Controlling the overhang surface quality is still a formidable challenge in manufacturing the components with complex structures during laser powder bed fusion(LPBF).This study systematically uncovers the effects of t...Controlling the overhang surface quality is still a formidable challenge in manufacturing the components with complex structures during laser powder bed fusion(LPBF).This study systematically uncovers the effects of the volume energy density(VED)and overhang angle on the evolution of surface morphology and corresponding surface roughness(Ra)of top and down-skin surfaces of IN718 superalloy samples.The results show that balling,Plateau-Rayleigh instability,open pore and humping caused by the material stacking are the main factors contributing to the apparent deterioration of top surface quality.When the VED is 80–100 J/mm^(3),the high down-skin surface roughness is attributed to the serious dross caused by recoil pressure and sinking of the melt pool.Using insufficient VED(15–50 J/mm^(3))can easily lead to poor metallurgical bonding and material spalling on the down-skin surface.In addition,overhang angle also significantly affects down-skin surface roughness due to the stair effect and the adhered unmelted powders.An improvement in the surface quality of down-skin surface is observed when the overhang angle increases.Based on the finding of this investigation,an optical VED(59.5 J/mm^(3))significantly improves the top and down-skin surface quality and porosity of overhang samples.This study provides an insight into synergy ascension of the top and down-skin surface quality in the overhang structure.展开更多
This paper presents the results of an experimental investigation dealing with the effect of bow overhang extensions on the quantity of shipping water over the foredeck in case of ships advancing in regular head waves....This paper presents the results of an experimental investigation dealing with the effect of bow overhang extensions on the quantity of shipping water over the foredeck in case of ships advancing in regular head waves. To perform this investigation, a series of free-running tests was conducted in regular waves using an experimental model of a multipurpose cargo ship to quantify the amount of shipping water. The tests were performed on five bow overhang variants with several combinations of wavelength and ship speed conditions. It was observed that the quantity of shipping water was affected by some parameters such as wavelength, ship speed, and bow shape in terms of an overhang extension. The results show the significant influence of an overhang extension, which is associated with the bow flare shape, on the occurrence of water shipping. These results involve the combined incoming regular waves and model speed.展开更多
A 74-year-old man presented with a three-year history of foreign body sensation in the right eye after cataract surgery.He underwent uneventful trabeculectomy with mitomycin C(MMC) in the right eye seven years ago.Sli...A 74-year-old man presented with a three-year history of foreign body sensation in the right eye after cataract surgery.He underwent uneventful trabeculectomy with mitomycin C(MMC) in the right eye seven years ago.Slit-lamp examination revealed a large avascular filtration bleb overhanging on the cornea with a thin base connected to the conjunctiva.Preoperative ultrasound biomicroscopy(UBM) impressions were confirmed by leakage of aqueous from the incision intraoperatively.Surgical dissection and revision of the bleb was performed with satisfactory outcome.Histopathologic evaluation showed proliferation of fibrous tissue under the conjunctival epithelia with irregular cystoids change.The current case may be the first report of a post-trabeculectomy overhanging filtration bleb related to cataract surgery.The possible mechanism may be related to microleakage of the surgical wound after phacoemulsification which initiated the healing and scarring process.展开更多
