Tangential Velocity Profiles Research Articles

Upper limb kinematics after arthroscopic and open shoulder stabilization

Shoulder joint stability mediated by proprioception is often quantified by arm repositioning tests (i.e., static end-position accuracy), overlooking ongoing movement quality. This study assessed movement quality by adopting smoothness-related kinematic descriptors. We compared performance of healthy controls with that of patients in arthroscopic shoulder stabilization and open shoulder stabilization groups. We hypothesized that arm kinematics after arthroscopic intervention would more closely resemble healthy movements compared with patients after open shoulder stabilization surgery. Healthy controls (N = 14) were compared with patients after arthroscopic shoulder stabilization (N = 10) and open shoulder stabilization (N = 12). Right-hand dominant subjects (the affected side in patients) performed 135 unconstrained 3-dimensional pointing movements toward visual targets (seen through pinhole goggles; i.e., no arm vision). Arm kinematic data were recorded and offline analyzed to obtain hand tangential velocity profiles further used to compute the acceleration-to-movement time ratio, peak-to-mean velocity ratio, and number of velocity peaks ("symmetry," "proportion," and "fragmentation" features, respectively). Parametric and nonparametric statistics were used for comparisons (P ≤ .05). Control and arthroscopic shoulder stabilization groups presented similar acceleration-to-movement time ratio and peak-to-mean velocity ratio. Both groups differed from the open shoulder stabilization group (P = .001). Distributions of velocity peaks for control and arthroscopic shoulder stabilization groups were similar, whereas open shoulder stabilization and control subjects differed significantly (P = .028). Movement quality mediated by proprioception in arthroscopic shoulder stabilization patients matches that of healthy controls, whereas performance in open shoulder stabilization patients seems inferior compared with that in healthy controls, as assessed by smoothness-related measures (less symmetrical, more fragmented movements).

Temperature, velocity and air entrainment of fire whirl plume: A comprehensive experimental investigation

Comprehensive measurements were performed to examine the temperature, velocity (in axial and tangential directions) and air entrainment of propane fire whirl plume in a medium-scale fixed-frame facility. It is found that the radial profile of excess temperature varies consistently with the continuous flame shape and the radial decay rate of excess temperature decreases in the intermittent flame and plume. The centerline axial velocity depends on both the buoyancy and the axial pressure gradient related to the tangential velocity. A weak annular reverse flow is found outside the upward core at z/D⩽1.0, while the absolute axial velocity slightly increases with fire size. The growth of axial velocity core is found to be constrained by the reverse flow. The mean axial velocity radius is confirmed to be greater than the mean excess temperature radius in the continuous flame. The radial profile of tangential velocity varies steadily with height, and is little affected by heat release rate. The radial swirl flow consists of the vortex core, the quasi-free vortex and the near wall region, and the active reaction occurs in the vortex core. The plume growth rate increases with decreasing RiB (Richardson number) and three distinct regions are identified in different RiB ranges. The air entrainment is strong at the bottom inflow boundary layer, while the mass flow rate increases slowly with height as compared to buoyant pool fires. The suppression of air entrainment may be attributable to the radial force balance and stable stratification in the centrifugal acceleration filed. The entrainment coefficient in the continuous flame is about one to two orders of magnitude lower than that in a buoyant pool fire, and it generally increases with height in the plume of fire whirl, approaching the value for pure buoyant plume. The mean entrainment coefficient depends on the mean RiB by −1 power law for z⩽Hf.

AIR STREAM VELOCITY MODELLING IN MULTICHANNEL SPIRAL CYCLONE SEPARATOR

Numerical modelling problem is investigated in a gas aerodynamics multichannel spiral cyclone separator with a tangential inflow. Experimental and theoretical papers analysing cyclone separator with particularly complex turbulent flow were reviewed. The three-dimensional transport differential equations for incompressible laminar and turbulent flow inside the cyclone separator were presented. They were numerically solved by finite volume method using the Re-Normalisation Group (hereinafter RNG) k-ε turbulence model. The numerical air flow movement was modelled in cyclone separator with the following dimensions: 0.95 m height, 0.330 m diameter, 0.88 m height of spiral-cylindrical part, 0.39 m height of conical part, inflow dimensions (on the side of cylindrical part) according to the drawings were a × b = 28 × 95 mm. The mathematical model of air flow movement in cyclone separator was composed by Navier-Stokes (Reynolds) as the three-dimensional differential equation system. The modelling results were obtained by the tangential and axial velocity profiles in cyclone separator using RNG k-ε turbulence model, the inflow velocity from 4.1 m/s to 15.4 m/s coincided well with the experimental results. This is the first article testing for multichannel cyclone and determined distributions of aerodynamic parameters. The absolute error between experimental and modelling results changed from 0.01 to 0.24 units.

