advances of ship mooring of floating … · · 2017-10-28the safe mooring of ships in ports...

PIANC Bulletin AIPCN n°116, May 2004 mai79

RECENT TECHNOLOGICAL ADVANCES OF SHIP MOORING

ANALYSIS AND CONSTRUCTION OF FLOATING STRUCTURES

IN JAPAN

Haruo YONEYAMA

Head, Offshore Structures Division, Geotechnical

and Structural Engineering Department

Port and Airport Research Institute

3-1-1, Nagase, Yokosuka, Kanagawa 239-0826,

Japan

Tel.: +81 46 844 5060; Fax: +81 46 844 0255

E-mail: [email protected]

Tetsuya HIRAISHI

Head, Wave Division, Marine Environment and

Engineering Department

Port and Airport Research Institute

3-1-1, Nagase, Yokosuka, Kanagawa 239-0826,

Japan

Tel.: +81 46 844 5042; Fax: +81 46 841 3888


Shigeru UEDA

Professor, Department of Civil Engineering, Tottori

University

4-101, Koyamacho-Minami, Tottori 680-0946,

Japan

Tel.: +81 857 31 5286; Fax: +81 857 28 7899


Key words

Analysis, fl oating structure, moored ship, mooring, motions, technological development

Mots-clefs

Analyse, structure fl ottante, bateau amarré, mouillage, mouvements, développement technologique

I. TECHNOLOGY ON SHIP MOORING

1. INTRODUCTION

The safe mooring of ships in ports during rough weather conditions and the improvement of the port operation rate considering ship motions, are two major technical problems for port planning. Many ports in Japan face the

open seas. In such ports, long-period waves come inside of breakwaters and cause large motions of moored ships, such as low-frequency motions in a longitudinal direction and/or sub-harmonic motions in a transverse direction. These motions have a great infl uence on the safety of ship mooring and the port operation rate. Instances of mooring problems have been reported throughout the world as well as in Japan. For dealing with these problems, a numerical simulation method to simulate ship motions is a useful and effective tool. In the simulation, a moored ship is subjected to both irregular waves and gusty wind with non-linear load-defl ection characteristics of mooring system consisting of ropes and fenders. In association with the ship motions, the concept of allowable ship motions and allowable wave heights is essential to calculate the port operation rate as an index of harbour tranquility. Moreover, the proposed countermeasures to improve harbour tranquility are generally classifi ed into three categories: the construction of breakwaters and natural or artifi cial beaches, the improvement of mooring systems, and the advance judgment of cargo handling. Brief description is then made here on the instances of mooring problems, the application of the numerical simulation method of moored ships, the mooring method with ropes and fenders, the calculation of harbour tranquility, and the countermeasures against low-frequency ship motions.

2. PROBLEMS ON MOTIONS AND MOORINGS OF SHIPS

Some instances of mooring problems of ships have been reported around the world.

At the Port of Los Angeles, Vanoni (1950) described that seiche occurred and caused mooring problems when the period of the long-period waves coincided with the natural period of the basin. The long-period waves were generated in the oceans of the southern hemisphere and were propagated to the coast of Los Angeles. The recorded ship motions in the surge and sway directions were 3,2 m at the maximum with the period of more than 250 s.

At the Port of Cape Town in the Duncan Basin, Wilson (1965) reported that the ship motions caused the breaking of mooring ropes and interrupted the cargo handling operations. In the basin, the wave period became around 1 min even when the amplitude of the surface elevation was 15 cm. The cause of the accidents was the long-period waves entering the Duncan Basin and the secondary seiche generated by the long-period waves.

At the Marcona Pier for 150.000 DWT ore carriers in Peru, Kieth (1970) reported that fenders were damaged and mooring ropes were broken during the long-period sway motions of moored ships. Although the wave period was

PIANC Bulletin AIPCN n°116, May 2004 mai 80

about 16 s in one example, the period of the sway motions was in the range of 50 to 150 s. The long-period sway motions are called sub-harmonic motions that are caused by the asymmetry of the load-defl ection characteristics of the mooring system.

Similar instances of mooring problems have been observed at several ports recently in Japan.

At the port of Sendai facing the Pacifi c Ocean in the northern part of the main island of Japan, Nagai (1994) reported that 220.000 DWT crude oil tankers experienced low-frequency surge motions resulting in the suspension of cargo handling. The mooring problems were caused when the period of wave groups became long and almost equal to the natural period for surge motion.

