Photogrammetry, CAD Modeling and FE Analysis for Improving the Performance of a Spinnaker

Objectives： The sails fabrication knew a significant development under the impulse of sailing races like the America＇s Cup and the Volvo around the World Race. These competitions require advanced technologies to increase performance of the sails. In the paper, Reverse Engineering （RE） acquisition, CAD （Computer Aided Design） reconstruction and FE （Finite Element） analysis are used in the design phase for a spinnaker in order to maximize the performance of the sail boat. Materials and Methods： The comparison, between the design data and the characteristics in the real conditions of use of the sail （constant wind pressure acting on the sail）, was carried out by the reconstruction of the three-dimensional CAD model of the spinnaker shape in full-scale, using a non contact Reverse Engineering technique, the photogrammetry and by a FE non linear static analysis. Results： The results of this study show a good correspondence between the design data and the characteristics in the real conditions of use of the sail. Significance： The described methodology is useful for sail makers. It can be successfully adopted to generate three-dimensional CAD-FE models of a sail starting from a very cheap and fast Reverse Engineering non-contact procedure.

Multi-Volume CAD Modeling for Heterogeneous ObjectDesign and Fabrication

The current computer-aided technologies in design and product development, the evolution of CAD modeling, and a framework of multi-volume CADmodeling system for heterogeneous object design and fabrication are presented inthis paper. The multi-volume CAD modeling system is presented based on nonmanifold topological elements. Material identifications are defined as design attributes introduced along with geometric and topological information at the designstage. Extended Euler operation and reasoning Boolean operations for merging andextraction are executed according to the associated material identifications in thedeveloped multi-volume modeling system for heterogeneous object. An applicationexample and a pseudo-processing algorithm for prototyping of heterogeneous structure through solid free-form fabrication are also described.

A Novel Attribute-Based Encryption Approach with Integrity Verification for CAD Assembly Models

Cloud manufacturing is one of the three key technologies that enable intelligent manufacturing.This paper presents a novel attribute-based encryption(ABE)approach for computer-aided design(CAD)assembly models to effectively support hierarchical access control,integrity verification,and deformation protection for co-design scenarios in cloud manufacturing.An assembly hierarchy access tree(AHAT)is designed as the hierarchical access structure.Attribute-related ciphertext elements,which are contained in an assembly ciphertext(ACT)file,are adapted for content keys decryption instead of CAD component files.We modify the original Merkle tree(MT)and reconstruct an assembly MT.The proposed ABE framework has the ability to combine the deformation protection method with a content privacy of CAD models.The proposed encryption scheme is demonstrated to be secure under the standard assumption.Experimental simulation on typical CAD assembly models demonstrates that the proposed approach is feasible in applications.

Annotation and Retrieval System of CAD Models Based on Functional Semantics

CAD model retrieval based on functional semantics is more significant than content-based 3D model retrieval during the mechanical conceptual design phase. However, relevant research is still not fully discussed. Therefore, a functional semantic-based CAD model annotation and retrieval method is proposed to support mechanical conceptual design and design reuse, inspire designer creativity through existing CAD models, shorten design cycle, and reduce costs. Firstly, the CAD model functional semantic ontology is constructed to formally represent the functional semantics of CAD models and describe the mechanical conceptual design space comprehensively and consistently. Secondly, an approach to represent CAD models as attributed adjacency graphs（AAG） is proposed. In this method, the geometry and topology data are extracted from STEP models. On the basis of AAG, the functional semantics of CAD models are annotated semi-automatically by matching CAD models that contain the partial features of which functional semantics have been annotated manually, thereby constructing CAD Model Repository that supports model retrieval based on functional semantics. Thirdly, a CAD model retrieval algorithm that supports multi-function extended retrieval is proposed to explore more potential creative design knowledge in the semantic level. Finally, a prototype system, called Functional Semantic-based CAD Model Annotation and Retrieval System（FSMARS）, is implemented. A case demonstrates that FSMARS can successfully botain multiple potential CAD models that conform to the desired function. The proposed research addresses actual needs and presents a new way to acquire CAD models in the mechanical conceptual design phase.

Slicing 3D CAD Model Directly with ObjectARX

An algorithm for compensating the varying section contour within the extent of each layer thickness is proposed to improve the rapid prototyping part’s shape and size precision.

