An introduction to DHIs Mooring Analysis model content/presences/emea/uk/2016... · An introduction to DHIs Mooring Analysis model Poul Kronborg Product Area Owner, Marine MIKE Software

An introduction to DHIs Mooring Analysis model

Poul Kronborg

Product Area Owner, Marine MIKE Software Products

DHI

[email protected]

© DHI

1. Overview of Mooring analysis model and a preview of the coming

MIKE 21 Mooring Analysis (MA)

2. Model Validation

3. Example 1: Passing Vessel Induced Moored Vessel Motions

4. Example 2: Transshipment Terminal Operability

5. Questions

Agenda

01.

Overview of DHI

Mooring Analysis Software

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Moored Vessel Response Model

• Mooring Analysis model is under

active development

• Timeline of the model so far:

2011 – WAMSIM

2016 – DVRS

2017 – MIKE 21 MA

• MIKE 21 MA is still under

development, but examples of

the User Interface will be shown

Geographical coordinates for mooring system components

Irregular frequency filtering for single and multibody body systems

Greatly improved user interface

More accurate calculation of line and fender forces

Faster convergence to equilibrium position of the system

Improved temporal handling

Main developments in this phase

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Moored Vessel Modelling – MIKE 21 MA

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• MIKE 21 MA solves the equation of motion for the floating

vessel in all 6 degrees of freedom in the time domain

Applications:

Single Buoy Moorings

Passing Vessel Induced Vessel Response

Tandem Moored Vessels

Berth Operability/Downtime Analysis

Nearshore/Offshore Mooring Design

Floating Breakwaters / Wind Turbines

Moored Vessels Adjacent to Reflective Structures

Moored Vessels in Sheltered Areas

Accurate representation of vessel hull geometry and gyrostatic data.

Wave diffraction forces calculated from non-linear, non- uniform incident wave fields or flow fields produced by Mike21 and BW.

Implicitly resolves both bound and free long period waves in shallow water

Non-linear restoring forces due to mooring lines, fenders and posts

Frictional damping in the surge and roll modes due to scraping along a fender

Viscous surge and sway damping

Wind, current forces and 2nd order wave drift forces

Irregular frequency filtering for single body systems

Capabilities of MIKE 21 MA

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Overview of the M21MA Model

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Theoretical background for DVRS • FRC:

• Boundary element method code based on linear potential flow theory

• Solves radiation and diffraction problems in order to compute first order wave induced

frequency response functions of offshore structures (added mass, radiation damping,

exciting forces)

• Solves second order drift force frequency response functions based on momentum

conservation (far-field formula)

• MIKE 21 MA:

• Converts the frequency response functions from FRC to the mooring analysis simulation

time domain

• Calculates the exciting forces using Haskind relation from 2D (H,P,Q) or 0D (eta) wave

inputs

• Calculates second order drift forces from 2D (H,P,Q) or 0D (eta) wave inputs and FVRE

calculated drift force frequency response functions

• Calculates wind and current forces based on drag curves

• Calculates mooring forces based on force vs. deflection curves (line, fender)

• Uses the equation of motion for body dynamics to calculate the movement of the floating

bodies with the fourth order Runge-Kutta method

Placement in MIKE 21 In order to make it easier to find

this new implementation, we have

made a separate group under MIKE

21 called :

Maritime

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MIKE 21 Mooring Analysis (MA)

• Overall standard MIKE menu set-up

• Main items in menu tree:

• Material profiles

• Vessels

• Port Data

• Mooring Set-up

• Environmental Conditions

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MIKE 21 Mooring Analysis (MA): Material profiles

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MIKE 21 Mooring Analysis (MA): Vessels

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MIKE 21 Mooring Analysis (MA): Port Data

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MIKE 21 Mooring Analysis (MA): Mooring Setup

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MIKE 21 Mooring Analysis (MA): Mooring Setup

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MIKE 21 Mooring Analysis (MA): Mooring Setup

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MIKE 21 Mooring Analysis (MA): Mooring Setup

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MIKE 21 Mooring Analysis (MA): Mooring Line data

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MIKE 21 Mooring Analysis (MA): Environmental conditions

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MIKE 21 Mooring Analysis (MA): Output

Results – Cargo ship P2-class

No. of

lines Position

Initial set-up Optimised set-up

incl. shore tension

Max. force [kN] Max. force [kN]

1 stern line 221 153

2 stern line 223 157

3 aft spring line 258 203

4 aft spring line 251 199

5 fore spring line 258 175

6 fore spring line 291 170

7 bow line 173 150

8 bow line 172 150

9 aft breast line (with ST*) - 157

10 aft spring line (with ST*) - 183

11 fore spring line (with ST*) - 183

12 fore breast line (with ST*) - 114

OCIMF Recommendation :

