Calculation and simulation of the current effects on maritime safety in Haiphong fairway, Vietnam

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Calculation and simulation of the current effects on maritime safety
in Haiphong fairway, Vietnam
Prof. Dr. Luong Cong Nho1, Prof. Dr. Pham Ky Quang2, Dr. Vu Van Duy3,
PhD. Student Bui Van Cuong4, PhD. Student Co Tan Anh Vu5,
PhD. Student Nguyen Thanh Nhat Lai6.
1. Vietnam Maritime University, luongcongnho@vimaru.edu.vn
2. Vietnam Maritime University, phamkyquang@vimaru.edu.vn
3. Vietnam Maritime University, duyvv.vck@vimaru.edu.vn
4. Faculty of Navigation, Vietnam Maritime University, bvcuong1964@gmail.com
5. Faculty of Navigation, Vietnam Maritime University, vucotananh@gmail.com
6. Ho Chi Minh City University of Transport, nhatlai_hh@hcmutrans.edu.vn
Abstract: Haiphong is the biggest port in the Northern region, with 80 million tons of cleared goods
passing through it in 2015. Haiphong fairway with 85 km length with high density of the maritime
transports, plays the vital role in the Vietnam Northern waterway system. Moreover, in this one-direction
fairway still remain complicated natural features such as many bends, branches, shallow spots and strong
current and these factors are the potential causes for maritime accidents.
One of the reasons leading to these accidents in this channel (mainly grounding and collision) is the
direct effect of the current on the process of ship course control which is pre-programmed.
With the features mentioned above, this paper focuses on analyzing the areas which potentially have
maritime risks, as well as reasons for maritime accidents involving current effects such as: Interaction
between rudder and propeller; impact on vessel’s shell when altering course; rudder cavitation problems.
According to these facts, the authors built a research model and a mathematical one by basing on the
BEM method and simulating them by the Fluent-Ansys software. Then, results of simulated calculation
of the current effect on controlling ship course in the Haiphong fairway are presented in order to improve
the safety of navigation in this channel.
To prove research outcomes, authors conducted an experiment and visually monitored the process of
ship course control on M/V TAN CANG FOUNDATION in the Haiphong fairway.
Keywords: current effect, ship course, Haiphong fairway, rudder and propeller, rudder cavitation.
1. Analyzing some potential risk areas of maritime accidents in Haiphong
fairway
Currently, the task of guiding the vessel through navigational access channels to Hai Phong port is taken
on by pilot or the ship’s captain. The average number of vessels passing through the channels daily is
60, and at times, as many as 80 vessels do. Hai Phong fairway is one-direction with several avoiding
spots, along the channels, there are areas where river branches meet, and the crooked channels consist
of several areas with restricted depths and narrow parts. In addition, the hydrometeorological particulars
of these channels can cause difficulties to navigation, for example, the current at some places can be as
strong as 4.5 knots [4].
On average 45 maritime accidents occur annually (mainly collision and grounding). Some of them are
extremely serious and cause both severe damage to property and loss of human life [4]. The main causes
to maritime accidents are the ability of the captain and pilots when handling vessels. In addition, the
effect of strong currents on vessels’ maneuverability, deviating the ships from their planted tracks is also
another cause to these.
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Maritime accidents occur mainly in four areas (which are numbered by order of their locations, starting
from Hai Phong main port to the buoy № 0, as shown in figure 1), as following [4]:
Area I: The confluence of the Cam and Ruot Lon rivers. This is a very narrow area, with floodplains
near the mouth of Ruot Lon river on one side and the main berths of Hai Phong port on the other. The
channel depth is low and the current is strong in this area, especially at high water. Furthermore, small
vessels and watercrafts usually cross between the Cam river and the Ruot Lon river and this can easily
create the risk of collision with vessels moored to berth or being aground at Ruot Lon river bank.
Area II: The confluence of the Cam and the Bach Dang rivers. There are many floodplains near the
mouth of Bach Dang river. The traffic density in the area is extremely high, and the Rules of the Road
are not very well observed. With the tide, the current always tends to the direction of motion of the ship
