Upright Cylinder Research Articles

Prediction of the capillary pressure of fluid surrounding a cylinder representing an idealized rock structure in porous media

Liquids in oil-bearing porous media assume complex shapes that depend on the reservoir characteristics and the wetting properties of the liquid. The wide variation in the geometry of rock formations makes it difficult to accurately predict the capillary pressure of small volumes of liquid and hence the likelihood of being able to move it. Here, we consider the situation in which a small volume of liquid surrounds an upright cylinder on a flat substrate and predict the shape that the liquid takes and its capillary pressure. We validate our predictions by comparing with Surface Evolver simulations for a range of contact angles and cylinder radii.

Collective effect of thermal plumes on temperature fluctuations in a closed Rayleigh–Bénard convection cell

We report a systematic study of the collective effect of thermal plumes on the probability density function (p.d.f.) $P(\delta T)$ of temperature fluctuations $\delta T(t)$ in turbulent Rayleigh–Bénard convection. By decomposing $\delta T(t)$ into four basic fluctuation modes associated with single and multiple warm and cold plumes and a turbulent background, we derive an analytic form of $P(\delta T)$ based on the convolutions of the five independent modes. To test the derived form of $P(\delta T)$ in the multiple-plume regions, where the thermal plumes are heavily populated, we conduct time series measurements of temperature fluctuations in two convection cells; one is a vertical thin disk and the other is an upright cylinder of aspect ratio unity. For a given normalized position in most regions of the convection cell, all of the measured p.d.f.s $P(\delta T)$ for different Rayleigh numbers fall onto a single master curve, once $\delta T$ is normalized by its root-mean-square (r.m.s.) value $\sigma _T$ . It is found that the measured $P(\delta T/\sigma _T)$ at different locations along the symmetric horizontal and vertical axes of the convection cells can all be well described by the derived form of $P(\delta T/\sigma _T)$ . The fitted values of the parameters associated with the number of plumes in multiple plume clusters and their relative strengths and degrees of intermittency are closely linked to the spatial distribution of thermal plumes and local dynamics of the large-scale circulation in a closed convection cell. Our work thus provides a unified theoretical approach for understanding scalar p.d.f.s in a turbulent field, which is very useful not only for the present study but also for the study of many turbulent mixing problems of practical interest.

Mixed Convection in MHD Water-Based Molybdenum Disulfide-Graphene Oxide Hybrid Nanofluid through an Upright Cylinder with Shape Factor

In this work, water is captured as regular fluid with suspension of two types of hybrid nanoparticles, namely molybdenumdisulfide (MoS2) and graphene oxide (GO). The impact of Lorentz’s forces on mixed convective boundary-layer flow (BLF) is studied through an upright cylinder under the influences of thermal radiation. The shape factor is also assessed. The mathematical model for hybrid nanofluidis developed and, by implementing suitable similarity variables, the leading partial differential equations (PDEs) are altered into a non-linear ordinary differential equations (ODEs) system and then resolved through a bvp4c solver. The penetrations of varied parameters, such as thermal radiation, nanomaterials shapes (bricks, platelets, bricks and cylinders), magneto-hydrodynamics (MHD), and ratio parameters on the temperature and fluid velocity, along with the skin friction and the Nusselt number, are typified qualitatively via sketches. The opposing flow, as well as the assisting flow, is considered. The results indicate that the impact of hybrid nanofluid (HBNF) on the velocity and the temperature is more than nanofluid (NF). It is also scrutinized that the blade-shaped nanomaterials of hybrid nanofluid have a maximum temperature and brick-shaped nanomaterials have a low temperature. In addition, the friction factor and the heat transport rate decline due to the magnetic parameter and increase due to the shape factor. Moreover, the radiation uplifts the velocity and temperature, while the free stream Reynolds number declines the velocity and temperature. Finally, a comparison with available results in the literature are made and found in an excellent way. The ranges of constraints in this research are considered as: 0.01 ≤ λ ≤ 0.2 , 0 ≤ M ≤ 4 , 0 ≤ α ≤ 1.5 , 0 ≤ R d ≤ 1 , 1 ≤ Re a ≤ 3 , 0 ≤ ϕ 1 ≤ 0.1 and 0 ≤ ϕ 2 ≤ 0.003 .

