An expert system for aided design of ship systems automation

Zbigniew Kowalskia,*, Ryszard Arendta, Maria Meler-Kapciab, Stefan ZielnÂskib

aFaculty of Electrical and Control Engineering, Technical University of Gdansk, ul. Narutowicza 11/12, 80-952 Gdansk, PolandbFaculty of Ocean Engineering and Ship Technology, Technical University of Gdansk, ul. Narutowicza 11/12, 80-952 Gdansk, Poland

Abstract

The paper presents a structure and functions of an expert system for aided design of ship systems automation. The system was developed

on basis of a detailed analysis of the design process of ship systems automation. The system includes: knowledge bases regarding methods

and procedures of ship systems automation design, databases of automated objects, control devices and elements, requirements of classi®ca-

tion societies, and a subsystem for simulation investigations co-operating with the Matlab Simulink package and a knowledge base. In the

creation of the system the shell expert system Exsys Developer was used. This system is characterised by a rule-oriented representation of

knowledge, backward and forward chaining inference methods, various con®dence modes to handle uncertain reasoning including fuzzy

logic, and possibility of co-operation with other software and databases. The databases were made using the MS Access software. q 2001

Elsevier Science Ltd. All rights reserved.

Keywords: Expert systems; Knowledge engineering; Design ship automation; Simulation investigation

1. Introduction

Increasing competition, the drop in the price of ships, and

high rates of interest have forced shipyards to make consid-

erable reductions in ship design and building cycles. It is

essential to use the latest information technology (Bertram,

2000), especially with regard to ship's automation design

process, which is realised in the ®nal stage of the ship's

design, based on very wide range of information. For this

reason, within a research project, on the Faculty of Electri-

cal and Control Engineering at the Technical University of

Gdansk, with co-operation of an interdisciplinary team, an

attempt to use arti®cial intelligence methods in a system

with knowledge base for ship power system automation

design was made.

Working out a laboratory implementation of the system

required a series of research works, especially: detailed

analysis and description of the designing process of ship

systems automation, creation databases and knowledge

bases regarding this process and designing and starting-up

of a complex, multifunction computer system to be

performed (Kowalski, Arendt & Zielinski, 1999; Kowalski,

Arendt, Zielinski & Meler-Kapcia, 2000). Within the

project, speci®city of design of ship systems automation

(preliminary design, commission project, technical project)

with ranges of demanded documentation by classi®cation

societies, shipping companies and shipyards were estab-

lished. A database of equipment, elements and systems

automation of ship and requirements of classi®cation socie-

ties was developed using MS Access software. It contains

information on automation objects and systems on ships

already built and catalogue information regarding control

elements. The design of ship systems automation is based,

to a large degree, on applying information in the design of

systems automation on ships already built. For this purpose,

an algorithm determining the similarity of the ship that is

being designed to particular ships stored in the database was

elaborated.

The shell expert system Exsys Developer was used in the

creation of the system. This software is characterised by a rule-

oriented representation of knowledge, backward and forward

chaining inference methods, various con®dence modes to

handle uncertain reasoning including fuzzy logic, and possi-

bility of co-operation with other software and databases

(Mulawka, 1996; Multilogic Exsys Developer, 1999).

The subsystem for simulation investigations co-operating

with the Matlab Simulink package containing a library of

models of selected control objects and systems was accom-

plished as well (Arendt, 2000; Arendt & Kowalski, 1999).

This subsystem co-operates with a knowledge base and

enables quick evaluation of correctness of the assumed

design solutions of control and on adjustment of designed

systems.

Expert Systems with Applications 20 (2001) 261±266PERGAMON

Expert Systemswith Applications

0957-4174/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.

PII: S0957-4174(00)00064-6

www.elsevier.com/locate/eswa

* Corresponding author. Tel.: 148-58-347-2811; fax: 148-58-347-2487.

E-mail address: zkowal@ely.pg.gda.pl (Z. Kowalski).

2. Functions of the system

On a basis of detailed analysis of the design process of

ship systems automation and the knowledge acquisition

results (Gavrilova & Chervinskaya, 1992), problems were

selected, for which aiding utility software was made, using

the Exsys Developer expert system, Access database and

Matlab/Simulink package. Apart from its traditional role

of supplying information, the database system performs

the role of the supplementing functions of the expert system.

