Surface Representation Method Research Articles

A curved surface representation method for convolutional neural network of wake field prediction

The goal of this study is to develop a prediction method to recognize the wake field behind a ship using a convolutional neural network (CNN) model. First, a new representation method for a 3D curved surface is proposed suitable for the CNN, called an image-based hull form representation (IHR). The advantages of the proposed method are the high fidelity of its hull form representation using more than 20,000 input data points and its fast prediction speed, which requires less than 0.01 s for a task that traditionally took more than an hour to estimate by physics-based simulation. The IHR regards that a two-dimensional grid formed on the 3D curved hull surface, which is used for structured-grid-based CFD, as a data set with the same data structure as the image data. Because CNNs recognize image data at accuracy rates higher than humans, a CNN is also be expected to recognize 3D surface characteristics with higher accuracy than humans. The image data are represented by three primary colors (cyan, magenta, yellow) in vertical and horizontal (i × j) pixels. The hull-form-structured grid can also be expressed as an i × j structure data with (x, y, z) coordinates that have the same data structure as the three primary colors in the image data. A CFD calculation data set of 2730 ship types with different stern shapes was constructed to verify the proposed method. The validation results proves that the root mean squared error of the proposed model is 0.005 to predict axial wake velocity on a propeller plane, and the coefficient of determination R2 achieves 0.986. In addition, the estimation speed for each hull-form prediction is 100,000 times faster than are physics-based simulations. The results lead to the conclusion that the representation method of a curved surface and the proposed prediction method of the stern wake field is a promising tool in the initial hull form design.

A general purpose contact algorithm using a compliance contact force model for rigid and flexible bodies of complex geometry

The analysis of multi-flexible-body dynamics (MFBD) has been an important issue in the area of computational dynamics. Also, dynamic analysis of many mechanical systems often involves contacts among rigid and flexible bodies. But, until now, the contact analysis in the multi-flexible-body dynamics has still remains a big, challenging area. In order to simulate the contact phenomena, this study uses a compliant contact force model based on the Hertzian contact theory. When generating the contact force with a compliant contact force model, a penetration depth and a contact reference frame (a contact point and normal and tangent directions) must be determined from the geometrical information of the rigid and flexible body surfaces.For robust and efficient general purpose contact algorithms, the contact algorithms are divided into four main parts which are a surface representation, a pre-search, and a detailed search and a contact force generation. In the surface representation part, we propose a general surface representation method which can be used for complex rigid and flexible bodies. In the pre-search, the algorithm performs collision detection and composes the input data sets for the detailed search. Then, in the detailed search, the penetration depth and contact reference frame are calculated in order to generate the contact force by using the compliant contact force model. Finally, in the contact force generation part, we evaluate the contact force and the Jacobian matrix which can be used for the implicit integrator.The new general purpose contact algorithm is called GGEOM (General GEOMetry) contact, because it can use general rigid and flexible geometries.

Modulated surface textures for enhanced light trapping in thin-film silicon solar cells

Substrates with a modulated surface texture were prepared by combining different interface morphologies. The spatial frequency surface representation method is used to evaluate the surface modulation. When combining morphologies with appropriate geometrical features, substrates exhibit an increased scattering level in a broad wavelength region. We demonstrate that the improved scattering properties result from a superposition of different light scattering mechanisms caused by the different geometrical features integrated in a modulated surface texture.

Investigation of the adjoint method in aerodynamic optimization using various shape parameterization techniques

This paper studies the effect of design variables vector on automatic aerodynamic shape optimization in the adjoint method. Three shape techniques are studied: surface points, relations of the NACA 4-digit airfoil series and Hicks-Henne "Bump" Functions. First, this paper presents the complete formulation of the optimal design problem for the Euler equations. Second, the implementation of these surface representation methods are explored. Finally, results are presented for inverse and drag minimization problems. The results show that the mechanism, value and the trend of drag reduction during the optimization strongly affected by the type of design vector.

