Added mass

About: Added mass is a research topic. Over the lifetime, 2849 publications have been published within this topic receiving 47899 citations.

Quasi-2D dynamic jamming in cornstarch suspensions: visualization and force measurements

Abstract: We report experiments investigating jamming fronts in a floating layer of cornstarch suspension. The suspension has a packing fraction close to jamming, which dynamically turns into a solid when impacted at a high speed. We show that the front propagates in both axial and transverse direction from the point of impact, with a constant ratio between the two directions of propagation of approximately 2. Inside the jammed solid, we observe an additional compression, which results from the increasing stress as the solid grows. During the initial growth of the jammed solid, we measure a force response that can be completely accounted for by added mass. Only once the jamming front reaches a boundary, the added mass cannot account for the measured force anymore. We do not, however, immediately see a strong force response as we would expect when compressing a jammed packing. Instead, we observe a delay in the force response on the pusher, which corresponds to the time it takes for the system to develop a close to uniform velocity gradient that spans the complete system.

Parametric response of cantilever Timoshenko beams with tip mass under harmonic support motion

Abstract: The parametric response of a thick cantilever beam with a tip mass subjected to harmonic axial support motion is investigated. The Timoshenko beam theory is used to assess the effects of rotary inertia and shear deformation for the beam. In this regard, different modal amplitudes for transverse displacement and angle of rotation of the cross-section are considered. This yields a more accurate description of the dynamic model. The governing equations of motion are then derived for an arbitrary axial support motion which provide the flexibility of choosing the number of characteristic modes of the beam. To formulate a simple, physically correct dynamic model for stability and periodicity analysis, the general governing equations are truncated to only the first mode of vibration. Using Green’s function and Schauder’s fixed point theorem, the necessary and sufficient conditions for the existence of periodic oscillatory behavior of the beam are established. Consequently, the phase domains of periodicity and stability for various values of the physical characteristics of the beam-mass system and harmonic base excitation are presented. Depending on the values of the excitation amplitude and frequency in the stable and unstable regions, the solution exhibits many shapes besides the transition periodic shapes. A numerical example assessing the role of slenderness ratio of the beam, is presented to demonstrate the effectiveness of the proposed study. Results indicate that for a given beam system with a known excitation, increasing the tip mass would almost always reduce the stable periodic region. The effect of the beam model assumption on the periodic domain is also studied. Results show that using purely flexural or even the Euler–Bernoulli model rather than Timoshenko, would produce an incorrect periodic region.

Dissipation and oscillatory solvation forces in confined liquids studied by small-amplitude atomic force spectroscopy

Abstract: We determine conservative and dissipative tip–sample interaction forces from the amplitude and phase response of acoustically driven atomic force microscope (AFM) cantilevers using a non-polar model fluid (octamethylcyclotetrasiloxane, which displays strong molecular layering) and atomically flat surfaces of highly ordered pyrolytic graphite. Taking into account the base motion and the frequency-dependent added mass and hydrodynamic damping on the AFM cantilever, we develop a reliable force inversion procedure that allows for extracting tip–sample interaction forces for a wide range of drive frequencies. We systematically eliminate the effect of finite drive amplitudes. Dissipative tip–sample forces are consistent with the bulk viscosity down to a thickness of 2–3 nm. Dissipation measurements far below resonance, which we argue to be the most reliable, indicate the presence of peaks in the damping, corresponding to an enhanced 'effective' viscosity, upon expelling the last and second-last molecular layer.