Some of these functions, i.e. making the technical speci®ca-

tion, calculation of similarity between ships, calculation of

costs of automation, or creation of technical conditions

necessary for systems automation, are performed in co-

operation of the database with the Exsys Developer system,

while others by the database system itself.

The functions of the system include:

² gathering and sharing of numerical, text and graphic

information regarding ships already built and catalogue

information about elements and control systems;

² searching in the database for the most similar shipÐfrom

the point of view of automationÐto the one being

designed (information regarding this ship may be applied

while performing other tasks);

² making the technical speci®cation of engine room auto-

mation and general ship systems;

² evaluation of the costs of ship automation during the

stage of preliminary design;

² selection of checking and measurement equipment;

² making block diagrams and function diagrams of systems

automation;

² access to database containing rules of selected classi®ca-

tion societies;

² creation of technical conditions for enquiries for main

control systems;

² making other documents in the form of result reports

during the process of ship systems automation design;

and

² checking the project solutions through simulation inves-

tigations, based on the library of mathematical models of

main engine room units and systems.

A general outline of the system realisation is shown in Fig. 1.

2.1. Searching for the most similar ship to the one being

designed

In the performance of many functions of the expert

system for the design of ship system automation requires

the use of information stored in database of ships already

built. For this purpose, an algorithm was created, which

applies an approach called case-based reasoning (Kowalski,

Meler-Kapcia & Zielinski, 2000; Lee & Lee, 1999), where

ships already built described by information stored in the

database are treated as the similar cases. The algorithm uses

some parameters characterising considered ships. Similari-

ties of examined parameters are calculated in the following

areas: general data; main propulsion; power station; and

selected installations. For these areas, partial similarities

are calculated. The weighted sum of these similarities quan-

ti®es the similarity of the entire ship. Depending on the type

of these parameters, one of the following similarity calcula-

tion methods was assumed.

A test of exact likeness is used with regard to text and

numerical parameters, such as: type of ship; classi®cation

society; class of automation; type of main engine; type and

number of propellers; number of gears; type of main power

generating unit; number and type of auxiliary power gener-

ating units; and type of shaft power generator. The values of

these parameters stored in the database are compared with

the values of appropriate parameters of ships already built.

Z. Kowalski et al. / Expert Systems with Applications 20 (2001) 261±266262

Fig. 1. General outline of the system realisation.

If these values are identical, then 1 is entered in the appro-

priate table, if dissimilar, 0 is entered.

Symmetrical similarity with lower bound is applied with

regard to numerical parameters with greater ranges of values

such as: number of main engines, number of main power

generating units and parameters of chosen installations. In

this method, similarity of a chosen parameter is determined

in accordance with the relation:

S�p� � 1 2up1 2 p2u

max{p1; p2} 2 pd

where: p1 is the value of the parameter of the ship being

designed, p2 is the value of the same parameter of the ship

already built and pd is the lower bound of parameter value.

Fuzzy logic is used for numerical parameters like: displa-

cement of the ship, number of refrigerated containers, power

and rpm of main engine and power generating units and the

number of valves of chosen installations. This method

allows to determine the degree of similarity for any number

of parameters simultaneously.

The similarities calculated in the database system are

passed to Exsys expert system, where they are fuzzi®ed

together with the parameters whose similarity is directly

calculated using fuzzy logic. The whole calculation process

is repeated for each ship built which is stored in the data-

base. After similarity calculations have been performed, in

Exsys system, the maximum partial similarities are passed

to the database, via text ®le, together with identi®cation tags

of corresponding ships, and maximum of total similarity of

the ship. On their basis, the database system searches for

similar ship data.

2.2. Technical speci®cation of the automation

This is a basic document determining the range of auto-

mation and is the basis for further design work. After a close

analysis of many variants of the projects, a so-called stan-

dard form of technical speci®cation of ship engine room

automation systems was de®ned, which was assumed as a

basis for creating a prototype expert system. The system

involves two variants of making technical speci®cations:

² based on user replies attached to the speci®cation

templateÐmade completely by Exsys Developer, from

where appropriate data are passed to the database table of

speci®cations of ships already built;

² through utilisation of information regarding similar

shipsÐperformed as an application of the Access data-

base system, from where data forming the technical

speci®cation are passed to Exsys system in order for a

speci®cation report to be made.

