Structural Design of High Ice Class LNG Tankers

1
Structural Design of High Ice Class LNG Tankers
Claude Daley1 Andrew Kendrick2 Han Yu3
Byeong-Jae Noh4
1
3
2
4
2

• Overview

Extensive gas reserves have been discovered in
the Canadian and Russian Arctic Development these
reserves will require a new generation of highly
ice-capable LNG tankers. The authors are jointly
conducting a research project to address the
challenges of designing these new vessels.
3
The Arctic
Sakhalin Heavy FY ice
Yamal Peninsula FY and MY ice, Kara Gate
ridges and shallow water
Northern Canada heavy MY and glacial ice
Baltic FY ice, ridges
4
Overview
Marine LNG transportation is a cost effective way
to deliver the gas to market Ice-going LNG ships
present several unique challenges

• size LNG vessels are much larger than most ice
  going ships
• speed LNG ships need to maintain high
  throughput and so may operate at relatively high
  speeds in ice
• season LNG shipment must be a year-round
  operation, even through the coldest and darkest
  times
• LNG the containment system presents a unique
  challenge

5
Overview
LNG ships have multiple barriers. The ship itself
has both an outer and inner hull The membrane
type LNG containment system has several layers
for cargo containment The hull structure and
cargo containment system must be designed for ice
loads and ice load effects
6
Overview

• A close-up sketch of the CCS shows the many
  barriers
• liquid barriers
• thermal barriers
• deformation barriers
• strength barrier
• All must be ice-load capable.

7
Background
As of 2006, IACS introduced new Unified
Requirements for Polar Ships UR I1. Polar Class
Description and. Application. UR I2. Structural
Requirements. UR I3. Machinery requirements The
Polar Class rules have several new features

• scenario-based design, with the load derived from
  collision mechanics, which links loads with ice
  conditions and operations
• limit-state structural assessment, with plastic
  capacity being the focus

8
Joint Research Project
Starting in 2006, ABS, HHI and BMT agreed to work
towards developing the design tools needed to
create a high ice class LNG tanker. It was
agreed that these LNG vessels would need to use
the latest available knowledge, as they represent
a unique class of ship. This paper focuses on
the structural requirements.

• We have developed ice load and structural
  assessment tools that follow the ideas in the new
  IACS UR for Polar Ships, but expand the range of
  load scenarios used
• With this expanded set of loads, the structure
  will be assessed with linear and non-linear
  finite element analysis

9
IACS UR I2 Load Scenario
The basic load scenario in the Polar Rules is an
oblique collision on the bow.

• Ice load depends on
• ice shape (fixed)
• pressure-area terms (class dependent)
• ice thickness and flexural strength (class
  dependent)
• collision modelled using Popov assumptions

10
LNG Load Scenarios
Weve extended the scenario in the Polar Rules
with 20 additional ice interaction cases. Here
are 3 collision cases
11
LNG Load Scenarios
And 3 with alternate contact geometries
12
LNG Load Scenarios
And 3 more load scenarios
13
LNG Load Scenarios
And 3 more load scenarios
14
LNG Load Scenarios
And 2 more load scenarios
15
Solving for Ice Loads
16
Solving for Ice Loads
Once we have the ice crushing energy as a
function of penetration depth, we can solve for
the penetration depth. We do this by equating
the effective collision energy with the crushing
energy In general the force is Which lets us
write And We pull all this together to get
17
Solving for Ice Loads examples of geometry
functions Table 5
18
Analyzing Structure- Once we have the various
collisions modelled, we can develop a load patch
to apply to a finite element model. At this point
we follow a process, just as was used to develop
the design load in the We need to account for
load peaks. We also would like to express the
load as a rectangle for practicality.
19
Analyzing Structure- The whole process looks
like
20
Concluding Comments-

• We have an approach that lets us
• Calculate loads for various scenarios
• Find load patches in a manner comparable to PC
  ice classes
• Check the hull response with linear and
  non-linear FE analysis
• Check the ice load effects on the CCS
• This is a new and comprehensive system, that
  builds on the new IACS Polar Rules, reflecting
  the state-of-the-art in our knowledge of ice
  loads and structural strength.

21

• Thank you.
• Comments? Questions?