Page 370 - Practical Design Ships and Floating Structures

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proposed concept, the prototype system is accessible through WWW-browser on Internet. To input a
detected crack damage into the system, the user selects the name of the ship and the name of the tank
(Figd (a)(b)). After the 3D structural model is shown in the browser by using VRML, the user walk
through in the 3D structural model to choose the location of the damage (Fig.4(c-l)(c-2)). After the
user choose the type of the damage (Fig.4(d)), the information of the damage can be input from the fill-
form as shown in Fig.4(e).

For the assessment of the crack damages stored in the database, we consider to evaluate the possibility
of unstable failure and fatigue life caused by the detected crack. In order to evaluate the stress intensity
factors (SIF), the calculation method is defined in the database depending on the crack geometry.
Necessary parameters for calculation are not only dimensions of crack and plates, but also the
information about the load. In this study, we assume that the finite element shell analysis is carried out
beforehand under a certain wave load, such as the load with excess probability @lo8 derived from
long-term prediction. And also it is assumed that the result of the analysis is stored in the FEM-objects
defined in the database (Kawamura et ai. 1998). For example, if the crack is a surface crack, the
probleni is assumed to be a plate with semi-elliptic center crack. By computing both tensile load and
bending load from stress information stored in FEM-objects, SIF by tensile load and SIF by bending
are calculated (Murakami et ul. 1987), and the total SIF is used for evaluation of unstable failure by
comparing it with fiacture toughness (&) stored in the Material-object. Next, fatigue life assessment is
carried out based on the Paris's law. In order to calculate the SIF range, equivalent effective stress
range (DNV 1984) is used. Then, the fatigue life is computed by the SIF range and the parameters (c, rn)
stored in a Material-object. Fig.4(f) shows an example of the evaluation for the crack damage.

As shown above, the interface to use the information system of damages can be developed on WWW
environment. It is possible to say that the proposed architecture of the information system is useful to
construct a system to support evaluation and management of damages of ship structures.

4 SHIP INSPECTION SUPPORTING SYSTEM BY USING A PORTABLE COMPUTER

4. I Concept of the Ship Inspection Supporting System
One of the important ship inspections is the close-up survey where a surveyor enters into tanks of the
ship and directly watch and search damages existed in the tank. In the present inspection, after a
surveyor enters into a tank, he looks around a place where damages likely to occur based on the survey
program or on his experiential knowledge. When the surveyor detects damages, he records the situation
of the damage. For example, the location of the damage may be recorded by writing down the tank
number, longitudinal number and fiame number into a memo pad. In a certain case, the damages may
be sketched in the memo pad or a photo is taken by using a digital still camera. After the inspection,
the detailed drawing of the damage is prepared from the recorded information, and the repair plan is
made based on them. The problems of the present close-up survey process can be considered as follows.
(1) The performance of the inspection such as the detectability of damages is highly dependent on the
knowledge and experience of the surveyor.
(2) Since there is no unified expression for damages detected in the inspection, it is difficult to utilize
the result of inspection efficiently and rationally.

In this study, we proposed a ship inspection supporting system by using a portable (wearable) computer
carried by the surveyor in the ship hull inspection in order to overcome the above problems. We
consider the following three items as the role of the system.
(1) Electronic manual, by which efficient inspection is possible by surveyors with a little experience.
(2) The inspection support by displaying the information about the history of the inspection and about