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This paper describes an approach to convey quality-oriented strategies to CAD trainees by embedding quality criteria into rubrics so as to force CAD trainees to understand them early in their instruction. To this end, the paper analyzes how CAD quality criteria can be organized around quality dimensions and embedded into rubrics in order to enforce quality modeling during the CAD training of novice product designers. Hence, the ambit of this study is training with history-based parametric feature-based MCAD systems, although the general conclusions are believed to be adaptable to other CAD training scenarios. Furthermore, it introduces an approach based on progressive refinement, which results in an assertions map that indicates quality dimensions vs. sequence of tasks for CAD models. The map illustrates how the expand–contract strategy adapts the rubrics to CAD trainee progress and assists them in comprehending the different dimensions of the rubrics. The paper also highlights lessons learned on the suitability of using separate rubrics for different tasks, the need of accurately timing the expand–contract process, and on the convenience of supporting rubrics with suitable teaching, which must convey good practices and evaluation tools through rubrics. The experiments describe the different lessons learned and illustrate the suggested process for replicating our approach for further developing rubrics adapted to other scenarios. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents an integrated and therefore novel approach of tool path generation and simulation for milling in the field of dental technology. Both the geometry of the dental implants and the characteristics of the cutter, machine and raw material have an immediate influence on the stability of the milling process and the quality of the result. Regarding this issue, the paper focuses on the construction of tool path segments on a triangulated surface using an isoparametric and isogeodesic approach. The segments are subsequently chained and simulated in order to provide an optimized tool path in terms of path length and feed rate. The simulation particularly evaluates a tool load to guide feed rate selection and the distance error of the machined surface. Implicit representations of surfaces and solids by means of level sets are applied where appropriate in order to increase robustness and universality of tool path construction. [Copyright &y& Elsevier]

Abstract: Designing materials for targeted performance requirements as required in Integrated Computational Materials Engineering (ICME) demands a combined strategy of bottom–up and top–down modeling and simulation which treats various levels of hierarchical material structure as a mathematical representation, with infusion of systems engineering and informatics to deal with differing model degrees of freedom and uncertainty. Moreover, with time, the classical materials selection approach is becoming generalized to address concurrent design of microstructure or mesostructure to satisfy product-level performance requirements. Computational materials science and multiscale mechanics models play key roles in evaluating performance metrics necessary to support materials design. The interplay of systems-based design of materials with multiscale modeling methodologies is at the core of materials design. In high performance alloys and composite materials, maximum performance is often achieved within a relatively narrow window of process path and resulting microstructures. Much of the attention to ICME in the materials community has focused on the role of generating and representing data, including methods for characterization and digital representation of microstructure, as well as databases and model integration. On the other hand, the computational mechanics of materials and multidisciplinary design optimization communities are grappling with many fundamental issues related to stochasticity of processes and uncertainty of data, models, and multiscale modeling chains in decision-based design. This paper explores computational and information aspects of design of materials with hierarchical microstructures and identifies key underdeveloped elements essential to supporting ICME. One of the messages of this overview paper is that ICME is not simply an assemblage of existing tools, for such tools do not have natural interfaces to material structure nor are they framed in a way that quantifies sources of uncertainty and manages uncertainty in representing physical phenomena to support decision-based design. [Copyright &y& Elsevier]

Abstract: Rigid body simulations require collision detection for determining contact points between simulated bodies. Collision detection performance can become dramatically slow, if geometric models of rigid bodies have intricate inaccessible regions close to their boundaries, particularly when bodies are in close proximity. As a result, frame rates of rigid body simulations reduce significantly in the states in which bodies come into close proximity. Thus, removing inaccessible regions from models can significantly improve rigid body simulation performance without influencing the simulation accuracy because inaccessible regions do not come in contact during collisions. This paper presents an automated pair-wise contact preserving model simplification approach based upon detection and removing of inaccessible regions of a given model with respect to another colliding model. We introduce a pose independent data-structure called part section signature to perform accessibility queries on 3D models based on a conservative approximation scheme. The developed approximation scheme is conservative and does not oversimplify but may undersimplify models, which ensures that the contact points determined using simplified and unsimplified models are exactly identical. Also, we present a greedy algorithm to reduce the number of simplified models that are needed to be stored for satisfying memory constraints in case of a simulation scene with more than two models. This paper presents test results of the developed simplification algorithm on a variety of part models. We also report results of collision detection performance tests in rigid body simulations using simplified models, which are generated using developed algorithms, and their comparison with the identical performance tests on respective unsimplified models. [Copyright &y& Elsevier]

Abstract: Existing works in optimization of five-axis machining mainly focus on the machining efficiency and precision, while the dynamic performance of the machine tools has not been fully addressed, especially in high-speed machining, in which the rotary actuators have limited dynamic ability. In this paper, a study is reported on how to generate a tool path so that the maximal angular accelerations of the rotary axes of the five-axis machine can be reduced. Two independent methods are proposed for this task: (1) by optimizing the setup of the workpiece on the machine’s table, and (2) by finding better tilt and yaw angles for the tool orientations. In this paper, the setup parameters of the workpiece are incorporated into the inverse kinematic equations, and angular acceleration functions are established according to the numerical solutions of those equations. While varying the tool orientations unquestionably would affect the surface quality of the machining, we introduce the so called Domain of Geometric Constraints that will restrict the allowable tilt and yaw angle of the tool at the cutter contact points on the part surface, so to ensure the satisfaction of the requirement of both local-gouging-free and cusp-height. For the first method–finding the optimal workpiece setup–a heuristic-based approach, i.e., the Genetic Algorithm (GA), is adopted, whereas for the second method–the constrained optimization of tool orientations–we present an elaborate algorithm based on the results from the analysis conducted by the authors. At the end of the paper, computer simulation experiments are reported that demonstrate the effectiveness of our proposed methods and algorithms. [Copyright &y& Elsevier]

Abstract: Since the introduction of the concept of “Digital Earth”, almost every major international city has been re-constructed in the virtual world. A large volume of geometric models describing urban objects has become freely available in the public domain via software like ArcGlobe and Google Earth. Although mostly created for visualization, these urban models can benefit many applications beyond visualization including city scale evacuation planning and earth phenomenon simulations. However, these models are mostly loosely structured and implicitly defined and require tedious manual preparation that usually takes weeks if not months before they can be used. Designing algorithms that can robustly and efficiently handle unstructured urban models at the city scale becomes a main technical challenge. In this paper, we present a framework that generates seamless 3D architectural models from 2D ground plans with elevation and height information. These overlapping ground plans are commonly used in the current GIS software such as ESRI ArcGIS and urban model synthesis methods to depict various components of buildings. Due to measurement and manual errors, these ground plans usually contain small, sharp, and various (nearly) degenerate artifacts. In this paper, we show both theoretically and empirically that our framework is efficient and numerically stable. Based on our review of the related work, we believe this is the first work that attempts to automatically create 3D architectural meshes for simulation at the city level. With the goal of providing greater benefit beyond visualization from this large volume of urban models, our initial results are encouraging. [Copyright &y& Elsevier]

