In June 1998, two of our vessels were increasing speed during the maneuvering speed range following departure from port, when an unusual vibration occurred in the high pressure turbine resulting in the deformation of the rotor. It is generally accepted that a sufficient warming-up period for the main steam turbine engine in the start and speed up phases will help to avoid any unusual vibrations. However, turbine manufacturers have not issued any specific guidelines for warming-up procedures or completion of the warming-up operation. The main turbine engines currently installed on board vessels put in service have no devices to monitor turbine casing temperature or expansion to help indicate when sufficient warm-up has taken place. This investigation had the objective of establishing more precise guidelines for the warming-up of main steam turbine engines, in order to prevent vibration-induced damage when sailing out from ports. The results of this investigation are based on data gathered from simple thermometers and expansion measuring devices installed on turbine casings, which measured the thermal changes in high pressure turbines as propulsion engines were used in port depar-ture.
The objective of this study is to evaluate sliding wear resistance of anticorrosive Ni and Cr base electroplatings and Ni-P electroless plating in seawater. Sliding wear tests against Al2O3 and bearing steel (SUJ2) were carried out in artificial seawater using an electrochemical potentiostat. Friction and wear were measured, and the wear track and the corrosion products at the contact were analyzed by SEM and ESCA. As the results, the corrosive wear of the platings is affected by material properties of the counterface. Under the electrode and catholic potentials for practical use, Ni base platings show more superior corrosive wear resistance than Cr base platings sliding against Al2O3. In the case of the counterface of SUJ2, the corrosive wear hardly occurs on the platings except for Ni-P electroless plating. Main factors of the surface damage within this experimental condition are anticorrosion of the platings and adhesion between the platings and the counterface.
Large eddy simulation (LES) of turbulent premixed combustion is carried out in the present study. A flamelet model based on the G-equation is used as a combustion model of premixed flames. In the context of LES, the turbulent burning velocity (ST) is required to obtain a closed form of the G-equation. Unfortunately, the turbulent burning velocity is not a well-defined quantity and the scatter of experimental data is very large, so that no universal model is available for ST. Hence, two models of ST, which are considered to be the most standard at present, are compared to investigate their influence on the configuration of the premixed flames through LES. In addition to the lack of its predictability, ST is generally modeled by experimental fits of the mean turbulent burning velocity in Reynolds aver-aging context. In conducting LES, the root-mean-square velocity fluctuation must be replaced with the subgrid-scale (SGS) velocity fluctuation, which has close relation to a SGS model for turbulent motion. Therefore, we also examine the influence of two SGS models on the flame configuration. The SGS models to be compared here are the Smagorinsky model and the structure-function model. To carry out the numerical investigation, we consider a simple model combustor with a cylindrical premixer and a rectangular combustion chamber, where a simple premixed hydrogen-air jet flame is stabilized in a backward-facing step without swirling. Through the present LES, it is shown that the numerically predicted configuration of the premixed flame depends strongly upon the model equations of the turbulent burning velocity and upon the SGS models for turbulence.