Influence of marine main engine foundations on the results of vibration calculations

The article presents an influence of foundations of slow-speed main engine body on the results of numerical analysis of the engine dynamic stiffnesses and thermal deformations. The engine body is much stiffer than its foundation pads and ship hull (double bottom) – boundary conditions of the engine. Especially for the high power, marine engines, the correct model of the boundary conditions plays a key role during the analyses. Therefore, modelling method of engine foundation (boundary conditions) of that kind of model is essential during the analyses. During shaft line alignment and crankshaft springing analyses, knowledge of dynamic stiffnesses characteristics and thermal displacements of radial (main) bearings is significant. Those data of marine main engine body are difficult to estimate because of lack of available documentation and complicated shape of the engine and ship hull. The article 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 (power: 40000 kW, revolutions: 94 rpm) mounted on a 3000 TEU (twenty-foot container equivalent unit) container ship (length: 250 m). Numerical analyses were performed with usage of Nastran software based on Finite Element Method. The FEM model of the engine body comprised over 800 thousand degree of freedom

THERMAL DISPLACEMENT OF CRANKSHAFT AXIS OF SLOW-SPEED MARINE ENGINE

The paper presents analysis of displacement of a crankshaft axis caused by temperature of marine, slow-speed main engine. Information of thermal displacement of a power transmission system axis is significant during a shaft line alignment and a crankshaft springing analysis. Warmed-up main engine is a source of deformations of an engine body as well as a ship hull in the area of an engine room and hence axis of a crankshaft and a shaftline. Engines' producers recommend the model of parallel displacement of the crankshaft axis under the influence of an engine heat. The model gives us the value (one number!) of the crankshaft axis displacement in the hot propulsion system's condition. This model may be too simple in some cases. Presented numerical analyses are based on temperature measurements of the main engine body and the ship hull during a sea voyage. The paper presents computations of MAN B&W K98MC type engine (power: 40000 kW, revolutions: 94 rpm) mounted on 4500 TEU container ship (length: 290 m). Propulsion system is working in nominal, steady-state conditions; it is the basic assumption during the analyses. Numerical analyses were preformed with usage of Nastran software based on Finite Element Method. The FEM model of the engine body comprised over 800 thousand degree of freedom. Stiffness of the ship hull (mainly double bottom) with the foundation was modelled by a simple cuboid. Material properties of that cuboid were determined on the base of separately performed calculations

Ograniczenia modelowania na przykładzie analiz dynamiki wału korbowego

Analizowane zjawiska fizyczne należy upraszczać maksymalnie mocno, ale tak, żeby powstałe modele dawały poprawne przewidywania wyników eksperymentalnych. Naukowiec powinien jednak zdawać sobie sprawę z ograniczeń i zakresu stosowalności danego modelu. Inżynier nie może zapominać, że posługuje się tylko modelem rzeczywistości, który ma swoje ograniczenia - zakres stosowalności. W pracy przedstawiono analizy dynamiki układu tłokowo-korbowego silnika okrętowego ze szczególnym uwzględnieniem ruchu wału korbowego. W świetle współczesnych badań, świat fizyczny jest nieliniowy i dynamiczny w stanach dalekich od stanu równowagi. Jednakże większość problemów inżynierskich jest modelowanych liniowo, jako zjawiska statyczne bądź quasi-statyczne. Podejście to jest użyteczne i optymalne, ale nie można zapominać o ograniczeniach takich modeli. Wykazano, że pomimo przyjęcia ściśle deterministycznych oraz w pełni liniowych równań mechaniki, przewidywalność dokładnych parametrów ruchu jest ograniczona. Rozważono ruch prostego obiektu mechanicznego: obrót wału korbowego silnika. W rozważanym przypadku jest to wał korbowy 10-cylindrowego, okrętowego silnika wolnoobrotowego: 10K98 firmy MAN B&W. Założono, że znana jest z nieskończoną (!) dokładnością prędkość obrotowa wału, która jest dodatkowo niezmienna. Przyjęto, że również czas jest możliwy do wyznaczenia nieskończenie dokładnie. W takim przypadku względne położenie wykorbienia określa w pełni deterministyczna prosta zależność. W celu znajomości położenia danego wykorbienia w dowolnej chwili czasu musimy jeszcze znać warunki początkowe. Kąt obrotu w chwili t=0 wyznaczono niezwykle dokładnie, ale ze skończoną dokładnością. Wykazano, że po pewnym czasie położenie wykorbienia jest całkowicie niezdeterminowane. Co więcej, ruch układu tłokowo-korbowego charakteryzuje się naturalną zmiennością, nawet po pominięciu zmienności sił wymuszających. Wpływa to dodatkowo na ograniczenia modelowania rozważanego deterministycznego układu fizycznego

