Abstract
A system and a method to warn a ship crew of potential violent motions in the immediate near future for the oceangoing vessel when operating in seas. Violent ship motions not only discomfort ship crews, damage cargos and ship structures, but also pose potential capsizing risk to ships. The system includes motion sensors; computer hardware and software; and warning devices. The sensors measure the ship roll, pitch, yaw, and rudder motions. The time histories of these motions are stored in the hardware and constantly analyzed using Finite Fourier Transform (FFT) to detect the nonlinear inertial coupling effect which is newly discovered by the inventor and believed to be the root cause leading to violent motions and capsizing. Based on the inventor's theory of nonlinear instability and inertial coupling effect, the invented method detects nonlinear yaw instability potential and inertial coupling events, and provides warnings to master to reduce potential yaw nonlinear instability, to avoid inertial coupling roll response, rudder induced oscillations, and broaching, and to prevent capsize in seas.
Claims
1. A warning system comprising: a) a sensor mounted on a moving oceangoing vessel and configured to collect roll, pitch, and yaw motion data of the said moving oceangoing vessel; b) a sensor mounted on the said moving oceangoing vessel and configured to collect rudder movement data of the said moving oceangoing vessel; c) a data recorder comprising: a data storage configured to store the time histories of the said motion data of the said vessel and the specification of the said vessel; d) a computer software programmed to perform Finite Fourier Transform analyses by FFT for the said time histories of motion data; e) means for identifying a potential yaw nonlinear instability of an oceangoing vessel and producing a warning signal responsive to the condition I.sub.x<I.sub.z<I.sub.y; f) means for calibration computing for roll response coefficient threshold .sub.Threshold for the said oceangoing vessel; g) means for detecting roll response coefficient exceedance for the said oceangoing vessel and producing a warning signal in response thereto; h) means for detecting a potential broaching for the said oceangoing vessel and producing a warning signal responsive to the condition .sub.11=.sub.21; i) means for detecting a rudder induced oscillation for the said oceangoing vessel and producing a warning signal responsive to the condition .sub.yaw=.sub.41 or .sub.yaw=.sub.42 or .sub.yaw=.sub.43 or .sub.yaw=.sub.44.
2. The system of claim 1 wherein the said sensor for roll, pitch, and yaw motion data collection may further comprise a plurality of sensors.
3. The system of claim 1 wherein the said data storage may be installed on board the said vessel.
4. The system of claim 1 wherein the said data storage may be installed remotely in other places other than the said vessel.
5. The system of claim 1 wherein the said software may be installed in an onboard computer.
6. The system of claim 1 wherein the said software may be installed remotely and the Finite Fourier Transform analyses by FFT are performed through web service.
7. The system of claim 1 further comprising: a) the predetermined Roll.sub.max to be in the range of 10% to 90% of the maximum roll for a ship to capsize in order to trigger the roll response coefficient exceedance alarm; b) the time span T.sub.R for Finite Fourier transform analyses is given by Math. 18; c) the minimum roll damping b.sub.1 for calculating the roll response coefficients in Math.13 and Math. 14 is in the range of 0.1% to 10% of the critical roll damping; d) the maximum roll response coefficient .sub.max is calculated by Math. 19; e) means for calculating the associated yaw frequency .sub.yaw.
8. The system of claim 1 wherein the said warning signal comprising visual and audible alarms.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram of a violent motion and capsizing warning system in accordance with the disclosure.
[0019] FIG. 2 is a diagram of motion sensors in accordance with the disclosure.
[0020] FIG. 3 is a diagram of a motion time history recording system in accordance with the disclosure.
[0021] FIG. 4 is a diagram of vessel specifications in accordance with the disclosure.
[0022] FIG. 5 is a flow chart for calculating the inertial coupling roll response coefficient threshold in accordance with the disclosure.
[0023] FIG. 6 is a flow chart for identifying potential broaching in calibration mode in accordance with the disclosure.
[0024] FIG. 7 is a flow chart for detecting potential violent roll or capsizing due to the inertial coupling effect in accordance with the disclosure.
[0025] FIG. 8 is a flow chart for identifying potential broaching in detecting mode in accordance with the disclosure.
[0026] FIG. 9 is a flow chart for identifying potential rudder induced oscillation in accordance with the disclosure.
[0027] FIG. 10 are time histories of roll, pitch, and yaw for a linearized ship dynamic system in accordance with the disclosure.
[0028] FIG. 11 are time histories of roll, pitch, and yaw for a full nonlinear ship dynamic system in accordance with the disclosure.