to the shore of Thuy Nguyen district. Therefore, there are very high risks of collision and running
aground in this area.
Figure 1 Four potential risk areas of maritime accidents in Haiphong fairway
a) Area I; b) Area II; c) Area III; d) Area IV
Area III: The junction of the Cam river, Nam Trieu, Cai Trap and Ha Nam channels. There are many
shallow areas at the water near Dinh Vu peninsula and the mouth of the Bach Dang river. The traffic
density is high and the nature of traffic is complicated in this area, especially between buoys №
30 and № 32. In addition, this area is known to be with strong and unstable currents, along with several
anchorage areas and ferry terminals.
Area IV: The junction of Ha Nam, Cai Trap channels and the inland waterway leading to Quang Ninh
provice. Many inland ships, barges and water crafts cross the channel to enter Cai Trap channel,
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especially around buoys № 19, № 21 and № 23. Furthermore, the area where larger vessels enter Lach
Huyen chanel is accompanied by extremely strong and unstable current. The large number of both
seagoing and inland waterway vessels passing through Cai Trap and Ha Nam channels makes the risk
of maritime accidents in this area more serious.
Summary: In order to assist the captain and pilot in deciding the optimal routes to guide their ships
through the above - mentioned areas, which will enhance the safety of navigation in the area, the authors
have carried out the calculation and simulation of the current effects on the course keeping ability of
vessels navigating in the fairways of Hai Phong port by calculating three problems, namely: Impact on
vessel’s shell when altering course; Interaction between rudder and propeller; Rudder cavitation
problems, based on the results of field surveys, by analysizing values and evaluation practice received,
with the experimental data are performed on the M/V TAN CANG FOUNDATION operating on the
navigational access channels to Hai Phong Port.
2. Research models and mathematical principles
2.1 The model ship for research
Our research object is the effects of current on the course keeping ability of vessels navigation in
Haiphong fairway. In order to facilitate the field surveys and collect experimental data for calculation
and simulation, the authors used a congruent model of M/V TAN CANG FOUDATION (figure 2) (this
is a container ship with the capacity of 420 TEU operating in the route between Hai Phong port and Sai
Gon port) [1, 2, 4, 7].
Figure 2 The model congruent of M/V TANCANG FOUNDATION
The first problem: When the ship alters her course, the current impact on vessel’s shell will make
additional forces (not considering the effects of the wind). To determine the additional force as well as
to analyse its effects on the ship’s maneuverability, we gave a research model according to figure 3 [3].
Figure 3 The research model with conditions as described in the situation of the first problem
Air outlet Air inlet
Water-liquid outlet Water-liquid inletFree surface
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The second problem: The interaction between rudder and propeller with different combinations of
propeller rotation and rudder angle, as illustrated in figure 4 is researched and the result of which is
analysed to find the optimal combination to keep the vessel on the pre-programmed orbit [2, 5, 6].
Figure 4 The research model for solving the second problem
The third problem: Calculating and stimulating the effects of cavitation rudder (figure 5) can help
determine the steering forces of ship during this period. The results will be used to assess the effects of
cavitation rudder on course keeping abilities of vessels navigating in Haiphong fairway.
Figure 5 The research model for solving the third problem
2.2 Mathematical principles
We apply CFD in researching the effects of current on course keeping abilities of vessels navigating in
the area. For three proposed problems, the VOF (volume of fluid) model, mixture for cavitation problem
and others models, such as [1, 2, 3, 9]: k-, k-,... are used.
- The method of VOF for solving differential equations with various phases, by adding the value of
volume fraction, if αk is the volume fraction of the number k phase, then:
1
1
n
k
k
  (1)
If k is the density of the number k phase, the density of the mixture will be:
1
n
k k
k
  (2)
Propeller
R
u
dd
er
Rudder Input
Propeller Output
Tr
an
sit
io
n
al
zo
n
e
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Then, we solve major differential equations to determine specific values:
1
1
k
n
k
k k pk kp
kk
v s m m
t 
 
