To study ice-induced vibration of a compliant conical structure, a series of model tests were performed from 2004 to 2005. In the tests, the ice sheet before the compliant conical structure was found to fail in two-ti...To study ice-induced vibration of a compliant conical structure, a series of model tests were performed from 2004 to 2005. In the tests, the ice sheet before the compliant conical structure was found to fail in two-time breaking. From 2005 to 2006, this type of ice failure was studied through more groups of tests. The tests show that two-time breaking is the typical failure of ice before steep conical structures, and is controlled by other factors at the same time, such as ice speed and the angle of the cone.展开更多
For the study on the ice-induced vibration of a compliant mono-cone structure,a series of model tests were performed from 2004 to 2006.In these tests,the ice sheet before the compliant conical structure was found to b...For the study on the ice-induced vibration of a compliant mono-cone structure,a series of model tests were performed from 2004 to 2006.In these tests,the ice sheet before the compliant conical structure was found to be failed in two-time breaking.Based on this important finding,model tests study of the ice force on a compliant multi-cone structure were performed from 2006 to 2007.In these tests,the ice sheet broke before each single cone non-simultaneously.The exciting energy of the total ice force was found to be in a wide range of frequencies,and the structure can be easily excited with nonlinear resonance.展开更多
The problem of ice induced vibration is common to ocean engineering of cold region countries. To study the ice induced vibration of a compliant conical structure, a series of model tests have been performed and some b...The problem of ice induced vibration is common to ocean engineering of cold region countries. To study the ice induced vibration of a compliant conical structure, a series of model tests have been performed and some breakthrough progresses made. The ice sheet before the compliant conical structure is found to fail by two-time breaking in the tests. The process of two-time breaking behaves in two modes, and the general control of the ice and structural conditions determine the mode in which the ice force would behave. Two dynamic ice force functions are established respectively for the two modes of two-time breaking process in this paper. The numerical simulation results are in good agreement with the measured results, indicating that the dynamic ice force functions given in this paper can fully reflect the real situation of the dynamic ice force on a compliant conical structure.展开更多
This paper presents the development of a novel compliant polymorphing wing capable of chord and camber morphing for small UAVs.The morphing wing can achieve up to 10%chord extension and±20°camber changes.The...This paper presents the development of a novel compliant polymorphing wing capable of chord and camber morphing for small UAVs.The morphing wing can achieve up to 10%chord extension and±20°camber changes.The design,modeling,sizing,manufacturing and mechanical testing of the wing are detailed.The polymorphing wing consists of one continuous front spar fixed to the fuselage and a rear spar on each side of the wing.Each rear spar can translate in the chordwise direction(chord morphing)and rotate around itself(camber morphing).A flexible elastomeric latex sheet is used as the skin to cover the wing and maintain its aerodynamic shape whilst allowing morphing.The loads from the skin are transferred to the spars using the compliant cellular ribs that support the flexible skin and facilitate morphing.Pre-tensioning is applied to the skin to minimize wrinkling when subject to aerodynamic and actuation loads.A rack and pinion actuation system,powered by stepper motors,is used for morphing.Aero-structural design,analysis and sizing are conducted.Performance comparison between the polymorphing wing and the baseline wing(non-morphing)shows that chord morphing improves aerodynamic efficiency at low angles of attack while camber morphing improves efficiency at high angles of attack.展开更多
The response statistics of a compliant offshore structure excited by slowly varying wave drift forces is calculated by use of a numerical path integral solution method. The path integral solution is based on the Ganss...The response statistics of a compliant offshore structure excited by slowly varying wave drift forces is calculated by use of a numerical path integral solution method. The path integral solution is based on the Ganss-Legendre interpolation scheme, and the values of the response probability density are obtained at the Gauss quadrature points in sub-intervals. It is demonstrated that a distinct advantage of the path integral solution is that the joint probability density of the response displacement and velocity is one of the by products of the calculations. This makes it possible to calculate the mean level up-crossing rates, which provides estimates of the exceedance probabilities of specified response levels for given time periods.展开更多
