Quay walls mooring capacity increasing/Krantiniu svartavimo gebos didinimas.

Paulauskas, V. ; Wijffels, J.

1. Introduction

Quay walls construction and mooring equipment such as bollards, hocks and other elements are calculated on the basis of wind, waves, current, ice possible forces [1-6]. At the same time new loading and unloading equipment in terminals has high intensively, sometimes up to 1500-2000 tons per hour in bulk terminals and up to 6000-10000 tons in liquid cargo terminals. Ships during loading operations change draft very fast [7-9]. Traditional ship's mooring equipment in case of delay slash mooring ropes of the ship creating big additional floating forces, which have an influence on quay walls construction via quay wall mooring equipment and ship's and quay wall mooring equipment as well [10, 11].

This article analyses and evaluates the theoretical basis and practical experience and design results of:

--aerodynamic and hydrodynamic loads on ships;

--ships floating forces and loads on the ship and quay wall mooring equipment;

--the accompanying mooring schemes;

--the use of mooring programs.

These components and specific ship and berth data will be a part of the analysis to minimise the probability of accidents and damage to the berth, berth furniture, ship, etc. [12, 13].

Mooring software will assist in the composition of the mooring schemes for a specific berth and ship and/or the maximum safe mooring wind and other conditions.

Ship's floating forces during its handling operations are very important and sometimes can create hundreds or thousands kN additional loads on quay walls and ship's mooring equipment.

2. Reasons and theoretical aspects of quay walls strength decreasing

Quay walls strength decreasing is mainly linked with long exploitation time of the quay wall (50-70 years), accidents with ships during mooring, loading, unmooring operations or substandard situations, such as hydrodynamic influence of a moving ship depends or wind pulsation or waves acting on the ship and big additional inertia forces of the ship.

The aerodynamic (wind) loads on ships in seaports are similar to aerodynamic loads on ship' s offshore (Fig. 1). In those cases the wind speed varies from 0 m/sec at ground/water level up to the average or maximum values at 5 till 7 m above the ground/water level [11, 13]. Aerodynamic loads on the ship consist of:

--constant aerodynamic load components ([F.sub.c]);

--periodical (harmonic) aerodynamic load components ([F.sub.p]);

[FIGURE 1 OMITTED]

The constant aerodynamic loads can be determined as [14, 15]

[F.sub.C] = [C.sub.a] [[[rho].sub.1]/2] ([S.sub.x] sin [q.sub.a] + [S.sub.y] cos [q.sub.a])[v.sup.2.sub.ac] (1)

where [F.sub.C] is constant aerodynamic load; [C.sub.a] is aerodynamic coefficient can be derived from ship's data, of which the model was tested in an aerodynamic tube; [[rho].sub.1] is density of air, kg/[m.sup.3]; varies from: 1.3096 kg/[m.sup.3] at 0[degrees]C to 1.1703 kg/[m.sup.3] at 30[degrees]C, average value: 1.25 kg/[m.sup.3]; [S.sub.x] is longitudinal projected area of the ship above the waterline, [m.sup.2]; [S.sub.y] is transverse projected area of the ship above the waterline, [m.sup.2]; [q.sub.a] is angle of wind direction to the ship's axes; [v.sub.ac] is design speed of the wind at a height of 10 m above water level, m/sec.

Periodical (harmonic) aerodynamic loads can be determined by the acceleration

[F".sub.P] = [[4[[pi].sup.2]t/[[tau].sup.2]] a] [sin [2[pi]t/[tau]]] (2)

[F.sub.P] = [F".sub.P]m (3)

where [F.sub.p] is periodical (harmonic) aerodynamic load; [tau] is period of gust of wind, sec; m is ship's mass, ton; t is running time, s.; a is integration constant

a = [C.sub.a] [[[rho].sub.1]/4] [DELTA][v.sup.2.sub.a]([S.sub.x] sin [q.sub.a] + [S.sub.y] cos [q.sub.a]) (4)

The maximum periodical (harmonic) aerodynamic load ([F.sub.Pmax]) will occur at sin [2[pi]t/[tau]] = 1.