[0029] FIG. 12 is ship motion time histories of an example experiment.
[0030] FIG. 13 is the FFT frequencies and magnitudes of motions in Win1 of FIG. 12.
[0031] FIG. 14 is the time histories and the largest eight FFT components of motions in Win1 of FIG. 12.
[0032] FIG. 15 is the time histories and the Fourier approximations of motions in Win1 of FIG. 12.
[0033] FIG. 16 is the FFT frequencies and magnitudes of motions in Win3 of FIG. 12.
[0034] FIG. 17 is the time histories and the Fourier approximations in Win3 of FIG. 12.
[0035] FIG. 18 is the frequencies and magnitudes of the largest eight Fourier components of motions in Win3 of FIG. 12.
DESCRIPTION
[0036] The following text and figures set forth a detailed description of specific examples of the invention to teach those skilled in the art how to make and utilize the best mode of the invention.
[0037] Referring to FIG. 1, a violent motion and capsizing warning system 100 is part of or associated with the ship management computer (not shown). The system 100 includes a motion sensor module 101, a computing service module 200, and alarming device comprising 113, 115 and 116. The computing service module includes a data recording module 102, a vessel specification module 103, a yaw nonlinear instability check module 104, a visual alarming module comprising 105 and 106, a calibration module 107, a broaching check module 108, a calibration check module 109, a detection computing module 110, a broaching check module 111, a roll response coefficient exceedance check module 112, a rudder induced oscillation check module 114.
[0038] Referring to FIG. 2, the motion sensor module includes at least a roll sensor 101-1, a pitch sensor 101-2, a yaw sensor 101-3, and a rudder sensor 101-4 which measure the roll, pitch, yaw, and rudder motions constantly and send the time history data to the data recording module 102 where the time history data are stored in a readable hardware as shown in FIG. 3. The vessel specification module 103 as shown in FIG. 4 includes loading condition specifications 103-1 such as moments of inertia for roll (I.sub.x), pitch (I.sub.y) and yaw (I.sub.z), the roll characteristics 103-2 which includes the roll natural frequency u and the minimum roll damping coefficient b.sub.1, and a pre-determined value module 103-3 which is a maximum roll peak value, Roll.sub.max used to trigger alarm. The vessel loading specification information, I.sub.x, I.sub.y, I.sub.z needs to be current and as accurate as possible. The roll natural frequency needs to be consistent with the current GM condition and as accurate as possible. The minimum roll damping coefficient b.sub.1 required for the system is not the roll damping obtained in the roll decay test which is the common test for roll damping. This minimum roll damping coefficient represents the minimum value the roll damping could reach during heavy seas. In general, the minimum roll damping happens when high wave crest is amidships in a following sea such that the bow and stern of a ship are both exposed in the air. If the minimum roll damping coefficient B.sub.1 is not available, a small default value such as 10% of the roll damping obtained by a roll decay test may be used. The maximum roll peak value Roll.sub.max represents a tolerance level that the ship master wants to set to trigger an alarm. This value depends on the current ship righting arm curves, ship type, and the sea state the ship is going to encounter. Therefore, this value is vessel and sea state dependent. In general, this value is much smaller than the roll angle at which the ship could capsize. Preferably, Roll.sub.max is between 10-90% of the maximum roll to capsize a ship. The above information in 103 may be determined before the vessel leaving a port. In the check module 104 as shown in FIG. 1, the computing service 200, which may be performed by a computer installed on board or through web service, compares the moments of inertial for roll, pitch, and yaw. If the yaw moment of inertia is found to be in the middle between the roll and pitch moments of inertia, i.e. I.sub.x<I.sub.z<I.sub.y, a visual alarm signal is generated to alert the crew for a potential yaw nonlinear instability since sharp yaw velocity in maneuver may become large enough to exceed the yaw angular velocity threshold defined in Math. 18 and the ship may lose its yaw control and experience a sudden large roll motion. As an example, if the loading condition of Ro/Ro ferry MV Sewol made the pitch moment of inertia to be the largest one among the three moments of inertia, the warning system invented will give warning to the crew for a potential yaw nonlinear instability so that the crew needs to be very careful to avoid broaching and to turn the ship very slowly to prevent capsizing.