The effect of inclination on vortex-induced vibration of a circular cylinder with a base column

The vortex-induced vibration (VIV) of an inclined cylinder can be affected by its end condition. This paper numerically investigates the effect of inclination on the VIV of an elastically mounted rigid cylinder with a base column, which derives from a floating offshore wind turbine (FOWT). The numerical methods are validated against an existing VIV study of a finite-length cylinder. Two inclination angles, i.e. −5° and −10°, are studied to simulate the relatively small wind-induced inclination experienced by FOWTs. Results from stationary simulations show that differences between the force coefficients of inclined and upright cylinders are rather small. Nevertheless, contrary to the finding from previous VIV studies that the effect of inclination on the response of a cylinder with small inclination angles is limited, the present investigation reveals that the maximum response amplitude of the cylinder increases by about 20% when the inclination angle grows to −10° due to the presence of the base column. Meanwhile, the inclination leads to a reduction in the width of the lock-in regime. The impacts of inclination are further discussed via forced vibration studies with same oscillation parameters, which show that the upper part of the cylinder is more affected by the inclination compared to the base column with a considerable decrease in the amplitude of lift coefficient. The discrepancies in fluid forces are substantiated by analysing the pressure distribution on specified spanwise sections of the cylinder surface.

Turbulent temperature fluctuations in a closed Rayleigh–Bénard convection cell

We report a systematic study of spatial variations of the probability density function (PDF) $P(\unicode[STIX]{x1D6FF}T)$ for temperature fluctuations $\unicode[STIX]{x1D6FF}T$ in turbulent Rayleigh–Bénard convection along the central axis of two different convection cells. One of the convection cells is a vertical thin disk and the other is an upright cylinder of aspect ratio unity. By changing the distance $z$ away from the bottom conducting plate, we find the functional form of the measured $P(\unicode[STIX]{x1D6FF}T)$ in both cells evolves continuously with distinct changes in four different flow regions, namely, the thermal boundary layer, mixing zone, turbulent bulk region and cell centre. By assuming temperature fluctuations in different flow regions are all made from two independent sources, namely, a homogeneous (turbulent) background which obeys Gaussian statistics and non-uniform thermal plumes with an exponential distribution, we obtain the analytic expressions of $P(\unicode[STIX]{x1D6FF}T)$ in four different flow regions, which are found to be in good agreement with the experimental results. Our work thus provides a unique theoretical framework with a common set of parameters to quantitatively describe the effect of turbulent background, thermal plumes and their spatio-temporal intermittency on the temperature PDF $P(\unicode[STIX]{x1D6FF}T)$.

MHD Thin Film Flow and Thermal Analysis of Blood with CNTs Nanofluid

Our main objective in the present work is to elaborate the characteristics of heat transport and magneto-hydrodynamics (MHD) finite film flow of human blood with Carbon Nanotubes (CNTs) nanofluids over a stretchable upright cylinder. Two kinds of CNTs nanoparticles, namely (i) SWCNTs (single walled carbon nanotubes) and (ii) MWCNTs (multi walled carbon nanotubes), are used with human blood as a base liquid. In addition, a uniform magnetic field (B) has been conducted perpendicularly to the motion of nanoliquid. The transformation of the partial differential structure into a non-linear ordinary differential structure is made by using appropriate dimensionless quantities. The controlling approach of the Homotopy analysis method (HAM) has been executed for the result of the velocity and temperature. The thickness of the coating film has been kept variable. The pressure distribution under the variable thickness of the liquid film has been calculated. The impacts of different variables and rate of spray during coating have been graphically plotted. The coefficient of skin friction and Nusselt number have been presented numerically. In addition, it is noticed that the thermal field of a nanoliquid elevates with rising values of ϕ and this increase is more in SWCNTs nanofluid than MWCNTs nanofluid.