Exsys system allows to make speci®cations in the form of a

report generated after inference process has been completed.

The inference process is performed in accordance with the

production rules stored in the knowledge base. The rules

determine which replaceable elements are to be contained

in the report (technical speci®cation) depending on the input

information (data). A general diagram of realisation of this

function is presented in Fig. 2.

A complete set of input data, for the approved design

(speci®cation) is always passed to the database of ships

already built. Co-operation and constant exchange of infor-

mation between the expert system and database via text ®les

is, therefore, necessary.

Costs of the automation systems are evaluated and tech-

nical conditions for system automation equipment are

created on the basis of results obtained during creation of

the technical speci®cations. For the cost evaluation the auto-

matic equipment is divided into some groups of devices.

Each member of this group is described by some technical

parameters, which are included in the technical description.

It is assumed, that for each group the standard cost of device

(element) is known and is connected with given values of

parameters. For the designed ship, the cost of a given group

is evaluated by correction of the standard costs using coef®-

cients depending on the differences between values of

chosen parameters. An in¯ation ratio is also taken into

account. For more important devices the standard costs

can be prepared with consideration of some distributors of

automatic equipment.

2.3. Gathering and sharing of information regarding ship

systems automation

The database contains data regarding objects and

systems, as well as devices and elements of automation

taken from catalogues or used on ships already built. This

information can be searched in various cross-sections and

may treat: systems and elements of automation used in ships

already built; block and function diagrams of chosen

systems; elements and systems of automation from catalo-

gues (together with information regarding the distributors

and prices, as well as graphics of selected systems); systems

automation and functions performed by them; and the

degree of similarity of the ship being designed to ships

Z. Kowalski et al. / Expert Systems with Applications 20 (2001) 261±266 263

Fig. 2. A general diagram of the generation of technical speci®cations.

already built according to the chosen parameters as a basic

technical characteristic.

2.4. Selection of checking and measuring apparatus

This consists of choosing elements' control in the form of

sensors for particular checking and measurement points.

This selection may be done in various ways:

² by the designer himself or herself, on the basis of the

structure of checking and measurement points according

to suppliers and their catalogues of control elements;

² using the base project of a built ship matched automati-

cally or chosen by designer; and

² by adding on individual systems or objects of different

ships already built.

2.5. Making block and function diagrams

In the database of the developed system, there has been

provided the possibility to refer to a graphic module work-

ing in an AutoCAD system environment. These references

may treat ready-made diagrams of systems on ships already

built or they may treat the system currently under design

after selection of elements in the database has been done. A

library of graphic elements, standard diagrams and screen

tools was prepared in an AutoCAD system. Block and func-

tion diagrams, apart from being part of the technical

speci®cations, belong also to fundamental documents of

engine room automation design. They are created in strict

connection with diagrams developed in the other parts of

design of®ce.

2.6. Using the database of classi®cation societies rules

The database of rules of selected classi®cation societies is

meant for storing and making available information regard-

ing the rules of these societies. The main task of this system

is to make investigation of these issues convenient and ef®-

cient. For this purpose, a list of rules is generated, and on

request, their contents may be displayed. A supplementary

function of the system is a selection of equipment suppliers

that have certi®cates of these societies for the chosen equip-

ment. The database has a built-in web browser for ®les

saved in HTML format. Rules may be searched according

to the systems they have been applied in, or by key words,

e.g. power plant.

2.7. Making other result documents

After the designer's job is ®nished, or at any other stage,

it is possible to generate reports of major documents made

in the ship automation design process. Among these reports

are:

² statement of checking and measurement apparatus

including checking and measurement points with control

elements matched;

² block and function diagrams of particular engine room

systems;

² materials statement of sensors informing about their

parameters for particular points within the control

systems;

² an input/output list containing a statement of binary input

and output and analogue input;

² a list of suppliersÐchosen for possible delivery of auto-

mation elements and assemblies; and

² technical conditions for automation assemblies and

enquiries.

2.8. Simulation investigations of the ship's power subsystem

This is made possible by an application developed for the

Exsys expert system (Arendt & Kowalski, 1999). It is

assumed that application of mathematical models of the

ship's elements, units and systems may be a source of

deep knowledge in the expert system. The application

includes the option of entering data in dialogue mode by

the power subsystem designer. The program asks, in turn

about:

² the number of particular types of component elements of

the subsystem;

² the names of the elements used; and

² subsequent elements converting power, from ®rst to

last.