At the port of Tomakomai facing the Pacifi c Ocean, Kamiya (1995) observed that moored ships experienced low-frequency large motions and that the mooring ropes frequently broke when ocean waves were induced by low atmospheric pressures such as typhoons. At fi eld observations, the low-frequency surge motion of 8 m at the maximum and the long-period waves exceeding 100 s were observed on a 36.493 GRT ore carrier. Since the natural period for surge motion in the mooring system consisting of mooring ropes was almost 120 to 130 s, the low-frequency surge motions were induced by the long-period wave components.

At the port of Noshiro facing the Sea of Japan, Shiraishi (1996) reported that low-frequency ship motions had caused the breaking of mooring ropes several times at the ore carrier berth for 60.000 to 90.000 DWT ships since 1993. The causes of the low-frequency ship motions were clarifi ed through numerical simulations, and the countermeasures to reduce the low-frequency ship motions using the mooring system were decided on.

3. ANALYTICAL METHOD OF MOTIONS OF MOORED SHIP

The motions of a moored ship and the forces of mooring ropes and fenders have traditionally been estimated using a hydraulic model experiment. However, a numerical simulation method has recently become a useful and effective tool. The simulation method can compute the motions and mooring forces of a moored ship subjected to both waves and wind. It can also incorporate the irregularity of the wave and wind loads, and the non-linear load-defl ection characteristics of the mooring system such as mooring ropes and fenders in the simulation process (Ueda (1984)).

The motions and mooring forces of a moored ship can be calculated by solving the equation of motions. Since the moored ship has six components of motions, the equation of motions of the moored ship becomes a second order differential equation with six degrees of freedom. The equation of motions employed in the numerical simulation method is classifi ed into two types: the retardation function method (Cummins (1962)) and the constant coeffi cient method (Ueda (1984)).

Fig. 1 : Flow Chart of Numerical Simulation Method

Fig. 1 shows the fl ow chart of the numerical simulation method using the constant coeffi cient method in the Port and Airport Research Institute. In the procedure of the numerical simulation method, the computation conditions shall be determined at fi rst. The hydrodynamic and wave forces are calculated by the Strip Method (Takaishi (1977)). The hydrodynamic forces are treated as the added masses and the damping coeffi cients in the equation of motions. The wave forces for irregular waves are calculated by superpositioning the components of regular wave forces. The wind forces acting on the ship are calculated by use of Hughes’s experimental formula (Hughes (1930)). Furthermore, the current forces and the wave drifting forces can be incorporated in the numerical simulation method. Generally, since the load-defl ection characteristics of


fenders and mooring ropes are non-linear and some fenders exhibit large hysteresis, the non-linearity is incorporated in the numerical simulation method. The time series of the ship motions and mooring forces can be obtained in the time domain by numerically integrating the equation of motions by using Wilson-q method.

4. MOORING METHOD: MOORING ROPES AND FENDERS

Mooring ropes and fenders are generally used when ships are moored to quay walls. The kinds and arrangement of them have much effect on the ship motions and mooring forces. Textile ropes such as nylon or polypropylene and rubber fenders are ordinarily employed. Two types of rubber fenders are mainly used: buckling type and pneumatic type (Ueda (1984)). Fig. 2 shows the load-defl ection characteristics of two types of rubber fenders. The buckling type fenders exhibit stationary reaction part and large hysteresis on unloading, whereas the pneumatic type fenders exhibit hyperbolic load-defl ection characteristic and small hysteresis.

When a ship is moored to a quay wall with mooring ropes and buckling type fenders and the ship is subjected to waves without wind, sub-harmonic motions in the sway direction tend to occur (e.g. Lean (1971), Ueda (1984)). The sub-harmonic motions mean the phenomenon that the offshore sway motions become large and the period of the sway motions become a few times of the wave period. The strong asymmetry of the load-defl ection characteristics of the mooring system causes the sub-harmonic motions. The asymmetry of the mooring system becomes relatively weak and the sub-harmonic motions decrease by replacing the buckling type fenders with the pneumatic type fenders.