Boundary layer fluctuations in turbulent Rayleigh–Bénard convection

We report a combined experimental and numerical study of the effect of boundary layer (BL) fluctuations on the scaling properties of the mean temperature profile$\unicode[STIX]{x1D703}(z)$and temperature variance profile$\unicode[STIX]{x1D702}(z)$in turbulent Rayleigh–Bénard convection in a thin disk cell and an upright cylinder of aspect ratio unity. Two scaling regions are found with increasing distance$z$away from the bottom conducting plate. In the BL region, the measured$\unicode[STIX]{x1D703}(z)$and$\unicode[STIX]{x1D702}(z)$are found to have the scaling forms$\unicode[STIX]{x1D703}(z/\unicode[STIX]{x1D6FF})$and$\unicode[STIX]{x1D702}(z/\unicode[STIX]{x1D6FF})$, respectively, with varying thermal BL thickness$\unicode[STIX]{x1D6FF}$. The functional forms of the measured$\unicode[STIX]{x1D703}(z/\unicode[STIX]{x1D6FF})$and$\unicode[STIX]{x1D702}(z/\unicode[STIX]{x1D6FF})$in the two convection cells agree well with the recently derived BL equations by Shishkinaet al.(Phys. Rev. Lett., vol. 114, 2015, 114302) and by Wanget al.(Phys. Rev. Fluids, vol. 1, 2016, 082301). In the mixing zone outside the BL region, the measured$\unicode[STIX]{x1D703}(z)$remains approximately constant, whereas the measured$\unicode[STIX]{x1D702}(z)$is found to scale with the cell height$H$in the two convection cells and follows a power law,$\unicode[STIX]{x1D702}(z)\sim (z/H)^{\unicode[STIX]{x1D716}}$, with the obtained values of$\unicode[STIX]{x1D716}$being close to$-1$. Based on the experimental and numerical findings, we derive a new equation for$\unicode[STIX]{x1D702}(z)$in the mixing zone, which has a power-law solution in good agreement with the experimental and numerical results. Our work demonstrates that the effect of BL fluctuations can be adequately described by the velocity–temperature correlation functions and the new BL equations capture the essential physics.

Clear-water scour and flow field alteration around an inclined pile

The present experimental study investigates the scour pattern and the near-wake flow field alteration around an emergent rigid cylinder, which is inclined towards the downstream direction. Three different inclination angles were tested separately, namely 14°,30°, and 42° with respect to the wall-normal axis. The induced flow and scour patterns were assessed and compared with the well-known case of the emergent upright cylinder (inclination angle 0°). The experiments were conducted for steady flow conditions in a 26 m long recirculating flume and the flow velocity measurements were conducted with an acoustic Doppler velocimeter. For the clear-water scour experiment, a false bed with a sand-pit was installed within the flume and a laser scanner was utilized to render a detailed representation of the scoured bed. The results show how the scouring gets mitigated with increasing inclination angle. Spatial distribution of time-averaged and fluctuation velocity patterns are presented, which exhibit that the vertical mixing gets significantly enhanced behind the inclined cylinder with increasing inclination angle, while the lateral mixing gets weakened at the upper flow region. An upward flow is seen at the immediate downstream of the inclined pile close to the bed, which becomes stronger with the inclination angle. Energy spectra as well as joint frequency distributions of velocity components were analyzed together with the time series, revealing that the inclination of the pile alters the wake significantly. The results further indicate that with increasing inclination angle the pile becomes more streamlined and the vortex shedding gets suppressed.

