Abstract: A seismic testing apparatus is provided in which linear motion or excitation of a horizontally disposed table is achieved simultaneously along three mutually orthogonal axes by means of independently operable hydraulic-actuator assemblies. Rotational or torsional motion of the table about the linear excitation axes is resisted by separate, mechanical rotation-inhibiting means each consisting of a torsionally rigid structure disposed parallel to the table and perpendicularly to their respective associated axes of excitation. The torsionally rigid structures are each connected to the table at two spaced-apart points, with all four points of connection lying in the same plane.

Abstract: An underwater shear wave vibrator apparatus has a housing with a vibratory generating system mounted inside the housing for generating a force along an axis substantially parallel to the underwater seabed surface. A coupling apparatus which has an attachment surface and an underside surface for engaging the seabed is connected through a pivotal arm to the housing. A hydraulic apparatus is used for positioning the seabed engaging apparatus normal to the force axis of the vibratory generating apparatus by movement about the pivotal attachment so as to maintain contact of the seabed engaging apparatus with the seabed as the vibratory generating apparatus applies force against the seabed. Apparatus is also included for maintaining orientation of the underside surface of the positioning apparatus as the positioning apparatus moves the seabed engaging means.

Abstract: A torsionally stiff flexure support for the slip plate in a vibration apparatus is provided permitting predetermined linear motion along the axis of vibration by longitudinal bending of the flexure, but by virtue of its torsional stiffness blocking pivoting movement about the center axis of the slip plate.

Abstract: Apparatus for subjecting a test specimen to vibrational forces has a base, a first preselected massmounted for reciprocal movement relative to the base and a second preselected mass elastically coupled to the first mass to produce a resonant condition at a preselected frequency of reciprocal movement.

Abstract: The present invention provides a hydrostatic bearing type coupling for a vibrating machine. The coupling is interposed between a vibration table upon which a test specimen or the like is mounted and a vibrator in such a way that even when the vibration table is caused to vibrate three-dimensionally, there are free movements in the two directions.

Abstract: A hydraulic vibration tester comprises an actuator comprising a piston reciprocable in a cylinder connected with a vibration testing table and a direct drive type servo valve for supplying pressure fluid alternately to opposite ends of the cylinder. The servo valve comprises a spool valve member reciprocable in the bore of a valve body by a magnetic coil supplied with alternating current and located in a direct current magnetic field. At opposite ends of the spool valve member there are coned disc springs acting to bias the spool valve member to a median position and acting to allow only an axial reciprocating movement of the spool valve member at a frequency in the range of 650 Hz to 2000 Hz. The passages connecting the servo valve with the activator have a resonant frequency in the same range so as to achieve an effective vibration test in the high frequency range.

Abstract: The invention relates to a method and device for detecting changes in the mechanical state of the members of a structure implanted in the sea, whereby each member is subjected to impacts and after each impact, the simultaneous signals of excitation and dynamical response of the member are recorded, the signals of identical frequency being processed in order to define a ratio which varies with the frequency and presents peaks. The aforesaid operations are repeated at regular intervals, a watch being kept for any shifts in the peaks which could indicate a change in the structure.

Abstract: Driver bar assembly for vibration test apparatus, comprising a bar element and a retainer element separably connected thereto; the bar element having a normally vertically disposed base attachable to a pivotally mounted shaker head and a normally horizontally disposed flange adapted to lie in a common plane with and spaced from a slip plate to be driven by the shaker head; the retainer element having a first bracket in which the bar element flange is bracketable, and a second bracket in which the slip plate is bracketable opposite the bar element flange, whereby the flange and slip plate spacing is bridged in vibration transmitting relation between the shaker head and the slip plate; the retainer element being separable from the slip plate and the bar element flange without relative movement of the slip plate and shaker head, the bar element and shaker head being freely angularly movable relative to the slip plate in the separated condition of the retainer element and the bar element.

Abstract: Hydrostatic bearing apparatus adapted to mount a shaker-coupled, dimensionally temperature dependent test piece for vibratory oscillation along a predetermined test axis. The apparatus comprises a support block having a compliant section defining a bore, a shaft axially journaled in the bore and defining therewith a bearing locus paraxial with the test axis. Bracket means is provided securing the test piece to the shaft beyond the locus for bearing-guided test axis oscillation, the bearing locus being test axis paraxially bodily displaceable responsive to displacement of the compliant section in test piece dimensional change accommodating relation.

Abstract: Pneumatically driven vibrators coupled to resonating, self-attenuating structures define a shaker which, when included in a vibration system, enables a test item to be vibration tested under controlled conditions of multi-frequency, multi-degree-of-freedom acceleration history, to achieve a frequency spectrum and acceleration-level control of a broadband quasi-random vibration output in the frequency range, for example, from 40 Hz to 2 kHz for vibration testing of equipment. The driving set of annular structure responds to an intense vibration spectrum, created by the attached pneumatic vibrators, with multi-modal forced and resonant frequencies in limited directions. The driven set of annular structure, holding the test hardware, responds with forced and harmonic oscillations to a vibration field transmitted from the driving set of structure through a specially designed elastomeric path.

Abstract: Controllability and performance of resonating, compliant, simply excited, self-attenuating driving and driven sets of structures coupled to pneumatic vibrators is usefully enhanced by means of altering mode shapes by forcibly creating nodes and partial nodal lines and by means of intensifying power transmitted to test items by forcibly increasing acceleration transmissibility. These devices, when included in a vibration system, enable different test items to be vibration tested at selectable repeatable levels under controlled conditions of multi-frequency, multi-degree-of-freedom acceleration history, to achieve a frequency spectrum and acceleration-level control of a broadband quasi-random vibration output. Specific design of the size, mass, and resonant behavior of the driving and driven structure sets with appropriate transmissibility characteristics of the elastomeric interface results in controlled multi-modal, uniform RMS acceleration, multi-degree-of-freedom, frequency-bounded vibration testing.