Fig. 2 : Load-Defl ection Characteristics of Fenders

On the other hand, the kinds of mooring ropes are quite important for low-frequency ship motions in the surge direction (Shiraishi (1998)). When a ship is moored with textile ropes subjected to long-period waves of more than 60 s, for instance, low-frequency ship motions are induced. However, when the ship is moored with wire ropes subjected to the same waves, low-frequency ship motions do not occur. This means that when the natural period of the mooring system almost corresponds to the period of long-period waves, the low-frequency ship motions become large. The use of wire ropes instead of textile ropes to moor a ship is an effective countermeasure against low-frequency ship motions. However, the mooring forces tend to increase in the mooring system of wire ropes because of the hard load-defl ection characteristics, and thus there is a probability of the breaking of the wire ropes. Textile tail ropes are needed at the end of the wire ropes to decrease the mooring forces.

5. CALCULATION OF HARBOUR TRANQUILITY

The port operation rate used as an index of harbour tranquility is presently provided by wave heights in front of the quay walls. However, it is reasonable to estimate the port operation rate from possibility of cargo handling based on the ship motions. This is attributed to the fact that the wharf operation effi ciency at a berth greatly depends on the motions of a moored ship subjected to waves and wind. The cargo handling at a berth may occasionally be interrupted and/or suspended if ship motions exceed the allowable ones. The wharf operation effi ciency, then, should be defi ned based on the allowable ship motions for cargo handling in terms of the type and size of a ship and cargo handling equipment.

The allowable ship motions were determined for each component of ship motions. Ueda (1989) investigated the instances of the interruption and suspension of cargo handling due to the ship motions in the ports of Japan and proposed the allowable ship motions for general cargo ships, grain carriers, ore carriers and tankers. They estimated the allowable ship motions through executing the numerical simulations of moored ships, and evaluated and revised the estimated values based on the opinions of cargo handling operators. PIANC (1995) compiled the allowable ship motions by referring to previous studies.

An alternative method for calculating the wharf operation effi ciency was presented by Ueda (1989). Fig. 3 shows the block chart for the calculation of the wharf operation effi ciency. According to this method, the wharf operation effi ciency based on the allowable ship motions might be smaller than that based solely on the wave height in front of a berth when a ship is exposed to long-period waves. The


method becomes simple if the criteria such as the allowable wave heights are defi ned in terms of wave periods and directions for various types and sizes of ships. Accordingly, Ueda (1994a) proposed the allowable wave heights for cargo handling at berths based on the results of numerical simulations of the ship motions. The proposed allowable wave heights become small when wave periods become long and the sizes of ships become small.

6. COUNTERMEASURES AGAINST LOW-FREQUENCY SHIP MOTIONS

Low-frequency ship motions at ocean-facing ports are mainly caused by long-period wave components existing in ports. It is said that long-period water surface elevations in ports are mainly produced by two phenomena: harbour oscillations and long-period waves. As for the harbour oscillations, large abnormal tidal oscillations with periods of 10 to 60 min sometimes occur in some ports in Japan. The port of Nagasaki is well known as a port where the large harbour oscillations called ‘Abiki’ occur. The harbour oscillations are induced by the resonance of water inside a port with long-period waves from the outer sea. Takayama (1991) demonstrated by numerical simulations and fi eld observations that seiche on a continental shelf induce the remarkable harbour oscillations called ‘Abiki’. However, the harbour oscillations are not necessarily the main cause of the low-frequency ship motions because the periods

of the oscillations are much longer than the natural surge periods of moored ships. On the other hand, as for the long-period waves, recent research has revealed that the long-period waves are composed of set-down waves bounded in the grouping waves and the free long waves, and that the long-period waves have wave periods of approximately 1 to 5 min. Since the natural surge periods of moored ships are ordinarily about 1 to 3 min, the ship motions are harmonized and amplifi ed by the long-period waves. Hiraishi (1998) proposed the standard and simplifi ed frequency spectra including the long and short period wave components to reproduce the low-frequency ship motions in the numerical simulation.

Several countermeasures to reduce the low-frequency ship motions are proposed as follows (Hiraishi (1997), Shiraishi (1998)):

1) To reduce the energy of long-period waves inside a port by constructing breakwaters and natural or artifi cial beaches,

2) To prevent the resonance of ship motions with long-period waves by improving the mooring system,

3) To predict wave conditions and ship motions from the viewpoint of berth operation.