Heat transfer enhancement using rectangular vortex promoters in confined quasi-two-dimensional magnetohydrodynamic flows

Heat transfer efficiency from a duct side-wall in which an electrically conducting fluid flows under the influence of a transverse magnetic field is investigated. A quasi-two-dimensional magnetohydrodynamic model is employed to model the flow using high-resolution numerical simulation. The gap height and angle of attack of a rectangular cylinder, with aspect ratio α=1/2 and blockage ratio β=1/4, are independently varied to establish relationships between obstacle configuration and heat transfer efficiency. The heat transfer efficiency is measured through an efficiency index given by the ratio of heat transfer enhancement to pressure drop penalty in comparison to an empty duct case. At gap height ratios 1.15⩽G/Lc<2 for an upright cylinder above a heated lower wall, thermal enhancement and efficiency can be improved; with a peak thermal efficiency of η=1.6 occurring at G/Lc=1.5. Additional increases in thermal efficiency for an obstacle at the duct centre-line (G/Lc=2) can be achieved through inclining the cylinder at γ=-7.5°,γ=-37.5° and 0°<γ⩽22.5°. However, these configurations offered no improvement over simply offsetting an upright cylinder at a gap height ratio of G/Lc=1.5. For a cylinder offset at G/Lc=1.5, varying the incidence angle through -37.5°<γ⩽22.5°,-7.5°⩽γ<0° and 0°<γ⩽15° can lead to additional thermal efficiency benefits; with a global peak efficiency of η=1.7 occurring at γ=-37.5°. The streamwise distribution of the local time-averaged Nusselt number and the effect of Hartmann dampening for 100⩽Ha⩽2000 on heat transfer and flow dynamics are also investigated. A net power balance analysis reveals that in fusion applications the heat transfer enhancement dominates over the pumping power cost to produce net benefits for even modest heat transfer enhancement.

Gas migration regimes and outgassing in particle-rich suspensions

Understanding how gases escape from particle-rich suspensions has important applications in nature and industry. Motivated by applications such as outgassing of crystal-rich magmas, we map gas migration patterns in experiments where we vary (1) particle fractions and liquid viscosity (10 Pa s – 500 Pa s), (2) container shape (horizontal parallel plates and upright cylinders), and (3) methods of bubble generation (single bubble injections, and multiple bubble generation with chemical reactions). We identify two successive changes in gas migration behavior that are determined by the normalized particle fraction (relative to random close packing), and are insensitive to liquid viscosity, bubble growth rate or container shape within the explored ranges. The first occurs at the random loose packing, when gas bubbles begin to deform; the second occurs near the random close packing, and is characterized by gas migration in a fracture-like manner. We suggest that changes in gas migration behavior are caused by dilation of the granular network, which locally resists bubble growth. The resulting bubble deformation increases the likelihood of bubble coalescence, and promotes the development of permeable pathways at low porosities. This behavior may explain the efficient loss of volatiles from viscous slurries such as crystal-rich magmas.

Intensified heat transfer in modulated rotating Rayleigh–Bénard convection

Heat transfer in a Rayleigh-Bénard configuration consisting of a vertical cylinder, which is rotating about its axis, can be intensified considerably when the rotation rate is modulated harmonically in time. Such time-dependent rotation introduces an Euler force into the governing equations which leads to a particular modification of the flow that is shown to support a Nusselt number (Nu) that is considerably higher than in case of constant rotation. We use direct numerical simulation of the incompressible Navier–Stokes equations to perform a comprehensive parameter study of the flow-structuring and associated heat transfer investigating primarily the effect of variations in the frequency with which the rotation rate varies. We consider flow in an upright cylinder of unit aspect ratio which is heated from below and cooled at the top. At sufficiently strong Euler forces the temporal variation of Nu shows a striking dynamics with periods of gradual increase in Nu with more rapid oscillations superimposed, next to rather catastrophic events in which the entire flow-structure that supported high levels of Nu collapses entirely and it returns to a value more similar to that attained at steady rotation. During periods of oscillatory build-up of Nu, high levels of turbulence gradually become more pronounced from the outer cylinder wall inward and a gradually stronger thermal column arises along the centreline of the cylinder. This flow structure can support Nu up to 250% larger than without rotation, a value otherwise achievable only by employing phase transition.

