Abstract: A core material for a shock insulation support, comprising, in parts by weight: steel shot of 150-300 parts, zirconia particles of 50-150 parts and rubber particles of 50-100 parts. Further provided are a shock insulation support comprising the core material, and a preparation method for the shock insulation support. The core material for a shock insulation support, and the shock insulation support dissipates earthquake energy by means of a dry friction energy dissipation mechanism, having high damping and excellent shock insulation performance.

Abstract: The present invention relates to a tower damper adapted to be mounted in a wind turbine tower, the tower damper comprising a pendulum structure adapted to be suspended in the wind turbine tower; a plurality of springs arranged to dampen movements of the pendulum structure; a suspension arrangement for suspending the pendulum structure; and a chamber holding a damping liquid into which damping liquid the pendulum structure is at least partly immersed. The present invention further relates to a wind turbine comprising a tower damper.

Abstract: A mount for supporting a power train in the vehicle, may include a stopper assembly combined on an internal surface of a housing to be disposed in an annular shape along the vicinity of the outsides of insulators combined with the housing, wherein the stopper assembly may include: an external ring combined on the internal surface of the housing; and a plurality of stopper members fixed on an internal surface of the external ring to be positioned along the vicinity of the outsides of the insulators, each of the a plurality of stopper members being spaced from each other to be in contact with an internal insulator of the insulators.

Abstract: A rotary viscous vibration damper or absorber has a hub part which can be fastened to a crankshaft of an engine, in particular of an internal combustion engine, and a vibration damper ring which is mounted such that it can be rotated relative to the hub part. A shear gap which is filled with a silicone oil is formed between the hub part and the vibration damper ring, in which shear gap flange bushings for guiding the vibration damper ring are mounted. The flange bushings are composed of a liquid crystal polymer.

Abstract: A thermal encapsulation apparatus for reducing heat loss from a vehicle component includes an insulating layer which, together with a surface of the component, forms a cavity between them. The apparatus also includes at least one baffle located within the cavity so as to define at least one cell therein. Within the cell, a convective-driven airflow caused by a temperature gradient between the surface of the component and the insulating layer is recirculated. The apparatus allows the component to store heat when it is not operational so that upon restarting the component, e.g. the vehicle engine, there is reduced friction in the moving parts, particularly in relatively cool ambient temperatures.

Abstract: The present invention relates to a turbomachine blade or vane arrangement having a first turbomachine blade or vane, a second turbomachine blade or vane adjacent to it, and at least one tuning element guide housing with at least one cavity, in which at least one tuning element is arranged with play of movement for impact contact with the tuning element guide housing, with the tuning element guide housing being arranged at least in part in a recess, in particular in a frame, of the first turbomachine blade or vane, where the second turbomachine blade or vane has at least one first rib for securing the tuning element guide housing arranged in the recess.

Abstract: A blade for a turbomachine, in particular a compressor or turbine stage of a gas turbine, having at least one matrix having a first impact chamber (10) in which at least one impulse element (11) is disposed with play, at least one second impact chamber (20) whose volumetric centroid is offset from a volumetric centroid of the first impact chamber (10) along a first matrix axis (A) and in which at least one impulse element (21) is disposed with play, and at least one third impact chamber (30) whose volumetric centroid is offset from the volumetric centroid of the first impact chamber (10) along a second matrix axis (B) transversely to the first matrix axis (A) and in which at least one impulse element (31) is disposed with play, the first matrix axis (A) and an axis of rotation (R) of the turbomachine forming an angle of at least 60° and no more than 120° is provided.

Abstract: A damping mechanism of a camera tripod head includes a fixing seat, a spindle connected to the fixing seat, damping devices fitted on the spindle, and a rotary seat. Each damping device includes a damping disc, a stop block fitted on the spindle, and a drive device for pushing the stop block to slide along the spindle. The damping disc includes an inner ring and an outer ring. The stop block is movable to disengage from the inner ring of the damping disc by the drive device. The drive device includes a push lever, a seesaw plate hinged to the fixing seat, and a cam mounted on the fixing seat. One end of the push lever leans against the stop block. One end of the seesaw plate leans against another end of the push lever. Another end of the seesaw plate leans against the cam.

Abstract: The present invention relates to an adjustable guide vane for a turbomachine, having a vane element and a turning disk, which has a first impact chamber, in which an impulse element is arranged with play of movement.

