Protection of Fuel Tanks Safety ahead! - GL Group

More documents

Recommendations

Info

MARITIME SERVICES | CHINA Tracking Down Vibration Analyzing problems, implementing fast turn around solutions: Germanischer Lloyd’s engineers are active around the world Shanghai, one of the leading ports in Asia, is a major center of the Asian shipbuilding industry. This is why Germanischer Lloyd is right on the spot – with engineering services tailored to meet the demands of these shipyards. On your marks – wait for the call – go! When it comes to his job, Ulrich Behrens has two principles he always adheres to: whenever his expertise is required somewhere, he doesn’t waste any time. And whenever he swings into action, he does so with a holistic vision. “We not only carry out measurements, we also make specific recommendations,” he says. “Measurements, analysis and a solution to the problem, all in one package – that is our special strength. And if necessary, we deliver it all within a very short time,” he adds. Behrens, head of Engineering Services at Germanischer Lloyd, Shanghai, is a vibration and noise expert specializing in investigating mechanical vibrations that exceed the limits permitted by ISO 6954. Such excessive vibration may cause discomfort and health problems. Good Vibrations, Bad Vibrations Take the case of a tanker newbuilding a few months ago. Behrens received a call from the shipping agent just before the sea trial. The problem: vibration had been encountered on the bridge deck and found to be extremely unpleasant, not only for the shipping agent. Initial measurements seemed to indicate that the limits were being exceeded. “At this stage, you cannot possibly make a well-founded statement about the causes,” says Behrens who has many years of experience. “That the vibration level extended so far into the perceptible range was certainly alarming,“ but that was all we knew. What we needed was an objective picture of these subjective sensations.” Behrens analyzed the problem, figuring in boundary conditions such as mass distribution, the deck pillars, etc. He deduced a natural frequency SHANGHAI. of 17.5 Hz for the local subsystem. A single-hull This tanker under construction. corresponded to a propeller speed of 105 rpm, which evidently caused the excessive resonance in the deckhouse. On occasion of the sea trial of the sister ship, Ulrich Behrens was able to verify his conclusions during a phased run-up of the engine. In the service speed range, the frequency levels were far above limits. Based on his analysis, Beh- 30 nonstop 4/2006 Foto: Sabine Vielmo rens was immediately able to discuss possible solutions with the shipyard’s designers and the shipping agent. They unanimously decided to add two support pillars in the central part of the deckhouse. Subsequent measurements showed that the vibration level was now ranging within the limits and had in fact decreased by a factor of 3. This timely solution to the problem – before the delivery of further units of the series – saved both the yard and the owner considerable expense. “Having to fi nd remedies to the excessive vibration problem at a later time would have been much more costly,” says Behrens. “What is more, one must always expect consequential damage with amplitudes of this scale.” Analyzing and correcting vibration problems constitutes only part of the wide-ranging activities of GL’s Engineering Services in Shanghai. The office closely cooperates with the Hamburg headquarters to provide customers with access to the entire spectrum of GL’s engineering AUDIENCE. Ulrich Behrens presenting the Engineering Services of Germanischer Lloyd at the fair „Maritime Vietnam“ in Ho Chi Minh City.
BACKGROUND Finite Elements: Computing to Achieve Equilibrium What do a heavily loaded cargo ship in heavy seas and a Formula I racing car taking a curve at 170 km/h have in common? As different as these two situations may appear, it is not only the individuals steering these vehicles that are put to the test, but also the vehicles themselves. Both the ship and the car are travelling in a borderline situation that exposes their materials to extreme stress. It is the engineer’s job to design the vehicles so they will withstand these borderline stress loads. There are numerous mathematical approaches to determine the relationship between force and deformation so as to properly dimension each basic component. But frequently these methods are inadequate for real-life requirements, especially so in complex structures. How can an engineer manage this seemingly impenetrable mess of loads, points of application of force, and section moduli? Small solutions. The answer is a scientifi c method that breaks up large problems into many individual partial problems that are fi rst solved independently. All these small solutions can then be merged into one big