Similarity measures for mid-surface quality evaluation

Mid-surface models are widely used in engineering analysis to simplify the analysis of thin-walled parts, but it can be difficult to ensure that the mid-surface model is representative of the solid part from which it was generated. This paper proposes two similarity measures that can be used to evaluate the quality of a mid-surface model by comparing it to a solid model of the same part.Two similarity measures are proposed; firstly a geometric similarity evaluation technique based on the Hausdorff distance and secondly a topological similarity evaluation method which uses geometry graph attributes as the basis for comparison. Both measures are able to provide local and global similarity evaluation for the models.The proposed methods have been implemented in a software demonstrator and tested on a selection of representative models. They have been found to be effective for identifying geometric and topological errors in mid-surface models and are applicable to a wide range of practical thin-walled designs.     

Constructive generation of the medial axis for solid models

The medial axis (MA) is a simplified representation of complicated models which is widely used in current research. However, the efficient generation of the MA for complicated solid models continues to pose a challenge. In this study, a constructive approach for the generation of the MA is proposed for solid models after they are voxelized. With this method, the MA of the model constructed from two operand models via a Boolean operation is efficiently generated by merging the MAs of the operand models in a certain way, instead of regenerating them from scratch. To support the proposed method, the affected region of the resultant model is computed first using a Boolean operation. Second, only the MA in the affected region is regenerated by distance dilation. Third, the complete MA of the resultant model is constructed by combining the newly generated MA with the unchanged MAs of the operand models. In this study, the accuracy and complexity are analyzed for the final MA and some examples are given to illustrate the performance of the proposed method.     

An approach for extracting non-manifold mid-surfaces of thin-wall solids using chordal axis transform

This paper proposes an approach for extracting non-manifold mid-surfaces of thin-wall solids using the chordal axis transform (CAT) (Prasad in CNLS Newsletter—Center for Nonlinear Studies, Los Alamos National Laboratory, vol 139, 1997). There is great demand for extracting mid-surfaces as it is used in dimension reduction. Quadros and Shimada previously used CAT in extracting 2-manifold mid-surfaces of a particular type of thin-wall solids. The proposed approach is an extension of the previous approach (Quadros and Shimada in 11th international meshing roundtable, 2002) in order to extract non-manifold mid-surfaces of general thin-wall solids. The three steps involved in extracting the mid-surface of a thin-wall solid are: (1) generating a tet mesh of a thin-wall solid without inserting interior nodes; (2) generating a raw mid-surface by smart cutting of tets; and (3) remeshing the raw mid-surface via smart clean-up. In the proposed approach, a discrete model (i.e., a tet mesh without any interior nodes) is used instead of working directly on a CAD model. The smart cutting of tets using CAT yields correct topology at the non-manifold region in the raw mid-surface. As the raw mid-surface is not directly suitable for engineering purposes, it is trimmed using a smart clean-up procedure and then remeshed. The proposed approach has been implemented using C++ in commercial ALGOR finite element analysis software. The proposed approach is computationally efficient and has shown effective results on industrial models.     

A study on robot path planning from a solid model

CAD/CAM technologies have been developed and are beginning to penetrate rapidly into industries. At present, however, there are many problems that should be solved before CAD/CAM technologies can play their proper role in the total process. In an effort to improve CAD/CAM current circumstances, a trial CAE system which generates an operation path of a robot from a solid-model built-in CAD process, has been examined. In this system, solid models are built by performing set operations such as addition, subtraction, intersection between several primitives or solid models. Processing is made for a solid model represented by B-rep (boundary representation). To ease the processing, curved faces such as spherical, cylindrical, or conical surfaces, are approximated by several flat planes. As a first step, by assuming Gaussian spatial distribution for a painting gun, path planning of a painting robot for a convex solid body has been examined. A scanning plane is defined for each flat plane and a path of robot effector is generated on this plane.     