• Wire: 55% MBL

• Synthetic ropes: 50% MBL

• Polyamide: 45% MBL

Here: 0.50*480 kN = 240 kN

Results – Mooring forces of further investigated vessel types

Ship type MBL [kN] Reduced MBL

[kN] Max. force [kN]

Percentage of

line usage

Cargo ship P2-class

(8 Lines) 480 240 291 121%

Cargo ship P2-class

(8 + 4 lines with st) 480 240 203 85%

Pontoon

(ballasted) 990 495 144 29%

Pontoon

(loaded) 990 495 280 57%

Jack-up ship 1

(initial set-up 6 lines) 512 230 263 114%

Jack-up ship 1

(6 lines + 2x spring

lines)

512 230 180 78%

Jack-up ship 2

(initial set-up 12 lines) 850 425 277 65%

Results - Motions of further investigated vessel types

Ship type Surge [m] Sway [m] Heave [m] Roll [°] Pitch [°] Yaw [°]

Cargo ship P2-class

(8 Lines) 4.49 0.06 0.40 1.62 0.19 0.16

Cargo ship P2-class

(8 + 4 lines with st) 2.72 0.05 0.40 0.60 0.19 0.14

Pontoon

(ballasted) 0.19 0.03 0.39 0.11 0.18 0.08

Pontoon

(loaded) 0.94 0.17 0.41 0.34 0.20 0.51

Jack-up ship 1

(initial set-up 6 lines) 2.40 0.12 0.40 0.21 0.21 0.40

Jack-up ship 1

(6 lines + 2x spring lines) 1.58 0.12 0.40 0.13 0.19 0.32

Jack-up ship 2

(initial set-up 12 lines) 0.94 0.17 0.39 0.22 0.20 0.14

02.

Model Validation

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Validation of DVRS – Port of Brisbane

Passing Vessel induced Moored vessel motions

• Passing Tanker – 46,900 m3

• Passing distance – 130m

• Passing speed – 8knots

• Line pre-tension – 10 tonnes

Scale Model

Numerical Model

Drawdown comparison

Measured (black) DVRS (blue)

Comparison of vessel motions

Measured (black) DVRS (blue)

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Square root of

surface elevation

spectra

(HS=4.91m, TP=11.0s at

offshore boundary)

Measured (blue)

WAMSIM (red)

Square root of vessel

motion spectra

Measured (blue)

WAMSIM (red)

• LNG Carrier

• 6 linear – elastic mooring

lines

• 2 linear – elastic fenders

• L – shaped Harbour

Validation of WAMSIM – LNG moored in Sheltered Harbour

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• Two LNG Tankers moored

side by side

• 4 linear – elastic mooring

lines

• 2 linear – elastic fenders

• 4 chains

Validation of WAMSIM – Tandem Moored Vessels

Square root of vessel motion spectra

Vessel 1 Vessel 2

Swell Hs Swell Tp Swell Direction Wind Hs Wind Tp Wind Sea Direction

1.5m 16s 25deg 0.5m 7.5s 0deg

03.

Example 1: Passing Vessel Induced Moored

Vessel Motions

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• Port of Brisbane (PoB) is one of Australia’s fastest growing

container Ports

• Channel optimisation to allow larger vessels to transit

• DHI undertook numerical modelling study to identify the affects

of moored vessel motions induced by passing ships at several

key berths

Port of Brisbane Channel Optimisation

Integrated Impact Assessments

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• navigational studies

• channel sedimentation studies

• dredge spill investigations;

• marine ecology and water quality impact assessments

• collision risk with marine mega fauna

• oil spill risk assessment

• underwater sound pollution

• Numerical modelling is often undertaken to solve one particular task

• Limits potential for coupled impact assessment and often makes it difficult

to compare independent studies

• Integrated numerical modelling platform provides the foundation for

multipurpose investigations

• PoB model capabilities :

Wave & Hydrodynamic Modelling

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• DHI’s spectral forecast model for Australian waters (OzSea) to

model locally generated wind waves and swell

• MIKE 21 HD FM to model tidally driven circulation in Moreton Bay

• Spatial resolution refinements of triangular mesh down to 10 m

were made within the navigation channel

• Inner section of the shipping channel, the model resolution was

increased to a 3 x 3m quadrangular mesh

• Validation of the HD model against recorded water levels was

undertaken at five stations

Passing Vessel Modelling

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• Drawdown is generated by a drop in surface elevation along

the length of the hull of the moving vessel.

