Rigid Cylindrical Rod Research Articles

Dynamics of a single cavitation bubble near a cylindrical rod

In this study, we studied the dynamics of a laser-induced single cavitation bubble near a rigid cylindrical rod. We experimentally and numerically investigated the effects of the cylindrical rod on the dynamics of the growth and collapse of the single bubble at different relative wall distances. First, we performed the experiments using a high-speed camera to analyze the shape of the bubble collapse qualitatively. Second, we performed a numerical simulation using a fully compressible two-phase mixture model and an interface capturing scheme to analyze the dynamics of the single cavitation bubble. We analyzed different quantitative parameters, such as maximum velocity of the microjet and the pressure impact load for the bubble at various relative wall distances. The results showed that the bubble dynamics collapsing near the cylindrical rod differed significantly from the single bubble collapse near solid flat plates. A shape of mushroom can be formed during the collapse of the single bubble near the cylindrical rod at the smaller relative wall distances, such as γ = 0.3, 0.4, and 0.5. This mushroom-shaped bubble was not observed for the cases near the solid flat plates in the previous research or near the higher relative wall distances in our present results. In addition, our numerical results revealed that a mushroom-shaped bubble for the cases γ = 0.4, 0.5, and 0.7 may induce a lower jet impact load near the solid surface compared with the case γ = 1.0 with an oval-shaped bubble near the solid boundary.

Estimate of Drag Coefficient for a Finite Patch of Rigid Cylinders

AbstractThis note presents laboratory measurements of the drag coefficient for a finite patch of vegetation that was simulated with a limited number of rigid cylindrical rods. The experiment was de...

A versatile plug microvalve for microfluidic applications

Most of the available microvalves include complicated fabrication steps and multiple materials. We present a microvalve which is inspired from macroplug valves. The plug microvalve is fabricated by boring a hole through a rigid cylindrical rod and inserting it through a microfluidic chip. It simply functions by rotating the rod which aligns or misaligns the valve port with the microchannel. The rod is made up of a rigid material for applying the valve to an elastic polydimethylsiloxane (PDMS) microchannel. The valve can also be used for a rigid channel by inserting the rod into an elastic tubing. Therefore, the presented microvalve can be used for both elastomeric and thermoplastic channels. The plug microvalve can be applied to a prefabricated microchannel and does not require modification of the mold design. We have verified the repeatability and robustness of the valve by repetitive operation cycles using a servo motor. The plug microvalve is adaptable to numerous microfluidic applications. We have shown three modes of operation for the microvalve including fluid flow control across multiple intersecting channels. Integrating the microvalve to some commonly used microfluidic designs, we demonstrated the versatility and the practicality of the microvalve for controlling flow focusing, microdroplet sorting and rapid chemical agent detection. This low-cost microvalve significantly minimizes the prototyping time for microfluidic systems.

Vertical velocity distribution in open-channel flow with rigid vegetation.

In order to experimentally investigate the effects of rigid vegetation on the characteristics of flow, the vegetations were modeled by rigid cylindrical rod. Flow field is measured under the conditions of submerged rigid rod in flume with single layer and double layer vegetations. Experiments were performed for various spacings of the rigid rods. The vegetation models were aligned with the approaching flow in a rectangular channel. Vertical distributions of time-averaged velocity at various streamwise distances were evaluated using an acoustic Doppler velocimeter (ADV). The results indicate that, in submerged conditions, it is difficult to described velocity distribution along the entire depth using unified function. The characteristic of vertical distribution of longitudinal velocity is the presence of inflection. Under the inflection, the line is convex and groove above inflection. The interaction of high and low momentum fluids causes the flow to fold and creates strong vortices within each mixing layer. Understanding the flow phenomena in the area surrounding the tall vegetation, especially in the downstream region, is very important when modeling or studying the riparian environment. ADV measures of rigid vegetation distribution of the flow velocity field can give people a new understanding.

Measurements of Fluctuation in Drag Acting on Rigid Cylinder Array in Open Channel Flow

AbstractIn this study, an array of rigid cylindrical rods was used to simulate emergent vegetation stems that were subject to unidirectional open channel flows. The instantaneous drag force experienced by the rods was measured with a load cell. In addition, the particle image velocimetry (PIV) technique was applied to sample the flow information in a horizontal plane, and wave gauges were used to record the fluctuation in the water-surface elevation. The results show that the drag fluctuation normalized by the mean value may reach as high as 133% when the Reynolds number (defined based on the stem diameter) varied in the range from 400 to 1,100. High fluctuations were also observed in the flow velocity and flow depth under similar flow conditions.