BACKGROUND Overhanging filtering bleb is a common complication after trabeculectomy and surgical repair is an effective treatment when the patient presents with apparent symptoms.Filtering bleb relevant infection incl...BACKGROUND Overhanging filtering bleb is a common complication after trabeculectomy and surgical repair is an effective treatment when the patient presents with apparent symptoms.Filtering bleb relevant infection including in the filtering bleb itself and even endophthalmitis in some severe cases has been reported.However,corneal fungal infection after filtering bleb repair is rarely reported.CASE SUMMARY A 57-year-old Chinese man who had sensations of redness and foreign body sensations in the left eye 3 wk after repair of overhanging filtering bleb.3 wk ago,due to sensations of a foreign body in the left eye for 3 years with worsening for 3 mo.The patient was diagnosed as overhanging filtering bleb and underwent a repair of overhanging filtering bleb.Postoperative,the filtering bleb formed well and the intraocular pressure is normal.But the patient gradually develop redness,pain and a grey infiltrate of the cornea in the eye.Finally it developed into fungal corneal ulcer.Through asking the medical history,we found the patient had irregularly self-medicated for years with glucocorticoid eye drops for years to relieve the foreign body sensation in the eye caused by filtering bleb overhanging.Because the glucocorticoid eye drops he used years ago had provide normal sensation to the eye.After 3 mo of anti-fungal treatment,the inflammation was controlled.CONCLUSION In addition to avoiding the development of overhanging filtering bleb after trabeculectomy,the present case report also suggests that clinicians should pay more attention to the patient’s ocular self-medication history.Particularly in patients with a history of glaucoma or eye surgery.Because these patients may be exposed to more types of eye drops than other individuals,they may select the wrong medi-cations for long-term use,based on their previous experience.展开更多
Nowadays rotating machinery grows and develops extremely fast due to its multi-branch application.Although the fields of rotordynamics and rotor balancing had a strong background based on previous experience in order ...Nowadays rotating machinery grows and develops extremely fast due to its multi-branch application.Although the fields of rotordynamics and rotor balancing had a strong background based on previous experience in order to perform efficient and safe operation for the rotating machines,still there are problems which are hard to be dealt with in some special cases.One of them is balancing of the rotor with huge overhang.Rotor with overhang is inherent to have console modes,which previously often were observed separately from the other modes in rotordynamic literature.In such a way console modes,their behavior,order of appearance and interaction with other modes were described in current paper in more details.Obtained results confirmed that console modes obey the principle of orthogonality in the same way as all other modes and hence could be efficiently balanced using modal balancing method.Simulation results revealed likelihood of such phenomena as modes order transition,when the rotor has an overhang.As a consequence perfectly balanced console rotor could not be so due to modes order transition effect when the bearing stiffness in situ differs from bearing stiffness of balancing equipment.Described results will be useful for engineers who are involved in area of rotating machinery vibration tuning for the rotor with huge overhang and benefit them to recognize these modes efficiently and to perform balancing successfully.展开更多
The destabilization of overhanging rock is a dangerous geological problem.In this study,a generalized model of typical overhanging cliffs from the Three Gorges Reservoir area in China with different fracture angles,fr...The destabilization of overhanging rock is a dangerous geological problem.In this study,a generalized model of typical overhanging cliffs from the Three Gorges Reservoir area in China with different fracture angles,fracture lengths,and free surface depths is constructed to investigate the cracking and deformation behavior of overhanging rocks.Laboratory tests and deformation field monitoring using the digital image correlation(DIC)method are performed on these specimens to reproduce the destabilization and failure process of overhanging rock under external loading.The influence of peak load is found to be the most sensitive to the fracture length,followed by the free surface depth,and to be the least sensitive to the fracture angle.The DIC-based strain fields reveal that the fracture angle and free surface depth significantly alter the crack propagation paths,whereas the influence of the fracture length is weaker.These parameters also affect the crack initiation time.The relative displacement evolution characteristics indicate that fracture angle,fracture length,and free surface depth affect the shape and size of the rotating block,the rotation center,and the rotation pivot point and degree,respectively.The grayscale characteristic evolution trends are similar for all examined overhanging rock specimens.The evolution of the grayscale indices based on DIC can be divided into high-frequency oscillation,smooth decline(or smooth downward concavity),and stable development stages.Furthermore,the multistage properties of the indices can be used to identify the fracture state of overhanging rocks,providing a theoretical basis for graded early warning of rockfall disasters.展开更多