Calculation reliability of natural vibrations of ship hull and superstructure

The ship hull vibration has a great impact on the performance, safety of the devices, structures, and the sailor's comfort when working on the ship. With increases in ship sizes and speeds, shipboard vibration becomes a significant concern in the design and construction of ships. Therefore, designing a ship without any excessive vibration is an important issue and should be studied through analysis right in the design phase. To ensure minimum vibration in a proposed new design; avoid damage to structures, machinery or equipment (mechanically suitable); meeting the requirements of the crew's living environment and working conditions. The ship's natural vibrations are determined to right from the design stage, which will help ship designers and structures avoid dangerous resonance areas. In this study, a three-dimensional finite element model representing the entire ship hull, including the deckhouse and machinery propulsion system, has been developed using numerical modelling implemented in Patran-Nastran software for local and global vibration analyses of the container ship 2000 TEU. Vibration analyses have been conducted under two conditions: free– free (dry) and in-water (wet). The wet analysis has been implemented using Mfluid elements in Nastran software. Because of the global ship free vibration analysis, global natural frequencies and mode shapes have been determined. Combined with the frequency of the main engine and the propeller, the resonant regions with higher frequencies are determined by the resonant graph of the hull. The application of the finite element method for ship vibration analysis shows the optimal of numerical modelling method compared to other traditional methods. This will help other technical problems to be solved with the support of the finite element method

METHODS OF CRACKS DETECTION IN MARINE STRUCTURES' WELDED JOINTS BASED ON SIGNALS' TIME WAVEFORM ANALYSIS

The paper presents two methods of crack detection in ship hulls. The methods are dedicated for structural health monitoring (SHM) of responsible welded joints. The system will be based on vibrodiagnostic - signals will be measured by piezoelectric accelerometers and/or fibre optic sensors. In SHM systems of welded joints of thin-walled structures, a vibrodiagnostic method is the most promising. Its most important advantage is that it is both effective and relatively low costly. There are two general methods of vibrodiagnostic signal analysis: the most frequently used are spectrum analysis and time waveform analysis. The spectrum analysis concerns changes of natural frequency. In marine exploitation conditions, the frequencies changes might be imperceptible. The first method presented in the article is based on the evaluation of the mean value distribution of the amplitude spectrums calculated with the time window method. Second proposed method was based on the determination of damping decrement in function of time. Due to the complexity of the responses run, the proposed method consisted of calculating the damping decrement using the response approximation with different functions. It has been shown that the changes analysis of damping decrement applied to welded plates enables the assessment of the quality associated with the weld. A calculation algorithm as well as and the exemplary results from the proposed methods used for some selected samples with different type of welds are included in the paper. The results of the tests show that the analysis based on proposed methods indicates that they differ significantly depending on the welds, indicating their quality and cracks that are associated with them

Diagnostic benchmarks on dynamic characteristics of thin-walled marine damaged structures

Among structural health monitoring (SHM) methods of thin-walled structures, a vibrodiagnostic method is one of the most promising. The accelerometer recorded responses provide diagnostic information that requires mathematical processing to extract the essential dynamic characteristics. The authors have been looking for new parameters - diagnostic benchmarks which can be applied to non-destructive, automatic testing of thin-walled marine structures (especially their welded joints) like ship hulls. All characteristics have been based on recorded data generated during the vibration tests of welded joints with and without failures. For this purpose, the authors proposed method based on: FFT windowing analysis, benchmark with using 2D or 3D time – frequency dynamic characteristics and the determination of damping decrement in function of time. The work presents the algorithm and exemplary results obtained from the application of proposed method to several selected sample plates with different type of welds