Fig. 3 : Block Chart for Calculation of Wharf Operation Effi ciency


The energy of long-period waves inside a port is crucial for the low-frequency ship motions. The composed wave heights inside the port usually become twice larger than those of incident long-period waves because the waves are perfectly refl ected on vertical sea and quay walls. Therefore, the wave heights may decrease in case that the walls are replaced with natural or artifi cial beaches. Hiraishi (2003) used numerical simulations to show that mild sandy beaches and a wave-absorbing double slit caisson wall are applicable as the energy absorbers for long-period waves.

At the port of Noshiro, countermeasures to improve the mooring system were employed at a 60.000 DWT bulk carrier berth (Shiraishi (1998)). The countermeasures were determined based on the results of the numerical simulations of a moored ship for the original mooring system and some substitutions. The mooring ropes were changed from nylon ropes to super textile ropes with nylon tail ropes. The super textile ropes have the same load-defl ection characteristics as wire ropes. One new dolphin was also constructed with mooring winches on it. Some of the buckling type fenders were then replaced with pneumatic type fenders. After modifying the mooring system, fi eld observations of the moored ship were carried out for a 75.590 DWT bulk carrier. The mooring conditions for the fi eld observations are shown in Fig. 4. Moreover, the numerical simulations of the moored ship were performed for the original mooring system and for the modifi ed mooring system under waves and wind. The moored ship motions are shown in Fig. 5. The sub-harmonic motions and the low-frequency motions occur for the original mooring system, but the modifi ed mooring system effectively restrains those motions. Through the countermeasures, the natural period of the surge ship motions was changed from 150 to 80 s and the low-frequency ship motions were reduced to about half of the motions for the original mooring system.

Fig. 4 : Mooring Conditions for the Field Observations

Aside from this, Yoneyama (2003) carried out fundamental model experiments of a reduction system for low-frequency ship motions. The system effectively reduces the low-frequency ship motions by automatically changing the natural period of the mooring system with computer-controlled hybrid mooring winches.

As for the prediction of the wave conditions and ship motions, a real-time predicting system was developed for

predicting wave conditions and motions of moored ships in ports (Ueda (1994b)). The system assists the harbour and berth administrators in judging whether mooring or cargo handling is possible or not for ships scheduled to enter the port. The system was actually installed and demonstrated at a crude oil tanker berth belonging to an oil refi ning company.

(a) Observation Results (Modifi ed Mooring System)

(b) Calculation Results (Modifi ed Mooring System)

(c) Calculation Results (Original Mooring System)

Fig. 5 : Observation and Calculation Results

7. FUTURE OUTLOOK

To improve the speed and effi ciency of cargo handling is a critical issue in port planning, design and construction at present. In particular, research activities on the countermeasures against long-period waves have been selectively carried out in recent years. As one of the outcomes of the research activities, a technical manual on the countermeasures against long-period waves is going to be complied and published.


II. TECHNOLOGY ON FLOATING STRUCTURES

1. INTRODUCTION

Recently in Japan, development of coastal zones has been actively promoted to create comfortable, favorable and attractive port and harbor areas. To this end, facilities such as residences, shopping centers, restaurants, convention and exhibition halls, museums, amusement parks, athletic fi elds and fi shing parks have been organically located and constructed. Some facilities among them involve fl oating structures. Floating structures are suited to deepwater areas where waves and wind are not so remarkable. The fl oating structures must be safely moored even during windstorms such as typhoons. In addition, the motions of the fl oating structures in operation must be less than the allowable motions to secure the safety and amenity of customers. Brief description is made here on the technological development of fl oating structures in Japan, the mooring technology using dolphins with rubber fenders, the major examples of fl oating structures, and the construction of fl oating disaster prevention bases.

2. TECHNOLOGICAL DEVELOPMENT OF FLOATING STRUCTURES

The fl oating structures have been mostly constructed in bays, lakes or the sea areas that are well sheltered by islands

and peninsulas. Since waves and wind acting on the fl oating structures are not so strong in such sites even in typhoon seasons, the motions of them are not so large and they can be easily moored there. On the other hand, when the fl oating structures are located at places facing the open seas, the design of mooring facilities is crucial for the safety of the customers and the fl oating structures themselves. Some of the fl oating structures have been constructed in such open seas together with the breakwaters and/or appropriate mooring facilities such as dolphin with fender systems.

