Alaska Department of T ransportation & Public Facilities Alaska University T ransportation Center

54 Pages·2014·2.37 MB·English

by  Andrew T. Metzger

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i Alaska University Transportation Center Alaska Department of Transportation
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i Duckering Building Room 245 Research, Development, and Technology
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i P.O. Box 755900 Transfer
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Fairbanks, AK 99775-5900 2301 Peger Road
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INE/ AUTC 14.17 DOT&PF Report Number
4000(102)CB
Disclaimer
Notice
This document is disseminated under the sponsorship of the U.S. Department of
Transportation in the interest of information exchange. The U.S. Government assumes no
liability for the use of the information contained in this document. The U.S. Government
does not endorse products or manufacturers. Trademarks or manufacturers’ names appear
in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement
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Author’s Disclaimer
Opinions and conclusions expressed or implied in the report are those of the authors.
They are not necessarily those of the Alaska DOT&PF or funding agencies.

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1. AGENCY USE ONLY (LEAVE BLANK) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

Report No. 4000(102)CB December 2014 Final Report

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Cordova Floating Ferry Dock Alaska DOT&PF AKSAS 4000(102)CB
(T2-12-16)
6. AUTHOR(S)
Andrew T. Metzger, Ph.D., P.E.

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT
Alaska University Transportation Center NUMBER
University of Alaska Fairbanks
INE/AUTC 14.17
Duckering Building Room 245
P.O. Box 755900
Fairbanks, AK 99775-5900
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY
REPORT NUMBER
State of Alaska, Alaska Dept. of Transportation and Public Facilities
Research and Technology Transfer Report # 4000(102)CB
2301 Peger Rd
Fairbanks, AK 99709-5399
11. SUPPLENMENTARY NOTES

12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

No restrictions
13. ABSTRACT (Maximum 200 words)

This study began the evaluation of the Cordova floating ferry dock using the ANSYS AQWA software. The AQWA software models the effects of
waves, wind and current on floating structures. Floating bodies are modeled as a point-mass with inertial and hydrostatic characteristics. As part of the
study, the critical wave characteristic was defined. During the modeling it was found that AQWA can only model rigid bodies and that the Cordova
floats experience a wide range of wave periods and directions. Consequently, AQWA requires adaptation to fully model the ferry dock at Cordova.
15. NUMBER OF PAGES
14- KEYWORDS : Floating docks (Pmhbmpmff) 54

16. PRICE CODE

N/A
17. SECURITY CLASSIFICATION OF 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT
REPORT OF THIS PAGE OF ABSTRACT

Unclassified Unclassified Unclassified N/A

NSN 7540-01-280-5500 STANDARD FORM 298 (Rev. 2-98)
Prescribed by ANSI Std. 239-18 298-1
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SI* (MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
in inches 25.4 millimeters mm
ft feet 0.305 meters m
yd yards 0.914 meters m
mi miles 1.61 kilometers km
AREA
in2 square inches 645.2 square millimeters mm2
ft2 square feet 0.093 square meters m2
yd2 square yard 0.836 square meters m2
ac acres 0.405 hectares ha
mi2 square miles 2.59 square kilometers km2
VOLUME
fl oz fluid ounces 29.57 milliliters mL
gal gallons 3.785 liters L
ft3 cubic feet 0.028 cubic meters m3
yd3 cubic yards 0.765 cubic m3
meters NOTE: volumes greater than 1000 L shall be
MASS
oz ounces 28.35 grams g
lb pounds 0.454 kilograms kg
T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")
TEMPERATURE (exact degrees)
oF Fahrenheit 5 (F-32)/9 Celsius oC
or (F-32)/1.8
ILLUMINATION
fc foot-candles 10.76 lux lx
fl foot-Lamberts 3.426 candela/m2 cd/m2
FORCE and PRESSURE or STRESS
lbf poundforce 4.45 newtons N
lbf/in2 poundforce per square inch 6.89 kilopascals kPa
APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol
LENGTH
mm millimeters 0.039 inches in
m meters 3.28 feet ft
m meters 1.09 yards yd
km kilometers 0.621 miles mi
AREA
mm2 square millimeters 0.0016 square inches in2
m2 square meters 10.764 square feet ft2
m2 square meters 1.195 square yards yd2
ha hectares 2.47 acres ac
km2 square kilometers 0.386 square miles mi2
VOLUME
mL milliliters 0.034 fluid ounces fl oz
L liters 0.264 gallons gal
m3 cubic meters 35.314 cubic feet ft3
m3 cubic meters 1.307 cubic yards yd3
MASS
g grams 0.035 ounces oz
kg kilograms 2.202 pounds lb
Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T
TEMPERATURE (exact degrees)
oC Celsius 1.8C+32 Fahrenheit oF
ILLUMINATION
lx lux 0.0929 foot-candles fc
cd/m2 candela/m2 0.2919 foot-Lamberts fl
FORCE and PRESSURE or STRESS
N newtons 0.225 poundforce lbf
kPa kilopascals 0.145 poundforce per square inc h lbf/in2
*SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. (Revised
March 2003)