Continuum transport model of Ogston sieving in patterned nanofilter arrays for separation of rod‐like biomolecules

This article proposes a simple computational transport model of rod-like short dsDNA molecules through a microfabricated nanofilter array. Using a nanochannel consisting of alternate deep wells and shallow slits, it is demonstrated that the complex partitioning of rod-like DNA molecules of different sizes over the nanofilter array can be well described by continuum transport theory with the orientational entropy and anisotropic transport parameters properly quantified. In this model, orientational entropy of the rod-like DNA is calculated from the equilibrium distribution of rigid cylindrical rod near the solid wall. The flux caused by entropic differences is derived from the interaction between the DNA rods and the solid channel wall during rotational diffusion. In addition to its role as an entropic barrier, the confinement of the DNA in the shallow channels also induces large changes in the effective electrophoretic mobility for longer molecules in the presence of EOF. In addition to the partitioning/selectivity of DNA molecules by the nanofilter, this model can also be used to estimate the dispersion of separated peaks. It allows for fast optimization of nanofilter separation devices, without the need of stochastic modeling techniques that are usually required.

Effect of friction and cavity depth on the elastic indentation of a cylindrical rod

Using finite element analysis, the elastic displacement of a rigid cylindrical rod pushed by an axial load into an existing cavity of the same diameter as the rod located in the surface of a half space was studied. It was found that such displacement is proportional to the applied load and decreases with increasing depth of the cavity. It is the largest for the slip condition over all the contact surfaces and the smallest for the stick condition over the same surfaces. Also for the same load, the maximum von Mises stress under the punch decreases with increasing depth of the cavity. If not glued to the punch, both the bottom and the lateral surfaces of the cavity are in contact with the punch during deformation.

Scalar Wave Diffraction by a Rigid Cylindrical Rod of Finite Length with Impedance Ends

AbstractA uniform asymptotic high frequency solution is presented for the problem of diffraction of plane harmonic sound waves by an acoustically rigid cylindrical rod of finite length with the ends characterized by the same surface impedance. This problem is described by a modified Wiener‐Hopf equation of the third kind and then solved approximately. The solution involves two infinite sets of constants satisfying two infinite systems of linear algebraic equations. Numerical solutions of these systems are obtained for various values of the parameters of the problem and their effects on the diffraction phenomenon are shown graphically.

An engineering penetration/perforation model of hemispherical nosed rigid cylindrical rods into strain-hardening targets

We propose a four-stage model of the penetration/perforation by hemispherical-nosed rigid cylindrical rods into targets whose materials exhibit strain-hardening effects. During each stage of the penetration process, a kinematically admissible velocity field involving one or more unknown parameters is assumed. These parameters are determined by minimizing the rate of plastic dissipation. From this velocity field, the incremental deformations of the target, the penetration depth, the resisting force acting on the penetrator and hence its deceleration are evaluated. We propose a criterion for the formation and ejection of the cylindrical plug in the target and use it to study problems involving the perforation of the target. Computed results for the exit speed of the penetrator and, when the targets are not perforated, of the penetration depth are found to match well with the corresponding test values.

Effect of frictional force on the steady state axisymmetric deformations of a viscoplastic target

We study steady state axistmmetric deformations of a thick viscoplastic target being penetrated by a fast-moving long rigid cylindrical rod with a hemispherical nose. The deformations of the target appear steady to an observer situated on the penetrator nose tip and moving with it. The objective of this work is to investigate the effect of the frictional force acting on the target/penetrator interface upon the deformations of the target. It is postulated that the frictional force at a point on the target/penetrator interface is proportional to the normal traction there and depends upon the speed of the target particle relative to the penetrator. It is found that the frictional force affects significantly the variation of the tangential speed and the second invariant of the strain-rate tensor on the penetrator nose surface, but minimally the distribution of the normal stress there, since the dominant component of the normal stress is the hydrostatic pressure which is affected little by the consideration of friction forces.

Steady state axisymmetric penetration of a kinematically hardening thermoviscoplastic target

We study axisymmetric thermomechanical deformations of a thick target being penetrated by a fast-moving rigid cylindrical rod with a hemispherical nose, and presume that target deformations appear steady to an observer situated at the penetrator nose tip. Both isotropic and kinematic hardening of the target material are considered. It is found that kinematic hardening increases the normal stress acting on the penetrator nose surface and the temperature rise of target particles abutting the penetrator. However, the value of the hydrostatic pressure at a point in the deforming target region is affected very little by the consideration of kinematic hardening. For suitable values of material parameters appearing in the evolution equation of the back-stress, the computed values of the back-stress at target particles abutting the penetrator nose surface equal three times the yield stress of the target material in a quasistatic simple compression test.