Abstract: A cushioning device for high heel shoes includes a layer of energy field generators producing electric/magnetic fields, and a chamber filled with an ER/MR fluid. The strengths of electric/magnetic fields are positioned in preassigned locations of the layer, according to the pressure distribution of foot. The viscosity of the ER/MR fluid can be adjusted by different strengths of electric/magnetic fields, so that different locations of foot can receive different supports from the cushioning device to enhance the comfort.

Abstract: A blade assembly including a rotor; a body portion connected to the rotor and having a space therein; and at least one vibration reduction member provided in the space.

Abstract: The present invention relates to a turbomachine blade (100; 200) with a base element, which has a blade part (1) for flow diversion and a blade root (2), a first guide (110; 210), fixed on the base element, in which a first element (111; 211) is movably guided, and a second guide (120; 220), fixed on the base element, in which a second element (121; 221) is movably guided, wherein a dynamic of the first element in the first guide and a dynamic of the second element in the second guide are designed differently, and the first guide (110; 210) is arranged in a half, nearer to the base root, of a radial height (H) of the base element, and the second guide is arranged in a half, more remote from the blade root, of the radial height of the base element.

Abstract: A support platform isolator system for a turf maintenance vehicle. The isolator system may include one or more rear isolators, and one or more forward isolators, the isolators positioned between a chassis of the vehicle and a support platform. The isolator system may not only reduce “metal-on-metal” noise between the chassis and the platform, but may also attenuate vibration and/or shock loads transmitted to the platform. In addition, the system may assist in locating the platform on, and retaining the platform to, the chassis. The isolators of the system may form primary contact areas between the chassis and the platform.

Abstract: An airfoil includes an airfoil structure defining a damping network that includes a first cavity, a second cavity, a flow passage connecting the first and second cavities. The airfoil further includes a damping material configured to flow through the damping network. A method of forming an airfoil includes forming an airfoil body having a damping network that includes a first cavity, a second cavity, and a flow passage connecting the first and second cavities. The method further includes adding a damping material configured to flow through the damping network.

Abstract: A shock absorber oil composition of the invention includes a base oil: (A) at least one of phosphate, amine phosphate salt, phosphite and amine phosphite salt; (B) an amide compound; and (C) an N-substituted derivative of sarcosine.

Abstract: A claw pole type motor is provided and includes: a rotor which includes a magnet and a rotation shaft around which the magnet is attached; and a stator which includes a bobbin, a winding wound around the bobbin, and a yoke which includes a plurality of pole teeth disposed to oppose the magnet and which is located outside the winding, wherein a vibration suppressing means is provided which makes contact with a distal end portion of the pole tooth and by which the pole tooth is pressure-supported on an inner circumferential surface of the bobbin, whereby the pole tooth is suppressed from vibrating.

Abstract: A stator angular sector for a turbine engine compressor including: an outer shroud and an inner shroud, and at least one vane extending radially between the shrouds. The outer shroud includes first and second mounting mechanisms for mounting the stator angular sector on a casing of the engine, which mechanisms are oriented parallel to the axis in opposite directions and connected together by an intermediate portion. The outer shroud includes at least one axial end portion extending from the intermediate portion with which at least one damper-forming insert is configured to come into contact, such that beyond a given value for amplitude of vibration of the end portion, the damper insert and the end portion are configured to move relative to each other to vary total moving mass moving with the end portion, thereby modifying vibratory behavior of the end portion.

Abstract: A Tuned Mass Damper (TMD) for damping oscillations of a hanging vertical pump structure includes a removable mass symmetrically configured within the pump structure diameter and supported by a mechanism which provides damped mobility relative to the pump structure so as to absorb and dampen pump vibrations and oscillations. The TMD mass is easily removable before tipping of the pump between horizontal and vertical orientations during maintenance. In some embodiments, the TMD mass comprises fluid pumped by the pump to fully or partially fill a housing, the fluid being gravitationally drained therefrom when the pump is not operating. In other embodiments the TMD mass is supplied by removable solid weights. Damped mobility is provided by springs damped by mechanical or fluid friction, or by obstructed movement of fluid within a partially filled housing. In embodiments, the TMD mass is at least 5% of the total mass of the pump structure.

Abstract: A device for controlling the flow of a liquid or gaseous medium, has at least one flow opening for the medium, and a movable valve element for controlling the flow opening. At least one damping body, which is preferably viscoelastic and acts on the valve element, is provided for obtaining a large dynamic range of the device in order to control flow in a fine, precise, and oscillation-free manner across a broad range of flow volume.

