Improvement of ship design practice using a 3D CAD model of a hull structure

Robotics and Computer-Integrated Manufacturing 24(2008)105–124

Improvement of ship design practice using a 3D CAD

model of a hull structure

Myung-Il Roh a,?,Kyu-Yeul Lee b ,Woo-Young Choi c ,Seong-Jin Yoo d

Department of the Naval Architecture and Ocean Engineering,Seoul National University,Shinlim-Dong,Seoul,151-742,Republic of Korea b

Department of the Naval Architecture and Ocean Engineering,and Research Institute of Marine Systems Engineering,Seoul National University,

Shinlim-Dong,Seoul,151-742,Republic of Korea

Department of the Naval Architecture and Ocean Engineering,Seoul National University,Shinlim-Dong,Seoul,151-742,Republic of Korea d

Department of the Naval Architecture and Ocean Engineering,Seoul National University,Shinlim-Dong,Seoul,151-742,Republic of Korea

Received 15December 2005;received in revised form 18May 2006;accepted 25July 2006

Abstract

At the initial stage of ship design,a hull structural model,that is,a 3D CAD model of a hull structure is not generated by the existing shipbuilding CAD system because it is time-consuming and requires much effort.Without the hull structural model,a designer must manually calculate the production material information of a building block by using 2D drawings,parent ship data,and design experiences at the initial planning and scheduling stages.At the initial stage of hull structural analysis,the designer manually generates a structural analysis model,that is,a ?nite element model of the hull structure.Moreover,the piping model,that is a 3D CAD model of the pipes in the hull structure,is generated independently of the hull structural model at the detailed design stage.To lighten the burden imposed on the designer,we developed an initial hull structural modeling system in our previous https://www.360docs.net/doc/e44040290.html,ing this system,a designer can rapidly and easily generate the hull structural model at the initial stage of design.In this study,the generation methods of the production material information of a building block,the structural analysis model,and the piping model based on the hull structural model are developed.The applicability of the developed methods are demonstrated by applying them to a deadweight 300,000ton very large crude oil carrier (VLCC).The results show that the developed methods can quickly generate the corresponding information or models at the initial design stage.

Keywords:Hull structural model;Production material information;Structural analysis model;Piping model;Ship design

1.Introduction

1.1.Ship production process

A ship is a huge structure made up of a large number of hull structural parts.Here,a hull structure represents the body of the ship,and a hull structural part represents a part that is placed on the hull structure to secure the structural strength of the ship.A deadweight 300,000ton very large crude oil carrier (hereafter simply referred to as

the ‘300K VLCC’)has a length,breadth,and depth of about 320,60and 30m,respectively.Thus,unlike an automobile,a ship cannot be constructed all at once.The ship is ?rst divided into a number of building blocks (e.g.about 200building blocks in the case of the 300K VLCC).Here,a building block is a unit production element of a ship.Each building block is assembled in the assembly shop near the https://www.360docs.net/doc/e44040290.html,rge building blocks called erection blocks are made by joining several building blocks together.Then,the large building blocks are moved onto the dock and welded to each other according to a suitable sequence,called the block erection,to complete the ?nal assembly of the ship.Essentially,the construction process of a ship is similar to that of a large product by use of Lego blocks.

https://www.360docs.net/doc/e44040290.html,/locate/rcim

?Corresponding author.Tel.:+8228808378;fax:+8228864920.

E-mail addresses:myungil.roh@https://www.360docs.net/doc/e44040290.html, (M.-I.Roh),

kylee@snu.ac.kr (K.-Y.Lee),wychoi7@snu.ac.kr (W.-Y.Choi),sjyoo81@snu.ac.kr (S.-J.Yoo).

1.2.Background of this study

At the initial stage of planning and scheduling,the designer of a shipbuilding company normally determines the work sequences and methods,necessary resources,work duration,etc.based on existing enterprise resources.To perform these tasks,the designer needs the production material information of the ship to be constructed.The production material information includes the weight,center of gravity,painting area,joint length for welding,etc.Basically,this information for the building block units can be regarded as given at these stages.Presently,designers manually calculate such information,as shown in Fig.1,by using 2D drawings,parent ship data,and design experiences.Thus,the accuracy and reliability of the calculated information are quite low.This calculation is possible only if the data of the parent ships are available,and it is very dif?cult to perform such calculation for building an entirely new ship where no previous data exist.

At the initial stage of hull structural analysis,a designer performs a structural analysis to meet the increasing request of ship owners and ship classi?cation societies for ?nite element analysis.This task generally consists of three sub tasks:pre-processing,solving,and pros-processing task.In the pre-processing task,a designer generates a structural analysis model,that is,a ?nite element model of the hull structure.Presently,designers generate such a model manually by using 2D drawings and design experiences,as shown in Fig.2.Several tens of days are required to generate the model.In the past,the solving task,the second subtask,requires the most time in the structural analysis.However,advanced computers have

reduced the time required for the solving task in ?nite element analysis.Thus,the pre-processing time required to generate the structural analysis model is longer than the solving time.

At the initial stage of piping design,a designer generates a pipe and instrument diagram (P&ID).This diagram shows how a number of pipes are connected between equipments such as the main engine,generator,etc.Then,at the stage of detailed piping design,the designer generates a piping model,that is,a 3D CAD model of pipes in the hull structure,by 3D modeling,as shown in Fig.3.However,the piping model is generated independently of the hull structural model;thus,the changes in the hull structural model do not affect the piping model and vice versa.

If a hull structural model,that is,a 3D CAD model of the hull structure,can be generated at the initial design stage,the production material information of a building block can be accurately generated by dividing the hull structural model into a number of building blocks (‘block division’),the structural analysis model can be rapidly generated by applying an automatic mesh generation algorithm to the hull structural model,and the piping model can be generated faster than usual by considering the hull structural model.1.3.Related works

Many shipbuilding companies are now attempting to perform hull structural modeling and generate the hull structural model at the initial design stage.Although many shipbuilding CAD systems such as the TRIBON [1],IntelliShip [2],NUPAS-CADMATIC [3],FORAN [4],etc.are available,there is yet a CAD system supporting the

Block division drawing

Manual generation of the production material

information

weight

center of gravity painting area

joint length for welding …

Input information for the block division

2D drawings Data of parent ships Design experiences

…Manual calculation

Fig.1.Existing procedure of manually generating the production material information at the initial stage of planning and scheduling.