[0039] Referring to FIG. 1 and FIG. 5, the calibration module 107 communicates with the module 103 to get the roll natural frequency .sub.10 and communicates with the module 102 to get the time histories of motions for the most recent time span of T.sub.R which is the time duration for the FFT analyses and may be determined as
T.sub.R=2n/.sub.10, n=2, 3, . . . 10.Math. 18
[0040] The preferred number for n is 2, although the number could be larger such as 10 or higher. The maximum roll peak ||.sub.max in the most recent time span T.sub.R is identified in 107-1. The FFT analyses for the roll, pitch, and yaw data in the time span T.sub.R are performed in 107-2. Since the waveform frequency resolution for FFT analyses is proportional to 1/T.sub.R, Lower frequencies than this resolution are not able to be detected. To solve this resolution problem, the data in the time span may be mirrored several times to increase the data samples. Therefore, by mirroring the data we may increase the time span several times as well. Then the FFT analyses may be performed for the mirrored data. Fast Fourier transform may be used for the finite Fourier analyses. Therefore, the number of data samples is required to be in the power of 2, for example,2.sup.6 or higher. The higher the power goes the more accurate the results would be. The roll, pitch, and yaw motions may be described as finite Fourier series as given in Math. 9, Math. 10, and Math. 11, respectively. The amplitudes and frequencies in Math.9, Math. 10 and Math.11 are obtained by the FFT analyses performed in 107-2. The roll responses due to the 2NN inertial coupling moments in Math. 12 can be obtained using Math. 13 and Math. 14. The number N is preferred to be 8 although it may be larger up to 20 or smaller than 8. If the maximum roll peak in this time span T.sub.R is equal to or greater than the value Roll.sub.max set in 103-3, i.e. ||.sub.max>Roll.sub.max which is checked in 107-3, the maximum roll peak to trigger the alarm has been exceeded. The maximum roll response coefficient .sub.max defined in Math. 19 in the same time span T.sub.R is calculated in 107-5.
[00004]
wherein the 2NN roll responses are given in Math.13 and Math.14. This .sub.max is set to be the coefficient threshold in 107-6, i.e. .sub.Threshold=.sub.max. Then the calibration procedure is considered done in 107-7. The system continues to 108 for broaching check, to 109 for calibration check, and to 110 for detection computing. On the other hand, however, if the maximum roll peak in this time span T.sub.R is less than the value Roll.sub.max set in 103-3, i.e. ||.sub.max<Roll.sub.max which is checked in 107-3, the calibration is considered not done in 107-4. Then the system continues to 108 for broaching check and to 109 for calibration check, and goes back to 107 for the next time span as shown in FIG. 1
[0041] For example, FIG. 12 shows the time histories of roll, pitch, yaw and rudder of an experiment run by Pauling J. R. etc. 1972, Experimental studies of capsizing of intact ships in heavy seas, Technical report AD-753653, University of California, Berkeley. The data in Win1 of FIG. 12 has been extracted for FFT analyses. The roll natural frequency for this ship was found to be .sub.10=0.79. The time span T.sub.R in Win1 equals 15.9 seconds in this case. The maximum roll peak in Win1 was found to be ||.sub.max=47 degrees. Note that the 47 degrees roll was quite large for the ship and the ship almost capsized in Win1. Let us set the Roll.sub.max in 103-3 to be 25 degrees for demonstration purpose. FIG. 13 shows the FFT frequencies and magnitudes of the roll, pitch, yaw, and rudder for the data in Win1 of FIG. 12. The largest eight components for each motion are identified as shown in FIG. 13. The time histories of motions and the largest eight components with the amplitudes and frequencies obtained from FFT analyses are shown in FIG. 14. The phases of these components are adjusted to best fit the original data in Win1 of FIG. 12 when the eight components are combined as shown in FIG. 15. The maximum of the 128 roll responses may be obtained in 107-5 as below for this case.
[00005]
at the frequency .sub.24-.sub.31=0.79 =.sub.10. The roll damping coefficient was assumed to be 0.4% of the critical roll damping for this case. The calibration check in 107-3 says that the maximum roll peak to trigger the alarm has been exceeded, i.e. ||.sub.max=47>Roll.sub.max=25. Therefore, the coefficient threshold was found to be .sub.Threshold7.12 in this case.
[0042] Referring to FIG. 1 and FIG. 6, the broaching check is performed in the module 108. If the frequency .sub.11 of the largest amplitude roll component obtained in 107-2 is equal to the frequency .sub.21 of the largest amplitude pitch component obtained in 107-2, a potential broaching may happen according to Math. 16. The system will generate audible and visual alarms in 108-2, saying potential broaching. If these two frequencies do not match each other, the system goes to 108-3 and the alarm in 108-2 will be turned off if it is on.
