Publications

Torczynski, J.R.; O'Hern, Timothy J.; Clausen, Jonathan C.; Koehler, Timothy P.

Abstract not provided.

Torczynski, J.R.; O'Hern, Timothy J.; Clausen, Jonathan C.; Koehler, Timothy P.

Abstract not provided.

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.; Koehler, Timothy P.

Abstract not provided.

O'Hern, Timothy J.

Abstract not provided.

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.; Koehler, Timothy P.

We develop an idealized experimental system for studying how a small amount of gas can cause large net (rectified) motion of an object in a vibrated liquid-filled housing when the drag on the object depends strongly on its position. Its components include a cylindrical housing, a cylindrical piston fitting closely within this housing, a spring suspension that supports the piston, a post penetrating partway through a hole through the piston (which produces the position-dependent drag), and compressible bellows at both ends of the housing (which are well characterized surrogates for gas regions). In this system, liquid can flow from the bottom to the top of the piston and vice versa through the thin annular gaps between the hole and the post (the inner gap) and between the housing and the piston (the outer gap). When the bellows are absent, the piston motion is highly damped because small piston velocities produce large liquid velocities and large pressure drops in the Poiseuille flows within these narrow gaps. However, when the bellows are present, the piston, the liquid, and the bellows execute a collective motion called the Couette mode in which almost no liquid is forced through the gaps. Since its damping is low, the Couette mode has a strong resonance. Near this frequency, the piston motion becomes large, and the nonlinearity associated with the position-dependent drag of the inner gap produces a net (rectified) force on the piston that can cause it to move downward against its spring suspension. Experiments are performed using two variants of this system. In the single-spring setup, the piston is pushed up against a stop by its lower supporting spring. In the two-spring setup, the piston is suspended between upper and lower springs. The equilibrium piston position is measured as a function of the vibration frequency and acceleration, and these results are compared to corresponding analytical results (Torczynski et al., 2017). A quantitative understanding of the nonlinear behavior of this system may enable the development of novel tunable dampers for sensing vibrations of specified amplitudes and frequencies.

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM

Torczynski, J.R.; O'Hern, Timothy J.; Clausen, Jonathan C.; Koehler, Timothy P.

Models and simulations are employed to analyze the motion of a spring-supported piston in a vibrated liquid-filled cylinder. The piston motion is damped by forcing liquid through a narrow gap between a hole through the piston and a post fixed to the housing. As the piston moves, the length of this gap changes, so the piston damping coefficient depends on the piston position. This produces a nonlinear damper, even for highly viscous flow. When gas is absent, the vibration response is overdamped. However, adding a little gas changes the response of this springmass-damper system to vibration. During vibration, Bjerknes forces cause some of the gas to migrate below the piston. The resulting pneumatic spring enables the liquid to move with the piston so as to force very little liquid through the gap. Thus, this "Couette mode" has low damping and a strong resonance near the frequency given by the pneumatic spring constant and the total mass of the piston and the liquid. Near this frequency, the amplitude of the piston motion is large, so the nonlinear damper produces a large net force on the piston. To analyze the effect of this nonlinear damper in detail, a surrogate system is developed by modifying the original system in two ways. First, the gas regions are replaced by upper and lower bellows with similar compressibility to give a well-defined "pneumatic" spring. Second, the upper stop against which the piston is pushed by its lower supporting spring is replaced with an upper spring, thereby removing the nonlinearity from the stop. An ordinary-differential-equation (ODE) drift model based on quasi-steady Stokes flow is used to produce a regime map of the vibration amplitudes and frequencies for which the piston is up or down for conditions of experimental interest. These results agree fairly well with Arbitrary Lagrangian Eulerian (ALE) simulations of the incompressible Navier-Stokes (NS) equations for the liquid and Newton's 2nd Law for the piston and bellows. A quantitative understanding of this nonlinear behavior may enable the development of novel tunable dampers for sensing vibrations of specified amplitudes and frequencies.

Jones, Elizabeth M.; Reu, Phillip L.; O'Hern, Timothy J.; Sweatt, W.C.

Abstract not provided.

Torczynski, J.R.; O'Hern, Timothy J.; Clausen, Jonathan C.

Abstract not provided.

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.

Abstract not provided.

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.

Abstract not provided.

Journal of Fluids Engineering, Transactions of the ASME

Cooper, Paul; Martin, C.S.; O'Hern, Timothy J.

The 90th Anniversary of the Fluids Engineering Division (FED) of ASME will be celebrated on July 10-14, 2016 in Washington, DC. The venue is ASME's Summer Heat Transfer Conference (SHTC), Fluids Engineering Division Summer Meeting (FEDSM), and International Conference on Nanochannels and Microchannels (ICNMM). The occasion is an opportune time to celebrate and reflect on the origin of FED and its predecessor-the Hydraulic Division (HYD), which existed from 1926-1963. Therefore, the FED Executive Committee decided that it would be appropriate to publish concurrently a history of the HYD/FED. Accordingly, they commissioned Paul Cooper, C. Samuel Martin, and Timothy O'Hern to prepare this paper, which would document the division's past. A brief work in this direction had appeared in the 2010 FED Newsletter (Morgan, W. B., 2010, Brief History of ASME's Hydraulic/Fluids Engineering Division, Fluids Engineering Division Newsletter, New York, pp. 6-7), and the research by Martin for the present paper had been under way for several years prior to that (Cooper, P., 2010, "History of the FED," FED Executive Committee at the ASME-CSME Fluids Engineering Summer Conference (FEDSM-2010), Montreal, QC, Canada, Aug., p. 14).