Manual generation of

nodes

2D drawing

Manual generation of

elements

Manual input of attributes of each

element

material thickness …

Structural analysis model

(finite element model of the hull structure)

Fig.2.Existing procedure of manually generating the structural analysis model at the initial stage of hull structural analysis.

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initial design stage where design changes arise very frequently.Thus,such systems cannot provide a hull structural model,which is required to generate the production material information and the structural analy-sis model and which must be referenced by the piping model,to a designer at the initial design stage.For solving this problem,an initial hull structural modeling system was developed in our previous study [5].Using the system,the designer can rapidly and easily generate the hull structural model at the initial design stage.Readers can ?nd more details about the developed system in Ref.[5].

Existing systems like the TRIBON and IntelliShip can generate some of the production material information such as the weight and center of gravity of a building block.They cannot generate the information such as the joint length for welding,which can be generated from the relationship between hull structural parts.Moreover,the information such as the weight and center of gravity of a building block can be generated only after ?nishing a 3D modeling of a hull structure at the detailed or production design stage.Lee [6]performed modeling of a bulk carrier by using the VDS system of the Intergraph,and then generated the limited production material information of a building block such as the weight,center of gravity,and painting area after performing the block division.Lee et al.[7]proposed an initial hull structural modeling https://www.360docs.net/doc/e44040290.html,ing the system,it was possible to generate the hull structural model and the limited production material information of a building block such as the weight,center of gravity,and painting area at the initial design stage.However,this system could only perform modeling of a VLCC.Moreover,the proposed data structure cannot represent the relationship between hull structural parts.Thus,the joint length of a building block could not be generated.

The generation of the structural analysis model at the initial design stage has been the focus of studies in practical engineering ?elds as well as academic ?elds.Most academic researches [8–13]have studied only the single-type ship,that is,one type of ships such as the VLCC,bulk carrier,container ship,lique?ed natural gas (LNG)carrier,etc.In these researches,a model of not the whole hull structure but the midship region,that is,the center region of the hull structure was generated.Then,an automatic mesh genera-tion algorithm in the commercial structural analysis

program such as the ANSYS,PATRAN/NASTRAN,etc was used.As practical engineering researches,Kim et al.[14]generated the structural analysis model using simple information about a ship such as the hull form and ship compartment information.Their research has a simple but robust algorithm.However,the algorithm can generate the structural analysis model of a hull structure having only longitudinal hull structural parts.Jang et al.[15]generated the structural analysis model,using 2D drawings in IGES format.They developed an automatic mesh generation algorithm,which re?ects on design practice and is based on the commercial pre-processing program (PATRAN).How-ever,a designer must carry out a tedious pre-task before executing the algorithm.For example,the designer must delete all symbols and texts except geometric information in the 2D drawings beforehand.

Existing systems like the TRIBON and IntelliShip can support piping modeling as well as hull structural https://www.360docs.net/doc/e44040290.html,ing these systems,a designer can generate the hull structural model and the piping model,simultaneously but independently.That is,in piping modeling,the hull structural model is used only as a background model.Thus,the changes in the hull structural model cannot affect the piping model and vice versa,even with design changes.Academic researches [16–19]related to the generation of the piping model have been studied as well.These researches have focused on the generation of the optimal route of pipes,and however they were not of practical use for generating the piping model in shipbuilding companies.Many of the systems and researches that have been performed have limitations,as mentioned above.To overcome these limitations,we developed new methods for generating the production material information of a building block,the structural analysis model,and the piping model based on the hull structural model,respec-tively.

2.Hull structural model considering the relationship between hull structural parts

2.1.Generation of the hull structural model

At the initial design stage,a function-oriented product de?nition process,which is focused on functions such as

Manual generation of

the pipe and instrument diagram

Initial piping design stage

Manual generation of the 3D piping model

No relation!

Detailed piping design stage

Production piping design stage

Manual generation of 2D drawings for production

Pipe piece drawing

Pipe installation drawing

Fig.3.Existing procedure of generating the piping model at the initial,detailed,and production stages of piping design.

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the arrangement,rough de?nition of the shape,and determination of the dimension of the hull structural parts,is necessary to calculate the structural strength and the estimated production cost,and to satisfy rules and regulations.In contrast,at the production design stage,production drawings are generated.Hull structural model-ing units at the initial design stage that carries out the product de?nition process are structure systems such as the web frame system,stringer system,girder system,https://www.360docs.net/doc/e44040290.html,ing our previously developed system,we generated an initial hull structural model,that is,a 3D CAD model of the hull structure by initial modeling of the whole hull structure,in which bigger hull structural parts such as the structure systems were used.Then,a detailed hull structural model was generated by detailed modeling of the hull structure,in which smaller hull structural parts were used.Finally,the production hull structural model of a building block unit was generated by production modeling of each building block after the block division process.In this manner,the developed system generated the structural model of the whole hull structure having high level-of-detail in early time.Fig.4shows the hull structural modeling concept of a structure system unit,which is suitable for use at the initial design stage.2.2.Relationship between hull structural parts

All shipbuilding CAD systems have a representation method,which describes the relationship between the hull structural parts.This relationship is used in the generation of the production material information of a building block or in the generation of the structural analysis model.The

relationship between the hull structural parts contains the information on how two parts connected;that is,it speci?es which hull structural part is welded with which hull structural part.Fig.5shows the representation method of the relationship between the hull structural parts in the hull structural model,which was generated from a developed system in our previous study.

In the developed system,a seam was introduced to represent the relationship between the hull structural parts in the hull structural model.The seam can be regarded as a joint line or welding line between the hull structural parts.There are two types of seams:the ?llet seam and the butt seam.The ?llet seam represents the joint line between a horizontal and vertical part,for example,the joint line between ‘Panel’and ‘Stiffener 1’in Fig.5.The butt seam represents the joint line between two horizontal parts.In the hull structural model,the seam contains the hull structural parts that are welded by the seam and the geometric information of the seam as its design attributes.For example,‘Seam 1’has ‘Panel’and ‘Stiffener 1’which are welded by ‘Seam 1’and a joint line (‘Curve 1’)as the design attributes.Here,‘Curve 1’was generated by the intersection calculation between them when ‘Stiffener 1’was placed on ‘Panel’.‘Curve 1’corresponds to the geometric information and intersection calculation result of ‘Seam 1’.Thus,the hull structural parts,which are welded to each other by the seam,can be obtained from the corresponding seam in the hull structural model.Further-more,the joint line can be immediately obtained from the geometric information of the corresponding seam without having to perform any additional intersection calculation.This representation method allows ef?cient use of the

Modeling unitDetailed hull structural model at the production design stage

Block division

Modeling unit at the initial design stage

Production hull structural model of a building block unit

Detailed modeling

Initial hull structural model

Web frame system

Stringer system

Girder system

Modeling of a structure system unit

Fig.4.Hull structural modeling concept of a structure system unit at the initial design stage.