• Simulate the drawdown wave induced by passing vessel in

MIKE 21 HD

• Pressure field representing the moving stencil was

interpolated onto the model domain grid

• Pressure field generated from 3D vessel grid files and

interpolated to a 2D stencil

• Spatial resolution of 0.2 m x 0.2 m

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Passing Vessel Annimation

Passing Vessel Modelling

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Vessel LOA (m) Beam

(m) Draft (m)

Displacement

(m3)

MR 10.4 183 33 10.4 48,180

LR 10.4 226 32.5 10.4 60,507

MR 11.2 183 33 11.2 52,200

LR 11.2 226 32.5 11.2 65,622

• 9 passing vessel scenarios were

modelled in total.

• Focus on 2 tankers at 2 load states

• For equivalent draft, LR tankers are

~10-15,000m3 heavier than MR tanker

• Results from MIKE 21 HD directly fed

into moored vessel model

Results – Surge Motions of Moored Vessel

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• The largest vessel motions occur at

the Caltex Berth

• All except the Cement berth, the

MR vessel causes larger overall

moored vessel motions than the LR

for equivalent draft.

• Although the maximum drawdowns

from the passing of the LR tankers

at the berths are higher, the

moored vessel motions are lower at

most berths.

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• The vessel generating the maximum drawdown varies with

distance from the vessel to the edge of the model boundary

• For two vessels with identical draft and almost identical

width, although the maximum extent of the drawdown field

is greater for the longer vessel, the wider draw down wave

dissipates more slowly with distance.

• As a result, the longer vessel will only cause larger draw

down than the short vessel after a certain distance away

from the hull.

Passing distance threshold

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• Although the maximum extent of the

drawdown field is larger for the LR

tanker, the water level induced

pressure gradients at the moored

vessel are lower under the passing LR

scenario.

• Lower in line and transverse gradients

from the passing of the LR tanker

results in lower turning moments of

the vessel

Drawdown variability

04.

Example 2: Transshipment Terminal Operability

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Transshipment Terminal Operability Objective

• Development of an offshore transhipment facility for the transfer of iron ore from shallow draft vessels to ocean going vessels

• Determine operability of a number of tandem moored vessel systems

• Process:

• Run FRC for each of the multibody systems (Nves)

• Create single body MIKE 21 MA setups (mooring system) in MIKE 21 MA for each of the multibody systems and convert these to multibody setups (Nves)

• Determine environmental forcings to be run in order to adequately calculate operability (Nenv)

• Use MIKE 21 MA setups as templates to generate batches of MIKE 21 MA setups for each mooring system and environmental condition. In total Nves * Nenv MIKE 21 MA setups will be generated

• Determine the number of scenarios which exceed operability threshold for each mooring system and calculate operability by: Nfailed / Nenv

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Transshipment Terminal Operability FVRE and DVRE setups

• 8 Multibody systems were run

• Up to 4 bodies were run in this study

• 3 body case shown as example

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• Environmental forcing conditions were provided as hourly values over the years 2000-2015

• Timeseries’ of the environmental conditions were created for each hour. This resulted in 90,000+ distinct environment conditions

• Winds: Constant timeseries of wind speed and direction was generated for each simulation

• Current: Constant timeseries of current speed and direction was generated for each simulation

• Waves:

• Hs, Tp and direction were provided for both swell and wind wave components

• Using the Pierson Moskowitz spectrum and the Hs and Tp provided with MIKE’s random wave generator, timeseries’ of surface elevation of the swell and wind wave for each simulation was generated and processed to MIKE 21 MA inputs

• 90,000+ Wave, Wind and Current Conditions

Transshipment Terminal Operability Environmental Conditions

Transshipment Terminal Operability Results

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• Example Run Times:

• FRC: 3 body case, 7824 submerged panels = 27hrs

• Mike 21 MA: 90,000 simulations = 2 days

• The final result were operability tables detailing the operability for each mooring system.

• This was extended to detail the operability in each year and month between 2000-2015.

• These results helped the client choose which mooring system to develop

Scenario Individual Relative Combined

Scenario A 97% 98% 97%

Scenario B 95% 97% 95%

Scenario C 94% 98% 95%

Summary

• MIKE 21 MA is a highly sophisticated model which, in conjunction with MIKE 21 FM HD & BW can accurately

represent vessel motions as a result of highly complex, non – linear wave fields

• Easy to use GUI with well defined inputs/outputs

• Outputs are all dfs0 and post-processing is easily done with the MIKE 21 toolbox PP tools

• MIKE 21 MA is capable of accurately assessing moored vessel response from the most simple cases (single

vessel in open water) to very complex cases (multiple vessels, reflective quays)

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Thank you Poul Kronborg [email protected]

© DHI