solution. This is what the fi nite-element method (FEM) is all about. It owes much of its success to the introduction of powerful yet affordable computers that can handle the enormous amounts of individual calculations involved in this method. Big system. Simply put, the FEM substitutes a virtual structure of a large but fi nite number of individual, simple elements assumed to have simple elastic properties for the specifi c component. These elements are assumed to be interconnected at individual points called nodes. Loads and the resulting deformation of the elements cause node movements or forces within the structure. The challenge consists in creating an equilibrium between these inner forces and the external forces. This leads to an enormous equation system that often comprises hundreds of thousands of elements and can be solved to produce the desired values. A job for Mr Silicon: many computer applications today use the FEM. services and its team of about 50 mechanical engineers, naval architects, physicists and mathematicians. On-site service teams at locations around the globe, such as Ulrich Behrens in Shanghai, profit from this network tremendously. “We go wherever we are needed,” says Karsten Fach, Head of Engineering Services at GL. Modern means of communication are important prerequisites for rapid analysis and problem-solving, he emphasizes. Unique Expertise One of the key competence areas that enable GL to deliver its unique customer focus is structural strength. With GL ShipLoad, Germanischer Lloyd offers a user-friendly program for computing load spectra for reliable finite-element analysis (FE analysis, see info box) of a ship. Using the graphical user interface, ship, wave and cargo parameters can be applied to the FE model quickly and reliably; hydrographic and hydrodynamic calculations are integrated. The calculation process provides the designer with selected, substantiated and realistic load assumptions for optimal dimensioning of the hull based on the given requirements. Another software product that supplies Engineering Services with outstanding results is the GL ShipModel application for hull design – an extension developed in-house of the widely used MSC.Patran package, and a pioneering Foto: Eberhard Petzold Foto: Renault CHINA | MARITIME SERVICES achievement in many ways. “The development of structural models for analyzing strength, vibrations and ship acoustics is not supported by any commercial software vendor,” Karsten Fach says. Another new trail was blazed when GL engineers developed a high-speed trimaran 130 meters in length. Initially, there was no experience available, nor were there any established rules covering the envisaged ship design. What to do? In the end, the GL specialists paved the road to success by combining computational fluid dynamics derived from the world of automotive engineering with their experience gained from other ship types. Precisely this is what distinguishes GL’s Engineering Services, Karsten Fach explains. “We make our own developments with our own staff, thereby achieving a level of subject-specific know-how that is simply unique worldwide.” But GL does not guard this expertise jealously. “It is my job to pass on the knowledge,” says GL’s Shanghai expert, Ulrich Behrens. To this end, he is currently working on the presentation documents for the first vibration seminar to be held by the GL Academy – an Asian debut. ■ JI For further information: Ulrich Behrens, GL Engineering Services Shanghai, Phone: +86 138 16504332, E-Mail: ulrich.behrens@gl-group.com nonstop 4/2006 31
Page 1 and 2: The Magazine for Customers and Busi
Page 3 and 4: Dear Readers, The year 2006 will be
Page 5 and 6: News from the Maritime Services ECO
Page 7 and 8: VIETNAM Two New Offi ces November w
Page 9 and 10: MILESTONES New Agreement Hapag-Lloy
Page 11 and 12: Germanischer Lloyd’s Carefree Sof
Page 13 and 14: ments for cargo oil tanks, the prob
Page 15 and 16: Fig. 3 Fig. 4 Fig. 5 tanks, placing
Page 17 and 18: It gives technical advice for updat
Page 19 and 20: Cool Transport The shipping of peri
Page 21 and 22: Fortunately, the emergency service
Page 23 and 24: Fluids in Motion What can earthquak
Page 25 and 26: Photo: istockphoto.com ULTRASOUND.
Page 27 and 28: ed to gather more experience in age
Page 29: EAST ASIA | MARITIME SERVICES Quali
Page 33 and 34: Waste Overboard? Proper waste dispo
Page 35 and 36: Sassnitz 14 ° 15 ° death sentence
Page 37 and 38: Dr Gottfried Braun, Quality Managem
Page 39 and 40: WINDENERGIEZIRKEL HANSE Bracing the
Page 41 and 42: This year it is 2,000 MW. So we tru
Page 43 and 44: © Maciej Dominik - FOTOLIA Just A
Page 45 and 46: Fotos: Istockphoto.com (2) INSPECTI
Page 47 and 48: Rules for Classifi cation and Const

Protection of Fuel Tanks Safety ahead! - GL Group

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?