Steady state penetration of elastic perfectly plastic targets

Steady state axisymmetric deformations of an elastic perfectly plastic target being penetrated by a fast moving rigid cylindrical rod have been analyzed by the finite element method. The target is assumed to obey the von Mises yield criterion and the associated flow rule. Contact between target and penetrator has been assumed to be smooth. A mixed formulation, in which two components of the velocity and four components of the deviatoric stress tensor at each node point, and the hydrostatic pressure at the centroid of an element are taken as unknowns, is employed. This should give a better estimate of tractions acting on the penetrator nose, and hence of the axial resisting force experienced by the penetrator. The effect of the penetrator speed, its nose shape and the elasticity of the target material on the target deformations, and the axial force experienced by the penetrator, has been studied. The consideration of elastic effects helps delineate the elastic-plastic boundary in the target.

Steady-state penetration of transversely isotropic rigid/perfectly plastic targets

Axisymmetric deformations of a transversely isotropic, rigid/perfectly plastic target being penetrated by a long rigid cylindrical rod with an ellipsoidal nose have been analyzed. The deformations of the target appear steady to an observer situated at the penetrator nose tip. The contact between the target and the penetrator is assumed to be smooth. Computed results show that the deformation field adjacent to the penetrator nose surface is significantly influenced by the nose shape, and the ratio of the yield stress in the axial direction to that in the transverse direction. The axial resisting force experienced by the penetrator is found to depend strongly upon the nose shape and the ratio of the yield stress in the axial to that in the transverse direction, but weakly upon the square of the penetration speed.

Plasma Formation in a Neutral Gas by a Short-Pulsed, High-Current Electron Beam

Numerical investigations were made of plasma formation in the interaction of an electron beam (600 kV, 10 kA peak, 3 ns FWHM) with a neutral gas (0.8–8 Torr Ar). In the numerical model, the beam is assumed to be a rigid cylindrical rod, and the plasma formation processes are assumed as follows: initially, high-energy beam-electron impact ionizes the gas, and the space-charge electric field of the beam is neutralized by the ions produced. Then, the beam-induced axial electric field becomes dominant, causes gas breakdown, and drives the plasma current. A plasma of density ∼1014 cm-3 and temperature ∼5 eV is produced in the beam-gas interaction. The numerical results approximately agree with the experimental ones for the plasma current and for the singly-ionized line emission.

Stress analysis for an elastic half space containing an axially-loaded rigid cylindrical rod

The axially symmetric elastostatic problem of a half space containing a partially embedded, axially-loaded, rigid cylindrical rod is investigated. The rod is assumed to be in bonded contact with the half space and the half space surface is perpendicular to its axis. The problem is formulated by means of Hankel integral transforms and reduced to systems of coupled singular integral equations, where the unknown quantities are the normal and the shear stresses acting on the entire surface of the rod. Numerical solutions are obtained for several values of the aspect ratio, i.e. of radius to length, and for sufficiently small values of this ratio the results appear to be comparable to those of Muki and Sternberg for an axially-loaded rod. Comparison is also made for the percentage of the vertical resultant load carried by the base of rod with the results obtained by Poulos and Davis for a single axially-loaded incompressible pile.

Phase separation of polyelectrolyte solutions

AbstractIt is shown theoretically that phase separation may arise in solutions of polyelectrolytes due to electrostatic interactions alone. Two models are considered thermodynamically. In both models the free energy is represented as the sum of an entropy of mixing term and an electrostatic free energy term, while the van der Waals attractions are neglected. In the one model, electrically charged rigid cylindrical rods are in solution with an equivalent amount of counterions but without additional electrolyte. The free electrical energy, in this case, is given by the expression of Lifson and Katchalsky. In the other model the solution contains two types of macroions of opposite charge. The macroions are flexible coils carrying a number of univalent charges, the charge density being sufficiently low. The electrical free energy in this case may be approximated by the Debye‐Hückel expression. For both models, it is shown that the decrease in the electrical free energy in a phase separation can, at given temperature and pressure, more than compensate for the increase in the entropy of mixing term. The effects of polymer concentration, dielectric constant, charge density, and salt content follow directly from the thermodynamic treatment of the models.