Abstract: In this paper the swept volume with self-penetration (or self-intersection) of the cutter is presented. The complete swept volume (SV), which describes the side and bottom shape of a milling cutter undergoing self-penetration, is generated by using the Gauss map method proposed in the authors’ previous paper [Lee SW, Nestler A. Complete swept volume generation—part I: swept volume of a piecewise -continuous cutter at five-axis milling via Gauss map. Computer-Aided Design 2011; 43(4): 427–41]. Based on the Gauss map method, the comprehensive analysis of envelope profiles of the tool is accomplished. Through the analysis the necessary condition of the self-penetration of the cutter at five-axis movement is identified. After having classified movement types of the milling cutter in an in-depth manner, the topologically consistent boundary of SV is generated by trimming the invalid facets interior to the SV. To demonstrate the validity of the proposed method, a cutting simulation kernel for five-axis machining has been implemented and applied to cavity machining examples such as intake ports of automobile engines and so forth where the self-penetration occurs. The proposed method is proved to be robust and amenable for the practical purpose of the NC simulation. [Copyright &y& Elsevier]

Abstract: In this paper, we revisit the point-in-polyhedron problem. After reviewing previous work, we develop further insight into the problem. We then claim that, for a given testing point and a three-dimensional polyhedron, a single determining triangle can be found which suffices to determine whether the point is inside or outside the polyhedron. This work can be considered to be an extension and implementation of Horn’s work, which inspired us to propose a theorem for obtaining determining triangles. Building upon this theorem, algorithms are then presented, implemented, and tested. The results show that although our code has the same asymptotic time efficiency as commonly used octree-based ray crossing methods, in practice it is usually several times and sometimes more than ten times faster, while other costs such as preprocessing time and memory requirements remain the same. The ideas proposed in this paper are simple and general. They thus extend naturally to multi-material models, i.e., polyhedrons subdivided into smaller regions by internal boundaries. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the new advances carried out for Simucal. Simucal was introduced in  and it is a footwear virtual simulator designed to perform studies of comfort and functionality in CAD footwear design. In this paper, a new finite element model for the deformation of shoe upper materials in gait is presented. This model provides a physical interpretation from the point of view of the contact mechanics to the previous model used in Simucal, as well as the new form of the problem allows that new materials and models can be easily computed. This paper also presents a wider description of the simulator, specifying the main tasks of the two main programs included in Simucal such as the initial fit performed by the Aligner. Finally, the process carried out to obtain the feet animation database is described. [Copyright &y& Elsevier]

This paper presents a novel investigation of the effectiveness of haptic feedback for designing a class of interconnected multi-body systems such as passive mechanisms. The traditional application of haptic feedback in the design process has been in applications such as parts assembly or mold design. The design of the mechanism discussed in this paper is for applications where the user needs to manipulate the mechanism in order to interact with an environment. The objective of the design is to have the link ratios so that it can allow the user better movement control of the mechanism and thus give a better force amplification when there is a sudden change in the contact reaction force with the application environment. A haptic device is used as a design interface between the designer of such mechanisms and the virtual mechanism model. For this preliminary investigation, we used a four-bar mechanism. In our case study, we choose, as an example, to use the net distance travel of a tool when penetrating inside a model of a deformable surface as the design objective to minimize. The effects on the variation of this distance travelled can then be studied by adjusting some of the key design parameters used in the mechanism. To evaluate our proposed haptic-aided design environment, an informal preliminary user study was conducted, where each subject explored a sampled design space of the mechanism. The results of the user study suggest that the usage of a haptic device in the design of this class of mechanism can expedite the design process. [Copyright &y& Elsevier]

In this paper we propose an approximation method for circular arcs by quartic Bézier curves. Using an alternative error function, we give the closed form of the Hausdorff distance between the circular arc and the quartic Bézier curve. We also show that the approximation order is eight. By subdivision of circular arcs with equi-length, our method yields the curvature continuous spline approximation of the circular arc. We confirm that the approximation proposed in this paper has a smaller error than previous quartic Bézier approximations. [Copyright &y& Elsevier]

Abstract: Clothing simulation and animation are of great importance in computer animation. If cloth simulations could be improved to the point that they could generate realistic cloth motion in real-time, they would find uses in many aspects of daily life such as in fashion design and manufacturing. The area of cloth simulation and animation is full of technical challenges: creating more realistic results, achieving faster run-times, and developing methods capable of constructing and simulating more complex garments. This paper provides an overview of the key procedures involved in the creation of clothed characters, describes the current state-of-the-art techniques, and proposes the research problems that most require further study. Three technical aspects of cloth simulation are considered in this paper: garment construction, physically based simulation, and collision resolution. [Copyright &y& Elsevier]

This paper presents a swept envelope approach to determining tool position for five-axis ruled surface machining. The initial tool position is traditionally located to contact with two directrices of a ruled surface. The swept profile of the tool is then determined based on the tool motion. By comparing the swept profile with the ruled surface, the tool position is corrected to avoid machining errors. The cutter''s swept envelope is further constructed by integrating the intermediate swept profiles, and applied to NC simulation and verification. This paper presents the explicit solution for the swept profile of a taper-end cutter in five-axis ruled surface machining. The relation of the ruled surface geometry, the tool motion and the machining errors is developed. Therefore, the error sources can be detected early and prevented during tool path planning. The explicit swept envelope indicates that the machined surface is not a ruled surface in five-axis ruled surface machining. Manufacturing industries should take extra care in high precision ruled surface machining. Computer illustrations and example demonstrations are shown in this paper. The results reveal that the developed method can accurately position tool location and reduce machining errors for five-axis ruled surface machining. [Copyright &y& Elsevier]