A B-spline based heterogeneous modeling and analysis of proximal femur with graded element

Bone is a complex biological tissue and natural heterogeneous object. The main objective of this study is to simulate quasi-static loading of bio-objects like human femur with B-spline based modeling and its 3D finite element analysis with graded element. B-spline surface representation method is extended to represent material composition to develop heterogeneous solid model of proximal femur. Lagrangian graded element is used to assign inhomogeneous isotropic elastic properties in finite element model to improve the performance. Convergence study is carried out with finite element model in single leg stance load condition. To test the feasibility of the model, sensitivity of simulation is investigated. To validate the model, numerical results are compared with those of an experimental work for the same specimen in simple stance load condition obtained from one of the reference paper. Good agreement is achieved for vertical displacement and strains in most of the locations.

Accurate and Scalable Surface Representation and Reconstruction from Images

We introduce a new surface representation method, called patchwork, to extend three-dimensional surface reconstruction capabilities from multiple images. A patchwork is the combination of several p...

Accurate and Scalable Surface Representation and Reconstruction from Images

We introduce a new surface representation method, called patchwork, to extend three-dimensional surface reconstruction capabilities from multiple images. A patchwork is the combination of several patches that are built one by one. This design potentially allows for the reconstruction of an object with arbitrarily large dimensions while preserving a fine level of detail. We formally demonstrate that this strategy leads to a spatial complexity independent of the dimensions of the reconstructed object and to a time complexity that is linear with respect to the object area. The former property ensures that we never run out of storage and the latter means that reconstructing an object can be done in a reasonable amount of time. In addition, we show that the patchwork representation handles equivalently open and closed surfaces, whereas most of the existing approaches are limited to a specific scenario, an open or closed surface, but not both. The patchwork concept is orthogonal to the method chosen for surface optimization. Most of the existing optimization techniques can be cast into this framework. To illustrate the possibilities offered by this approach, we propose two applications that demonstrate how our method dramatically extends a recent accurate graph technique based on minimal cuts. We first revisit the popular carving techniques. This results in a well-posed reconstruction problem that still enjoys the tractability of voxel space. We also show how we can advantageously combine several image-driven criteria to achieve a finely detailed geometry by surface propagation. These two examples demonstrate the versatility and flexibility of patchwork reconstruction. They underscore other properties inherited from patchwork representation: Although some min-cut methods have difficulty in handling complex shapes (e.g., with complex topologies), they can naturally manipulate any geometry through the patchwork representation while preserving their intrinsic qualities. The above properties of patchwork representation and reconstruction are demonstrated with real image sequences.

MESHGRID—A Compact, Multiscalable and Animation-Friendly Surface Representation

MESHGRID is a novel, compact, multiscalable and animation-friendly surface representation method, which has been introduced in MPEG-4 . The MESHGRID representation attaches a description of the "global connectivity" between the vertices on the object's surface (i.e., the 3-D connectivity wireframe) to a regular 3-D grid of points (i.e., the reference grid). MESHGRID efficiently encodes the 3-D connectivity wireframe by using a new type of 3-D extension of Freeman chain-code. MESHGRID does not explicitly store the polygons of the surface, since the 3-D connectivity wireframe has particular connectivity properties allowing for the unambiguous derivation of the triangulation. The reference grid is a smooth vector field defined on a regular discrete 3-D space. This grid is efficiently compressed by using an embedded 3-D wavelet-based multiresolution intra-band coding algorithm. MESHGRID can be efficiently exploited for QoS since it allows for three types of scalability in both view-dependent and view-independent scenarios, including: 1) resolution scalability, i.e., the adaptation of the number of transmitted vertices; 2) shape precision, i.e., the adaptive reconstruction of the reference grid positions; and 3) vertex position scalability, i.e., the change of the precision of known vertex positions with respect to the reference grid. Furthermore, in addition to the classical vertex-based animation, MESHGRID also supports specific animation capabilities, such as: 1) rippling effects by changing the position of the vertices relative to corresponding reference grid points and 2) reshaping on a hierarchical basis of the regular reference grid and its attached vertices.