Dynamics of large-scale circulation of turbulent thermal convection in a horizontal cylinder

AbstractA systematic study of the effects of cell geometry on the dynamics of large-scale flows in turbulent thermal convection is carried out in horizontal cylindrical cells of different lengths filled with water. Four different flow modes are identified with increasing aspect ratio$\Gamma $. For small aspect ratios ($\Gamma \leq 0.16$), the flow is highly confined in a thin disc-like cell with a quasi-two-dimensional (quasi-2D) large-scale circulation (LSC) in the circular plane of the cell. For larger aspect ratios ($\Gamma &gt;0.16$), we observe periodic switching of the angular orientation$\theta $of the rotation plane of LSC between the two longest diagonals of the cell. The sides of the container along which the LSC oscillates changes at a critical aspect ratio$\Gamma _{c}\simeq 0.82$. The measured switching period is equal to the LSC turnover time for$\Gamma \leq \Gamma _c$, shows a sharp increase at$\Gamma _{c}$and decays exponentially to the LSC turnover time with increasing$\Gamma $. For$\Gamma \geq 1.3$, a periodic rocking of LSC along the long axis of the cylinder is also observed. The measured probability density function$P(\theta )$of the LSC orientation$\theta $peaks at the two diagonal positions, and its shape is described by a phenomenological model proposed by Brown &amp; Ahlers (Phys. Fluids, vol. 20, 2008b, 075101; J. Fluid Mech., vol. 638, 2009, pp. 383–400). Using this model, we describe the dynamics of the LSC orientation$\theta $by stochastic motion in a double-well potential. The potential is predicted from a model in which the sidewall shape produces an orientation-dependent pressure on the LSC. This model also captures key features of the four flow modes. The experiment reveals an interesting array of rich dynamics of LSC in the horizontal cylinders, which are very different from those observed in the upright cylindrical convection cells. The success of the model for both upright and horizontal cylinders suggests that it can be applied to different geometries.

Getting a grip: different actions and visual guidance of the thumb and finger in precision grasping

We manipulated the visual information available for grasping to examine what is visually guided when subjects get a precision grip on a common class of object (upright cylinders). In Experiment 1, objects (2 sizes) were placed at different eccentricities to vary the relative proximity to the participant's (n=6) body of their thumb and finger contact positions in the final grip orientations, with vision available throughout or only for movement programming. Thumb trajectories were straighter and less variable than finger paths, and the thumb normally made initial contact with the objects at a relatively invariant landing site, but consistent thumb first-contacts were disrupted without visual guidance. Finger deviations were more affected by the object's properties and increased when vision was unavailable after movement onset. In Experiment 2, participants (n=12) grasped 'glow-in-the-dark' objects wearing different luminous gloves in which the whole hand was visible or the thumb or the index finger was selectively occluded. Grip closure times were prolonged and thumb first-contacts disrupted when subjects could not see their thumb, whereas occluding the finger resulted in wider grips at contact because this digit remained distant from the object. Results were together consistent with visual feedback guiding the thumb in the period just prior to contacting the object, with the finger more involved in opening the grip and avoiding collision with the opposite contact surface. As people can overtly fixate only one object contact point at a time, we suggest that selecting one digit for online guidance represents an optimal strategy for initial grip placement. Other grasping tasks, in which the finger appears to be used for this purpose, are discussed.