While multi-axis additive manufacturing is found to be a good solution to the inherent limitations of conventional 2.5D additive manufacturing, it is a much more sophisticated process. Among different existing multi-axis process planning algorithms, we are interested in those based on a scalar field, in which print slices are the iso-surfaces of a scalar field embedded in the 3D model. In this paper, we propose a partitioned-based print sequence planning algorithm and an adaptive slicing algorithm, which together determine a complete multi-axis printing process for an arbitrary solid model. The first algorithm iteratively subdivides the model into a set of components such that a collision-free print sequence can be established among the components. The second algorithm then extracts print slices from each component such that all these slices satisfy the self-support condition. Since an arbitrary model may not satisfy both the self-support and collision-free requirements, we also define certain critical printability rules at the beginning to check whether a given input model with its associated scalar field is printable. The generated print slices and print sequence by the proposed two algorithms are guaranteed to be printable. Furthermore, a shorter total fabrication time and a better surface quality are achieved. Physical experiments of four test models are performed on a homebuilt multi-axis FDM printer, whose results verify the capabilities of the proposed algorithms. • A new print sequence planning algorithm based on partitioning for a 3D model associated with a scalar field is proposed. • An adaptive slicing paradigm for scalar field-based multi-axis printing is proposed to reduce the print time. • The developed algorithms guarantee printability, i.e., self-support and collision-free. • Computer simulations and physical experiments are performed on four models to validate the correctness of our algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we present a method for generating smooth 5-axis tool-paths for computer numerical control (CNC) machining, that are assured to be globally accessible. We do so, for a given ball-end cutter and cutter contact curve, and a general arrangement of model and obstacle freeform surfaces. The proposed method is based on a conservative computation of accessibility for (small) finite surface and orientation elements. A conservative estimate ensures the correctness of the solution, and allows us to define a continuous accessible volume in the tool’s configuration space. This global accessibility volume, in turn, allows us to plan an accessible tool-path, and optimize it globally. The conservative approach we use allows accessibility computations to be made for an entire cutter contact curve, eliminating the need to compute accessibility for individual cutter contact points, along with the shortcomings that such a sampling approach would introduce. We present examples using the proposed method, that turns paths specified on the surface (cutter contact curves) into valid 5-axis tool-paths with orientation information. We also present results using a CNC machining simulation software, validating the proposed approach and demonstrating realistic manufacturing processes using the proposed methods. [ABSTRACT FROM AUTHOR]

Flank milling of a surface means to use the linear side of a tool to machine the surface while subject to all the necessary constraints such as collision-free and maximum cusp height. For a general freeform surface, it is always necessary to require multiple passes of a tool path to machine the surface. Because of the much-enlarged material removal rate by flank milling, at least at the semi-finish stage, it is preferred over the conventional machining type of point-milling, especially for those heavy and large industrial parts such as centrifugal impellers and turbine blades. Unfortunately, due to the much-worsened tool-surface collision condition in flank milling, for a complex part surface, it is extremely difficult to determine a correct collision-free multi-pass flank milling tool path while satisfying the maximum cusp height requirement. In this paper, we present an algorithm for this problem. The crux of our method is the establishment of a collision-conscious vector field on an offset surface of the part surface, which encapsulates degrees of both local gouging and global accessibility. This offset mesh is further segmented such that each patch will have only a curl-free vector field. The level-set method is then utilized to fit a scalar field on each patch whose iso-curves naturally form a set of initial tool cutter contact rulings, which are further optimized and propagated to constitute a stripification of the patch comprising a set of quad strips, while respecting the constraints of no-overcut, collision-free, and maximum cusp height. Finally, for each patch, a multi-pass flank milling tool path is generated based on the rulings of the optimized quad strips. Both computer simulation and physical cutting experiments have been carried out, and the experimental results give a positive confirmation on the correctness and effectiveness of the proposed method. • A new multi-pass flank milling method for complicated surface mesh is proposed. • A collision-conscious vector field considers tool path accessibility and smoothness. • The field helps to partition the part and each partition is covered by quad strips. • The tool paths are generated on the strips tending to the machining constraints. • Simulations and experiments have verified the effectiveness of our method. [ABSTRACT FROM AUTHOR]

Generating structured meshes is often an expensive process, limiting the use of high-fidelity numerical simulation methods for design, especially when the design is not yet fixed and design updates are likely. For hexahedral meshes generated by decomposing a B-Rep model into regions for which simple meshing strategies are known, robustly propagating design modifications to the decomposed representation and subsequent mesh is very challenging. In this paper, an approach is presented to propagate parametric update and feature changes to structured meshes. Geometric and topological modifications on the design model are identified first, enabling the equivalent modifications to be identified on the decomposition of the design model. Virtual topology operations used to generate the initial decomposition are combined with the meshing constraints of individual sub-regions to update the decomposition and associated mesh locally. The approach is demonstrated for a number of design updates. [Display omitted] • Design modifications are propagated to structured meshes obtained by decomposition. • Virtual topology is used to decompose and mesh a CAD model. • Design changes are identified from the B-Rep and linked to the decomposed model. • Hexahedral meshing constraints are used to update the partitioning strategy. • Only modified volume cells are automatically re-meshed. [ABSTRACT FROM AUTHOR]

With the innovation in 3D modeling software, more and more 3D models are becoming available in recent decades. To facilitate efficient retrieval and search of large 3D model databases, an effective shape classification algorithm is badly in need. In this paper, we propose a new feature descriptor named Principal Thickness Images (PTI) that encodes the boundary surface and the voxelized constituents of a 3D shape into three gray-scale images. With the support of PTI, we extend the kernel sparse representation-based classification from 2D case to non-rigid 3D models. Our classification algorithm inherits the robustness of kernel sparse representation and is able to achieve a high success rate and strong reliability on non-rigid models from the SHREC’11 non-rigid 3D models dataset. Numerous tests demonstrate superior performance of the proposed method over previous 3D shape classification approaches. [ABSTRACT FROM AUTHOR]

We are witnessing the emergence of a new paradigm in the modeling of material structures . It stems from the digitization of manufacturing and is fueled by advances in additive manufacturing and material science. This paper strives to provide a critical examination of this new paradigm in a historical and technological context and to show that it requires non-trivial extensions and generalizations of the classical theoretical foundation and algorithmic solutions originally developed for solid modeling. Specifically, it requires new models and data-intensive representations for materials, physical behavior, and manufacturing processes across multiple scales. In particular, we argue that most computational tasks that support traditional and emerging manufacturing may be formulated systematically and addressed in terms of relations ( conversions , synthesis , change propagation updates , verification , and other harmonization activities) among four views (manifestations) of an engineered artifact: Functional , which captures the design constraints and tolerances on shape, properties, and behavior; Designed , which represents a toleranced design that satisfies these constraints; Planned , which defines a manufacturing process plan; Simulated , which models the expected outcome of the process plan; and a Real sample set of physical artifacts produced by executing the process plan on a particular manufacturing technology. Based on this formulation, we outline important directions for a research agenda aimed at enabling, driving, and amplifying further advances in digital design and manufacturing. [ABSTRACT FROM AUTHOR]