   
   (3)
The value of volume fraction is determined by time step:
1 1
1 1 1
1
k
n n n n n
n n nk k k k
k k kf pk kp
f k
U s m m V
t 
    (4)
In the equation: n - the previous time step; (n+1) - the current time step; αkf - the representative value of
volume fraction of the number k phase; V - the volume of the calculating element; Uf - the volume of
water flowing through the surface according to linear methods;
kpm - the mass transferred from phase
number p to phase number k; sαk = 0.
The velocity distribution and energy can be determined by momentum equation and energy equation:
 tv v v p v v g F
t
  
      
 (5)
 eff hE v E p k T st 

    

 (6)
T - temperature; E - energy and the value of E can be determined according to (7):
1 1
/
n n
k k k k k
k k
E E 
   (7)
The standard equation describes the flow and turbulence effect in the mixture model. The vapor transport
equation determines the vapor mass fraction fvap by the following equation.
 . . . .j vapvap vap vap e c
j j j
ff f u R R
t x x x
 
   
     
(8)
In which: Re, Rc dependent on the values of static pressure p and saturation vapor pressure pvap:
If p < pvap: 
2
1
3
vapch
e e l vap vap
l
p pvR C f 
 
 (9)
If p > pvap: 2
3
vapch
c c l l vap
l
p pvR C f 
 
 (10)
In which: vch - characteristic velocity (m/s); Ce, Cc - empirically constants (Ce = 0.02; Cc = 0.01) [8,10].
3. Analysing results
3.1 The result of the first problem
Due to the limitation of the article, we calculate two situations with input parameters as following:
- Situation 1: The ship’s true course is 0000, the speed Vs is 5 m/s, wind speed Vw is 0 m/s.
- Situation 2: The ship’s true course is 0150, the speed Vs is 5 m/s, wind speed Vw is 0.
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Figure 6 The simulation results of the distribution of static pressure on both sides of the vessel
(the submerged area only) (a) and contour of volume fraction (air) (b)
In situation 1, the distribution of static pressure on both sides of the ship is nearly symmetrical. In order
to have a more detailed look, we can analyse one waterline as following:
Figure 7 The simulation results of the distribution of static pressure (a)
and pressure coefficient along the surveyed waterline (b)
Based on the result shown in figure 7, we come to the verdict: The distribution of static pressure on both
side of the waterline is symmetrical and the pressure distributing coefficient along the waterline on both
side of the vessels are near equal. There is no additional force impact on the ship’s hull in this situation.
When the ship alters her course to 0150 (situation 2), this situation can be considered as if the current
flew around the ship’s hull with an angle of 150 to the ship’s center line. The simulation result is
measured on the same waterline as in situation 1.
Figure 8 The simulation results of the distribution of static pressure
on both sides of the vessel (submerged area only)
a) b)
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Figure 9 The simulation results of the distribution of static pressure (a)
and pressure coefficient along the surveyed waterline (b)
Based on the result shown in figure 9, we come to the verdict: The distribution of static pressure on two
sides of the vessel is not symmetrical. Specifically, the pressure coefficient Cp is divided into two lines
with noticeable difference, which indicates the presence of additional force impact on the ship’s hull. In
this article, we do not carry out qualitative calculations for different specific situations but rather
introduce the procedures and expanded possibility for the research problem.
3.2 The result of the second problem
The simulation results are the contours of axial velocity and contours of turbulent viscosity on the
transitional zone when experiencing two situations with different propeller rotation, the first time with
n1 = 90 r.p.m and the second with n2 = 150 r.p.m (which correspond with the lowest and highest r.p.m
of M/V TAN CANG FOUNDATION when operating in the fairway).
Situation 1: n1 = 90 r.p.m (figure 10).
Figure 10 The simulation results of contours of axial velocity and contours of turbulent viscosity
Situation 1: n2 = 150 r.p.m (figure 11).
Figure 11 The simulation results of contours of axial velocity and contours of turbulent viscosity
Based on the received results as illustrated on figure 10 and figure 11, it is clear that the steering forces
correspond with various combinations of r.p.m and the rudder angle can be determined in order to find
