Pinion Tooth Surface Generation Strategy of Spiral Bevel Gears

Aviation spiral bevel gears are often generated by spiral generated modified（SGM） roll method.In this style,pinion tooth surface modified generation strategy has an important influence on the meshing and contact performances.For the optimal contact pattern and transmission error function,local synthesis is applied to obtain the machine-tool settings of pinion.For digitized machine,four tooth surface generation styles of pinion are proposed.For every style,tooth contact analysis（TCA） is applied to obtain contact pattern and transmission error function.For the difference between TCA transmission error function and design objective curve,the degree of symmetry and agreement are defined and the corresponding sub-objective functions are established.Linear weighted combination method is applied to get an equivalent objective function to evaluate the shape of transmission error function.The computer programs for the process above are developed to analyze the meshing performances of the four pinion tooth surface generation styles for a pair of aviation spiral bevel gears with 38/43 teeth numbers.The four analytical results are compared with each other and show that the incomplete modified roll is optimal for this gear pair.This study is an expansion to generation strategy of spiral bevel gears,and offers new alternatives to computer numerical control（CNC） manufacture of spiral bevel gears.

An Investigation of Effect of Stand-Off Distance on the Material Removal Characteristics and Surface Generation in Fluid Jet Polishing

Fluid jet polishing(FJP)is a versatile polishing process that has many advantages compared to other polishing processes.Stand-off distance(SOD)is one of the key parameters in flu id jet polishi ng.However,relatively little research work has been carried out to investigate its effect of SOD on material removal characteristics and surface generation in FJP.In this paper,a systematic investigation of the effect of SOD on the tool influence function and surface topography in FJP was conducted.Experiments were designed for FJP two kinds of materials corresponding to ductile and brittle materials.They are nickel copper(NiCu)alloy and BK7 optical glass,respectively.In this study,the SOD was varied from 2 to 35 mm.Analysis and discussions were made on its effect on the shape of TIF,material removal rate,and surface topography.It is interesting to note that the TIF shape becomes a Gaussian-like shape with large SOD both on NiCu and BK7,which provides a novel way to optimize the TIF in FJP.The variation of the material removal rate and surface roughness versus SOD on NiCu and BK7 were also determined from the experimental results.Moreover,the surface topography of NiCu and BK7 were characterized from the results measured from the white light interferometer and scan electron microscope.The outcome of the study provides a better understanding of the material removal characteristics and surface generation mechanism in FJP.

PDE Surface Generation with Combined Closedand Non-Closed Form Solutions

Partial differential equations (PDEs) combined with suitably chosen boundaryconditions are effective in creating free form surfaces. In this paper, a fourth order partialdifferential equation and boundary conditions up to tangential continuity are introduced. Thegeneral solution is divided into a closed form solution and a non-closed form one leading to a mixedsolution to the PDE. The obtained solution is applied to a number of surface modelling examplesincluding glass shape design, vase surface creation and arbitrary surface representation.

Development of Texture Mapping Approaches for Additively Manufacturable Surfaces

manufacturing(AM)technologies have been recognized for their capability to build complex components and hence have ofered more freedom to designers for a long time.The ability to directly use a computer-aided design(CAD)model has allowed for fabricating and realizing complicated components,monolithic design,reducing the number of components in an assembly,decreasing time to market,and adding performance or comfort-enhancing functionalities.One of the features that can be introduced for boosting a component functionality using AM is the inclusion of surface texture on a given component.This inclusion is usually a difcult task as creating a CAD model resolving fne details of a given texture is difcult even using commercial software packages.This paper develops a methodology to include texture directly on the CAD model of a target surface using a patch-based sampling texture synthesis algorithm,which can be manufactured using AM.Input for the texture generation algorithm can be either a physical sample or an image with heightmap information.The heightmap information from a physical sample can be obtained by 3D scanning the sample and using the information from the acquired point cloud.After obtaining the required inputs,the patches are sampled for texture generation according to non-parametric estimation of the local conditional Markov random feld(MRF)density function,which helps avoid mismatched features across the patch boundaries.While generating the texture,a design constraint to ensure AM producibility is considered,which is essential when manufacturing a component using,e.g.,Fused Deposition Melting(FDM)or Laser Powder Bed Fusion(LPBF).The generated texture is then mapped onto the surface using the developed distance and angle preserving mapping algorithms.The implemented algorithms can be used to map the generated texture onto a mathematically defned surface.This paper maps the textures onto fat,curved,and sinusoidal surfaces for illustration.After the texture mapping,a stereolithography(STL)model is generated with the desired texture on the target surface.The generated STL model is printed using FDM technology as a fnal step.

