Michio Horigome

Paper: A new ship's auto pilot design through a stochastic model

A new type of ships autopilot system is designed by a statistical approach. A ships motion at sea is described by a multi-variable autoregressive model using minimum AIC (Akaikes Information Criterion) procedure. Through the fitted model, the ships behavior is analyzed and an optimal control law for a ship under a newly introduced criterion function is derived. The feasibility of our control system is checked by both digital and hybrid simulations. The results of the simulation show that with our controller the yaw motion is depressed through smoother and less rudder motion than that of the conventional autopilot systems and the ill effect of rolling is avoided. It is expected that the controller has another merit: it is quite robust for possible changes of external environments. Finally, a successful result of an actual sea test is briefly discussed. Thus, the possibility of realizing an entirely new autopilot system by a stochastic model is demonstrated.

Quantification of sequential failure logic for fault tree analysis

Abstract Fault tree analysis (FTA) is generally accepted as an efficient method for analyzing system failures. It is well known that a fault tree (FT) is equivalent to a minimal cut set fault tree with all minimal cut-AND structures. The minimal cut-AND structure is an AND conjunction of an output and all inputs that compose a minimal cut set. For the structure, the failed state of the output becomes true when all failed states of inputs exist simultaneously. There are cases where the output of the minimal cut-AND structure depends not only on all failed states of inputs but also on the sequence of occurrences of those failures. This sequential failure logic (SFL) is equivalently expressed with Priority-AND gates in FTA, where inputs to the gates have constant failure and repair rates. A probabilistic model for analysis of SFL was proposed and equations with multiple integration for arbitrary number of inputs were derived from the model. However, it is usually difficult to solve the multiple integration when the number of inputs exceeds a certain range. This paper presents analytical solutions of the probability that the output is in a failed state at time t and the statistically expected number of failures of the output per unit time at time t for the special case where inputs are characterized by common failure and repair rates. In addition, the analysis of FT involving SFL is demonstrated by means of software Mathematica.

Statistical Analysis of the Maintenance of Field Date on Gantry Crane Wire Ropes

Though a gantry crane (GC) is indispensable for loading and unloading cargo on to a ship, there have almost never been reported about its characteristics of reliability and maintainability from the practical and statistical viewpoint. Therefore, the object of this paper is to make clear the relationships among the method, policy and reasons of replacement of wire rope which is the most important part in GC. We pick up the data of the wire rope from many parts which compose GC and then analyze its maintenance data through the Weibull probability paper and Weibull type of the cumulative hazard paper. First we discuss the outline of maintenance method of the wire rope based on the theoretical equations and next propose newly the statistical analysis of the data gathered from the maintenance field. Finally, we show that the results obtained here have very useful information about the relationship between the maintenance method and the cumulative number of cargo dealt with GC.

Maintenance Assessment Based on Success Ratio in Deterioration Diagnosis

It is well known any preventive maintenance method is not always useful in cases where system failures roughly follow the exponential distribution. In order to overcome this weakness, the monitoring maintenance was introduced recently and attracted the attention of the engineers as one of the most effective methods to prevent a system from defects and failures. The present authors, Horigome and I, lately introduced the success ratio of fault diagnosis they investigated the characteristics of the preventive maintenance from the viewpoints of the reliability improvement ratio, the maintenance cost and the maintenance numbers. In this case, it is assumed that the system failure occurs through some malfunction, and follows to an exponential distribution. Then the newly obtained results are discussed. Finally it is shown that they are very useful for analysis or investigation on the maintenance in the field.

A Proposal of Availability Modle and its Applications

There are two distinct types of maintenance action, namely preventive one and corrective one. Preventive maintenance is performed at regular time intervals and can contribute significantly towards the increase of reliability and availability. It must be scheduled carefully in order that the availability is maximized through optimizing regular interval. On the other hand, corrective maintenance is performed when the system fails, and so the occurrence of corrective maintenance action is a random. From these considerations, it is clear that time is the most important factor in maintainability, and therefore, we classify maintenance data into two groups, ie, scheduled maintenance data and unscheduled maintenance one. Next, based on these classified data, we propose the new availability model which modifies Policy II given by R. Barlow and L. Hunter. Finally, we show the usefulness of the new model proposed here by applying these theoretical results to real data of the marine propulsion system.

Instrumentation System of Trainning Ship “Shiojimaru” and Its Actual Results

In this paper we describe the outline of an instrumentation system installed in“Shiojimaru”built for Tokyo University of Mercantile Marine as the trainning ship in 1987, and its actual ship test results over past two years. First we give the concepts and construction of the system for instrumentation which are classified into two groups; one group is a system for ordinary navigation and another is for study and development of the ship and its system. Next, in order to show an composed control system concretely, we pick up the engine speed control system as an example from various control systems and then illustrate the new system composed of computers, electronic devices, local area network (LAN) system and so on. Finally, we show our experimental results obtained by actual ship tests, for example, the results of the main engine speed and the Z test controlled by a direct digital control (DDC) .