JPH10325765A - Method for measuring wave compelling force while taking account of bay water oscillation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To moor a vessel in safety by handling the long period wave component of a wave compelling force acting on the hull as a bay water oscillation in the long period hull motion of a vessel moored in a harbor thereby enhancing the oscillation simulation accuracy of a moored vessel. SOLUTION: The block 50 of a wave force analyzing program using a traveling wave includes an ocean phenomenon data 51, i.e., the period, the direction of wave and the depth of water, a feature data of hull 52, i.e., the length, width, draft, and the like, of the vessel, and a wave force analysis 53. The block 60 of a wave force analyzing program using bay water oscillation includes an ocean phenomenon data 61, i.e., the period, the direction of wave and the depth of water, a wave force analysis 64 by bay water oscillation, and calculation 65 of wave compelling force. For the wave period of shorter than 20 sec, a wave data inside the harbor and the wave force analyzing program by traveling wave are employed. For the long period component of 20 sec or longer, a wave data outside the harbor and the wave force analyzing program by bay water oscillation are employed. Consideration of the bay water oscillation contributes to enhancement of the accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a wave forcing force in consideration of bay water vibration, which is used for a simulation of a ship moored in a port.

[0002]

2. Description of the Related Art Since a high-precision simulation is required for evaluating the safety of a ship mooring, direct on-site observations are made, and the wave forcing is calculated using time-series data of in-port and out-of-port waves. That is being done. Conventionally, when calculating wave forcing using on-site observation data of waves,
Wave forcing data is calculated using in-port wave data obtained near a moored vessel. First, the component division of the time series data of the in-port wave is performed using fast Fourier transform (FFT), and the cycle, amplitude, and phase of the component wave are calculated. On the basis of these data, a wave forcing force per unit amplitude is obtained by using a wave force analysis program for traveling waves. The period, amplitude, and phase data of the component wave also become wave forcing data during time series analysis. As for the wave direction,
At the same time, dominant wave direction is set from observation or visual observation.
The wave direction is required when using a wave force analysis program for traveling waves.

[0003] The wave force analysis program for traveling waves is a numerical analysis simulation for calculating the wave force acting on a hull in a given wave cycle. As an analysis method,
A boundary element method, a finite element method, or the like can be considered, but a method for calculating a velocity potential in a fluid is used. This is because pressure and even force are easily determined from velocity potential. The input data in the wave force analysis program for traveling waves includes marine condition data and hull specification data. The sea condition data is the water depth, wave period, and wave direction of the sea area. The wave period and wave direction are for component waves extracted from port time series data. The hull specification data is input data representing the characteristics of the hull, such as the length, width, draft, drainage, center of gravity of the hull, mesh coordinate points of the hull boundary, and the like. The wave force of the traveling wave is analyzed based on the input data, and the wave forcing force per unit amplitude is calculated.
This is performed for all component waves, and these are combined to become wave forcing input data during time series analysis.

[0004]

In recent years, moored vessels have been subject to long-period fluctuations, such as a sudden start of the vessel in spite of the calm weather without wind and waves and sea conditions, and the movement of the vessel due to bottom swell. There have been cases where cargo handling has been suspended. In this case, in addition to stopping cargo handling, the mooring line may be cut, the fenders may be over-compressed, shear-compressed, and the vessel may have to go offshore. For this reason, long-period swaying of ships moored in the port becomes a problem. It has been found that long-period sway is a resonance between long-period waves in the harbor and the natural period of the moored vessel, and as countermeasures, a method of suppressing the intrusion of long-period waves into the port by extending the breakwater, a ship mooring system, For example, a method of preventing long-period waves and resonance of the mooring system by changing fenders and mooring lines has been considered.

