k. zhang

Semiconductor lasers generate a significant amount of heat during operation, which can lead to various issues, including performance degradation and structural deformation of the housing. To address these challenges, this study proposes a novel cooling channel design inspired by the natural vascular architecture of plant leaves. This biomimetic design, referred to as the bionic vane cooling channel, has been optimized by manipulating key variables such as the height of the cooling gap, the angle between the primary and secondary channels, and the rate of water flow at the inlet. A comprehensive series of computational fluid dynamics (CFD) simulations and numerical analyses were conducted. The results indicate that with a constant inlet Reynolds number (Re), an increase in the height of the cooling gap significantly enhances the heat dissipation capacity. Specifically, when the cooling gap height in type I, type II, and type III structures is increased from 2 mm to 4 mm, the Nusselt Number (Nu) improves by 25.74%, 12.48%, and 15.80%, respectively. Additionally, adjusting the angle between the primary and secondary channels also increases the heat dissipation capacity. For example, increasing the angle from 45° to 65° results in Nu improvements of 42.07%, 26.07%, and 30.84% for Models I, II, and III, respectively. At a Reynolds number of 20,000, the enhancements in Nu were found to be 90.96%, 36.19%, and 50.41%, respectively. The study further includes a simulation analysis of the radiator's structural deformation. The findings suggest that increasing the angle between the primary and secondary channels can significantly reduce deformation. For instance, at an angle of 45°, deformation exceeded 4 × 10-3 mm, whereas at 65°, the deformation was less than 1 × 10-3 mm. This study introduces a novel approach to enhancing both the heat dissipation efficiency and the operational stability of semiconductor lasers.

To explore the diffusion characteristics of the hippocampus injury (HI) in children during the complex acute febrile seizure (CAFS) through multiple b value (1000-2000 s/mm2) of diffusion-weighted imaging (DWI).

This prospective observational study enrolled children with HI during CAFS, and nasopharyngeal and sinus disease (NSD). The multiple b value from DWI of the hippocampus were scanned.

A total of 41 children were included, with 21 of them had HI during CAFS, while the other 20 children were NSD. There was significant difference in apparent diffusion coefficient (ADC) values of the left and right hippocampus between children with HI during CAFS and NSD (r < 0.05). The corresponding ADC graphs were relatively clear at b = 1000 s/mm2 and 1200 s/mm2.

Hippocampal DWI scans at b = 1000 s/mm2 and 1200 s/mm2 might be recommended clinical b value point for diffusion characterization of HI.

A hybrid Reynolds-averaged Navier-Stokes (RANS) large eddy simulation (LES) method is applied in this work. It called very-large-eddy simulation (VLES) turbulence closure model. The aim of this present study is firstly to validate the accuracy of this method for a specific engineering application (a trapped vortex combustor) and secondly to describe its flow characteristics. The trapped vortex combustor is a new concept that utilizes a large recirculation vortex to stabilize the flame. An accurate prediction of the turbulent flow is meaningful for the trapped vortex combustor. The time-averaged velocity, root-mean-square (rms) velocity, and flow pattern are compared with the experimental data. And the LES model, RANS BSL k-ω model, and RANS k-ɛ model are also applied for the simulation with different mesh resolutions. The results show that the VLES BSL k-ω model provides improved accuracy for velocity prediction. The classical large vortex structure for the trapped vortex combustor is captured qualitatively by the VLES BSL k-ω model also. In addition, the vortex breakdown and processing vortex cone are visualized using the Q-criterion. Furthermore, the VLES BSL k-ω model is not sensitive to the gird resolution. The VLES method is able to predict the turbulent flow of trapped vortex combustor relatively well‎.

The biological surface structure comprising fish scales and a mucous membrane exhibits good turbulent drag reduction ability. Based on this structure, a bionic frictional drag reduction model composed of a grooved structure and mucous membrane was established herein, and its efficacy in reducing the resistance of a turbulent boundary layer was analyzed. Accordingly, the drag reduction performance of the bionic structure was investigated through large eddy simulations. The results revealed that the mucous membrane was evenly distributed on the groove wall through secretion, and effectively improved the drag reduction rate of the groove wall. The bionic grooves and mucous membrane structure successfully inhibited the turbulent kinetic energy, turbulence intensity, and Reynolds stress. The grooved structure improved the shape of the Λ vortex structure and the mucous membrane reduced the number of three-dimensional (3D) vortex structures. Furthermore, the streak structure near the bionic structure wall was reduced and its shape was regularized, which intuitively demonstrates the turbulence suppression ability of the proposed bionic structure. This paper presents the results of a hydrodynamic analysis of the frictional drag reduction characteristics of a bionic structure consisting of grooves and viscous membranes acting on the turbulent boundary layer of a wall.

A novel Halbach permanent magnet array with rectangle section and trapezoid section is proposed and optimized in this paper. The analytical model of the premanent magnet segment is established based on the surface current method, which is numerically efficient and can be utilized to evaluate the magnetic field closely with the premanent magnet segment’s configurations. The analytical model of the Halbach array is acquired based on the superposition principle and coordinate transformation. The fundamental component of the magnetic flux density and the sinusoidal distortion rate are chosen as the optimization object. And the optimization is executed on the Halbach array with one specific set of dimensions by the genetic algorithm in global scale. The effectiveness of the optimization is validated by the finite element analysis. Compared to the traditional Halbach array with rectangle section, the magnetic field created by the optimized proposed Halbach array in this paper owns better performance.

The mucous membrane on the fish surface has excellent drag reduction performance. The mucous membrane can be regarded as the viscoelastic fluid, and a bionic friction drag reduction model is proposed with the consideration of a Carreau viscoelastic model-based mucus secretion process. Then, the drag reduction effect of the mucous membrane on the classical wall turbulence boundary layer is investigated by large-eddy simulations. Results show that the bionic mucous membrane is conducive to reducing the turbulence, and can achieve a drag reduction rate of about 14%. This study provides a hydrodynamics understanding of the drag reduction characteristics of the bionic mucous membrane.

Nonreacting flow characteristics are important for determining the performances of combustors. In the present work, the effects of mainstream swirling on the nonreacting flow characteristics of an outer-cavity trapped vortex combustor are investigated by introducing swirlers. The results are first validated by particle image velocimetry measurements by considering four swirl numbers (0, 0.4, 0.6, and 0.8) and three velocity sets. The results show that the addition of swirlers in the mainstream introduces 3D flow not only in the mainstream but also in the cavities. As the swirl number increases, the size of the low-velocity region near the center-line of the combustor increases both in the axial and radial directions. The cavity flow maintains the dual-vortex pattern for most cases; however, for certain cases with high mainstream velocities and high swirl numbers (0.6, 0.8), multiple-vortex patterns are observed. The mixing results are discussed in terms of turbulence intensity and kinetic energy. The turbulence intensities of the combustor outlet for a swirl number of 0.8 are found to increase by approximately 250-350% compared to the case without swirling, indicating dramatically enhanced mixing.

The aim of the paper is to develop a grey model for short term forecasting of natural gas consumption and production in China and USA respectively. To enhance its prediction accuracy, the outliers are found by the error of the latent information function, and then corrected according to the test sample and the future trend. The sequence with corrected outliers is used to construct a grey model. The proposed model is employed to predict the natural gas consumption and production in China and USA. The results have demonstrated that the proposed model can raise the forecast accuracy of the grey model, and it also indicates that China will inevitably face a massive expansion in natural gas imports.