Recent advances in nonlinear passive vibration isolators

A method is performed by an electronic device with a display and a touch-sensitive surface. The method includes: displaying a progress icon; while providing content with the electronic device: detecting a contact at a location that corresponds to the progress icon; detecting movement of the contact, wherein movement of the contact comprises a first component of movement on the touch-sensitive surface in a direction corresponding to movement on the display parallel to a first predefined direction and a second component of movement on the touch-sensitive surface in a direction corresponding to movement on the display perpendicular to the first predefined direction; and, while continuing to detect the contact on the touch-sensitive surface, moving the current position within the content at a scrubbing rate, wherein the scrubbing rate decreases as the second component of movement on the touch-sensitive surface increases.

Device, method, and graphical user interface for moving a current position in content at a variable scrubbing rate

A nonlinear energy sink (NES) approach is proposed for whole-spacecraft vibration reduction. Frequency sweeping tests are conducted on a scaled whole-spacecraft structure without or with a NES attached. The experimental transmissibility results demonstrate the significant reduction of the whole-spacecraft structure vibration over a broad spectrum of excitation frequency. The NES attachment hardly changes the natural frequencies of the structure. A finite element model is developed, and the model is verified by the experimental results. A two degrees-of-freedom (DOF) equivalent model of the scaled whole-spacecraft is proposed with the two same natural frequencies as those obtained via the finite element model. The experiment, the finite element model, and the equivalent model predict the same trends that the NES vibration reduction performance becomes better for the increasing NES mass, the increasing NES viscous damping, and the decreasing nonlinear stiffness. The energy absorption measure and the energy transition measure calculated based on the equivalent model reveals that an appropriately designed NES can efficiently absorb and dissipate broadband-frequency energy via nonlinear beats, irreversible targeted energy transfer (TET), or both for different parameters. [DOI: 10.1115/1.4035377]

Nonlinear Energy Sink for Whole-Spacecraft Vibration Reduction

We investigate the bending behavior of functionally graded (FG) nanobeams with internal porosity and subjected to a hygro-thermo-mechanical loading. The Eringen's Nonlocal Theory (ENT) is here applied for the numerical study, while considering a uniform porosity within the nanobeam. The mechanical and thermal properties of FG materials are assumed to vary throughout the thickness. The equations of motion are derived from the Hamilton's law and solved with the Navier's procedure. A key point of the work is to explore the effect of the material length-scale, power-law index, porosity volume fraction, temperature rise, and moisture concentration on the global deflection of nanobeams, as useful for practical applications.

Structural response of porous FG nanobeams under hygro-thermo-mechanical loadings

Space antenna reflectors are used by space vehicles to communicate with ground stations. These reflectors are generally subject to broadband random vibration and shock conditions during shipment and vehicle launch. While active vibration control methods can reduce any unexpected responses, sensors, controllers, power amplifiers, and actuators are all required to implement the control system. These additional external devices increase both the weight and the cost of the reflector, and reduce the reliability and safety of the space product. This study proposes a novel self-sensing vibration control method and applies a self-sensing electromagnetic transducer to suppress the vibration of a space antenna reflector. This transducer is used bifunctionally, acting as both an isolator and a velocity sensor. The vibration control principle of the proposed method is analyzed. A governing equation is established using the finite element method. A type of degree of freedom reduction method is used to obtain the response of the space antenna reflector. A ground experiment is then set up. The results demonstrate that the proposed self-sensing vibration control method can reduce the second-order and third-order vibrations of the space antenna reflector by 4 and 9 dB, respectively.

Self-Sensing Electromagnetic Transducer for Vibration Control of Space Antenna Reflector

Small launch vehicles present an economically viable method for placing small satellites into orbit. These launch vehicles would be even more attractive to satellite customers if they could provide a softer ride to orbit. Passive whole-spacecraft vibration isolation systems have been developed for small launch vehicles to greatly reduce the dynamic launch loads. To date, two types of isolation systems have been designed.

Multi-axis whole-spacecraft vibration isolation for small launch vehicles

: A spacecraft is subjected to very large dynamic forces from its launch vehicle during its ascent into orbit. These large forces place stringent design requirements on the spacecraft and its components to assure that the trip to orbit will be survived. The severe launch environment accounts for much of the expense of designing, qualifying, and testing satellite components. Reduction of launch loads would allow more sensitive equipment to be included in missions, reduce risk of equipment or component failure, and possibly allow the mass of the spacecraft bus to be reduced. These benefits apply to military as well as commercial satellites. This paper reports the design and testing of a prototype whole-spacecraft isolation system which will replace current payload attach fittings, is passive-only in nature, and provides lateral isolation to a spacecraft which is mounted on it. This isolation system is being designed for a medium launch vehicle and a 6500 lb spacecraft, but the isolation technology is applicable to practically all launch vehicles and spacecraft, small and large. The isolator significantly reduces the launch loads seen by the spacecraft. Follow-on contracts will produce isolating payload attach fittings for commercial and government launches.

Whole-Spacecraft Passive Launch Isolation

A passive, multi-axis, highly damped, shock load isolation mount which can serve as a complete one-piece mount, particularly of a spacecraft to its launch vehicle or launch vehicle adaptor structure, or can serve in multiplicity as necessary to provide a complete shock load isolation mounting system. When used as a one-piece mount or used in multitude as a system, the invention provides substantial reduction in the shock load transmission to a payload from its support base for both axial loads and lateral loads. The unique multi-layered, opposed beam, contorted load path flexure design combined with a shear wall type constrained layer damping treatment provides substantial shock load isolation in a durable, reliable, lightweight, and compact form.

Passive, multi-axis, highly damped, shock isolation mounts for spacecraft

Whole-spacecraft passive launch isolation

The excitations from the engines of launch vehicles and the aerodynamics of flight produce large vibrations which are highly detrimental to spacecraft during launch. Significant dynamic loads often exist in all three translations and for rotations as well, therefore, complete six degree-of-freedom vibration load isolation is often desired. The disclosed device utilizes a previously disclosed passive axial vibration isolation device to simply and effectively create a passive three-axis vibration isolation device suitable for effecting a six degree-of-freedom whole-spacecraft passive vibration isolation system. The vibration isolation system design can be simply tuned to address various dynamic load frequency bands of concern, including isolation for pyrotechnic shock. The resulting system is compact and lightweight and can be easily utilized with existing launch vehicle-to-payload support structures.

Three-axis, six degree-of-freedom, whole-spacecraft passive vibration isolation system

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