Resumen
This process is for carrying out the inclining experiment on ships by means of inclinometers and its fundament is an algorithm developed to be able to use gravitational inclinometers on ships discriminating the component of the signal due to the roll angle, even though the ship is rolling, and in a methodology that its fundament is to consider the equilibrium conditions from a dynamic point of view taking into account the perturbations of the roll torque, distinguishing it from the traditional methodology, based on static consideration of the process. The procedure is materialised in equipment that consists of an original system to calibrate the inclinometer and another system, that allows to register the evolution in time of the measurement, analyse it and establish reliability indexes. The system developed also allows to determine the centre of gravity of the ship by means of a new system independent of the inclining experiment.
Reivindicaciones
1. A procedure to obtain the parameters for the stability of ships by measurements with inclinometers characterised because for the measurement of the heeling angle of a ship, in the equilibrium conditions of the inclining experiment, is composed of the following 3 stages: 1) Checking, calibration and setting to zero of the inclinometer on land. 2) In the case of using gravitational inclinometers: Filtering the registers of the inclinometer eliminating the component due to the ships rolling motion, and obtaining the evolutions of the heeling angle in the different equilibrium conditions of the inclining experiment. 3) Analysis of the registers of the heeling angle obtained and the determination of the optimal zones in which the uncontrolled heeling moments have been minimum with the purpose to assign the ships heeling angle, in each equilibrium condition, more precise and also assign the precision of the measurement with the purpose of its validation or its repetition. 2. A procedure to obtain the stability parameters of ships by means of measurements with inclinometers, according to claim 1. characterised because the checking, calibrating and setting to zero procedure of the inclinometer consists in: 1) Placing the levelling platform (figure 2) on a stable table and, with the help of a two dimensional spirit level, it is levelled. 2) The inclinometer is then used, which is placed on the coupling piece (figure 1), as a precision level, placing it on the levelling platform in a direction parallel to the levelling screws (H and I in figure 2), reading are taken from the signal from the inclinometer. 3) Later the inclinometer is turned 180° and reading are again taken. If the two previous readings are not the equal, the levelling screws are adjusted until the two reading converge. In this moment the inclinometer is in a horizontal position with a precision of a hundredth of a degree and the "zero" value is assigned. 4) Then, with the help of the calibrated angle generators (figure 3), the inclinometer is placed with the different angles that these pieces give (figure 4), and the calibration of the inclinometer is checked. If it were to be necessary, and with the help of these pieces, the inclinometer is again calibrated. 3. A procedure to obtain the stability parameters of ships by means of measurements with inclinometers, according to claim 1. characterised because the filtering of the registers is applied to the case in which gravitational inclinometers are used and consists in an algorithm that filters the signal corresponding to the heeling angle of the signal obtained by the inclinometer. The explain the algorithm we presume that the inclinometer is situated at a height "h" above the gyrating axis and subjected to an irregular oscillatory motion 1°) The Fourier Transform of the inclinometers register is made 2°) Each harmonic of the Fourier Transform is corrected in the following way: φ = g g + ω 2 h C <img class="EMIRef" id="458033520-ib0013" /> If h is above the gyration axis. φ = g g - ω 2 h C <img class="EMIRef" id="458033520-ib0014" /> If h is under the gyration axis. With: φ: Amplitude of the heeling angle corresponding to the harmonic. g: Gravity acceleration. ω: Angular frequency of the harmonic. C: Amplitude of the signal from the inclinometer corresponding to the harmonic. 3°) All the harmonics constituting the signal corresponding to the register of the evolution of the angle in time are added. 4. A procedure to obtain the stability parameters of ships by measurements with inclinometers according to claims 1, characterised because the determination of the heeling angle is carried out by the analysis of the registers of the evolutions of the heeling angle to fix the optimum zones in which the uncontrolled heeling moments have been minimal, with the purpose to assign the heeling angle of the ship, in each equilibrium condition, more precisely and assign also the precision of the measurement. 1°) The length of the register is established in function of the natural period of the roll of the ship. Around about 20 times the natural period of the roll motion. 2°) With the obtained register, the relation of maximums and minimums is generated with the instants in which they are produced. 3°) From this relation, are eliminated those pars of consecutive maximums and minimums separated in time by less than 1.5 seconds (filtering harmonics with a period inferior to 3 seconds). 4°) From the previous relation a table is built having as first element, M 1 + 2 m 2 + M 3 4 , <img class="EMIRef" id="458033520-ib0015" /> corresponding with the second instant (t<2> ) of the previous relation and the last, M n - 2 + 2 m n - 1 + M n 4 , <img class="EMIRef" id="458033520-ib0016" /> with the second last instant (t<n-1> ) of the previous relation. 