Abstract: A system and method of controlling engine vibration mounted within a vehicle including at least one hydraulic mount, each mount including a fluid chamber. A pair of accelerometers sense relative acceleration across the mount between the engine and the frame and generate a relative acceleration signal. A control unit is electrically connected to the accelerometers. The control unit is adapted to generate an electronic control signal in response to the relative acceleration signal. The control device is responsive to the electric control signal for controlling the damping force of the hydraulic mount. A control algorithm calibrates the control unit such that maximum vibration damping occurs at and around the engine resonance bounce frequency.

Abstract: A damper having a plurality of fluidic squeeze-film dampers acting in parallel. The damper of the present invention includes a plurality of fluidic squeeze-film dampers, each including a gap filled with viscous fluid provided between first and second damping elements. Each of the plurality of fluidic squeeze dampers creates an individual damping effect, which in the aggregate, act in parallel. As a result, the damper achieves (i) very high damping and stiffness over a relatively short stroke, (ii) compact size and (iii) adjustability to a limited degree by adjusting the gaps.

Abstract: A hydraulically damping bearing includes a damping fluid having a complex viscosity that is above the complex viscosity of polydimethyl siloxane within a first frequency range in which the damping fluid is excited upon the bearing being activated. The complex velocity of the damping fluid is below the complex viscosity of polydimethyl siloxane within a second frequency range in which the damping fluid is excited upon the bearing being activated.

Abstract: A vibration damper for a vehicle seat back is disclosed. The vibration damper includes an enclosure provided inside the upper end of a vehicle seat back. The enclosure includes a plurality of projections, preferably in the form of spaced apart, vertically extending pins, extending from one or more interior walls of the enclosure. A non-newtonian stress thickening fluid is provided within the enclosure. When the seat back is at rest the stress thickening fluid is free flowing within the enclosure. When the seat back is moved the stress thickening fluid is acted upon by the walls of the enclosure, the internally mounted pins, or both. As the walls and pins push on the fluid it comes under shear stress which causes the fluid to harden. As the pin passes through the hardened fluid they absorb energy and dampen the motion.

Abstract: A vibration isolating system is disclosed. The vibration isolating system comprises a passive mechanical system comprising a damping assembly, a first resilient member coupled in series with the damping assembly, and a second resilient member coupled in parallel with the series combination of the damping assembly and the first resilient member. The vibration isolating system further comprises a support member coupled in series with the passive mechanical system, a viscoelastic mount coupled to the support member, and a motion limiter coupled to the support member such that the passive mechanical system transmits a force to the support member when the passive mechanical undergoes longitudinal displacement greater than a predetermined displacement.

Abstract: A composite cable and method provides for control of the cable, and particularly its vibration modes, in response to a wide range of resonant and non-resonant energy input. The cable comprises a non-Newtonian fluid (NNF) in a cavity of a flexible tube. The NNF is characterized by viscosity that varies with shear stress. A load applies shear stress to the NNF changing its viscosity to dampen motion of the cable. The cable may comprise inner and outer tubes that are separated by a NNF. The inner tube may be filled with the same or different NNF, a Newtonian fluid or void. A magnetic field magnetic field may be applied to further control the viscosity of the NNF. The magnetic field may be controlled in response to a sensed condition of the cable indicative of shear stress in the NNF to provide either positive or negative feedback.

Abstract: A fluid shear actuated brake mechanism includes an outer hub secured to a hoist frame, a main brake disc stack engaged between the outer hub and a hoist drum shaft, an actuator hub helically engaged with the outer hub, and an actuator disc stack engaged between the actuator hub and the shaft. The main disc stack and the actuator disc stack are immersed in a fluid. Rotation of the shaft in a load lowering direction generates fluid shear in the actuator disc stack which rotates the actuator hub in a lowering direction and advances it toward the main disc stack, compressing it and the actuator disc stack. Rotation of the shaft in an opposite load lift direction retract the actuator hub from the main disc stack.