Major fl oating structures constructed up to now are tabulated in Table 1. Several of the fl oating structures in the table are former passenger and freight ships such as the Hikawa Maru, the Scandinavia Maru, the Oriana, the Soya and the Fuji of the Antarctic observation ships, the Hakkoda Maru and the Masyu Maru of the Seikan ferryboats. In addition, newly constructed fl oating structures such as the Floating Island, the Floating Pier, the Aquapolis, the Pukarisanbashi Pier, the Oil Storage Bases, and the Floating Disaster Prevention Bases are also listed in the table. The fl oating structures shall be generally moored at the same sites for a long term. Since the ships naturally have no special mooring facilities to survive in severe windstorms, the mooring facilities for them must be carefully designed.

For designing the fl oating structures, much attention shall thus be paid to the examination of the safety of mooring facilities. The procedure of the examination is specifi ed by Ueda (1991) in the following manner.

No Name Open Purpose Location Properties Moorings

1 Hikawa Maru 1961 Restaurant, Exhibition Yokohama 12,000GT, 163m Chains

2 Scandinavia Maru 1970 Hotel Numazu 5,105GT, 127m Chains

3 Aquapolis (removed) 1975 Exhibition Okinawa 104 x 100 x 32m Chains

4 Soya 1979 Museum Tokyo 2,734GT, 83m Dolphins

5 Fuji 1985 Museum Nagoya 5,250GT, 100m Dolphins

6 Oriana (removed) 1987 Restaurant, Exhibition Beppu 41,920GT, 245m Dolphins

7 Floating Island 1989 Aquarium, Exhibition Onomichi 130 x 40 x 5m Chains

8 Hakkoda Maru 1990 Restaurant, Exhibition Aomori 132 x 17.9 x 4.4m Pier

9 Kamigoto Oil Storage Base 1990 Oil Storage Base Nagasaki 390 x 97 x 27.6m Dolphins

10 Masyu Maru 1991 Restaurant, Exhibition Hakodate 132 x 17.9 x 7.2m Dolphins, Pier

11 Pukarisanbashi Pier 1991 Passenger Terminal Yokohama 24 x 24 x 3.2m Dolphins

12 Floating Pier 1993 Ferry Terminal Hiroshima 150 x 30 x 4m Dolphins

13 Shirashima Oil Storage Base 1996 Oil Storage Base Kitakyusyu 397 x 82 x 25.4m Dolphins

14 Floating Disaster Prevention Base 2000 Disaster Prevention Base Yokohama 80 x 25 x 4m Dolphins, Chains

15 Floating Disaster Prevention Base 2000 Disaster Prevention Base Osaka 80 x 40 x 4m Dolphins

16 Floating Disaster Prevention Base 2000 Disaster Prevention Base Nagoya 40 x 40/20 x 3.8m Dolphins

Table 1 : Major Floating Structures


1) Estimation of the wind speed for the required return period

2) Estimation of the wave condition at the location from the deepwater wave condition for the required return period

3) Calculation of the wind forces, wave forces and hydrodynamic forces acting on the fl oating structure

4) Determination of the load-defl ection characteristics of the mooring facilities

5) Calculation of the motions of the fl oating structure and the mooring forces

6) Design of the mooring facilities to meet the safety requirement

7) Detail design of the fl oating structures In the design of fl oating structures, the motions of

the fl oating structures and the forces of the mooring facilities should be fully examined by hydraulic model experiments and/or numerical simulations. The design conditions such as irregular waves, gusty wind, tidal level, properties of mooring facilities, and so on must be considered in performing the experiments or the numerical simulations.