DESIGN AND CAD SYSTEM OF THE TOOL FOR DRILL FLUTE

Based on the principles of differential geometry and kinematics, a mathematical model is developed to describe the grinding wheel axial cross-section with the radial cross-section of the flute in a given drill under the basic engagement condition between the generating flute and the generated grinding wheel （or disk milling tool）. The mathematical model is good for the flute in the radial cross-section consisting of three arcs. Furthermore, a CAD system is also developed to represent the axial cross-section of the grinding wheel （or disk milling tool）. With the system, the grinding wheel （or disk milling tool） axial cross-section that corresponds to the three-arc flute cross section can be conveniently simulated. Through the grinding experiment of drill flutes, the method and the CAD system are proved to be feasible and reasonable.

Solid model edit distance: a multi-application and multi-level schema for CAD model retrieval

We present the solid model edit distance(SMED),a powerful and flexible paradigm for exploiting shape similarities amongst CAD models.It is designed to measure the magnitude of distortions between two CAD models in boundary representation(B-rep).We give the formal definition by analogy with graph edit distance,one of the most popular graph matching methods.To avoid the expensive computational cost potentially caused by exact computation,an approximate procedure based on the alignment of local structure sets is provided in addition.In order to verify the flexibility,we make intensive investigations on three typical applications in manufacturing industry,and describe how our method can be adapted to meet the various requirements.Furthermore,a multilevel method is proposed to make further improvements of the presented algorithm on both effectiveness and efficiency,in which the models are hierarchically segmented into the configurations of features.Experiment results show that SMED serves as a reasonable measurement of shape similarity for CAD models,and the proposed approach provides remarkable performance on a real-world CAD model database.

A review of edge-based 3D tracking of rigid objects

Three-dimensional(3D)tracking of rigid objects plays a very important role in many areas such as augmented reality,computer vision,and robotics.Numerous works have been done to pursue more stable,faster,and more accurate 3D tracking.Among various tracking methods,edge-based 3D tracking has been widely used owing to its many advantages.Furthermore,edge-based methods can be mainly divided into two categories,methods without and those with explicit edges,depending on whether explicit edges need to be extracted.Based on this,representative methods in both categories are introduced,analyzed,and compared in this paper.Finally,some suggestions on the choice of methods in different application scenarios and research directions in the future are given.

A deep learning approach to the classification of 3D CAD models

Model classification is essential to the management and reuse of 3D CAD models.Manual model classification is laborious and error prone.At the same time,the automatic classification methods are scarce due to the intrinsic complexity of 3D CAD models.In this paper,we propose an automatic 3D CAD model classification approach based on deep neural networks.According to prior knowledge of the CAD domain,features are selected and extracted from 3D CAD models first,and then preprocessed as high dimensional input vectors for category recognition.By analogy with the thinking process of engineers,a deep neural network classifier for 3D CAD models is constructed with the aid of deep learning techniques.To obtain an optimal solution,multiple strategies are appropriately chosen and applied in the training phase,which makes our classifier achieve better performance.We demonstrate the efficiency and effectiveness of our approach through experiments on 3D CAD model datasets.

Design and Implementation of 3D Model Database for General-Purpose 3D GIS

To improve the reusability of three-dimensional （3D） models and simplify the complexity of natural scene reconstruction, this paper presents a 3D model database for universal 3D GIS. After the introduction of its extensible function architecture, accompanied by the conclusion of implicit spatial-temporal hierarchy of models in any reconstructed scene of 3D GIS for general purpose, several key issues are discussed in detail, such as the storage and management of 3D models and related retrieval and load method, as well as the interfaces for further on-demand development. Finally, the validity and feasibility of this model database are proved through its application in the development of 3D visualization system of railway operation.

STEP-based Feature Recognition System for B-spline Surface Features

The geometrical and topological information of 3D computer aided design （CAD） models should be represented as a neut- ral format file to exchange the data between different CAD systems. Exchange of 3D CAD model data implies that the companies must exchange complete information about their products, all the way from design, manufacturing to inspection and shipping. This informa- tion should be available to each relevant partner over the entire life cycle of the product. This led to the development of an international standard organization （ISO） neutral format file named as standard for the exchange of product model data （STEP）. It has been ob- served from the literature, the feature recognition systems developed were identified as planar, cylindrical, conical and to some extent spherical and toroidal surfaces. The advanced surface features such as B-spline and its subtypes are not identified. Therefore, in this work, a STEP-based feature recognition system is developed to recognize t--spline surface features and its sub-types from the 3D CAD model represented in AP203 neutral file format. The developed feature recognition system is implemented in Java programming language and the product model data represented in STEP AP203 format is interpreted through Java standard data access interface （JSDAI）. The developed system could recognize B-spline surface features such as B-Spline surface with knots, quasi uniform surface, uniform surface, rational surface and Bezier surface. The application of extracted B-spline surface features information is discussed with reference to the toolpath generation for STEP-NC （STEP AP238）.