CIMAC Congress - Schiff & Hafen

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<strong>CIMAC</strong> CONGRESS | BERGEN 2010 felt, to a degree which varies from one individual to another. Although the matter from a medical point of view is still somewhat obscure, there is scientific evidence that some people are sensitive to infra-sound to a degree that can documented objectively. Accordingly, some noise regulations today stipulate maximum allowable noise level within a wide frequency spectrum, including values at infrasound frequencies. Therefore, the acoustic engineer cannot ignore the issue of infra-sound, apart from disturbance caused by noise within the audible spectrum. Conventional silencers can indeed yield satisfactory attenuation at all relevant frequencies, but stringent demands regarding low-frequency performance tend to call for ample accommodation space and for an allowance to design for rather big pressure drops. This is in conflict with the fact that available space is often narrow, for instance on board ships. Also, a high backpressure can retract from engine performance and can cause unwanted increase of thermal loading of combustion chambers. The paper presents a novel silencer concept that combines three per se well-known silencer principles in an optimal way. The first of these principles is the reactive sound-reflection principle; a silencer according to this principle in acoustic theory is sometimes referred to as a low-pass filter, since it attenuates noise of frequencies higher than a lower cut-off frequency. The second principle is the sound-absorptive principle which provides mainly high frequency attenuation. The third principle is the Helmholtz resonator principle in which sound confined to a certain frequency band is being absorbed. Each principle has its pros and cons: The reactive silencer can provide noise reduction within a wide frequency spectrum, but there is a pressure-drop penalty. A resonator, on the other hand, can be designed for an insignificant pressure drop, but its bandwidth is rather narrow. Additional problems with a resonator are, that its resonance frequency is sensitive to temperatur variations, and that the frequency at which maximum attenuation is needed will change with rotational speed of the engine, making exact tuning difficult. The various principles can be combined in such a way that the attenuation spectrum of a reactive stage is supplemented at the lower end by a resonator. Automatic tuning of the resonator can be performed by a robust feed-forward control loop which can compensate for frequency shifts caused by changed rotational speed of the engine. The paper presents the theoretical basis for the new silencer concept, supported by empirical verification, as well as an evaluation of its fitness from a practical application point of view, as related to an ongoing field project. 10:30 June 16th Room Klokkeklang (5–1) Component & Maintenance Technology – Piston Engines – Components Recent development in analysis and design of principal bearings of large two stroke diesel engines P. Rønnedal, H. W. Christensen, MAN Diesel & Turbo SE, Denmark The two stroke crosshead low speed diesel engine has been a preferred prime mover in the merchant marine for mostly a century. Although its basic working principle has not been changed, the demand for still higher power, produced at the lowest possible fuel consumption, from a machine occupying a minimum of space, has constantly increased the demands to its three principal bearings, main bearing, crank pin bearing, and crosshead bearing. This paper deals with design techniques for bearings as applied in modern large two stroke diesel engines. Simulation methodology as well as design verification techniques by measurements are described. Most important, the actual design features, as developed using the illustrated techniques, are shown. Calculation results from in house simulation software including advanced combinations of loadgeneration and Elasto Hydro Dynamic (EHD) analysis are demonstrated, in particular for a newly developed main bearing assembly, and for the Blended- Edge (BE) main bearing applied in MAN B&W two stroke diesel engines. Also simulation results for the wide pad crosshead bearing, which has been introduced in the ME-B engine series, are given. Major design particulars, bearing application range, and service experience are illustrated in each case. The actual geometry of a bearing journal, even when produced within strict tolerances of cylindricity, may strongly influence the distribution of hydraulic pressure in the oil film. A method of in situ measuring the shape of a main bearing journal in detail is presented, and the influence of typical imperfections discussed. Measurements of the oil film thickness of the main bearings during full operation, made on the 4T50MX test engine in Copenhagen, are shown in correlation with the equivalent simulation results, and illustrating the development on the main bearing components. In parallel with the mechanical/geometrical development, also the issue of material properties are addressed. Traditionally Babbitt has been the preferred bearing material for a number of reasons. However stronger Tin-Alu bearings have also been used for decades. MAN B&W diesel engines use both type of materials, and recent developments aim at merging best properties for both type of materials in one. MAN has worked on this development for well over four years now, and the first service trials are presented. Trends in engine design and their impact on engine bearing design and performance C. Forstner, Miba Gleitlager GmbH, Austria Latest engine designs are committed to ultimate performance and low cost of ownership which in turn means high power density and fuel efficiency combined with engine downsizing and extended service intervals. The consequences are weight-optimized and hence more flexible engine components as well as cost reduction at the expense of material and surface quality. At the same time engine speed, Brake Mean Effective Pressures and Exhaust Gas Recirculation rates are increasing to match the performance and emission targets. All of the above mentioned measures are directly affecting the load and operating conditions of conrod small end bushings, connecting rod big end and main bearings. In order to cope with this challenge new bearing design and material solutions have been developed. This paper will focus on late-breaking topics like recommended surface quality of crankshafts, fretting damages at conrod big