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RISS 인기검색어
- 검색키워드
- 저자 : Huizhen Li (검색결과 5 건)
- 무료
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- 유료
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Singularity-free path optimization of the parallel test mechanism for artificial hip joints
Huizhen Zhang,Gang Cheng,Xianlei Shan,Yang Li 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.4
This paper focuses on the singularity-free optimization for the working path of a 3SPS+1PS type parallel mechanism which is used for the simulation of hip joint motion. Kinematic and dynamic models of the test mechanism were set up with the vector method and the principle of virtual power, respectively. Based on the Jacobian matrix, the kinematic and dynamic performance evaluation indices were defined. The working path of the test mechanism traverses the singular surface twice. Optimization weas conducted with the attitude of the virtual reference coordinate system as the design variable, the mean value of the motion transmission performance index and the mean value and the standard deviation of the driving force in the working path as the optimization objectives, and the reachable workspace as the constraint condition. The equivalent working path of the test mechanism after optimization had no singularity. Moreover, the motion transmission performance improved evidently and the driving force changed smoothly.
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Parametric study of an undulating plate in a power-extraction regim
Xiaojing Sun,Jihua Zhang,Huizhen Li,Diangui Huang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.1
Our previous studies suggest that instead of propulsion, a body undergoing lateral traveling-wave-like motions can also work like a kinetic energy harvester which extracts energy from moving fluids including wind and water currents. Parameters including wavelength, dimensionless wave velocity and amplitude have critical effects on the energy extraction efficiencies of this type of undulating foil energy harvester. In this paper, a two-dimensional, numerical simulation of a flexible plate undergoing a traveling wave motion was then conducted. At a given dimensionless wave speed, it is found that there exits an optimum wavelength at which this type of energy harvester can extract the maximum amount of kinematic energy from the flow. Moreover, the optimum value of the wavelength increases as amplitude increases. A high efficiency area appears under the optimal combination of wavelength and amplitude. At a given amplitude, the optimal dimensionless wave speed for maximum power extraction decreases with increasing wavelength. The high efficiency area of the undulating plate resulting from the optimal combination of wavelength and wave speed is identified. At a given wave length, there is an optimal value of amplitude at which the maximum energy extraction can be achieved. In this case, a high efficiency area representing the optimal combination of amplitude and wave speed has also been discovered.
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Chenglei Liu,Yan Xi,Mei Li,Qiong Jiao,Huizhen Zhang,Qingcheng Yang,Weiwu Yao 대한영상의학회 2019 Korean Journal of Radiology Vol.20 No.5
Objective: To determine whether diffusion kurtosis imaging (DKI) is effective in monitoring tumor response to neoadjuvant chemotherapy in patients with osteosarcoma. Materials and Methods: Twenty-nine osteosarcoma patients (20 men and 9 women; mean age, 17.6 ± 7.8 years) who had undergone magnetic resonance imaging (MRI) and DKI before and after neoadjuvant chemotherapy were included. Tumor volume, apparent diffusion coefficient (ADC), mean diffusivity (MD), mean kurtosis (MK), and change ratio (ΔX) between preand post-treatment were calculated. Based on histologic response, the patients were divided into those with good response (≥ 90% necrosis, n = 12) and those with poor response (< 90% necrosis, n = 17). Several MRI parameters between the groups were compared using Student’s t test. The correlation between image indexes and tumor necrosis was determined using Pearson’s correlation, and diagnostic performance was compared using receiver operating characteristic curves. Results: In good responders, MDpost, ADCpost, and MKpost values were significantly higher than in poor responders (p < 0.001, p < 0.001, and p = 0.042, respectively). The ΔMD and ΔADC were also significantly higher in good responders than in poor responders (p < 0.001 and p = 0.01, respectively). However, no significant difference was observed in ΔMK (p = 0.092). MDpost and ΔMD showed high correlations with tumor necrosis rate (r = 0.669 and r = 0.622, respectively), and MDpost had higher diagnostic performance than ADCpost (p = 0.037) and MKpost (p = 0.011). Similarly, ΔMD also showed higher diagnostic performance than ΔADC (p = 0.033) and ΔMK (p = 0.037). Conclusion: MD is a promising biomarker for monitoring tumor response to preoperative chemotherapy in patients with osteosarcoma.
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