[F.sub.Pmax] = [4[[pi].sup.2]t/[[tau].sup.2]] a m (5)

The maximum aerodynamic loads on a ship will be

[F.sub.Pmax] = [F.sub.C] + [F.sub.Pmax] (6)

The location and direction of the ship and the direction of the aerodynamic and hydrodynamic loads will have a determining effect for the fender and mooring systems of the berths and ships: In case they are directed to the berth the ship will be pushed to the berth (Fig. 2):

--the fender-system will absorb a part of the aerodynamic and hydrodynamic loads;

--the periodical aerodynamic and hydrodynamic loads will not have a considerable influence, due to the restricted movements of the ship.

In case they are directed from the berth the ship will be pushed from the berth (Fig. 3):

--the mooring-system will take the aerodynamic and hydrodynamic loads;

--the ship is pushed from the berth by constant aerodynamic and hydrodynamic loads;

--the ship will have movements along the berth due to periodical aerodynamic and hydrodynamic loads, which will create significant inertia loads.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Ship's floating loads can be calculated as follows [11]

[F.sub.F] = q[increment of Q] (7)

where q are number tons per 1 cm draft; [increment of Q] is quantity of the cargo unloaded from ship.

Aerodynamic and hydrodynamic loads of the wind, current and waves can be calculated by EAU 2004 methodic, BS 6349 standard methodology or could be used Optimoor simulator system [3, 16, 17]. Ship's floating loads could be added to the aerodynamic and hydrodynamic loads. Fig. 4 shows a ship's typical mooring scheme. The mooring line numbers are clarified in Table 1 [1, 10].

[FIGURE 4 OMITTED]

The mooring capacity is defined by:

--allowable mooring line load;

--capacity of the mooring line winch;

--allowable bollard load;

--configuration of the mooring line winches and hawseholes (fairleads) on the ship;

--variation of the mooring lines' lengths.

As a consequence of wind gusts, angled wind impact, etc. (inertia, current, waves loads) the ship will surge, sway, heave, pitch, roll and yaw (Fig. 5). The restrictions of the mooring lines, bollards and fender system will create the addition to the constant loads: the periodical aerodynamic, hydrodynamic and inertia loads.

[FIGURE 5 OMITTED]

The location of the fairleads on the ships in relation to the positions of the bollards on the berth can lead to wide mooring line angles in the vertical plane ([alpha]), see Fig. 6. In some cases [alpha] can be up to 70[degrees]-80[degrees]. Another reducing factor will be mooring line angles in the horizontal plane ([beta]) [13], see Fig. 7.

This wide mooring line angle will reduce the horizontal mooring capacity and allow movement of the moored ship. Mooring lines from the bow and the opposite side of the berth side of the ship at the stern will reduce the wide mooring line angle and could have a positive effect on the mooring capacity. A higher pretensioned load on the breast lines necessity to force the ship close to the berth is limited with regards to the balance of the ship. As a consequence of the reduced effectiveness of the forward and quarter breast lines, the bow, spring and stern mooring lines, with a sharper mooring line angle, will take a part of the breast mooring line loads. To avoid movements from the berth in case of unfavourable high aerodynamic and hydrodynamic loads one is inclined to increase the pretension of the mooring lines and/or increase the number of mooring lines. This could lead to utilize the quay wall construction, mooring lines, bollards, etc. to the limit. At a gust the limit capacity of the quay wall construction, mooring lines, bollards, etc. could be exceeded, creating dangerous situations, such as:

--uncontrollable movement of the ship from the berth, causing the collapse of the ship's catwalk to the berth;

--breaking of the mooring lines;

--breaking off of the bollards;

--collision of the ship with other berths and/or other ships;

--uncontrollable movement of the ship to the berth.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

Presented in this section theoretical aspects of the quay wall strength decreasing reasons and possible practical situations would be important and used for the case study.

3. Case study for the emergency quay wall

Emergency quay walls mainly link with accidents and technical parameters are changed without real improvement of the quay walls. Technical parameters of the quay walls after accidents decrease that means decrease quay walls payloads, mooring bollards capacity, possibilities of the quay wall anchor system and other technical parameters.

As an example (case study) is taken the emergency quay wall shown on Fig. 8. Mistakes of the detail project and construction works s and low quality of the construction make quay wall much weaker as were designed in technical project. As a result of the ship's aerodynamic, hydrodynamic and ship's floating forces acting and weakness of the real quay wall technical parameters quay wall movement to water side stimulated. During accident quay wall head about 40 m in length moves from 0.4 up to 1.0 m to the water direction. After excavation of the quay anchor wall it was fount were find that fixed points between quay wall anchors and quay anchor wall are very weak. Additionally during excavation of the quay wall it was found that the soil under quay wall head was not enough compressed during construction works and empty place is about 0.2 m in high.