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design information,that is,the intersection calculation result,and allows hull structural modeling at the initial design stage,at which design changes are often made.As mentioned above,the relationship between the hull structural parts is represented as the seam in the hull structural model of this study.Here,the length of the seam is called the joint length.Thus,in this study,the joint length for welding which is one of the important production material information of a building block can be calculated from the seam in the hull structural model.Moreover,some or all of the boundaries of each element of the structural analysis model are determined by the seam.The nodes of the structural analysis model are generated by the intersection calculation between the panel and the seam or between the seams.Thus,in this study,the nodes and elements of the structural analysis model can be generated from the seam in the hull structural model.More details about this will be described in Section 4.

3.Generation method of the production material information of a building block

3.1.Requirement unit of the production material information

As mentioned above,at the initial stage of planning and scheduling,the designer of a shipbuilding company normally determines the work sequences and methods,necessary resources,work duration,etc.based on existing enterprise resources.To perform these tasks,the designer needs the production material information of the ship to be constructed.Thus,a method that can generate this information is required.The production material informa-tion,which is essentially required to perform Computer-Aided Production Planning and Scheduling at the initial stage of process planning and scheduling,includes the weight,center of gravity,painting area,joint length for

welding,etc.Basically,this information for the building block units can be regarded as given at these stages.

On the other hand,at the initial design stage,a hull structural model of a whole hull structure is generated by hull structural modeling of a structure system unit,as explained in Section 2.1.Thus,a block division method,which divides the hull structural model into many building blocks,is necessary because the requirement unit of the production material information at the initial stage of process planning and scheduling (‘building block’)is different from the hull structural modeling unit at the initial design stage (‘structure system’).Fig.6shows the necessity of the block division method due to the reason explained above—the difference between the requirement unit of the production material information at the initial stage of process planning and scheduling,and the hull structural modeling unit at the initial design stage.

3.2.Overall process of the generation method of the production material information

Fig.7represents the overall process of the generation method of the production material information.The generation method includes the block division method developed in this study.

As shown in this ?gure,this process consists of four steps.First,a subdivision plane is generated to divide a hull structural model into a number of building blocks,as shown in Fig.7(a).Next,block seams are placed on the hull structural parts through the intersection calculation between the subdivision plane and all hull structural parts,as shown in Fig.7(b).Then,all hull structural parts are grouped into a building block unit using the block seams,as shown in Fig.7(c).Lastly,the production material information of each building block is generated from that of all hull structural parts existing in the corresponding building block,as shown in Fig.7(d).

Seam 1

Panel Stiffener 1Seam 1

Panel Panel Curve 1

Panel

Stiffener 2

Seam 2

Stiffener 1

Seam 1

“A seam represents

the welding line or the relationship information between hull structural parts.”

Seam 2

Panel Stiffener 2Seam 2Stiffener 1

Stiffener 1

Curve 2

Fig.5.Representation method of the relationship between hull structural parts in the hull structural model of this study.

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However,existing shipbuilding CAD systems such as the TRIBON and IntelliShip systems have some limitations in the generation of the production material information.The TRIBON system does not have the block division method because it is normally used to generate the production model of a building block unit at the production design stage,where the block division of a ship has already been determined.On the other hand,the IntelliShip system has the block division method but the system is inef?cient in grouping all the hull structural parts into a building block unit,as will be discussed in detail below.More details about the third steps of the overall process are as follows.In this study,we propose a new grouping method,which groups all the hull structural parts into a building block unit by using all the seams in the hull structural model.In the proposed method,two preconditions are considered.(1)Precondition 1:‘A seam has the relationship informa-tion between hull structural parts.’

As explained in Section 2.2,a seam is introduced to represent the relationship between hull structural parts in the hull structural model.The seam contains the hull structural parts that are welded by the seam and the geometric information of the seam as its design attributes.Thus,the information on a certain hull structural parts adjacent to a speci?c hull structural part can be found from the seam of the speci?c hull structural part

(2)Precondition 2:‘Two parts that are adjacent to each

other with a block seam exist in different building blocks.’

In some cases,a seam representing a joint line between two different hull structural parts can be used a division line to divide one hull structural part into two hull structural parts.Thus,a block seam,which is used for the block division,corresponds to a special case of the seam.Two different hull structural parts,which are welded to each other by the seam,exist in different regions divided by the seam.Similarly,two different hull structural parts,which are divided by the block seam,exist in different building blocks divided by the block seam.

Hull structural modeling unit at the initial design stage

Requirement unit of the production

material information at the initial process planning and scheduling stages

Block division

The deadweight 300,000 ton VLCC is generally divided into about 200 building blocks.

Fig.6.Necessity of the block division method.

Subdivision plane

Block seam

Block 1

Block 2

Block 1

Block 2

(a)

Subdivision plane

Block 1Block 2

(b)

(d)

(c)

Fig.7.Overall process of the generation method of the production material information developed in this study.

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With these two preconditions,the proposed grouping method can be summarized as illustrated in Fig.8. First,a simple hull structure consisting of a panel and stiffener is divided into a number of hull structural parts by internal seams and block seam,as shown in Fig.8(a). Through this step,seven hull structural parts are generated from the simple hull structure.Next,one of the seven hull structural parts is selected and used as a seed part for the grouping of the hull structural parts into a building block unit,as shown in Fig.8(b).Here,let us suppose that part‘1’is selected as the seed part among the seven hull structural parts. Then,all of the hull structural parts adjacent to the seed part are searched from the seams,i.e.,the internal seams and the block seam,in the selected part,as shown in Fig.8(c).If hull structural parts adjacent to the seed part with the block seam exist,they are temporarily stored for future use.In this?gure, parts‘2’,‘3’,and‘4’are adjacent to the seed part,part‘1’. Among these,part‘4’is adjacent to part‘1’with the block seam and thus,is stored temporarily.The hull structural parts existing in the same building block with that of part‘1’are searched by using part‘1’as the seed part.However,part‘4’exists in a different building block with that of part‘1’because parts‘1’and‘4’are adjacent to each other with the block seam;thus,part‘4’is stored temporarily.After this step,one of the searched parts in the previous step is selected and used as a new seed part,as shown in Fig.8(d).In the previous step,parts‘2’and‘3’were searched.Here,let us suppose that part‘2’is selected as the new seed part between parts‘2’and‘3’.Then,part‘5’is searched.At this time,hull structural parts that are adjacent to the seed part and have already been searched are excluded.However,part‘5’is adjacent to part‘2’with the block seam and thus,is stored temporarily.Then,the remaining part is used as the new seed part,as shown in Fig.8(e).Here,let us suppose that part‘3’is selected as the new seed part.Then,no hull structural part can be searched.That is,no hull structural part can be searched through the grouping process beginning with part‘1’as the seed part.Thus,the?rst building block(‘Block1’) consisting of parts‘1’,‘2’,and‘3’is generated because parts ‘2’and‘3’exist in the same building block with that of part ‘1’,as shown in Fig.8(f).

