Archive of Mechanical Engineering

A high performance and light-weight wound composite material wheel has been developed and is intended to be used for many purposes. One of these applications is marine current turbine (MCT). Traditionally, major problems influencing the design and operation of MCTs are fatigue, cavitation and corrosion due to the sea water. Considering these factors, implementation of composite materials, especially Kevlar fiber/epoxy matrix, in MCTs is explained in this paper. This novel design pattern of composite material marine current turbine (CMMCT) shows many advantages compared to conventional turbines. This paper investigated several factors which should be considered during this novel turbine design process such as the composite material selection, filament winding of composite wheel and turbine's structural and cavitation analysis. The power coefficient of CMMCT by using CFD is also obtained and the experimental facilities for testing CMMCT in a water towing tank are briefly described.

The dynamics of the turning process of a thin-walled cylinder in manufacturing is modeled using flexible multibody system theory. The obtained model is time varying due to workpiece rotation and tool feed and retarded, due to repeated cutting of the same surface. Instabilities can occur due to these consecutive cuts that must be avoided in practical application because of the detrimental effects on workpiece, tool and possibly the machine. Neglecting the small feed, the stability of the resulting periodic system with time-delay can be analyzed using the semi-discretization method. The use of an adaptronic tool holder comprising actuators and sensors to improve the dynamic stability is then investigated. Different control concepts, two collocated and two model-based, are implemented in simulation and tuned to increase the domain of stable cutting. Cutting of a moderately thin workpiece exhibits instabilities mainly due to tool vibration. In this case, the stability boundary can be significantly improved. When the instability is due to workpiece vibration, the collocated concepts fail completely. Model based concepts can still obtain some improvements, but are sensitive to modeling errors in the coupling of workpiece and tool.

The most important task in tests of resistance of aircraft structures to the terorist threats is to determine the vulnerability of thin-walled structures to the blast wave load. For obvious reasons, full-scale experimental investigations are carried out exceptionally. In such cases, numerical simulations are very important. They make it possible to tune model parameters, yielding proper correlation with experimental data. Basing on preliminary numerical analyses - experiment can be planned properly. The paper presents some results of dynamic simulations of finite element (FE) models of a medium-size aircraft fuselage. Modeling of C4 detonation is also discussed. Characteristics of the materials used in FE calculations were obtained experimentally. The paper describes also the investigation of sensitivity of results of an explicit dynamic study to FE model parameters in a typical fluid-structure interaction (FSI) problem (detonation of a C4 explosive charge). Three cases of extent of the Eulerian mesh (the domain which contains air and a charge) were examined. Studies have shown very strong sensitivity of the results to chosen numerical models of materials, formulations of elements, assumed parameters etc. Studies confirm very strong necessity of the correlation of analysis results with experimental data. Without such a correlation, it is difficult to talk about the validation of results obtained from "explicit" codes.

In high-performance optical systems, small disturbances can be sufficient to put the projected image out of focus. Little stochastic excitations, for example, are a huge problem in those extremely precise opto-mechanical systems. To avoid this problem or at least to reduce it, several possibilities are thinkable. One of these possibilities is the modification of the dynamical behavior. In this method the redistribution of masses and stiffnesses is utilized to decrease the aberrations caused by dynamical excitations. Here, a multidisciplinary optimization process is required for which the basics of coupling dynamical and optical simulation methods will be introduced. The optimization is based on a method for efficiently coupling the two types of simulations. In a concluding example, the rigid body dynamics of a lithography objective is optimized with respect to its dynamical-optical behavior.

The paper presents the development procedures for both virtual 3D-CAD and material models of fractured segments of human spine formulated with the use of computer tomography (CT) and rapid prototyping (RP) technique. The research is a part of the project within the framework of which a database is developed, comprising both 3D-CAD and material models of segments of thoracic-lumbar spine in which one vertebrae is subjected to compressive fracture for a selected type of clinical cases. The project is devoted to relocation and stabilisation procedures of fractured vertebrae made with the use of ligamentotaxis method. The paper presents models developed for five patients and, for comparison purposes, one for a normal spine. The RP material models have been built basing on the corresponding 3D-CAD ones with the use of fused deposition modelling (FDM) technology. 3D imaging of spine segments in terms of 3D-CAD and material models allows for the analysis of bone structures, classification of clinical cases and provides the surgeons with the data helpful in choosing the proper way of treatment. The application of the developed models to numerical and experimental simulations of relocation procedure of fractured vertebra is planned.

The impact of the transversely-oriented sinusoidal wall corrugation on the hydraulic drag is investigated numerically for the flow through the channel of finite width and with flat sidewalls. The numerical method, based on the domain transformation and Chebyshev-Galerkin discretization, is used to investigate the flow resistance of the laminar, parallel and pressure-driven flow. The obtained results are compared to the reference case, i.e., to the flow through the channel with rectangular cross section of the same aspect ratio. Simple explanation of the gain in the volumetric flow rate observed in the flow through spanwise-periodic channel with long-wave transversely-oriented wall corrugation is provided. In the further analysis, pressure drop in the flows with larger Reynolds numbers are studied numerically by means of the finite-volume commercial package Fluent. Preliminary experimental results confirm the predicted tendency.

The essential parameters for structure integrity assessment in Linear Elastic Fracture Mechanics (LEFM) are Stress Intensity Factors (SIFs). The estimation of SIFs can be done by analytical or numerical techniques. The analytical estimation of SIFs is limited to simple structures with non-complicated boundaries, loads and supports. An effective numerical technique for analyzing problems with singular fields, such as fracture mechanics problems, is the extended finite element method (XFEM). In the paper, XFEM is applied to compute an actual stress field in a two-dimensional cracked body. The XFEM is based on the idea of enriching the approximation in the vicinity of the discontinuity. As a result, the numerical model consists of three types of elements: non-enriched elements, fully enriched elements (the domain of whom is cut by a discontinuity), and partially enriched elements (the so-called blending elements). In a blending element, some but not all of the nodes are enriched, which adds to the approximation parasitic term. The error caused by the parasitic terms is partly responsible for the degradation of the convergence rate. It also limits the accuracy of the method. Eliminating blending elements from approximation space and replacing them with standard elements, together with applying shifted-basis enrichment, makes it possible to avoid the problem. The numerical examples show improvements in results when compared with the standard XFEM approach.