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2022 ◽  
Author(s):  
Dantong Shi ◽  
Kuan-Ting Lin ◽  
Milind A. Jog ◽  
Raj M. Manglik

Abstract The influence of swirl flow on enhanced forced convection in wavy-plate-fin cores has been investigated. Three-dimensional computational simulations were carried out for steady-state, periodically developed flow of air (Pr ~ 0.71) with channel walls subject to constant-uniform temperature and flow rates in the range 50 = Re = 4000. The recirculation that develops in the wall troughs and grows to an axial helix is scaled by the Swirl number Sw. As Sw increases, tornado-shaped vortices appear in the wave trough region mid-channel height, then extend longitudinally to encompass majority of the flow channel. As shown by the local wall-shear and heat transfer coefficient variations, the boundary-layer thinning upstream of the wave peak assists to intensify the momentum and heat transfer. However, the flow recirculation in wave trough impedes the local heat transfer at low Sw due to flow stagnation but promotes it at high Sw because of swirl-augmented fluid mixing. Swirling flows also create pressure drag that contributes substantively to the overall pressure loss. Its proportion grows as Sw, corrugation severity, and fin spacing increases to as much as 80% of the total pressure drop. The fin-wall curvature-induced secondary circulation nevertheless produces significantly enhanced convection, and more so in flows with higher Sw. It is quantified by Ff (or j), which is seen to increase log-linearly as fin corrugation aspect ratio and/or fin spacing ratio increases; the influence of cross-section aspect ratio is found to be marginal.


Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2451
Author(s):  
Zengliang Hao ◽  
Biao Yao ◽  
Yuhang Chen ◽  
Junting Luo

The U-shaped metal bellows expansion joint compensates for the pipeline displacement by its own deformation. The compensation performance of the metal bellows in the initial stage of tension and compression deformation is unstable. In this paper, the symmetrical cyclic tension and compression (SCTC) process of metal bellows was simulated by ABAQUS software. Then, the SCTC process experiment of metal bellows was completed on the universal material testing machine. The distribution law of axial load with displacement and that of axial stiffness and yield load with cycles of metal bellows were obtained. Finally, the X-ray diffraction peak confirmed the deformation-induced martensite in the wave trough and proved that the plastic strain and hardness values of metal bellows increased with the displacement amplitude. The microstructure in the wave trough area was observed by a Zeiss microscope, and the stability characteristics mechanism of the metal bellows was revealed. The martensite in the wave trough increases the grain boundary area under SCTC loading. The forward movement of the slip band in the grain caused by large deformation reached an equilibrium state with the resistance at the grain boundary, which promotes the macroscopic mechanical properties of the metal bellows to be stable characteristics under SCTC loading.


Author(s):  
Safa M Aldarabseh ◽  
Parviz Merati

Abstract This experiment was done to predict the evaporation rate from the wavy water surface under the different convection regimes ( free, forced, and mixed) at turbulent airflow conditions over a wide range of the ratio(Gr/Re2 ). Evaporation rate from wavy water surface is strongly affected by combinations between wave steepness and main airflow velocity above the wavy water surface. Experimental results show that no pattern can be followed for which combinations of evaporation rate will increase. Thus, only two facts can be noticed: the evaporation rate is larger than that measured under the same airflow velocity conditions with no waves existing on evaporated water surface because the airflow is smooth and attached along the still water surface and when increasing the wave steepness(H/L,H/T), Airflow will separate at the lee side of wave crest near to the bottom of the wave trough. Thus, vortex will generate in the airflow separation region. These vortexes are unstable and cause an increase in turbulence, reducing the water surface's resistance to vertical transport water vapor and increasing the evaporation rate. Also, experimental results show that the evaporation rates are somewhat less than that measured under the same airflow velocity with smaller wave steepness due to air trapped region observed at the leeside of the wave crest near the bottom of the wave trough. Evaporation rate is increasing with increase airflow velocity under the same convection regime.