激光粉末床熔融(laser powder bed fusion,LPBF)成形悬垂结构的应力与变形是实现复杂金属构件高质量、高精度制造的关键问题之一。通过基体预埋应变片的方式实现了悬垂结构LPBF成形过程应变数据的实时测量。基于原位应变测量系统研究了...激光粉末床熔融(laser powder bed fusion,LPBF)成形悬垂结构的应力与变形是实现复杂金属构件高质量、高精度制造的关键问题之一。通过基体预埋应变片的方式实现了悬垂结构LPBF成形过程应变数据的实时测量。基于原位应变测量系统研究了T形悬垂结构、低角度悬垂结构(5°和10°)LPBF过程的原位应变行为。深入研究了不同悬臂长度、不同成形工艺参数对T形悬垂结构原位应变行为的影响,并进一步分析了不同悬垂角度、支撑类型对低角度悬垂结构原位应变行为的影响。结果表明,T形悬垂结构的悬空长度越长,结构的变形越大;采用激光能量梯度、棋盘扫描策略可有效降低T形悬垂结构的变形。支撑结构设计可显著影响低角度悬垂结构的应变行为和成形质量,采用H1支撑设计策略(块体支撑间距0.8 mm+锥体支撑间距0.6 mm)的成形质量最佳。上述结果可为深入理解LPBF成形悬垂结构的变形行为和调控提供有效参考。展开更多
为了准确预测海底悬跨油气管道因涡激振动(vortex-induced vibration,VIV)导致的疲劳失效,基于S-N曲线和Miner线性累积损伤理论,并参考挪威船级社(det norske veritas,DNV)规范,构建了悬跨管道涡激振动疲劳寿命预测模型。通过ABAQUS有...为了准确预测海底悬跨油气管道因涡激振动(vortex-induced vibration,VIV)导致的疲劳失效,基于S-N曲线和Miner线性累积损伤理论,并参考挪威船级社(det norske veritas,DNV)规范,构建了悬跨管道涡激振动疲劳寿命预测模型。通过ABAQUS有限元软件进行三维仿真,获取模型经验系数,并进行实例计算及结果分析,以评估疲劳寿命的影响因素。研究结果表明:该模型能够精确计算管道疲劳寿命,且疲劳寿命随海流流速和悬跨长度的增加而减小,随管径的增加而增大。本研究可为管道设计和安全管理提供理论依据。展开更多
This paper studies additive manufacturing(AM) oriented structural topology optimization(TO).The minimum compliance design subject to overhang angle constraint with overhang length relaxation and horizontal minimum len...This paper studies additive manufacturing(AM) oriented structural topology optimization(TO).The minimum compliance design subject to overhang angle constraint with overhang length relaxation and horizontal minimum length control is considered.Although the overhang length relaxation allows additional flexibility for AM product design,there have been very limited studies on it.This paper elucidates that the overhang angle constraint we proposed can identify the lower boundary element that violates the overhang angle constraint.Taking advantage of this fact,we achieve the overhang length relaxation by specifying that the volume fraction of the elements that violate the overhang angle constraint in each local area of the design domain is less than a specified upper bound.A formula for estimating the maximum allowable overhang length of this method is proposed and verified.The horizontal minimum length constraint is also employed in this paper.While controlling the horizontal length size of the structural member,this constraint together with the overhang angle constraint with overhang length relaxation suppresses the hanging feature.The gradient-based optimization algorithm method of moving asymptotic(MMA) is used to solve the TO formulation.Numerical examples show the effectiveness of this method.It is observed that the new constraint alleviates the main issues of traditional overhang angle constraints,i.e.,gray element issue,stress concentration issue,and shattered structure issue.Compared with the strict traditional overhang angle constraint,the new formulation reduces structural compliance.展开更多
To study the nonlinear dynamic behavior of the bladed overhang rotor system with squeeze film damper (SFD), a blade-overhang rotor-SFD model is formulated using the lumped mass method and the Lagrange approach. The ca...To study the nonlinear dynamic behavior of the bladed overhang rotor system with squeeze film damper (SFD), a blade-overhang rotor-SFD model is formulated using the lumped mass method and the Lagrange approach. The cavitated short bearing model is employed to describe the nonlinear oil force of the SFD. To reduce the scale of the nonlinear coupling system, a set of orthogonal transformations is employed to decouple the one nodal diameter equations of blades, which are coupled with the dy- namical equations of the rotor, with other equations of blades. In this way, the original system with 16+4n (n≥3) degrees of freedom (DoF) is reduced to a system with 24 DoF only. Then the parametric excitation terms in the blade-overhang rotor-SFD model are simplified in terms of periodic transforma- tions. The coupling equations are numerically solved and the solutions are used to analyze the dy- namic behavior of the system in terms of the bifurcation diagram, whirl orbit, Poincaré map and spec- trum plot. A variety of motion types are found such as multi-periodic, quasi-periodic, and chaotic mo- tions. Moreover, the typical nonlinear dynamic evolutions including the periodic-doubling bifurcation and reverse bifurcation are noted. It is noticed that there exist apparent differences in the dynamic behavior between the blade-overhang rotor-SFD models without and with considering the effect of blades.展开更多