In the following step,a new grouping process begins with parts‘4’and‘5’,which had been stored previously,as shown in Fig.8(g).Here,let us suppose that part‘4’is selected as the seed part between parts‘4’and‘5’.Then, parts‘5’and‘6’are searched.After this step,one of the searched parts in the previous step is selected and used as the new seed part,as shown in Fig.8(h).In the previous step,parts‘5’and‘6’were searched.Here,let us suppose that part‘5’is selected as the new seed part between parts ‘5’and‘6’.Then,no hull structural part can be searched.In the next step,the remaining part is used as the new seed part,as shown in Fig.8(i).Here,let us suppose that part‘6’is selected as the new seed part.Then,part‘7’is searched. Then,the remaining part is used as the new seed part,as shown in Fig.8(j).Here,let us suppose that part‘7’is selected as the new seed part.Then,no hull structural part can be searched.Finally,no further search can be performed on the hull structural part through the grouping process beginning with part‘4’as the seed part,as shown in Fig.8(k).Thus,the second building block(‘Block2’) consisting of parts‘4’,‘’5’,‘6’,and‘7’,is generated because parts‘5’,‘6’,and‘7’exist in the same building block with that of part‘4’.

As explained above,the proposed grouping method uses the relationship between hull structural parts.Thus,this

the same block

None

Block seam

Internal seam

the same block

(e)(f)

(c)(d)

(j)(k)

(i)

(h)

finishes.

grouping

finishes.

seed part

None

Fig.8.Example of the grouping method of the hull structural parts using the relationship between the hull structural parts proposed in this study.

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method can accurately group the hull structural parts into a building block unit within a short time period.

On the other hand,the IntelliShip system uses a geometric test,which is called the point in-out test,to group all hull structural parts into a building block unit.The point in-out test [20]determines whether a test point (e.g.,the center of gravity of a hull structural part)is an in-point or out-point of a given region according to the number intersection points between the half-in?nite line generated toward an arbitrary direction from the test point and the boundary surfaces of a region.As a result,the test point is the out-point of a given region if the number intersection points is even,and is the in-point if the number intersection points is odd.

Fig.9shows the grouping method of the IntelliShip system for hull structural parts in a simple hull structure.First,a simple hull structure consisting of a panel and stiffener is divided into two block regions (‘Block region 1’and ‘Block region 2’)by the block seam,as shown in Fig.9(a).Here,the block region represents the region at which the boundary surfaces are the faces of the rectangular solid,subdivision planes,or hull form surface.Then,the simple hull structure is divided into seven hull structural parts by internal seams and a block seam,as shown in Fig.9(b).Then,the geometric test is performed between all hull structural parts and the ?rst block region (‘Block region 1’),and another geometric test is performed between all hull structural parts and the second block region (‘Block region 2’).Lastly,based on the result of the geometric test,the ?rst building block (‘Block 1’)corresponding to the ?rst block

region is generated by grouping the hull structural parts (parts ‘1’,‘2’,and ‘3’)belonging to the ?rst block region,and the second building block (‘Block 2’)corresponding to the second block region is generated by grouping the hull structural parts (parts ‘4’,‘5’,‘6’,and ‘7’)belonging to the second block region,as shown in Fig.9(c).

In this way,the geometric test based on the intersection calculation is the core of the grouping method in the IntelliShip system.This grouping method can be easily and compactly implemented.However,it requires much processing time and may have errors because of the numerical instability of the intersection calculation [20].4.Generation of the structural analysis model

4.1.Hull structural information in the hull structural model Fig.10gives an example of the hull structural informa-tion in the hull structural model of a panel (‘Panel 1’).As shown in this ?gure,the hull structural information representing the panel consists of four elements:‘BB (Base Boundary)’,‘Layer’,‘Property’,and ‘Model’.‘BB’repre-sents the outer boundary of the panel without regarding the shapes of elementary hull structural parts such as butt and ?llet seams,hole,slot hole,and ?ange.‘Layer’represents a list of the elementary hull structural parts placed on the panel.‘Property’represents the design attributes of the panel such as the thickness,material,thickening direction (shortly,direction),https://www.360docs.net/doc/e44040290.html,stly,‘Mod-el’represents the ?nal shape of the panel considering the

Block seam

Block 1

Block 2

Block seam

Block region 1

Block seam

Block region 2

Block region 1, 2

Perform the testing whether each part

exists in

the corresponding block region or not (The intersection calculation is required.).

Block region 2

This requires much processing time and may have errors during the geometric test.

(a)

234

Block 1Block 2

Subdivision

plane

(c)

(b)

Fig.9.Example of the grouping method of the hull structural parts using the geometric test in the IntelliShip system.

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shapes of the elementary hull structural parts.Here,‘BB’,‘Layer’,and ‘Property’correspond to the minimal product model information of the panel.‘Model’corresponds to the information needed to represent the 3D CAD model according to a designer’s intent (in this case,the model for hull structural modeling),and it can be generated using ‘BB’,‘Layer’,and ‘Property’.That is,the hull structural information of ‘BB’,‘Layer’,and ‘Property’is always kept in the hull structural model.On the other hand,the hull structural information of ‘Model’is temporarily generated from the information of ‘BB’,‘Layer’,and ‘Property’,in the manner the designer wishes at any time.