Abstract: A rotary damper comprises a first component, a second component mounted rotatably on the first, a braking fluid interposed, between the first and the second component, and a third component mounted rotatably on the second component. The second and the third component form a lateral support surface and a lateral shaft surface which is rotatable within the lateral support surface, rolling elements being interposed between these surfaces. The arrangement is such that, in a first direction of rotation (A), the third component can rotate freely with respect to the second, and, in a second direction of rotation (B), the third component is rigidly coupled to the second. Recesses are formed on the lateral shaft surface, these recesses accommodating corresponding rolling elements and being shaped so as to create, in the second direction of rotation, a centrifugal displacement of the rolling elements such that the elements are locked between the recesses and the lateral support surface.

Abstract: The present invention relates to a device for safety linking of a first member (4) to a second member (5). The first (38) and second (30) tubular portions are in communication via a gas-filled vibration-transferring means (26), at least below a specified force threshold. It is provided with at least two pressure chambers (27, 28) filled with a pressurized liquid. The two pressure chambers (27, 28) are integral with the one between the said first tubular portion (38) and the said second tubular portion (30). The two pressure chambers (27, 28) are separated by at least one piston (29) integral with the other (30) between the said first tubular portion (38) and the said second tubular portion (30). Use, in particular for fixing a turbojet engine to an attachment pylon of an aircraft.

Abstract: A shock energy absorber includes, in one example, a cylinder having a closed end and an open end, a sleeve fixed about the open end of the cylinder, and a damping material in the form of an ultra high molecular weight polyethylene material in the cylinder. A plunger is positioned to be driven into the damping material via the sleeve. When the plunger is impacted and driven into the damping material, the damping material changes from a solid to a viscous fluid state thereby enabling absorption of a significant amount of energy.

Abstract: A rotary damper (D) is constituted by: housings (11, 51); a silicon oil (21) being housed inside the housings (11, 51); a rotor (31) wherein a resistive portion (36) moving through the silicon oil 21 inside the housings (11, 51) is provided in an axial portion (32) which is housed inside the housings (11, 51) and projects from the housings (11, 51); and an O-ring (61) preventing the silicon oil (21) from leaking between the axial portion (32) and the housing (51), and multiple arc-like through-bores (37) are provided in the resistive portion (36) on a concentric circle, and depressed grooves (38) communicating with the arc-like through-bores (37) are provided. Accordingly, during the assembly, the air being mixed into the housing is not allowed to be excessively compressed, so that even if the rotor rotates bi-directionally, the noise being caused by the air being mixed into the housing can be prevented.

Abstract: An impact absorber employs dilatant (shear responsive) fluid that is subjected to a controlled, low amplitude, high frequency oscillatory stress which controls the stiffness of the fluid. Piezoelectric transducers, voice coils, and other forms of transducers may be used to apply controlled vibratory stress to the fluid. The energy absorber may be used in protective body armor, medical devices such as splints and casts, vehicle safety absorbers and many other products which benefit from ability to control the stiffness of the energy absorber.

Abstract: In a hydraulic shock absorber, a damping force generating device is provided between a piston side oil chamber and a rod side oil chamber of a cylinder, and in a compression stroke, a compression side flow path for circulating oil in the piston side oil chamber of the cylinder through an outside flow path of the cylinder toward the rod side oil chamber is provided in the damping force generating device, while in an extension stroke, an extension side flow path for circulating the oil in the rod side oil chamber of the cylinder through the outside flow path of the cylinder toward the piston side oil chamber is provided in the damping force generating device.

Abstract: Disclosed herein is the structure of a damper that is capable of improving the degree of freedom in design to optimize the damping characteristics of the damper and is capable of allowing the damper to be easily optimized and manufactured for a wide variety of dynamic stiffness characteristics of a tool body, and a manufacturing method using the same. A plurality of ring-shaped elastic members are disposed at opposite ends of a weight part. The weight part is connected to the tool body via the elastic members. Consequently, the weight part is moved relative to the tool body. The plurality of elastic members are mounted while spacers are disposed between the elastic members, and the spacers are moved with respect to the weight part in the axial direction thereof. A viscous fluid is filled in the region surrounded by the outer circumferential surfaces of the spacers, the elastic members, and the inner surface of a hollow part of the tool body.

Abstract: A power unit support structure adapted to provide vibration-damped support of an power unit of an automobile of FR longitudinal engine design on a vehicle body via engine mounts situated at two locations towards a vehicle front end and one location towards a vehicle back end, respectively. Of the engine mounts disposed at the three locations, a fluid-filled vibration-damping device exhibiting vibration-attenuating action based on flow action of non-compressible fluid filling the interior thereof is employed as a rear engine mount disposed at the vehicle back end, and the vibration-attenuating action based on the flow action of the non-compressible fluid is exhibited against vibration input in a vehicle longitudinal direction.