[0005] Further, the simulation of the motion of a moored ship is used to suppress the motion of the ship, the safety of the mooring system,
Etc. can be evaluated. In that case, generally,
Wave forcing acting on a ship is treated as a traveling wave from a certain wave direction. However, in a port surrounded by a breakwater, a traveling wave intruding directly or diffracted from a port entrance and a bay water vibration amplified in the port act on a ship moored in the port. The assessment of wave forcing is important, as long-period swaying of moored vessels in ports may be due in particular to amplified bay water vibrations in ports and resonances of the mooring system.

When a conventional wave forcing force acting on a ship is treated as a traveling wave from a predetermined wave direction by using the in-port wave data, the in-port wave data is a position that does not cause a problem in navigating in and out of the ship at the quay. It is measured using a wave gauge installed as close to the hull as possible. Since the wave forcing calculation is performed at the hull coordinate origin, generally the center of gravity of the ship, the in-port wave data measured as described above is:
There is a problem that it is necessary to convert to the hull coordinate origin in consideration of the spatial phase difference.

In view of these circumstances, one object of the present invention is to provide a long-period hull motion of a moored ship in a harbor, where long-period wave components of the wave forcing acting on the hull are treated as bay water vibrations and moored. An object of the present invention is to improve the accuracy of a ship motion simulation and to contribute to the study of safe mooring of a ship.

Another object of the present invention relates to treating wave forcing acting on a ship as a traveling wave from a predetermined wave direction using in-port wave data, which greatly affects long-period hull motion. The long-period wave component to be given is obtained by analyzing the bay water vibration so that the difficulty of setting the wave direction of the in-port wave can be reduced.

Another object of the present invention is to calculate a wave forcing force in consideration of bay water vibration so that a wave forcing force acting directly on a ship moored in a port can be obtained from wave data outside the port. Another object of the present invention is to eliminate the need to convert the in-port wave data measured near the hull to the origin of the hull coordinates, thereby saving labor.

[0010]

According to the present invention, when the wave period is equal to or greater than a certain value, the data of the time series division of out-of-port waves is used to convert the sea condition data, port shape data, and ship hull specification data. Based on the calculation of bay water vibration, the pressure at the hull boundary is derived, and the wave forcing per unit amplitude is derived by calculating the wave forcing. When the value is less than the value, the traveling wave that derives the wave forcing force per unit amplitude by calculating the wave force due to the traveling wave based on the sea condition data and the hull specification data using Analyzing wave force, forming wave force data based on the results of the wave force analysis by the bay water vibration and the wave force analysis by the traveling wave, measuring the wave force. Method, is provided

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A method for measuring a wave forcing force in consideration of bay water vibration for swaying simulation of a moored ship in a port according to the present invention will be described below with reference to FIGS.
The process of processing the conventional wave forcing data will be described below with reference to FIG.

First, FIG. 1 shows the shape of a harbor provided with an object berth for mooring a ship to which the measuring method according to the present invention is to be applied. The setting of the wave direction for a ship moored in a port is shown in FIG. FIG. 3 shows the mooring status of the ship and the external force conditions. The characteristics of the sway mooring force are shown in FIG. Based on these conditions, the process of calculating the wave forcing data in the measurement method according to one embodiment of the present invention is shown in FIGS. FIG. 5 (part 1) and FIG. 6 (part 2) are combined to show one process.

In the harbor shown in FIG. 1, the inside and outside of the harbor 104, 100 are divided into breakwaters 102, 103, a target berth 106, an outside port wave height meter 101 near the end of the breakwater, and a target berth. An existing in-port wave gauge 105 is provided.

Regarding the ship moored in the port shown in FIG.
The wave direction WD will be considered with respect to the mooring ship 107, the X coordinate, and the Y coordinate.

Regarding the ship, mooring conditions and external force conditions, as shown in FIG.
Ship 107 having mass M, dolphin-side mooring point (ai, b
i, ci) 151, a mooring line 153, a fender 154, and a ship-side mooring point (di, ei, fi) 152 are designated. Wind 161, the incident wave 162, and Radiation rays Deployment force ^{(m · d 2 x / dt} + n · dx / dt) 163 is considered. The incident wave forms an angle ω with respect to the X axis, and the wind forms an angle α with respect to the X axis.

