We present dynamic mode decomposition (DMD) for studying the hairpin vortices generated by hemisphere protuberance measured by two-dimensional (2D) time-resolved (TR) particle image velocimetry (PIV) in a water channe...We present dynamic mode decomposition (DMD) for studying the hairpin vortices generated by hemisphere protuberance measured by two-dimensional (2D) time-resolved (TR) particle image velocimetry (PIV) in a water channel. The hairpins dynamic information is extracted by identifying their dominant frequencies and associated spatial structures. For this quasi-periodic data system, the resulting main Dynamic modes illustrate the different spatial structures associated with the wake vortex region and the near-wall region. By comparisons with proper orthogonal decomposition (POD), it can be concluded that the dynamic mode concentrates on a certain frequency component more effectively than the mode determined by POD. During the analysis, DMD has proven itself a robust and reliable algorithm to extract spatial-temporal coherent structures.展开更多
It is shown that the leading edge protuberances on the flippers of a humpback whale can significantly improve the hydrodynamic performance. The present study numerically investigates the flow control mechanisms of the...It is shown that the leading edge protuberances on the flippers of a humpback whale can significantly improve the hydrodynamic performance. The present study numerically investigates the flow control mechanisms of the leading edge protuberances on a static wing and a pitching wing. For static wings, the performance in both laminar flow and turbulent flow are studied in the context of the flow control mechanisms. It is shown that the protuberances have slight effects on the performance of static wings in laminar flow. Also, it could be deduced that non-uniform downwash does not delay the stall occurrence in either laminar flow or turbulent flow. In turbulent flow, the leading edge protuberances act in a manner similar to vortex generators, enhancing the momentum exchange within the boundary layer. Streamwise vortices do contribute to the delay of the stall occurrence. The normal vorticity component also plays an important role in delaying the stall occurrence. However, for the pitching wing, the effect of leading edge protuberances is negligible in turbulent flow. Detailed analysis of the flow field indicates that for the wing with the leading edge protuberances, the leading edge vortices become more complex, while the thrust jet and the vortices in the wake are not changed significantly by the leading edge protuberances.展开更多
In this study, we presented new theory of effusive and explosive of volcanic eruptions. New explanation of eruption mechanisms was done by using the Elemental Buoyancy Theory and new K-Th-U structure of Earth, develop...In this study, we presented new theory of effusive and explosive of volcanic eruptions. New explanation of eruption mechanisms was done by using the Elemental Buoyancy Theory and new K-Th-U structure of Earth, developed early by author. During investigation of effusive eruptions, it was given clear answer on the question why the light chemical elements, mainly silicon and sulfur compound, currently dominate in the volcanic ashes, gases, and in the magma lavas. At investigation of explosive mechanism, we analyzed 38 strong eruptions with Volcanic Explosivity Index (VEI) more than 4+. It was shown that there is a link between the planet configurations and volcanic eruptions. It can be found that volcano eruptions occurred at the different types of planet alignments. The phenomenon does depend neither on planet mass nor on the relative positions of planets. Also the phenomenon does not depend on the distance between planets, but often eruptions were observed when the distances between planets are multiple units. Also in work, it was demonstrated that the planet alignment affects not only natural processes on the Earth, but also impact the Sun activity. Based on the comparison phenomenon on the Earth and Sun, we get new mechanism to rapidly rising up pressure under the lithospheric planes by gravity vortexes. This gravity vortex was called as terrestrial magmatic protuberances.展开更多
干涉配合可大幅度提高接头疲劳寿命。对基于应力波加载的钛合金干涉螺栓的高速安装过程进行了理论分析,对其安装工艺参数进行研究。研究表明:基于应力波加载的高速安装方法的安装阻力明显小于同等条件下准静态安装方法的安装阻力,干涉...干涉配合可大幅度提高接头疲劳寿命。对基于应力波加载的钛合金干涉螺栓的高速安装过程进行了理论分析,对其安装工艺参数进行研究。研究表明:基于应力波加载的高速安装方法的安装阻力明显小于同等条件下准静态安装方法的安装阻力,干涉量1%、1.5%和2%下最大安装阻力分别为3.92 k N、5.64 k N和6.11 k N;安装阻力随干涉量和安装次数增加而升高,随加载速度增加而降低;多次安装容易造成孔壁划伤,同时发现加载速度过大容易引起螺栓头损伤;干涉配合紧固件安装时孔边最大凸瘤高度与干涉量、安装速度和安装次数、摩擦因数正相关。展开更多
