Short-Term Forecasting for Harbor Waterway Currents Speeds

Cheng Gong,Yan Lv,Chunjiang Zhang,Xiyuan Wang,Wei Huangfu,Zhongshan Zhang 보안공학연구지원센터 2014 International Journal of Multimedia and Ubiquitous Vol.9 No.12

The ocean currents speeds in the harbor waterway are directly related to the ability of the ship to in or out the harbor. Accurately predict the speeds can assist the ship to choose the right time for sailing. To solve this problem, we chose two models of linear and non-linear prediction. We had set sensors in Qinhuangdao for a long time, then using the collected data for training. Our test is using a lot of random data to train and predict with different steps and orders. The results show that both methods can use less original data to train the model, and finally achieve preferably prediction. According to the characteristics of Qinhuangdao harbor, Auto-Regressive (AR) model is more appropriate than Support Vector Regression (SVR) model.

Improvement of the Representative Volume Element Method for 3-D Scaffold Simulation

Cheng Lv-Sha,Kang Hyun-Wook,Cho Dong-Woo The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.10

Predicting the mechanical properties of the 3-D scaffold using finite element method (FEM) simulation is important to the practical application of tissue engineering. However, the porous structure of the scaffold complicates computer simulations, and calculating scaffold models at the pore level is time-consuming. In some cases, the demands of the procedure are too high for a computer to run the standard code. To address this problem, the representative volume element (RVE) theory was introduced, but studies on RVE modeling applied to the 3-D scaffold model have not been focused. In this paper, we propose an improved FEM-based RVE modeling strategy to better predict the mechanical properties of the scaffold prior to fabrication. To improve the precision of RVE modeling, we evaluated various RVE models of newly designed 3-D scaffolds using FEM simulation. The scaffolds were then constructed using microstereolithography technology, and their mechanical properties were measured for comparison.

Improvement of the Representative Volume Element Method for 3-D Scaffold Simulation

Lv-Sha Cheng,Hyun-Wook Kang,Dong-Woo Cho 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.10

Predicting the mechanical properties of the 3-D scaffold using finite element method (FEM) simulation is important to the practical application of tissue engineering. However, the porous structure of the scaffold complicates computer simulations, and calculating scaffold models at the pore level is time-consuming. In some cases, the demands of the procedure are too high for a computer to run the standard code. To address this problem, the representative volume element (RVE) theory was introduced, but studies on RVE modeling applied to the 3-D scaffold model have not been focused. In this paper, we propose an improved FEM-based RVE modeling strategy to better predict the mechanical properties of the scaffold prior to fabrication. To improve the precision of RVE modeling, we evaluated various RVE models of newly designed 3-D scaffolds using FEM simulation. The scaffolds were then constructed using microstereolithography technology, and their mechanical properties were measured for comparison.

A Pipe Heat Insulation Device Featuring Vacuum Valve Box Structure

Fang-jiang Lv,Cheng-cheng Shao 한국디자인학회 2014 디자인학연구 Vol.27 No.4

Integrated Calibration for the Cross Magnetic Gradiometer

Cheng Chi,Jun-Wei Lv,Dan Wang,Zhen-Tao Yu,Jing-Li Huang 한국자기학회 2017 Journal of Magnetics Vol.22 No.3

The magnetic gradiometer onboard a maneuverable vehicle is subjected to not only magnetometer errors and misalignment errors but also magnetic interference of vehicle. Measurement precision of the magnetic gradiometer is greatly affected by those errors, so an integrated error calibration method is proposed in this paper. Firstly, considering vector magnetometer errors and magnetic interference, an integrated error calibration model for vector magnetometer is established, and ellipsoid fitting parameters are calculated by the least square algorithm under ellipsoid restriction, then the error calibration matrices are solved by the Cholesky factorization. Secondly, the misalignment error calibration matrices are obtained by solving the Orthogonal Procrustes problem. Finally, simulations and experiments with a cross magnetic gradiometer are performed to verify effectiveness and robustness of the proposed method. Results show that the proposed method can effectively calibrate the cross magnetic gradiometer, and measurement accuracy of the cross magnetic gradiometer is increased greatly.

