Ocean Engineering: Teresa Abramowicz-Gerigk, Zbigniew Burciu, Wojciech Górski, Maciej Reichel
Ocean Engineering: Teresa Abramowicz-Gerigk, Zbigniew Burciu, Wojciech Górski, Maciej Reichel
Ocean Engineering: Teresa Abramowicz-Gerigk, Zbigniew Burciu, Wojciech Górski, Maciej Reichel
Ocean Engineering
journal homepage: www.elsevier.com/locate/oceaneng
Full scale measurements of pressure field induced on the quay wall by bow T
thrusters – indirect method for seabed velocities monitoring
Teresa Abramowicz-Gerigka,∗, Zbigniew Burciua, Wojciech Górskib, Maciej Reichelc
a
Faculty of Navigation, Gdynia Maritime University, Al. Jana Pawla II 3, 81-345, Gdynia, Poland
b
Enamor Ltd., Inzynierska 1, 81-512, Gdynia, Poland
c
The Foundation for Safety of Navigation and Environment Protection, Chrzanowskiego 36, 80-278, Gdansk, Poland
A R T I C LE I N FO A B S T R A C T
Keywords: The paper presents the results of full-scale experimental investigation of loads generated on the quay wall by
Bow thruster jet bow thrusters during unberthing of a self-manoeuvring vessel. The presented research allowed for the com-
Full-scale measurements parison of the measurements results with generally accepted empirical prediction methods and confirmed the
utility of the developed measuring setup for the on-line monitoring of jet induced loads. The conclusions from
the research are focused on the strengths and limitations of the presented measuring method and its applicability
for the on-line monitoring of loads induced by bow thrusters on seabed protection along the quay wall.
1. Introduction the cube root of the applied power which means that the outflow ve-
locities can reach several m/s.
The bow thruster induced wash is the reason of degradation pro- Different types of seabed protection are used to prevent negative
cesses of the seabed and seabed protections situated along the quay effects of stress fluctuations on the surface layer of the seabed (PIANC,
wall. The sediments movement and relocation of seabed protection 2015). Ship Masters should comply with the requirements related to
elements reduce the under keel clearance and in case of large damages operational limits for the propellers and thrusters power used during
can affect the stability of the quay wall. These phenomena are normally port manoeuvers dependent on the seabed resistance to scoring or da-
included in design processes and should be introduced in complex mage. The limits can be exceeded in emergency cases when all available
safety assessment methods of ship and port operation (Gerigk, 2015; means can be used to ensure ship safety.
Rutkowski, 2016; Santos et al., 2014). The more precise estimation of berthing and unberthing loads closer
Bow thruster wash is important in shallow inland waterways, lake to their real values allows accepting fewer restrictions for propeller and
and river harbours with dynamic changes of depths. In modernized sea thruster power used during manoeuvres. The higher limits mean the
ports a growing number of high powered big vessels operated in con- widening of an operational window for self-manoeuvring and decrease
fined areas increase the importance of vessels impact on port con- of the operational costs related to the tug boats assistance.
structions with significant share of the propeller and thruster jet in- There are several empirical methods commonly used for the pre-
duced wash. Very large container vessels can perform manoeuvres in diction of a jet velocity distribution. The existing design guidelines
very tight areas in strong weather conditions up to the port operational provide the useful empirical formulae but some modern vessels like
limits using their thrusters and propellers to increase the efficiency of large containerships are out-of-the-range of the conservative solutions
manoeuvres assisted by tug boats. (http://www.pianc.org/edits/articleshop.php?id=2015180 PIANC,
The average bow thruster power of most widely operated self 2015).
manoeuvring vessels like ferries in terms of the projected windage area The empirical methods and simplified CFD simulations of seabed
is assumed from 0.5 kW/m2 to 0.96 kW/m2, which for 150 m −170 m scoring are based on main parameters of propellers and thrusters not
in length ferry gives usually bow thrusters power about 2 × 1200 kW. considering the actual characteristics what can be also a reason for the
The ultra large container ships over 8000 TEU (twenty feet equivalent uncertainty in thrust assessment especially important for inland vessels
unit), 300–400 m in length are equipped with several 2000–3500 kW (Skupien and Prokopowicz, 2014; Jachowski, 2008).
thrusters. The power of bow thrusters installed on cruise vessels can The assessment of possible jet induced damages is dependent on the
reach 5500 kW (Wartsila, 2016). The outflow velocity is proportional to available information of exceedance of jet velocity limits and
∗
Corresponding author.
E-mail addresses: tagerigk@am.gdynia.pl (T. Abramowicz-Gerigk), zbj@am.gdynia.pl (Z. Burciu), wojciech.gorski@enamor.pl (W. Górski), maciejr@portilawa.com (M. Reichel).
https://doi.org/10.1016/j.oceaneng.2018.05.036
Received 8 February 2018; Received in revised form 5 April 2018; Accepted 17 May 2018
0029-8018/ © 2018 Published by Elsevier Ltd.
