小曲率曲线孔手携式仿形气割机的研制与应用

对内靠模小曲率曲线孔手携式仿形气割机的仿形原理,气割的曲率半径理论计算以及气割机有关结构特点、技术性能和电磁辊、电机、电气控制原理进行了较系统地叙述与分析.

双曲率兜孔静音轴承保持架设计

传统深沟球轴承浪形保持架兜孔一般采用球形或椭球形结构,轴承在高速运转时滚动体不能充分润滑,存在噪声大、滚动体可能被划伤、使用寿命短等问题。文中在总结对比国内外保持架设计研究方法的基础上,以改善滚动体和保持架的润滑为目标,设计了一种具有双曲率兜孔结构的浪形保持架,分析了所设计保持架的减振降噪机理,最后通过测试验证了该结构能够有效地减振降噪,达到了静音轴承的标准。

电子束加工技术在微细弯孔加工中的应用研究

利用电子束在磁场中偏转的原理 ,使其在工件内部偏转 ,可加工出微细弯孔。控制电子束的速度和磁场强度 ,即可控制曲率半径。本文对电子束加工微细弯孔的有关问题进行了研究 ,导出了相关的物理方程 ,为微细弯孔的加工提供了理论依据。

Curvatures estimation on triangular mesh

Curvatures are important geometric attributes of surfaces. There are many applications that require as a first step the accurate estimation of curvatures at arbitrary vertices on a triangulated surface. Chen and Schmitt (1992) and Taubin (1995) presented two simple methods to estimate principal curvatures. They used circular arcs to approximate the normal curvature. We find this may cause large error in some cases. In this paper, we describe a more accurate method to estimate the normal curvature, and present a novel algorithm to estimate principal curvatures by simplifying the Chen and Schmitt’s method. Some comparison results are also shown in this paper.

Preparation of precursor for stainless steel foam

The effects of polyurethane sponge pretreatment and slurry compositions on the slurry loading in precursor were discussed,and the performances of stainless steel foams prepared from precursors with different slurry loadings and different particle sizes of the stainless steel powder were also investigated.The experimental results show that the pretreatment of sponge with alkaline solution is effective to reduce the jam of cells in precursor and ensure the slurry to uniformly distribute in sponge,and it is also an effective method for increasing the slurry loading in precursor;the mass fraction of additive A and solid content in slurry greatly affect the slurry loading in precursor,when they are kept in 9%-13% and 52%-75%,respectively,the stainless steel foam may hold excellent 3D open-cell network structure and uniform muscles;the particle size of the stainless steel powder and the slurry loading in precursor have great effects on the bending strength,apparent density and open porosity of stainless steel foam;when the stainless steel powder with particle size of 44 μm and slurry loading of 0.5 g/cm3 in precursor are used,a stainless steel foam can be obtained,which has open porosity of 81.2%,bending strength of about 51.76 MPa and apparent density of about 1.0 g/cm3.

Effect of Porosity on the Wind Loads on a Hyperbolic Paraboloid Canopy Roof

A discussion is made of the wind force coefficients for designing the main wind force resisting systems of H.P. （Hyperbolic-Paraboid）-shaped porous canopy roofs on the basis of a wind tunnel experiment. Roof models with a number of small circular holes were made of nylon resin using laser lithography. The porosity was changed from 0 （solid） to 0.4. Besides the porosity, the geometric parameters of the models were the rise to span ratio and slope of the roof. The overall aerodynamic forces and moments acting on a model were measured by a six-component force balance in a turbulent boundary layer. The results indicate that the porosity significantly reduces the wind loads. The design wind force coefficients for porous canopy roofs can be provided by those for solid roofs with the same configuration multiplied by a reduction factor. The proposed wind force coefficients are verified by a comparison of the load effect predicted by the proposed wind force coefficients with the maximum load effect obtained from dynamic analyses using the time history of wind force and moment coefficients. The axial forces induced in the columns supporting the roof are regarded as the load effect for discussing the design wind loads.

A relative permeability model for deformable soils and its impact on coupled unsaturated flow and elasto-plastic deformation processes.

Relative permeability is an indispensable property for characterizing the unsaturated flow and induced deformation in soils. The widely used Mualem model is inadequate for deformable soils because of its assumption of a rigid pore structure and the resultant unique dependence of the tortuosity factor on the volumetric water content. In this study, a unified relationship between the relative permeability and the effective degree of saturation was proposed for deformable soils by incorporating our newly developed water retention curve model into the original Mualem model, in which a new tortuosity factor was defined using the fractal dimension of flow paths and the mean radius of water-filled pores for representing the effect of pore structure variation. The modified deformation-dependent relative permeability model was verified using test data on five types of soils; the verification revealed a much better performance of the proposed model than the original model, which commonly overestimates the relative permeability of deformable soils. Finally, the proposed model was implemented in a coupled numerical model for examining the unsaturated flow and elastoplastic deformation processes in a soil slope induced by rain infiltration. The numerical results showed that the deformation-dependent nature of relative permeability has a remarkable effect on the elastoplastic deformation in the slope and that neglect of the deformation-dependent behavior of relative permeability causes overestimation of the depth of failure.