한반도 식생의 녹색화에 대한 시계열적 분석

Lv, Guan Ting,ZHUYONGYAN,Liu, Wei Qi,Huang, Xiao,Li, Cheng Lei,Cui, Gui Shan 한국기후변화학회 2019 한국기후변화학회지 Vol.10 No.4

The vegetation is feedback on environmental change due to global warming. Also, the growth status of vegetation and the coverage area of vegetation are greatly affected by the environmental changes. The quantitative change of vegetation growth status is the primary task of vegetation response to environmental changes. In this study, the Global Inventory Modeling and Mapping Studies (GIMMS) based Normalized Difference Vegetation Index (NDVI) and CRU climate data are used to analyze the spatio‐temporal characteristics of vegetation greening evolution and its response to climate change from 1982 to 2015 in the Korean Peninsula by applying the partial correlation and trend analysis. The results show that the average NDVI value of the Korean Peninsula in the period 1982‐2015 was 0.68, among which the average NDVI in North Korea and South Korea was 0.69 and 0.67, respectively. The NDVI of the Korean Peninsula between 1982 and 2015 increased by 0.6x10‐3 year‐1. The increasing trend prior to and after 1998 was 2.5×10‐3 year‐1 and 0.9×10‐3 year‐1, respectively. During the 1982‐2015 years, the NDVI of DPRK and South Korea have grown mainly with the trend of 0.2×10‐3 year‐1 and 1.1×10‐3 year‐1, respectively. According to the analysis of NDVI and climatic factors, the distribution of NDVI in the three‐time series of Korean Peninsula is consistent in spatial distribution. According to the results of partial correlation analysis of climate factor and NDVI distribution in Korean Peninsula, the region has significant partial correlation with temperature change. The climate factor of temperature is the main driver of NDVI change, which plays a key role in controlling NDVI change accumulation.

Diffusion-Weighted Magnetic Resonance Imaging in the Diagnosis of Cerebral Venous Thrombosis : A Meta-Analysis

Lv, Bin,Jing, Feng,Tian, Cheng-lin,Liu, Jian-chao,Wang, Jun,Cao, Xiang-yu,Liu, Xin-feng,Yu, Sheng-yuan The Korean Neurosurgical Society 2021 Journal of Korean neurosurgical society Vol.64 No.3

Objective : A role of diffusion-weighted imaging (DWI) in the diagnosis of cerebral venous thrombosis (CVT) is not well-understood. This study evaluates the effectiveness of DWI in the diagnosis of CVT. Methods : Literature search was conducted in electronic databases for the identification of studies which reported the outcomes of patients subjected to DWI for CVT diagnosis. Random-effects meta-analyses were performed to achieve overall estimates of important diagnostic efficiency indices including hyperintense signal rate, the sensitivity and specificity of DWI in diagnosing CVT, and the apparent diffusion coefficient (ADC) of DWI signal areas and surrounding tissue. Results : Nineteen studies (443 patients with 856 CVTs; age 40 years [95% confidence interval (CI), 33 to 43]; 28% males [95% CI, 18 to 38]; symptom onset to DWI time 4.6 days [95% CI, 2.3 to 6.9]) were included. Hyperintense signals on DWI were detected in 40% (95% CI, 26 to 55) of the cases. The sensitivity of DWI for detecting CVT was 22% (95% CI, 11 to 34) but specificity was 98% (95% CI, 95 to 100). ADC values were quite heterogenous in DWI signal areas. However, generally the ADC values were lower in DWI signal areas than in surrounding normal areas (mean difference-0.33×10-3 ㎟/s [95% CI, -0.44 to -0.23]; p<0.00001). Conclusion : DWI has a low sensitivity in detecting CVT and thus has a high risk of missing many CVT cases. However, because of its high specificity, it may have supporting and exploratory roles in CVT diagnosis.

