Direct simulation for CAD models undergoing parametric modifications

We propose a novel approach—direct simulation—for interactive simulation with accuracy control, for CAD models undergoing parametric modifications which leave Dirichlet boundary conditions unchanged. This is achieved by computing offline a generic solution as a function of the design modification parameters. Using this parametric expression, each time the model parameters are edited, the associated simulation solution for this model instance can be cheaply and quickly computed online by evaluating the derived parametric solution for these parameter values. The proposed approach furthermore works for models undergoing topological changes, and does not need any mesh regeneration or mesh mapping. These results are achieved by use of the proper generalized decomposition model reduction technique, in combination with R-functions. We believe this is the first approach that can interactively simulate the physical properties of a CAD model, even undergoing topological change, without expensive re-computation. The approach is demonstrated for linear elasticity analysis; numerical results demonstrate its simulation accuracy and efficiency in comparison with the classic FE method

VIRTUE : integrating CFD ship design

Novel ship concepts, increasing size and speed, and strong competition in the global maritime market require that a ship's hydrodynamic performance be studied at the highest level of sophistication. All hydrodynamic aspects need to be considered so as to optimize trade-offs between resistance, propulsion (and cavitation), seakeeping or manoeuvring. VIRTUE takes a holistic approach to hydrodynamic design and focuses on integrating advanced CFD tools in a software platform that can control and launch multi-objective hydrodynamic design projects. In this paper current practice, future requirements and a potential software integration platform are presented. The necessity of parametric modelling as a means of effectively generating and efficiently varying geometry, and the added-value of advanced visualization, is discussed. An illustrating example is given as a test case, a container carrier investigation, and the requirements and a proposed architecture for the platform are outlined

XVoxel-Based Parametric Design Optimization of Feature Models

Parametric optimization is an important product design technique, especially in the context of the modern parametric feature-based CAD paradigm. Realizing its full potential, however, requires a closed loop between CAD and CAE (i.e., CAD/CAE integration) with automatic design modifications and simulation updates. Conventionally the approach of model conversion is often employed to form the loop, but this way of working is hard to automate and requires manual inputs. As a result, the overall optimization process is too laborious to be acceptable. To address this issue, a new method for parametric optimization is introduced in this paper, based on a unified model representation scheme called eXtended Voxels (XVoxels). This scheme hybridizes feature models and voxel models into a new concept of semantic voxels, where the voxel part is responsible for FEM solving, and the semantic part is responsible for high-level information to capture both design and simulation intents. As such, it can establish a direct mapping between design models and analysis models, which in turn enables automatic updates on simulation results for design modifications, and vice versa -- effectively a closed loop between CAD and CAE. In addition, robust and efficient geometric algorithms for manipulating XVoxel models and efficient numerical methods (based on the recent finite cell method) for simulating XVoxel models are provided. The presented method has been validated by a series of case studies of increasing complexity to demonstrate its effectiveness. In particular, a computational efficiency improvement of up to 55.8 times the existing FCM method has been seen.Comment: 22 page

Geometry Modeling for Unstructured Mesh Adaptation

The quantification and control of discretization error is critical to obtaining reliable simulation results. Adaptive mesh techniques have the potential to automate discretization error control, but have made limited impact on production analysis workflow. Recent progress has matured a number of independent implementations of flow solvers, error estimation methods, and anisotropic mesh adaptation mechanics. However, the poor integration of initial mesh generation and adaptive mesh mechanics to typical sources of geometry has hindered adoption of adaptive mesh techniques, where these geometries are often created in Mechanical Computer- Aided Design (MCAD) systems. The difficulty of this coupling is compounded by two factors: the inherent complexity of the model (e.g., large range of scales, bodies in proximity, details not required for analysis) and unintended geometry construction artifacts (e.g., translation, uneven parameterization, degeneracy, self-intersection, sliver faces, gaps, large tolerances be- tween topological elements, local high curvature to enforce continuity). Manual preparation of geometry is commonly employed to enable fixed-grid and adaptive-grid workflows by reducing the severity and negative impacts of these construction artifacts, but manual process interaction inhibits workflow automation. Techniques to permit the use of complex geometry models and reduce the impact of geometry construction artifacts on unstructured grid workflows are models from the AIAA Sonic Boom and High Lift Prediction are shown to demonstrate the utility of the current approach