The aerodynamic loads of wind turbine blades are substantially affected by dynamic stall induced by the variations of the angle of attack of local airfoil sections.The purpose of the present study is to explore the ef...The aerodynamic loads of wind turbine blades are substantially affected by dynamic stall induced by the variations of the angle of attack of local airfoil sections.The purpose of the present study is to explore the effect of leading-edge protuberances on the fluctuation of the aerodynamic performances for wind turbine airfoil during dynamic stall.An experimental investigation is carried out by a direct force measurement technique employing force balance at a Reynolds number Re=2×105.The phase-averaged and instantaneous aerodynamic loads of the pitching airfoil,including the baseline and the wavy airfoil,are presented and analyzed.The phase-averaged results indicate that the effects of dynamic stall for the wavy airfoil can be delayed or minimized compared to the baseline airfoil,and the negative damping area of the wavy airfoil is significant decreased in full-stall condition.These effects of leading-edge protuberances are more notable at a higher reduced frequency.For the instantaneous aerodynamic loads of the wavy airfoil,there is an observable reduction in fluctuations compared with baseline case.Furthermore,spectral analysis is applied to quantitatively undercover the nonstationary features of the instantaneous aerodynamic loads.It is found that the leading edge protuberances can reduce the harmonics of the aerodynamic force signal,and enhance the stability of the aerodynamic loads under different reduced frequencies.In conclusion,leading-edge protuberances are found effective to reduce the fluctuation characteristics of the aerodynamic loads during the dynamic stall process,and help to improve the stability and prolong the service life of the wind turbine blades.展开更多
BACKGROUND Supra-and infratentorial acute epidural hematoma(SIEDH)is a common posterior cranial fossa epidural hematoma located at the inner surface of the squamous part of the occipital bone(SOB).Traditionally,surgic...BACKGROUND Supra-and infratentorial acute epidural hematoma(SIEDH)is a common posterior cranial fossa epidural hematoma located at the inner surface of the squamous part of the occipital bone(SOB).Traditionally,surgical treatment of the SIEDH requires a combined supra-infratentorial craniotomy.AIM To analyze the morphological characteristics of the SOB and introduce a single supratentorial craniotomy for SIEDH.METHODS Skull computed tomography(CT)scan data from 32 adult patients were collected from January 1,2019 to January 31,2020.On the median sagittal plane of the CT scan,the angle of the SOB(ASOB)was defined by two lines:Line A was defined from the lambdoid suture(LambS)to the external occipital protuberance(EOP),while line B was defined from the EOP to the posterior edge of the foramen magnum(poFM).The operative angle for the SIEDH(OAS)from the supra-to infratentorial epidural space was determined by two lines:The first line passes from the midpoint between the EOP and the LambS to the poFM,while the second line passes from the EOP to the poFM.The ASOB and OAS were measured and analyzed.RESULTS Based on the anatomical study,a single supratentorial craniotomy was performed in 8 patients with SIEDH.The procedure and the results of the modified surgical method were demonstrated in detail.For males,the ASOB was 118.4±4.7 and the OAS was 15.1±1.8;for females,the ASOB was 130.4±5.1 and the OAS was 12.8±2.0.There were significant differences between males and females both in ASOB and OAS.The smaller the ASOB was,the larger the OAS was.The bone flaps in 8 patients were designed above the transverse sinus intraoperatively,and the SIEDH was completely removed without suboccipital craniotomy.The SOB does not present as a single straight plane but bends at an angle around the EOP and the superior nuchal lines.The OAS was negatively correlated with the ASOB.CONCLUSION The single supratentorial craniotomy for SIEDH is reliable and effective.展开更多
BACKGROUND Submucosal protuberance caused by fish bone insertion into the digestive tract has rarely been reported.These cases usually include patients with clear signs such as a history of fish intake,pain,and dyspha...BACKGROUND Submucosal protuberance caused by fish bone insertion into the digestive tract has rarely been reported.These cases usually include patients with clear signs such as a history of fish intake,pain,and dysphagia,as well as positive findings on endoscopy and imaging.Here,we report a case of a fish bone hidden in the submucosal protuberance of the gastric antrum during endoscopic submucosal dissection without preoperative obvious positive signs.CASE SUMMARY A 58-year-old woman presented with epigastric pain for the past 20 d and a submucosal protuberance.Abdominal computed tomography and endoscopic ultrasonography did not indicate the presence of a fish bone.We assumed the cause to be an ordinary submucosal eminence and performed an endoscopic submucosal dissection to confirm its essence.During the operation,a fish bone approximately 20 mm in length was found incidentally.CONCLUSION Our report could potentially prevent the oversight of embedded fish bones and associated adverse effects in patients with similar presentation.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10832001 and 10872145)the State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences
