DNV hull structure course

Đây là tài liệu hay trong ngành đóng tàu thủy hiện nay. Tài liệu khá chi tiết giúp các bạn có thể nhanh chóng tiếp thu mọi kiến thức trong ngành. Tài liệu hiện khá phổ biến rộng rãi. Chúc các bạn thành công

Hull Structure

Course

DNV

2005

Hull Structure Course

Objective:

After completion of the course, the participants should have gained knowledge of basic hull strength and understanding of how to perform better hull inspections.

Hull Structure Course

Purpose:

To train technical personnel about the basics of hull structure.

Target group is technical personnel within ship

owner / manager organization in need of

improved competence in structural matters, with

special focus on Bulk Carriers and Oil Tankers.

• Fore & aft ship

• Hull structural breakdown Oil Tanker

Day 3

• Hull structural breakdown Bulk Carrier

Day 4

• Fore & aft ship

• Hull structural breakdown Container Carrier

Agenda day 1

09.00-09.15 Welcome & Introduction

09.15-09.45 Expectation & presentation of participants

12.30-13.15 Lunch

13.15-14.15 Structural connections

14.15-15.45 Failure mode fatigue

15.45-16.45 Buckling & Indent

Agenda day 2

09.00 – 09.15 Answers to review questions

09.15 – 10.30 Structural breakdown fore and aft ship 10.30 – 10.45 Introduction to tank

Agenda day 4

09.00 - 09.30 Answers to review questions from day 1 09.30 - 10.30 Structural breakdown fore and aft ship 10.30 - 11.00 Introduction – Container Carriers

Slide 1

Basic Hull Strength

Module 2: Basic Hull Strength

Basic Hull Strength

Objectives

After completion of this module the participants should have

gained:

1 Understanding of:

The behaviour of simple beams with loads and corresponding

shear forces and moments.

The applicable local and global loads on the hull girder and the

corresponding shear forces and bending moments.

Shear area: The beam has to have a sufficient cross sectional area to

take up the external load and transfer this towards the end supports.

Bending: When a beam is loaded it will bend dependent on its stiffness

and its end connections A single load from above causes compression

stress on the upper side and tension stress on the lower side of the beam.

A

A

Section A-A

Bending moment

Basic Hull Strength

Simply supported beam

Bending Moment

M=Q x ℓ

Q=F/2 Q=F/2

ℓ

F

L/2

L/2

Slide 5

Basic Hull Strength

Simply supported beam

Shear Force

Q=pL/2

Q=pL2

M=pL 2 /8

Basic Hull Strength

Beam with fixed ends - distributed load

L

Shear Force

Bending Moment

Q=pL/2

Q=pL/2

No rotation!

Slide 7

Basic Hull Strength

Beam with spring supported ends

p

Shear force and bending moment distribution varies with degree of

end fixation (spring stiffness)

Degree of end fixation = 0

k k

Degree of end fixation = 1

Simply supported Fixed ends

Basic Hull Strength

Symmetrical load – full fixation

End fixation

Structural clamping – spring support

Slide 9

Basic Hull Strength

• Load on structure is important with regard to fixation bottom longs connection to transverse bulkhead

Beam – fixation at ends

Non symmetry in loads

gives less fixation or even

forced rotation

Symmetric load gives full

fixation

Loaded Empty

Basic Hull Strength

Slide 11

Basic Hull Strength

Stress levels – elastic & inelastic region

Elastic region: σ < σyield

- A beam exposed to a stress level below

the yield stress, will return to its original

shape after the load is removed, Simple

beam theory valid

In-elastic region: σ = > σyield

- A beam exposed to stresses above the

yield stress will have a permanent

deformation after removing the load

(yielding, buckling, fractures)

Elastic region

σ = ε * E

Basic Hull Strength

High Tensile Steel (HTS)

Material grades NVA - NVE

• Measure for ductility of material (prevent brittle fracture)

• Material grade dependent on location of structure and

thickness of plate

NVANVBNVDNVE

MSHT28HT32HT36

Slide 13

Basic Hull Strength

Bending stress - Simple beam with load

A A

A A

Max stress at flanges.

Zero stress at neutral axis:

F

n.a

Basic Hull Strength

Shear stress - Simple beam with load

A A

A A

Area effective in

transferring load

to the supports

Distribution of the stress

Max shear stress at neutral axisis of profile:

Section A-A F

Slide 15

Basic Hull Strength

Bending and shear stress flow

A A

A A F

Section A-A

Shear stress is transferred in the web, τ

Basic Hull Strength

Beam stiffness and section modulus

As the axial stresses are transferred in the flange of a beam, it is the flange

area that is governing a beam’s ‘bending stiffness’

3 212

1

y A

Slide 17

Basic Hull Strength

Shear stress & shear area

The load is carried in shear towards the supports by the web

y

t h

Basic Hull Strength

Flatbar (slabs)

Easy with regard to production, flatbar stiffeners have poor buckling strength properties, low section modulus mostly applied in deck and upper part of side - long bhd.