Experiments on the periodic oscillation of free containers driven by liquid sloshing

AbstractExperiments on the time-periodic liquid sloshing-induced sideways motion of containers are presented. The measurements are compared with finite-depth potential theory developed from standard normal mode representations for rectangular boxes, upright cylinders, wedges and cones of$9{0}^{\ensuremath{\circ} } $apex angles, and cylindrical annuli. It is assumed that the rectilinear horizontal motion of the containers is frictionless. The study focuses on measurements of the horizontal oscillations of these containers arising solely from the liquid waves excited within. While the wedge and cone exhibit only one mode of oscillation, the boxes, cylinders and annuli have an infinite number of modes. For the boxes, cylinders and one of the annuli, we have been able to excite motion and record data for both the first and second modes of oscillation. Frequencies$\omega $were acquired as the average of three experimental determinations for every filling of mass$m$in the dry containers of mass${m}_{0} $. Measurements of the dimensionless frequencies$\omega / {\omega }_{R} $over a range of dimensionless liquid masses$M= m/ {m}_{0} $are found to be in essential agreement with theoretical predictions. The frequencies${\omega }_{R} $used for normalization arise naturally in the mathematical analysis, different for each geometry considered. Free surface waveforms for a box, a cylinder, the wedge and the cone are compared at a fixed value of$M$.

The inertial regime of drop impact on an anisotropic porous substrate

AbstractAxisymmetric droplet impact on a hydrophilic substrate with one pore of relatively large radius is numerically studied using diffuse-interface methods. The flows above the substrate and in the capillary are fully resolved by a Navier–Stokes solver that accounts for contact-angle hysteresis. Upon impact, the infiltration of the drop into the capillary is seen to follow one or more of the three regimes identified in recent experiments (Delbos, Lorenceau &amp; Pitois, J. Colloid Interface Sci., vol. 341, 2010, p. 171): complete penetration, partial penetration as a slug, and re-entry with bubble entrapment. The agreement on experimentally measured quantities, such as transition criteria and slug lengths, is quantitative. On this basis we reveal previously unidentified flow phenomena, investigate flow details that are not accessible experimentally, expand the parameter space considered previously, identify the key asymptotic regimes in the penetration transient, generalize the results in terms of relevant dimensionless groups, and provide a further step (using a multi-capillary arrangement as an idealization of a porous substrate) towards the ultimate purpose of such work, which is the understanding of inertial effects with porous substrates, including eccentric impacts. The significant effect of impact inertia is revealed as a spatial anchoring of a stagnation region, formed and persisting for most of the transient. As a consequence, fluid within an upright cylinder is destined to enter the capillary, and this is in agreement with the hypothesis of Delbos et al. in interpreting the amounts of liquid found inside the capillary, except that the radius of the cylinder is 30 % greater than the capillary radius. The remainder of the liquid spreads laterally on the substrate surface, and the slug regime is a consequence of this partition. Numerical experiments also indicate that after reaching the maximum-spread area, the lamella on the substrate tends to refill the capillary and entrap a bubble, unless contact-angle hysteresis hinders the radially inward motion of the lamella.

Chaos in a soda can: Non-periodic rocking of upright cylinders with sensitive dependence on initial conditions

It has been known for over a hundred years that all physically realizable motions of an ideal axisymmetric cylinder, rolling without slip on its flat circular bottom atop a flat horizontal surface, are periodic in the cylinder’s angular rates and quasi-periodic overall. Here, we show that slight asymmetries in the cylinder, say the addition of an off-center point-mass, result in non-periodic motions with exponentially increasing sensitivity to initial conditions, making the dynamics chaotic.

Potential distributions from electroacoustic polarization sources

Imaging with the ultrasonic vibration potential is based on recording current from a time varying polarization generated by a colloidal or ionic solution irradiated by ultrasound. Here, potential distributions between two parallel grounded electrodes are calculated for colloidal infinite layers, upright cylinders, and spheres. The calculations are valid for any source of externally imposed time varying polarization that gives rise to an oscillating electric displacement vector between the electrodes. The results of the calculations confirm several qualitative characteristics of the frequency dependence of the current reported in imaging experiments.

