Patent Description:
When vessels are sailing they may experience large variations in sea-states and weather conditions. The energy balance of the power plant of a vessel is effected by the sea-state and weather conditions in which the vessel is operating. Knowledge about environmental conditions may be used to take the influence of weather effect out of the total energy balance analysis in the power system design and to be used in the on-board advisory system. This information is crucial for the power system designers to consider for the dynamic load variations and to properly dimension the system for example for a dynamic positioning (DP) or Transit operations. It is therefore a need for an environmental condition indicator influencing the power and energy used by the vessel. Additionally the knowledge about the environmental condition enables comparing different vessel designs and vessel performance.

The sea state, the general condition of the surface of the open sea, varies over time, and there exist various ways of characterizing sea state by statistics, including various properties of the waves, such as wave height, period, and power spectrum.

Sea state is typically assessed by buoys, wave radars or satellites. Different hydro-mechanical approaches are used, including statistics for characterization of wave height, direction, period, energy spectra etc. Due to the complexity, existing wave measuring sensor systems tend to be costly. The sensor systems may typically make use of different types of gyro sensors, accelerometers etc..

In order to reduce the instrument cost, other methods of identifying the sea state have been researched. This methods estimate the sea state estimation using vessel response, or ship motion response, to the environment. These methods rely on calculating wave spectrums, complex transformation and feature extraction. Due to the complex methodology, the calculation of sea state has required significant processing power, and introduced delays that complicate dynamic positioning operation of vessels.

It is therefore a need for system and method for vessel environment assessment that is simple to implement in a real system, numerically cheap and that introduces little delay.

A goal with the present invention is to overcome the problems of prior art, and to disclose a system and a method.

The invention solving the above mentioned problems is a vessel environmental condition assessment method and a vessel environmental condition assessment system according to the independent claims.

In the following description, various examples and embodiments of the invention are set forth in order to provide the skilled person with a more thorough understanding of the invention. The specific details described in the context of the various embodiments and with reference to the attached drawings are not intended to be construed as limitations. Rather, the scope of the invention is defined in the appended claims.

With reference to <FIG>, the invention is in a first embodiment a vessel environmental condition sensing method comprising receiving a motion signal <NUM> from a motion measurement unit on board a vessel. An energy operator <NUM> is applied to the motion signal <NUM> to determine an energy signal <NUM> representative of the environmental condition for the vessel.

The energy signal describes the dynamics of the motions of a vessel on the sea. The value of the energy signal reflect the vessel's response to the environmental conditions, such as weather and/or wave conditions.

Different vessels may respond differently to the same weather conditions. The value of the energy signal for two different vessels in the same weather conditions may therefore be different for each of the vessels. according to the invention, the energy operator <NUM> is the Teager Kaiser (TK) instantaneous energy operator. The TK operator is expressed as <MAT> where <MAT> is the TK operator of signal <MAT>, and <MAT> is a discrete time signal. The implementation of the instantaneous energy operator for the discrete signal is simple, numerically cheap and only introduces <NUM> Sa (sample delay), thus is considered a delay-less solution.

According to the invention, the method further comprises classifying the energy signal into a plurality of environmental condition classes for the vessel, each environmental condition class being defined by an energy signal threshold value. In one example there are three environmental condition classes, where an energy signal below a first threshold represents good environmental conditions, an energy signal between the first threshold and a second threshold, the second threshold being higher than the first threshold, represents medium environmental conditions, and an energy signal higher than a third threshold, the third threshold being higher than the second threshold, represents bad environmental conditions. However, any number of classes may be used. Exemplary methods of building a classifier based on the energy signals are perceptron or k-means clustering. Any other clustering method applicable may be used.

The motion measurement unit senses the movements of a vessel on which the motion measurement unit is positioned, and translates those movements into an electrical signal. A vessel on sea have six degrees of freedom or motions; three rotational motions, pitch, roll and yaw; and three translational motions, heave, sway and surge. A motion measurement unit comprises one or more movement sensors that measures movement in one or more of those six degrees of freedom. In one embodiment, the motion measurement unit comprises at least one of an inertial measurement unit, an inclinometer or an angular rate sensor.

With reference to <FIG>, a motion measurement unit <NUM> comprises a movement sensor <NUM>. The movement sensor <NUM> outputs an analog electrical signal, x(t). The analog electrical signal, x(t) then undergoes digital signaling processing (DSP) <NUM> into a discrete time signal by well-known technologies. The first step is signal conditioning <NUM>, typically using an amplifier <NUM> and an anti-aliasing filter <NUM>. After the signal conditioning <NUM>, the conditioned analog signal x_a(t) is transformed into a digital sequence by an analog-to-digital converter (ADC) <NUM>. The input to the ADC, x_a(t), is a real-valued function of a continuous variable, t. For each value of t, the function x_a(t) may be any real number. The output of the ADC <NUM> is a bit stream that corresponds to the discrete-time sequence, x_a[n], with an amplitude that is quantized, for each value of n, to one of a finite number of possible values. After the ADC <NUM>, the digital signal x[n] may be converted from one sampling rate to another sampling rate by a sample rate conversion process <NUM>, e.g. change from a <NUM> signal to a <NUM> signal. The sample rate conversion may be performed in the DSP <NUM> unit and/or in a data logger external to the DSP unit. The energy operator is applied to the discrete motion signal x[n] in a processor <NUM> to determine an energy signal <MAT>.

