An Unsteady Model for Aircraft Icing Based on Tightly-Coupled Method and Phase-Field Method

An unsteady tightly-coupled icing model is established in this paper to solve the numerical simulation problem of unsteady aircraft icing. The multi-media fluid of air and droplets is regarded as a single medium fluid with variable material properties. Taking the droplet concentration as the phase parameter and the droplet resistance coefficient as the interphase force, the mass concentration distribution of the droplet is obtained by solving the Cahn–Hilliard equation. Fick’s law is introduced to improve the Cahn–Hilliard equation to predict the droplet shadow zone. On this basis, the procedure of the unsteady numerical simulation method for aircraft icing is established, including grid generation, the dual-time-step method to realize the unsteady calculation of the air and droplet tightly-coupled mixed flow field, and the improved shallow water icing model. Finally, through the comparative analysis of numerical examples, the effectiveness of the new model in predicting the droplet impact characteristics and the droplet shadow zone are verified. Compared with other icing models, the ice shapes predicted by the unsteady tightly-coupled model were found to be the most consistent with the experiments. In the icing comparison conditions in this manuscript, the prediction accuracy of the ice thickness at the stagnation point of the leading edge was up to 35% higher than that of LEWICE.

Monitoring of Recovery Process at Yeongildae Beach, South Korea, Using a Video System

Once a beach is eroded by storm waves, it is generally recovered under milder wave conditions. To prevent or reduce damage, it is therefore important to understand the characteristics of the site-specific recovery process. Here, we present the results, based on a data set from a video monitoring system and wave measurements, of the recovery process in a pocketed beach located inside a bay where the shoreline retreated harshly (~12 m, on average, of beach width) during Typhoon TAPAH (T1917) in September 2019. It took about 1.5 years for the beach to be recovered to the level before the typhoon. During this period, the erosion and accretion were repeated, with the pattern highly related to the wave power (Pw); most of the erosion occurred when Pw became greater than 30 kWatt/m, whereas the accretion prevailed when Pw was no greater than 10 kWatt/m. The recovery pattern showed discrepancies between different parts of the beach. The erosion during storm events was most severe in the southern part, whereas the northern shoreline did not significantly change even during TAPAH (T1917). In contrast, the recovery process occurred almost equally at all locations. This discrepancy in the erosion/accretion process was likely due to human intervention, as a shadow zone was formed in the northern end due to the breakwaters, causing disequilibrium in the sediment transport gradient along the shore. The results in this study could be applied in designing the protection plans from severe wave attacks by effectively estimating the size of coastal structures and by correctly arranging the horizontal placement of such interventions or beach nourishment. Although the application of these results should be confined to this specific site, the method using wave energy parameters as criteria can be considered in other areas with similar environments, for future planning of beach protection.

Diffusion controls the ventilation of a Pacific Shadow Zone above abyssal overturning

Mid-depth North Pacific waters are rich in nutrients and respired carbon accumulated over centuries. The rates and pathways with which these waters exchange with the surface ocean are uncertain, with divergent paradigms of the Pacific overturning: one envisions bottom waters upwelling to 1.5 km depth; the other confines overturning beneath a mid-depth Pacific shadow zone (PSZ) shielded from mean advection. Here global inverse modelling reveals a PSZ where mean ages exceed 1400 years with overturning beneath. The PSZ is supplied primarily by Antarctic and North-Atlantic ventilated waters diffusing from below and from the south. Half of PSZ waters re-surface in the Southern Ocean, a quarter in the subarctic Pacific. The abyssal North Pacific, despite strong overturning, has mean re-surfacing times also exceeding 1400 years because of diffusion into the overlying PSZ. These results imply that diffusive transports – distinct from overturning transports – are a leading control on Pacific nutrient and carbon storage.