文摘We present dynamic mode decomposition (DMD) for studying the hairpin vortices generated by hemisphere protuberance measured by two-dimensional (2D) time-resolved (TR) particle image velocimetry (PIV) in a water channel. The hairpins dynamic information is extracted by identifying their dominant frequencies and associated spatial structures. For this quasi-periodic data system, the resulting main Dynamic modes illustrate the different spatial structures associated with the wake vortex region and the near-wall region. By comparisons with proper orthogonal decomposition (POD), it can be concluded that the dynamic mode concentrates on a certain frequency component more effectively than the mode determined by POD. During the analysis, DMD has proven itself a robust and reliable algorithm to extract spatial-temporal coherent structures.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11072152,1472173)
文摘It is shown that the leading edge protuberances on the flippers of a humpback whale can significantly improve the hydrodynamic performance. The present study numerically investigates the flow control mechanisms of the leading edge protuberances on a static wing and a pitching wing. For static wings, the performance in both laminar flow and turbulent flow are studied in the context of the flow control mechanisms. It is shown that the protuberances have slight effects on the performance of static wings in laminar flow. Also, it could be deduced that non-uniform downwash does not delay the stall occurrence in either laminar flow or turbulent flow. In turbulent flow, the leading edge protuberances act in a manner similar to vortex generators, enhancing the momentum exchange within the boundary layer. Streamwise vortices do contribute to the delay of the stall occurrence. The normal vorticity component also plays an important role in delaying the stall occurrence. However, for the pitching wing, the effect of leading edge protuberances is negligible in turbulent flow. Detailed analysis of the flow field indicates that for the wing with the leading edge protuberances, the leading edge vortices become more complex, while the thrust jet and the vortices in the wake are not changed significantly by the leading edge protuberances.
文摘In this study, we presented new theory of effusive and explosive of volcanic eruptions. New explanation of eruption mechanisms was done by using the Elemental Buoyancy Theory and new K-Th-U structure of Earth, developed early by author. During investigation of effusive eruptions, it was given clear answer on the question why the light chemical elements, mainly silicon and sulfur compound, currently dominate in the volcanic ashes, gases, and in the magma lavas. At investigation of explosive mechanism, we analyzed 38 strong eruptions with Volcanic Explosivity Index (VEI) more than 4+. It was shown that there is a link between the planet configurations and volcanic eruptions. It can be found that volcano eruptions occurred at the different types of planet alignments. The phenomenon does depend neither on planet mass nor on the relative positions of planets. Also the phenomenon does not depend on the distance between planets, but often eruptions were observed when the distances between planets are multiple units. Also in work, it was demonstrated that the planet alignment affects not only natural processes on the Earth, but also impact the Sun activity. Based on the comparison phenomenon on the Earth and Sun, we get new mechanism to rapidly rising up pressure under the lithospheric planes by gravity vortexes. This gravity vortex was called as terrestrial magmatic protuberances.
文摘干涉配合可大幅度提高接头疲劳寿命。对基于应力波加载的钛合金干涉螺栓的高速安装过程进行了理论分析,对其安装工艺参数进行研究。研究表明:基于应力波加载的高速安装方法的安装阻力明显小于同等条件下准静态安装方法的安装阻力,干涉量1%、1.5%和2%下最大安装阻力分别为3.92 k N、5.64 k N和6.11 k N;安装阻力随干涉量和安装次数增加而升高,随加载速度增加而降低;多次安装容易造成孔壁划伤,同时发现加载速度过大容易引起螺栓头损伤;干涉配合紧固件安装时孔边最大凸瘤高度与干涉量、安装速度和安装次数、摩擦因数正相关。
基金the National Natural Science Foundation of China(Grant 51736008)"Transformational Technologies for Clean Energy and Demonstration",Strategic Priority Research Program of the Chinese Academy of Sciences(Grant XDA21050303).
