additional navigational widths of inland vessels passing cross current fields - pianc … · 2017....

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Additional navigational widths of inland vessels passing cross current fields Bernhard Söhngen, Nicole Maedel, Lucia Hahne, Ismael Verdugo, Jose Iribarren

Introduction

smart rivers 2011 · Sven Wurms · 14.09.2011

• Review of the German Guidelines “Cross currents from discharge and inlet structures in waterways”

Parameter study to assess the additional navigation width needed in the reach of the structures in a straight channel

Aim: Detection of the main parameters influencing the additional navigational width in order to develop a formula

Presenter

Presentation Notes

To review the German Guidelines “Cross currents from discharge and inlet structures in waterways” and to support the PIANC INCOM WG 141 “Design guidelines for inland waterways”, a parameter study to assess the additional navigation width needed in the reach of the structures in a straight channel was carried out. The aim of the study was to detect the main parameters influencing b in order to develop a formula, approximating observed values for fairway design purposes.

The models Methods


distance to bank x

width of the inlet/outlet structure w0

cross current velocity v0,cross

additional navigational width b

main current vmain

• CFD-Model (13 different current fields)

• Real-Time Simulator and

Numerical autopilot model (78 different manoeuvres)

• Theoretical consideration

semi empirical formula

Presenter

Presentation Notes

modell-region: straight channel with an rectangle inlet or outlet structure. (inlet: water come into the channel; outlet: water goes out at the channel) We produced 13 different current fields with a CFD-Modell. In total 78 different manoeuvres of inland going vessels, passing the cross currents were investigated at SIPORT21, using a Real-time Ship Bridge Simulator and the simulation software SHIPMA, where the ships are steered by an autopilot. Beside the experimental data, a theoretically based empirical formula was derived.

Numerical models of the current fields model region and variations

Methods


Presenter

Presentation Notes

Varieed parameters (see table): depht of the channel (h), width of the inlet/outlet structure (w0), main current (v_main), cross current velocity (v_cross), direction (inlet/outlet) The current fields were calculated by the CFD-code Nast3D of BAW. We took a LES-Turbulence model by an equidistant grid with an edge length of 0.25 m. The model region is a rectangle with three open boundaries, see figure 1. Only one side, which forms the channel bank and where the ship is sailing alongside, is modelled mostly to be an impermeable, vertical wall. In the part of the inlet or outlet structure (inlet structure: water enters the channel and a water jet will be formed; outlet structure: water leaves the channel), a defined velocity (vcross), perpendicular to the wall direction, was given. At the left boundary in upper figure, a defined inlet velocity (vmain) was given. The bottom of the channel is defined as a closed wall with slip condition. (The longitudinal and lateral dimensions of the model region were fitted to the current field considered. )

Real-Time Simulator and Numerical autopilot model Methods


considered parameters: • Type of inland vessel (Europe ship, Large Motor Ship, Push Tow Unit Convoy) • ship draught • ship speed • power of bow thruster • width of the inlet or outlet structure • distance to the to bank • driving direction

manoeuvring strategy:

keep the vessel at the required distance from the bank

using all the manoeuvre means on board.

Presenter

Presentation Notes

The manouvres were done with a Real-time Simulator and in comparism and addition to that with a Numerical auto pilot. considered parameters were: … the manouvring strategy was: …

Theoretical consideration

Leeway

Methods


Compensation by drifting

g

cross

vvwb ⋅≈

w

crosss v

vlwb ⋅≈ ),min(

Presenter

Presentation Notes

To derive an appropriate formula for the additional navigational width in a cross current field, we used two different models of thought. The first estimates the leeway of the ship, assuming a fully flexible ship with no moment of inertia, like a string of particles drifting as a current. This is illustrated in the left figure. The displacement of the ship b is depending in this case on the cross current velocity vcross and the time, the ship needs to cross the current field t. The time t depends on the width of the cross current field w and the ship speed over the ground vg. So, the additional width by leeway is approximately: This formula is reasonable, if the helmsman doesn’t react in any way on the cross current field and accepts the leeway. On the other hand, the captain is able to react by compensating the drift by inclining the ship against the cross current. This second model of thought is shown in right figure. So the ship is able to hold the line. If the cross current field is smaller than the ship (w<ls), we assume, that the additional width b will be reduced by the ratio w/ls. These both models of thoughts define borderline cases between no or very late reaction of the helmsman and the autopilot on the current field respectively or an immediately reaction by steering against the cross current. Both models of thought can take place crossing a current field. As a first estimate we assume that both strategies are plausible, so we take the mean.

