Numerical investigation of the unsteady flow of a hybrid CRP pod propulsion system at behind-hull condition

Zhang, Yuxin,Cheng, Xuankai,Feng, Liang The Society of Naval Architects of Korea 2020 International Journal of Naval Architecture and Oc Vol.12 No.-

Flows induced by hybrid CRP pod propulsion systems (CRP-POD) are fundamentally characterized by unsteadiness. This work presents a numerical study on the unsteady flow of a CRP-POD at behind-hull condition based on CFD (Computational Fluid Dynamics). Unsteady RANS method is adopted, coupled with SST k-u turbulence model and sliding mesh method. The propeller thrusts and torques obtained by CFD is validated by model tests and acceptable agreements are obtained. The time histories of shingle-blade loads and pressures near the hull surface are recorded for the analysis of unsteady flow features. The cases of forward propeller alone and aft propeller alone are also computed to distinguish the hull-propeller interaction and propeller-propeller interaction. The results show the blade loads of both forward and aft propellers strongly fluctuate with phase angles. For the forward propeller, the blade load fluctuation is mainly governed by the hull-propeller interaction, while the aft blade load is remarkably affected by the propeller-propeller interaction in terms of the load average and fluctuation pattern. The fields of pressure, vorticity and velocity are also analyzed to reveal the unsteady flow features.

Numerical investigation of the unsteady flow of a hybrid CRP pod propulsion system at behind-hull condition

Zhang, Yuxin,Cheng, Xuankai,Feng, Liang The Society of Naval Architects of Korea 2020 International Journal of Naval Architecture and Oc Vol.12 No.1

Flows induced by hybrid CRP pod propulsion systems (CRP-POD) are fundamentally characterized by unsteadiness. This work presents a numerical study on the unsteady flow of a CRP-POD at behind-hull condition based on CFD (Computational Fluid Dynamics). Unsteady RANS method is adopted, coupled with SST k-u turbulence model and sliding mesh method. The propeller thrusts and torques obtained by CFD is validated by model tests and acceptable agreements are obtained. The time histories of shingle-blade loads and pressures near the hull surface are recorded for the analysis of unsteady flow features. The cases of forward propeller alone and aft propeller alone are also computed to distinguish the hull-propeller interaction and propeller-propeller interaction. The results show the blade loads of both forward and aft propellers strongly fluctuate with phase angles. For the forward propeller, the blade load fluctuation is mainly governed by the hull-propeller interaction, while the aft blade load is remarkably affected by the propeller-propeller interaction in terms of the load average and fluctuation pattern. The fields of pressure, vorticity and velocity are also analyzed to reveal the unsteady flow features.

Degradation of organic micropollutant by vacuum ultraviolet process: a kinetics study

Laxiang Yang,Yuxin Feng,Zhixing Gao 한국화학공학회 2021 Korean Journal of Chemical Engineering Vol.38 No.8

Vacuum ultraviolet (VUV) process has been regarded as a novel advanced oxidation process for its unique way of generating HO• via direct photolysis of water. This study investigates the kinetics of the VUV process for degradation of a typical pesticide, glyphosate (GLY), by using a photoreactor equipped with a precision sampler. The precision sampler enables us to take samples at distances ranging from 0.1 to 1.5 cm to the irradiation source so that GLY degradation by VUV in different parts of the reaction volume can be evaluated. The results of experiments on H2O2 production from VUV photolysis of water confirmed that there existed an extremely uneven distribution of VUV flux and HO• generated in the VUV process. Enhancing mass transfer by agitation could significantly increase GLY degradation efficiency by improving the distribution of HO•. The initial concentrations of water and GLY governed the reaction kinetics of GLY degradation in the VUV process. As the solution pH increased from 5.0 to 9.0, the overall degradation efficiency of GLY decreased from 97.6% to 77.8%. Depending on their molar absorption coefficients, inorganic anions affected adversely on the degradation of GLY by VUV in the order of NO3 >HCO3  (alkalinity)>Cl>SO4 2. As a strong HO• scavenger, natural organic matter shows a much more adverse impact on GLY degradation than that of inorganic anions. Based on the experimental results, this study has provided insights into the kinetics of VUV process for pollutant degradation.