Turbulent swirling flow in a dynamic model of a uniflow-scavenged two-stroke engine

It is desirable to use computational fluid dynamics for optimization of the in-cylinder processes in low-speed two-stroke uniflow-scavenged marine diesel engines. However, the complex nature of the turbulent swirling in-cylinder flow necessitates experimental data for validation of the used turbulence models. In the present work, the flow in a dynamic scale model of a uniflow-scavenged cylinder is investigated experimentally. The model has a transparent cylinder and a moving piston driven by a linear motor. The flow is investigated using phase-locked stereoscopic particle image velocimetry (PIV) and time-resolved laser Doppler anemometry (LDA). Radial profiles of the phase-locked mean and rms velocities are computed from the velocity fields recorded with PIV, and the accuracy of the obtained profiles is demonstrated by comparison with reference LDA measurements. Measurements are carried out at five axial positions for 15 different times during the engine cycle and show the temporal and spatial development of the swirling in-cylinder flow. The tangential velocity profiles in the bottom of the cylinder near the end of the scavenge process are characterized by a concentrated swirl resulting in wake-like axial velocity profiles and the occurrence of a vortex breakdown. After scavenge port closing, the axial velocity profiles indicate that large transient swirl-induced structures exist in the cylinder. Comparison with profiles obtained under steady-flow conditions shows that the scavenge flow cannot be assumed to be quasi-steady. The temporal development of the swirl strength is investigated by computing the angular momentum. The swirl strength shows an exponential decay from scavenge port closing to scavenge port opening corresponding to a reduction of 34 %, which is in good agreement with theoretical predictions.

Dark matter density profile and galactic metric in Eddington-inspired Born–Infeld gravity

We consider the density profile of pressureless dark matter in Eddington-inspired Born–Infeld (EiBI) gravity. The gravitational field equations are investigated for a spherically symmetric dark matter galactic halo, by adopting a phenomenological tangential velocity profile for test particles moving in stable circular orbits around the galactic center. The density profile and the mass distribution, as well as the general form of the metric tensor is obtained by numerically integrating the gravitational field equations, and in an approximate analytical form by using the Newtonian limit of the theory. In the weak field limit, the dark matter density distribution is described by the Lane–Emden equation with polytropic index n = 1, and is nonsingular at the galactic center. The parameter κ of the theory is determined so that the theory could provide a realistic description of the dark matter halos. The gravitational properties of the dark matter halos are also briefly discussed in the Newtonian approximation.

Linear stability of the Moore-Saffman model for a trailing wingtip vortex

This paper presents an investigation of the stability of a trailing vortex using mean flow profiles given by an approximate solution of the Navier-Stokes equations. The axial and tangential velocity profiles obtained from this solution, deduced by Moore and Saffman [“Axial flow in laminar trailing vortices,” Proc. R. Soc. London, Ser. A 333, 491–508 (1973)], agree well with experiments involving wings at slight angles of attack. In particular, the Moore-Saffman profiles better describe the jet-like and wake-like axial flows near the center of the vortex than does the much-studied Batchelor vortex. We determine solutions numerically for these profiles and find that they are well suited to describe the flow at short and intermediate distances behind the wingtip. Growth rates for unstable perturbations are presented for different values of n, the wingtip loading parameter. These growth rates are shown to be somewhat larger than those obtained for the Batchelor vortex, and instability persists for larger values of the swirl. The largest amplification rates were found to occur near n = 0.5, the value corresponding to elliptic loading. This is within the range 0.44 < n < 1.0, where the core axial flow is wake-like. For n < 0.44, the flow in the vortex core is jet-like and the growth rates of unstable perturbations become progressively smaller, with all modes damped for n ≈ 0.25.