Spoutable bed height and pressure fluctuation of a novel annular spouted bed with V-shaped deflector

A novel annular spouted bed consisting of two homocentric upright cylinders with different diameters was developed. The nozzles and V-shaped deflectors were located in the bottom of annular space between the inner and outer cylinders. The effects of hold-up, bed material, total flowrate and nozzle structure on the hydrodynamic characteristics of the novel annular spouted bed were investigated. The results show that there exist three different zones for the particle flow in the annular spouted bed: the moving packed zone, the dense-phase spouted fluidizing zone and the dilute-phase zone. With the increase of hold-ups, the height of the dense-phase spouted fluidizing zone tends to increase in the annular spouted bed, while the moving packed zone is only limited within the V-shaped deflectors. The maximum spoutable amount for high air flowrate is larger than that for low air flowrate. Both the spoutable bed height and the local mean relative pressure for high air flowrate are higher than those for low air flowrate at the same hold-ups of particles. The nozzle structure also has important effects on the spoutable bed height and the local relative pressure in the annular spouted bed.

Mixing Characteristics of a Novel Annular Spouted Bed with Several Angled Air Nozzles

A novel spouted bed, namely, an annular spouted bed with several angled angled air nozzles, has been proposed for dryness, catalytic pyrolysis, and gasification of biomass. It consists of two concentric upright cylinders with eight annularly located angled air nozzles between inner and outer cylinders. A rotating cone is adopted as an accessorial feeder. Experiments have been performed to study mixing characteristics of the annular spouted bed. The test materials studied are soybean and black bean. The effect of feeding mode and air velocity as well as static bed height on particle mixing of the spouted bed under various operating conditions was investigated. In addition, the lateral particle motion was studied experimentally and theoretically.

Tilt and translation motion perception during off-vertical axis rotation

The effect of stimulus frequency on tilt and translation motion perception was studied during constant velocity off-vertical axis rotation (OVAR), and compared to the effect of stimulus frequency on eye movements. Fourteen healthy subjects were rotated in darkness about their longitudinal axis 10 degrees and 20 degrees off-vertical at 45 degrees /s (0.125 Hz) and 20 degrees off-vertical at 180 degrees /s (0.5 Hz). Perceived motion was evaluated using verbal reports and a joystick capable of recording tilt and translation in both sagittal and lateral planes. Eye movements were also recorded using videography. At the lower frequency, subjects reported the perception of progressing along the edge of a cone, whereas at the higher frequency they had the sensation of progressing along the edge of an upright cylinder. Tilt perception and ocular torsion significantly increased as the tilt angle increased from 10 degrees to 20 degrees at the lower frequency, and then decreased at the higher frequency. The phase lag of ocular torsion increased as a function of frequency, while the phase lag of tilt perception did not change. Horizontal eye movements were small at the lower frequency and showed a phase lead relative to the linear acceleration stimulus. While the phase lead of horizontal eye movements decreased at 0.5 Hz, the phase of translation perception did not vary with stimulus frequency and was similar to the phase of tilt perception during all conditions. A second data set was obtained in 12 subjects to compare motion perception phase when using a simple push-button to indicate nose-up orientation, continuous setting of pitch tilt alone, or continuous setting of tilt and translation in both pitch and roll planes as in the first data set. This set of measurements indicated that in the frequency range studied subjects tend to lead the stimulus when using a push-button task while lagging the stimulus when using a continuous setting of tilt with a joystick. Both amplitude and phase of tilt perception using the joystick were not different whether concentrating on pitch tilt alone or attempting a more complex reporting of tilt and translation in both sagittal and lateral planes. During dynamic linear stimuli in the absence of canal and visual input, a change in stimulus frequency alone elicits similar changes in the amplitude of both self-motion perception and eye movements. However, in contrast to the eye movements, the phase of both perceived tilt and translation motion is not altered by stimulus frequency over this limited range. These results are consistent with the hypothesis that neural processing to distinguish tilt and translation stimuli differs between eye movements and motion perception.