The force-finding process of the cable-net in the deployable mesh reflector antenna,AstroMesh,is investigated to optimize the pretension distribution and satisfy surface accuracy.Since the geometry and topology of the...The force-finding process of the cable-net in the deployable mesh reflector antenna,AstroMesh,is investigated to optimize the pretension distribution and satisfy surface accuracy.Since the geometry and topology of the mesh reflector antennas are given as a constraint with the boundary condition assumed to be fixed,the force-finding process can be performed on a constant equilibrium matrix to obtain a feasible set of forces.Then,the equilibrium matrix can be rewritten in terms of force modes after the singular value decomposition.The object of force design is to minimize the deviation of member forces and,therefore,the surface accuracy can be guaranteed by transforming an optimization of the distribution of prestresses into an optimization with multiple prestress modes.Finally,numerical examples solved by the sequential quadratic programming(SQP)algorithm and the genetic algorithm are given to validate the efficiency of the proposed method.The comparison results show that the genetic method can converge to the optimized point after approximately 50 iterations while the converging process of the sequential quadratic programming method depends largely on the initial points.展开更多
Intensity modulated radiation therapy （IMRT） requires the determination of the appropriate multileaf collimator settings to deliver an intensity map. The purpose of this work was to attempt to regulate the shape bet...Intensity modulated radiation therapy （IMRT） requires the determination of the appropriate multileaf collimator settings to deliver an intensity map. The purpose of this work was to attempt to regulate the shape between adjacent multileaf collimator apertures by a leaf sequencing algorithm. To qualify and validate this algorithm, the integral test for the segment of the multileaf collimator of ARTS was performed with clinical intensity map experiments. By comparisons and analyses of the total number of monitor units and number of segments with benchmark results, the proposed algorithm performed well while the segment shape constraint produced segments with more compact shapes when delivering the planned intensity maps, which may help to reduce the multileaf collimator＇s specific effects.展开更多
Fourier Descriptors（FD） has been widely used in image analysis and computer vision for shape recognition as they can be made independent of translation,rotation,as well as scaling.They have also been used for develo...Fourier Descriptors（FD） has been widely used in image analysis and computer vision for shape recognition as they can be made independent of translation,rotation,as well as scaling.They have also been used for developing methods for the analysis and synthesis of four-bar linkages for path generation.This paper focuses on a comparative study of Fourier descriptors derived from various shape signatures of planar closed curves.This includes representations based on Cartesian coordinates,centroid distance,cumulative angle,and curvature.The comparison is conducted not only using commonly used criteria for shape representation and identification but also in the context of shape based retrieval of kinematic constraints for task centered mechanism design.Examples are provided to seek to extract geometric constraints such as circle,circular arc,ellipse and line-segment from a given motion.展开更多
A trajectory shaping guidance law based on virtua angle （TSGLBVA） is proposed for a re-entry vehicle with the constraints of terminal impact angles and their time derivatives. In the view of differential properties ...A trajectory shaping guidance law based on virtua angle （TSGLBVA） is proposed for a re-entry vehicle with the constraints of terminal impact angles and their time derivatives. In the view of differential properties of the maneuvering trajectory, a virtual angle and a virtual radius are defined. Also, the shaping trajectory of the vehicle is established by the polynomials of the virtual angle. Then, four optimized parameters are selected according to the theorem of parameters transformation presented in this paper. Finally, a convergent variant of the Nelder-Mead algorithm is adopted to obtain the reference trajectory, and a trajectory feedback tracking guidance law is designed. The simulation results demonstrate that the TSGLBVA ensures the re-entry vehicle to impact a target precisely from a specified direction with smal terminal load factor command, as well as to obtain a maximum or constrained terminal velocity according to various requirements.展开更多
In shape memory materials,that have been trained to have a two way shape memory effect(TWSM),themartensitic variants are classified into two groups,i.e.,preferentially oriented variants and self-accommodatingvariants....In shape memory materials,that have been trained to have a two way shape memory effect(TWSM),themartensitic variants are classified into two groups,i.e.,preferentially oriented variants and self-accommodatingvariants.Applied stress may promote or constrain the transition of preferentially oriented variants and so changetransformation temperatures but has no essential effect on self-accommodating variants.According to the pointof view mentioned above,some experimental phenomena during thermocycling of a TWSM device may be ex-plained,such as the absence of synchronization between the plot of resistance change.temperature and the plotof memory strain vs.temperature.展开更多
基金The National Natural Science Foundation of China(No.51308106,51578133)the Natural Science Foundation of Jiangsu Province(No.BK20130614)+3 种基金the Specialized Research Fund for the Doctoral Program of Higher Education(No.20130092120018)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Excellent Young Teachers Program of Southeast Universitythe Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX18_0105)
文摘The force-finding process of the cable-net in the deployable mesh reflector antenna,AstroMesh,is investigated to optimize the pretension distribution and satisfy surface accuracy.Since the geometry and topology of the mesh reflector antennas are given as a constraint with the boundary condition assumed to be fixed,the force-finding process can be performed on a constant equilibrium matrix to obtain a feasible set of forces.Then,the equilibrium matrix can be rewritten in terms of force modes after the singular value decomposition.The object of force design is to minimize the deviation of member forces and,therefore,the surface accuracy can be guaranteed by transforming an optimization of the distribution of prestresses into an optimization with multiple prestress modes.Finally,numerical examples solved by the sequential quadratic programming(SQP)algorithm and the genetic algorithm are given to validate the efficiency of the proposed method.The comparison results show that the genetic method can converge to the optimized point after approximately 50 iterations while the converging process of the sequential quadratic programming method depends largely on the initial points.
