Comparing of Direct and Sensitivity-Base Model Updating Methods in Structural Dynamics and Its Application for Updating of Cantilever Model

Reliable finite element (FE) modeling in structural dynamics is very important for studies related to the safety of structural components used in industry. FE model updating is a tool to produce these reliable models. The method uses an initial FE model and experimental modal data of the structural components to modify physical parameters of the initial FE model, and a number of approaches have been developed to perform this task. This paper presents an overview of model updating and particularly its application for updating of cantilever model. An example of the need for model updating is a cantilever beam, where often the beam is assumed to be rigidly fixed at the clamped end. However, during tests it is often found that the beam has either a small rotation or deflection at the clamped end. If one has to construct the FE model without the knowledge of the experimental modal data, the natural assumption would be to include an ideal, fixed boundary condition, which may not be true. Even with such a simple structure the FE model is not reliable a priori, and based on intuition or engineering judgments it is difficult to estimate the values of the boundary stiffnesses. However, after creating an initial FE model, the model should be updated based on the experimental modal data obtained from modal tests so that the FE model may be used with confidence for further analysis.

Adaptive Methods for Non-Linear Empirical Similitude Method

Several problems in engineering realm pose modeling and simulation difficulty due to severe non–linear behavior and debilitating singular or stiff conditions that act as additional impediments. In many such instances advanced numerical schemes are employed to either relax or simplify the PDE that defines the physical process to obtain reasonable output from the simulation. Digressing from this traditional approach, we present an experimental similitude method in this paper to analyze non–linear systems. Combined with the use of original mapping algorithms, we discuss the benefits of empirical similarity techniques and present a heat transfer example for exposition.

Math-Based Control Logic Development for Automotive Industrial Applications: Issues, Challenges and Solution

Intensive global competition forces automotive manufacturers to develop and produce vehicles at lower cost with shorter life cycles and better quality. Faster Vehicle Development Process (VDP) improve profitability by reducing the time and cost related to designing, engineering and launching a new vehicle model. More importantly, it enables automotive makers to react quickly to trend shift in market, e.g., recent shift from SUV (Sports Utility Vehicle) to small fuel efficient vehicle. However, the current manufacturing system design (especially control logic design), key part of VDP, is labor intensive and time consuming, and design quality and performance are highly dependent on the designer’s knowledge and experience. This paper discusses the issues and challenges identified in the current logic development process. A new method to automatically generate control logic using formal method is proposed. In this approach, the required information is collected and modeled as Automata. Possible control logic sequences are then calculated and the optimal one is identified from a set of alternative solutions. This paper also discusses how to implement and integrate the proposed method into the automotive manufacturing engineering process. The method is applied to automotive industry examples, and results are presented. Based on these case studies, this math-based approach can improve the quality of controls logic codes, and reduce ramp-up time and engineering cost significantly.

Multi-Objective System Optimization of Engine Crankshafts Using an Integration Approach

The ever increasing computer capabilities allow faster analysis in the field of Computer Aided Design and Engineering (CAD & CAE). CAD and CAE systems are currently used in Parametric and Structural Optimization to find optimal topologies and shapes of given parts under certain conditions. This paper describes a general strategy to optimize the balance of a crankshaft, using CAD and CAE software integrated with Genetic Algorithms (GAs) via programming in Java. An introduction to the groundings of this strategy is made among different tools used for its implementation. The analyzed crankshaft is modeled in commercial parametric 3D CAD software. CAD is used for evaluating the fitness function (the balance) and to make geometric modifications. CAE is used for evaluating dynamic restrictions (the eigen-frequencies). A Java interface is programmed to link the CAD model to the CAE software and to the genetic algorithms. In order to make geometry modifications to our case study, it was decided to substitute the profile of the counterweights with splines from its original “arc-shaped” design. The variation of the splined profile via control points results in an imbalance response. The imbalance of the crankshaft was defined as an independent objective function during a first approach, followed by a Pareto optimization of the imbalance from both correction planes, plus the curvature of the profile of the counterweights as restrictions for material flow during forging. The natural frequency was considered as an additional objective function during a second approach. The optimization process runs fully automated and the CAD program is on hold waiting for new set of parameters to receive and process, saving computing time, which is otherwise lost during the repeated startup of the cad application.

Application of a New Cylindrical Element Formulation in Finite Element Structural Analysis of FGM Hollow Cylinders

Functionally graded materials are advanced composite materials consisting two or more material ingredients that are engineered to have a continuous spatial variation of properties. There are a few analytical methods available to solve the governing equations of FGM made structures, confined to some specific and limited shapes, loadings and boundary conditions. Hence the numerical methods such as FEM are used to treat these materials. In previous studies the finite element method was used to solve thin walled FG structures like shells and plates by modification of the conventional shell and plate elements. Solving the thick walled FG structures confronts some difficulties. One of the methods to overcome this problem is laminating the structure across the direction of material variation, assuming constant material properties in each layer. When the thickness is increased, the number of layers representing the FGM should be also increased to produce an accurate result. Increasing the number of elements implies great time consumption and required memory space. One of the most commonly shapes present in FG structures are hollow cylinders whose analysis is so complicated that may not be done by conventional elements. In this study a superelement approach is chosen to confront the problem. Design and application of superelements in efficient prediction of the structural behavior in a short time has been one of the research interests in the last decade. The superelements are designed for special problems so that they could substitute a huge number of conventional elements in modeling and analysis. In this study a new cylindrical superelement is incorporated to model the functionally graded cylinders, and modal analysis is performed. The advantage of this cylindrical superelement lies in the fact that no lamination is needed, anymore and only a few superelements can predict the vibration behavior of FG cylinders accurately. Several examples are solved based on the new element formulation and the natural frequencies and mode shapes are obtained. Comparison of the findings with the conventional elements reveals time saving and accuracy of the results.