基金This work was supported by the National Natural Science Foundation of China(Nos.52130204,52174376)the Guangdong Basic and Applied Basic Research Foundation(No.2021B1515120028)+5 种基金the Science and Technology Innovation Team Plan of Shaan Xi Province(No.2021TD-17)the Youth Innovation Team of Shaanxi Universities,Thousands Person Plan of Jiangxi Province(No.JXSQ2020102131)the Joint Research Funds of the Department of Science&Technology of Shaanxi Province and Northwestern Polytechnical University(No.2020GXLH-Z-024)the Science Research Funds of Xi'an City(No.21ZCZZHXJS-QCY6-005)the Fundamental Research Funds for the Central Universities(No.D5000210902)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(Nos.CX2021056,CX2021066,CX2022033),China.
文摘Controlling the overhang surface quality is still a formidable challenge in manufacturing the components with complex structures during laser powder bed fusion(LPBF).This study systematically uncovers the effects of the volume energy density(VED)and overhang angle on the evolution of surface morphology and corresponding surface roughness(Ra)of top and down-skin surfaces of IN718 superalloy samples.The results show that balling,Plateau-Rayleigh instability,open pore and humping caused by the material stacking are the main factors contributing to the apparent deterioration of top surface quality.When the VED is 80–100 J/mm^(3),the high down-skin surface roughness is attributed to the serious dross caused by recoil pressure and sinking of the melt pool.Using insufficient VED(15–50 J/mm^(3))can easily lead to poor metallurgical bonding and material spalling on the down-skin surface.In addition,overhang angle also significantly affects down-skin surface roughness due to the stair effect and the adhered unmelted powders.An improvement in the surface quality of down-skin surface is observed when the overhang angle increases.Based on the finding of this investigation,an optical VED(59.5 J/mm^(3))significantly improves the top and down-skin surface quality and porosity of overhang samples.This study provides an insight into synergy ascension of the top and down-skin surface quality in the overhang structure.
文摘This paper presents the results of an experimental investigation dealing with the effect of bow overhang extensions on the quantity of shipping water over the foredeck in case of ships advancing in regular head waves. To perform this investigation, a series of free-running tests was conducted in regular waves using an experimental model of a multipurpose cargo ship to quantify the amount of shipping water. The tests were performed on five bow overhang variants with several combinations of wavelength and ship speed conditions. It was observed that the quantity of shipping water was affected by some parameters such as wavelength, ship speed, and bow shape in terms of an overhang extension. The results show the significant influence of an overhang extension, which is associated with the bow flare shape, on the occurrence of water shipping. These results involve the combined incoming regular waves and model speed.
基金supported by the Natural Science Foundation of Guangdong Province in China(grant No.2015A030313052)
文摘A 74-year-old man presented with a three-year history of foreign body sensation in the right eye after cataract surgery.He underwent uneventful trabeculectomy with mitomycin C(MMC) in the right eye seven years ago.Slit-lamp examination revealed a large avascular filtration bleb overhanging on the cornea with a thin base connected to the conjunctiva.Preoperative ultrasound biomicroscopy(UBM) impressions were confirmed by leakage of aqueous from the incision intraoperatively.Surgical dissection and revision of the bleb was performed with satisfactory outcome.Histopathologic evaluation showed proliferation of fibrous tissue under the conjunctival epithelia with irregular cystoids change.The current case may be the first report of a post-trabeculectomy overhanging filtration bleb related to cataract surgery.The possible mechanism may be related to microleakage of the surgical wound after phacoemulsification which initiated the healing and scarring process.