Modeling and coupling characteristics for an airframe-propulsion-integrated hypersonic vehicle

Lv, Chengkun,Chang, Juntao,Dong, Yilei,Ma, Jicheng,Xu, Cheng Techno-Press 2020 Advances in aircraft and spacecraft science Vol.7 No.6

To address the problems caused by the strong coupling of an airbreathing hypersonic vehicle's airframe and propulsion to the integrated control system design, an integrated airframe-propulsion model is established, and the coupling characteristics between the aircraft and engine are analyzed. First, the airframe-propulsion integration model is established based on the typical nonlinear longitudinal dynamical model of an air-breathing hypersonic vehicle and the one-dimensional dual-mode scramjet model. Thrust, moment, angle of attack, altitude, and velocity are used as transfer variables between the aircraft model and the engine model. The one-dimensional scramjet model can accurately reflect the working state of the engine and provide data to support the coupling analysis. Second, owing to the static instability of the aircraft model, the linear quadratic regulator (LQR) controller of the aircraft is designed to ensure attitude stability and height tracking. Finally, the coupling relationship between the aircraft and the engine is revealed through simulation examples. The interaction between vehicle attitude and engine working condition is analyzed, and the influence of vehicle attitude on engine safety is considered. When the engine is in a critical working state, the attitude change of the aircraft will not affect the engine safety without considering coupling, whereas when coupling is considered, the attitude change of the aircraft may cause the engine unstart, which demonstrates the significance of considering coupling characteristics.

Inductances Evaluation of a Squirrel-Cage Induction Motor with Curved Dynamic Eccentricity

Lv, Qiang,Bao, Xiaohua,He, Yigang,Fang, Yong,Cheng, Xiaowei The Korean Institute of Electrical Engineers 2014 Journal of Electrical Engineering & Technology Vol.9 No.5

Eccentricity faults more or less exist in all rotating electrical machines. This paper establishes a more precise model of dynamic eccentricity (DE) in electrical machines named as curved dynamic eccentricity. It is a kind of axial unequal eccentricity which has not been investigated in detail so far but occurs in large electrical machines. The inductances of a large three-phase squirrel-cage induction machine (SCIM) under different levels of curved DE conditions are evaluated using winding function approach (WFA). These inductances include the stator self and mutual inductances, rotor self and mutual inductances, and mutual inductances between stator phases and rotor loops. A comparison is made between the calculation results under curved DE and the corresponding pure DE conditions. It indicates that the eccentricity condition will be more terrible than the monitored eccentricity based on the conventional pure DE model.

Relative Abundance of a Vector of Scrub Typhus, Leptotrombidium sialkotense, in Southern Yunnan Province, China

Yan Lv,Xian-Guo Guo,Dao-chao Jin,Wen-Yu Song,Rong Fan,Cheng-Fu Zhao,Zhi-Wei Zhang,Ke-Yu Mao,Yun-Ji Zou,Zhi-Hua Yang 대한기생충학ㆍ열대의학회 2020 The Korean Journal of Parasitology Vol.58 No.2

The chigger mite Leptotrombidium sialkotense is one of the 6 main vectors of scrub typhus in China. Before present study, L. sialkotense was found in some parts of Hunan province, China with a narrow geographical distribution. During field investigation 2016-2017, we found L. sialkotense in Jingha, southern Yunnan, China. Of 15 small mammal host species, L. sialkotense were collected from 6 species of the hosts. Rattus brunneusculus was a dominant host of L. sialkotense, from which 98.3% of the mites were collected. The chigger mite showed a relatively high infestation prevalence (PM=11.7%) and mean abundance (MA=0.5) in comparison with the rest 5 host species. These results reveal a certain host specificity of L. sialkotense to a rat R. brunneusculus. The mite L. sialkotense showed an aggregated distribution on the host (P<0.05). A positive correlation observed between L. sialkotense and the body length of hosts. There was a positive interspecific association between L. sialkotense and 2 other dominant vectors, L. deliense and L. scutellare.