4.2.Difference between the hull structural model and the structural analysis model

Fig.11gives an example of the hull structural model and the corresponding structural analysis model of the panel (‘Panel 1’)at the initial design stage.As shown in this ?gure,the hull structural model of the panel contains various elementary hull structural parts,such as ‘Butt

seam’,‘Fillet seam 1’,‘Fillet seam 2’,y ,‘Fillet seam 5’,‘Slot hole’,and ‘Flange’,placed on the panel.On the other hand,the structural analysis model of the panel consists of nodes and elements (or meshes).In the structural analysis model,a boundary of each element is determined by the outer boundary of the panel and ?llet seams.Each node exists on the outer boundary of the panel or the ?llet seams.Thus,elementary hull structural parts except for the ?llet seam are generally not considered when generating the structural analysis model at the initial hull structural analysis stage.

4.3.Overall process of the generation method of the structural analysis model

As described above,the structural analysis model is different from the hull structural model.However,all information needed to generate the structural analysis model exists in the hull structural information in the hull structural model,as shown in Fig.10;i.e.,the information for generating the structural analysis model can be

Panel 1

BB Face 1

Layer

MiddleLayer

Butt seam Slot hole

Flange

Property

Thickness

Material

…

Model

Body Face 1’…

Hull structural information in the hull structural model of ‘Panel 1’

Model

Base Boundary (BB)

Butt seam

Flange Property

Thickness, material, direction, …

Merging

“Base Boundary”,“Layer”, and “Property”

Representation for the hu

ll structural modeling

Minimal product model information

Panel 1

Slot hole 1Butt seam

Flange

Slot hole 2

Panel 2

Panel 3

FrontLayer

Fillet seam 1Fillet seam 2

Fillet seam 3

…Stiffener 1

Stiffener 2Stiffener 3

Fillet seam 1

Fillet seam 2Fillet seam 3Fillet seam 4Fillet seam 5

Fillet seam 1, 2, 3, 4, 5

Slot hole 1

Butt seam Flange

Fillet seam 1

Fillet seam 2Fillet seam 3Fillet seam 4Fillet seam 5

Panel 1

Information for representing

the 3D CAD model Layer Fig.10.Example of the hull structural information in the hull structural model of the panel (‘Panel 1’).

seam 3seam 4seam 5

Hull structural model of the ‘Panel 1’

Structural analysis model of the ‘Panel 1’

seam 3seam 4seam 5

Fig.11.Example of the hull structural model and the corresponding structural analysis model of the panel (‘Panel 1’)at the initial design stage.

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generated by reconstructing the topological information of ‘Model’from ‘BB’,‘Layer’,and ‘Property’,as follows.First,an outer boundary of the panel is extracted from ‘BB’.That is,only the edges on the outer boundary of the panel are extracted from ‘BB’.Next,only the ?llet seams placed on the panel are extracted from ‘Layer’.Then,‘Property’is extracted as it is.Finally,all the different types of extracted information are merged into one,that is,‘Model’.As a result,the information for generating the structural analysis model is given as a new a type of information,‘Model’,and ‘Model’becomes the base model for generating the structural analysis model.Here,although ‘Model’is a non-manifold model [21,22]recon-structed from the hull structural information in the hull structural model,it appears to be a wireframe-like model.Now,let us see in detail how the structural analysis model is generated from the hull structural information.Fig.12shows the overall process of the generation method of the structural analysis model developed in this study.In the ?rst step (Fig.12(a)),edges on the outer boundary of the panel are extracted from ‘BB’in the hull structural information.Edges on the ?llet seams placed on the panel are also extracted from ‘Layer’.Moreover,‘Property’is extracted as it is.The thickening direction of the panel among ‘Property’is used at the third step,and the thickness and the material of the panel will become the properties of the elements to be generated later.For readers’convenience,suppose that the outer boundary of the panel consists of four edges (‘E1’,‘E2’,‘E3’,and ‘E4)and each ?llet seam consists of one edge (‘E5’for ‘Fillet seam 1’,‘E6’for ‘Fillet seam 2’,‘E7’for ‘Fillet seam 3’,and ‘E8’for ‘Fillet seam 4’).

In the second step (Fig.12(b)),all extracted edges are merged into one using a Boolean operation such as ‘UNION’.As a result,a non-manifold model,that is,a base model for generating the structural analysis model is generated.In the base model,a vertex,which is shared by two and more edges,becomes a node of the structural analysis model.More details about this step are as follows.(1)Intersection points are generated by the intersection calculation between the edges.As described in the ?rst step,some of the edges come from the outer boundary of the panel and the other edges come from the ?llet seams.(2)Then,each intersection point is inserted into the corre-sponding edge using an Euler operator such as ‘SEMV (Split Edge and Make Vertex)[21].For example,through this step,‘E1’is changed into four edges (‘E11’,‘E12’,‘E13’,and ‘E14),as shown in Fig.12(b).As mentioned earlier,a vertex generated from the intersection point corresponds to a node in the structural analysis model.In the third step (Fig.12(c)),a list of the nodes constructing each element is generated using an outer normal vector at each node.Here,the outer normal vector at each node can be obtained from the thickening direction of the panel,which is one of properties of the panel.The list of the nodes can be generated by tracking the edge that is most left to the searching direction at each node.More details about this step are as follows.(1)One vertex is randomly selected as a seed node.Suppose that ‘N12’is selected as the seed node in this example,as shown in Fig.12(c).The seed node is added to the list of the nodes.At ?rst,‘N12’is also marked as a start node.(2)Then,one edge ‘E62’sharing ‘N12’can be selected,and thus,‘N13’is selected as the other node of ‘E62’.In this case,the searching

from seam

(b)

(a)

(d)

(c)

node

Seed node

Element

Fig.12.Overall process of the generation method of the structural analysis model.

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direction for generating the list of the nodes is the direction from‘N12’to‘N13’.(3)At‘N13’,three edges sharing this node exist:‘E82’,‘E63’,and‘E83’.Using the outer normal vector at‘N13’and the Fleming’s right hand rule,the edge (in this case,‘E82’),which is most left to the current search direction(‘N12’to‘N13’)at‘N13’,can be found.(4)Now, the next seed node is‘N13’,and the next search direction is the direction from‘N13’to‘N8’.Here,‘N8’is the other node of‘E82’.The above process is repeated with the next seed node and the next search direction until the next seed node becomes the start node‘N12’.