Point fingerprint: A new 3-D object representation scheme

This paper proposes a new, efficient surface representation method for surface matching. A feature carrier for a surface point, which is a set of two-dimensional (2-D) contours that are the projections of geodesic circles on the tangent plane, is generated. The carrier is named point fingerprint because its pattern is similar to human fingerprints and plays a role in discriminating surface points. Corresponding points on surfaces from different views are found by comparing their fingerprints. The point fingerprint is able to carry curvature, color, and other information which can improve matching accuracy, and the matching process is faster than 2-D image comparison. A novel candidate point selection method based on the fingerprint irregularity is introduced. Point fingerprint is successfully applied to pose estimation of real range data.

Towards 3-D model-based video coding

In the domain of telecommunication applications, videophony, teleconferency, the representation and modelization of human face, and its expressions, knows an important development. In this paper, we present the basic principles of image sequences coding with main approaches and methods to lead to 3D model-based coding. Then, we introduce our 3D wire-frame model with which we have developed some compression and triangulated surface representation methods. An original approach to simulate and reproduce facial expressions with radial basis functions is also presented.

Determining interference between pairs of solids defined constructively in computer animation

This paper presents theory and implementation of a method for detecting interference between a pair of solid objects. Often at times, when performing simulations, two solids may unwittingly interpenetrate each other. The two components of the system presented in this paper are: (1) a surface representation method to model solid objects; and (2) a method for detecting interference. Body representation of a solid in this system is based upon enveloping each solid with surfaces (called positive entities). Most computer aided design (CAD) systems use solid modeling techniques to represent solid objects. Since most solid models use Boolean operations to model complex objects, a method is presented to envelop complex objects with parametric surfaces. A method for tracing intersection curves between two surfaces is also presented. Discontinuities on surfaces are defined as negative entitics in order to extend the method to complex solids. Determining interference is based upon a numerical algorithm for computing points of intersection between boundary curves and parametrized entities. The existence of segments of these curves inside the boundary of positive and negative entities is established by computing the circulation of a function around the boundary curve. Interference between two solids is then detected. No limitations are imposed on the convexity or simplicity of the boundary curves treated.

Volumetric error analysis of a multi-axis machine tool machining a sculptured surface workpiece

Abstract The objective of this research is to develop a geometric error model for multi-axis machine tools based on a closed-loop configuration. In this study, the geometric error model of each axis is derived by using 4×4 homogeneous transformation matrix. The ideal cutter location of the sculptured workpiece surface is calculated using the Bezier bicubic parametric surface representation method and machine geometric errors. The actual cutter locations is calculated by considering runout error of the cutting tool and machine geometric errors. Then, the step-by-step volumetric error analysis method is suggested on the basis of the closed-loop configuration of the multi-axis machine tools. The simulation study shows the simplicity and effectiveness of the proposed strategy.

CW laser machining of hard ceramics—II. Effects of multiple reflections

Beam guiding effects during laser machining of ceramics due to multiple reflections in the groove are analyzed theoretically for two extreme cases—purely specular and purely diffuse reflections. Specular reflections are valid for materials that have a smooth surface during laser evaporation (small optical roughness as compared to the laser wavelength). For such cases the material surface is divided into a number of rectangular patches using a bicubic surface representation method. The net radiative flux for these patch elements is obtained by ray tracing methods. The resulting radiative flux due to specular reflections is combined with the three-dimensional conduction equation governing conduction losses into the medium, and the resulting groove shape and depth are found through an iterative procedure. Diffuse reflections are valid for materials that have a very rough surface during material removal. To address beam coupling due to diffuse reflections, irradiation calculations employing view factor theory were combined with the three-dimensional conduction model. Considering multiple reflections results in an increased effective absorptivity and deeper grooves, accompanied by a flatter profile near the centerline and steeper slopes in the other parts of the groove cross-section. For the tested set of parameters, material removal rates are increased by up to 40% by specular reflections, and up to 70% by diffuse reflections. Experiments with hot-pressed silicon nitride ceramic showed increased beam coupling for deeper grooves (high power and/or slow scanning speeds) as predicted by considering multiple reflections. The agreement between theoretical calculations and experimental data for material removal rate and groove shape was good, if multiple reflections were assumed to be diffuse.