the optimal combination to keep the ship on the pre-programmed orbit. The outcome of this research
will be published on sequence reports.
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3.3 The result of the third problem
In case of the rudder angle of α = 350 (the maximum permitted rudder angle) and the input parameter of
speed is 7,5 m/s (the highest permitted speed for vessels navigating in the fairway), with profil in the
midship position of the rudder, the calculated results with specific values are displayed on the coloured
column on the left of each figure, specifically: The distribution of water-vapor phase, pressures
coefficient and pressure distribution on figure 12.
Figure 12 The simulation results of water - vapor phase (a),
pressures coefficient (b), pressure distribution (c)
This is the situation where the cavitation can be seen most clearly, because, as the input parameters of
current speed and rudder angle are of the highest values.
On figure 12a, it is clear that the size of the cavitation area reaches 100% in water-vapor phase, starting
from the edge to profil and enclosed on profil with the length of the cavitation area on profil is 0.175 m.
According to the classification of cavitation, this is partial cavitation.
In addition, there is also a cavitation area on the edge of profil, which is shown on figure 13.
Figure 13 The simulation result of cavitation area on the edge of profil
The pressure coefficients and the pressure distribution on the profil are shown in figure 12b and figure
12c. The cavitation area will have the value of static pressure equal to the saturation vapour pressure of
water, which is 3540 N/m2. This explains why the pressure coefficient in this area is of horizontal type
(it is called the cavitation length l). With different input parameters of speed, the values of l will vary
and the cavitation area on the edge of profil will change accordingly.
Moreover, the type of cavitation in this area is partial cavitation, which is a type of unstable cavitation
that forms, grows, and disappears in certain cycles. This makes the value of steering force to fluctuate
while maintaining speed and steering angle and causes difficulties to maneuvering of ship. The
calculated results of partial cavitation area in one cycle are shown below:
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Figure 14 Contours of volume fraction (water-vapor phase): a) time = 0.0046s;
b) time = 0.0158s; c) time = 0.0664s; d) time = 0.0754s; e) time = 0.083s; f) time = 0.0956s
Based on the result shown in figure 14, we come to the verdict: the cycle of partial cavitation in rudder
profil in this situation is: T = 0.0956s - 0.0046s = 0.091s.
With 3D calculation, the cavitation area can be calculated according to true conditions. The calculation
and simulation results with the conditions of rudder angles α = 00 and α = 300 at the ship’s speed of 7,5
m/s are shown in figure 15.
Figure 15 The simulation results of the proportion of water - vapor phase: a) α0 = 00; b) α0 = 300
By analysing the results shown on figure 15, we come to the verdict:
- When the rudder angle α0 = 00, the proportions of water - vapor phase on the rudder and the surrounding
are nearly zero;
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- When the rudder angle α0 = 300, the proportions of water - vapor phase are high and reach nearly 100%
on the edge of rudder, then decreases in the surrounding areas.
4. Conclusion
We apply CFD in researching the effects of current on the course keeping ability of vessels navigation
in Haiphong fairway, through analysing three problems: The effects of additional force when the ship
alters her course; the interaction between rudder and propeller on keeping the ship on proposed orbit;
the effects of rudder cavitation on steering force. The results of these researches show the procedures to
calculate and steps needed to be taken to quantify research result for each type of ship.
In the following steps, the authors will analyse and assess the effects of the mentioned-above factors on
the manoeuvrability of vessels navigating in Hai Phong fairway. Therefore it will help the captain or
pilot decide suitable actions to keep the vessels on pre-programmed orbit, and thus, enhance the safety
of navigation, especially for vessels navigating through the danger areas in Haiphong fairway.
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