Mass Collides Research Articles

A novel mass damper enabled by three types of mass attachments and internal vibro impacts

To integrate the merits of linear, nonlinear, and impact-type mass dampers in one device, a novel vibro-impact tri-mass damper (VITM) is proposed. The VITM consists of three types of mass attachments including a linear mass damper, a nonlinear mass damper, and a slightly damped stiffness-free mass between them. By sharing a same moving path, the free middle mass collides with the linear and nonlinear mass dampers due to asynchronous motions among them. Unlike conventional impact-type mass dampers whose vibro impacts are between the mass damper and the structure, those vibro impacts are between adjacent auxiliary masses and do not cause excessive acceleration in the structure. First, the working principles and mathematical descriptions of VITM are presented. The VITM is then experimentally realized and tested on a three-story steel-frame structure. Numerical analyses are subsequently conducted to examine the control performance of the VITM in comparison with four existing mass dampers when subjected to impulsive and stochastic excitation. The results show that the VITM outperforms the other devices with high control effectiveness, strong robustness against both frequency and energy changes, and limited space demand. The enhancement of the VITM is associated with multiple control mechanisms especially the fast energy dissipation via the frequent and efficient vibro impacts. These favorable features equip the VITM to be an applicable control strategy in complex loading environments like earthquakes.

Experimental Simulations of Hypervelocity Impact Penetration of Asteroids Into the Terrestrial Ocean and Benthic Cratering

AbstractSeafloor cratering is an important process that records the impact history of the Earth, affects projectile survivability, and determines the mass of ejecta from benthic rock that is transported to the atmosphere. We report experimental hypervelocity impacts of chondrite and other projectiles (olivine, stainless‐steel, polycarbonate) on a water‐covered iron target to derive a scaling relationship for benthic cratering. In situ observations of 5‐km/s impacts quantify the deceleration of projectiles in the water column by shock‐induced deformation and fragmentation. The minimum water depths at which multiple craters appeared on the benthic target were two and four times the projectile diameter for chondrite and stainless steel, respectively. Based on the observed deceleration of projectiles in water, the cratering efficiency of a benthic target for a given impact velocity is predicted to follow an exponential decay law in terms of water depth normalized by projectile diameter (H/d), given by πv ∝ exp(−(H/d)/κ), when a projectile of original mass collides with the target. Comparing the volume of the largest crater in the experiments and that derived from the scaling relation, mass ratios of the largest projectile fragment to original projectile in the 5‐km/s impact were calculated to be 0.1–0.3 (H/d = 2–6) and 1.0 ± 0.3 (H/d = 5.5) for chondrite and stainless steel, respectively. Using the scaling relationship, the volume of the transient crater on oceanic crust by an asteroid impact is estimated to be smaller than previously predicted by hydrocode simulation when the asteroid fragmentation in the water column controls seafloor cratering.

On stability in a case of oscillations of a pendulum with a mobile point mass

Abstract Motion in a uniform gravitational field of a modified pendulum in the form of a thin, uniform rod, one end of which is attached by a hinge, is investigated. A point mass (for example, a washer mounted on the rod) can move without friction along the rod. From time to time, the point mass collides with the other end of the rod (if, for example, at this end of the rod a rigid plate of negligibly small mass is attached perpendicular to it). The collisions are assumed to be perfectly elastic. There exists such a motion of the pendulum in which the rod is at rest (it hangs) along the vertical passing through its suspension point, but the point mass moves along the rod, periodically bouncing up from its lower end to some height not exceeding the rod length. The nonlinear problem of the orbital stability of this periodic motion of the pendulum is investigated. In the space of two dimensionless parameters of the problem, stability and instability regions are found.

Measurement of Dynamic Responses of a Force Sensor against Small Impact Forces with Various Durations

At present, a method for evaluating dynamic characteristics of force sensors against small and short-duration impact forces has been developed. In this method, a small mass collides with a force sensor and the impact force is measured with high accuracy as the inertial force of the mass. A pneumatic linear bearing is used in order to realize linear motion with sufficiently small friction acting on the mass, i.e., the moving part of the bearing. Using this method, the dynamic characteristics of the force sensor are evaluated in detail: small and various-duration impact forces with maximum values of approximately 0.4-6.0 N and full width at half maximum (FWHM) of approximately 0.6-2.8 ms are applied to the force sensor and the impact responses of the force sensor are evaluated.