文摘The aerodynamic loads of wind turbine blades are substantially affected by dynamic stall induced by the variations of the angle of attack of local airfoil sections.The purpose of the present study is to explore the effect of leading-edge protuberances on the fluctuation of the aerodynamic performances for wind turbine airfoil during dynamic stall.An experimental investigation is carried out by a direct force measurement technique employing force balance at a Reynolds number Re=2×105.The phase-averaged and instantaneous aerodynamic loads of the pitching airfoil,including the baseline and the wavy airfoil,are presented and analyzed.The phase-averaged results indicate that the effects of dynamic stall for the wavy airfoil can be delayed or minimized compared to the baseline airfoil,and the negative damping area of the wavy airfoil is significant decreased in full-stall condition.These effects of leading-edge protuberances are more notable at a higher reduced frequency.For the instantaneous aerodynamic loads of the wavy airfoil,there is an observable reduction in fluctuations compared with baseline case.Furthermore,spectral analysis is applied to quantitatively undercover the nonstationary features of the instantaneous aerodynamic loads.It is found that the leading edge protuberances can reduce the harmonics of the aerodynamic force signal,and enhance the stability of the aerodynamic loads under different reduced frequencies.In conclusion,leading-edge protuberances are found effective to reduce the fluctuation characteristics of the aerodynamic loads during the dynamic stall process,and help to improve the stability and prolong the service life of the wind turbine blades.
基金Supported by Key Research and Development Plan of Shaanxi Province,China,No.2021SF-298,and No.2018SF-137.
文摘BACKGROUND Supra-and infratentorial acute epidural hematoma(SIEDH)is a common posterior cranial fossa epidural hematoma located at the inner surface of the squamous part of the occipital bone(SOB).Traditionally,surgical treatment of the SIEDH requires a combined supra-infratentorial craniotomy.AIM To analyze the morphological characteristics of the SOB and introduce a single supratentorial craniotomy for SIEDH.METHODS Skull computed tomography(CT)scan data from 32 adult patients were collected from January 1,2019 to January 31,2020.On the median sagittal plane of the CT scan,the angle of the SOB(ASOB)was defined by two lines:Line A was defined from the lambdoid suture(LambS)to the external occipital protuberance(EOP),while line B was defined from the EOP to the posterior edge of the foramen magnum(poFM).The operative angle for the SIEDH(OAS)from the supra-to infratentorial epidural space was determined by two lines:The first line passes from the midpoint between the EOP and the LambS to the poFM,while the second line passes from the EOP to the poFM.The ASOB and OAS were measured and analyzed.RESULTS Based on the anatomical study,a single supratentorial craniotomy was performed in 8 patients with SIEDH.The procedure and the results of the modified surgical method were demonstrated in detail.For males,the ASOB was 118.4±4.7 and the OAS was 15.1±1.8;for females,the ASOB was 130.4±5.1 and the OAS was 12.8±2.0.There were significant differences between males and females both in ASOB and OAS.The smaller the ASOB was,the larger the OAS was.The bone flaps in 8 patients were designed above the transverse sinus intraoperatively,and the SIEDH was completely removed without suboccipital craniotomy.The SOB does not present as a single straight plane but bends at an angle around the EOP and the superior nuchal lines.The OAS was negatively correlated with the ASOB.CONCLUSION The single supratentorial craniotomy for SIEDH is reliable and effective.
文摘BACKGROUND Submucosal protuberance caused by fish bone insertion into the digestive tract has rarely been reported.These cases usually include patients with clear signs such as a history of fish intake,pain,and dysphagia,as well as positive findings on endoscopy and imaging.Here,we report a case of a fish bone hidden in the submucosal protuberance of the gastric antrum during endoscopic submucosal dissection without preoperative obvious positive signs.CASE SUMMARY A 58-year-old woman presented with epigastric pain for the past 20 d and a submucosal protuberance.Abdominal computed tomography and endoscopic ultrasonography did not indicate the presence of a fish bone.We assumed the cause to be an ordinary submucosal eminence and performed an endoscopic submucosal dissection to confirm its essence.During the operation,a fish bone approximately 20 mm in length was found incidentally.CONCLUSION Our report could potentially prevent the oversight of embedded fish bones and associated adverse effects in patients with similar presentation.
