Identification of shaft line alignment with insufficient data availability
The paper presents a method of identification parameters of shaft line alignment in case of the lack of producers' data. Proper shaft line alignment is often a problem for repair shipyards, for aged ships without sufficient documentation. Author proposed combined experimental-analytical method for identified some existing parameters and checking (and eventually correcting) power transmission system's foundation. Specialised software has been developed for shaft line alignment calculations with influence coefficients. An example analysis has been performed for cargo ships with medium-speed main engine and second one with slow-speed propulsion system. Multivariant computations supported by measurements of the ships' shaft line have been carried out.
Stiffness characteristics and thermal deformations of the frame of high power marine engine
In the subject-matter literature detail data on stiffness of the crankshaft foundation connected with the frame of marine main engine are still lacking. Thermal deformation models of the engine's casing, proposed by engine producers, are excessively simplified. However the parameters are crucial for the shaft-line alignment analysis as well as for the analysis of interactions between the shaft-line and engine crankshaft, especially in the case of high power engines. This paper presents a determination method of the marine engine body characteristics as well as results of example computations performed for a Sulzer 7 RTA 84 C engine installed on a ~3000 TEU container ship. It has been demonstrated that the producer's assumption about parallel displacement of the crankshaft axis in thermal working conditions is too rough. The thermal deformation of the engine is of hogging character, which results in significant change of the moment load exerted on the crankshaft and shaft line. The stiffness parameters recommended by the producers for the shaft-line alignment are estimated correctly, however they represent only engine's body flexibility, without taking into account ship's hull flexibility.
The paper presents a comparative analysis of non-destructive testing methods used in the assessment of welded joints. The authors describe the methodology of conducting tests on welded plates using the vibration method. On the basis of the FFT analysis of responses from accelerometers, spectral characteristics were calculated, and then used along with statistical measures to develop a comparative method in non-destructive testing of welded joints. This method will make it possible to quickly and easily distinguish plates with non-defective welded joints from plates with faulty welds. The paper presents test results for a non-defective plate weld (sample no. 2202), a plate with defective edge fusion (sample no. 2127) and one with a cracking along the entire sample length (sample no. 2132). The article points out the limitations of the proposed method and the need for further research
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.