Reconstruction of distorted structures in fault shadow zone based on Full Connected Network

Lateral changes in velocity about faults can give rise to fault shadow (FS) zones on time-migrated data volumes, which can result in structural interpretation artifacts in the fault trap reservoir. To address this issue we proposed a new reconstruction method of FS distortion structures based on a deep learning fully connected network (FCN). We use the three dimensional (3D) stratigraphic dip attributes to quantitatively delineate the extend of the FS zone. Then, we train an model to construct a nonlinear trend surface based on the structures of the stratigraphic reflectors that fall outside the shadow zone. Finally, we use this nonlinear trend surface to compensate the distorted structure within the FS zone. We calibrate our method using synthetic data and show that the method can accurately recover the structural data within the FS distortion zone. We then test the effectiveness of our workflow by applying it to recover real FS distortation sturctures in the Pearl River Mouth Basin of the South China Sea. The results confirm that our method significantly reduces the drilling depth error in the FS zone. Compared with the traditional polynomial fitting method, the multi-layer, multi-parameter and flexible nonlinear activation function of FCN is more capable of reconstructing nonlinear geological structures in the FS zone. We find the FCN-based geological reconstruction method to be both efficient and effective for exploring the potential structures in the FS zone and thereby in avoiding the risks of structural failure.

On the use of complex rays to analyse the sonic boom of the Carancas meteorite at I08BO station located into shadow zone

<p><span>The International Monitoring System (IMS) network of the Comprehensive nuclear-Test-Ban Treaty (CTBT) detects powerful natural and artificial infrasonic sources. One of these sources are meteorites which produce multi-arrival pressure signatures similar to explosion </span><span>onces</span><span>. Long range sonic boom modeling allows to distinguish these sources from one another. Our documented case is the Carancas meteorite </span><span>that</span><span> impacted the ground in Peru on September 15th, 2007, near </span><span>the IMS </span><span>infrasound station I08BO. Since this station is located within the shadow zone, classical ray tracing cannot be used to capture the characteristics of the recorded arrivals. </span><span>Analytic continuation into complex plane of emission parameters of the ray tracing method allows to analyse the propagation in shadow zone for full</span><span>y</span><span> three dimensional problems. Contribution of complex ray ordinary differential equations integration and optimisation algorithm allows to compute complex eigenrays. Simulated infrasound wave arrival times, azimuth</span><span>s</span><span> and apparent velocities at the station are compared with Carancas records.</span></p>

Infrasound transmission in the "shadow zone" observed on balloons in the lower stratosphere

<p>The temperature and wind structure of the lower atmosphere creates an "acoustic shadow", where acoustic propagation is not expected to occur from a ground based source. This region begins several tens of kilometers from the source and typically ends between one hundred and two hundred kilometers range in the downwind direction of the stratospheric jet. Ground microbarometers still occasionally record acoustic arrivals in this zone due to tropospheric waveguides and/or scattering off of stratospheric structure not accounted for in atmospheric models. However, the properties of these signals in the lower stratosphere (above the tropospheric duct) is unknown, because they have never been previously observed on sensors at these altitudes. Here we present a set of acoustic arrivals from ground explosions recorded on balloons in the lower stratosphere during the mini-BOOSTER campaign in Sweden. Although some of the balloons were in the shadow zone, they still recorded a variety of waveforms from each event. Dual payloads on tethers show that the acoustic waves came from below in these instances. We discuss the provenance of these signals and implications for acoustic transmission in regions where geometric ray theory predicts their absence.</p>

Simulation of aeration of buildings erected on complex terrain

The problem of improving the environment by rational use of natural resources is currently very relevant. By means of theoretical and experimental metrological and aerodynamic studies, the infiltration processes between the internal and external air environment during the wind flow around buildings of buildings erected on complex terrain, as well as the adjacent territories of residential development, are established, which allows us to assess the heat loss and ventilation conditions of buildings under wind pressure. A model of the formation of the circulation zone for different geometric parameters of buildings, wind flow velocity and slope steepness is developed, which allows preliminary forecasting of the aeration regime of the adjacent territories. Zones of backwater and calm wind in the adjacent territories were identified. A model of the wind shadow zone has been compiled, which allows the designer to zone the territory adjacent to the building at the design stage, taking into account the aeration regime of the development.