Impact Response Measurement of Contact Lenses

Impact response of contact lenses is measured using the Levitation Mass Method (LMM). In the LMM, a small mass collides with contact lenses and the impact force is measured with high accuracy as the inertial force of the moving part. A pneumatic linear bearing is used to achieve linear motion with sufficiently small friction acting on the moving part. Hysteresis loop and consumed energy as mechanical characteristics of contact lenses are also calculated.

DYNAMIC CHARACTERISTICS MEASUREMENTS OF A FORCE TRANSDUCER AGAINST SMALL AND SHORT-DURATION IMPACT FORCES

Abstract A method for evaluating the dynamic characteristics of force transducers against small and short-duration impact forces is developed. In this method, a small mass collides with a force transducer and the impact force is measured with high accuracy as the inertial force of the mass. A pneumatic linear bearing is used to achieve linear motion with sufficiently small friction acting on the mass, which is the moving part of the bearing. Small and short-duration impact forces with a maximum impact force of approximately 5 N and minimum half-value width of approximately 1 ms are applied to a force transducer and the impulse responses are evaluated.

Dynamic landslide processes revealed by broadband seismic records

We use broadband seismic recordings to trace the dynamic process of the deep‐seated Akatani landslide that occurred on the Kii Peninsula, Japan, which is one of the best recorded large slope failures. Combining analyses of the seismic records with precise topographic surveys done before and after the event, we can resolve a detailed time history of the mass movement. During 50 s of the large landslide, we observe a smooth initiation, acceleration with changes in basal friction, and reversal of the momentum when the mass collides with the opposite valley wall. Of particular importance is the determination of the dynamic friction during the landslide. The coefficient of friction is estimated to be 0.56 at the beginning of the event and drops to 0.38 for most of the sliding. The change in the frictional level on the sliding surface may be due to liquefaction or breaking of rough patches and contributes to the extended propagation of the large landslide.

Analysis of Steady Collision Vibration in Cantilever Beam Having an Attached Mass (The Case Where Structural Damping and Viscous Damping is Considered in System)

This paper deals with response analysis of collision vibration in continuous system excited by periodic displacement with arbitrary functions. A system of steady vibration in a cantilever beam having an attached mass at free-end is considered. The cantilever beam has structural damping in the beam, and it is being put in the viscous fluid with hydrodynamic drag. The attached mass collides elastically with the coil spring clamped on asymmetrical faces when the amplitude of mass exceeds the clearance between the coil spring and the attached mass. Then, the restoring force is assumed to be an asymmetric piecewise-linear system. For such a system, the beam undergoes a nonlinear vibration when the attached mass collides with the coil spring. In order to analyze harmonic, superharmonic and subharmonic resonances for the system, Fourier series method is applied to obtain an exact solution for resulting vibration. Next, the numerical calculation is performed to obtain the resonance curves. The numerical results show effects of the mass ratio, the amplitude ratio of excitation, the spring constant ratio, the structural damping ratio and the external damping ratio on the resonance curves. The numerical experiments are also carried out to verify the numerical results.

Energy Transfer in a Three Body Momentum Exchange Impact Damper

Impact vibration such as a floor vibration caused by jumping of children or vibration of a press machine is very important engineering problem. The momentum exchange impact damper has been proposed to solve these problems. The basic principle of this damper is based on the energy transfer on collision of three body systems. However energy or momentum transfer at the impact is not explained theoretically. This paper considers the energy transfer incurred during collisions in three body systems. The three body systems considered herein consists of an impact mass, a main body and an absorber mass. When the impact mass collides with the main body, part of its kinetic energy is transferred to the main body. When the main body simultaneously collides with the absorber mass, part of the kinetic energy of the main body is transferred to the absorber mass. Consequently, the main body receives a small amount of shock and it is possible to keep the main body nearly stationary. In this study, the influence of contact frequency and natural frequency of the system on the energy transfer during collision is analyzed. A theoretical model is developed to analyze the effect of various system parameters. It is shown that the maximum transfer of energy that can be obtained occurs when the contact frequencies are the same. The theoretical analysis is validated with experimental results.