Abstract: A low-cost, multi-axis, quasi-random vibration system includes pneumatically driven vibrators coupled to a resonating, self-attenuating shaker structure to achieve a frequency spectrum and acceleration-level control of a broadband quasi-random vibration output in the frequency range, for example, from 40 Hz to 2 kHz for vibration testing of equipment. The shaker structure consists of flexible interconnected structures whose primary or driving structure acts to mechanically process the vibratory input of the coupled vibrators and whose supporting or driven structure supplies a further vibrational processing to supply the test item with multi-axis multimodal input. Automatic control and pseudo-random modulation of air pressure of the pneumatic vibrators provide closed-loop broadband acceleration-spectrum control and spectrum smearing to enhance frequency content and to prevent the shaker from locking onto any particular vibration frequency, especially a natural frequency of the shaker.

Abstract: A spherical shaped plate and an orifice opening are oriented such that the edge of the plate can span and cover part of the orifice opening. Stops are provided to prevent a full 360.degree. rotation. The plate shape and wedge opening can be configured such that, as the angular position of the plate changes, the orifice area changes according to the predetermined relationship. The plate and the opening may be enclosed in a gas tight housing, with a stepping motor exterior to the housing coupled via a shaft passing through the housing to the plate. The plate angular position versus orifice area relationship is determined in combination with a desired linear angular position versus gas pressure curve, for use in copending patent application Ser. No. 897,821, filed herewith entitled "Quasi-Random Pneumatic Vibration Facility and Automatic Frequency Modulating System Therefor" by Henry T. Abstein, Jr., Dennis B. Page, James M. Kallis, Charles F. Talbott, Jr. and Richard L. Baker.

Abstract: Pneumatically driven vibrators coupled to resonating, self-attenuating structures define a shaker which, when included in a vibration system, enables a test item to be vibration tested under controlled conditions of multi-frequency, multi-degree-of-freedom acceleration history, to achieve a frequency spectrum and acceleration-level control of a broadband quasi-random vibration output in the frequency range, for example, from 40 Hz to 2 kHz for vibration testing of equipment. The driving set of structure responds to an intense vibration spectrum, created by the attached pneumatic vibrators, with multi-modal forced and resonant frequencies in limited directions. The driven set of structure, holding the test hardware, responds with forced and harmonic oscillations to a vibration field transmitted from the driving set of structure through a specially designed elastomeric path.

Abstract: A method for visually indicating the natural frequencies of a vibrating member utilizing an improved instrument strobed through suitable frequency pick-ups such as accelerometers indiscriminately placed on the vibrating structure to be analyzed.

Abstract: The installation comprises means for subjecting a specimen-holder table to vibrations with respect to a massive support structure in two perpendicular directions, and guiding means which are independent of the vibration means. The guiding means are located between on the one hand the table and at least one connecting member and on the other hand the connecting member and the massive support structure. The connecting member is in mechanical relationship with the table and the massive structure solely by virtue of the guiding means.

Abstract: Apparatus for supporting a vibrational shear wave transducer and coupling shear-wave energy into the earth's surface. The apparatus includes separate lateral base plate assemblies having the vibrator assembly operatively disposed therebetween, and the vibrator frame structure includes necessary hydraulic porting structure and supports manifold and servo valve control structure to provide a unitary, improved form of transducer apparatus. Each of the lateral base plate assemblies further includes a removable earth-coupling structure in the form of inverted pyramid or cleat structure having characteristic apex angles in both the lateral and longitudinal dimension so that earth coupling of energy is optimally effected.

Abstract: An earthquake simulating machine has a vibrating platform mounted in a frame. The platform is driven by a hydraulic piston which reciprocates the platform through a lever system having a mechanical advantage of about ten to one. The vibration of the platform is isolated from the frame by shock absorbing bushings which support the lever system. Shock absorbing feet may be used to support the frame. The hydraulic piston is controlled by a hydraulic circuit and by an electrical circuit which provides the input to the hydraulic circuit. A feedback circuit monitors the output vibration of the platform.

Abstract: The present invention relates to an improved hydraulic vibrator of the type which includes a fixed double rod piston and a reaction mass reciprocally disposed around the piston forming a hydraulic cylinder therein so that when hydraulic fluid is introduced to the cylinder relative to the piston the reaction mass is reciprocated. By the present invention a pair of sleeves are slidably disposed on the piston rods, portions of which can be selectively moved into the cylinder to decrease the displacement of the cylinder and thereby increase the frequency range of vibrations producible by the vibrator.

Abstract: A fluid film levitated horizontally oriented disc is self-centering and floating above another similar mating surface stationary disc. A means for varying the natural period of free oscillation of the levitated disc within the normal earthquake band of frequencies and a means for damping out such free oscillations along with a means for transducing positional differences between the discs into signals wherein earth tremors arriving from any horizontal direction may be recorded.

Abstract: A slip plate assembly is provided for shaker-head generated vibration testing of a test piece being exposed to thermal cycling between preselected test temperature extremes in a closed environment. The assembly comprises a pair of opposed plate elements, a first plate element being beyond the closed environment and a second plate element exposed to test temperatures within the closed environment. Pin means is provided defining a singular locus of vibration transmitting connection between the first plate and the second plate in dimensionally temperature-responsive relation.