Abstract: A rotary damper includes a driven-to-rotate member having integrally a driven-to-rotate part for coupling to a drive member and a first inner cylindrical wall, the first inner cylindrical wall including a locking part at a bottom end of the first inner cylindrical wall; a fixed support member for holding the driven-to-rotate member so as to rotate freely; a receiving part formed between the fixed support member and the driven-to-rotate member; and a seal member for sealing an outer perimeter of the receiving part so that the driven-to-rotate member and the fixed support member are capable of relative rotation. A viscous fluid is provided inside the receiving part for damping relative rotation between the driven-to-rotate member and the fixed support member.

Abstract: A rotary damper includes a driven-to-rotate member with a driven-to-rotate part for coupling to a drive member, a fixed support member for holding the driven-to-rotate member so as to rotate freely, a receiving part formed between the fixed support member and the driven-to-rotate member, a seal for sealing an outer perimeter of the receiving part so that the driven-to-rotate member and the fixed support member are capable of relative rotation, and a viscous fluid inside the receiving part for damping the relative rotation between the driven-to-rotate member and the fixed support member. The rotary damper is easy to assemble by virtue of eliminating the accumulation of unwanted air inside the receiving part. Since air does not mix with the viscous fluid, the torque precision can be made constant.

Abstract: A strut (12) is configured for an active suspension system (142) which provides electronic control for both the force applied by the strut (12) and the dampening characteristics of the strut (12). A compressible fluid (18) is used within the strut (12), and preferably includes a compressible base fluid and electromagnetic field responsive particles (132) which are suspended in the compressible base fluid. The electromagnetic field responsive particles (132) are preferably closely matched in density and modulas of elasticity to that of the compressible base fluid to prevent sedimentation of the particles (132) and to maintain the elasticity of the compressible fluid (18). The amount compressible fluid (18) within the strut (12) is electronically controlled to determine the force applied by the strut (12) and a field strength applied to the compressible fluid in a fluid flow passage is electronically controlled to determine the dampening characteristics of the strut (12).

Abstract: A rotary damper includes a driven rotary member having a driven rotary part for engaging a driving member, and a stationary support member for rotatably supporting the driven rotary member. A housing is disposed between the stationary support member and the driven rotary member, and a viscous fluid is disposed in the housing for damping the driven rotary member when the driven rotary member rotates relative to the stationary support member. A sealing member is disposed on the housing for sealing an outer peripheral edge of the housing so as to allow the driven rotary member to rotate relative to the stationary support member. An opening is formed in the driven rotary member or the stationary support member for communicating a portion of the housing inside the sealing member with atmosphere. The opening is closed when or after the driven rotary member and the stationary support member are assembled.

Abstract: A magnetorheological damper device is provided having an increased shear interface area per unit volume of device, which enhances the stroking force of the damper.

Abstract: Apparatus are provided for a damping system. The system includes a housing having an inner surface defining a passage therethrough, a first bellows disposed within the passage, the first bellows having an outer surface and spaced apart from the housing inner surface to define a first chamber having a volume, a second bellows disposed within the passage, the second bellows having an outer surface and spaced apart from the housing inner surface to define a second chamber having a volume, a restrictive flow passage in fluid communication with the first and second chambers, fluid disposed within the first chamber, the second chamber, and the restrictive flow passage, and a piston coupled to the second bellows and disposed at least partially within the restrictive flow passage, the piston configured to selectively receive a force to thereby move the piston through the housing passage.

Abstract: A gear damper has a fixed first part and a second part rotatable relative thereto, with a gear formed on the second part. A continuous annular seal is provided between the first and second parts, and a substantially continuous layer of damping fluid is provided between the first and second parts.

Abstract: The hydraulic cylinder or shock absorber arrangement has a cylinder unit limiting an inner space in which a medium in the form of a gas or a liquid is intended to be placed. A forwardly and backwardly movable piston unit is placed such that it can slide within the space that is defined by the piston into a first chamber and a second chamber. An inlet/outlet is defined in the respective chambers of the cylinder unit for the addition to and removal of medium from the chambers together with devices that co-acts in order to determine the relative position of the piston within the cylinder unit.