Individual head-related transfer functions (HRTFs) are essential in applications like fitting hearing-assistive devices (HADs) for providing accurate sound localization performance. Individual HRTFs are usually obtained through intricate acoustic measurements. This paper investigates the use of a three-dimensional (3D) head model for acquisition of individual HRTFs. Two aspects were investigated; whether a 3D-printed model can replace measurements on a human listener and whether numerical simulations can replace acoustic measurements. For this purpose, HRTFs were acoustically measured for four human listeners and for a 3D printed head model of one of these listeners. Further, HRTFs were simulated by applying the finite element method to the 3D head model. The monaural spectral features and spectral distortions were very similar between re-measurements and between human and printed measurements, however larger deviations were observed between measurement and simulation. The binaural cues were in agreement among all HRTFs of the same listener, indicating that the 3D model is able to provide localization cues potentially accessible to HAD users. Hence, the pipeline of geometry acquisition, printing, and acoustic measurements or simulations, seems to be a promising step forward towards in-silico design of HADs. [ABSTRACT FROM AUTHOR]

In gross motion of flexible one-dimensional (1D) objects such as cables, ropes, chains, ribbons and hair, the assumption of constant length is realistic and reasonable. The motion of the object also appears more natural if the motion or disturbance given at one end attenuates along the length of the object. In an earlier work, variational calculus was used to derive natural and length-preserving transformation of planar and spatial curves and implemented for flexible 1D objects discretized with a large number of straight segments. This paper proposes a novel idea to reduce computational effort and enable real-time and realistic simulation of the motion of flexible 1D objects. The key idea is to represent the flexible 1D object as a spline and move the underlying control polygon with much smaller number of segments. To preserve the length of the curve to within a prescribed tolerance as the control polygon is moved, the control polygon is adaptively modified by subdivision and merging. New theoretical results relating the length of the curve and the angle between the adjacent segments of the control polygon are derived for quadratic and cubic splines. Depending on the prescribed tolerance on length error, the theoretical results are used to obtain threshold angles for subdivision and merging. Simulation results for arbitrarily chosen planar and spatial curves whose one end is subjected to generic input motions are provided to illustrate the approach. [ABSTRACT FROM AUTHOR]

The hexahedral mesh (hex mesh) is usually preferred to the tetrahedral mesh (tet mesh) in finite element methods for numerical simulation. In finite element analysis, a valid hex mesh requires that the scaled Jacobian value at each mesh vertex is larger than 0 . However, the hex mesh produced by lots of prevailing hex mesh generation methods cannot be guaranteed to be a valid hex mesh. In this paper, we develop a constrained volume iterative fitting (CVIF) algorithm to fill a given triangular mesh model with an all-hex volume mesh. Starting from an initial all-hex mesh model, which is generated by voxelizing the given triangular mesh model, CVIF algorithm fits the boundary mesh of the initial all-hex mesh to the given triangular mesh model by iteratively adjusting the boundary mesh vertices. In each iteration, the movements of the boundary mesh vertices are diffused to the inner all-hex mesh vertices. After the iteration stops, an all-hex volume mesh that fills the given triangular mesh model can be generated. In the CVIF algorithm, the movement of each all-hex mesh vertex is constrained to ensure that the scaled Jacobian value at each mesh vertex is larger than 0 , etc. Therefore, the all-hex mesh generated by the CVIF algorithm is guaranteed to be a valid all-hex mesh. [ABSTRACT FROM AUTHOR]

Lens system design is an important factor in image quality. The main aspect of the lens system design methodology is the optimization procedure. Since optimization is a complex, non-linear task, soft computing optimization algorithms can be used. There are many tools that can be employed to measure optical performance, but the spot diagram is the most useful. The spot diagram gives an indication of the image of a point object. In this paper, the spot size radius is considered an optimization criterion. Intelligent soft computing scheme Support Vector Regression (SVR) is implemented. In this study, the polynomial and radial basis functions (RBF) are applied as the SVR kernel function to estimate the optimal lens system parameters. The performance of the proposed estimators is confirmed with the simulation results. The SVR results are then compared with other soft computing techniques. According to the results, a greater improvement in estimation accuracy can be achieved through the SVR with polynomial basis function compared to other soft computing methodologies. The SVR coefficient of determination R 2 with the polynomial function was 0.9975 and with the radial basis function the R 2 was 0.964. The new optimization methods benefit from the soft computing capabilities of global optimization and multi-objective optimization rather than choosing a starting point by trial and error and combining multiple criteria into a single criterion in conventional lens design techniques. [ABSTRACT FROM AUTHOR]

For several years, Digital Mock-Up (DMU) has been improved by the integration of many tools as Finite Element (FE) Analysis, Computer Aided Manufacturing (CAM), and Computer Aided Tolerancing (CAT) in the Computer Aided Design (CAD) model. In the geometrical model, the tolerances, which specify the requirements for the proper functioning of mechanical systems, are formally represented. The nominal modeling of the parts and assemblies does not allow the prediction of the tolerance impacts on the simulation results as the optimization of mechanical system assemblability. So, improving the CAD model to be closer to the realistic model is a necessity to verify and validate the mechanical system assemblability. This paper proposes a new approach to integrate the tolerances in CAD model by the determination of the configurations with defects of a CAD part, used in a mechanical system. The realistic parts are computed according to the dimensional and geometrical tolerances. This approach provides an assembly result closer to the real assembly of the mechanical system. The Replacement of the nominal parts by the realistic ones requires the redefinition of the initially defined assembly mating constraints. The update of the mating constraints is performed by respecting an Objective Function of the Assembly (OFA). Integrating tolerances in CAD allows the visualization and simulation of the mechanical assemblies’ behavior in their real configuration and the detection of possible interference and collision effects between parts which are undetectable in the nominal state. [ABSTRACT FROM AUTHOR]