基金supported by National Natural Science Foundation of China (No. 10805012)Fundamental Research Funds for the Central Universities (Nos. 2010HGXJ0216, 2012HGXJ0057, 2012HGXJ0062, 2012HGXJ0071, 2012HGBZ0190)Seed Foundation of Hefei University of Technology (2012HGZY0007)
文摘Intensity modulated radiation therapy （IMRT） requires the determination of the appropriate multileaf collimator settings to deliver an intensity map. The purpose of this work was to attempt to regulate the shape between adjacent multileaf collimator apertures by a leaf sequencing algorithm. To qualify and validate this algorithm, the integral test for the segment of the multileaf collimator of ARTS was performed with clinical intensity map experiments. By comparisons and analyses of the total number of monitor units and number of segments with benchmark results, the proposed algorithm performed well while the segment shape constraint produced segments with more compact shapes when delivering the planned intensity maps, which may help to reduce the multileaf collimator＇s specific effects.
基金supported by National Science Foundation under Collaborative Research grants to Stony Brook University (Grant No. CMMI-0856594)University of Maryland at Baltimore County (Grant No. CMMI-0900517)supported by National Natural Science Foundation of China under Oversea Scholar Research Collaboration to Shanghai Jiao Tong University (Grant No. 50728503)
文摘Fourier Descriptors（FD） has been widely used in image analysis and computer vision for shape recognition as they can be made independent of translation,rotation,as well as scaling.They have also been used for developing methods for the analysis and synthesis of four-bar linkages for path generation.This paper focuses on a comparative study of Fourier descriptors derived from various shape signatures of planar closed curves.This includes representations based on Cartesian coordinates,centroid distance,cumulative angle,and curvature.The comparison is conducted not only using commonly used criteria for shape representation and identification but also in the context of shape based retrieval of kinematic constraints for task centered mechanism design.Examples are provided to seek to extract geometric constraints such as circle,circular arc,ellipse and line-segment from a given motion.
基金This project is supported by the National Natural Science Foundation of China （No. 50775044, 50805025） and Provincial Natural Science Foundation of Guangdong （No. 8151009001000040）.
文摘A trajectory shaping guidance law based on virtua angle （TSGLBVA） is proposed for a re-entry vehicle with the constraints of terminal impact angles and their time derivatives. In the view of differential properties of the maneuvering trajectory, a virtual angle and a virtual radius are defined. Also, the shaping trajectory of the vehicle is established by the polynomials of the virtual angle. Then, four optimized parameters are selected according to the theorem of parameters transformation presented in this paper. Finally, a convergent variant of the Nelder-Mead algorithm is adopted to obtain the reference trajectory, and a trajectory feedback tracking guidance law is designed. The simulation results demonstrate that the TSGLBVA ensures the re-entry vehicle to impact a target precisely from a specified direction with smal terminal load factor command, as well as to obtain a maximum or constrained terminal velocity according to various requirements.
文摘In shape memory materials,that have been trained to have a two way shape memory effect(TWSM),themartensitic variants are classified into two groups,i.e.,preferentially oriented variants and self-accommodatingvariants.Applied stress may promote or constrain the transition of preferentially oriented variants and so changetransformation temperatures but has no essential effect on self-accommodating variants.According to the pointof view mentioned above,some experimental phenomena during thermocycling of a TWSM device may be ex-plained,such as the absence of synchronization between the plot of resistance change.temperature and the plotof memory strain vs.temperature.