For the sway mooring force K (x) · X,
As shown in FIG. 4, the spring constant k1 for the mooring line
The spring constant kf for s, constant reaction type and increasing reaction force type fenders is considered.

Generally, the motion simulation of a moored ship is a time-series analysis in which the equation of motion of the moored ship is solved sequentially for each time step. An example of a simulation of a moored ship sway will be described with reference to FIG.

The input data block 200 includes hull specification data 201, mooring condition data 202, wave resistance data 203, wave forcing data 204, and wind pressure data 2
05, tidal force data 206, calculation condition data 207, and the like. The condition calculation block 300 includes a restoring force coefficient 301, division 302 into each motion direction, generation of wave forcing force 303, generation of wind pressure and tidal force 304, and the like.
From the time series analysis block 400, the amount of motion of the moored ship,
The reaction force of the fender, the tension of the mooring line, and other time-series outputs are output.

The hull specification data is input data representing the characteristics of the hull, such as the length, width, draft, displacement, or moment of inertia about each axis, and the position of the center of gravity of the hull. Here, the hull is generally treated as a rigid body, and the coordinate system is often taken with the center of gravity of the ship as the origin. The mooring condition data is input data relating to a mooring force for mooring a ship including fenders and mooring lines to a quay or the like. Regarding the fenders, the number, height, mounting position, deformation amount, and characteristic data of the reaction force of the fenders that come into contact with the hull are listed. For mooring lines, the number of mooring lines, the mounting position on the hull side and the quay side, the characteristic data of elongation and tension, and the initial tension are given.

The wave making force is a fluid force which the still water hull shakes and receives from the fluid around the hull. This fluid force is divided into an additional mass term that is proportional to acceleration and a damping force term that is proportional to speed, and is a resistance force that depends on the oscillation cycle. These data can be input as an additional mass coefficient and a damping coefficient, respectively, but can also be input as a constant additional mass and a memory influence function in a form independent of a period.
It must be obtained separately by numerical simulation. This is a program for analyzing wave force by traveling waves.

The wave forcing is a wave force caused by an incident wave acting on a fixed hull. When a wave is given as a regular wave (single wave), one period / amplitude and phase, and also separately obtained by a numerical simulation or the like (wave force analysis program by traveling wave), it also depends on its period (and wave direction) The data input of only the wave forcing force per unit amplitude in ()) may be used. On the other hand, the Bretschneider-Easy type, generally known as the ocean wave spectrum, JON
When a wave is treated as an irregular wave using SWAP spectrum or the like, or time series data of a wave directly in the vicinity of a moored ship (in-port wave), the period of each component wave constituting the irregular wave
It is necessary to input data of the amplitude and phase, and the wave forcing force per unit amplitude of the component wave.

The wind pressure data is input data relating to drag due to wind acting on the moored ship. Generally, a drag coefficient, a pressure receiving area, and an average wind speed / wind direction are input. When inputting as a fluctuating wind, time series data of a fluctuating wind speed is created from a Davenport spectrum or the like, or time series data of a wind speed obtained directly by on-site observation is input. The wind direction may also be input as time-series data.

The tidal force data is input data relating to drag due to a tidal current acting on a moored ship. Generally, a drag coefficient, a pressure receiving area, and a flow velocity / flow direction are input. The calculation condition data is input data for controlling calculation contents such as a time step, the number of steps, and whether or not to consider wind pressure when performing a numerical simulation.

Referring to FIGS. 5 and 6, a description will be given of a process of calculating wave forcing data in a method for measuring wave forcing in consideration of bay water vibration for simulating motion of a ship moored in a port as an embodiment of the present invention. Is done. 5 and 6 are combined to show a process of calculating wave forcing data.