3. MOORING TECHNOLOGY USING DOLPHINS WITH RUBBER FENDERS

The type of mooring facilities shall be selected in consideration of such items as the size of fl oating structures, water depth, soil condition of the seabed, and so on. Generally, chain systems and wire systems may be employed in relatively deep sea areas, and dolphin with fender systems, piers and intermediate buoy or sinker systems may be employed in relatively shallow water areas. Anchors and sinkers are used in the chain systems and the wire systems. Piles, jackets, rubber fenders, mooring ropes, and wires are used for the dolphins and the piers. As for the chain systems and the wire systems, chains and wires tend to hinder navigation and mooring of ships. The dolphins and the piers are acceptable in this regard. As shown in Table 1, most fl oating structures in Japan are moored to the dolphins with or without the chains and the mooring ropes. The dolphins with fender systems are discriminative mooring facilities in shallow seas in Japan that are different from deep seas such as the North Sea. The development of rubber fenders with high and reliable performance enabled their applications to the large fl oating structures. Since rubber fenders and mooring ropes have non-linear load-defl ection characteristics, the properties of mooring facilities should be determined considering stationary forces and variable forces acting on the fl oating structures.

4. MAJOR EXAMPLES OF FLOATING STRUCTURES

4.1 The Oriana

The Oriana shown in Pic. 1 used to be a deluxe passenger ship on the British-American and British-Australian Lines. The Oriana had been moored in the basin south of the 1st pier of the Port of Beppu since 1987 (Ueda (1991)). However, it has already been removed. The mooring facilities consist of dolphins and rubber fenders. The return period of 50 years was determined from the lifetime of the facility of 20 years. The design 10-min mean wind speed was estimated at 33,9m/s, and the design signifi cant wave height and period of 3,3 m and 7,0 s at the maximum were determined, respectively. The rubber fenders are buckling type, and the size of the biggest ones is 3,0 m and two of them are installed in series. For designing the dolphins, stability for sliding, over turning, revolution and bearing capacity are examined. In the design, the numerical simulations were carried out considering the wave and wind conditions, and the non-linear load-defl ection characteristics of the fenders.

Pic. 1 : Oriana

4.2 The Kamigoto and Shirashima Offshore Oil Storage Bases

The Kamigoto and Shirashima Offshore Oil Storage Bases are the only two fl oating structures for oil stockpiling in the world (Ikegami (1994), Ito (1994)).

The Kamigoto Oil Storage Base shown in Pic. 2 is the fi rst fl oating type oil storage base completed at the Kamigoto District in 1990. The site is calm due to the sheltering effect by islands and artifi cial banks. The base consists of fi ve huge storage barges having a maximum capacity of 880 km³ each moored with large dolphins and rubber fenders. Three dolphins (two mooring dolphins and a loading/mooring dolphin) are installed around the barge. The rubber fenders are buckling type and 3,0m in both height and diameter.


Model experiments and numerical simulations were carried out under the design environmental conditions of the 100-year return period for designing the mooring facilities. The design 10-min mean wind speed was estimated at 51,0m/s, and the design signifi cant wave height and period of 5,5m and 10,0 s were determined, respectively. The fi eld measurements of the mooring facilities were performed before the full operation, and the safety of them was confi rmed.

Pic. 2 : Kamigoto Offshore Oil Storage Base

On the other hand, the Shirashima Oil Storage Base shown in Pic. 3 was completed at Shirashima Island in 1996. The mooring basin is calm because it is surrounded by four breakwaters. The base consists of eight huge storage barges having a maximum capacity of 700km³ each moored with large dolphins and rubber fenders. Four mooring dolphins are allocated to hold the position of the barge. Four out of the total 18 dolphins are loading/mooring dolphins. The rubber fenders are hollow cylinder shape of buckling type and 2,5m high. The return period for the design was set at 100 years, and the design signifi cant wave height and period of 3,0 m and 11,0 s were considered, respectively. Numerical simulations were carried out to calculate the reaction forces of the fenders on the dolphins. On completion of the mooring of the No.2 barge, a verifi cation test was conducted on the No.1 barge over a period of one year, and the design conditions were validated.

Pic. 3 : Shirashima Offshore Oil Storage Base

4.3 The Yumemai Bridge

The Yumemai Bridge shown in Pic. 4 was constructed to connect Yumeshima and Maishima reclaimed islands across the North Waterway in the Port of Osaka (Maruyama (2002)). The bridge is a movable fl oating arch bridge standing on two fl oating pontoons, and can swing around the pivot axis with the assistance of tugboats. It has a total length of 940 m with a fl oating part length of 410 m and width of 38,8 m for six traffi c lanes. This swing type fl oating bridge was selected following a feasibility study conducted from the technological and economical points of view. The bridge is horizontally supported by a mooring system consisting of dolphins, movable reaction walls and rubber fenders. The rubber fenders are the same buckling type cell fenders with a large hysteresis load-defl ection characteristic as the Kamigoto and Shirashima Offshore Oil Storage Bases. The design 10-min mean wind speed was 42,0m/s, and the design signifi cant wave height and period of 1,4 m and 7,7 s at the maximum were used, respectively. Many model experiments were carried out to assure the safety and easy driving of the bridge.