The problems of ice-induced vibration have been noticed and concerned since the 1960s, but it has not been well resolved. One reason is that the dynamic interaction between ice and structure is so complicated that pra...The problems of ice-induced vibration have been noticed and concerned since the 1960s, but it has not been well resolved. One reason is that the dynamic interaction between ice and structure is so complicated that practical ice force model has not been developed. The recent full-scale tests conducted on jacket platforms in the Bohai Sea presented that ice could cause intense vibrations which endanger the facilities on the deck and make discomfort for the crew. In this paper, the strategy of mitigation of ice-induced offshore structure vibration is discussed. Based on field observations and understanding of the interaction between ice and structure, the absorption mitigation method to suppress ice-induced vibration is presented. The numerical simulations were conducted for a simplified model of platform attached with a Tuned Mass Danlper （TMD） under ice force function and ice force time history. The simulation results show that TMD can fa- vorably reduce ice-induced vibrations, therefore, it can be considered to be an alternative approach to utilize. Finally, the application possibilities of utilizing TMDs on other miniature offshore structures in ice-covered areas of marginal oil fields are discussed.展开更多
Precision motion actuation is a key technology for miniature medical robotics in a variety of applications,such as optical fibre-based diagnosis and intervention tools.Conventional inductive actuation mechanisms are c...Precision motion actuation is a key technology for miniature medical robotics in a variety of applications,such as optical fibre-based diagnosis and intervention tools.Conventional inductive actuation mechanisms are challenging to scale down.Piezoelectric materials offer a scalable,precise,fast and high-force method but at a limited displacement range.In previous work,the combination of piezoelectric beams(benders)with compliant motion translation structures has been shown to be promising for robotic micro-actuation.In this paper,this approach is employed to implement a three degrees of freedom delta robot,suitable for catheter,diagnostic optical fibre and microsurgery tool manipulation.The fabrication process combines additive manufacturing,origami structuring and piezoelectric beam assembly.Closed-loop control is implemented using a new,on-board visual feedback concept.In contrast to typical optical motion systems,the fully internal visual feedback offers system compactness with precise and reliable camera-to-marker geometry definition.By employment of this method,a delta robot with motion accuracy of 7.5μm,resolution of 10μm and 8.1μm precision is demonstrated.The robot is shown to follow a range of programmable trajectories under these specifications,and to compensate for externally applied forces typically expected during microsurgery manipulations.This is the first,to our knowledge,demonstration of micromotion control using internal visual feedback,and it opens up the way for high-resolution compact microrobots.展开更多
基金This project is financially supported by the National High Technology Research Development Program of China(863Program) by the National Natural Science Foundation of China(Grant No.50609015)
文摘To study ice-induced vibration of a compliant conical structure, a series of model tests were performed from 2004 to 2005. In the tests, the ice sheet before the compliant conical structure was found to fail in two-time breaking. From 2005 to 2006, this type of ice failure was studied through more groups of tests. The tests show that two-time breaking is the typical failure of ice before steep conical structures, and is controlled by other factors at the same time, such as ice speed and the angle of the cone.
基金supported bythe National High Technology Research and Development Program of China(863Program,Grant No.2003AA602150-3)the National Natural Science Foundation of China(Grant No.50609015)
文摘For the study on the ice-induced vibration of a compliant mono-cone structure,a series of model tests were performed from 2004 to 2006.In these tests,the ice sheet before the compliant conical structure was found to be failed in two-time breaking.Based on this important finding,model tests study of the ice force on a compliant multi-cone structure were performed from 2006 to 2007.In these tests,the ice sheet broke before each single cone non-simultaneously.The exciting energy of the total ice force was found to be in a wide range of frequencies,and the structure can be easily excited with nonlinear resonance.
文摘The problem of ice induced vibration is common to ocean engineering of cold region countries. To study the ice induced vibration of a compliant conical structure, a series of model tests have been performed and some breakthrough progresses made. The ice sheet before the compliant conical structure is found to fail by two-time breaking in the tests. The process of two-time breaking behaves in two modes, and the general control of the ice and structural conditions determine the mode in which the ice force would behave. Two dynamic ice force functions are established respectively for the two modes of two-time breaking process in this paper. The numerical simulation results are in good agreement with the measured results, indicating that the dynamic ice force functions given in this paper can fully reflect the real situation of the dynamic ice force on a compliant conical structure.
