Marko Kegl

Implementation of an ANCF beam finite element for dynamic response optimization of elastic manipulators

Theoretical and practical aspects of an absolute nodal coordinate formulation (ANCF) beam finite element implementation are considered in the context of dynamic transient response optimization of elastic manipulators. The proposed implementation is based on the introduction of new nodal degrees of freedom, which is achieved by an adequate nonlinear mapping between the original and new degrees of freedom. This approach preserves the mechanical properties of the ANCF beam, but converts it into a conventional finite element so that its nodal degrees of freedom are initially always equal to zero and never depend explicitly on the design variables. Consequently, the sensitivity analysis formulas can be derived in the usual manner, except that the introduced nonlinear mapping has to be taken into account. Moreover, the adjusted element can also be incorporated into general finite element analysis and optimization software in the conventional way. The introduced design variables are related to the cross-section of the beam, to the shape of the (possibly) skeletal structure of the manipulator and to the drive functions. The layered cross-section approach and the design element technique are utilized to parameterize the shape of individual elements and the whole structure. A family of implicit time integration methods is adopted for the response and sensitivity analysis. Based on this assumption, the corresponding sensitivity formulas are derived. Two numerical examples illustrate the performance of the proposed element implementation.

A friction model for dynamic analyses of multi-body systems with a fully functional friction clutch

This article focuses on the development and experimental verification of a friction model to be implemented in a fully functional friction clutch. The resulting clutch model is intended to be employed in commercial software code AVL Excite, which imposes special requirements also for the underlying friction model. These requirements are related to model implementation, available input data, required output data, model complexity, numerical stability, and model parameters. Since for a fully functional clutch the ability to render true stick is crucial, the elasto-plastic friction model is chosen as a basis. This model is investigated in detail and modified adequately in order to meet all of the requirements and to deliver stable and satisfactory results. For validation purposes, a special test bed was built to measure the transmitted torques through the friction contact under various realistic load cases, including all operation phases of the friction clutch. Parallel to experimental measurements, multi-body simulations were done with the modified friction model within the target software. A very satisfactory agreement of simulation and measurement results was achieved.

Parameterization based shape optimization: theory and practical implementation aspects

Purpose – To present an approach to parameterization based shape optimization of statically loaded structures and to propose its practical implementation.Design/methodology/approach – In order to establish a convenient shape parameterization, the design element technique is employed. A rational Bezier body is used to serve as the design element. The design element is used to retrieve the nodal geometrical data of finite elements (FEs). Their field geometrical data are obtained using the FE own internal functions. For practical implementation it is proposed to establish the optimization cycle by two separately running processes. The data exchange is established by using self‐descriptive and platform‐independent XML conforming data files.Findings – The proposed approach offers an unified approach to shape optimization of skeletal, as well as continuous structures. Structural shape may be varied smoothly with a relative small set of design variables. The employment of a gradient‐based optimization algorithm ...

Guidelines for Improving Diesel Engine Characteristics

Diesel engine characteristics depend significantly on the engine type. But, even for a given engine type, the engine characteristics can still be varied in a wide range in dependence on engine management, exhaust gas after treatment, and usage of alternative fuels (Fino et al. 2003; Gray and Frost 1998; Maiboom et al. 2008; Peng et al. 2008; Stanislaus et al. 2010; Twigg 2007) (Fig. 3.1). Engine management and alternative fuels usage offer a possibility to reduce the formation of harmful emissions. On the other hand, exhaust gas after treatment techniques enable a reduction of harmful emissions already produced by the engine.

Biodiesel as Diesel Engine Fuel

In recent years, the interest to use biodiesel as a substitute for mineral diesel has been increasing steadily. Biodiesel is a renewable fuel, consisting of various fatty acid methyl esters with the exact composition depending on the feedstock. This is a distinctly different composition than the hydrocarbon content of mineral diesel. In spite of that, biodiesel has many properties very close to those of mineral diesel. Consequently, the required biodiesel-related modifications of the diesel engine are typically rather minor. On the other hand, because of its different chemical character, biodiesel has several properties, which differ from those of mineral diesel just enough to offer an opportunity to reduce harmful emissions without worsening other economy and engine performances. It should be noted, however, that biodiesel properties may depend heavily on its raw materials.

Diesel Engine Characteristics

Diesel engine is a compression ignition engine of a 2- or 4-stroke type. From the p − V diagrams (Fig. 2.1), it can be seen that the duration of the whole diesel cycle is 360°CA for the two-stroke engine and 720°CA for the four-stroke engine. The whole cycle consists of the following phases: intake of air, compression of air, fuel injection, mixture formation, ignition, combustion, expansion, and exhaust. The intake phase begins with the intake valve opening and lasts till the intake valve closing. After that the intake air is compressed to a level corresponding to compression ratios from 14:1 to 25:1 (Bauer 1999) or even more. The compression ratio e is a geometrical quantity, defined as

Improvement of engine performance using an optimization procedure

\varepsilon =\frac{V_{\max }}{V_{\min }}=\frac{V_{\mathrm{h}}+{V}_{\mathrm{c}}}{V_{\mathrm{c}}},