5°) Selecting, from the representation of the table, the most stable zone of the register. For this, is chosen the continuous zone of the register whose duration is half the time of the register and whose mean quadratic error of the values contained in the zone, are minimum. The average value of the values of this zone will be the value assigned to the heeling angle. The reliability index will be the mean quadratic error and in the cases where there is no zone sufficiently stable of the register, it will recommend to repeat the measurement. 6°) When uniform uncontrollable heeling moments are produced (systematic errors), for example a constant wind abeam of the ship, the equipment is implemented with one (or various) anemometer(s) and weather vane(s) to register simultaneously with the heeling angle its information and measure the systematic errors of the measurement due to the wind. 5. A procedure to obtain the stability parameters of ships by measurements inclinometers characterised because the determination of the centre of gravity of a ship is carried out by the simultaneous registers of two inclinometers situated on the ship on its centre line and on the same vertical and because it comprehends the following operations: 1°) Checking / calibrating and setting to zero of the inclinometers. The signals generated by the two inclinometers must be completely identical when the inclinometers are in the same conditions, whether static or dynamic. For this a static calibration and a dynamic calibration is carried out by placing the two inclinometers on a mechanical oscillator and adjusting the filters of the system so that it is within the frequency band around the natural period of the ships roll, the signals are completely identical. 2°) Register and processing the signals of the two inclinometers. The signals received from the inclinometers during a sufficiently long time (in the order of 100 times the natural period of the ships roll) are registered. From the registers: 1°) Is established a set of KG values (distance from the ships c.o.g. to the base line) fixing a minimum KG, a maximum KG and increment of the KG. 2°) For each KG of the previous set is applied the algorithm to the registers C1 (t) and C2(t) from the two inclinometers obtaining C1corr(t) and C2corr(t) in the following way: a) The Fourier Transform of the registers C1(t) and C2(t) is done. b) Each harmonic of the Fourier Transform has its deviation due to the roll motion and it is corrected in the following way: φ ω 1 = g g + ω 2 h 1 C ω 1 <img class="EMIRef" id="458033520-ib0017" /> For the C1 inclinometer φ ω 2 = g g + ω 2 h 2 C ω 2 <img class="EMIRef" id="458033520-ib0018" /> For the C2 inclinometer With: φ<ω> 1: Roll angle amplitude corresponding to the harmonic from the C1 inclinometer. φ<ω> 2: Roll angle amplitude corresponding to the harmonic from the C2 inclinometer. g: Gravity acceleration. ω: Angular frequency of the harmonic. h1= KC1-KG (being KC1 the inclinometers height above the base line). h2= KC2-KG (being KC2 the inclinometers height above the base line). C<ω> 1: Amplitude of the inclinometers signal corresponding to the C1 inclinometer. C<ω> 2: Amplitude of the inclinometers signal corresponding to the C2 inclinometer. c) All the harmonics from each inclinometer are added and the signals obtained are C1corr(t) and C2corr(t). 3°) The value of the KG is calculated for which the two registers, C1corr(t) y C2corr(t), are equal, which corresponds to the vertical position of the centre of gravity of the ship. 6. A procedure to obtain the stability parameters of ships by means of characterised inclinometers is because the determination of the GM (metacentric height) is carried out from the roll natural period by statistic spectral analysis from the roll register, that comprehends the following operations: 1°) Checking / calibrating and setting to zero of the inclinometer on land. 2°) Obtaining the coefficient that relates the roll natural period of the ship with its metacentric height, doing the inclining experiment to determine the metacentric height (GM) and recording registers of the ships roll in different navigation conditions, to obtain the roll natural period of the ship. 3°) Register and processing of the inclinometers signal. The signal coming from the inclinometer during a sufficiently long enough time (in the order of 100 times the ships natural period) is registered, and from the registers is done a statistic spectral analysis. 7. A procedure to obtain the stability parameters of ships by means of measurements with inclinometers, according to claim 6, characterised by the statistic spectral analysis consisting in: 1) Dividing the main register into smaller samples and given a specific time, that is established in function of the type of ship. 2) Each sample of the main register is subjected to a Fourier Transform, over a rang of periods that cover the possible roll natural periods of the ship, and choosing the maximum length of the sample that is a multiple of the period over which is applied the Fourier Transform, obtaining for each sample two spectrums, the normalised (all the samples have the same weight) and the accumulated. 3) From the study of both spectrums is determined the roll natural period of the ship (T<φ> ) and the metacetric height (GM) obtained from the formula: GM = K ⋅ B / T φ 2 <img class="EMIRef" id="458033520-ib0019" /> Being K the coefficient obtained in the trails carried out with the ship and B its beam.