A Parametric Wind–Pressure Relationship for Rankine versus Non-Rankine Cyclostrophic Vortices

AbstractA parametric tangential wind profile model is presented for depicting representative pressure deficit profiles corresponding to varying tangential wind profiles of a cyclostrophic, axisymmetric vortex. The model employs five key parameters per wind profile: tangential velocity maximum, radius of the maximum, and three shape parameters that control different portions of the profile. The model coupled with the cyclostrophic balance assumption offers a diagnostic tool for estimating and examining a radial profile of pressure deficit deduced from a theoretical superimposing tangential wind profile in the vortex. Analytical results show that the shape parameters for a given tangential wind maximum of a non-Rankine vortex have an important modulating influence on the behavior of realistic tangential wind and corresponding pressure deficit profiles. The first parameter designed for changing the wind profile from sharply to broadly peaked produces the corresponding central pressure fall. An increase in the second (third) parameter yields the pressure rise by lowering the inner (outer) wind profile inside (outside) the radius of the maximum. Compared to the Rankine vortex, the parametrically constructed non-Rankine vortices have a larger central pressure deficit. It is suggested that the parametric model of non-Rankine vortex tangential winds has good potential for diagnosing the pressure features arising in dust devils, waterspouts, tornadoes, tornado cyclones, and mesocyclones. Finally, presented are two examples in which the parametric model is fitted to a tangential velocity profile, one derived from an idealized numerical simulation and the other derived from high-resolution Doppler radar data collected in a real tornado.

MATHEMATICAL MODEL OF THE MULTI-CHANNEL SPIRAL CYCLONE / DAUGIAKANALIO SPIRALINIO CIKLONO ORO GREIČIŲ TYRIMAS

The article deals with a problem of experimental investigation and numerical simulation of gas aerodynamics of a multi-channel spiral cyclone with a tangential inlet. The paper presents an overview of experimental and theoretical works on the cyclones having a particularly complex turbulent flow and focuses on three-dimensional transport differential equations for a non-compressible laminar and turbulent flow inside the cyclone. The equations have been solved applying the numerical finite volume method using the RNG (Re–Normalisation Group) k-ε turbulence model. The numerical simulation of the flow cyclone has been carried out. The height of the cyclone is 0.80 m with 0.33 m in diameter, the height of the spiral–cylindrical part – 0.098 meters and that of the cone – 0.45 m. Inlet dimensions (cylindrical part on the side), in accordance with drawings makes a×b = 28×95 mm. The mathematical model for the air traffic movement cyclone has accounted for Navier-Stokes (Reynolds) three-dimensional differential equations. The simulation results have been obtained with reference to the cyclone of tangential velocity profiles using RNG k-ε turbulence model. The inlet velocity of 5.1 m/s slightly differs from experimental results, thus making an error of 7%. Article in Lithuanian. Santrauka Nagrinėjama dujų aerodinamikos daugiakanaliame spiraliniame ciklone eksperimentinio tyrimo ir skaitinio modeliavimo problema. Apžvelgti eksperimentiniai ir teoriniai ciklonų, kuriuose susidaro ypač sudėtingas sūkurinis srautas, tyrimai. Pateiktos nespūdžiojo laminarinio ir turbulentinio srauto tekėjimo ciklono viduje diferencialinės trimatės pernašos lygtys. Jos skaitiškai spręstos baigtinių tūrių metodu taikant RNG (Re – Normalisation Group) k–ε turbulencijos modelį. Atliktas skaitinis oro srauto judėjimo ciklone modeliavimas. Ciklono aukštis 0,80 m, skersmuo 0,33 m, spiralinės-cilindrinės dalies aukštis 0,098 m, kūginės – 0,45 m, įtekėjimo angos matmenys (cilindrinės dalies šone) pagal brėžinius yra a×b = 28×95 mm. Oro srauto judėjimo ciklone matematinį modelį sudaro Navjė ir Stokso (Reinoldso) trimačių diferencialinių lygčių sistema. Modeliavimo rezultatai, t. y. taikant RNG k–ε turbulencijos modelį (įtekėjimo greitis 5,1 m/s) gauti tangentinio greičio ciklone kitimo duomenys, nežymiai (su 7 % paklaida) skyrėsi nuo eksperimentinių rezultatų.