Hypersonic Waverider Surface Development Using Aerodynamic Flow Around Conical Bodies

Developing the waverider based hypersonic vehicles is an inverse design process in which shape is developed from a known flow field by tracing of streamlines to form a stream surface. The flow field can be based on a solution of Taylor Maccoll equation for a specified shock or cone angle. This Paper discusses the development of waverider shapes for hypersonic reentry vehicles.

Methanol Adsorption on TiO2 Film Studied by Sum Frequency Generation Vibrational Spectroscopy

A broadband infrared surface sum frequency generation vibrational spectroscopy （SFG-VS） and an in situ UV excitation setup devoted to studying surface photocatalysis have been constructed. With a home-made compact high vacuum cell, organic contaminants on TiO2 thin film surface prepared by RF magnetron sputtering were in situ removed under 266 nm irradiation in 10 kPa 02 atmosphere. We obtained the methanol spectrum in the CH3 stretching vibration region on TiO2 surface with changing the methanol pressure at room temperature. Features of both molecular and dissociative methanol, methoxy, adsorbed on this surface were resolved. The CH3 symmetric stretching vibration frequency and Fermi resonance of molecular methanol is red-shifted by about 6-8 cm-1 from low to high coverage. Moreover, the recombination of dissociative methanol and H on Surfaces in vacuum was also observed. Our results suggest two equilibria exist： between molecular methanol in the gas phase and that on surfaces, and between molecular methanol and dissociative methanol on surfaces.

Hybrid Surface Mesh Adaptation for Climate Modeling

Solution-driven mesh adaptation is becoming quite popular for spatial error control in the numerical simulation of complex computational physics applications,such as climate modeling.Typically,spatial adaptation is achieved by element subdivision (h adaptation) with a primary goal of resolving the local length scales of interest.A sec- ond,less-popular method of spatial adaptivity is called'mesh motion'(r adaptation); the smooth repositioning of mesh node points aimed at resizing existing elements to capture the local length scales.This paper proposes an adaptation method based on a combination of both element subdivision and node point repositioning (rh adaptation). By combining these two methods using the notion of a mobility function,the proposed approach seeks to increase the flexibility and extensibility of mesh motion algorithms while providing a somewhat smoother transition between refined regions than is pro- duced by element subdivision alone.Further,in an attempt to support the requirements of a very general class of climate simulation applications,the proposed method is de- signed to accommodate unstructured,polygonal mesh topologies in addition to the most popular mesh types.

Analysis of Machinable Structures and Their Wettability of Rotary Ultrasonic Texturing Method

Tailored surface textures at the micro- or nanoscale dimensions are widely used to get required functional performances. Rotary ultrasonic texturing （RUT） technique has been proved to be capable of fabricating periodic micro- and nanostructures. In the present study, diamond tools with geometrically defined cutting edges were designed for fabricating different types of tailored surface textures using the RUT method. Surface generation mechanisms and machinable structures of the RUT process are analyzed and simulated with a 3D-CAD program. Textured surfaces generated by using a triangular pyramid cutting tip are constructed. Different textural patterns from several micrometers to several tens of micrometers with few burrs were successfully fabricated, which proved that tools with a proper two-rake-face design are capable of removing cutting chips efficiently along a sinusoidal cutting locus in the RUT process. Technical applications of the textured surfaces are also discussed. Wetting properties of textured aluminum surfaces were evaluated by combining the test of surface roughness features. The results show that the real surface area of the textured aluminum surfaces almost doubled by comparing with that of a flat surface, and anisotropic wetting properties were obtained due to the obvious directional textural features.

Integrated Simulation Method for Interaction between Manufacturing Process and Machine Tool

The interaction between the machining process and the machine tool （IMPMT） plays an important role on high precision components manufacturing. However, most researches are focused on the machining process or the machine tool separately, and the interaction between them has been always overlooked. In this paper, a novel simplified method is proposed to realize the simulation of IMPMT by combining use the finite element method and state space method. In this method, the transfer function of the machine tool is built as a small state space. The small state space is obtained from the complicated finite element model of the whole machine tool. Furthermore, the control system of the machine tool is integrated with the transfer function of the machine tool to generate the cutting trajectory. Then, the tool tip response under the cutting force is used to predict the machined surface. Finally, a case study is carried out for a fly-cutting machining process, the dynamic response analysis of an ultra-precision fly-cutting machine tool and the machined surface verifies the effectiveness of this method. This research proposes a simplified method to study the IMPMT, the relationships between the machining process and the machine tool are established and the surface generation is obtained.