T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 4. The relationship between the flow velocity and dynamic pressure va-
lues: pB – dynamic pressure calculated from Bernoulli equation; pm – measured
values of the dynamic pressure, pB-pm - absolute error; % relative error - re-
lative percentage error.
Fig. 5. The free surface deformation with eddies observed during unberthing of
Fig. 3. Full-scale pressure measurement results – an example of the laboratory m/f Stena Baltica at Helskie II Berth in Port of Gdynia.
tests carried out in the towing tank.
Fig. 5.
where: p [Pa] – is the dynamic pressure, v[m/s] is the flow velocity. The unsteady turbulent flow generated by bow thrusters near the
The diagram showing the difference between the dynamic pressure quay wall is the cause of pressure oscillations, periodical in a short time
values measured during the tests and calculated from Bernoulli Eq. (2) of constant settings of bow thrusters. The oscillations are considered as
is presented in Fig. 4. The observed relative percentage error was less the main cause of braking of the polypropylene ropes connecting sand
than 5%. filled bags of seabed protection. The turbulent events such as eddies and
p = 0.5 ρv 2 turbulent bursting play a critical role in the sediment scouring and
(2)
transport.
where v[m/s] is the flow velocity, ρ = 1000 kg/m is the water density.
3
The collected pressure distribution is dependent on the flow direc-
tion near the wall. The sensors positioned perpendicular to the wall can
2.3. Full-scale field measurements of bow thruster jet induced pressure measure the total pressure corresponding to the water velocity. Velocity
components perpendicular to the wall give the positive readings above
The flow induced during unberthing of m/f Stena Baltica, observed the static pressure value corresponding to the water depth level. The
on the free surface at Helskie II berth in Port of Gdynia is presented in velocity components lateral to the wall cause the pressure decrease and
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 6. Full scale measurements - time history of pressure collected during unberthing manoeuvre U1: Ci, i = 1, …,8 number of a column of pressure sensors; PMj,
j = 1, …,8 - pressure sensors in each column.
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 6. (continued)
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Three values and their relations are crucial when calculating velo-
cities behind a working propeller: efflux velocity, longitudinal decay
and radial decay of axial velocity. Different empirical methods pre-
sented in the literature can be used to calculate these values, all di-
viding the description of propeller velocities in two regions, i.e. zone of
flow establishment and zone of established flow (Hamill, 1987).
Pd = 1 2 ρw U0 2Q (4)
Fig. 7. 3D distribution of the bow thruster induced pressure field [kPa] mea-
sured in the successive seconds t = 3,5 s and t = 7 s on the quay wall during where Pd – is the bow thruster generated power [W], ρw - is the water
unberthing manoeuvre U1: Ci, i = 1, …,8 - columns of pressure sensors, PMj, density [kg/m3].
j = 1, …,8 - pressure sensors in each column.
Combining equations (3) and (4) the resultant formula for calcula-
tion of the initial flow velocity U0 in front of a bow thruster may be
negative readings below the pressure values corresponding to the water written a follows:
depth level. The time histories of pressure generated on the quay wall 1
3
collected during unberthing manoeuvre U1 are presented in a separate P
U0 = 1.37 ⎜⎛ d 2 ⎟⎞
drawing for each from 8 columns Ci, i-1, …,8 of 8 pressure sensors PMj,
⎝ ρw DP ⎠ (5)
j = 1, …,8 (Fig. 6).
The most frequent unberthing procedure of a ferry was a combi- From a practical point of view, it is more suitable to transform Eq.
nation of transverse and forward ship motion. The significant pressure (5) to the form including the bow thruster diameter DBT (6). Usually the
values were collected in column C6 at sensors PM2, PM3 and PM4 in bow thruster diameter is about 2%–5% larger than the propeller dia-
front of the outlet opening of working bow thruster BT1 at the begin- meter:
ning of the manoeuvre and in columns C7 and C8 when the ship started DBT = 1.02 − 1.05DP (6)
to move forward. No pressure changes were observed in column C1.