In the last step(Fig.12(c)),each element is generated from the list of the nodes constructing the corresponding element,which is generated at the third step.For example, the element‘EL1’consists of four nodes‘N12’,‘N13’,‘N8’, and‘N7’.Properties of the panel extracted at the?rst step such as the thickness and the material is used as properties of the generated element.By repeating the third and last steps for all nodes,which are generated at the second step, the structural analysis model can be generated.

5.Generation of the piping model

5.1.Overall procedure of piping modeling

Fig.13shows the difference between the existing and proposed procedures of piping modeling.

As shown in this?gure,a pipe and instrument diagram (P&ID)is generated by a designer at the initial stage of piping design.This task is same in two procedures:the

existing and proposed procedures.However,the difference between two procedures exists in generating the piping model at the detailed stage of piping design.In the existing piping modeling procedure,given the P&ID as input,the designer performs piping modeling of all pipes one by one at the detailed stage of piping design.As a result,a piping model can be generated by the designer,however,is independent of the hull structural model.Thus,the changes in the hull structural model cannot affect the piping model and vice versa,even with design changes.

In the proposed piping modeling procedure,given this diagram as input,a designer can rapidly perform piping modeling by using a pipe tray at the detailed piping design stage.Here,the pipe tray,also called a pipe support, represents a virtual object,on which several pipes are placed together.Through this step,a piping model can be generated by the designer in early time,even in the initial stage of piping design after the P&ID is generated.This step is generally used for generating the piping model from the beginning.Next,pipes that are generated by the designer are automatically converted into objects related with the hull structure.That is,all bending positions as well as the start and end positions of each pipe,also called the route of a pipe,are automatically converted into positions related with the nearest hull structural part such as a panel in the hull structural model.Through this step,the piping model related with the hull structure can be?nally generated.Moreover,the changes in the hull structural model can be re?ected on the piping model and vice versa.

Thus,this step is generally used for modifying the existing

Pipe piece

drawing

Pipe installation

drawing

Production piping

design

stage Existing piping modeling procedure Proposed piping modeling procedure

Initial piping design stage

Detailed piping design stage

Pipe piece drawing

Pipe installation

drawing

Future works

Manual generation of

2D drawings for production

Manual generation of

the P&ID

Manual generation of

the 3D piping model

one by one

Rapid modeling

by using the pipe tray

Manual generation of

the P&ID

(a)

Automatic conversion

into the route of the pipe

having the relationship

with the hull structure

(b)

Piping model

to be related with

the hull structural model

Piping model

to be independent of

the hull structural model

Automatic generation of

2D drawings for production

Focus of this study

* P&ID: pipe and instrument diagram

Fig.13.Difference between the existing and proposed procedures of piping modeling.

M.-I.Roh et al./Robotics and Computer-Integrated Manufacturing24(2008)105–124115

piping model.More details about each step are described in the following sections.

Finally,2D drawings for production such as a pipe piece drawing and pipe installation dialog are generated by the designer at the production piping design stage.In the existing piping modeling procedure,these drawings are partly manually generated by the designer.In the proposed piping modeling procedure,these drawings are automati-cally generated.However,the automatic generation of these drawings is out of scope in this study but will be studied in future works.

5.2.Rapid generation of the piping model using the pipe tray Fig.14shows the difference between the generation methods of the piping model in existing shipbuilding CAD systems and those of this study.In existing systems such as the TRIBON and IntelliShip systems,given the P&ID as input,the designer determines the start position,end position,and bending positions of each pipe.Then,using the systems,the designer generates each pipe passing through the given positions of the pipe one by one.That is,the designer can generate a piping model by inputting the given positions of all the pipes in the systems.For example,as shown in Fig.14(a),the designer should input ?ve positions such as ‘P1’,‘P2’,y ,and ‘P5’to generate ‘PIPE 1’,which connects ‘EQ 1’and ‘EQ 2’,where ‘P1’and ‘P5’represents the start and end positions of the pipe,respectively.‘P2’,‘P3’,and ‘P4’represent the bending positions of the pipe.One the other hand,in the developed method in this study,given this diagram as input,the designer determines the start position,end position,and progressing directions at the start and end positions of each pipe.The designer also determines the positions and progressing directions of each pipe tray.Here,the pipe tray,also called the pipe support,represents a virtual object on which several pipes are placed together.Then,using the developed method,the designer can automatically generate each pipe,which passes through the given positions and pipe trays,is as orthogonal as possible,and has the minimum number of bending.That is,using the developed method,the designer can automatically generate a piping model by only inputting the given positions and progressing directions of all pipes and trays.For example,as shown in Fig.14(b),the designer should input four positions such as ‘P1’,‘P2’,‘P3’,and ‘P4’,and four progressing directions such as ‘D1’,‘D2’,‘D3’,and ‘D4’to generate ‘PIPE 1’,where ‘P1’and ‘P4’represent the start and end positions of the pipe,respectively.‘D1’and ‘D4’represent the progressing directions of the pipe at the start and end positions,respectively.Similarly,‘P2’and ‘P3’represent the positions of the pipe trays such as ‘Tray 1’and ‘Tray 2’.‘D2’and ‘D3’represent the progressing directions at the pipe trays.Through this step,the designer can obtain all the bending positions of ‘PIPE 1’,also called the route of the pipe,and the acquisition of all the bending positions means the generation of the piping model of ‘PIPE 1’.

Fig.15shows an example of the generation of the piping model by automatic routing in the developed method.

Plan view d

h b _r e d h b a _r e d h b _r e er_abhd d

h b _s o f d

h b _s o f shell

l l e h s P1(px1, py1, pz1)

P2(px2, py2, pz2)

P3(px3, py3, pz3)

P4(px4, py4, pz4)

P5(px5, py5, pz5)

P1(px1, py1, pz1)D1(dx1, dy1, dz1)

P2(px2, py2, pz2)D2(dx2, dy2, dz2)

P3(px3, py3, pz3)D3(dx3, dy3, dz3)

P4(px4, py4, pz4)D4(dx4, dy4, dz4)

PIPE 1

(b)

(a)engine room deck of the deadweight

300,000 ton VLCC Fig.14.Difference in the generation methods of the piping model between the existing shipbuilding CAD systems and the developed method in this study.

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This?gure shows the generation method of‘PIPE1’when the four positions such as‘P1’,‘P2’,‘P3’,and‘P4’,and four progressing directions such as‘D1’,‘D2’,‘D3’,and‘D4’of the pipe and pipe trays are given as inputs.

