Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: When a sailing ship passes a moored ship the moored ship experiences forces and
moments. These forces and moments cause the moored ship to move. The resulting ship
motions due to the passing ship can sometimes be more severe than the ship motions due
to ocean waves and can cause serious accidents at moorings such as the failing of mooring
lines or even the total break away of the ship from the berth. Since bulk carriers and tankers
were traditionally the largest seafaring ships, passing ship studies have focused mainly on
these vessels, but recently container ships have grown to a comparable size. In this study an
existing numerical model “Passcat” is validated with physical model measurements for a
Post Panamax container ship passing a Panamax bulk carrier. Other existing mathematical
formulae are also evaluated by comparison with these model tests.
In the physical model tests the passing speed (V), passing distance (G), depth draft ratio
(d/D) and the presence of walls and channels were varied. It was found that the passing ship
forces are proportional to the passing speed to the power of 2.32. This is slightly higher than
the generally accepted quadratic relationship for passing ship induced forces. Similar
relationships were found for the other variables.
The numerical model results were compared to the physical model measurements by
determining agreement ratios. A perfect agreement between the numerical and physical
models would result in an agreement ratio of 1. Agreement ratio boundaries, wherein
agreement would be regarded as good, were drawn between 0.7 and 1.3. The numerical
model, Passcat, was found to under predict the passing ship forces. It was found that
Passcat is valid for a wide range of sensitivities and remains within the agreement ratio limits
as long as passing speed is limited to 10 knots (kt), depth draft ratio to more than 1.164,
passing distance to less than four times the moored ship beam (Bm) for surge and sway
estimation and passing distance to less than three times the moored ship beam for yaw
estimations. These limits are true for no structures in the water. For structures in the water
only the passing speed limits are different. When quay walls are present, the surge and
sway forces will only provide acceptable answers at passing speeds below 9kt. When 9Bm
or 12Bm channels are present, the sway force will only provide acceptable answers at
passing speeds below 7kt. When a 6Bm channel is present, the yaw moments will only
provide acceptable answers at passing speeds below 6kt.
From the mathematical model evaluation study it was found that empirical or semi empirical
methods can not provide answers with good agreement to the physical model when walls or
channels are present. For the open water case, it is only the Flory method that can provide
answers with good agreement to the physical model for surge, sway and yaw forces. The
Flory method can provide answers with acceptable agreement within narrow boundaries of
passing distance (1 to 2 times the beam of the moored ship), passing speed (4 kt to 14 kt)
and depth draft ratio (less than 1.7). The numerical model, Passcat can be used with little
effort to provide answers with better agreement to the physical model for a larger range of
variables. / AFRIKAANSE OPSOMMING: Wanneer ’n skip verby ‘n vasgemeerde skip vaar, ondervind die vasgemeerde skip kragte en
momente. Hierdie kragte induseer beweging van die vasgemeerde skip. Die beweging kan
soms groter wees as die effek van wind of golwe. Indien die bewegings groot genoeg is kan
dit van die vasmeer lyne van die skip laat breek, of al die lyne laat breek sodat die skip vry in
die hawe ronddryf. Aangesien erts skepe en tenk skepe vir jare die grootste skepe in the
wêreld was, het die meeste van die skip interaksie studies op daardie skepe gefokus. Die
grootte van behouering skepe het egter in die onlangse tye gegroei om dimensies soortgelyk
aan die van erts en tenk skepe te hê. In hierdie studie word ’n bestaande numeriese model
“Passcat” gestaaf met fisiese model metings op ’n Post Panamax behoueringskip wat verby
‘n Panamax erts skip vaar. Bestaande wiskundige formules is ook getoets deur dit met
dieselfde fisiese model metings te vergelyk. In die fisiese model studie is die spoed van die skip (V), tussenafstand (G), diepte diepgang
verhouding (d/D) en die teenwoordigheid van kaai mure en kanale in die water getoets. Daar
is gevind dat die kragte op die vasgemeerde skip direk eweredig is aan die spoed van die
skip tot die mag 2.32. Dit is effens meer as die algemeen aanvaarde kwadratiese verhouding
tussen vloeistof sleurkrag en vloeisnelheid asook tussen skip interaksie kragte en vaar
snelheid. Soortgelyke verhoudings is vir al die veranderlikes bereken.
Numeriese model resultate is vergelyk met die fisiese model om die verhouding van
ooreenstemming te bepaal. ’n Perfekte ooreenstemming word voorgestel deur ’n verhouding
van ooreenstemming van 1. Grense waarbinne die verhouding van ooreenstemming as
goed beskou word is getrek tussen 0.7 en 1.3. Daar is gevind dat die numeriese model,
Passcat, kragte oor die algemeen onderskat. Passcat is geldig vir 'n breë reeks van
veranderlikes en sal geldig bly solank die skip spoed tot 10 knope, diepte diepgang
verhouding tot meer as 1.164, tussenafstand tot minder as vier skipwydtes (Bm) vir 'surge'
en 'sway' kragte en tot minder as drie skipwydtes vir 'yaw' momente beperk word. Hierdie
grense is opgestel vir geen strukture in die water. Vir strukture in die water word slegs die
skip spoed aangepas. Wanneer daar mure in die water is sal 'surge' en 'sway' slegs geskikte
antwoorde gee as die skip spoed tot 9 knope beperk word. Vir 9Bm of 12Bm kanale sal
geskikte antwoorde vir 'sway' kragte slegs voorkom met 'n skip spoed minder as 7 knope. Vir
6Bm kanale sal geskikte antwoorde vir 'yaw' momente slegs voorkom met 'n skip spoed van
minder as 6 knope. Van die wiskundige model evaluasie studie is gevind dat empiriese of semi empiriese
metodes nie resultate met goeie ooreenstemming tot the fisiese model metings kan gee,
wanneer daar kaai of kanaal mure in die water is nie. Vir die oopwater geval is dit slegs die
Flory metode wat antwoorde kan voorsien wat goed ooreenstem met die fisiese model vir
'surge', 'sway', en 'yaw' kragte. Die Flory metode voorsien hierdie resultate binne noue
grense vir tussenafstand (1 tot 2 wydtes van die vasgemeerde skip), verbyvaar spoed (4
knope tot 14 knope) en diepte diepgang verhouding (minder as 1.7). Die numeriese model,
Passcat, kan met min moeite antwoorde bereken wat beter ooreenstemming vir 'n groter
reeks veranderlikes gee.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17958 |
| Date | 12 1900 |
| Creators | Swiegers, Pierre Brink |
| Contributors | Toms, G., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 374 p. : ill. |
| Rights | Stellenbosch University |
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