The energy operator is applied to discrete signals of pitch, roll, heave, yaw, surge or sway signals. In a fourth embodiment that may be combined with any of the embodiments above, the motion signal comprises at least one of a pitch, roll, heave, yaw, surge or sway signal, and the energy signal representative of the environmental condition is a pitch energy signal, a roll energy signal, heave energy signal, yaw energy signal, surge energy signal or sway energy signal, respectively. The environmental condition may be classified based on one of pitch energy signal, the roll energy signal, the heave energy signal, the yaw energy signal, the surge energy signal, the sway energy signal, or any combination of them. The pitch energy signal, the roll energy signal, and the heave energy signal are more preferred for determining vessel response on the environmental conditions, and particularly efficient is the pitch energy signal. <FIG> is an exemplary plot of determined pitch energy and roll energy for a vessel. As shown in <FIG> determining signal energy is particularly efficient to provide a clear separation of the information included in vessel motion measurement, which provides for classification of the vessel response on the environmental conditions. In one related embodiment, the environmental condition is a weather condition.

<FIG> illustrates schematically a motion measurement unit <NUM> positioned on board a vessel <NUM>, The motion measurement unit <NUM> outputs discrete motion signals x[n]. The discrete motion signals x[n] may be input to a data logger <NUM> for storage and/or sample rate conversion. The discrete motion signal x[n] is output from the data logger <NUM> to a computer <NUM> to apply energy operator to the discrete motion signal x[n] and determine an energy signal <MAT> as described above. The computer <NUM> may also receive the discrete motion signal x[n] directly from motion measurement unit <NUM>. In one alternative embodiment, the energy signal may be determined on board the vessel and used for on-board advisory systems <NUM>, such as Energy Management where the pitch energy signal may be a Wave Indication input.

The data logger <NUM> may also be configured to transfer the discrete motion signal x[n] from the vessel <NUM> to shore <NUM>. The transfer may be performed using any suitable wireless communication, wired connection or physical connection to the data logger <NUM>. On shore, a computer <NUM> apply the energy operator to the discrete motion signal x[n] and determines an energy signal <MAT> as described above. On shore, the energy signal may also be determined from archived data. Then then energy signal may be used in ship Design & Systems <NUM> to:.

Another embodiment of the invention is a vessel environment condition assessment system comprising a motion measurement unit <NUM> on board a vessel <NUM> configured to sense the vessels motion. The motion measurement unit <NUM> is configured to output a motion signal <NUM> of the vessel <NUM> to a processor <NUM>, <NUM> adapted to receive the motion signal of the vessel. The processor <NUM>, <NUM> applies an energy operator <NUM> to the motion signal <NUM> to determine an energy signal <NUM> representative of the environmental condition.

In a related embodiment, the motion measurement unit <NUM> of the environment condition assessment system comprises at least one of an inertial measurement unit, an inclinometer or an angular rate sensor.

According to the invention, the processor <NUM>, <NUM> applies a Teager Kaiser energy operator.

The processor <NUM>, <NUM> is further adapted to classifying the energy signal <NUM> into a plurality of environmental condition classes for the vessel, each environmental condition class defined by an energy signal threshold value. The motion signal <NUM> of the vessel <NUM> input to the processor <NUM>, <NUM> comprises one or more of a pitch signal, roll signal, heave signals, yaw signal, surge signal or sway signal, and the energy signal <NUM> representative of the environmental condition is a one or more of a pitch energy signal, a roll energy signal, a heave energy signal, a yaw energy signal, a surge energy signal or a sway energy signal. The processor <NUM>, <NUM> may classify the environmental condition based on one of the pitch energy signal, the roll energy signal, the heave energy signal, the yaw energy signal, the surge energy signal, the sway energy signal, or any combination thereof.

In a further embodiment, energy signal <NUM> may be input to an on-board advisory systems <NUM> on board the vessel <NUM>.

In a further embodiment, the energy signal <NUM> may be input to a ship design and system <NUM> on-shore <NUM>.

Claim 1:
A vessel environmental condition assessment method, comprising;
receiving a motion signal (<NUM>) from a motion measurement unit (<NUM>) on board a vessel (<NUM>); applying an energy operator (<NUM>) to the motion signal to determine an energy signal (<NUM>), the energy operator (<NUM>) is an instantaneous Teager Kaiser, TK, energy operator wherein the TK operator is expressed as: <MAT> and where Ψd(x[n]) is the TK operator of signal x[n], and x[n] is a discrete motion signal,
wherein the energy signal (<NUM>) is classified into one or more environmental condition classes for the vessel wherein each environmental condition class being defined by an energy signal (<NUM>) threshold value, and wherein the energy signal (<NUM>) is representative of the environmental condition for the vessel.