Research in material behavior involves the study of relationships between material composition and capacities to negotiate internal and external pressures. Tuning material composition for performance allows for the integration of multifaceted functionality and embedded responsiveness within minimal material means. The relationships of material composition and system performance can be dissected into properties of topology (in count, type and association), forces (as the simulation of contextual pressures ), and materiality (material properties and constraints of fabrication). When resourcing information about these aspects of material behavior from biological or technological systems, the physical precedents, as specimens and/or models, serve as the primary, and often sole, exemplar. While this is necessary to initiate the study of material make-up as it relates to specific morphological performance, there is an inherent limit when asking how and to what degree the knowledge resourced from that instance applies when alterations from the norm are generated. This research proposes the possibility for testing variants of a morphological system using physical models as the precedent while incorporating multiple means of computational analysis for extensive exploration. The framework begins with the initial stage of deducing principles, regarding material organization and behavior, through comparative physical and computational study. Subsequently, through methods of abduction, new vocabularies of form and potentials in performance are generated primarily through computational exploration. The framework is shaped by research into the design and materialization of complex pre-stressed form- and bending-active architectures. A novel aspect of this framework is the development of a software environment called springFORM . In this environment, material behavior is simulated using basic spring-based (particle system) methods. The novel contribution of this software is in providing means for both manual and algorithmic manipulations of mesh topologies and material properties during the form-finding process. A series of architectural prototypes, which range in scale, define rules for the relationship between topological-material complexity and the sequencing of particular exploratory methods. The studies define the value of the physical precedent as it engenders further material prototypes, spring-based explorations and simulations with finite element analysis. These rules and methods are further elaborated upon through studying the particularly fascinating structural capacity of banana leaf stalks, a material system which is stiff in bending yet highly flexible in torsion. Of interest is a functional robustness which allows for the negotiation of both self-weight and wind loading for a large and fully integrated leaf structure. Methods of simulation and meta-heuristics are developed to address the continual material and topological differentiation of the banana leaf stalk. Case studies are based upon examination of specimens from the species Musa acuminata and Ensete ventricosum. Mechanical properties and geometric descriptions of isolated moments within the stalk provide the basis for computational comparison. Fundamental properties and behaviors are extracted from the plant specimens, yet a full description is not possible because of the plant’s intricate spatial structure. In this case, the computational means serve to elucidate upon the behavior of the complete system as well as provide avenues for exploring its variants. This paper describes an extensible and calibrated framework which can foster enhanced biomimetic insights by explorations which are based upon but extend well beyond initial biological and/or technological precedents. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel parallel 3D Delaunay triangulation algorithm for large-scale simulations on parallel computers. Our method keeps the 3D boundary representation model information during the whole parallel 3D Delaunay triangulation process running on parallel computers so that the solid model information can be accessed dynamically and the meshing results can be very approaching to the model boundary with the increase of meshing scale. The model is coarsely meshed at first and distributed on CPUs with consistent partitioned shared interfaces and partitioned model boundary meshes across processors. The domain partition aims at minimizing the edge-cuts across different processors for minimum communication cost and distributing roughly equal number of mesh vertices for load balance. Then a parallel multi-scale surface mesh refinement phase is iteratively performed to meet the mesh density criteria followed by a parallel surface mesh optimization phase moving vertices to the model boundary so as to fit model geometry feature dynamically. A dynamic load balancing algorithm is performed to change the partition interfaces if necessary. A 3D local non-Delaunay mesh repair algorithm is finally done on the shared interfaces across processors and model boundaries. The experimental results demonstrate our method can achieve high parallel performance and perfect scalability, at the same time preserve model boundary feature and generate high quality 3D Delaunay mesh as well. [ABSTRACT FROM AUTHOR]

In this paper, a generic uniform scallop tool path generation method for five-axis machining is presented. Unlike the conventional methods which are based on the local surface geometry assumptions, this method is inspired by cutting simulation. Initially, the designed surface is planted with dense grasses. If a cutter is put onto the surface, the affected grasses will be cut short. All the affected grasses form a grass ring on the surface. When the cutter moves along the previous tool path, the envelope of the grass rings will form a machining band. Based on the machining band, cutter contact points can be found on the surface to ensure that the cutting edge touches exactly on the side of the band. These cutter contact points are fitted to construct the next tool path. In this way, all the tool paths can be generated recursively. An optimization is also developed to improve the computing efficiency of the path generation process. The proposed uniform scallop tool path generation method is generic. It can be popularized to (1) any kind of end mill with various sizes, (2) any kind of parametric surface and (3) directional- or contour-parallel tool path topologies. Another salient feature of this method is that it is free of local surface geometry assumptions, so the obtained tool paths are more precise. The proposed method is implemented and evaluated with several freeform surface examples. The feasibility of the method is also verified by actual cutting experiment. [ABSTRACT FROM AUTHOR]

Abstract: Since its inception, computer aided 3D modeling has primarily relied on the Windows, Icons, Menus, Pointer (WIMP) interface in which user input is in the form of keystrokes and pointer movements. The brain–computer interface (BCI) is a novel modality that uses the brain signals of a user to enable natural and intuitive interaction with an external device. In this paper we present a human factors study on the use of an Emotiv EEG BCI headset for 3D CAD modeling. The study focuses on substituting the conventional computer mouse- and keyboard-based inputs with inputs from the Emotiv EEG headset. The main steps include (1) training the headset to recognize user-specific EEG/EMG signals and (2) assigning the classified signals to emulate keystrokes which are used to activate/control different commands of a CAD package. To assess the performance of the new system, we compared the time taken by the users to create the 3D CAD models using both the conventional and BCI-based interfaces. In addition, to exhibit the adaptability of the new system, we carried out the study for a set of CAD models of varying complexity. [Copyright &y& Elsevier]

Abstract: In this paper the authors present research into an integrative computational design methodology for the design and robotic implementation of fibre-composite systems. The proposed approach is based on the concurrent and reciprocal integration of biological analysis, material design, structural analysis, and the constraints of robotic filament winding within a coherent computational design process. A particular focus is set on the development of specific tools and solvers for the generation, simulation and optimization of the fibre layout and their feedback into the global morphology of the system. The methodology demonstrates how fibre reinforced composites can be arranged and processed in order to meet the specific requirements of architectural design and building construction. This was further tested through the design and fabrication of a full-scale architectural prototype. [Copyright &y& Elsevier]

Abstract: 3D garments are created by assembling 2D patterns on human models in current mainstream garment modeling methods, which usually calls for professional design skills. The high coupling between the 2D pattern making and 3D garment design blocks the designers’ creations. In this paper, a novel approach that decouples the high coupling between garment design and pattern making is proposed. Our approach is examples based. 3D new garment models are created on individual human models by compositing 3D parts from garment examples rather than 2D patterns. The main benefit of our approach is that it is easy to operate and capable to create elegant individualized garments with highly detailed geometries. Garment prototypes represented in Coons surface automatically generated from individual human models are used to guide the garment parts composition and locally parameterize the garment parts. With the local parameterization, the garment parts and the newly created garment models can be interactively edited by altering the parametric curves on the garment prototypes. Our approach makes it possible for both the designers and the common customers to express their creations and imaginations conveniently in a 3D graphical way. [Copyright &y& Elsevier]

Abstract: Surface subdivision gains popularity in surface design owing to its flexible applications for geometry with complicated topology and simple computational scheme, and the geometric partial differential equation (GPDE) method is an advanced technology for constructing high-quality smooth surfaces. In this paper, we composite these two ingredients to form a unified method for freeform surface design. We choose the mean curvature flow and Willmore flow as our driven GPDEs, and the finite element method coupled with a hybrid Loop and Catmull–Clark subdivision algorithm as the numerical simulation method. This research presents a novel technique to evaluate the finite element basis functions and the first attempt for constructing the GPDE subdivision surface with hybrid control meshes consisting of triangles and quadrilaterals. Numerical experiments show that the construction method is efficient and robust, yielding high-quality hybrid subdivision surfaces. [Copyright &y& Elsevier]