The data block 10 of the time series division of the harbor wave includes the steps of obtaining the harbor wave time series, wave direction 11, fast Fourier transform 12, and component wave period, amplitude and phase 13. The process 20 of identifying that the wave period is less than a certain value (eg, less than 20 seconds) causes the data to proceed from block 10 to block 50 of the traveling wave wave power analysis program only if it is eligible for this identification.

The block 30 of the data on the division of the time series of the out-of-port waves includes the steps of obtaining the time series of the out-of-port waves, the wave direction 31, the fast Fourier transform 32, and the period, amplitude and phase 33 of the component waves. . Wave period is a certain value or more (for example, 20 seconds or more)
According to the process of identifying 40, the data proceeds from the block 30 to the analysis program 60 for wave power due to bay water oscillation and the wave forcing data 70 only if it is eligible for this identification.

In the block 50 of the program for analyzing the wave force by the traveling wave, the cycle L, the wave direction, the water depth, etc. as the sea condition data 51, the ship hull specification data 52 as the ship master L, ship width B, draft d, drainage W, ship weight center Analysis of the wave coordinates of the hull boundary, mesh coordinate points, etc. and traveling waves (frequency domain analysis)
53 are included.

The block 60 of the analysis program of the wave force caused by the bay water vibration includes the period, wave direction,
Analysis of wave force due to bay water vibration (output pressure at hull boundary) 64, and wave forcing, such as water depth etc., harbor boundary mesh coordinate points etc. as port shape data 62, hull boundary mesh coordinate points etc. as hull specification data 63 Calculation of force (output of wave forcing force per unit amplitude) 65 is included.

The wave forcing data block 70 includes the period, amplitude, and phase 71 of the component wave, and the wave forcing 72 per unit amplitude of the component wave. The wave forcing data output from block 70 is an input to the time series analysis.

The calculation of the wave forcing data shown in FIGS. 5 and 6 will be further described. The waves originally present in the harbor are excited in the harbor by traveling waves and out-of- harbor waves which enter directly or diffracted from the harbor. There is a bay water swing that is done. When calculating the wave forcing acting on the moored vessels in the port, it is necessary to evaluate these appropriately. Therefore, the in-port wave data is separated into traveling wave components and bay water vibration components. Generally, since the cycle of wind waves and swells is about 10 to 15 seconds, the inner cycle of the component wave is less than a certain value, for example, less than 20 seconds is a traveling wave, more than a certain value, for example, 20 seconds or more is bay water vibration. Set. The wave forcing of the traveling wave component is calculated by appropriately setting the wave direction and overlapping the wave forcing of the component waves as in the conventional case.

A description will now be given of the calculation of the wave forcing force using the above-mentioned field observation data of the waves. Wave forcing data is calculated using time-series data of in-port and out-of-port waves obtained near the moored vessel. Here, first, the component division of the time series data of the in-port and out-of-port waves is performed using the fast Fourier transform. The cycle / amplitude and phase of the component wave are calculated by fast Fourier transform. Among these data, for the wave cycle of less than 20 seconds, the wave forcing force per unit amplitude is obtained by the above-described wave force analysis program by the traveling wave using the in-port wave data. The cycle / amplitude and phase data of the component waves of the harbor waves also become wave forcing data during time series analysis. For the wave direction, the dominant wave direction is set at the same time from observation or visual observation. The wave direction of the in-port wave is required when using the above-described wave force analysis program for traveling waves.

On the other hand, for a wave period of 20 seconds or more, a wave forcing force per unit amplitude is obtained by using a wave outside the harbor by a program for analyzing a wave force due to bay water vibration described later. The cycle / amplitude and phase data of the component waves of the out-of-port waves also become wave forcing data during time series analysis. For the wave direction, the dominant wave direction is set at the same time from observation or visual observation.
The wave direction of this out-of-port wave is required when using a program for analyzing the wave force due to bay water vibration described later.