As shown in Fig.15(a),there are three sub-regions for the pipe routing.The?rst one is the sub region which exists between‘EQ1’and‘Tray1’;the second one is the sub region which exists between‘Tray1’and‘Tray2’;and the last one is the sub region which exists between‘Tray2’and ‘EQ2’.In the developed method,all allowable routes of the pipe are automatically generated in each sub region.As shown in the large circle of Fig.15(a),three routes are generated in the sub region which exists between‘Tray2’and‘EQ2’.The?rst one(1)is orthogonal to the global coordinates and has one bending;the second one(2)is inclined to the global coordinates and has two bendings; and the last one(3)is orthogonal to the global coordinates and has three bendings.The developed method selects the route that is the most orthogonal and has the minimum number of bendings as the optimal route of the pipe.Thus, the last one is selected the optimal route of the pipe in the sub region which exists between‘Tray2’and‘EQ2’.This process is repeated in all sub regions.As a result,the?nal route of‘PIPE1’can be obtained,as shown in Fig.15(b). That is,all bending positions of pipe such as‘P5’,‘P6’,and ‘P7’can be generated by automatic routing.

Now,suppose that the designer generates‘PIPE2’, which connects‘EQ3’and‘EQ4’.In the existing systems, as shown in Fig.16(a),the designer must input?ve positions such as‘P6’,‘P7’,y,and‘P10’to generate‘PIPE 2’.As a result,the designer can generate a piping model of ‘PIPE2’.However,‘PIPE1’and‘PIPE2’interfere with each other.Thus,to remove the interferences between them,the designer has to modify all the bending positions, that is,the routes of‘PIPE1’and‘PIPE2’,as shown in Fig.16(b).This task is tedious and time consuming. Furthermore,it is hard to remove the interferences among a number of pipes.

One the other hand,in the developed method,as shown in Fig.17(a),the designer inputs two positions such as‘P5’and‘P6’,and two progressing directions such as‘D5’and ‘D6’to generate‘PIPE2’.Here,‘Tray1’and‘Tray2’, which were used to generate‘PIPE1’,are used as they are. Thus,additional input for pipe trays is not necessary in this case.As a result,the designer can automatically generate a piping model of‘PIPE2’;that is,the piping model of‘PIPE2’is generated by the generation method described earlier and shown in Fig.15.However,‘PIPE1’interferes with‘PIPE2’.The developed method modi?es the routes of the pipes automatically to remove the interferences between them.In the modi?cation,pipes in the trays are swapped until the interferences between the pipes are removed.As shown in Fig.17,the interferences between‘PIPE1’and‘PIPE2’can be removed by swapping them in‘Tray1’and‘Tray2’.In this manner, the developed method can automatically remove the interferences between pipes,even the interferences among a number of pipes.

In short,the developed method can rapidly generate the piping model by automatic routing and modi?cation. Automatic routing and modi?cation are generally used for generating a piping model from the beginning.

er_bhd

Main engine

EQ 4

EQ 2

Tray 2Tray 1

Plan view

This study

_r e

b a_r e

fos_bhd

shell

P1, D1

P2, D2

P3, D3

P4, D4

after automatic routing

(b)

before routing

(a)

Main engine

EQ 4

EQ 2

Tray 1

Plan view

er_abhd

fos_bhd

shell

PIPE 1

P1(px1, py1, pz1)

D1(dx1, dy1, dz1)

P2(px2, py2, pz2)

D2(dx2, dy2, dz2)

P3(px3, py3, pz3)

D3(dx3, dy3, dz3)

P4(px4, py4, pz4)

D4(dx4, dy4, dz4)

Tray 2

Sub region

for routing

bending

margin(1) orthogonal and 1 bending

Optimal route

(2) inclined and

2 bending

(3) orthogonal and

3 bending

Tray 2

Sub region for routing

between ‘EQ 2’and ‘Tray 2’

Automatically

generated

bending position

bending

margin

Fig.15.Example of the generation of the piping model by automatic routing in the developed method.

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5.3.Generation of the piping model considering the

relationship with the hull structure

Fig.18shows an example of the generation of the piping model in relation with the hull structure by automatic conversion in the developed method.As shown in Fig.18(a),the bending positions and progressing directions at each bending position are given as inputs after the optimal route of ‘PIPE 1’is generated.Here,the progressing direction at the bending position indicates the

Existing systems

Fig.16.Example of the generation of the piping model by manual modi?cation in existing

systems.

Plan view

This study

h b _r e d

h b a _r e (a) before modification

(b) after automatic modification

Plan view d h b _r e d h b a _r e PIPE 1PIPE 2

PIPE 2PIPE 1

Fig.17.Example of the generation of the piping model by automatic modi?cation in the developed method.

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direction vector at the current bending position toward the next bending position.Also,an outer normal vector of each panel is given from the thickening direction of the panel in the hull structural model.To relate the pipe with the hull structure,the developed method automatically converts all bending positions as well as the start and end positions of the pipe into positions related with the nearest hull structural part such as a panel in the hull structural model.Let us examine position ‘P5’.The panel ‘er_bhd’is searched if the nearest panel in the progressing direction or the

Pla n view

This study

h b _r e d h b a _r e PIPE 1

Pla n view

d h b _r

e d

h b a _r e PIPE

o i s r e v n o c c i t a m o t u a r e t f a )b (n

o i s r e v n o c e r o f e b )a (

Fig.18.Example of the generation of the piping model in relation with the hull structure by automatic conversion in the developed method.

Existing systems Fig.19.Route of the pipe regardless of the changes of the hull structure in the existing systems.

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inverse direction is searched.Then,‘P5’can be represented as the new position ‘er_bhd àb ’,where ‘b ’is the distance between the bending position ‘P5’and the panel ‘er_bhd’.Similarly,‘P1’,‘P4’,‘P6’,and ‘P7’can be also represented as the positions related with the nearest hull structural part.As shown in Fig.18(b),‘P1’,‘P4’,‘P6’,and ‘P7’can be represented as the new positions ‘fos_bhd+a ’,‘er_abhd+e ’,‘fos_bhd àc ’,and ‘er_abhd+d ’,respectively.In this manner,the piping model of ‘PIPE 1’in relation with the hull structure is ?nally generated.

Suppose that design changes are made in the hull structure.As shown in Fig.19(b),the panel ‘fos_bhd’moves toward the +y direction by the value ‘A ’and the panel ‘fop_bhd’moves toward the ày direction by the same value.Though the panels are moved,the route of ‘PIPE 1’is not changed in the existing systems.No change

Plan view

This study

(a) before the change

of the hull struc ture

(b) after the change

of the hull struc ture

Plan view

Fig.20.Automatic change of the route of the pipe according to the changes of the hull structure in the developed method.

