Abstract: A look-ahead detection system (LADS) that actively controls the suspension of at least some of the seats in a watercraft to drastically reduce the shock and/or vibrations experienced by passengers within the seats caused by waves, other water conditions and/or the bending of the craft as it travels through the water. The look-ahead detection system utilizes downward-looking sensors to help the system predict when the craft will strike the water and how strong the impact will be. That is, the look-ahead detection system uses the sensors to look forward in time and down in space.

Abstract: A dynamic degaussing system includes a magnetic field sensor for generating a sensor signal in response to a sensed magnetic field. The magnetic sensor is coupled to a controller that produces an output signal based on the sensor signal. The controller may include feedforward and feedback control loops. The output signal of the controller controls a magnetic field generator which generates a magnetic field so as to attenuate the sensed magnetic field. According to one aspect of the invention, a vessel is provided with a reduced magnetic signature and a control system for controlling magnetic fields about a podded electric motor. The control system employs feed-forward and feedback control in tandem. The control system may be dynamically adapted to changing physical characteristics of the motor. Control signals are generated in response to sensed or predicted magnetic fields internal to, or external to, the motor.

Abstract: An active suspension system is used to control the motion of a passenger seat in a high speed watercraft. A forward looking wave sensor is used in connection with a feed-forward wave impact shock predictor to determine characteristics of impending dynamic forces applied via the impact of the watercraft on waves. Information concerning the impending dynamic forces is used by a passenger seat suspension and control system to attenuate the shock effects on passengers, where such effects are characterized by large-amplitude, short-duration accelerations recurring at a low frequency and/or irregularly.

Abstract: A hull (11) has mounted thereon a number of accelerometers (20) arranged to provide a data signal corresponding to movement or vibration of the hull (11) to which each is fixed. The hull (11) and/or a thrust block (18) has mounted thereon a number of mass dampers (21) that are controlled by a detector (23) arranged between the accelerometers (20) and mass dampers (21). The detector (23) calculates from the data signal generated by the accelerometers (20) different modes of resonance so as to determine the onset of the excitation of a particular resonance mode and controls the mass dampers (21) so as to generate forces to selectively dampen the resonance mode.

Abstract: A look-ahead detection system (LADS) that actively controls the suspension of at least some of the seats in a watercraft to drastically reduce the shock and/or vibrations experienced by passengers within the seats caused by waves, other water conditions and/or the bending of the craft as it travels through the water. The look-ahead detection system utilizes downward-looking sensors to help the system predict when the craft will strike the water and how strong the impact will be. That is, the look-ahead detection system uses the sensors to look forward in time and down in space.

Abstract: A dynamic degaussing system includes a magnetic field sensor for generating a sensor signal in response to a sensed magnetic field. The magnetic sensor is coupled to a controller that produces an output signal based on the sensor signal. The controller may include feedforward and feedback control loops. The output signal of the controller controls a magnetic field generator which generates a magnetic field so as to attenuate the sensed magnetic field. According to one aspect of the invention, a vessel is provided with a reduced magnetic signature and a control system for controlling magnetic fields about a podded electric motor. The control system employs feed-forward and feedback control in tandem. The control system may be dynamically adapted to changing physical characteristics of the motor. Control signals are generated in response to sensed or predicted magnetic fields internal to, or external to, the motor.

Abstract: An active suspension system is used to control the motion of a passenger seat in a high speed watercraft. A forward looking wave sensor is used in connection with a feed-forward wave impact shock predictor to determine characteristics of impending dynamic forces applied via the impact of the watercraft on waves. Information concerning the impending dynamic forces is used by a passenger seat suspension and control system to attenuate the shock effects on passengers, where such effects are characterized by large-amplitude, short-duration accelerations recurring at a low frequency and/or irregularly.

Abstract: A hull (11) has mounted thereon a number of accelerometers (20) arranged to provide a data signal corresponding to movement or vibration of the hull (11) to which each is fixed. The hull (11) and/or a thrust block (18) has mounted thereon a number of mass dampers (21) that are controlled by a detector (23) arranged between the accelerometers (20) and mass dampers (21). The detector (23) calculates from the data signal generated by the accelerometers (20) different modes of resonance so as to determine the onset of the excitation of a particular resonance mode and controls the mass dampers (21) so as to generate forces to selectively dampen the resonance mode.

Abstract: A compliant structure, such as a rubber pad, is used to simplify the resonance pattern of a vibrating object. According to one aspect of the invention, a support system is provided with a device for applying electromagnetic forces to the vibrating object, and the compliant structure is used to support the electromagnetic device. The electromagnetic device is positively controlled as a function of (A) the position of the vibrating object and (B) the position of the electromagnet. The compliant structure may also be used to further attenuate high frequency vibration transmission. According to one aspect of the invention, the compliant structure permits some rocking and/or rotational motion of the electromagnet to simplify the vibration transmission mechanism. According to another aspect of the invention, the compliant structure operates as a slightly-damped stiff spring in the axial direction of the electromagnet.

