JPH0433376B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for estimating waves using ship motion, among methods for quantitatively estimating wave information on a ship in transit.

[Conventional technology]

Generally, when the waves in the area where a ship is sailing become larger,
Since marine accidents are more likely to occur and ship speeds are significantly reduced, it is important to accurately predict waves in order to ensure safe and economical navigation. This wave prediction is based on current wave information reported from ships in transit.

[Problem that the invention seeks to solve]

However, since wave observation is carried out while the ship is sailing, it is mostly done by visual observation, which relies on experience and has the disadvantage that accurate observation cannot be performed due to individual differences. It had

[Means for solving problems]

In order to solve these problems, this invention
Accurate current wave information is estimated from data obtained from ship motion caused by waves and known data.

[Effect]

The obtained data is converted from encounter frequency display to wave frequency display to obtain true wave information.

〔Example〕

FIG. 1 is a flowchart showing the procedure for estimating true wave information according to the present invention. First, as shown in step 100, hull motion is recorded.
The ship's motion at this time is induced by the waves, and is detected by a gyro accelerometer mounted on the ship and recorded on a data recorder or the like. In general, since ocean waves are irregular, their motion and acceleration also change irregularly, so they are in a temporally continuous state,
In other words, it is necessary to record it in chronological order. There are the following six types of ship motions at this time, and actual measurements will be made for some of these motions and some accelerations.

a surging Forward and backward movement of the ship.

b Swaying Lateral movement of the ship.

c Heaving vertical movement of the ship.

d rolling Shaking around the longitudinal axis of the ship (rolling).

e pitching Shaking around the axis in the direction of the short side of the ship (pitching).

f Yawing Rocking about a vertical axis (bow rolling).

Next, steps are taken based on this record of hull motion.
Obtain the spectrum and cross spectrum of the hull motion as shown in 101.

Next, in step 102, the wave spectrum and directional distribution function are determined using the motion spectrum and cross spectrum. In actual ocean waves, waves from all directions can be considered to reach a ship at the same time. The reason why it is necessary to find the directional distribution function is that the wave spectrum has a different shape depending on the direction. Since the data obtained in step 102 is in encounter frequency representation, it is converted into wave frequency representation as shown in step 103. Here, before giving a detailed explanation of step 103, the difference between the display methods of the encounter frequency display and the wave frequency display will be explained.

As shown in Figure 2, buoy 1 is floated on the water surface,
When a water pressure sensor 2 is suspended from the buoy 1, changes in water pressure are detected by the water pressure sensor 2 as the buoy 1 moves up and down with waves. Now, assuming that the wave is a sine wave, a signal expressed by the following equation (1) can be obtained from the water pressure sensor 2.

Z=ω ² Acosωt ...(1) However, each symbol is as follows.

Z: Output signal A: Wave amplitude ω: Wave circular frequency When buoy 1 in Fig. 2 is moved in the direction of wave movement shown by the arrow or in the opposite direction, equation (1) becomes equation (2). Become.

Zm＝ω ² _e Acosω _et ...(2) However, ω _e is the circular frequency of encounter, and when the water pressure sensor 2 moves in the direction of wave propagation, it is expressed by equation (3), and when it moves in the opposite direction, it is expressed by equation (4). It is expressed as

ω _e =ω−KV ...(3) ω _e =ω+KV ...(4) where K is the wave number and V is the moving speed.

Therefore, if a wave is seen from a moving object,
Depending on its direction of movement, the circular frequency of the wave increases or decreases. Therefore, expressions using the true specifications of waves as in equation (1) are called wave frequency expressions, and expressions using the apparent specifications of waves are called encounter frequency expressions.

Now, since the data obtained in step 102 is obtained based on the record of the ship's motion, it is an encounter frequency display, and what is needed is the data of the waves themselves, so it is necessary to convert them to a wave frequency display. be.

Now, when the ship is moving in the direction of wave travel, the encounter frequency will be as follows.

ω _e =ω−KV =ω−V/gω ² ...(5) where g is the gravitational acceleration.

Equation (5) shows changes as shown in FIG. 3, and a maximum of three ωs correspond to one type of ω _e0 . Therefore, for waves advancing from the front of the hull,
The correspondence between ω _e0 and ω is uniquely determined, but for waves advancing from the rear of the ship, a maximum of three ω correspond to one ω _e .

When the _wave spectrum in a certain direction expressed _by the encounter frequency ω _e obtained in step ₁₀₂ is expressed as shown in FIG. The component of _e0 has a value of S(ω _e0 ). This component is the third
As shown in the figure, it corresponds to the components ω1, ω2, and ω3, but it is not clear from the above data how these are determined. However, there should exist a wave spectrum represented by the wave frequencies shown in FIG. 5, which corresponds to the wave spectrum represented by the encounter frequencies shown in FIG.

Here, if the spectrum in Figure 5 is PM type, if the average wave frequency is known, S(ω1),
The ratio of S(ω2) and S(ω3) is determined. That is,
The ratio of allocating S(ω _e0 ) to S(ω1), S(ω2), and S(ω3) can be found.

It is assumed that an actual wave is rarely represented by one type of PM wave spectrum, and therefore can be represented by the sum of multiple PM wave spectra having different average wave periods. For this reason, set an appropriate wave period, for example, average wave period of 4, 6, 8, 10, 12 seconds, etc., and calculate the actual wave spectrum by the sum of PM wave spectra with each of these average wave periods. Approximate. The significant wave heights of these PM wave spectra are determined in step 103 so that the difference between the wave spectrum of the encounter frequency display and the approximate wave spectrum is minimized.

〔Effect of the invention〕

As explained above, this invention obtains data obtained by converting data obtained from ship motion into a wave frequency display using a PM type spectrum having a known wave period, so it is possible to obtain true wave information. This has the effect that it cannot be detected accurately.

[Brief explanation of drawings]

Fig. 1 is a flowchart showing the method of the present invention, Fig. 2 is a side view showing the positional relationship between the buoy and the sensor, Fig. 3 is a graph showing the relationship between the encounter circle frequency and the back circle frequency, and Fig. 4. is a graph showing the spectrum of the encountering waves, and Figure 5 is a graph showing the true spectrum of the waves. 1...Buoy, 2...Water pressure sensor.

Claims (1)

[Claims] 1 Record the time series of ship motion induced by waves, obtain spectrum data and cross-spectrum data of the ship motion based on this record, and combine this obtained data with the known response of the ship. This method utilizes ship motion, which is characterized by obtaining wave information in encounter frequency display from a function, and obtaining data obtained by converting this wave information into wave frequency display using several types of PM wave spectra with known wave periods. Wave estimation method.