[0043] Referring to FIG. 1 and FIG. 7, the detection computing module 110 communicates with the module 103 to get the roll natural frequency .sub.10 and communicates with the module 102 to get the time histories of motions for the most recent time span of T.sub.R which is the time duration for the FFT analyses. T.sub.R is determined by Math. 18. The preferred number for n is 2, although the number could be larger such as 10 or higher. The FFT analyses for the roll, pitch, yaw, and rudder data in the time span T.sub.R are performed in 110-1. The roll, pitch, and yaw motions can be described as finite Fourier series as given in Math. 9, Math. 10, and Math. 11, respectively. The amplitudes and frequencies in Math.9, Math. 10, and Math.11 are obtained by the FFT analyses performed in 110-1, respectively. The rudder motion can be also described as finite Fourier series as given in Math. 21 with the amplitudes and frequencies obtained in 110-1.
=.sub.m=1.sup.NA.sub.4mcos(.sub.4mt+.sub.4m)+.sub.40.Math.21
[0044] The maximum roll peak ||.sub.max in the time span T.sub.R is identified in 110-2. The roll responses due to the 2NN inertial coupling moments in Math. 12 can be obtained using Math. 13 and Math. 14. The number N is preferred to be 8 although it may be larger up to 20 or smaller than 8. The maximum roll response coefficient .sub.max defined in Math. 19 in the time span T.sub.R is calculated in 110-3. The associated yaw frequency .sub.yaw obtained also in 110-3 is the yaw frequency associated with the inertial coupling moment which generates the maximum roll response coefficient .sub.max obtained in 110-3. If the maximum roll peak is greater than the value Roll.sub.max set in 103-3, i.e. ||.sub.max>Roll.sub.mwhich is checked in 110-4, the maximum roll peak to trigger the alarm has been exceeded. The system goes to 110-6 to further check whether the maximum roll response coefficient .sub.max obtained in 110-3 exceeds the coefficient threshold .sub.Threshold obtained in 107-6. If .sub.max>.sub.Threshold, the system goes to 110-5 indicating the roll response coefficient .sub.max exceeding. If .sub.max<.sub.Threshold, it means that the coefficient threshold .sub.Threshold obtained in 107-6 is too high and needs to be updated by the value obtained in 110-3. This update is performed in 110-7. Then the system goes to 110-5 indicating the roll response coefficient .sub.max exceeding. On the other hand, if the maximum roll peak is less than the value Roll.sub.max set in 103-3, i.e. ||.sub.max<Roll.sub.max, the system goes to 110-8 indicating the roll response coefficient .sub.max not exceeding.
[0045] For example, in the demonstration case in FIG. 12 the coefficient threshold .sub.Threshold was found to be 7.12 as shown in Math. 20 based on the data in Win1 of FIG. 12. Similarly, FFT analyses have been performed for Win2 which is a successive time span to Win1 in FIG. 12. Based on the same procedure as above, the maximum roll peak in Win2 was found to be ||.sub.max=28 degrees which is larger than the preset Roll.sub.max=25 degrees in 103-3. According to detection computing 110, the system goes to 110-6 in FIG. 7. The maximum roll response coefficient .sub.max was found to be 3.56 in 110-3. In this case, 110-6 check in FIG. 7 shows negative. Therefore, the coefficient threshold needs to be updated, i.e., .sub.Threshold=3.56 which is the new coefficient threshold. From now on, the detection computing 110 will use the new coefficient threshold for future detection until its next update. The system has checked broaching in 111 (explained in FIG. 8 below) in FIG. 1 and it showed negative for Win2. Since ||.sub.max=28>Roll.sub.max=25, 112 roll response coefficient check in FIG. 1 is positive in this case. Then the rudder induced oscillation has been checked in 114 and it showed also negative for this case of Win2. Therefore, only alarm 115 is triggered in this case.
[0046] Referring to FIG. 1 and FIG. 8, after detection computing 110 finished, the system goes to broaching check at 111. If the frequency .sub.11 of the largest roll component amplitude obtained in 110-1 is equal to the frequency .sub.21 of the largest pitch component amplitude obtained in 110-1, a potential broaching may happen according to Math. 16. The system will generate audible and visual alarms in 111-2, saying potential broaching. If these two frequencies do not match each other, the system goes to 111-3 and the alarm in 111-2 will be turned off if it is on. This completes the broaching check.