2021 ◽  
Author(s):  
Jinjie Zhou ◽  
Yingle He ◽  
Jinchuan Shen ◽  
Fadl A Essa ◽  
Jingui Yu

Abstract Nickel-based single crystal alloys have excellent mechanical properties due to its unique two-phase structure and interface. Therefore, molecular dynamics methods were used to simulate nanoindentation and microstructural evolution. We found the indenter reaction force and hardness of the Ni3Al phase is the largest. The pop-in event in Ni3Al phase is more obvious than that in the Ni phase and Ni/Ni3Al phase. Because lots of dislocations in the Ni3Al phase break through the barrier of the interface and cut into the Ni phase, while dislocations in the Ni phase only slip inside the Ni phase. Moreover, we found that the position of the starting point of the adhesion force recovery is mainly related to the elastic recovery of the material. The stronger the elastic recovery of the phase, the smaller the depth value corresponding to the starting point of the recovery. We further studied the variation of potential energy with indentation depth and found that the change of wave trough of the load-displacement (P-h) curve is related to stacking fault energy. This study has important theoretical guiding significance for the in-depth understanding and engineering application of the mechanical properties of nickel-based single crystal alloys.


2021 ◽  
Vol 9 (4) ◽  
pp. T1133-T1141
Author(s):  
Feng Tan ◽  
Jun-Xing Cao ◽  
Xing-Jian Wang ◽  
Peng Bai ◽  
Jun Liu ◽  
...  

The Shaximiao Formation in the Zhongjiang Gas Field of the Sichuan Basin was initially a high-productivity gas field with the bright spot channel as the vital exploration target. With further development, gas wells were obtained in some nonbright spot areas, which caused interpreters to pay great attention to the channels with nonbright spot abnormal amplitudes. We have developed a method to delineate nonbright spot channels from the complicated sand-mudstone contact relationship. First, we classified sandstone into types I, IIa, IIb, and III, depending on the responses of the amplitude variation with offset from the drilled data, to produce a forward model. We the explain why the hidden channel cannot be identified using the full-angle stack seismic data based on this model. Afterward, we put forward a difference, between the synthetic seismogram responses of bright and nonbright channels, in creating seismic-to-well ties for nonbright channels. This difference from bright channels is that the synthetic data’s wave peak is not corresponding to the peak of the real seismic data. The wave trough has the same situation. Finally, we used far-angle stack seismic data to calculate coherent energy and instantaneous spectral attributes (the latter produced for red-green-blue blending) to identify the hidden channel. We observed that parts of the channel are more clearly visible in the far-angle stack than in the full-angle stack data. In the latter situation, we cannot describe the geometric shape of the channel elaborately. The Shaximiao Formation example is a relatively effective analog for nonbright spot plays compared with elsewhere.


2021 ◽  
Vol 9 ◽  
Author(s):  
Yan Liu ◽  
Zhaochun Shi ◽  
Guohua Wang ◽  
YuYing Yan ◽  
Yingchao Zhang

In order to obtain the power generation of the thermoelectric power generator (TEG) group, a similar structure of the disc sandwich structure and an experimental system are built to analyze the power generation performance and temperature characteristics. To improve heat transfer and move heat from the hot side to the cold side, heat pipes with high thermal conductivity are arranged on the adjacent cold and hot plates of the TEG. The similar sandwich structure has 17 cold plates and 17 hot plates for the TEG pieces, which are connected in series on the circuit. Working conditions are hot air flow and cold water flow; hot air temperature and cold water temperature are set to a fixed temperature. The power generation of a single TEG is tested for verifying linear changes in the power generation performance with temperature differences (Td). Experimental results are that the power generation is improved by the air flow and water flow increasing. The water flow has a smaller effect on the power generation than the air flow. In the cold side of TEG pieces, the temperature of the cold side showed a gradual upward trend, the temperature of the hot side showed a wave trough phenomenon, and the Td showed a wave trough phenomenon. The hot air flow and the cold water changing cannot weaken the temperature trend of the hot side and the cold side. The hot air flow can more significantly increase the Td than the cold water.