Detail feature recognition and decomposition in solid model

A methodology for abstracting features from a 3D solid model based on a new detail-level metric method is proposed. Filleting the whole boundary of an object with constant fillet radius has the effect of low-pass filtering. Taking advantage of the effect, detail-level of boundary entities can be rated. This paper investigates an approach to fillet polyhedral model and then develops a simple way to detect detailed boundary elements. Taking detailed entities as the indicators, detail features are recognized and extracted. In the detailed entities detection and decomposition cycle of the corresponding detail features, detail features are decomposed from the model one by one in terms of their locality. Detail feature decomposition directly results in geometric simplification of a 3D object. The method proposed in this paper can be applied in efficient modeling for CAE from CAD models.     

Graph-based feature recognition for injection moulding based on a mid-surface approach

This paper presents a novel CAD feature recognition approach for thin-walled injection moulded and cast parts in which moulding features are recognised from a mid-surface abstraction of the part geometry. The motivation for the research has been to develop techniques to help designers of moulded parts to incorporate manufacturing considerations into their designs early in the design process. The main contribution of the research has been the development of an attributed mid-surface adjacency graph to represent the mid-surface topology and geometry, and a feature recognition methodology for moulding features. The conclusion of the research is that the mid-surface representation provides a better basis for feature recognition for moulded parts than a B-REP solid model. A demonstrator that is able to identify ribs, buttresses, bosses, holes and wall junctions has been developed using C++, with data exchange to the CAD system implemented using ISO 10303 STEP. The demonstrator uses a commercial algorithm (I-DEAS) to create the mid-surface representation, but the feature recognition approach is generic and could be applied to any mid-surface abstraction. The software has been tested on a range of simple moulded parts and found to give good results.     

Constructing a 3-D mesh model for electrical cardiac activity simulation.

The 3-D ventricle model in this study was reconstructed from a series of MRI torso cross-section data. We used a 3-D voxel array to represent the ventricle. As in cardiac simulations proposed by previous studies, the activation sequence and body surface ECG were simulated in this model. But to reduce the amount of elements in the model, so that the amount of parameters in the model can be handled numerically, we propose another approach to simulate cardiac activity. A mesh model was constructed on the closed surface formed by epicardiac and endocardiac surfaces of the ventricle. We propose a method to simulate the activation sequence on the epicardiac and endocardiac surfaces of the mesh model. As with the uniform double layer theorem, body surface ECG can be estimated in terms of epicardiac and endocardiac surface current source. Consequently, we can also generate ECG waveforms corresponding to this mesh simulation. Both the depolarization sequence and ECG simulated by the mesh model resemble those generated by the 3-D voxel model. However, the mesh model greatly simplified the process of ECG simulation. Both the simulation of depolarization and ECG estimation were expressed in terms of clear and simple mathematical representations. Consequently, we can analytically investigate the effects of the mesh model's parameters on the cardiac activation sequence and ECG. It could be a useful tool to numerically study the relation of ECG waveforms and electrical activity of the heart.     

Adaptive tetrahedral remeshing for modified solid models

During the engineering design process, a designed engineering component is usually repeatedly modified and analyzed to reach final design objectives, and completely mesh regeneration for each design change is very time consuming. An efficient remeshing approach for modified solid models using existing prior existing meshes is proposed in this paper to resolve this issue. It is mainly achieved via three main steps: different face (between the input model and its modification) identification, local destruction zone generation, and local mesh regeneration. In this approach, by carefully selecting a destruction zone to be removed from the original mesh model, a final geometric adaptive mesh model of the modified model is generated, which is very important for downstream analysis accuracy control. Additionally, the complex boundary of the variation region that needs to be remeshed is set up by merging the boundaries of modified region and the destruction zone without using complex intersection operations, which ensure the approach’s robustness. Experimental results on practical engineering parts are also shown to demonstrate the method’s performance.     