Conventional profiles in ship structures

Angle bar (rolled and welded)

Angle bar will twist when exposed to lateral load due to symmetric profile This effect gives additional stress at supports due to skew bending Angle bars are more prone to fatigue cracking than symmetrical profiles (Ref sketch next page)

non-Due to the skew bending, which gives a moment in the web-plate at welded connection to the plate, angle bars are also more critical with regard to grooving (necking) corrosion

Slide 19

Basic Hull Strength

An angle bar profile will twist when exposed to lateral loads due

to asymmetric profile which gives additional stress at supports

due to skew bending

Additional bending

stress in web

X Z

MODEL: T1-1 DEF = 203 4: LINEAR ANALYSIS NODAL DISPLACE ALL

MAX = 1.46 MIN = 0

.696E-1 139 278 418 557 696 835 974 1.11 1.25 1.39

Side longs internal pressure

Angle bar (rolled / built up)

Basic Hull Strength

Bulb profile (single / double bulb)

Bulb profiles are favourable with regard to coating application.

Single bulb which is most common will (as for the L-profile) have some skew bending when exposed to lateral load.

T- Profile

The T-profile is symmetrical and will not be prone to skew bending Favourable with regard to fatigue strength The profile may have large section modulus Some T-profiles on single skin VLCC’s have been found critical with regard to buckling due to

a high and thin web-plate with a small flange on top.

Conventional ship structure profiles

Slide 21

Basic Hull Strength

Hierarchy of hull structures

Plate – Stiffener – Stringer / girder – Panel – Hull

Stresses in a hull plate due to external sea pressure, are transferred

further into the hull structure through the hierarchy of structures.

Basic Hull Strength

Level 1: Plate - simple beam

Water pressure Stiffener Plating

A strip of plating considered as a beam with fixed ends and evenly distributed load

NO

ROTATION

Slide 23

Basic Hull Strength

Level 2 Longitudinal - simple beam

Longitudinal between two web frames

Symmetric load fwd and aft of web frames gives no rotation -

fixed ends

Max shear and bending moment

at supports (web frames)

Basic Hull Strength

Level 3 : Transverse web - simple beam

Beam with fixed ends and concentrated loads from the bottom longitudinals

SF Max shear and bending

Slide 25

Basic Hull Strength

Level 3 Longitudinal girder with

Single beam with fixed ends and concentrated loads from the transverse web frames

Max Shear and bending moment towards ends

Basic Hull Strength

Beams, load transfer

Double bottom structure

Centre girder

Floor / transverse bottom girder Side girder

Loads taken up by the bottom plating are transferred through the hierarchy

of structures into the hull

Slide 27

Basic Hull Strength

Single skin structure

CL girder

Transverse bottom girder /web frame

Longitudinal bulkhead

Bottom longitudinals

with plating

Loads taken up by the bottom plating are transferred through the hierarcy

of structures into the hull

Beams, load transfer

Basic Hull Strength

Damage experience

• Level 1 Plate supported at stiffeners

• Level 2 Stiffener supported at webframe

• Level 3 Webframe supported at panel

• Level 4 Panel – hull girder

Consequences of damages level 1-4 above!

Slide 29

Basic Hull Strength

Single beam VS Hull girder

A vessel’s hull has many of the same properties as a single beam

Hence simple beam theory may be applied when describing the nature of a

Basic Hull Strength

Hull girder bending

When a vessel’s hull is exposed to loading, it will bend similarly as a

single beam

Slide 31

Basic Hull Strength

Single beam VS Hull girder

Section A-A

Hull Girder Shear stress, τ

Deck and bottom acts as flanges in the ‘hull girder’, while ship sides

and longitudinal bulkheads, act as the web

Basic Hull Strength

Stress hierarchy in ship structure

Local stress : Plate / stiffener

Girder stresses: Webframes / Girders /Floors

Hull girder stresses; Deck & bottom / Side /

long Bhd.

Slide 33

Basic Hull Strength

Case Module 2: Loads Buzz Groups

• For a beam with fixed ends and evenly distributed

load, i.e from sea pressure, is it true that:

– Bending stresses are zero at one location

– Reaction forces are equal at both ends

– No rotation at ends

– Bending stresses are positive (tension) in one flange

and negative (compression) in the other in the middle

of the span

– Shear stresses are highest in the middle of the span

– Shear forces are carried by the web

Basic Hull Strength

Case Module 2: Beams Buzz Groups

• Is it correct that the transverse girders are

supported by the longitudinal stiffeners?

• Are the longitudinals inside a tank structure for

example bottom longitudinals between webframes normally fixed or simply supported?

Slide 35

Basic Hull Strength

Summary: Beams

• BM and Shear force

• Stress axial / bending / shear

• Section modulus / Moment of inertia / Shear area

• Stress distribution Bending and shear

• BM and SF distribution depending on load and end fixation

• Profile types and properties

• Structural hierarchy plates-stiffeners-girder-panel

Basic Hull Strength

Loads acting on a ship structure

Slide 37

Basic Hull Strength

Loads acting on a ship structure

1 Internal loads: - Cargo

Basic Hull Strength

Static and Dynamic loads

Static local load: The local load, internal and external

due to cargo / ballast pressure

Dynamic local load: External - dynamic wave loads,

Internal - due to acceleration

Static global loads: Global Bending Moment and Shear

Force

Slide 39

Basic Hull Strength

Static and Dynamic loads

Total external local load acting on a vessel:

Max at the bottom

Note the relative size of static / dynamic pressure is not to scale!