2021 ◽  
Author(s):  
Kathrin Wapler ◽  
Marcus Beyer

<p>Tornados pose a significant threat to life, property, and economy. Thus, an analysis of tornadoes is of high relevance. An understanding of historical events, e.g. regarding the characteristics of tornadic storms compared to multi-year storm statistics, may help to improve the situational awareness of future tornado events.</p><p>In this study, tornadic storms with a tornado intensity of F2 or stronger on the Fujita scale that occurred in recent years (2016 – 2020) in Germany were analyzed in detail. The four F3 tornadoes (Bützow, Affing, Bonndorf and Roetgen) and sixteen F2 tornadoes, which developed on 17 different days occurred in various parts of Germany. Most of the analysed tornadoes occurred from May to early September. The other three cases are typical winter cases that differ significantly from the summer cases in some aspects that are discussed where applicable. One case which happened in the third decade of September has characteristics form both, summer and winter, and is thus the only hybrid case. The great majority of all cases occurred during the second half of the day, most of them between 12 and 18 UTC. The most active hour was 16 to 17 UTC.</p><p>Regarding forecasting, similarities and differences of the prevailing synoptic and mesoscale conditions are assessed in addition to the convective environment of the events. Furthermore, the type of convection is analysed. The goal is to anticipate typical characteristics that enhance the threat of a potentially dangerous tornado situation. Using these findings may then help to strengthen the awareness of the forecaster. Two situations in mid- and upper-level flow are typical for the occurrence of strong tornadoes. On the majority of the analysed tornadic days, the event happened on the forward flank of a long wave trough that was slowly propagating eastward. The other typical situation is a vivid short wave trough passing rather fast over the area of interest from West to East.</p><p>Regarding nowcasting, a multi-source approach was applied to best analyse the events. For this purpose, radar reflectivity and rotation data were combined with lightning detection in order to analyse the tornadic storms with respect to storm mode and storm evolution as well as lightning and rotation characteristics. In many cases, radar radial wind data showed a persistent rotation track. The automatically detected mesocyclones had a vertical depth between 2.5 and 11 km at the time of the tornado, the diameter was above 8 km. The base of the rotation was low compared to multi-year statistics of all mesocyclonic storms. The lighting activity of the tornadic storms was high. In many cases, a lightning jump occurred between 5 and 120 minutes before the event.</p>


Eye ◽  
2021 ◽  
Author(s):  
Xiaofan Jiang ◽  
Omar A. Mahroo

AbstractThe dark-adapted human electroretinogram (ERG) response to a standard bright flash includes a negative-going a-wave followed by a positive-going b-wave that crosses the baseline. An electronegative waveform (or negative ERG) results when the b-wave is selectively reduced such that the ERG fails to cross the baseline following the a-wave. In the context of a normally sized a-wave, it indicates a site of retinal dysfunction occurring after phototransduction (commonly at the photoreceptor to bipolar cell synapse). This is an important finding. In genetic disease, the pattern of ERG abnormality can point to variants in a small group of genes (frequently those associated with congenital stationary night blindness and X-linked retinoschisis, but negative ERGs can also be seen in other conditions including syndromic disease). In acquired disease, there are numerous causes, but specific features may point to melanoma-associated retinopathy (MAR). In some cases, the visual symptoms precede the diagnosis of the melanoma and so the ERG findings can initiate investigations facilitating early detection and treatment. Negative ERGs can occur in other paraneoplastic conditions, and in a range of other diseases. This review will outline the physiological basis for the negative ERG, report prevalences in the literature from different cohorts, discuss the range of causes, displaying examples of a number of ERG phenotypes, highlight features of a clinical approach to patients, and briefly discuss further insights relating to current flows shaping the a-wave trough and from single-cell transcriptome analysis.


2021 ◽  
Vol 71 (1) ◽  
pp. 17
Author(s):  
Nelson Quispe-Gutiérrez ◽  
Vannia Aliaga-Nestares ◽  
Diego Rodríguez-Zimmermann ◽  
Martí Bonshoms ◽  
Raquel Loayza ◽  
...  

Cutoff lows (COLs) are infrequent events in the tropics that can cause extreme rainfall, flash flooding and landslides in arid areas, such as western South America. In this study, the life cycle of a COL in the southeastern Pacific at the beginning of April 2012 was analysed using the ERA-Interim reanalysis dataset. This paper examines: (1) the precursor flow evolution prior to the COL, its development and dissipation by applying the quasi-geostrophic and vorticity equations; and (2) the influence of the COL in the heavy precipitation events over the western Peruvian Andes. During April 2012, the highest amount of precipitation was recorded in Chosica (850 masl) with 37mm on 5 April. Days prior to the formation of the COL, a subtropical trough deepened by the amplification of a ridge over the tropical Pacific and the incursion of cold air from medium and low levels into the trough. The strong cyclonic vorticity advection was intensified by a short-wave trough embedded inside a long-wave one that strengthened the system on 5 April 2012. In the dissipation stage, warm vertical advection predominated, resulting in the reabsorption of the COL by a new trough. Understanding the behaviour COL systems is important for reducing the impact of these extreme weather events on lives and infrastructure in densely populated areas.


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