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ACKNOWLEDGMENTS
The author wish to acknowledge the technical support provided by the following:
• W. Seeling who help me with implementation of ANSYS AQWA software.
• Oceana Francis who provided the wave analysis and predictive data.

The author also acknowledges the funding provided by the Alaska Department of Transportation
& Public Facilities and the assistance of the Alaska University Transportation Center.

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Table of Contents

Acknowledgements …………………………………………………………………………………………………………………………………4
Project Summary ……………………………………………………………………………………………………………………………………..6
Annex A ……………………………………………………………………………………………………………………………………………………8
Annex B ………………………………………………………………………………………………………………………………………………….15
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Project Synopsys

The Cordova Float study was authorized by AKDOT&PF to evaluate the behavior of the floating
ferry dock at Cordova, Alaska. The purpose of the study was to gain further insight into the
forces between the “floats” used to support the ferry landing structure. The system uses a
number of pre-fabricated steel floats that are locked together to act as a support for the dock
super structure. The methodology used in the project was to model the Cordova Float system
using the ANSYS AQWA software.
ANSYS AQWA is an engineering analysis software for investigating the effects of waves, wind
and current of floating structures. Floating bodies are modeled as a point-mass with inertial and
hydrostatic characteristics of the actual body. The software has the ability to model wave
diffraction off the body and realistically demonstrate its behavior when subjected to waves,
currents, etc.
The development of the input variables can be found in Annex B. The following wave
parameters with the probability of exceedance of <1% were developed:

Critical wave height, H1/100 = 2.5 meters,
Critical wave period, T1/100 = 6.8 seconds, and
Critical wave direction = 23°.
Preliminary results of the hydro dynamics for an individual float are in Annex A.
The Cordova Float assembly was modeled as shown in the Figure 1. The floats are locked
together with very short/ stiff mooring line elements. The intent was to use the mooring line
forces to estimated forces and bending moments between barges; in all six degrees of freedom.
During the initial analysis the following challenges or the use of AQWA were identified:
• Float Modeling: AQWA can only model rigid bodies (it is not an FEM software).
However, the floats are not rigid (stiffness is not infinite) and accurate modeling will
need to reflect this. Stiffness of the mooring line elements that connect the floats are
input by the user and could be calibrated to reflect the stiffness of the floats being
connected as well as the actual physical connecting hardware. This may require
additional analysis of the floats as a shell structure (FEM analysis).
• The site of the Cordova Float is subject to a range of wave periods, propagating from a
range of directions. Annex B can serve as a basis for estimating an envelope of wave
periods and directions. Numerous analysis runs will have to be executed to determine
the maximum design forces between floats. The number of runs could be pared down
by considering predominate wave direction(s), but still using a range of wave periods.

These barriers must be overcome before a truly meaningful analysis can be completed.
However, based on the limited runs completed, excessive pitch and roll at wave periods of
about 3.1 seconds which is similar to the natural frequency of the pitch and roll.

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At this point, it was decided not to continue with the next phase of the project due to the time,
costs and uncertainties of overcoming the barriers noted. However, the information provided in
Annex B provides useful information for future work on the Cordova harbor.

Figure 1. Cordova Float model subjected to wave conditions.

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ANNEX A
Preliminary Analysis of Float System

Float 1
10’x20’x7’
Diffraction analysis
Panel size 0.2m sq; water depth 10m
Note:; similar to natural frequency in pitch and roll

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~doubled damping and run again:
Roll at 60deg with wave approach angle at 90deg
Doubled again and ran again:
End-on waves

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