TS-118
Advanced Maintenance for Marine Diesel Engine Based on Structural and Functional Modeling
Masayoshi NUMANO*, Eiko ISHIMURA*, Sumito NISHIO*
ABSTRACT
Maintenance work for a propulsion engine system has been one of the most important ones onboard. Periodic inspection and repairs as a preventive maintenance are essential procedures to avoid onboard maintenance in case of occurrence of failures. As a propulsion engine system consists of a large number of components, it takes much labor and time to make a maintenance schedule and to do actual maintenance works. Maintenance data can be used as a basis of deterioration prediction of each component, therefore, accumulation of the data and statistical analysis of them are essential for the preventive maintenance.
We propose a structural modeling and a functional modeling as a container that accumulates those maintenance data and gives relations among them. The structural model has components and mechanical thermal and chemical relations among them. Initial definition of the model is given as a default one by a system designer. Initial relations are also set according to recommendations by the designer. Two types of soundness of each component can be considered each corresponding to wear and accumulation of damage. MTBF (Mean Time Between Failure) is used in the deterioration parameter. For example, the soundness index is linearly decreasing to the threshold in the time interval related to the corresponding MTBF. Once some relationship or mechanism has been found, the deterioration model can be improved according to the new knowledge.
Observation with various sensors and human inspections modifies the present states of the model and the running data are accumulated. This model can be used in searching causes of failures and in predicting damages induced by the failures. This model is also useful for making an appropriate maintenance schedule.
Key Words: Marine Engine. Maintenance, Functional Modeling, Soundness Index
1. INTRODUCTION
Maintenance work for a propulsion engine of ships is one of the most essential works onboard, especially for ocean-going ships. Most of the marine propulsion engines are diesel engines and they are all tailor-made while those for automobiles are ready-made. The maintenance work is, therefore, different for each engine. It gives much complexity to the maintenance work for marine engines. Engineers are engaged in daily maintenance works according to the maintenance schedule indicated by land operators, in addition to the ordinary engine operation itself.
On the other hand, operational expertise is quite restricted into few engineers, almost one, Chief Engineer. An effective support system for maintenance work to marine engines should be, therefore, developed and installed onboard. A macroscopic simulation using qualitative modeling of the engine has been proposed and discussed [1]. We add a concept of soundness to this methodology and introduce the new concept in this paper.
As the complete modeling is almost impossible, we adopt default model in the initial state and an improvement procedure through additions of a precise model one by one.
2. STRUCTURAL AND FUNCTIONAL MODELING
2.1 Definition of Elements and Relations
Various data for the engine maintenance can be properly dealt with in a structural and functional model of the target engine. Temperatures and pressures of gas, water, lubricant and fuel are measured with relevant sensors. Relevant elements of the target engine are defined for storing those data. An assembly of these elements makes a data container of the target engine. Time histories of various state variables of each element are contained in it and can be drawn out according to the specific view for detection of abnormal conditions or failures.
An onboard engine monitoring system gathers various engine monitoring data and throw them through onboard network. The structural model catches those data and stores them into appropriate elements as historical data. Relations among state variables of the elements make time changes in each state variable contained in each element and it can be easily simulated for diagnosis and future prediction. As available data for those state variables are quite restricted, rest of all state variables should be estimated through this simulation with defined relations and available state variables. A structural and functional modeling has been done by the definition of elements and relations among them.
Relations are classified into functional sub systems, such as an air intake system, an exhaust system, a fuel supplying system, a combustion system, a power transfer system, etc. Each relation has two faces; one is a microscopic relation like force interaction or exchange of substances, the other is a rather macroscopic one like wear or fatigue. These relations are used in simulations for estimation of the present state, prediction of future change or identification of causes of failures.
2.2 Default Status and Improvement
The definition of the structural and functional model should be constructed at the design stage step by step. Default status of the model also is defined then as a designed status. Elements and relations can be easily modified, replaced or added. Thus the model can be improved also step by step. The improvement can be provided by land support centers, e.g., shipping companies, engine manufacturers, etc.
3. INTERACTION AMONG ELEMENTS OF MODEL
3.1 Initial State
To use the structural and functional model for the maintenance work, variables of each element and relations should be properly initialized. The initialization process should be done during test runs before an actual commission.
* Ship Research Institute
6-38-1, Shinkawa, Mitaka, Tokyo 181-0004, Japan
FAX: +81 422 41 3126, E-mail: numano@srimot.go.jp