基金Supported by the Science and Technology Project of Education Department of Jilin Province,No.JJKH20201089KJ.
文摘BACKGROUND Overhanging filtering bleb is a common complication after trabeculectomy and surgical repair is an effective treatment when the patient presents with apparent symptoms.Filtering bleb relevant infection including in the filtering bleb itself and even endophthalmitis in some severe cases has been reported.However,corneal fungal infection after filtering bleb repair is rarely reported.CASE SUMMARY A 57-year-old Chinese man who had sensations of redness and foreign body sensations in the left eye 3 wk after repair of overhanging filtering bleb.3 wk ago,due to sensations of a foreign body in the left eye for 3 years with worsening for 3 mo.The patient was diagnosed as overhanging filtering bleb and underwent a repair of overhanging filtering bleb.Postoperative,the filtering bleb formed well and the intraocular pressure is normal.But the patient gradually develop redness,pain and a grey infiltrate of the cornea in the eye.Finally it developed into fungal corneal ulcer.Through asking the medical history,we found the patient had irregularly self-medicated for years with glucocorticoid eye drops for years to relieve the foreign body sensation in the eye caused by filtering bleb overhanging.Because the glucocorticoid eye drops he used years ago had provide normal sensation to the eye.After 3 mo of anti-fungal treatment,the inflammation was controlled.CONCLUSION In addition to avoiding the development of overhanging filtering bleb after trabeculectomy,the present case report also suggests that clinicians should pay more attention to the patient’s ocular self-medication history.Particularly in patients with a history of glaucoma or eye surgery.Because these patients may be exposed to more types of eye drops than other individuals,they may select the wrong medi-cations for long-term use,based on their previous experience.
文摘Nowadays rotating machinery grows and develops extremely fast due to its multi-branch application.Although the fields of rotordynamics and rotor balancing had a strong background based on previous experience in order to perform efficient and safe operation for the rotating machines,still there are problems which are hard to be dealt with in some special cases.One of them is balancing of the rotor with huge overhang.Rotor with overhang is inherent to have console modes,which previously often were observed separately from the other modes in rotordynamic literature.In such a way console modes,their behavior,order of appearance and interaction with other modes were described in current paper in more details.Obtained results confirmed that console modes obey the principle of orthogonality in the same way as all other modes and hence could be efficiently balanced using modal balancing method.Simulation results revealed likelihood of such phenomena as modes order transition,when the rotor has an overhang.As a consequence perfectly balanced console rotor could not be so due to modes order transition effect when the bearing stiffness in situ differs from bearing stiffness of balancing equipment.Described results will be useful for engineers who are involved in area of rotating machinery vibration tuning for the rotor with huge overhang and benefit them to recognize these modes efficiently and to perform balancing successfully.
基金supported by the China National Natural Science Foundation(Grant No.42362034)the Applied Basic Research Foundation of Yunnan Province,China(Grant No.202401AS070068).
文摘The destabilization of overhanging rock is a dangerous geological problem.In this study,a generalized model of typical overhanging cliffs from the Three Gorges Reservoir area in China with different fracture angles,fracture lengths,and free surface depths is constructed to investigate the cracking and deformation behavior of overhanging rocks.Laboratory tests and deformation field monitoring using the digital image correlation(DIC)method are performed on these specimens to reproduce the destabilization and failure process of overhanging rock under external loading.The influence of peak load is found to be the most sensitive to the fracture length,followed by the free surface depth,and to be the least sensitive to the fracture angle.The DIC-based strain fields reveal that the fracture angle and free surface depth significantly alter the crack propagation paths,whereas the influence of the fracture length is weaker.These parameters also affect the crack initiation time.The relative displacement evolution characteristics indicate that fracture angle,fracture length,and free surface depth affect the shape and size of the rotating block,the rotation center,and the rotation pivot point and degree,respectively.The grayscale characteristic evolution trends are similar for all examined overhanging rock specimens.The evolution of the grayscale indices based on DIC can be divided into high-frequency oscillation,smooth decline(or smooth downward concavity),and stable development stages.Furthermore,the multistage properties of the indices can be used to identify the fracture state of overhanging rocks,providing a theoretical basis for graded early warning of rockfall disasters.
