Calculation and simulation of the current effects on maritime safety in haiphong fairway, vietnam

170 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 S[.]

Calculation and simulation of the current effects on maritime safety

in Haiphong fairway, Vietnam Prof Dr Luong Cong Nho 1 , Prof Dr Pham Ky Quang 2 , Dr Vu Van Duy 3 , PhD Student Bui Van Cuong 4 , PhD Student Co Tan Anh Vu 5 ,

PhD Student Nguyen Thanh Nhat Lai 6

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

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,

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 threeproblems, namely: Impact on

vessel’s shell when altering course; Interaction between rudder and propeller; Rudder cavitation

problems, based on the resultsof field surveys, by analysizingvaluesand evaluation practicereceived, with the experimental data are performed on the M/V TAN CANG FOUNDATIONoperating 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 thefield surveysand collectexperimental data forcalculation 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

Water-liquid outlet Free surface Water-liquid inlet

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

1

1

n k k







Ifkis the density of the number k phase, the density of the mixture will be:

1

n

k k k



Propeller

Rudder Input

Propeller Output

Then, we solve major differential equations to determine specific values:

1

1

k

n k

k k

The value of volume fraction is determined by time step:

1

k



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;

kp

m - 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:

 v  v v p  v v t g F





 E v E p  k eff T s h



T - temperature; E - energy and the value of E can be determined according to (7):

/

The standard equation describes the flow and turbulence effect in the mixture model The vapor transport equation determines the vapor mass fraction fvapby the following equation

j

v a p

f

In which: Re, Rcdependent on the values of static pressure p and saturation vapor pressure pvap:

1 3

v a p

c h

l

v



3

v a p

c h

l

v



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 Vsis 5 m/s, wind speed Vwis 0 m/s

- Situation 2: The ship’s true course is 0150, the speed Vsis 5 m/s, wind speed Vwis 0

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 150to 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)

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 Cpis 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