This paper presents an advanced octree(AO-rep) model and an implicit formula of a generalized cutter model for five-axis milling simulation.First,the main ideal of the AO-rep model is building a hierarchical structure...This paper presents an advanced octree(AO-rep) model and an implicit formula of a generalized cutter model for five-axis milling simulation.First,the main ideal of the AO-rep model is building a hierarchical structure and representing solid volumes.The AO-rep model utilizes an octree to cull unrelated voxels,and generates a small-scale voxel model in grey octants when a cutter intersects these octants.Using a simplified intersection computation between a cube and triangles in E^3,an STL model can be converted into its AO-rep model at a preprocessing stage.Second,the authors formulate an implicit function of a generalized cutter in moving cutter frame,and determine the function in fixed workpiece frame using the theory of a rigid body motion.Finally,the authors make a simulation of machining an impeller.The result shows that the proposed approach has a high performance of time and space.展开更多
The leaf area index(LAI) is a critical biophysical variable that describes canopy geometric structures and growth conditions.It is also an important input parameter for climate,energy and carbon cycle models.The scali...The leaf area index(LAI) is a critical biophysical variable that describes canopy geometric structures and growth conditions.It is also an important input parameter for climate,energy and carbon cycle models.The scaling effect of the LAI has always been of concern.Considering the effects of the clumping indices on the BRDF models of discrete canopies,an effective LAI is defined.The effective LAI has the same function of describing the leaf density as does the traditional LAI.Therefore,our study was based on the effective LAI.The spatial scaling effect of discrete canopies significantly differed from that of continuous canopies.Based on the directional second-derivative method of effective LAI retrieval,the mechanism responsible for the spatial scaling effect of the discrete-canopy LAI is discussed and a scaling transformation formula for the effective LAI is suggested in this paper.Theoretical analysis shows that the mean values of effective LAIs retrieved from high-resolution pixels were always equal to or larger than the effective LAIs retrieved from corresponding coarse-resolution pixels.Both the conclusions and the scaling transformation formula were validated with airborne hyperspectral remote sensing imagery obtained in Huailai County,Zhangjiakou,Hebei Province,China.The scaling transformation formula agreed well with the effective LAI retrieved from hyperspectral remote sensing imagery.展开更多
基金supported by the National Science and Technology Major Project under Grant No.2012ZX01029001-002
文摘This paper presents an advanced octree(AO-rep) model and an implicit formula of a generalized cutter model for five-axis milling simulation.First,the main ideal of the AO-rep model is building a hierarchical structure and representing solid volumes.The AO-rep model utilizes an octree to cull unrelated voxels,and generates a small-scale voxel model in grey octants when a cutter intersects these octants.Using a simplified intersection computation between a cube and triangles in E^3,an STL model can be converted into its AO-rep model at a preprocessing stage.Second,the authors formulate an implicit function of a generalized cutter in moving cutter frame,and determine the function in fixed workpiece frame using the theory of a rigid body motion.Finally,the authors make a simulation of machining an impeller.The result shows that the proposed approach has a high performance of time and space.
基金supported by the National Natural Science Foundation of China(Grant Nos.91025006,40871186,40730525)National Basic Research Program of China(Grant No.2007CB714402)National High Technology Research and Development Program of China(Grant Nos.2009AA12Z143,2009AA122103)
文摘The leaf area index(LAI) is a critical biophysical variable that describes canopy geometric structures and growth conditions.It is also an important input parameter for climate,energy and carbon cycle models.The scaling effect of the LAI has always been of concern.Considering the effects of the clumping indices on the BRDF models of discrete canopies,an effective LAI is defined.The effective LAI has the same function of describing the leaf density as does the traditional LAI.Therefore,our study was based on the effective LAI.The spatial scaling effect of discrete canopies significantly differed from that of continuous canopies.Based on the directional second-derivative method of effective LAI retrieval,the mechanism responsible for the spatial scaling effect of the discrete-canopy LAI is discussed and a scaling transformation formula for the effective LAI is suggested in this paper.Theoretical analysis shows that the mean values of effective LAIs retrieved from high-resolution pixels were always equal to or larger than the effective LAIs retrieved from corresponding coarse-resolution pixels.Both the conclusions and the scaling transformation formula were validated with airborne hyperspectral remote sensing imagery obtained in Huailai County,Zhangjiakou,Hebei Province,China.The scaling transformation formula agreed well with the effective LAI retrieved from hyperspectral remote sensing imagery.