Various methods have been proposed as a bay water vibration analysis program. In general, the amplitude amplification factor (ζi / η) at each point in the harbor is calculated from the wave data outside the harbor at a given wave cycle.
i, ηi: out-of-port waves, ζi: in-port waves) and water level fluctuations are numerical simulations.
Here, in the bay water vibration calculation of the type for obtaining the velocity potential, not only the amplitude amplification factor but also the velocity potential and the pressure in an arbitrary port water area can be obtained. The input data in the analysis program of wave force due to bay water vibration includes sea condition data, port shape data, and hull specification data. The oceanographic data is the water depth, wave period, and wave direction of the sea area. The wave cycle and wave direction are for the component waves extracted from the out-of-port wave time series data. The port shape data is input data representing the characteristics of the port, such as mesh coordinate points at the port boundary. The hull specification data is input data representing characteristics of the hull, such as mesh coordinate points at the hull boundary.

Based on the above input data, the wave force due to the bay water vibration is analyzed to calculate the pressure at the hull boundary. Thereafter, a wave forcing force per unit amplitude is calculated using a wave forcing calculation program. The above flow is performed for all out-of-port wave component waves, and they are collectively used as wave forcing input data during time series analysis. In this case, since the wave forcing acting on the hull can be obtained directly from the out-of-port wave data, it becomes unnecessary to set the wave direction in the in-port wave component.

As described above, the calculation of the wave forcing data in consideration of the bay water vibration is performed when the wave cycle is less than a predetermined value, for example, 20 waves.
Calculate the period / amplitude and phase of the component wave of a short-period wave component of less than about a second from a harbor wave, and a long-period wave component of a predetermined value or more, for example, about 20 seconds or more, from an out-of-port wave. The wave forcing force per hit is calculated by a wave force analysis program by traveling waves, a wave force analysis program by bay water vibration, and a wave forcing calculation program.

A conventional process of calculating wave forcing data will be described with reference to FIG. 8 to compare it with the process of calculating wave forcing data according to one embodiment of the present invention.

In order to evaluate the safety of ship mooring, a more accurate simulation is required. Conventionally, direct on-site observation is performed, and wave forcing is calculated using time-series data of in-port and out-of-port waves. It became so. The calculation of the wave forcing when the wave observation data is used is performed as follows. Wave forcing data is calculated using the in-port wave data obtained near the moored vessel. Here, first, the component division 500 of the time series data of the in-port wave is subjected to the fast Fourier transform 50.
2 is performed. The cycle / amplitude and phase 503 of the component wave are calculated by fast Fourier transform. Based on these data, a wave forcing force 603 per unit amplitude is obtained by using a program of a wave force analysis 600 by a traveling wave described later. The cycle / amplitude and phase data of the component wave also become wave forcing data 700 during the time series analysis. For the wave direction, the dominant wave direction is set at the same time from observation or visual observation. The wave direction is required when using a program for analyzing a wave force by a traveling wave, which will be described later.

The program of the wave force analysis 603 by the traveling wave is a numerical analysis simulation for calculating the wave force acting on the hull in a given wave cycle. Here, as the analysis method, a boundary element method or a finite element method can be considered, but a type for calculating a velocity potential in a fluid is used. This is because the pressure and the force can be easily obtained from the velocity potential. The input data in the program of the wave force analysis 603 by the traveling wave includes the sea condition data 601 and the hull specification data 602.

The oceanographic data is obtained from the depth of the sea area and the wave period.
It is wave direction. The wave cycle and wave direction are for the component waves extracted from the in-port wave time-series data. The hull specification data is input data representing the characteristics of the hull, such as the length L, width B, draft d, drainage W, center of gravity of the hull, mesh coordinates of the hull boundary, and the like. Based on these input data, a wave force analysis (frequency domain analysis) 603 by a traveling wave is performed to calculate a wave forcing force per unit amplitude. The above-described flow is performed for all component waves, and these are collectively used as wave forcing input data during time series analysis.