[FIGURE 8 OMITTED]

According detail project (layouts) under crane rails VHP (very high pressure) columns were designed for the support crane rails, which should be create in filled sand. It is very complicated VHP columns to create in filled sand conditions, and in fact in the mentioned quay wall such columns were not found at all, just some separate concrete pieces were found during excavations (Fig. 9). The mentioned quay wall was operated very intensively and until quay wall renovation works it is necessary to make exact calculations, preparing useful operation conditions (payloads, capacity of the quay wall mooring bollards, ships mooring schemes etc.) to avoid additional damage of the quay wall during operation on emergency and losses of the cargo flows (Figs. 10 and 11). One of the main problems, which was necessary to solve--minimize tension forces of quay wall anchor system.

[FIGURE 9 OMITTED]

[FIGURE 10 OMITTED]

[FIGURE 11 OMITTED]

For the study were taken bulk ships with the main parameters: L = 200 m, B = 27.0 m, T = 8.0 m (in ballast), [S.sub.x] = 2800 [m.sup.2] (in ballast).

For the calculations were used Classical modified (including inertia forces) determination method, EAU 2004 and BS6349 methodologies and Optimoor simulation model.

[FIGURE 12 OMITTED]

Bulk ships mooring limitations to the quay wall have shown, that it is necessary find technical solutions for the increasing ships mooring possibilities by additional mooring bollards, which are not directly linked with quay wall construction.

Future calculations and simulations of the new quay wall situation with using storm bollards are shown on Figs. 12 and 13.

[FIGURE 13 OMITTED]

For the more easy and flexible using of quay wall territory in case of normal external conditions (when it is not necessary to use storm bollards), it is recommended install special clause inside the quay wall (in a sunken pit) bollards, as shown on Fig. 14.

[FIGURE 14 OMITTED]

Received aerodynamic, hydrodynamic, inertia and floating forces must be spread on the quay wall mooring bollards including special storm bollards. The mention of calculated forces are the basis for the ship' s mooring schemes preparation and finally concrete limitations of wind, current direction and velocity, as well inertia and floating (Figs. 15 and 16.).

[FIGURE 15 OMITTED]

[FIGURE 16 OMITTED]

4. Conclusions

In evaluation of emergency quay walls is very important to find the possibilities to continue quay walls exploitation.

The main horizontal forces on the quay walls anchor system should be studded and later evaluated.

The presented in the article methodic evaluation and calculation of the forces acting on emergency quay wall including inertia and floating forces can be used for the practical tasks.

At severe aerodynamic and hydrodynamic conditions it will not always be possible to prevent movements of a moored ship.

In advance the study for each type of ship, should be made.

The article addresses the expected behaviour at severe aerodynamic, hydrodynamic, inertia and floating conditions of the moored ship at the destined berth.

Received April 25, 2011

Accepted April 05, 2012

References

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[2.] BS 6349: 2000--British Standard Maritime Structures--Part 1: Code of Practice for General Criteria, British Standard Institution, July 2003.

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[13.] Paulauskas, V; Paulauskas, D.; Wijffels, J. 2008. Ships mooring in complicated conditions and possible solutions, Proceedings of the 12th International Conference "Transport Means--2008", Kaunas, Technologija, 67-70.

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V. Paulauskas, Klaipeda University, Manto 84, 92294 Klaipeda, Lithuania, E-mail: donatasp@takas.lt

J. Wijffels, Joep Wijffels Consultancy, Churchilllaan 418, 4532 MC Terneuzen, The Netherlands, E-mail: j.wijffels@inter.nl.net

http://dx.doi.org/ 10.5755/j01.mech.18.2.1569

Table 1

Mooring ropes number, names and purposes

Mooring        Mooring line           Purpose
line (hawse)       name
number

1             Bow (FWD)         Prevent backwards
              long line         movement

2             Bow (FWD)         Prevent backwards
              line              movement

3             Forward           Keep close to berth
              Breast line

4             After Bow         Prevent from
              Spring line       advancing

5             Forward Quarter   Prevent from moving
              Spring line       back

6             Quarter Breast    Keep close to berth
              line

7             Stern (AFT)       Prevent forwards
              line              movement

8             Stern (AFT)       Prevent forwards
              long line         movement