Negative values about −4 kPa were collected in columns C2 and C3 Eq. (5) may be transformed to Eq. (7):
after 10 s of the manoeuvre, the lower values about −6 kPa were ob- 1
3
served in columns C4 and C5 just at the beginning of the manoeuvre Pd ⎞
U0 = 1.41 ⎜⎛ 2
⎟
and they increased to −2 kPa after 15 s, when the ship moved forward. ⎝ ρw DBT ⎠ (7)
3D distribution of pressure field in successive seconds t = 3,5 s and
It should be also noted that two factors reducing the efflux velocity
t = 7 s during unberthing manoeuvre U1 is presented in Fig. 7.
have to be taken into account: energy loss coefficient and thrust loss
The time history of pressure generated on the quay wall collected
coefficient. Actually, it is not possible to estimate both factors properly,
during unberthing manoeuvre U2 is presented in Fig. 8.
however based on experiments (Blaauw and van de Kaa, 1978) the most
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 8. Full scale measurements - time history of pressure collected during unberthing manoeuvre U2: Ci, i = 3, …,7 - number of a column of pressure sensors; PMj,
j = 1, …,8 - pressure sensors in each column.
common formula to calculate the efflux velocity, including losses, is (PIANC, 2015) of necessary bed protections.
presented in Eq. (8).
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 8. (continued)
The generally accepted methods recommended by PIANC (PIANC, where: r is the radial distance to the propeller axis.
2015) and used in practice called German method (Fuehrer and Table 3 presents the radial decay of axial velocity at the propeller
Römisch, 1977) and Dutch method (Blaauw and van de Kaa, 1978) radius r equal to half propeller diameter and distance from the bow
estimate the zone of flow establishment as 2.6 and 2.8 propeller dia- thrusters x equal to 0.4 B for bow thrusters BT1 and BT2 calculated with
meters respectively. different methods.
Stewart (1992) and Hashmi (1993) in their latest research propose a The radial decay of axial velocity is about 90%, only in the method
value of 3.25 propeller diameters as the end of the zone of flow es- proposed by Albertson et al. (1950) is about 50%.
tablishment, while Lam et al. (2011) suggested 3.68 propeller dia-
meters. 3.4. Quay wall and bed velocities
In most of the cases the proposed description for the maximum axial
velocity in the zone of established flow may be written according to Eq. When a bow thruster, assumed as the ducted propeller, is directed
(9). towards a quay wall, the water jet strikes the wall directly and is de-
x 2
c flected from this area in all directions. The five zones of flow dis-
Umax / U0 = c0 + c1 ⎛ ⎞⎜ ⎟
tinguished by Schmidt (2000) are presented in Fig. 11.
D
⎝ P⎠ (9)
The bow thruster jet observed in CFD simulation is presented in
where: Ct is the thrust coefficient, β - is the blade area ratio, P’ - is the Fig. 12.
pitch ratio equal to propeller pitch related to the propeller diameter. The jet velocity in the zone of flow establishment (Zone 1) is as-
Table 2 presents the values of coefficients c0, c1 and c2 of Eq. (9) sumed as:
proposed by different authors.
Umax = U0
Hashmi (1993) presented another way to describe the axial velocity
decay using an exponential equation Eq. (10). In Zone 2 i.e. zone of established flow, the equations presented in
paragraphs 2.1–2.3 may be used to predict the jet velocities. The
Umax / U0 = 0.638e(−0.097x / DP ) [−] (10)
equation describing jet velocity in Zone 2 is valid for the distance up to
0.7 L, where L is the distance between bow thruster outlet opening and
3.3. Radial decay of axial velocity quay wall, because of the velocity decrease when jet is approaching the
wall.
It is assumed that the radial decay of axial velocity has a normal Zone 3 where the jet hits the wall is called the pressure zone, since
(Gaussian) distribution around the axis and is valid only in the zone of the kinetic energy is converted into pressure, which finds its maximum
established flow. The equation for radial decay has therefore the fol- where the velocity is zero. The conversion of the flow velocity to
lowing form: pressure takes place over a distance of 0.3 L in front of the wall.
Zone 4, radial wall jet zone, is characterised by the conversion of the
1 r2 ⎞ pressure back to kinetic energy, flowing radially from the pressure
Ux , r / Umax = exp ⎛−
⎜
2 2
⎟
⎝ 2C r x ⎠ (11) point. At the distance of 0.3 L, the flow velocity reaches its maximum
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 10. Maximum and minimum dynamic pressure values collected during
unberthing manoeuvres: Ci, i = 1, …,8 - number of the column of pressure
sensors; PMj, j = 1, …,8 - pressure sensors in each column.
Table 2
Coefficients c0, c1, c2 proposed in different methods.
Method c_0 c_1 c_2
Table 3
Radial decay of axial velocity for BT1 and BT2 calculated with different
methods.
Method cr −
1 Ux,r/Umax(Dp/2)
2Cr 2
BT1 BT2
again.
According to Römisch (1975) the loss of velocity during the change
of flow direction due to the wall is negligible. The velocity in Zone 5,
i.e. at the bottom, is therefore equal to the velocity just in front of the
quay wall.