Providing the Ability of Working Remotely on Local Company Server via VPN

Increasingly popular remote work requires the use of modern network technologies to provide employees in a remote location with access to the company’s IT resources. The answer to the needs of remote access to files and server services can be the use of clouds and VPS. However, this involves high costs and requires entrusting the enterprise’s data to the providers of these services. Both for reasons of data security and too high costs, enterprises sometimes cannot use these technologies. The solution to the problem may be the use of encrypted VPN tunneling, which allows the device to be connected at a remote location to the company’s local network and use its resources as if it was connected to the local network with physical transmission medium

Introduction to the examination of thin-walled structures using the vibrodiagnostic method

The article presents a methodology of non-destructive diagnostic vibratory tests of welded plates with geometrical parameters that classify them into a group of thin-walled panels. On the basis of such plates, most ship constructions are created. In previous works, the authors dealt with the study of welded joints in plates with significant thicknesses and developed for them a number of methods for assessing the quality of welded joints. Vibrodiagnostics is a NDT method that allows the use of a variety of techniques and tools. It enables measurements to be made in both a contact and non-contact way depending on the requirements of the structure and the environment. Vibrodiagnostic method is one of the most modern NDT methods, which uses modern measurement tools and computer analysis of data. On the basis of the developed methods, the authors intend to verify their application to plates from real welded constructions, which will be performed in typical shipyard conditions by welders. Such tests are important due to their use for the construction of a real SHM ship construction monitoring system. These methods allow for the examination of the condition of ships’ structural plates and can detect defects in welded joints that prevent ships from operating under severe sea conditions. The article presents the laboratory stand, the sensor layout, results, and their initial analysis

Modelling method of dynamic characteristics of marine thin-walled structure

Thin-walled structures are very popular in industries, especially in the field of shipbuilding. There are many types of equipment and structures of ships, which are made up of thin-walled structures such as hull, deck and superstructure. Therefore, the analysis and understanding of the static and dynamic characteristics of a thin-walled structure are very important. In this article, we focus on vibration analysis of a typical thin-walled structurerectangular plate, a basic structure of the hull. Vibration analysis of a rectangular thin plate is conducted by two methods: numerical modelling method of the finite element on Patran-Nastran software platform and experimental method implemented in the laboratory of Gdynia Maritime University. Thin rectangular plate is fixed one end by four clamping plates and is modelled with finite elements and different meshing densities. The numerical model of thin rectangular plate is divided into four cases. Case 1, thin rectangular plate, and clamping plates are modelled with two-dimensional elements. Case 2, the rectangular thin plate is modelled with two-dimensional elements; the clamping plates are modelled with three-dimensional elements. Case 3, both the rectangular thin plate and clamping plates are modelled with three-dimensional elements. Case 4, the rectangular thin plate, and clamping plates are modelled with three-dimensional elements with larger mesh density to increase the accuracy of the calculation results. After that, the results of vibration analysis according to the numerical modelling method on Patran-Nastran software platform for these cases were compared with the measurement results. From there, assess the accuracy of analysis results of selected numerical model methods and the ability to widely apply this numerical model method to other marine structure

Marine Propulsion System Failures—A Review

International audienceFailures of marine propulsion components or systems can lead to serious consequences for a vessel, cargo and the people onboard a ship. These consequences can be financial losses, delay in delivery time or a threat to safety of the people onboard. This is why it is necessary to learn about marine propulsion failures in order to prevent worst-case scenarios. This paper aims to provide a review of experimental, analytical and numerical methods used in the failure analysis of ship propulsion systems. In order to achieve that, the main causes and failure mechanisms are described and summarized. Commonly used experimental, numerical and analytical tools for failure analysis are given. Most indicative case studies of ship failures describe where the origin of failure lies in the ship propulsion failures (i.e., shaft lines, crankshaft, bearings, foundations). In order to learn from such failures, a holistic engineering approach is inevitable. This paper tries to give suggestions to improve existing design procedures with a goal of producing more reliable propulsion systems and taking care of operational conditions