Continuous multi-axis printing has drawn more and more attention owing to its unique advantages of eliminating the need of support (at least in theory) when printing complex models with overhang features and significantly reducing the stair-step effect of the conventional three-axis printing. For continuous multi-axis printing, the printing layers are typically not planar but curved, so to capitalize the extra DOFs provided by the rotary axes of the printer. When a printing layer is concave (i.e., its curvature vector points inward at the printing point), the potential nozzle-layer local gouging becomes a serious concern, which is especially problematic for metal printing wherein the size of the nozzle head is usually large. Unfortunately, this convexity issue has received little attention in the existing curved slicing algorithms, making them prone to the local gouging quandary. In this paper, we propose a novel curved layer decomposition algorithm based on the use of (only the positive sides of) ellipsoidal surfaces. To facilitate the generation of ellipsoidal printing layers for an arbitrary freeform solid model with a complex topology (e.g., having a non-zero genus number), the powerful algebraic technique of skeletonization is employed by our algorithm to first decompose the model into a suitable set of sub-entities, for each of which a series of ellipsoidal printing layers are then generated, wherein the parameters of ellipsoidal layers are adaptively adjusted to satisfy the necessary constraints such as support-free and other requirements. Preliminary experiments in both computer simulation and physical printing of the proposed algorithm are conducted, and the results give a positive validation on the effectiveness and feasibility of the proposed methodology. • A new curved-layer decomposition method based on ellipsoidal surface is developed. • The algebraic technique of skeletonization is employed to do the model segmentation. • An ellipsoid fitting scheme is proposed to allow continuous layer propagation. • The use of ellipsoids can reduce support structure and avoid local gouging problem. [ABSTRACT FROM AUTHOR]

Abstract: Common Design Structure Discovery (CDSD) is to identify local structures shared by multiple models. Nowadays it is mainly restricted to part models. Extending it to assembly models can produce a significant value for assembly design reuse. However, current descriptions of assembly models usually capture topological information qualitatively, considering little geometric information, and thus are not suitable for CDSD in assembly models (CDSDA). To counter this problem, this paper proposes a generic face adjacency graph (GFAG) which is extended from the face adjacency graph for B-Rep part model description. GFAG can transform abstract relationships in assembly models into measurable entities by introducing a concept of mating face pair (MFP), thus facilitating a more quantitative and consistent description of parts and relationships in assembly models. Corresponding to geometric faces and edges in a part model, GFAG treats parts and relationships in an assembly model as generic faces and generic edges respectively. To make GFAG have a higher discrimination capability, a node in GFAG captures the geometric information of a part together with its mating parts by shape parameters and also quantitatively incorporates a relationship between parts by shape parameters of an MFP. By doing so, GFAG can take more geometric information, together with topological information, into account quantitatively, and thus can be mapped into a 2D coordinate system for easy validation. We also extend a discovery algorithm to validate the feasibility of GFAG for CDSDA, and the results demonstrate the expected effectiveness. [Copyright &y& Elsevier]

Abstract: In order to inspect deformable parts, recent works use virtual deformation on a digitized version of a real-part to bring the part model back to its nominal shape. This simulation mimics the real process called fixturing, which is normally used by the manufacturer to bring back the part into its nominal shape once installed. To perform such virtual deformation Finite Element Methods (FEMs) are used in order to meet the precision requirements of the inspection process. This paper presents a method based on a spring–mass system, whose formulation is much simpler than the FEM, which allows the calculation of deformations of shell type parts with accuracy comparable to FEM. Furthermore, due to the simplicity in its formulation the algorithm can be implemented more easily than the FEM. The system is composed of two types of springs: one type models membrane behavior of the part’s mesh model and the second type models the flexion behavior between each mesh elements. We show that by applying the proposed mass-spring model, it is possible to reduce the calculation time by 80% over standard FEM calculation opening the door to real-time inspection. [Copyright &y& Elsevier]

Abstract: Detecting global exact symmetries in CAD models is of great importance in the research of CAD/CAE integration. Therefore, a method is proposed in this paper to rapidly detect the global exact rotational and reflectional symmetries in feature-based CAD models. The theories of determining the symmetries of the Boolean combinations of the features are framed. Based on these theories, our approach is processed as follows. First, the features of the CAD models are classified into congruent feature sets. Next, through the study on the relationship between feature information and the symmetries of features, by using only feature information, as many symmetries of the feature sets as possible are detected. Then these feature sets are sorted into an ordered sequence. Finally, symmetries of the entire model can be derived by successively merging and verifying the symmetries of feature sets in the ordered sequence. Experimental results show that the global exact symmetries can be robustly and rapidly detected. [Copyright &y& Elsevier]

Abstract: Currently in industry, design and communication of a product assembly is through the use of computer-aided design (CAD) systems. However, there are no commercial systems that can automatically generate feasible assembly sequence plans. There is past and current academic research in methods to provide automatic assembly sequence planning. Assembly sequence planning using a commercial system often relies on an expert assembly sequence planner, and it is predominantly done manually. This requires a great amount of time and expert knowledge; assembly sequence plans generated may not even be the most efficient. The ability to automatically generate assembly sequence plans will lead to the reduction of planning time, less reliance on the amount of knowledge required, and better plans at earlier stages of the design process. CAD models are based on feature constraints to create and define an assembly. The challenges to automatically generate assembly sequences using CAD models lie in intelligent reasoning and analysis of the modelled assembly data. Based on past research findings, there is a reason to believe that assembly constraints used in CAD assembly models can provide essential information related to the assembly process. This paper presents a system that can analyse and utilize assembly data available from a CAD model to generate assembly sequences. The system also considers a user input as a type of assembly constraint. The system is capable of producing a set of ranked feasible assembly sequence plans for an operator to evaluate. A matrix approach has been adopted to process the information retained from a CAD model. Interference and stability studies are carried out during the creation of assembly sequence plans. The outputs are ranked based on the ease of assembly and the stability of the generated assembly sequence plans. Case studies are used to evaluate the system and the feasibility of the output. A case study using a two stroke engine is presented, which demonstrates how the system generates assembly sequence plans. [Copyright &y& Elsevier]

Abstract: This paper presents a novel virtual maintenance application for maintenance safety evaluation (MSE) to provide recommendations on maintenance safety during the early stages of product design. The proposed methodology detects the potential defects via virtual maintenance technology, and safety evaluation could be carried out in a predictive way intuitively and systemically to decrease the possibility of accidents. After reviewing relevant publications, a MSE model with thorough consideration of the characters in the virtual maintenance environment was addressed. The model consists of evaluation contributors, evaluation criteria, and evaluation methodology. A case study on APU system maintenance was used to illustrate the performance of the evaluation model. The result showed the feasibility of virtual maintenance in improving maintenance safety designs. [Copyright &y& Elsevier]