Abstract: A rotary damper includes a cylindrical member having walls on an inner peripheral surface of a cylindrical chamber along a radial line, and a rotor member having vanes moving along the inner peripheral surface of the cylindrical chamber. A resistance force of a viscous fluid filled in the cylindrical chamber is applied to the vanes when the cylindrical member rotates relative to the rotor member. The rotor member is formed of a thermoplastic resin containing inorganic filler or fiber. Thus, the rotor member having high strength can be obtained.

Abstract: A vibration and displacement damper includes a plunger piston (10) sliding with a slight clearance inside a guiding cylinder (20). The plunger piston includes over a part of its length a piston ring (12) sliding inside a main chamber (13) provided in the cylinder, the ring including calibrated through-orifices (14) for a high-viscosity fluid filling the chamber on both sides of the ring. The device is intended to damp vibrations and displacements, in particular of cable stays.

Abstract: A fluid coupled speed retarder generating a restraining torque on a vehicule wheel system comprises a restraining shaft (50) coupled by a viscous fluid to a wheel (32) and axle (54) system through a coupling (30) which includes an impeller (48) with radial vanes (77) connected to the restraining shaft and a housing (44) with further radial vanes (46), the housing connected for rotation with the wheel (34). A braking force is developed upon demand by a selective locking of the restraining shaft (50) from motion, the relative motion between the impeller and housing in the viscous coupling generating the barking force.

Abstract: To provide a rotary damper having a compact shape with a short axial length and capable of absorbing an extremely high torque acting temporarily in the case of a door abruptly closing. In a rotary damper (1) in which a rotary member (5) includes: a basement portion (6) axially supported by a drive shaft (4); a torque adjustor (7) capable of relatively moving on the drive shaft (4); a slide member (8) positioned through and facing the torque adjustor (7); and a spring (9) for energizing the slide member (8) to a cam, the slide member (8) is moved in the radial direction by relatively moving the torque adjustor (7) to a position having a predetermined angle against the drive shaft (4), and a predetermined radial clearance is formed between an outer surface (8b) of the slide member (8) and an inner peripheral surface (3a) of a chamber, thereby changing the clearance to change a torque generated by the rotation of the rotational member (5).

Abstract: The hydraulic cylinder or shock absorber arrangement has a cylinder unit limiting an inner space in which a medium in the form of a gas or a liquid is intended to be placed. A forwardly and backwardly movable piston unit is placed such that it can slide within the space that is defined by the piston into a first chamber and a second chamber. An inlet/outlet is defined in the respective chambers of the cylinder unit for the addition to and removal of medium from the chambers together with devices that co-acts in order to determine the relative position of the piston within the cylinder unit.

Abstract: A rotary damper includes a cylindrical member having walls on an inner peripheral surface of a cylindrical chamber along a radial line, and a rotor member having vanes moving along the inner peripheral surface of the cylindrical chamber. A resistance force of a viscous fluid filled in the cylindrical chamber is applied to the vanes when the cylindrical member rotates relative to the rotor member. The rotor member is formed of a thermoplastic resin containing inorganic filler or fiber. Thus, the rotor member having high strength can be obtained.

Abstract: There is provided a damping device for making large a damping force per unit length in an axial direction thereof. The damping device 20 is provided with a motion conversion section 21 for converting a relative linear motion between the two object portions to a rotational motion of a rotation member 30 and a damping section 22 operatively connected to the motion conversion section and adapted to resist the rotational motion of the rotation member. The damping section 22 is formed with the rotation member 30, an inner peripheral side sealing layer 34 disposed on an inner peripheral side of the rotation member 30 and an outer peripheral side sealing layer 33 disposed on an outer peripheral side of the rotation member. The inner and outer peripheral side sealing structure are sealed with viscous medium.

Abstract: A damper for a weighing device including a cavity 4 in which a plate 12 can move, which plate is designed for being connected to a weight measuring device 2. The cavity 4 is closed tightly by a flexible membrane 14 and is partly filled with an oil, while leaving a volume of air or of a gas between the top 14a of the oil and the membrane 14, the plate 12 being totally immersed in the oil. The lower surface of the plate 12 and the bottom of the cavity 4 have shapes which are not planar and which are not parallel to each other, thus preventing the formation of a thin film of oil between them. The peripheral surface of the plate 12 and of the peripheral wall of the cavity 4 define therebetween a first constriction 15 of which the transverse section is constant whatever the position of the plate 12 in the cavity 4.