According to the method of measuring the wave forcing force in consideration of the bay water vibration for simulating the motion of a moored ship in a port according to the present invention, the longest of the wave forcing forces acting on the hull in the long-period hull motion of the ship moored in the port. The periodic component is treated as bay water vibration, which contributes to the improvement of the accuracy of the simulation of the motion of the moored ship, and is useful for the study of safe mooring of the ship. Conventionally, the wave forcing acting on the ship is treated as a traveling wave from a predetermined wave direction using the in-port wave data. However, as in the method of the present invention, a long-period wave component that greatly affects long-period hull motion is used. Regarding the above, it is possible to reduce the difficulty of setting the wave direction of the in-port wave by obtaining it from the bay water vibration analysis.

[Brief description of the drawings]

FIG. 1 is a diagram showing a shape of a port provided with a target berth for mooring a ship.

FIG. 2 is a diagram illustrating setting of a wave direction for a ship moored in a port.

FIG. 3 is a diagram showing a mooring state of a ship and external force conditions.

FIG. 4 is a diagram showing characteristics of a sway mooring force.

FIG. 5 is a diagram illustrating a part of a process of calculating wave forcing data in a measurement method according to an embodiment of the present invention.

FIG. 6 is a view similar to FIG. 5 and understood in conjunction with FIG. 5;

FIG. 7 is a diagram showing a simulation of a moored ship sway.

FIG. 8 is a diagram showing a conventional process of processing wave forcing data.

[Explanation of symbols]

 10: Division of time series of in-port waves 20: Identification of wave periods less than a certain value 30 ... Division of time series of out-of-port waves 40: Identification of wave periods of a certain value or more 50: Wave force by traveling waves Analysis program 60: Wave force analysis program due to bay water vibration 70 ... Wave forcing data 100 ... Out-of-port area 101 ... Out-of-port wave height meter 102, 103 ... Breakwater 104 ... In-port area 105 ... In-port wave height meter 106 ... Target berth 107 ... Mooring ship in port 151 Dolphin side mooring point 152 Vessel side mooring point 153 Mooring line 154 Fender 161 Wind 162 Incident wave 163 Radiation force WD Wave direction

Claims (9)

[Claims] 1. When the wave period is equal to or greater than a predetermined value, a bay water vibration is calculated based on sea condition data, port shape data, and hull specification data using time-series division data of out-of-port waves. Deriving the pressure at the hull boundary, deriving the wave forcing per unit amplitude by calculating the wave forcing, and analyzing the wave force due to bay water vibration, when the wave period is less than a certain value,
Analysis of wave force by traveling wave to derive wave forcing force per unit amplitude by calculating wave force by traveling wave based on sea condition data and hull specification data using time series division data of harbor waves Performing the wave force analysis based on the results of the analysis of the wave force due to the bay water vibration and the analysis of the wave force due to the traveling wave. 2. The data of the division of the out-of-port wave time series is formed by deriving the cycle, amplitude, and phase of the component wave by fast Fourier transform based on the out-of-port wave time series and wave direction, The method of claim 1. 3. The data of the time series division of the in-port wave is formed by deriving a cycle, an amplitude, and a phase of a component wave by fast Fourier transform based on the time series of the in-port wave and the wave direction. The method of claim 1. 4. The method according to claim 1, wherein the oceanographic data includes a period, a wave direction, and a water depth. 5. The method of claim 1, wherein the port shape data includes port boundary mesh coordinate points. 6. The method according to claim 1, wherein the hull specification data includes hull boundary mesh coordinate points. 7. The method according to claim 1, wherein the hull specification data includes a master, a width, a draft, a displacement, a center of gravity of the ship, and mesh coordinate points of the hull boundary. 8. The method according to claim 1, wherein the pressure at the hull boundary derived from the analysis of the bay water vibration is supplied to the wave forcing calculation step together with the hull specification data. 9. The method according to claim 1, wherein the data formed in the step of calculating the wave forcing force per unit amplitude is supplied to the time series analysis step as wave forcing data.