Abstract: All-hexahedral meshing and remeshing algorithms giving support to finite element modeling of manufacturing processes require continuous development for improving its overall robustness and applicability. This paper draws from a previous all-hexahedral algorithm presented by the authors and proposes new developments related to the construction of adaptive core meshes and processing of multi-objects that are typical of manufacturing applications. Along with the aforementioned improvements there are other developments that will also be presented due to their effectiveness in increasing the robustness of all-hexahedral algorithms. These include identification and simplification of boundary features, reconstruction of vertices and edges with minimum element distortion, smoothing of nodal points along edges and topology based mesh repair procedures to ensure completeness of edge representation. The presentation is enriched with examples taken from pure geometry and metal forming applications, and a resistance projection welding industrial test case consisting of four different objects is included to show the capabilities of selective remeshing of objects while maintaining contact conditions and local geometrical details that are critical for electro-thermo-mechanical numerical simulations. [Copyright &y& Elsevier]

Abstract: Along with the recent growth of industrial X-ray computerized tomography (CT) scanning systems, it is now possible to non-destructively acquire the entire meshes of assemblies. This technology has the potential to realize an advanced inspection process of an assembly, such as estimation of their assembly errors or examinations of their dynamic behaviors in motion using a model reflecting real assembled situations. However, to realize the process, it is necessary to accurately decompose the mesh and to extract a set of partial meshes, each of which corresponds to a single part, from the entire meshes of assemblies measured from the CT scans. Moreover, it is required to create models that are ready for dynamic behavior simulations. In this paper, we focus on CT scanned meshes of gear assemblies as examples, and propose beneficial methods for establishing such advanced inspections. We first propose a method that accurately decomposes the mesh into partial meshes, each of which corresponds to a single gear, using periodicity recognitions. The key idea is first to accurately recognize the periodicity of each gear, then to extract sets of topologically connected mesh elements where periodicities are valid, and finally to interpolate points in plausible ways from an engineering viewpoint to the area where surface meshes are not generated, especially the contact area between parts in the CT scanning process. We also propose a method for creating kinematic simulation models which can be used for a gear teeth contact evaluation using extracted partial meshes and their periodicities. Such an evaluation of teeth contacts is one of the most important functions in kinematic simulations of gear assemblies for predicting the power transmission efficiency, noise and vibration. The characteristics of the proposed method is that (1) it can robustly and accurately recognize periodicities from noisy scanned meshes, (2) it can estimate the plausible boundaries of neighboring parts without any previous knowledge from single-material CT scanned meshes, and (3) it can efficiently extract partial meshes from large scanned meshes containing millions of triangles in a few minutes. We demonstrate the effectiveness of our method on a variety of artificial and real CT scanned meshes. [Copyright &y& Elsevier]

Abstract: In the isogeometric analysis framework, a computational domain is exactly described using the same representation as the one employed in the CAD process. For a CAD object, various computational domains can be constructed with the same shape but with different parameterizations; however one basic requirement is that the resulting parameterization should have no self-intersections. Moreover we will show, with an example of a 3D thermal conduction problem, that different parameterizations of a computational domain have different impacts on the simulation results and efficiency in isogeometric analysis. In this paper, a linear and easy-to-check sufficient condition for the injectivity of a trivariate B-spline parameterization is proposed. For problems with exact solutions, we will describe a shape optimization method to obtain an optimal parameterization of a computational domain. The proposed injective condition is used to check the injectivity of the initial trivariate B-spline parameterization constructed by discrete Coons volume method, which is a generalization of the discrete Coons patch method. Several examples and comparisons are presented to show the effectiveness of the proposed method. During the refinement step, the optimal parameterization can achieve the same accuracy as the initial parameterization but with less degrees of freedom. [Copyright &y& Elsevier]

Abstract: The contact surface description is a very important field in the numerical simulation of problems involving frictional contact, which are among the most difficult ones in continuum mechanics, as is the case of sheet metal forming simulation. In this paper, a methodology to control the Nagata patch interpolation of piecewise linear meshes is proposed, in order to improve its applicability for tool surface description used in the numerical simulation of sheet metal forming processes. The interpolation can be applied either to triangular and quadrilateral Nagata patches, as well as structured and unstructured patches. The normal vectors needed for the Nagata interpolation are obtained through two distinct strategies. The first uses the information available in the CAD surface model, while the second resorts only to the piecewise linear mesh model information. In order to evaluate the interpolation accuracy, the Nagata patch is applied to describe a sheet metal forming complex shape part tool geometry. The results obtained show that, regardless of the strategy used to evaluate the surface normal vectors, the use of the proposed Nagata patch interpolation enables a large improvement in the geometric accuracy when compared with the models composed by piecewise linear elements. The use of CAD surface geometry to evaluate the surface normal vectors leads to the best Nagata patch interpolation in terms of shape and normal vector field accuracy. [Copyright &y& Elsevier]

Abstract: The interpretation of auxiliary entities as boundary entities in previous non-manifold boundary (NMB) representations may change a model’s intended topology and increase the complexity of the corresponding data structure. In this paper, entities appearing in a modeling process are classified into boundary and non-boundary entities. Non-boundary entities are usually embedded into embedding-space entities. These embedding relationships are described by inclusion topology. To support inclusion topology, a new mathematical framework—quasi-cell-complex, as well as a topological data structure—-Complex, are proposed. Quasi-cell-complex is an extension of cell-complex with inclusion topology supported. -Complex is an NMB representation, in which a new topological entity—embedder is created for inclusion topology and zone/disk is adopted to capture the complete adjacencies around a vertex. Thus, -Complex allows full adjacencies, incidence-ordering, and inclusion relationships to be derived, and the efficiency of most basic queries is several times faster than most state-of-the-art NMB representations, without increasing storage. Additionally, the benefits of inclusion topology for shape modeling and feature modeling are explored. [Copyright &y& Elsevier]

Abstract: A configuration space (-space) method was developed in a previous study to support the automation of the layout design of cooling systems. The main function of the -space is to capture all of the feasible geometry of the layout design so that a genetic algorithm (GA) can be used to explore the design space. This paper reports a further extension of the -space method in two respects. The new method overcomes the previous limitation of the non-variability of the design topology. By capturing useful information generated during the computation of the -space, the new method enables the GA to explore both the geometry and the topology of the design during the evolutionary process. A new technique is also developed that enables the method to handle user-defined constraints on the layout design. These constraints are captured by additional -spaces, and a special procedure is developed for computing the -spaces of cooling systems and generating candidate designs so that the resulting design always satisfies the constraints. Vigorous proof of the validity of the new method is provided, and a case study is presented to demonstrate the capability of the method in generating a practical layout design for a cooling system. [Copyright &y& Elsevier]

