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RISS 인기검색어
- 검색키워드
- 저자 : Xiaopeng Shi (검색결과 4 건)
- 무료
- 기관 내 무료
- 유료
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Ultimate Behavior and Design of Cold-Formed Steel Square Hollow Section Members
Xiaopeng Shi,Xin Cheng,Xiaxin Wang,Mohamad Mansour 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.3
The ultimate behavior and design of cold-formed steel square hollow section (SHS) members are investigated in the present study, with the focus on their local buckling behavior under pure compression and pure bending, as well as combinations of compression and bending. Finite element (FE) models are established and validated against existing experimental data collected from the literatures; the FE models take into account the initial local imperfections, geometric and material nonlinearities, and cold-formed eff ect. Following the validation, the FE models are utilized to perform a series of parametric studies, considering diff erent cross-section width-to-thickness ratios and loading cases. The stress distributions within the critical cross-section of the SHS members under diff erent loading conditions are investigated and an eff ective plastic width method (EPM) is proposed for the determination of the ultimate resistance of SHS in compression and bending. The numerically obtained results are used to assess the accuracy of the existing design rules stipulated in the Chinese and European design codes and the proposed EPM. It is shown that the proposed EPM is able to provide more accurate design predictions in relative to the codifi ed design approaches, owing largely to its rational considerations of the strain hardening, cold-formed eff ect and partial plasticity of the cold-formed SHS members.
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A new cavitation model considering inter-bubble action
Shi Yazhen,Luo Kai,Chen Xiaopeng,Li Daijin,Jia Laibing 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1
The process of cavitation involves generation, growth, coalescence, and collapse of small bubbles and is tremendously influenced by bubbleebubble interactions. To understand these interactions, a new cavitation model based on the transport equation is proposed herein. The modified RayleighePlesset equation is analyzed to determine the bubble growth rate by assuming equal-sized spherical bubble clouds. The source term in the transport equation is then derived according to the bubble growth rate with the bubble-bubble interaction. The proposed model is validated by various test simulations, including microscopic bubble cloud evolution as well as macroscopical two- and three-dimensional cavitating flows. Compared with previous models, namely the Kunz and Zwart cavitation models, the newly proposed model does not require adjustable parameters and generally results in better predictions both microscopic and macroscopical cases. This model is more physical.
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Reconstruction of 7T-Like Images From 3T MRI
Bahrami, Khosro,Shi, Feng,Zong, Xiaopeng,Shin, Hae Won,An, Hongyu,Shen, Dinggang IEEE 2016 IEEE transactions on medical imaging Vol.35 No.9
<P>In the recent MRI scanning, ultra-high-field (7T) MR imaging provides higher resolution and better tissue contrast compared to routine 3T MRI, which may help in more accurate and early brain diseases diagnosis. However, currently, 7T MRI scanners are more expensive and less available at clinical and research centers. These motivate us to propose a method for the reconstruction of images close to the quality of 7T MRI, called 7T-like images, from 3T MRI, to improve the quality in terms of resolution and contrast. By doing so, the post-processing tasks, such as tissue segmentation, can be done more accurately and brain tissues details can be seen with higher resolution and contrast. To do this, we have acquired a unique dataset which includes paired 3T and 7T images scanned from same subjects, and then propose a hierarchical reconstruction based on group sparsity in a novel multi-level Canonical Correlation Analysis (CCA) space, to improve the quality of 3T MR image to be 7T-like MRI. First, overlapping patches are extracted from the input 3T MR image. Then, by extracting the most similar patches from all the aligned 3T and 7T images in the training set, the paired 3T and 7T dictionaries are constructed for each patch. It is worth noting that, for the training, we use pairs of 3T and 7T MR images from each training subject. Then, we propose multi-level CCA to map the paired 3T and 7T patch sets to a common space to increase their correlations. In such space, each input 3T MRI patch is sparsely represented by the 3T dictionary and then the obtained sparse coefficients are used together with the corresponding 7T dictionary to reconstruct the 7T-like patch. Also, to have the structural consistency between adjacent patches, the group sparsity is employed. This reconstruction is performed with changing patch sizes in a hierarchical framework. Experiments have been done using 13 subjects with both 3T and 7T MR images. The results show that our method outperforms previous methods and is able to recover better structural details. Also, to place our proposed method in a medical application context, we evaluated the influence of post-processing methods such as brain tissue segmentation on the reconstructed 7T-like MR images. Results show that our 7T-like images lead to higher accuracy in segmentation of white matter (WM), gray matter (GM), cerebrospinal fluid (CSF), and skull, compared to segmentation of 3T MR images.</P>
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Youhua Li,Lubing Shi,Zhongming Liu,Xiaopeng Wang,Xuetao Qiao,Zhihong Zhang,Shidang Yan 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12
For high-speed, heavy-load gear units, the meshing tooth surfaces are generally under the mixed lubrication state, which is crucial for gear pitting or micro pitting damage. To clarify the effects of lubrication state on tooth pitting damage, carrying out both numerical and experimental studies on the contact severity of gears under different lubrication states is necessary. In this paper, a 3D line-contact elasto hydrodynamic lubrication model considering fractal surface roughness was developed and used to investigate the lubrication characteristics of involute gears. Both the distributions of pressure and film thickness fluctuated under the rolling contact of rough surfaces. The fluctuations became more substantial with the increase of load and roughness. Furthermore, from the calculated film thickness ratio λ, the contact of gear tooth surfaces with a fractal roughness of Ra = 0.8 μm was always under full lubrication state (λ > 1). When the roughness was increased to Ra = 3.2 μm, the contact was first transmitted into the mixed lubrication state (0.2 < λ < 1) under the load of 1000 N*m and finally deteriorated to boundary lubrication state (λ < 0.2) under the load of 2000 N*m. The boundary lubrication state that occurred under the contact of highly rough surfaces could induce the formation of gear pitting damage. The contact fatigue test showed the gear tooth surface roughness increased from 0.7 μm to around 2.7 μm after 8 million running cycles and then suffered pitting failure after another 2 million cycles, which was consistent with the simulation analysis prediction.
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