Lech Murawski

THE INFLUENCE OF CHANGES IN THE ROTATIONAL SPEED OF THE SHAFT JOURNAL SLIDE BEARING ON THE ACOUSTIC EMISSION SIGNAL

The paper presents preliminary studies of a slide bearing operation by using an acoustic emission. These studies were designed to test the usability of this method for the diagnosis and monitoring of bearings in marine drive system (in particular, stern tube bearing). This paper proposes a method of testing the operating status of the slide bearing using acoustic emission. It discusses the research station, where the study was conducted. The authors paid special attention to the impact of rotation speed of the shaft journal bearing sliding to change some parameters of the acoustic emission signal. The gathered results were analysed and it was evaluated how the rotational speed of the shaft journal affects the individual signal parameters of acoustic emission. Additionally, the sensitivity of the method was evaluated. The article describes: the basics of testing with using the acoustic emission, parameters of the acoustic signal (the acoustic emission burst count, arrival time, duration time, signal amplitude, signal energy and RMS) and the equipment necessary for measurements by using this method. This method, unlike the ultrasonic testing detects only the active wave source, and it is very sensitive to detect changes in the moment when the installation is operating under load. It proposes to use the acoustic emission method to study operational conditions of a slide bearing. Slide bearings are used in many constructions of mechanisms, machines and equipment. They are a strategic element of their design and their improper work leads to the machine damage in a very short period of time, which automatically excludes it from further exploitation. For this reason, the correct assessment of the technical condition of slide bearing and knowledge of the current operating conditions of the slide bearing are extremely important (particularly in the case of bearings in marine propulsion system).

Analysis of ability to detect defects in welding structures with usage of dynamic characteristics spectrums

Non-destructive methods of testing (NDT) welded joints are nowadays intensively developing due to their numerous advantages. The most significant of them are the possibility of objects diagnosis in the place of their work without the necessity of disassembling or long outage, lower costs of realization as well as considerably lower insalubrity for people conducting the tests. Study of dynamic characteristics of welded elements creates a good possibility for welded joints assessment in comparison to other known non-destructive testing methods. The main reasons are Fourier analysis (FFT), damping analysis, differences in signals or their answers. Presented method can be used in classical NDT tests as well as in structural health monitoring (SHM). Assumptions for quality evaluation methods of welded plates using spectrums analysis of dynamic characteristics are presented in the article. In order to provide the high quality of research, the measuring devices of Bruel & Kjaer Company are used. Both, the testing methodology and possibility of using vibration method in welded joints testing are presented. The attention is also drawn to the vital testing elements like proper selection of impact hammer ending and impact place as well as the problem of repeatability of diagnostic signals. The value of repeatability of obtained signals will be of critical importance in the comparative method, which is under development. The results of initial testing of plates with proper and faulty welded joints have been analysed. Among welding faults, the boundary bonding and crevice have been considered. The analysis of impact hammer dispersion values in correlation to the spectrum of dynamic characteristic has been conducted. Statistic methods have been used for the assessment.

STIFFNESS CHARACTERISTICS OF MAIN BEARINGS FOUNDATION OF MARINE ENGINE

During shaftline alignment and crankshaft springing analyses, knowledge of stiffness of radial bearings is essential. Dynamic stiffnesss characteristics of marine main body are difficult to estimate because of lack of available documentation and complicated shape of the body. In the literature, there is a lack of the detailed data on the stiffness of the crankshaft foundation in the frame of marine main engine. Those parameters are crucial for the shaft line alignment analysis as well as for the analysis of interactions between the shaft line and the crankshaft. Especially for the high power engines, the correct model of the boundary conditions plays a key role during the analysis. The paper presents the methodology of the characteristics determination of the marine engine’s body as well as the example of computations for a MAN B&W K98MC type engine mounted on a ~3000 TEU container ship. The model of main engine body is relatively big – it contains over 800 thousand degree of freedom. The elasticity of ship hull has been estimated and taken into account during analysis. It has been found, that static stiffness parameters recommended by the producer for the shaft line alignment are evaluated correctly, however they represent only the flexibility of the engine’s body, not taking into account the flexibility of the ship’s hull. What is more, the dynamic magnification of vibration amplitudes is not taken into account.

STRENGTH PROPERTY OF POLYMER-WOOD COMPOSITE

Wood is one of the oldest construction materials. Nowadays, in the shipbuilding industry wood is almost forgotten. Wood has a lot of advantages in comparison to other materials, e.g. steel. However, some of wood characteristics are inconvenient. Layers are integrated part of wood construction - it is a natural composite. It is a big advantage of the wood, but there is too big difference between soft and hard woods layer. Modified wood might be very interesting “new” material for marine industry. Especially, polymer-wood composite seems to be very promising. One of the authors developed surface saturation methodology of the wood by polymer. Several measurement tests were performed. Some of the new material characteristics have been specify as a results of the tests. Stiffness and averaged material constants have been determined as well as material data of separate composite layers. The experiments were simulated by numerical calculations. Numerical analysis was compared with measurements. After model verification, several other analyses (e.g. detailed stress distribution in the composite) were performed. That kind of analysis of material data where very difficult, or even impossible, for obtain by measurements. Numerical analysis was performed by Patran-Nastran commercial software based on Finite Element Method. The authors plan to use experimental and calculations data for more specified analysis (included dynamic analysis) and plan to improve that polymer-wood composite can be used in marine industry with benefits.

Method of determining the structural parameters of wood-polymer composite

A composite material consisting of woody skeleton and polymerized methacrylate has been developed and characterized. This paper presents an experimental program and the results concerning mechanical properties and strength of wood modified with polymerized methacrylate. In the article, there are examples of structural elements made of natural wood. Wood is a composite consisting of the layers of soft and hard wood. Wood is a composite and porous material. The porosity, which is a serious defect of wood, may be simultaneously its advantage. Wood saturation with different impregnates to minimize its disadvantages. If the wood pores will fill the monomer there is obtained the wood polymer composite. This composite is classified as of fiber composites. Such composite is effectively protected against degradation; it is durable in use, and show an improvement in mechanical properties. Design constructions of surface modified wood require the determination of fundamental material constants. Therefore, for the determination of these parameters is very important obtaining the appropriate research material. The surface impregnation of wood allows obtaining strength characteristics in a function of polymer content. This allows to model its, and then design and perform specific ship structures. In the wood, there are three directions in relation to the annual rings. Wood properties, especially mechanical properties, are different in the selected directions. For the computation takes the orthogonal anisotropy in which there are three mutually orthogonal planes of symmetry, for which there is symmetry properties of the wood.