Abstract: In the present paper, the tooth contact characteristics and the error sensitivity of the ease-off dual-torus double-enveloping hourglass worm drive (the DTT worm drive) are considered. The ease-off hourglass worm drive is composed of a standard hourglass worm and a modified worm wheel. In order to determine the instantaneous contact point of the mismatched worm pair, the two-stage downhill secant method (the TSDS method) is proposed to be used for solving the nonlinear contact equations. Roughly speaking, the main merits of the TSDS method are lower sensitivity to the initial guess, without a request for computing the Jacobi matrix and no singularity near the genuine solution. After ascertaining the transient contact point, the momentary contact ellipse, the instantaneous transmission ratio and some other tooth contact features are worked out by means of an improved local synthesis approach, which is proposed for point contact gear drives in this article. The results of computerized simulation show that, the mismatched worm gear set is able to accomplish desirable point contact, and has respectable load carrying capacity. On the other hand, the mismatched worm gearing is insensitive to the alignment errors, and its property of the transmission error is advantageous to reduce the noise and vibration. [Copyright &y& Elsevier]

Abstract: The designers and manufactures in apparel industry have urgent needs in designing clothing with superior thermal functions with user-friendly and cost-effective design tools. This paper presents a multi-disciplinary strategy for computer-aided clothing thermal engineering design. It provides a systematical approach to integrate multi-disciplinary knowledge and transfer it into engineering-oriented design tools, thus the designers and manufacturers can easily carry out 1D, 2D and even 3D clothing thermal engineering designs according to the practical design requirements with a short design cycle and low design cost. The research work of this strategy begins from the investigation of the role of the thermal functions of clothing in the thermal comfort of human body. Then the framework is proposed to integrate the multi-disciplinary knowledge and illustrate the process to achieve the thermal engineering design of clothing. The important issues in the realization of computational simulation are addressed, including multi-scale model integration, data availability of characteristic parameters and hierarchical computational scheme. To issue easy-to-use design tools, the thermal functional design of clothing is quantified with important influence parameters, and the user-friendly wizard is designed for the CAD system development. Finally, the design applications of this strategy are discussed in terms of 1D, 2D and 3D thermal engineering designs with versatile CAD systems. [Copyright &y& Elsevier]

Abstract: Comfort test of footwear is mainly based on subjective perception of the wearer and a large number of subjects are required to obtain a reliable result. Therefore, the subjective comfort test is expensive and time consuming. Although the foot size and shape of a subject can be obtained by using a three-dimensional (3D) foot scanner, it is still difficult to create foot motion animations of each subject suitable for computer simulation. In this paper, we propose a fast approach to model foot deformation and present its application in simulating interaction with footwear towards footwear design. The simulation determines deformation of foot and footwear models. It can also determine stress distribution in the footwear. Given an initial foot model and a captured foot motion, human foot animation is created first. Then, the footwear model is fitted to the foot to compute the deformation and stress in the footwear. In this article, the boundary element method (BEM) is adopted. We demonstrate the results by conducting simulation of a captured gait motion. Experimental results showed that the method can be used to simulate human gait motion, and can determine deformation of footwear. [Copyright &y& Elsevier]

Abstract: This paper provides a general framework for the quantitative estimation of the effects of removing negative features on engineering analysis, or modification sensitivity for short. There are two main applications: (i) when defeaturing models so that finite element analysis may be carried out more quickly and with lower memory requirements, and (ii) when performing iterative design based on finite element analysis. Our approach can handle large as well as small features, and features with Neumann/natural boundary conditions prescribed on them; previous methods have difficulties in handling such cases. Estimation of the modification sensitivity is achieved by reformulating it as a modeling error caused by use of different mathematical models to describe the same engineering analysis problem. Results are obtained using the dual weighted residual (DWR) method in combination with a heuristic assumption of small variation of the dual solution after defeaturing. The final derived sensitivity estimator is expressed in terms of the difference of local boundary integrations over the feature boundary, which can be explicitly evaluated using solutions defined on the defeatured model. The algorithm’s performance is demonstrated using a Poisson equation. Comparisons to results obtained by previous approaches indicate that it is both accurate and computationally efficient. [Copyright &y& Elsevier]

Abstract: This paper presents a comprehensive and efficient framework for computer-aided appearance design based on BRDF (bidirectional reflectance distribution function) measurements. It covers all stages of a new product development including acquisition, processing and modeling of reflectance data, interactive rendering and evaluation of material appearance, and manufacturing operations. The proposed method eliminates the need of making a real physical prototype by providing a reliable surface appearance design process in which he/she can faithfully simulate the final surface appearance in the early design stage of a product. In addition, it enables us to manufacture the coating surface the same as the computer simulated surface from the known coating specification. The accuracy test between a real sample and the computer simulated one demonstrates that the proposed method satisfies an acceptable level of accuracy for industrial applications. A case study has been conducted to evaluate the user preference on the surface appearance of a digital handheld device which contains a combination of different coating surfaces. The case study successfully demonstrates that the user preference can be identified using the proposed method while changing the combination of different coating surfaces represented by BRDFs considering factors such as surrounding environments and age groups. [Copyright &y& Elsevier]

Abstract: This paper proposes a new method of pocketing toolpath computation based on an optimization problem with constraints. Generally, the calculated toolpath has to minimize the machining time and respect a maximal effort on the tool during machining. Using this point of view, the toolpath can be considered as the result of an optimization in which the objective is to minimize the travel time and the constraints are to check the forces applied to the tool. Thus a method based on this account and using an optimization algorithm is proposed to compute toolpaths for pocket milling. After a review of pocketing toolpath computation methods, the framework of the optimization problem is defined. A modeling of the problem is then proposed and a solving method is presented. Finally, applications and experiments on machine tools are studied to illustrate the advantages of this method. [Copyright &y& Elsevier]

Abstract: Although solid modelling based on partial differential equations (PDEs) has many advantages, such existing methods can either only deal with simple cases or incur expensive computational overheads. To overcome these shortcomings, in this paper we present an efficient PDE based approach to creating and manipulating solid models. With trivariate partial differential equations, the idea is to formulate an accurate closed form solution to the PDEs subject to various complex boundary constraints. The analytical nature of this solution ensures both high computational efficiency and modelling flexibility. In addition, we will also discuss how different geometric shapes can be produced by making use of controls incorporated in the PDEs and the boundary constraint equations, including the surface functions, tangents and curvature in the boundary constraints, the shape control parameters and the sculpting forces. Two examples are included to demonstrate the applications of the proposed approach and solutions. [Copyright &y& Elsevier]