Introducing the dimension L in Eq. (9) and using the most common
value proposed by Schmidt (2000) the axial velocity of the jet induced
by the bow thruster may be calculated according to Eq. (12) used in
German method (PIANC, 2015):
−1.0
L
Umax / U0 = 1.9 ⎛ ⎞
⎜ ⎟
⎝ DP ⎠ (12)
The maximum velocity at the seabed in front of the quay wall:
−1.0
L
Fig. 9. Distribution of the bow thruster induced pressure field [kPa] measured Umax seabed/ U0 = α1.9 ⎛ ⎞
⎜ ⎟
D
⎝ P⎠ (13)
in the successive seconds t, t = 9 s, 10 s, 12 s, on the berth wall during un-
berthing manoeuvre U2: t – time; Ci, i = 3,…,7 - columns of pressure sensors, Where α is the correction factor of value between 0 and 1, dependent
PMj, j = 1, …,8 - pressure sensors in each column. on L/Dp ratio and z – the distance between the propeller axis and
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
Fig. 11. Five zones of bow thruster jet induced flow near a vertical tight wall
originally presented by Schmidt (2000): z – height of bow thruster axis above
seabed, DBT – bow thruster tunnel diameter, L – distance between the wall and
bow thruster outlet opening.
Fig. 13. Changes of water level at the quay wall: time history of the whole
measurement and measurement in time from 0 to 10 min.
Fig. 12. CFD simulation of bow thruster jet during unberthing in shallow water:
h/T = 1.7.
Table 4
Bed velocities calculated using online pressure measurements and empirical
methods.
Measurement Calculation German method Dutch method Fig. 14. Scheme of the monitoring system for loads generated on the quay wall
(Römisch, 1975) and seabed.
⎝ DP ⎠ (14)
4 2,83 7,57 7,12 2,88 2,25 2,74 2.15
Both German and Dutch methods should be used as complete design
procedures independently. PIANC (2015) report does not distinguish
seabed (PIANC, 2015). Eq. (13) can be used when L/Dp is in the range any formula, however for vessels with bow thrusters situated close to
between 3 and 8, in other cases Eq. (12) should be applied. the quay wall, like inland cargo vessels, German method gives more
The Dutch method compiled from the studies done by Blaauw and than twice bigger bed velocities than Dutch method.
van de Kaa (1978), Verhey (1983), Blokland and Smedes (1996) re-
commend Eq. (14) to calculate the maximum velocity caused by bow 4. Indirect method of monitoring the seabed velocities generated
thruster jet at the bottom: by bow thrusters near the quay wall
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T. Abramowicz-Gerigk et al. Ocean Engineering 162 (2018) 150–160
where the turbulent jet hits the wall in Zone 3 are about 8 kPa and 4 kPa the form of a mattress of geotextile sand filled bags. It can save main-
respectively. The related velocities are 4 m/s and 2.8 m/s. tenance cost related to the replacement of a wide area of damaged
The mean pressure value obtained from full scale measurements on elements and allows avoiding the maintenance delays in operation of
the on the quay, velocity related to this pressure assumed as bed ve- the berth.
locity, initial velocities U0_BT1 and U0_BT2 for BT1 and BT2 thrusters
accordingly, velocities calculated at the distance L = 0,4 B – measured Acknowledgement
from the bow thruster outlet opening to the wall and z = 0.9 T (distance
between the bow thruster axis and seabed) using both German and This work was supported by the projects: RPPM.01.01.01-22-0068/
Dutch methods are presented in Table 4. 16-00, “Development of a prototype of a system for monitoring the
The bed velocities calculated using German method for transverse loads on berths and bed protection in the area of ship berthing along
thrusters are equal 2.88 m/s and 2.25 m/s for BT1 and BT2 accordingly. with the implementation of the final product on the market by Enamor
The same values obtained using Dutch method are equal to 2.74 m/s Ltd. company from Gdynia” within “Smart Specialisations of Pomerania
and 2.15 m/s. There is a good agreement of empirical prediction and Region – offshore technology, ports and logistics” European program
full scale measurement for the measured mean values. and 6/2010 NCBiR/MARTEC-2009/2-1/2010 “Safe Port Entry and
The maximum pressure values observed during a few seconds of the Berthing Ship and Port Advising System as an Element of Port ITS” –
manoeuvres U1 and U2 were about 8 kPa for BT1 and 7 kPa for BT2. project within ERA-NET MARTEC European Initiative, part conducted
The corresponding velocities are 4 m/s and 3.74 m/s accordingly. at Gdynia Maritime University, Poland, sponsored by The National
The difference of 1 m/s is not significant if we assume the seabed Centre for Research and Development.
protection designed for 7 m/s velocities. Considering high powered bow
thrusters of 5000 kW in shallow water the predicted bed velocities using References
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power of thrusters above the permissible limits. This is the most im-
portant factor in the prediction of the condition of seabed protections in
160