end bearings and the influence of crankshaft torsional vibration optimization on main bearing loads. Finally specific bearing design changes and adaptations of existing bearing types in order to achieve the required bearing performance and operational safety will be presented. Variable valve timing – a necessity for future large diesel and gas engines C. Mathey, ABB Turbo Systems Ltd., Switzerland Variable Valve Timing (VVT) systems have been used in the automotive industry for a number of years and very different techniques, including phase-shifting, variable valve lift and exhaust valve reopening, can all be found on the market. Beside its positive impact on emissions and fuel consumption, the main marketing focus is still on driveability or, in PR language, the “joy to drive”. While these systems could be described as standard automotive equipment today, it has been rare in the past for Variable Valve Timing to be applied to large diesel and gas engines. However, the 74 Ship & Offshore | 2010 | No. 3
Monday, 14 June Tuesday, 15 June Thursday, 17 June Wednesday, 16 June coming emissions regulations as well as further development work aimed at higher brake mean effective pressures of turbocharged large engines, especially those equipped with Miller-timing, will require more flexibility on the air management side. This paper shows and discusses some of the possibilities offered by Variable Valve Timing in respect of engine performance data, including transient behaviour, emissions and the turbocharging requirements. Also presented is the design of a newly developed variable valve train system that is currently undergoing an extensive validation and qualification program. The lay-out of this VVT has a considerable degree of flexibility, allowing it to be used on diesel and gas engines of different sizes and for different purposes and giving it the customising capability required by all large engine manufacturers. Even retrofitting on existing engines has been taken into account. The VVT system is designed in such a way that no external power supply is required for the operation and the control can be integrated in the engine management unit. Several design features of this hydraulic mechanical VVT are based on proven automotive design elements. First test results are presented in this paper. To develop and manufacture this new VVT system ABB Turbo Systems Ltd joined forces with a large German OEM supplier; it is planned for prototypes for testing on customers’ engines to be made available by the end of 2010. Revised fatigue assessment of welded twostroke engine structures D. Bachmann, S. Soennichsen, Wärtsilä Corporation, Switzerland In this paper the strategy of Wärtsilä 2- stroke for improvement of the reliability of the welded engine structure is presented. The strategy is based on three aspects such as production friendly and mechanically optimized design, welding quality control and instruction as well as the improvement and research on the fatigue limits of welded structures. The latter is investigated in this paper in detail. Therefore a fatigue test series has been performed with weld seam variation regarding weld root quality (lack of penetration) and post weld heat treatment. The paper closes by analyzing the consequences of the findings in these tests with regard to existing and future 2-stroke engine structures. Topology optimization of main mediumspeed diesel engine parts P. Böhm, D. Pinkernell, MAN Diesel & Turbo SE, Germany Due to the ongoing progress in computing power of computer hardware on the one hand and computational efficiency of simulation programs on the other hand, optimization by simulation gains importance in the development process of medium-speed diesel engines. This paper presents two studies of main diesel engine parts where topology and shape optimization methods have been successfully integrated into the design process at an early design phase. The first example describes a lightweight crankcase design of a V-engine for a whole set of cylinder numbers from 12V to 20V, the second one refers to an optimization of a crankshaft with main focus on web and counterweight design. It is demonstrated that topology optimization is an appropriate tool for lightweight design and that a weight reduction of more than twenty percent can be achieved. The method leads to new design recommendations expanding the wellknown field of experience. In both examples, the goal of weight reduction is accompanied by a comprehensive set of requirements and constraints which have to be ensured by the optimization procedure automatically. As the distribution of applied material in a given design space influences the dynamics of the system, requirements for dynamic stiffness and eigenmodes have to be incorporated into the optimization process. Geometrical properties like symmetries have to be guaranteed as well as specifications from manufacturing. The given examples illustrate that for main engine parts it is possible to build up a topology optimization processes including a large number of quality criteria concerning geometry, stiffness and dynamic behaviour. For example, modal frequency criteria are combined with constraints for bending and torsion. It is shown that it is feasible to define an appropriate set of load cases from a large number of applied timedependent forces and moments and to balance contributions from static and dynamic forces. When necessary, the presented overall optimization process ensures requirements with respect to strength by an additional shape optimization step, as in both examples it is not possible to incorporate constraints with respect to strength directly into the topology optimization procedure. Aspects from transferring design recommendations from topology optimization into a CAD based design are addressed as well as particular needs for handling models with a very large number of degrees of freedom.. 13:30 June 16th Room Peer Gynt Salen (11–3) Users’ Aspects – Marine Applications – Fuels Experience with measuring cylinder oil consumption rate C. Schneider, KRAL AG, Austria This paper presents practical experience with cylinder oil consumption measurement systems. After an analysis of tank level systems for energy booster-modules fuel-water-emulsion viscosity & temperature control steam / thermal oil / hot water heaters electric heaters fuel pulsation damping technical water systems ELWA Elektro-Wärme München A. Hilpolststeiner GmbH & CO.KG No. 3 | 2010 | Ship & Offshore 75
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