Self-Contradictions of Current Turbulence Theory and Liu’s New Turbulence Generation Theory

Turbulence is one of the most important but unresolved problems in modern fluid dynamics. Mathematically, one counterexample can overthrow a theory and we really do not need a second example. However, classical and current turbulence theories are filled with not only one but many self-contradictions. Therefore, we really do not have the right turbulence theory. The transition community believes that turbulence is generated by “vortex breakdown,” but the turbulence community believes there are coherent structures in fully developed turbulence after vortex breakdown. It is equivalent to say we study the structure of a house after the house collapses and breaks down. This is really ridiculous. There are many others. According to Liu, (1) flow transition is not a process of vortex breakdown but turbulence vortex structure buildup; (2) the nature of turbulence generation is that fluids cannot tolerate high shear and shear must transfer to rotation and form a very fast rotation core; (3) “shear layer instability” is the “mother of turbulence”; (4) turbulence small scales are generated by multiple-level shear layers that are generated by multiple level sweeps, ejections, negative and positive spikes; (5) large vortex provides energy to smaller vortices through fast rotation, which causes strong sweeps. According to Liu, the nature of the flow transition is mainly caused by vorticity rollup from the wall. Flow transition is vorticity redistribution and increment from near wall to whole boundary layer. In addition, flow transition is a process of non-rotational vorticity transferring to rotational vorticity

Region-Enhanced Feature Learning for Scene Semantic Segmentation

Semantic segmentation in complex scenes not only relies on local object appearance but also on object locations and the surrounding environment. Nonetheless, it is difficult to model long-range context in the format of pairwise point correlations due to its huge computational cost for large-scale point clouds. In this paper, we propose to use regions as the intermediate representation of point clouds instead of fine-grained points or voxels to reduce the computational burden. We introduce a novel Region-Enhanced Feature Learning network (REFL-Net) that leverages region correlations to enhance the features of ambiguous points. We design a Region-based Feature Enhancement module (RFE) which consists of a Semantic-Spatial Region Extraction (SSRE) stage and a Region Dependency Modeling (RDM) stage. In the SSRE stage, we group the input points into a set of regions according to the point distances in both semantic and spatial space. In the RDM part, we explore region-wise semantic and spatial relationships via a self-attention block on region features and fuse point features with the region features to obtain more discriminative representations. Our proposed RFE module is a plug-and-play module that can be integrated with common semantic segmentation backbones. We conduct extensive experiments on ScanNetv2 and S3DIS datasets, and evaluate our RFE module with different segmentation backbones. Our REFL-Net achieves 1.8% mIoU gain on ScanNetv2 and 1.0% mIoU gain on S3DIS respectively with negligible computational cost compared to the backbone networks. Both quantitative and qualitative results show the powerful long-range context modeling ability and strong generalization ability of our REFL-Net

A study on the dynamic tension of galloping conductors based on energy balance method

Dynamic tension variation caused by conductor galloping is a major impact on design and stable operation of overhead transmission lines. A formula to calculate tension variation caused by the conductor galloping was presented in this paper by using the energy balance method. And two important parameters and were proposed by the dimensionless analysis to study the factors influencing the dynamic tension. By comparison with the popular expression obtained by the length variation method, the formula deduced in this paper has more extensive applications and it was simplified to obtain the expression derived by the length variation method as the parameters and have the smaller values. Using the actual galloping conditions, the tension variation maximum against the different parameters was obtained and it can go up to 3-4 times as large as the initial tension for some extreme cases. Additional a finite element galloping model was used to verify the theoretical expression. The results by the theoretical calculation were agreement well with the numerical simulated values except the extremely large amplitude galloping conditions

Government regulation of emergency supplies under the epidemic crisis

This paper constructs a multi-oligopoly model of emergency supplies and analyses the market equilibrium results under normal conditions and epidemic conditions. The impacts of the degree of change in market demand, externalities, the material cost of emergency supplies and government regulation on the equilibrium results, especially on the prices of emergency supplies, are discussed. The results show that an increase in material cost will lead to low output and social welfare and a high price, under either normal conditions or epidemic conditions. Moreover, under epidemic conditions, the degree of change in market demand, externalities, material cost and the presence and mode of government regulation all have multiple and complex influences on the equilibrium results. Under epidemic conditions, both government output and price regulation can increase the supply of emergency supplies. In addition, when market demand changes drastically, consumer surplus and social welfare can be enhanced by the implementation of regulations. Particularly, price regulation is more effective when there is a high material cost

Decision Stages and Asymmetries in Regular Retail Price Pass-Through

We study the pass-through of wholesale price changes onto regular retail prices using an unusually detailed data set obtained from a major retailer. We model pass-through as a two-stage decision process that reflects both whether as well as how much to change the regular retail price. We show that pass-through is strongly asymmetric with respect to wholesale price increases versus decreases. Wholesale price increases are passed through to regular retail prices 70% of the time while wholesale price decreases are passed through only 9% of the time. Pass-through is also asymmetric with respect to the magnitude of the wholesale price change, with the magnitude affecting the response to wholesale price increases but not decreases. Finally, we show that covariates such as private label versus national brand, 99-cent price endings, and the time since the last wholesale price change have a much stronger impact on the first stage of the decision process (i.e., whether to change the regular retail price) than on the second stage (i.e., how much to change the regular retail price)

Nonlinear analysis of stress and strain for a clay core rock-fill dam with FEM

AbstractBased on the Duncan-Chang hyperbolic nonlinear elastic material model, this paper carried out the stress and strain numerical analysis of a clay core rock-fill dam, which is a certain building reservoir dam in Yunnan province. By loading on each layer step by step and with the static nonlinear finite element simulation of deposition, it obtained the results of the stress and deformation of the clay core rock-fill dam. The calculation showed that the great difference in deformation modulus causes non-smooth variations in deformation, stress and strain between the transition area and the rock-debris fill. From the analysis it can be seen that the present design of the dam is reasonable since no any abnormal stresses and deformations occurred in the dam. Moreover, this also indicated a feasible and provided a valuable evident for the optimization of cross-section zones in a project

Effect of mixing on mass transfer characterization in continuous slugs and dispersed droplets in biphasic slug flow microreactors

The mass transfer of slug flow, a widely applied flow pattern in microreactors, is still difficult to predict mainly due to the competing nature between convection and diffusion. This work focused on the influence of the mixing mechanism on the mass transfer performance under gas–liquid and liquid–liquid slug flow, in both continuous slugs and dispersed droplets. Colorimetric study with the resazurin oxidation system was implemented, where the mass transfer resistance was constantly located in the aqueous phase. In the hydrophilic glass microreactor, the convection featured by intensive internal circulation and/or inter-slug leakage flow dominated diffusion, leading to nearly-constant kLa along the channel under given flow rates. However, in the hydrophobic PTFE capillary, the stagnant region constituted a significant share in the aqueous droplet, indicating the prominent role of diffusion against convection therein. As a result, kLa values decreased along the main channel length in fixed operating conditions. Accordingly, prediction models were respectively correlated depending on mixing mechanisms. Moreover, mass transfer contributions from the bubble and droplet formation stages were also investigated. This work is expected to shed light on judicious process design and reliable predictions in microreactor operations