SnAP: A Comprehensive Software Package for the Simulation of Serial Manipulators

The solution of kinematics problem for serial manipulators is fundamental for their analysis, simulation and computer control, for this reason, this paper introduces the software package called SnAP (Serial n-Axes Manipulators), which is developed under the ADEFID framework [1], where the manipulator is conceptualized as a derived class from CRobokin, CMachine and CIpiSModel, which are fundamental ADEFID classes. SnAP has been developed with efficient algorithms in a closed-loop solution to solve direct kinematics, whereas for the case of inverse kinematics, matrix formulation, elimination and numerical methods are implemented. Furthermore, for the architecture definition, the user is able to display a dialog box in which the design parameters are set while the solid model is updated simultaneously showing the actual configuration. Since ADEFID provides tools to graphical interface with embedded control components, SnAP adopted them to not only simulate virtually, but also with a parametric prototype designed for this purpose.

Curve and Surface Fitting by Means of Rational B-Spline Functions

This paper presents a method to obtain the mathematical model of a free-form curve or a surface fitting a set of point coordinates by a rational B-spline (NURBS) formulation in the homogeneous R4 space. A method to evaluate the control points R4 coordinates is proposed by means of a two step process. In the first step, NURBS weights are evaluated by means of an optimization procedure making it possible to evaluate the best fitting parameterization as well. In the second step, the control point coordinates are computed by means of a linear least squares approach.

Tolerance Simulation of Compliant Sheet Metal Assemblies Using Automatic Node-Based Contact Detection

Tolerance simulation is a crucial tool for predicting the outcome in critical dimensions, and is used during early phases of product development in automotive industry. In order to increase the accuracy and the agreement with reality of the predictions even further, variation simulation software offer in some cases the possibility to perform compliant analysis, i.e. the parts are not restricted to be rigid. In compliant analysis contact modeling is an important feature. In this paper a simplified method for automatic contact detection, well suited for tolerance simulations, is suggested. Traditionally, those kinds of non-rigid simulations are very time consuming, but by using this kind of simplified contact modeling in the Monte Carlo simulations, the simulation times can be kept down. The method is tested on an industrial case study. The analyses are done with and without contact modeling and those results are compared to real inspection data. The contact modeling turns out to be an important feature; the correlation between the results with contact modeling and inspection data is much stronger than the correlation for simulations without contact modeling. When using the new contact modeling algorithm the correspondence between simulated data and inspection data is very satisfying and the algorithm seems to be faster than traditional finite element software.

Simulation of the Influence of Ship Voyage Profiles on Air Emissions

Simulation methodology is used to assess fuel related pollutants, CO2 and SO2, based on several reference ship voyages. Firstly, the definition of ton-mile specific emission factor is introduced. This emission factor is related to a wide range of factors extending from fuel parameters and engine operational condition to ship design and ship activity. In this case study, a simulation model is built that applies to both transient and stationary conditions. By running this model, ton-mile specific emission factors of CO2 and SO2, for both the full voyage and a single part of the voyage are achieved. The influences on exhaust emissions of ship speed fluctuation and in port operation strategy are considered, as well as the influence of loading fraction. After a series of simulations it is demonstrated that, a larger speed fluctuation and more intense variation of ship operational activities during maneuvering in port would cause higher emissions and the assumption of full load will underestimate the ton-mile specific emissions.

Integrated Topology and Fiber Optimization for 3-Dimensional Composites

The importance of computer aided engineering in product development processes and research has been increasing throughout the past years. As e.g. energy efficiency and therefore mechanical lightweight structures of new products plays a large role, optimization tools gained more and more importance. Weight reduction can be achieved by a change of the component’s design and by selection of adapted materials. Such an improved utilization of material can be implemented only if there is an accurate knowledge of the loads and the conditions on the material. As modern composite materials can make a clear weight reduction possible, appropriate tools and methods are necessary within the design process. Even for isotropic materials, the design of complex parts is not trivial. For the design of composites, additional parameters have to be considered, such as number and thickness of the plies and the orientation of fibers. Hence, design by intuition leads only in few cases to optimal parts. For the determination of the basic layout of a new design topology optimization can be used. It involves the determination of features such as the number, location and shape of holes and the connectivity of the domain. Today topology optimization is very well theoretically studied and also a very common tool in the industrial design process but is limited to isotropic materials. Several approaches for the determination of optimal fiber orientation have been presented in the past e.g. placing the fibers in the direction of the first main stress. Based on a finite element analysis, a method is presented that uses the orientation of main stresses to determine optimal orientations and thickness relations of plies. It is now applicable to complex 3D geometries. The result is a design proposal for the laminate structure (orientation and thicknesses of plies), taking multi-axial load cases into account. To determine a design proposal for complex 3D laminate structures, the application of both methods, topology and fiber optimization, is appropriate. Regarding an independent serial application of topology and fiber optimization it makes sense carrying out topology optimization in a first step and the determination of fiber orientations in a second step. An integrated approach might show even better results in certain cases. For that, we combined topology and fiber optimization in a two-level approach by optimizing laminate structure within each iteration of topology optimization process. In this paper topology and fiber orientation optimization are integrated into a straightforward, automatic way.