[0047] Referring to FIG. 1 and FIG. 9, after the broaching check 111, the system goes to 112 to check again the roll response coefficient exceedance. 112 is to confirm the previous conclusion obtained in detection computing 110. If the roll response coefficient .sub.max exceeding is true, the system goes to 114 to further check rudder induced oscillation as shown in FIG. 9. If the associated yaw frequency .sub.yaw is equal to anyone of the frequencies of the largest four rudder components as shown in 114-1 in FIG. 9, the associated yaw frequency .sub.yaw may be driven by that rudder frequency, indicating that the inertial coupling excited roll oscillation is driven indirectly by rudder. Therefore, the roll oscillation can be considered as rudder induced oscillation. If this is true, a rudder induced oscillation is detected in 114-2. The system goes to 116 in FIG. 1 to generate audible and visual alarms indicating inertial coupling roll response exceeded, and rudder induced oscillation at frequency .sub.yaw. The system then goes back to detection computing 110 to start the next cycle of detecting. If the roll response coefficient .sub.max exceeding in 112 is true, but no rudder induced oscillation is detected, the system goes to 115 to generate audible and visual alarms indicating inertial coupling roll response exceeded. Then the system goes back to detection computing 110 to start the next cycle of detecting. If the roll response coefficient .sub.max is not exceeding the threshold in 112, the system goes to 113 to turn off the alarms generated in 115 or 116 whichever is on. Then the system goes back to detection computing 110 to start the next cycle of detection. The system is running continuously without stop until the system is turned off manually.
[0048] For example, in the demonstration case in FIG. 12 the new coefficient threshold was found to be .sub.Threshold=3.56 after the detection computing for Win2 in FIG. 12. We have performed detection computing 110 for Win3 in FIG. 12. FIG. 16 shows the FFT frequencies and magnitudes of the roll, pitch, yaw, and rudder for the data in Win3 of FIG. 12. The largest eight components for each motion are identified as shown in FIG. 16. The time histories of motions in Win3 of FIG. 12 and the combined results of the Fourier approximations using the largest eight components for each motion are shown in FIG. 17. The frequencies and amplitudes of the largest eight finite Fourier components for Win3 in FIG. 12 are summarized in FIG. 18. The maximum roll peak was found in 110-2 to be ||.sub.max=45 degrees. The maximum of the 128 roll responses has been obtained in 110-3 for this case as below.
[00006]
at the frequency .sub.24-.sub.36=0.79=.sub.10. Since the Roll.sub.max=25 degrees and .sub.Threshold=3.56, 110-4 and 110-6 checks are both positive. The roll response coefficient .sub.max is exceeding, i.e. .sub.max=9.18>.sub.Threshold3.56. Since .sub.11=.sub.21=1.38 as shown in FIG. 18, the broaching alarm 111-2 is triggered. Th yaw frequency .sub.36 involved with the inertial coupling to generate the maximum roll response coefficient as shown in Math. 22 is the associated yaw frequency, i.e. .sub.yaw=.sub.36. Since FIG. 18 shows that the yaw frequency .sub.yaw=.sub.36 coincides with the first rudder frequency .sub.411.18, 114-1 check is positive. The rudder induced oscillation is detected in this case and the alarm 116 is triggered. Note that in Win3 of FIG. 12, the three alarms, i.e. broaching alarm 111-2, roll response coefficient exceeding alarm 116, and rudder induced oscillation alarm 116 are all triggered in this case. This is a dangerous situation for the ship to encounter. The time span of Win2 is from 201.375 to 217.25 and the time span of Win3 is from 330.25 to 346.125 seconds. As shown in FIG. 12, the ship capsized at 348.4 seconds, just 2 seconds after Win3. Note that the maximum roll response coefficient .sub.max=9.18 in Win3 is about 2.5 times larger than the threshold value detected at Win2. If the ship can follow the warning detected in Win2 by the system to keep the inertial coupling roll response level low and to avoid broaching and rudder induced oscillation in an earlier time, the ship could prevent capsizing.
[0049] It should be understood that the above descriptions may be implemented to many types of ships, for example, such as oil tankers, bulk carriers, containerships, fishing vessels, Ro/Ro ships, boats, military ships, vessels in lakes or some other appropriate type of vessels. It should also be understood that the detailed descriptions and specific examples, while indicating the preferred embodiment, are intended for purposes of illustration only and it should be understood that it may be embodied in a large variety of forms different from the one specifically shown and described without departing from the scope and spirit of the invention. It should be also understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise a preferred form of putting the invention into effect, and the invention therefore claimed in any of its forms of modifications within the legitimate and valid scope of the appended claims.