基金support of Khalifa University of Science and Technology under Research Publication Award(Khan)with Project No.8474000195。
文摘This paper presents the development of a novel compliant polymorphing wing capable of chord and camber morphing for small UAVs.The morphing wing can achieve up to 10%chord extension and±20°camber changes.The design,modeling,sizing,manufacturing and mechanical testing of the wing are detailed.The polymorphing wing consists of one continuous front spar fixed to the fuselage and a rear spar on each side of the wing.Each rear spar can translate in the chordwise direction(chord morphing)and rotate around itself(camber morphing).A flexible elastomeric latex sheet is used as the skin to cover the wing and maintain its aerodynamic shape whilst allowing morphing.The loads from the skin are transferred to the spars using the compliant cellular ribs that support the flexible skin and facilitate morphing.Pre-tensioning is applied to the skin to minimize wrinkling when subject to aerodynamic and actuation loads.A rack and pinion actuation system,powered by stepper motors,is used for morphing.Aero-structural design,analysis and sizing are conducted.Performance comparison between the polymorphing wing and the baseline wing(non-morphing)shows that chord morphing improves aerodynamic efficiency at low angles of attack while camber morphing improves efficiency at high angles of attack.
文摘The response statistics of a compliant offshore structure excited by slowly varying wave drift forces is calculated by use of a numerical path integral solution method. The path integral solution is based on the Ganss-Legendre interpolation scheme, and the values of the response probability density are obtained at the Gauss quadrature points in sub-intervals. It is demonstrated that a distinct advantage of the path integral solution is that the joint probability density of the response displacement and velocity is one of the by products of the calculations. This makes it possible to calculate the mean level up-crossing rates, which provides estimates of the exceedance probabilities of specified response levels for given time periods.
基金the National High Technology Research and Development Program of China(863 Program,Grant No. 2001AA602015)the National Natural Science Foundation of China (Grant No.10672029)
文摘The problems of ice-induced vibration have been noticed and concerned since the 1960s, but it has not been well resolved. One reason is that the dynamic interaction between ice and structure is so complicated that practical ice force model has not been developed. The recent full-scale tests conducted on jacket platforms in the Bohai Sea presented that ice could cause intense vibrations which endanger the facilities on the deck and make discomfort for the crew. In this paper, the strategy of mitigation of ice-induced offshore structure vibration is discussed. Based on field observations and understanding of the interaction between ice and structure, the absorption mitigation method to suppress ice-induced vibration is presented. The numerical simulations were conducted for a simplified model of platform attached with a Tuned Mass Danlper （TMD） under ice force function and ice force time history. The simulation results show that TMD can fa- vorably reduce ice-induced vibrations, therefore, it can be considered to be an alternative approach to utilize. Finally, the application possibilities of utilizing TMDs on other miniature offshore structures in ice-covered areas of marginal oil fields are discussed.
基金financially supported in part by the Engineering and Physical Sciences Research Council(EPSRC),United Kingdom(EP/P012779,Micro-Robotics for Surgery).
文摘Precision motion actuation is a key technology for miniature medical robotics in a variety of applications,such as optical fibre-based diagnosis and intervention tools.Conventional inductive actuation mechanisms are challenging to scale down.Piezoelectric materials offer a scalable,precise,fast and high-force method but at a limited displacement range.In previous work,the combination of piezoelectric beams(benders)with compliant motion translation structures has been shown to be promising for robotic micro-actuation.In this paper,this approach is employed to implement a three degrees of freedom delta robot,suitable for catheter,diagnostic optical fibre and microsurgery tool manipulation.The fabrication process combines additive manufacturing,origami structuring and piezoelectric beam assembly.Closed-loop control is implemented using a new,on-board visual feedback concept.In contrast to typical optical motion systems,the fully internal visual feedback offers system compactness with precise and reliable camera-to-marker geometry definition.By employment of this method,a delta robot with motion accuracy of 7.5μm,resolution of 10μm and 8.1μm precision is demonstrated.The robot is shown to follow a range of programmable trajectories under these specifications,and to compensate for externally applied forces typically expected during microsurgery manipulations.This is the first,to our knowledge,demonstration of micromotion control using internal visual feedback,and it opens up the way for high-resolution compact microrobots.
