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An Octree-Based Two-Step Method of Surface Defects Detection for Remanufacture
Yan He,Wen Ma,Yufeng Li,Chuanpeng Hao,Yulin Wang,Yan Wang 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.2
Accurate and quick detection has a significant bearing on overall productivity of remanufacture. 3D scanning technologies have been widely applied in defects detection by comparing the damaged model with the nominal model. In this process, a huge amount of point cloud data is required to ensure detection accuracy whereas resulting in large storage space and long processing time of detection. This paper proposed an efficient two-step method based on octree to detect defects accurately and quickly for remanufacturing. In this method, the damaged point cloud and the nominal point cloud are first registered. Then a two-step detection approach is developed to extract the surface defects, coarse detection and detailed extraction, where the octree method is applied to create an effective topology of discrete points and perform the Boolean operation for defects extraction. In coarse detection, rough location and size information of the defects are acquired from the whole point cloud data. Based on coarse detected boundary box containing defects, the detailed extraction step is applied to extract corresponding defects shape accurately. The feasibility of proposed method was validated by using a case to detect defects of a damaged turbine blade and the detection results can be used to generate restoration tool path. The results show that the proposed method outperforms state-of-art defects detection methods, which can reduce time by 74.03% and reduce error by 36.86%, respectively.
Seismic collapse risk of RC frames with irregular distributed masonry infills
Yan-Wen Li,Michael C.H. Yam,Ke Cao 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.3
Masonry infills are normally considered as non-structural elements in design practice, therefore, the interaction between the bounding frame and the strength contribution of masonry infills is commonly ignored in the seismic analysis work of the RC frames. However, a number of typical RC frames with irregular distributed masonry infills have suffered from undesirable weak-story failure in major earthquakes, which indicates that ignoring the influence of masonry infills may cause great seismic collapse risk of RC frames. This paper presented the investigation on the risk of seismic collapse of RC frames with irregularly distributed masonry infills through a large number of nonlinear time history analyses (NTHAs). Based on the results of NTHAs, seismic fragility curves were developed for RC frames with various distribution patterns of masonry infills. It was found that the existence of masonry infills generally reduces the collapse risk of the RC frames under both frequent happened and very strong earthquakes, however, the severe irregular distribution of masonry infills, such as open ground story scenario, results in great risk of forming a weak story failure. The strong-column weak-beam (SCWB) ratio has been widely adopted in major seismic design codes to control the potential of weak story failures, where a SCWB ratio value about 1.2 is generally accepted as the lower limit. In this study, the effect of SCWB ratio on inter-story drift distribution was also parametrically investigated. It showed that improving the SCWB ratio of the RC frames with irregularly distributed masonry infills can reduce inter-story drift concentration index under earthquakes, therefore, prevent weak story failures. To achieve the same drift concentration index limit of the bare RC frame with SCWB ratio of about 1.2, which is specified in ACI318-14, the SCWB ratio of masonry-infilled RC frames should be no less than 1.5. For the open ground story scenario, this value can be as high as 1.8.
Implicit Detection of Hidden Processes with a Local-Booted Virtual Machine
Yan Wen,Huaimin Wang,Jinjing Zhao 보안공학연구지원센터 2008 International Journal of Security and Its Applicat Vol.2 No.4
Currently stealth malware is becoming a major threat to the PC computers. Process hiding is the technique commonly used by stealth malware to evade detection by anti-malware scanners. On the defensive side, previous host-based approaches will be defeated once the privileged stealth malware controls a lower reach of the system. The virtual machine (VM) based solutions gain tamper resistance at the cost of losing the OS-level process view. Moreover, existing VM-based approaches cannot introspect the preinstalled OS which is just the protecting concern for PC users. In this paper, we present a new VM-based approach called Libra which accurately reproduces the software environment of the underlying preinstalled OS within the Libra VM and provides an OS-level semantic view of the processes. With our new local-booting technology, Libra VM just boots from the underlying host OS but not a newly installed OS image. Thus, Libra provides a way to detect the existing process-hiding stealth malware in the host OS. In addition, instead of depending on the guest information which is subvertable to the privileged guest malware, Libra adopts a unique technique to implicitly construct the Trusted View of Process List (TVPL) from within the virtualized hardware layer. Our evaluation results with real-world hiding-process rootkits, which are widely used by stealth malware, demonstrate its practicality and effectiveness.
Wen Yan,Nan Li,Bingqiang Han 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.3
The effects of sintering temperature on the pore characteristics and strength of porous corundum-mullite ceramics made from Al(OH)3, kaolinite gangue and MgCO3 were investigated through an X-ray diffractometer (XRD), scanning electron microscopy (SEM), mercury porosimetry measurement, etc. It was found that the sintering temperature strongly affects the formation of secondary mullite, and then changes the pore characteristics and strength. The formation of secondary mullite takes place extremely quickly at 1500 oC. The pore size distributions are bimodal in samples sintered at 1300 oC and 1400 oC,and mono-modal in samples sintered at 1500 oC and 1600 oC. The strength are the same and low when the sintering temperatures are 1300 oC and 1400 oC, and increase sharply when the sintering temperature is increased to 1500 oC. The most apposite mode is a sample sintered at 1500 oC which has a high mullite content (86.6 wt%), high apparent porosity (42%), high crushing strength (52 MPa) and a homogeneous pore size distribution.
Wen Yan,Qingjie Chen,Xiaoli Lin,Junfeng Chen,Nan Li 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.4
Corrosion of five corundum-mullite refractories with the different porous aggregates and the same matrix by the blast furnaceslag was conducted using the static crucible test. Effects of properties of corundum-mullite aggregates on the slag resistanceof refractories were investigated through X-ray diffractometer (XRD), scanning electron microscopy (SEM), and mercuryporosimetry measurement, etc. It is found that the porous corundum-mullite aggregates have different slag absorbing capacity,which affects the composition of the corroded aggregates and matrices at slag/refractory interface, and thus affects the slagcorrosion and penetration resistances. Comparing with the dense corundum-mullite refractory, the porous corundum-mulliteaggregate with 31.6% apparent porosity (AP) substituting the dense aggregates in the refractories does not make the slagresistance degenerate and reduces the bulk density by 16.7 wt%; whereas, when the APs of aggregates increase to 41.6-44.8%,the slag resistance sharply deceases. It is a successful case that the developed lightweight refractory with high slag resistancehas a potential application for working lining of high-temperature furnace.