Reu, Phillip L.; Jones, Elizabeth M.; O'Hern, Timothy J.; Sweatt, W.C.

Abstract not provided.

Journal of Fluids Engineering, Transactions of the ASME

Romero, L.A.; Torczynski, J.R.; Clausen, Jonathan C.; O'Hern, Timothy J.; Benavides, Gilbert L.

We show how introducing a small amount of gas can completely change the motion of a solid object in a viscous liquid during vibration. We analyze an idealized system exhibiting this behavior: a piston in a liquid-filled housing with narrow gaps between piston and housing surfaces that depend on the piston position. Recent experiments have shown that vibration causes some gas to move below the piston and the piston to subsequently move downward against its supporting spring. We analyze the analogous but simpler situation in which the gas regions are replaced by bellows with similar pressure-volume relationships. We show that the spring formed by these bellows (analogous to the pneumatic spring formed by the gas regions) enables the piston and the liquid to oscillate in a mode with low damping and a strong resonance. We further show that, near this resonance, the dependence of the gap geometry on the piston position produces a large rectified (net) force on the piston. This force can be much larger than the piston weight and tends to move the piston in the direction that decreases the flow resistance of the gap geometry.

Clausen, Jonathan C.; Torczynski, J.R.; O'Hern, Timothy J.

Abstract not provided.

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.

Abstract not provided.

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.

Abstract not provided.

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM

O'Hern, Timothy J.; Torczynski, J.R.; Clausen, Jonathan C.

Analysis, simulations, and experiments are performed for a piston in a vibrated liquid-filled cylinder, where the damping caused by forcing liquid through narrow gaps depends almost linearly on the piston position. Adding a little gas completely changes the dynamics of this spring-mass-damper system when it is subject to vibration. When no gas is present, the piston's vibrational response is highly overdamped due to the viscous liquid being forced through the narrow gaps. When a small amount of gas is added, Bjerknes forces cause some gas to migrate below the piston. The resulting pneumatic spring enables the liquid to move with the piston so that little liquid is forced through the gaps. This "Couette mode" thus has low damping and a strong resonance near the frequency given by the pneumatic spring constant and the piston mass. Near this frequency, the piston response is large, and the nonlinearity from the varying gap length produces a net force on the piston. This "rectified" force can be many times the piston's weight and can cause the piston to compress its supporting spring. A surrogate system in which the gas regions are replaced by upper and lower bellows with similar compressibility is studied. A recently developed theory for the piston and bellows motions is compared to finite element simulations. The liquid obeys the unsteady incompressible Navier-Stokes equations, and the piston and the bellows obey Newton's 2nd Law. Due to the large piston displacements near resonance, an Arbitrary Lagrangian Eulerian (ALE) technique with a sliding-mesh scheme is used to limit mesh distortion. Theory and simulation results for the piston motion are in good agreement. Experiments are performed with liquid only, with gas present, and with upper and lower bellows replacing the gas. Liquid viscosity, bellows compressibility, vibration amplitude, and gap geometry are varied to determine their effects on the frequency at which the rectified force makes the piston move down. This critical frequency is found to depend on whether the frequency is increased or decreased with time.

Torczynski, J.R.; O'Hern, Timothy J.; Clausen, Jonathan C.

Abstract not provided.

Clausen, Jonathan C.; Torczynski, J.R.; O'Hern, Timothy J.

Abstract not provided.

O'Hern, Timothy J.; Lord, David L.; Rudeen, David K.

Abstract not provided.

Torczynski, J.R.; Romero, L.A.; Clausen, Jonathan C.; O'Hern, Timothy J.

Abstract not provided.

Clausen, Jonathan C.; Torczynski, J.R.; Romero, L.A.; O'Hern, Timothy J.

Abstract not provided.

Physics of Fluids

Romero, L.A.; Torczynski, J.R.; Clausen, Jonathan C.; O'Hern, Timothy J.; Benavides, Gilbert L.

Abstract not provided.

O'Hern, Timothy J.; Torczynski, J.R.; Shelden, Bion S.; Romero, L.A.

Abstract not provided.

Mondy, L.A.; Bauer, Stephen J.; Hileman, Michael B.; Thompson, Kyle R.; Rao, Rekha R.; Shelden, Bion S.; Soehnel, Melissa M.; O'Hern, Timothy J.; Grillet, Anne M.; Celina, Mathias C.; Wyatt, Nicholas B.; Russick, Edward M.

We are developing computational models to elucidate the expansion and dynamic filling process of a polyurethane foam, PMDI. The polyurethane of interest is chemically blown, where carbon dioxide is produced via the reaction of water, the blowing agent, and isocyanate. The isocyanate also reacts with polyol in a competing reaction, which produces the polymer. Here we detail the experiments needed to populate a processing model and provide parameters for the model based on these experiments. The model entails solving the conservation equations, including the equations of motion, an energy balance, and two rate equations for the polymerization and foaming reactions, following a simplified mathematical formalism that decouples these two reactions. Parameters for the polymerization kinetics model are reported based on infrared spectrophotometry. Parameters describing the gas generating reaction are reported based on measurements of volume, temperature and pressure evolution with time. A foam rheology model is proposed and parameters determined through steady-shear and oscillatory tests. Heat of reaction and heat capacity are determined through differential scanning calorimetry. Thermal conductivity of the foam as a function of density is measured using a transient method based on the theory of the transient plane source technique. Finally, density variations of the resulting solid foam in several simple geometries are directly measured by sectioning and sampling mass, as well as through x-ray computed tomography. These density measurements will be useful for model validation once the complete model is implemented in an engineering code.