Partitioning total variance in risk assessment: Application to a municipal solid waste incinerator

Comprehensive health risk assessment based on aggregate exposure and cumulative risk calculations requires a better understanding of exposure variables and uncertainty associated with them. Although there are many sources of uncertainty in system models, two basic kinds of parametric uncertainty are fundamentally different from each other: natural/stochastic and epistemic uncertainties. However, conventional methods such as standard Monte Carlo Sampling (MCS), which assumes vagueness as random property, may not be suitable for this type of uncertainty analysis. An improved systematic uncertainty and variability analysis can provide insight into the level of confidence in model estimates, and it can aid in assessing how various possible model estimates should be weighed. The main goal of the present study was to introduce Fuzzy Latin Hypercube Sampling (FLHS), a hybrid approach for incorporating epistemic and stochastic uncertainties separately. An important property of this technique is its ability to merge inexact generated data of the LHS approach to increase the quality of information. The FLHS technique ensures that the entire range of each variable is sampled with proper incorporation of uncertainty and variability. A fuzzified statistical summary of the model results produces a detailed sensitivity analysis, which relates the effects of variability and uncertainty of input variables to model predictions. The feasibility of the method has been tested with a case study, analyzing total variance in the calculation of incremental lifetime risks due to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) for the residents living in the surroundings of a municipal solid waste incinerator (MSWI) in the Basque Country, Spain.     

Kinetic approach to the determination of the phase diagram of a solid solution

A binary mixture of 1,4-dichlorobenzene and 1,4-dibromobenzene, as a representative of a system that forms a solid solution, was measured in an adiabatic calorimeter. Several mixtures of different compositions were heated to 380 K, kept in the liquid phase at this temperature overnight, and then cooled slowly down to 250 K. The enthalpy path of the mixture measured during cooling carries the information that enables us to describe the crystallization process. In the first stage, crystallization develops rapidly and clearly deviates from equilibrium, while in the second stage it proceeds significantly slower, whereby we assume that the surface of the solid is in equilibrium with the existing liquid phase at the given temperature during cooling. Such an approach opposes the one that assumes equilibrium between the liquid and solid bulks, known as the equilibrium model. We show that by employing the kinetic model, the experimental enthalpy path of the mixture during cooling in the adiabatic calorimeter can be very successfully reproduced, while the equilibrium model fails in this aspect. Furthermore, we propose a procedure where the kinetic model is used to obtain the excess thermodynamic properties of the solid phase. These quantities enable the calculation of the liquid–solid phase diagram using the excess parameters obtained from the approach that does not assume the overall equilibrium between the phases during the crystallization process.     

Layered deformation of solid model using conformal mapping

In this paper, we present a solid model deformation method based on layered conformal mapping. For a solid model represented by base patch and height field, the shape of the model can be deformed by interactive means, such as changing the base patch by conformal mappings and adjusting the height field by a pre-defined function. In our method, the deformation is predictable and the transformation function of the deformation can be expressed analytically by Schwarz–Christoffel formula. To perform a deformation of a cylinder to a desired solid of rotation hierarchically, a generalized Schwarz–Christoffel formula is also introduced. Numerical examples show that the proposed method is convenient and efficient to deform solid models, especially to solids with genus zero.     

Simplification of a complex signal transduction model using invariants and flow equivalent servers

In this paper we consider the modeling of a portion of the signal transduction pathway involved in the angiogenic process. The detailed model of this process is affected by a high level of complexity due to the functional properties that are represented and the size of its state space. To overcome these problems, we suggest approaches to simplify the detailed representation that result in models with a lower computational and structural complexity, while still capturing the overall behavior of the detailed one.The simplification process must take into account both the structural aspects and the quantitative behavior of the original model. To control the simplification from a structural point of view, we propose a set of reduction steps that maintain the invariants of the original model. To ensure the correspondence between the simplified and the original models from a quantitative point of view we use the flow equivalent method that provides a way of obtaining the parameters of the simplified model on the basis of those of the original one.To support the proposed methodology we show that a good agreement exists among the temporal evolutions of the relevant biological products in the simplified and detailed model evaluated with a large set of input parameters.     