Theoretical consideration Methods


ht

cf sthH +≈ 1• Draught factor

• Fitting the parameters to the distance of ship path

• Consideration main current and turbulence

22, maincrossTcrosseffcross vvfvv +⋅+≈

(only for inlet cross currents)

Presenter

Presentation Notes

Draught factor:The bigger the draught of the ship is, the slower the ship is reacting to the helm and the working surface of the cross currents gets bigger. We assume the impact of the draught to the additional width as a linear factor: with an empirical factor (c_th=0.6). Fitting the parameters to the distance of ship path: Because the width of the cross current field increases and the velocity of the cross current decreases by the distance of the inlet/outlet structure, it is necessary to fit these parameters to the distance of the ship path, see figure. Left: The width of the inlet cross current field widens approximately with an angle of ≈12-16°, [1] Right: At the outlet structure, we can assume a radial flow towards the centre of a sink. … So we get for both casas a fitted width and a fitted cross current velocity. Consideration main current and turbulence: If there is a longitudinal or main current vmain in the channel, the simulations show, that the extra width of the swept area grows in comparison to the same boundary conditions without vmain. This may be the influence of turbulence fluctuations in the mixing zone of the water jet, formed by (only) inlet structures. To account for these effects, we add the velocity fluctuations in a free mixing zone to the cross current velocity: (see formula) as Hinze recommended. [Book: ”Turbulence”, J.O. Hinze, (McGraw-Hill, New York, 1975) ]

Theoretical consideration Methods


+⋅⋅=

gw

seffcrossH v

wv

lwvfb ),min(21

,

Draught factor

Fitting the parameters to the distance of ship path and considering main current and turbulence

leeway Compensation by drifting

Presenter

Presentation Notes

So we get this semi-empirical formula:

Results


+⋅⋅=

gw

seffcrossH v

wv

lwvfb ),min(21

,

The “additional width” b is defined as: Difference between the nearest and the furthermost point of the observed ship swept area relative to the bank.

Presenter

Presentation Notes

We come to the results: (Perhaps a small summary: We have 13 current fields, 78 manouvers and one semi-empirical formula) The results are the the additional width. They are defined as.

Comparison Autopilot and Real-time Simulator a possible human factor

Results


1.5 m 3.2 m

Presenter

Presentation Notes

To detect a possible human factor effect on the additional navigational widths we compare the results of the simulations using an autopilot to those of the real time simulator, see figure 8. The navigational widths of the Real-time Simulator were in average 1.5 m larger than the widths of the Autopilot. The corresponding standard deviation is quite large with about 3.2 m. Obviously, the steering problem is dominated by the cross current field. So, human factor effects (are present but) not dominant. And we can take the autopilot data as well as the Real-time Simulator data.

Dependencies of the additional widths Results


addi

tiona

l wid

th [m

]

width of inlet/outlet structure w0 [m] cross current velocity v0,cross [m/s]

inlet structure, Autopilot inlet structure, Real-time Simulator

outlet structure, Autopilot

Presenter

Presentation Notes

The results of the simulations showed first of all the expected nearly linear dependence of the additional width on the cross current velocity and the width of the inlet and outlet structure, satisfying existing experiences from scale model tests. The left Figure shows the additional width depending on the width of the inlet/outlet structure, holding all other parameters constant. The right Figure shows the additional width depending on the cross current velocity at the inlet structure, holding all other parameters constant.

Dependencies of the additional widths Results


velocity of the main current [m/s] power of bow thruster [kW]

inlet structure, Autopilot inlet structure, Real-time Simulator

outlet structure, Autopilot

addi

tiona

l wid

th [m

]

Presenter

Presentation Notes

We found an unexpected big influence of the velocity of the main current, which is caused among other things by the large scale turbulence in the mixing zone between cross and longitudinal flow in case of a strong and wide outlet structure as explained above. The right Figure shows the additional width depending on the power of bow thruster. There is no significant effect of using the thrusters perceptible.

Comparisons to theoretical considerations Results


sem

i em

piric

al fo

rmul

a

measured additional width [m]

2.3 m

Presenter

Presentation Notes

compare the values of the semi-empirical formula to the experimental results: In the different manoeuvres we varied among others the type of inland vessel, the ship draught and the power of the bow thrusters. The semi-empirical formula do not contain theses parameters, so we expect significant deviations between measurements and estimations from our set of formulae. But we found no significant dependency on these parameters. On the other hand, it is reasonable to assume a typical scatter of the data, especially in case of human beings steering the vessels (human factor). We could reproduce the results with a standard deviation of 2.3 m, see figure. This seems satisfactory facing the different scenarios considered. (For your joke:) The american guys are not interested in such small additional width?

Comparisons to theoretical considerations Results


sem

i em

piric

al fo

rmul

a

measured additional width [m]

Presenter

Presentation Notes

… The interpretation of the data and the calibration process of the semi-empirical formula are still in process. Especially because there is only a little number of data available at the moment, we can not verify the ts/h-effects satisfiable. Nevertheless, the semi empirical formula gives a good estimate on how different parameters influence the additional widths.


Thank you for your attention.

for further questions do not hesitate:

Prof. Dr. Bernhard Söhngen Federal Waterways Engineering and Research Institute Kußmaulstraße 17 76187 Karlsruhe, Germany [email protected] phone: 0049-721-9726-4600

additional navigational widths of inland vessels passing cross current fields - pianc … · 2017....

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