Max around the waterline

Basic Hull Strength

z Plotted sea pressure curve

is a sum of the static and dynamic contribution

z Constant in the midship area, increasing towards ends

Sea Pressure – static and dynamic contribution

Local sea pressure (example for a bottom longitudinal)

p (kN/m 2 )

Slide 41

Basic Hull Strength

• Global dynamic vertical and horizontal wave bending

moments give longitudinal dynamic stresses in deck, bottom

and side

Highest global dynamic loads for all longitudinal members

in the midship area

Static and Dynamic loads

Basic Hull Strength

Loads on foreship

Bottom Slamming Pressure

•Induced by waves in shallow draft

condition (ballast condition)

•Dominant for flat bottom structure

forward

Bow Impact Pressure

•Induced by waves, vessel speed, flare and waterline angle important factors

•Dominant for ship sides in the bow at full draught

Slide 43

Basic Hull Strength

Green Seas Loading:

• Dominant for hatch covers and fwd deck structure

(incl deck equipment, doors, openings etc)

Loads on deck

Basic Hull Strength

Weights and buoyancy

Steel weight, equipment and machinery

Buoyancy

Weight distribution of cargo and fuel

Slide 45

Basic Hull Strength

Static internal load from cargo

Static external sea

pressure

Dynamic internal load from cargo

Bulk Carrier typical load

Dynamic external

sea pressure

Basic Hull Strength

Internal load

- External load

= Net load on double bottom

Static and dynamic internal load from cargo

Net load on structure – ‘Ore hold’

Slide 47

Basic Hull Strength

Static and dynamic sea pressure

Net load on structure - empty hold

Net load from sea pressure

Basic Hull Strength

Alternate loading condition

Slide 49

Basic Hull Strength

Weights and buoyancy

Buoyancy and weights are not evenly distributed along

a ships length…

…hence, a global shear force and bending moment

distribution is set up on the hull girder

Basic Hull Strength

Hull girder still water bending

moment and shear force

Slide 51

Basic Hull Strength

Total hull girder bending moment MTotal = Mstill water + Mwave

Total BM acting on a vessel

Basic Hull Strength

Case 2 Module 2 – Loads/Materials

• Where in the hull girder cross section of a hull girder are the local dynamic loads due to sea pressure highest?

• Where along the hull girder are the dynamic sea

pressure loads highest?

• Where in the hull girder is the global dynamic bending

moment highest?

• Does a vessel in sagging condition experience

compression or tension in deck?

• A vessel in sagging condition experience flooding of a

empty tank in midship Will the hull girder bending moment increase or decrease?

Slide 53

Basic Hull Strength

Summary: Loads

• Static & dynamic

• Internal & external

• Load distribution

• Net load

• Longitudinal strength SF & BM

Basic Hull Strength

End of Module 2: Basic Hull Strength

Slide 1

Module 3:

Structural Connections

Module 3: Structural Connections

• Objectives of this Module:

After completion of this module the participants should have gained:

• Knowledge about connections between structural elements

• Understanding of the transfer of forces between structural elements and the relevant stress distributions

• Knowledge about how to improve the design of structural

connections

• Connections of girders/web frames

• Connections between panels

• Design details

• Full penetration welds (Full pen)

(Ref Rules Pt.3 Ch.1 Sec.11)

Module 3:

Structural Connections

Fillet welds:

• The most common type

Transferring shear forces (between profile and plate)

• Building welded sections

• Connections to other members

• NDT by magnetic particle or

dye penetrant

Leg length Throat thickness

Throat measure 3.5 mm

thickness-= leg length 5.0 mm

Weld Types – Fillet welds

Root Face 2-4 mm for full penetration welds

σ

Full penetration welds:

• To be used where stress level normal

to the weld is high

Transferring shear forces and forces normal to the weld

• Connections to other members in highly stressed locations

• NDT by ultrasonic, dye penetrant or magnetic particle

Gap <3 mm

Web-plating

Slide 11

Module 3:

Structural Connections

σx

Stress distribution for different details

Static stress in stiffener on top

σx

Design improvement

Slide 13

Module 3:

Structural Connections

End-brackets on girders - forces

Full Centre Tank

EmptyWingTank

High Stress Areas

High Stress Areas

Flange attached and supported

Improved design

High Stress Areas Soft bkts recommended Increased stress

at support bkts.

Stringer connection to inner side

Module 3:

Structural Connections

Girder bracket

End-brackets on girders

Typical crack location

Ref iii b) previous fig.

Slide 17

Module 3:

Structural Connections

Cross-Ties

Full Centre Tank

Full Centre/Empty Wing at full draught

= Max Compression in Cross Tie

Empty Centre/Full Wing at ballast draught

= Max Tension in Cross Tie

EmptyWingTank

Tank