Inner mass impact damper for attenuating structure vibration

The behaviors of a vibration system suppressed with an impact damper are investigated, where the impact damper is simplified as a combination of spring and viscous damping. The analytical theory for the optimal impact control algorithms for impact damper is developed, and the accurate expressions are derived for the optimal values of the impact damper damping and initial displacement in a single-degree-of-freedom structure. The relation between coefficient of restitution and impact damping ratio is obtained. The investigation shows that the effective reduction of the vibration response is nearly independent of the number of impacts, but primarily related to the type of collision which the impact mass collides with the main mass face-to-face. This theory is generalized to continuous structures. An example of an impact damper in a rotating cantilever beam demonstrates that the impact dampers are suitable for attenuating the impulse response of structures unconditional stable without the requirement of the accuracy of the modal information.

Analysis of Steady Impact Vibration in Continuous System Excited by Periodic Displacement with Arbitrary Function (The Case Where Analytical Model Is Simply-Supported-Beam with an Attached Mass)

This paper deals with impact vibration in continuous system excited by periodic displacement with arbitrary functions. The analytical model is a system of steady collision vibration with an attached mass in simply supported-beam at both ends. The attached mass collides elastically with clamped spring of asymmetrical faces. In order to clarify the main resonance of the system subjected to excitation by displacement, the resulting vibrations are analyzed using the Fourier series method and an exact solution is proposed for this system. Following the theoretical analyses, numerical calculations are performed, and the resonance curves are made using the resulting vibrations. Effects of the stiffness of clamped spring, the ratio of attached mass and the amplitude of excitation on the resonance curves are shown by numerical results. For verification of the analytical method, experiments are also performed. The numerical results are in a fairly good agreement with the experimental ones.

Free vibration analysis of a resilient impact damper

The free vibration of a vibratory system equipped with a resilient impact damper is studied. A simple model of impact damper is constructed using spring, mass and viscous damper. The important feature to be carried out in the analysis of this model is that the deformation of an impact damper during the collision with and the main mass can be formulated; therefore, the contact time is taken into consideration. This feature is important for a resilient rather than a rigid impact damper when the noise issue is concerned. The investigation showed that the effective reduction of the vibration response depends not on the number of impacts but primarily on the type of collision that the impact mass collides with the main mass face-to-face. Results also show that the clearance of an effective impact damper should be smaller than twice of the initial displacement of the main mass of the vibration system if the system is stimulated by an initial displacement only. Finally, an example of application of an impact damper on a cantilever beam is demonstrated.

A general timing condition for consecutive collision orbits in the limiting case � = 0 of the elliptic restricted problem

Consecutive collision orbits in the limiting case µ = 0 of the elliptic restricted three-body problem are investigated. in particular those in which the infinitesimal mass collides twice with the smaller (massless) primary. A timing condition is presented that allows the extension of previous results to the case of arbitrary relative orientation of the orbits of the infinitesimal mass and the smaller primary. The timing condition is expressed in two general forms - in terms of orbit parameters and eccentric (or hyperbolic) anomalies at the times of collision - for the specific cases of elliptic. parabolic or hyperbolic orbits of the infinitesimal mass. Some families of solutions are presented.

封入接点形スイッチの動作特性に関する一考察

To design a high speed sealed contacts, time durations of contacting noises are analyzed. The reed is replaced by two one-degree-of-freedom vibration systems. In the model, one mass collides and another vibrates with dynamic friction between contacts. Time duration of noises caused by rebounding, TA, is determined by coefficient of collision and parameter KA, defined as KA=ξ/ξ0ωA; velocity of collision ξ, angular frequency of vibration system ωA, and equivalent pressing distance ξ0. TA increases continuously with an increase of KA. Noises caused by free vibration, TB, is determined by equivalent friction coefficient between contacts and the parameter KA. TB increases in stair case with an increase of KA. Experimentally, in an unsymmetrical reed switch, noises are caused by rebounding and by free vibration. In a symmetrical reed switch, noises are caused by only free vibration. Each noise time duration agrees well with calculated values.