Pic. 4 : Yumemai Bridge


5. CONSTRUCTION OF FLOATING DISASTER PREVENTION BASES

The lessons of the Hyogoken-Nanbu earthquake disaster revealed that marine transportation and ports played an extremely important role in delivering cargo and personnel to the devastated region during assistance and restoration activities. This is attributed to the fact that fl oating structures including ships have the advantages of earthquake resistance and mobility. Therefore, the fl oating structures can be utilized as convenient and functional disaster prevention facilities. The fl oating disaster prevention bases were then provided in three bays: Tokyo Bay, Osaka Bay, and Ise Bay (Kozawa (2000)). The bases have four distinguishing features: 1) mooring facilities for a 1.000 DWT class cargo ship, 2) a heliport, 3) interior storage spaces for cargo, and 4) a track crane space for cargo handling. Different fl oating body structures were selected for the three bays considering technology development elements in the future ocean development and harbour applications. A steel structure, a prestressed concrete hybrid structure, and a reinforced concrete hybrid structure are chosen for Tokyo Bay, Osaka Bay, and Ise Bay, respectively, according to the installation and utilization conditions at each location. The constructed bases are movable type and can be easily attached to and detached from the mooring basins. The bases are used as fl oating piers at normal times, but if a disaster occurs in a region near a base, it will be towed there by tugboats to be used to transport cargo and personnel. The mooring methods used at normal times are mainly dolphins because of the shallow water areas. Moreover, the mooring methods to be used at the disaster locations are the anchor chain systems. The target locations of the bases are within the bays where they are positioned. The normal maximum towing limit conditions are the signifi cant wave height of 1,5m, the signifi cant wave period of 5,0 s, and the wind velocity of 16m/s.

Table 2 shows the specifi cations of the fl oating disaster prevention bases. Pic. 5 shows the fl oating disaster prevention base in Ise Bay. The base consists of two fl oating sections: Float-A and Float-B. The functions and characteristics of the bases are described as follows.

1) Tokyo Baya) The double decks of both sides of the fl oating structure

can be used to moor large and small ships.b) A forklift can be used for cargo handling inside the

fl oating structure.c) 1.000m³ of water can be stored for human use.

2) Osaka Baya) A space of 35 m by 40 m is available for a large

helicopter, and cargo can be handled on both sides of the fl oating structure.

b) A roof can be set up at normal times, and the roof can be removed in an emergency.

c) The mooring method consisting of wires and rubber fenders is employed to reduce the motions.

3) Ise Baya) Float-A and Float-B can be used separately.b) An integral fl oating structure can be confi gured by

connecting two fl oating sections.c) A quay wall with a length of 80 m can be provided by

connecting two fl oating sections in a different way.

Specifi cations Tokyo Bay Osaka Bay Ise Bay

StructuralType

SteelStructure

PC HybridStructure

RC Hybrid Structure

Float-A Float-B

Length (m) 80.0 80.0 40.0 40.0

Width (m) 25.0 40.0 40.0 20.0

Depth (m) 4.0 4.0 3.8 3.8

Area (m2) 2,000 3,200 1,600 800

StorageSpace (m3)

2,080 2,300 1,009 686

TugboatHorsepower

3,500 13,000 10,000 5,000

Mooring Method

Dolphins,Chains

Dolphins Dolphins

Table 2: Specifi cations of Three Disaster Prevention Bases

Pic. 5 : Floating Disaster Prevention Base in Ise Bay

6. FUTURE OUTLOOK

Floating structures will continue to be constructed in line with the active development of coastal zones. Among the fl oating structures, the research activities to develop fl oating container terminals by use of very large fl oating structures have been executed in recent years (Shiraishi (2003)). A technical report for the planning and designing of fl oating container terminals is going to be compiled and published.


7. REFERENCES

CUMMINS, W.E., 1962: "The Impulse Response Function and Ship Motions", Schiffstechnik, Bd.9, Heft 47, pp.101-109.

