used to assess the gas-entry pressure reduction and the intrinsic permeability increase after the gas tests in both directions.