A Voronoi path planning extracted from improved skeleton for dynamic environments

Lin Jiang,Jun Li,Yuxin Hu,Feng Pan,Jianyang Zhu,Bin Lei,Rui Lin 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.4

Aiming at the problems that the robot being in the process of navigation cannot meet the requirements of real-time and accuracy at the same time, moreover is too close to obstacles and lacks the initiative to avoid obstacles, a Voronoi diagram algorithm for improved skeleton extraction suitable for dynamic environment is proposed. On the one hand, firstly the grid map is preprocessed by binarization, corrosion and expansion, so the reduced skeleton map suitable for navigation is obtained, then the reduced skeleton map is extracted for searching the global path, finally the improved cubic spline smoothing algorithm is used to optimize the global path each planned, thus overcoming the defects of bloated and tortuous in the path obtaining by original Voronoi diagram algorithm. On the other hand, the position information of all obstacles is obtained by a single scan lidar. Firstly, segmenting and linearly fitting all laser point clouds to remove the known obstacles in the map. Then to mark new possible dynamic obstacles with circles of appropriate size. Secondly detecting dynamic obstacles by the alteration of their center coordinates, moreover, solving their motion equations. Finally expanding the cost map along the speed direction of dynamic obstacles and combining DWA dynamic window method to realize dynamic obstacle avoidance. Compared with the original DWA algorithm, it can predict the motion state of dynamic obstacles in advance, which improves the safety of the robot in the dynamic environment. Moreover, the effectiveness of the algorithm is verified by many simulation experiments and real environment experiments.

The Physiological Occlusion of the Central Canal May Be a Prerequisite for Syringomyelia Formation

Chuan Jiang,Xinyu Wang,Chunli Lu,Qian Li,Longbing Ma,Wei Li,Shengyu Cui,Kang Li,Xiang Wang,Yuxin Feng,Fengzeng Jian 대한척추신경외과학회 2023 Neurospine Vol.20 No.4

Objective: Syringomyelia is a common central nervous system disease characterized by the dilation of the central canal (CC). Regarding the pathogenesis of syringomyelia, cerebrospinal fluid (CSF) circulation obstruction in the subarachnoid space (SAS) of the spinal cord has been widely accepted. However, clinical and animal studies on obstructing the CSF in SAS failed to form syringomyelia, challenging the theory of SAS obstruction. The precise pathogenesis remains unknown. Methods: We utilized an extradural compression rat model to investigate the pathogenesis underlying syringomyelia. Magnetic resonance imaging enabled detection of syringomyelia formation. To assess CSF flow within the SAS, Evans blue was infused into the cisterna magna. Histological analysis allowed morphological examination of the CC. Furthermore, CSF flow through the CC was traced using Ovalbumin Alexa-Flour 647 conjugate (OAF-647). Scanning electron microscopy (SEM) enabled visualization of ependymal cilia. Results: The findings showed that the dura mater below the compression segment exhibited lighter coloration relative to the region above the compression, indicative of partial obstruction within the SAS. However, the degree of SAS occlusion did not significantly differ between syringomyelia (SM-Y group) and those without (SM-N group). Intriguingly, hematoxylin and eosin staining and CSF tracing revealed occlusion of the CC accompanied by reduced CSF flow in the SM-Y group compared to SM-N and control groups. SEM images uncovered impairment of ependymal cilia inside the syringomyelia. Conclusion: CC occlusion may represent a physiological prerequisite for syringomyelia formation, while SAS obstruction serves to initiate disease onset. The impairment of ependymal cilia appears to facilitate progression of syringomyelia.