Kinematic generation of ruled surface based on rational motion of point-line

This paper studies representation of rigid combination of a directed line and a reference point on it （here referred to as a ＂point-line＂） using dual quatemions. The geometric problem of rational ruled surface design is viewed as the kinematic prob- lem of rational point-line motion design. By using the screw theory in kinematics, mappings from the spaces of lines and point-lines in Euclidean three-dimensional space into the hyperplanes in dual quaternion space are constructed, respectively. The problem of rational point-line motion design is then converted to that of projective Bezier or B-spline image curve design in hyperplane of dual quatemions. This kinematic method can unify the geometric design of ruled surfaces and tool path generation for five-axis numerical control （NC） machining.

Fully Nonlinear Simulation for Fluid/Structure Impact：A Review

This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method （BEM）. Fully nonlinear boundary conditions are imposed on the unknown free surface and the wetted surface of the moving body. The review includes （1） vertical and oblique water entry of a body at constant or a prescribed varying speed, as well as free fall motion, （2） liquid droplets or column impact as well as wave impact on a body, （3） similarity solution of an expanding body. It covers two dimensional （2D）, axisymmetric and three dimensional （3D） cases. Key techniques used in the numerical simulation are outlined, including mesh generation on the multivalued free surface, the stretched coordinate system for expanding domain, the auxiliary function method for decoupling the mutual dependence of the pressure and the body motion, and treatment for the jet or the thin liquid film developed during impact.

Tunable terahertz wave difference frequency generation in a graphene/AlGaAs surface plasmon waveguide

Graphene-based surface plasmon waveguides(SPWs) show high confinement well beyond the diffraction limit at terahertz frequencies. By combining a graphene SPW and nonlinear material, we propose a novel graphene/AlGaAs SPW structure for terahertz wave difference frequency generation(DFG) under near-infrared pumps.The composite waveguide, which supports single-mode operation at terahertz frequencies and guides two pumps by a high-index-contrast AlGaAs∕Al Oxstructure, can confine terahertz waves tightly and realize good mode field overlap of three waves. The phase-matching condition is satisfied via artificial birefringence in an AlGaAs∕Al Ox waveguide together with the tunability of graphene, and the phase-matching terahertz wave frequency varies from 4 to 7 THz when the Fermi energy level of graphene changes from 0.848 to 2.456 eV. Based on the coupled-mode theory, we investigate the power-normalized conversion efficiency for the tunable terahertz wave DFG process by using the finite difference method under continuous wave pumps, where the tunable bandwidth can reach 2 THz with considerable conversion efficiency. To exploit the high peak powers of pulses, we also discuss optical pulse evolutions for pulse-pumped terahertz wave DFG processes.

A New Method for Efficient Generation of High Quality Triangular Surface Meshes

A novel method for the generation of unstructured triangular surface meshes is presented.The method is based on remeshing techniques including edge splitting/contraction and edge swapping.Normalized edge lengths,based on a metric derived from curvature or from a user–specified spacing,are employed as the remeshing criterion.It is assumed that the geometry is input in the form of composite parametric surfaces,with Ferguson or Nurbs type multiple patch representation.Examples involving typical aircraft geometries and a ship model,are included to demonstrate how high quality meshes can be efficiently generated on surfaces with a high degree of geometric complexity.

ISpliter:an intelligent and automatic surface mesh generator using neural networks and splitting lines

In this paper,we present a novel surface mesh generation approach that splits B-rep geometry models into isotropic triangular meshes based on neural networks and splitting lines.In the first stage,a recursive method is designed to generate plentiful data to train the neural network model offline.In the second stage,the implemented mesh generator,ISpliter,maps each surface patch into the parameter plane,and then the trained neural network model is applied to select the optimal splitting line to divide the patch into subdomains continuously until they are all triangles.In the third stage,ISpliter remaps the 2D mesh back to the physical space and further optimizes it.Several typical cases are evaluated to compare the mesh quality generated by ISpliter and two baselines,Gmsh and NNW-GridStar.The results show that ISpliter can generate isotropic triangular meshes with high average quality,and the generated meshes are comparable to those generated by the other two software under the same configuration.