Abstract: A compliant structure, such as a rubber pad, is used to simplify the resonance pattern of a vibrating object. According to one aspect of the invention, a support system is provided with a device for applying electromagnetic forces to the vibrating object, and the compliant structure is used to support the electromagnetic device. The electromagnetic device is positively controlled as a function of (A) the position of the vibrating object and (B) the position of the electromagnet. The compliant structure may also be used to further attenuate high frequency vibration transmission. According to one aspect of the invention, the compliant structure permits some rocking and/or rotational motion of the electromagnet to simplify the vibration transmission mechanism. According to another aspect of the invention, the compliant structure operates as a slightly-damped stiff spring in the axial direction of the electromagnet.

Abstract: An electro-magnet (11) is spatially coupled with respect to a support armature (15) by an operational gap (16) and their relative movement is automatically compensated by controlling a current (14) supplied to the electromagnet (11). The current (14) and hence a magnetic field (F) are controlled by a current controller (13) which incorporates a transfer function and is operated in a feedforward path (19) by a signal (18) from a sensor (17) which detects variations in the gap (16) between the electro-magnet (11) and the support armature (12). The current controller (13) is also operated in a feedback path (22) by a signal (21) from a sensor (20) which detects variations in the flux intensity of the magnetic field (F).

Abstract: An electromagnetic levitation device comprises an electromagnet (12) which is supported by a structure (13) and is arranged to attract armature (10) carried by another structure (11). Current to the electromagnet (12) is regulated by a control device (16) to ensure that the electromagnetic force exerted by the electromagnet (12) on the armature (10) is sufficient to cause and maintain levitation of the structures (11, 13) at a desired spacing (A in FIG. 1). A decoupling device (17) is arranged between the armature (10) and the structure (11) to accommodate a shock load (L) which reduces the flux gap (15) to zero and decouples the armature (10) from its support structure (11) by moving the stop (20) away from the structure (11). This significantly increases the extent of shock loading that can be tolerated before damage will be incurred.

Abstract: A vessel comprises a cylindrical hull (10) containing a structure (11) carrying machinery (M) supported from the hull (10) by electromagnetic levitation means (12-17) that maintain electromagnetic forces between flux gaps (24) which are arranged to extend radially of the adjacent hull (10) curvature and longitudinally of the hull (10). In this manner, the transmission of noise from the machinery (M) to the hull (10) is obviated so as to reduce the detectable acoustic signal emitted by the vessel and furthermore, radial expansion or contraction of the hull (10) is prevented from mechanical transmission to the structure (11) via the levitation means (12-17).

Abstract: The invention provides a vibration cancellation device for rigidly mounting to or forming part of an apparatus subject to vibration. The device comprises a mass supported by magnetic levitation but which is magnetically driven to provide vibration cancelling relative movement, movement sensors controlling the application of power, in a relative motion cancellation direction.

Abstract: A submarine is provided with a large number of individual fins, some of which are arranged to create a "slot" effect between them. The fins are controlled in a way which is dependent on which of them may be in service at a particular time so that manoeuvreability is substantially unaffected by damage to a limited number of them.

Abstract: The engine and other machinery within a marine vessel is mounted on a raft which is relatively flimsy compared with conventional constructions. The raft is supported by electromagnets, the current to which is controlled so as to avoid vibration and flexing which would otherwise take place and so as to reduce transmission of vibration to the hull and other parts of the ship.

Abstract: Sound in ducts can be reduced by using two cancelling sources spaced along the duct, and in order to reduce reflections upstream of the cancelling sources, sounds from these sources may be arranged to be in phase opposition upstream from the sources at all frequencies. Such an arrangement does not provide cancellation downstream at some frequencies. In the invention sound detected by a microphone is processed to generate a drive signal for a first source which tends to cancel sound in the duct partially, the remainder of the cancellation being provided by a sound source. A delay positioned between the sources is such that sounds from these sources are in phase at all frequencies of interest downstream of the second source.

Abstract: Some degree of cancellation of noise from an annular noise source can be achieved by using an annular noise generator surrounding the source and in antiphase therewith. However due to the dimensions of the annulus, constructive interference may occur at frequencies of interest. In the present invention an annular noise source is surrounded by inner and outer annular noise generators generating sounds which are in antiphase and in phase respectively with sounds from the noise source. Also sounds from the inner generator are of twice the amplitude of those from the source and the outer generator. In effect over a considerable frequency range, the noise source and the outer generator have a mean position which coincides with the inner generator and together they generate sounds which are of the same amplitude but opposite phase to sounds from the generator. Thus destructive interference occurs in the said frequency range.

Abstract: When sound waves are intentionally attenuated by systems using destructive interference temporal changes sometimes cause less than optimum performance. In the present invention the transfer function of a signal processing system connected between a sound detector and a sound generator destructively interfering with an unwanted sound is modified at intervals as a result of sequential measurements of the transfer function between the sound detector and a further sound detector downstream from the generator. For this purpose a data processor calculates the required transfer function and causes a data processor to vary the coefficients of a digital filter comprising the signal processing system.

Abstract: An active sound control system is described in which allowance is made in a relatively uncomplicated circuit for acoustic coupling between a sound generating system for generating a cancelling sound wave and a detector for sensing a sound wave to be cancelled. Unwanted sound from a source is detected by a microphone and cancelled by sound from a speaker connected by way of an amplifier to the microphone. The amplifier has a feedback processing system with a transfer function which takes account of acoustic feedback between the speaker and the microphone in deriving, with the amplifier, a signal to drive the speaker.