文摘为了准确预测海底悬跨油气管道因涡激振动(vortex-induced vibration,VIV)导致的疲劳失效,基于S-N曲线和Miner线性累积损伤理论,并参考挪威船级社(det norske veritas,DNV)规范,构建了悬跨管道涡激振动疲劳寿命预测模型。通过ABAQUS有限元软件进行三维仿真,获取模型经验系数,并进行实例计算及结果分析,以评估疲劳寿命的影响因素。研究结果表明:该模型能够精确计算管道疲劳寿命,且疲劳寿命随海流流速和悬跨长度的增加而减小,随管径的增加而增大。本研究可为管道设计和安全管理提供理论依据。
基金supported by the National Natural Science Foundation of China (Grant Nos.52075070 and 12032008)。
文摘This paper studies additive manufacturing(AM) oriented structural topology optimization(TO).The minimum compliance design subject to overhang angle constraint with overhang length relaxation and horizontal minimum length control is considered.Although the overhang length relaxation allows additional flexibility for AM product design,there have been very limited studies on it.This paper elucidates that the overhang angle constraint we proposed can identify the lower boundary element that violates the overhang angle constraint.Taking advantage of this fact,we achieve the overhang length relaxation by specifying that the volume fraction of the elements that violate the overhang angle constraint in each local area of the design domain is less than a specified upper bound.A formula for estimating the maximum allowable overhang length of this method is proposed and verified.The horizontal minimum length constraint is also employed in this paper.While controlling the horizontal length size of the structural member,this constraint together with the overhang angle constraint with overhang length relaxation suppresses the hanging feature.The gradient-based optimization algorithm method of moving asymptotic(MMA) is used to solve the TO formulation.Numerical examples show the effectiveness of this method.It is observed that the new constraint alleviates the main issues of traditional overhang angle constraints,i.e.,gray element issue,stress concentration issue,and shattered structure issue.Compared with the strict traditional overhang angle constraint,the new formulation reduces structural compliance.
基金Supported by the National Natural Science Foundation of China (Grant No. 10632040)the Natural Science Foundation of Hei-Long-Jiang Province of China (Grant No. ZJG0704)the Harbin Science & Technology Innovative Foundation of China (Grant No. 2007RFLXG009)
文摘To study the nonlinear dynamic behavior of the bladed overhang rotor system with squeeze film damper (SFD), a blade-overhang rotor-SFD model is formulated using the lumped mass method and the Lagrange approach. The cavitated short bearing model is employed to describe the nonlinear oil force of the SFD. To reduce the scale of the nonlinear coupling system, a set of orthogonal transformations is employed to decouple the one nodal diameter equations of blades, which are coupled with the dy- namical equations of the rotor, with other equations of blades. In this way, the original system with 16+4n (n≥3) degrees of freedom (DoF) is reduced to a system with 24 DoF only. Then the parametric excitation terms in the blade-overhang rotor-SFD model are simplified in terms of periodic transforma- tions. The coupling equations are numerically solved and the solutions are used to analyze the dy- namic behavior of the system in terms of the bifurcation diagram, whirl orbit, Poincaré map and spec- trum plot. A variety of motion types are found such as multi-periodic, quasi-periodic, and chaotic mo- tions. Moreover, the typical nonlinear dynamic evolutions including the periodic-doubling bifurcation and reverse bifurcation are noted. It is noticed that there exist apparent differences in the dynamic behavior between the blade-overhang rotor-SFD models without and with considering the effect of blades.