Encoded moire inspection based on a computer solid model

An investigation into a system linking a computer solid modeler to an active stereo imaging inspection station is presented. Given the computer solid model of a surface, a projected pattern can be encoded so that the reflections from the object's surface exhibit a uniformly simple pattern when the object's surface and the modeled surface are identical. Research concerning the method of generating projection patterns, as well as the sensitivity of the system, is discussed. A prototype system consisting of a computer graphics workstation; a flexible projector, and a machine vision system was used to inspect two different manufactured parts     

A hybrid SDF for the detailed representation of liquid–solid mixed surfaces

We propose a hybrid signed distance field (SDF) method for reconstructing the detailed surface of a model as it changes from a solid state to a liquid state. Previous particle‐based fluid simulations suffer from a noisy surface problem when the particles are distributed irregularly. If a smoothing scheme is applied to reduce the problem, sharp and detailed features can be lost by over‐smoothing artifacts. Our method constructs a hybrid SDF by combining level‐set values from the solid and liquid parts of the object. This makes it possible to represent the detailed features and smooth surfaces of an object when both solid and liquid parts are mixed in that object. In addition, the concept of a guiding shape is proposed, which uses a coordinate‐warping technique to query the level‐set values quickly. The guiding shape is constructed from the object before the simulation begins and some parts of it become liquid. To track the details of the initial solid shape and preserve it, the transformation of the guiding shape is accumulated while the phase‐shift is in progress. By warping the coordinates of this accumulated transformation of the guiding shape, the level‐set values of the solid part can be acquired very quickly. Copyright © 2015 John Wiley & Sons, Ltd.     

Accurate Simplification of Multi‐Chart Textured Models

Scanning and acquisition methods produce highly detailed surface meshes that need multi‐chart parameterizations to reduce stretching and distortion. From these complex shape surfaces, high‐quality approximations are automatically generated by using surface simplification techniques. Multi‐chart textures hinder the quality of the simplification of these techniques for two reasons: either the chart boundaries cannot be simplified leading to a lack of geometric fidelity; or texture distortions and artefacts appear near the simplified boundaries. In this paper, we present an edge‐collapse based simplification method that provides an accurate, low‐resolution approximation from a multi‐chart textured model. For each collapse, the model is reparameterized by local bijective mappings to avoid texture distortions and chart boundary artefacts on the simplified mesh due to the geometry changes. To better apply the appearance attributes and to guarantee geometric fidelity, we drive the simplification process with the quadric error metrics weighted by a local area distortion measure.     

Particle‐based simulation of bubbles in water–solid interaction

In this paper, a particle‐based multiphase method for creating realistic animations of bubbles in water–solid interaction is presented. To generate bubbles from gas dissolved in the water on the fly, we propose an approximate model for the creation of bubbles, which takes into account the influence of gas concentration in the water, the solid material, and water–solid velocity difference. As the air particle on the bubble surface is treated as a virtual nucleation site, the bubble absorbs air from surrounding water and grows. The density and pressure forces of air bubbles are computed separately using smoothed particle hydrodynamics; then, the two‐way coupling of bubbles with water and solid is solved by a new drag force, so the generated bubbles’ flow on the surface of solid and the deformation in the rising process can be simulated. Additionally, touching bubbles merge together under the cohesion forces weighted by the smoothing kernel and velocity difference. The experimental results show that this method is capable of simulating bubbles in water–solid interaction under different physical conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

A 2D model for shape optimization of solid oxide fuel cell cathodes

A topology optimization method is used to identify the optimal shape of the nano-composite cathode of a solid oxide fuel cell (SOFC). A simplified analysis model is used in computations aimed at reducing ohmic losses by optimizing the shape of the cathode to minimize resistance. The model of the SOFC is reduced to a periodic, 2D conduction problem with design-dependent ionic transfer boundary conditions. Special techniques are introduced to avoid physically inadmissible designs that would otherwise be allowed by the 2D model. Isoperimetric constraints on the perimeter and the amount of material are used in the problem. Numerical examples are provided to discuss the effect of material properties and the resource restrictions introduced by the constraints. The methodology discussed can be applied to similar problems involving design-dependent boundary conditions.