Hull structural modeling result of the VLCC

Enlarged view of the midship region of the VLCC

Fig.21.Result of hull structural modeling of the whole hull structure of the 300K VLCC by application of the developed system in our previous study.

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in the route is caused by that all bending positions as well as the start and end positions of the pipe are represented as real values,which are independent of the hull structure. Thus,the changes in the hull structure cannot affect the piping model.

On the other hand,in the developed method,all bending positions as well as the start and end positions of the pipe are converted into positions related with the nearest hull structural part by automatic conversion,as described above and shown in Fig.18.If the panels‘fos_bhd’and ‘fop_bhd’are moved as shown in Fig.20(b),the positions related with the panels such as‘P1’,‘P5’,and‘P6’are changed into the new positions and thus,the route of ‘PIPE1’is automatically changed.Thus,the changes in the hull structure can be immediately re?ected on the piping

model.

In short,in the developed method,the piping model in relation with the hull structure can be generated by automatic conversion.Automatic conversion can be effectively used for modifying the existing piping model.

6.Application to the deadweight300,000ton VLCC

The developed methods were successfully veri?ed by application in the generation of the production material information of a building block unit,in the generation of the structural analysis model,and in the generation of the piping model of various ships.This section presents portions of the veri?cation process for a300K VLCC. Fig.21presents the result of hull structural modeling of the whole hull structure of the300K VLCC by application of a developed system in our previous https://www.360docs.net/doc/e44040290.html,ing the developed system,one designer generated this result in about2–3days.

Fig.22presents the result of the generation of the production material information of a building block in the bottom region of the300K VLCC by application of the developed method.It took about?ve minutes to generate this result using the developed method.As shown in this?gure,the joint length between building blocks (‘erection material information’),which is required for block erection,and the joint length of a building block (‘assembly material information’),which is required for the block welding,as well as the weight,the center of gravity, and the painting area can be accurately generated by using the developed system.On the other hand,the TRIBON system can generate only limited production material information such as the weight and center of gravity of the building block after performing a production modeling of a building block unit at the production design stage.The IntelliShip system can also generate only limited produc-tion material information such as the weight and center of gravity of the building block after performing a detailed

Fig.22.Result of the generation of the production material information of the building block in the bottom region of the300K VLCC by application of the developed method.

Table1

Comparison of the production material information generated,between

the developed method and the TRIBON system

Item Unit Developed

system

TRIBON

system a

Weight ton301.4304.0

Center of gravity—(182.0,21.4,3.0)—

Painting area m23845.3—

Joint length between building blocks m294.0—

Joint length in the building block m1349.8—

a It was dif?cult to obtain the non-?lled data in the table of the TRIBON

system as they are con?dential information to the corresponding

shipbuilding company.

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modeling of the whole hull structure at the detailed design stage and performing the block division at the production design stage.

Table 1shows the comparison of the production material information generated,between the developed method and the TRIBON system.As shown in this table,for the information on the weight of the building block,there is an error of 0.9percent between them.It may be caused by the difference in the level-of-details of the building block between them:initial hull structural model vs.production hull structural model.Fig.23presents the result of the generation of the structural analysis model of the whole hull structure of the 300K VLCC by application of the developed method.Fig.24presents the fore body and after body regions.It took about twenty minutes to generate these results using the developed method.

Fig.25presents the result of the generation of the piping model of the engine room region of the 300K VLCC by application of the developed https://www.360docs.net/doc/e44040290.html,ing the developed method,one designer generated these results in about 30min.

Enlarged view of the midship region of the VLCC

Generation result of the structural analysis model of the VLCC

Fig.23.Result of the generation of the structural analysis model of the 300K VLCC by application of the developed method.

Fore body region

After body region Inside of the fore body region

Inside of the after body region Fig.24.Result of the generation of the structural analysis model of the fore body and after body regions of the 300K VLCC by application of the developed method.

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Fig.26presents an example of the automatic change of the routes of pipes in the engine room region according to the changes of the panel.This ?gure shows that the developed method generated the piping model in relation with the hull structure.7.Conclusions and future works

In the most of shipbuilding companies,without the hull structural model,designers have manually calculated the production material information of a building block by using 2D drawings,parent ship data,and design experi-ences at the initial stage of planning and scheduling.Similarly,designers have manually generated the structural analysis model at the initial stage of hull structural analysis.The piping model has been generated indepen-dently of the hull structural model at the detailed stage of piping design.

For solving these issues of manual and independent generations of information and models,we developed an initial hull structural modeling system.In this study,we developed the methods of generating the production material information of a building block,the structural analysis model,and the piping model based on the hull structural model.The developed methods were applied to a deadweight 300,000ton VLCC.The results show that the

Piping modeling result of the VLCC

Enlarged view of

the engine room region of the VLCC

Fig.25.Result of the generation of the piping model of the engine room region of 300K VLCC by application of the developed method.

Before the change of the panel

Automatic change of the route of the pipes

After the change of the panel

Plan view

Elevation view

Fig.26.Example of automatic change of the routes of pipes in the engine room region according to the changes of the panel.

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developed methods quickly generated the corresponding information or models at the initial design stage.That is,the production material information of a building block were accurately generated by dividing the hull structural model into a number of building blocks,the structural analysis model was rapidly generated by applying an automatic mesh generation algorithm to the hull structural model,and the piping model in relation with the hull structural model was generated faster than usual by performing automatic routing,modi?cation,and conversion.

Future works will investigate the transference of the structural analysis model generated by using the developed method to commercial structural analysis programs such as the ANSYS,PATRAN/NASTRAN,etc.for a structural analysis.Furthermore,although this study showed that the changes in the hull structural model could be re?ected on the piping model,as shown in Fig.26,it did not show that the changes in the piping model could to be re?ected on the hull structural model.The investigation of this reverse relationship will be examined in further research. Acknowledgement

This work was supported partially by Grant no.R01-2002-000-00061-0from the Basic Research Program of the Korea Science&Engineering Foundation,and by Grant no.10005460from the Korea Institute of Industrial Technology Evaluation and Planning.Also,this work has been partially supported by the Research Institute of Marine System Engineering of Seoul National University and EzGRAPH Co.,Ltd.

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