SAW diffraction field generated by source with finite aperture piezoelectric crystal surfaces

So far, the diffracted SAW field generated by an IDT with finite aperture on piezoelectric crystal surfaces is usually analyzed phenomenologically with the angular spectrum theory. A major approximation of this theory is to ignore the vector nature of the field by assuming that the wave field can be represented by a scalar as in optics. In this paper, a rigorous vector field theory of the surface excitation of elastic wave field in piezoelectric crystal developed by the authors is used to evaluate the SAW diffraction field adepately and precisely. As an example, numerical results for YZ-LiNbO3 are presented and compared with those obtained form the angular spectrum theory.

Theoretical investigation of some parameters into the behavior of quantum dot solar cells

The main goal of this paper is to determine the accurate values of two parameters namely the surface generation–recombination rate and the average total number of electrons density generated in the i-region. These values will enhance the performance of quantum dot solar cells（QDSCs）. In order to determine these values, this paper concentrates on the optical generation lifetime, the recombination lifetime, and the effective density state in QDs. Furthermore, these parameters are studied in relation with the average total number of electrons density. The values of the surface generation–recombination rate are found to be negative, which implies that the generation process is dominant in the absorption quantum dot region. Consequently, induced photocurrent density relation with device parameters is determined. The results ensure that QDSCs can have higher response photocurrent and then improve the power conversion efficiency. Moreover, the peak value of the average total number of electrons density is achieved at the UV range and is extended to the visible range, which is adequate for space and ground solar applications.

Adaptive Finite Element Modeling Techniques for the Poisson-Boltzmann Equation

We consider the design of an effective and reliable adaptive finite element method(AFEM)for the nonlinear Poisson-Boltzmann equation(PBE).We first examine the two-term regularization technique for the continuous problem recently proposed by Chen,Holst and Xu based on the removal of the singular electrostatic potential inside biomolecules;this technique made possible the development of the first complete solution and approximation theory for the Poisson-Boltzmann equation,the first provably convergent discretization and also allowed for the development of a provably convergent AFEM.However,in practical implementation,this two-term regularization exhibits numerical instability.Therefore,we examine a variation of this regularization technique which can be shown to be less susceptible to such instability.We establish a priori estimates and other basic results for the continuous regularized problem,as well as for Galerkin finite element approximations.We show that the new approach produces regularized continuous and discrete problemswith the samemathematical advantages of the original regularization.We then design an AFEM scheme for the new regularized problem and show that the resulting AFEM scheme is accurate and reliable,by proving a contraction result for the error.This result,which is one of the first results of this type for nonlinear elliptic problems,is based on using continuous and discrete a priori L¥estimates.To provide a high-quality geometric model as input to the AFEM algorithm,we also describe a class of feature-preserving adaptive mesh generation algorithms designed specifically for constructing meshes of biomolecular structures,based on the intrinsic local structure tensor of the molecular surface.All of the algorithms described in the article are implemented in the Finite Element Toolkit(FETK),developed and maintained at UCSD.The stability advantages of the new regularization scheme are demonstrated with FETK through comparisons with the original regularization approach for a model problem.The convergence and accuracy of the overall AFEMalgorithmis also illustrated by numerical approximation of electrostatic solvation energy for an insulin protein.

Towards critical and supercritical electromagnetic fields

The availability of ever stronger,laser-generated electromagnetic fields underpins continuing progress in the study and application of nonlinear phenomena in basic physical systems,ranging from molecules and atoms to relativistic plasmas and quantum electrodynamics.This raises the question:how far will we be able to go with future lasers?One exciting prospect is the attainment of field strengths approaching the Schwinger critical field Ecr in the laboratory frame,such that the field invariant E^(2)−c^(2)B^(2)>E_(cr)^(2) is reached.The feasibility of doing so has been questioned,on the basis that cascade generation of dense electron–positron plasma would inevitably lead to absorption or screening of the incident light.Here we discuss the potential for future lasers to overcome such obstacles,by combining the concept of multiple colliding laser pulses with that of frequency upshifting via a tailored laser–plasma interaction.This compresses the electromagnetic field energy into a region of nanometre size and attosecond duration,which increases the field magnitude at fixed power but also suppresses pair cascades.Our results indicate that laser facilities with peak power of tens of PW could be capable of reaching Ecr.Such a scenario opens up prospects for the experimental investigation of phenomena previously considered to occur only in the most extreme environments in the universe.