HIRAISHI, T., SHIRAISHI, S., NAGAI, T., YOKOTA, H., MATSUBUCHI, S., FUJISAKU, H., SHIMIZU, K., 1997: "Numerical and Field Survey on Port Facility Damage by Long Period Waves and Those Countermeasure", Technical Note of the Port and Harbour Research Institute, Ministry of Transport, Japan, No.873, (in Japanese).

HIRAISHI, T., 1998: "Observed Frequency Spectrum of Long Period Waves", Proc. ISOPE-1998, ISOPE, Montreal, Vol.III, pp.77-83.

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There are two major technical problems for port planning concerning ship moorings. One is the safe ship mooring in ports during rough weather conditions and the other one is the improvement of the port operation rate relating to ship motions. In the ocean-facing ports, the low-frequency motions and sub-harmonic motions of moored ships, which are caused by long-period waves, have a great infl uence on the safe ship mooring and the port operation rate. This paper therefore discusses the technical problems related to motions and the moorings of ships, and the countermeasure technology against them.

On the other hand, many fl oating structures have recently been located and constructed in the coastal zone of Japan. The fl oating structures must be safely moored even under severe environmental conditions such as typhoons. Their motions must be limited to secure the safety and amenity of customers in operation. In this context, this paper also discusses technological developments and major examples of the fl oating structures such as the fl oating oil storage bases, the fl oating bridge and the fl oating disaster prevention bases.

SUMMARY

RÉSUMÉ

Lors de la conception d'un port se posent deux diffi cultés principales. La première est d’assurer un mouillage des bateaux en toute sécurité, même lors de conditions météorologiques diffi ciles. La seconde est d’augmenter le taux d’activité et la cadence des mouvements de bateaux. Dans les ports ouverts sur l’océan, les mouvements sous-harmoniques et à basse fréquence des bateaux amarrés, causés par des ondes de grande période, ont une grande infl uence sur la sécurité des bateaux et sur le taux d’activité du port. Cet article traite ainsi des problèmes techniques rencontrés par les mouvements et les amarrages des bateaux, ainsi que des solutions technologiques qui peuvent y remédier.

D’autre part, de nombreuses structures fl ottantes ont récemment été construites dans les zones côtières au Japon. Ces structures doivent elles-aussi être solidement amarrées en prévision de conditions naturelles extrêmes, comme les typhons par exemple. Leurs mouvements doivent être limités afi n de garantir le confort et la sécurité des utilisateurs. Dans ce contexte, cet article évoque également les derniers développements technologiques en la matière ainsi que les principaux exemples de structures fl ottantes, comme les bases de stockage de pétrole, les ponts fl ottants ou les bases de prévention des catastrophes.

ZUSAMMENFASSUNG

Hinsichtlich des Festmachens von Schiffen gibt es zwei große technische Probleme bei der Hafenplanung. Eines betrifft das Festmachen in Häfen unter schlechten Wetterbedingungen, das andere betrifft die Verbesserung des Ladedurchsatzes bei Schiffsbewegungen. In Häfen mit seeseitiger Einfahrt haben niedrigfrequente und sub-harmonische Bewegungen angelegter Schiffe, verursacht durch lang-periodische Wellen, einen großen Einfl uss auf ein sicheres Festmachen und auf die Umschlagsrate des Hafens. In diesem Artikel werden die technischen Probleme bzgl. Bewegung und Festmachen von Schiffen diskutiert und Gegenmaßnahmen erläutert.

Auf der anderen Seite wurden an der japanischen Küste in jüngster Zeit viele schwimmende Vorrichtungen gebaut. Diese müssen sicher verankert sein, selbst bei widrigen Umweltbedingungen, wie z. B. Taifunen. Ihre Bewegungsfähigkeit muss begrenzt werden, um Sicherheit und Annehmlichkeit der Kunden sicherzustellen. In diesem Zusammenhang werden in diesem Artikel technische Entwicklungen diskutiert und wichtige Beispiele für schwimmende Vorrichtungen vorgestellt, wie z. B. schwimmende Öllagertanks, schwimmende Brücken und schwimmende Katastrophenschutz-Vorrichtungen.

advances of ship mooring of floating … · · 2017-10-28the safe mooring of ships in ports...

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