The collected data are stored in a frame and displayed

on screen during a session so that the designer can

con®rm their correctness.

Knowledge developed in the form of production rules is

used for evaluating the correctness of a project and all

collected data. The rules evaluating the correctness of the

project show whether the accepted goal has been reached,

for the assumed con®dence of the statement. Depending on

the goal indicated by the rules and the degree of its con®-

dence, the rules determine the further work of the program.

The following cases are possible:

² the collected data are incomplete, badly matched, or a

designed subsystem has an unacceptable structure;

² the collected data indicate a non-typical structure of the

designed power subsystem; and

² the entered data are correct and complete.

In the ®rst case, the designer may ®nish the work of the

program or start anew, collecting data characterising the

designed power subsystem. In the second case he or she

can start anew, collecting data or switch on to a simulation

session. In the third case, the program may proceed to a

simulation session without operator interference.

The data describing the elements and structure of the

designed subsystem collected in the frame are the base for

Z. Kowalski et al. / Expert Systems with Applications 20 (2001) 261±266264

the speci®cations of the simulation model. For this purpose,

an M-®le of the Matlab/Simulink simulation program is

created by:

² subsequent adding of M-®les from the library with speci-

®cations of models of component elements to the M-®le

of the simulation model of the designed power subsys-

tem;

² adding the parameters of the graphic image of the simu-

lation model of the designed power subsystem, de®ned

using production rules.

Algorithms for creating simulation models of the designed

subsystems also apply knowledge collected in the form of

production rules.

After the ®le podsyst.m is completed with the simulation

model of the designed power subsystem, the Matlab

program is run. Next, the procedure Startup.m automatically

runs the Simulink program with the model, displaying a

graphic image of the simulation model of the designed

power subsystem.

The propulsion subsystem of a ship composed of two

Diesel engines working parallel through clutches to a

moment stackup gear, propeller shaft to a ®xed pitch propel-

ler has been presented as an example. After the data have

been entered, the expert system creates the simulation

model (Fig. 3). During the simulation session, the designer

gains, from the investigations, the knowledge necessary to

assess the completed project.

3. Summary

The process of designing systems automation is complex

and dif®cult to formalise, and furthermore, it requires

processing large amounts of data. As a result, in order to

aid this process, such tools were accepted as: an expert

system and database which would enable a structuralisation

of designing knowledge and collecting broad sets of data.

The developing of the system was preceded by a detailed

analysis of the design process, conducted in close co-opera-

tion with automation designers as experts on whose experi-

ence and intuition hitherto ship automation design has been

based.

The application thus createdÐ system consisting of a

database of ship automation and engine room elements

and devicesÐis a convenient and user-friendly tool aiding

the process of automation design in the most time-consum-

ing and laborious areas, such as designing checking and

measurement apparatus. This application was made on the

basis of MS Access system and may work both on its own

(within a narrower range) and in co-operation with the

Exsys expert system.

A feature of the system is the possibility to use data on

ships already built; however, incorporation of such data into

the database is dif®cult, as data has to be converted in order

to be compatible with the system structure. As new ships are

built, the database of these ships will be successively

expanded.

The developed application simulation investigation

makes it possible to run very effective simulations of the

designed systems. The process of acquiring data describing

the designed power subsystem and automatic transition to

an investigations session takes only a few minutes. The

investigations allow for an assessment of basic technical

requirements regarding transient processes taking place

during start-up, shut-down, change of parameters of the

subsystem, as well as the appearance of factors disturbing

the system's operation.

The development of an option is being considered, where

the simulation investigation process and evaluation of the

results would be fully controlled by the expert system.

Acknowledgements

The authors are grateful to Professor W. Traczyk from

Warsaw University of Technology and Professor T. Gavri-

lova from St. Petersburg State Technical University, for

valuable discussions and suggestions during the develop-

ment of the presented system. This research was supported

by the Scienti®c Research Committee under grant No.

8T11A00813.

Z. Kowalski et al. / Expert Systems with Applications 20 (2001) 261±266 265

Fig. 3. The structure of a simulation model of a designed propulsion subsystem.

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