Using Parametric CAD and FDM to Produce High Fidelity Anatomical Structures for Thoracentesis Training

Currently available thoracentesis medical training simulators lack tactile realism and do not represent the physiological variations in patient characteristics, impeding optimal experiential learning. By systematically implementing advanced computer-aided design (CAD) techniques and additive manufacturing (AM) tools, with a flexible design methodology, thoracic wall representations for a 2-year-old male, an 18-year-old female, and a 30-year-old male, with complete skeletal structures necessary for palpation sequencing were modelled. Models for the 2-year-old male and 18-year-old female were fabricated, complete with realistic tissues that accurately represent the various discrete tissue layers of the human thoracic cross section. Clavicular growth rates were used to develop factors with which to scale the skeletal models to represent a range of patient demographics. Parametrically modelled mould sets enable the modification of tissue thickness to account for varying thoracic wall thicknesses observed in the thoracentesis demographic. Through the implementation of scaling factors based on skeletal growth rates from the literature to represent different patient groups, clavicle sizing accuracy ranging from 0.4%-1.3% was achieved, and intercostal space measurement accuracy of 0.7%-2.8% was achieved as compared to target values from the literature. Improvements to simulated tissue were observed, with a 28.54% improvement in terms of peak force, 20.17% for impulse, and 36.31% for pulse width, when compared to the THM-30, a currently available popular model

Parametric modeling for simulation based hypersonic vehicle design

The conceptual design stage offers the most opportunity for innovation and the capability to reveal costly design errors early. Integrating high fidelity design and simulation tools into the conceptual design stage enables engineers to develop design variations quickly and affordably. This work focuses primarily on the development and utilization of parametric modeling methods as they apply to a simulation based design process. It will also address the impacts to conceptual design development time. A blended wing-body (BWB) hypersonic wave rider demonstrates how state-of-the-art solid modeling techniques can be coupled to high fidelity CFD analysis codes to perform top down design. Performance trends are identified for several trade study variations which represent a single iteration through the simulation based design process. Performance metrics are based on interpretations from higher level customer, regulatory, business, and other requirements. The process of cascading these requirements down to the component level is the definition of top-down-design. This bidirectional tracing of requirements allows vehicle development to progress in a manner such that any change of the vehicle can be assessed in terms of the overarching requirements

FABRICATION AND OPTIMAL-DESIGN OF BIODEGRADABLE STENTS FOR THE TREATMENT OF ANEURYSMS

An aneurysm is a balloon-like bulge in the wall of blood vessels, occurring in major arteries from the heart and brain. Biodegradable stent-assisted coiling is expected to be the ideal treatment of wide-neck complex aneurysms. A number of biodegradable stents are promising, but also with issues and/or several limitations to be addressed. From the design point of view, biodegradable stents are typically designed without structure optimization. The drawbacks of these stents often cause weaker mechanical properties than native arterial vessels. From the fabrication point of view, the conventional methods of the fabricating stent are time-consuming and expensive, and also lack precise control over the stent microstructure. As an emerging fabrication technique, dispensing-based rapid prototyping (DBRP) allows for more accurate control over the scaffold microstructure, thus facilitating the fabrication of stents as designed. This thesis is aimed at developing methods for fabrication and optimal design of biodegradable stents for treating aneurysms. Firstly, a method was developed to fabricate biodegradable stents by using the DBRP technique. Then, a compression test was carried out to characterize the radial deformation of the stents fabricated. The results illustrated the stent with a zigzag structure has a higher radial stiffness than the one with a coil structure. On this basis, the stent with a zigzag structure was chosen to develop a finite element model for simulating the real compression tests. The result showed the finite element model of biodegradable stents is acceptable within a range of radial deformation around 20%. Furthermore, an optimization of the zigzag structure was performed with ANSYS DesignXplorer, and the results indicated that the total deformation could be decreased by 35% by optimizing the structure parameters, which would represent a significant advance of the radial stiffness of biodegradable stents. Finally, the optimized stent was used to investigate its deformation in a blood vessel. The deformation is found to be 0.25 mm in the simulation, and the rigidity of biodegradable stents is 7.22%, which is able to support the blood vessel all. It is illustrated that the finite element analysis indeed helps in designing stents with new structures and therefore improved mechanical properties