Turbulent Couette–Taylor flows with endwall effects: A numerical benchmark

The accurate prediction of fluid flow within rotating systems has a primary role for the reliability and performance of rotating machineries. The selection of a suitable model to account for the effects of turbulence on such complex flows remains an open issue in the literature. This paper reports a numerical benchmark of different approaches available within commercial CFD solvers together with results obtained by means of in-house developed or open-source available research codes exploiting a suitable Reynolds Stress Model (RSM) closure, Large Eddy Simulation (LES) and a direct numerical simulation (DNS). The predictions are compared to the experimental data of Burin et al. (2010) in an original enclosed Couette–Taylor apparatus with endcap rings. The results are discussed in details for both the mean and turbulent fields. A particular attention has been turned to the scaling of the turbulent angular momentum G with the Reynolds number Re. By DNS, G is found to be proportional to Reα, the exponent α=1.9 being constant in our case for the whole range of Reynolds numbers. Most of the approaches predict quite well the good trends apart from the k–ω SST model, which provides relatively poor agreement with the experiments even for the mean tangential velocity profile. Among the RANS models, even though no approach appears to be fully satisfactory, the RSM closure offers the best overall agreement.

Minimum power consumption for drag reduction on a circular cylinder by tangential surface motion

AbstractWe investigate the effect of a prescribed tangential velocity on the drag force on a circular cylinder in a spanwise uniform cross flow. Using a combination of theoretical and numerical techniques we make an attempt at determining the optimal tangential velocity profiles which will reduce the drag force acting on the cylindrical body while minimizing the net power consumption characterized through a non-dimensional power loss coefficient (${C}_{\mathit{PL}} $). A striking conclusion of our analysis is that the tangential velocity associated with the potential flow, which completely suppresses the drag force, is not optimal for both small and large, but finite Reynolds number. When inertial effects are negligible ($\mathit{Re}\ll 1$), theoretical analysis based on two-dimensional Oseen equations gives us the optimal tangential velocity profile which leads to energetically efficient drag reduction. Furthermore, in the limit of zero Reynolds number ($\mathit{Re}\ensuremath{\rightarrow} 0$), minimum power loss is achieved for a tangential velocity profile corresponding to a shear-free perfect slip boundary. At finite $\mathit{Re}$, results from numerical simulations indicate that perfect slip is not optimum and a further reduction in drag can be achieved for reduced power consumption. A gradual increase in the strength of a tangential velocity which involves only the first reflectionally symmetric mode leads to a monotonic reduction in drag and eventual thrust production. Simulations reveal the existence of an optimal strength for which the power consumption attains a minima. At a Reynolds number of 100, minimum value of the power loss coefficient (${C}_{\mathit{PL}} = 0. 37$) is obtained when the maximum in tangential surface velocity is about one and a half times the free stream uniform velocity corresponding to a percentage drag reduction of approximately 77 %; ${C}_{\mathit{PL}} = 0. 42$ and $0. 50$ for perfect slip and potential flow cases, respectively. Our results suggest that potential flow tangential velocity enables energetically efficient propulsion at all Reynolds numbers but optimal drag reduction only for $\mathit{Re}\ensuremath{\rightarrow} \infty $. The two-dimensional strategy of reducing drag while minimizing net power consumption is shown to be effective in three dimensions via numerical simulation of flow past an infinite circular cylinder at a Reynolds number of 300. Finally a strategy of reducing drag, suitable for practical implementation and amenable to experimental testing, through piecewise constant tangential velocities distributed along the cylinder periphery is proposed and analysed.

Effect of Viscosity on the Separation Ability of a Hydrocyclone

On bases of numerical simulation and theoretical analysis, two cases of media, water and slurry (a kind of pseudoplastic power-law fluids), were used in the same hydrocyclone under the same operating condition. The Compare results show that the effect of the medium viscosity on the radial-velocity profile is slight; on the other hand, the effect of the media viscosity on the tangential-velocity profiles is important. The increase of the media viscosity produces not only the increase of the viscous resistance but also the steep reducing of the peak value of tangential-velocity profiles, which means that the inward viscous force loading upon the particles are enforced, on the other hand , the outward centrifugal force loading on the particles reduces greatly. The increase of the media viscosity leads to the great decrease of the separation ability of a hydrocyclone.

Considerations on the Numerical Modeling and Performance of Axial Swirlers Under Relight Conditions

Numerical modeling of aero engine combustors under relight conditions is a matter of continuously increasing importance due to the demanding engine certification regulations. In order to reduce the complexity and the cost of the numerical modeling, common practice is to replace the atomizer’s swirlers with velocity profiles boundary conditions, very often scaled down from nominal operating conditions assuming similarity of the swirler flowfield. The current numerical study focuses on the flowfield characteristics of an axially swirled atomizer operating within a windmilling engine environment. The scalability of the velocity profile from higher power settings is examined. Observations on the performance of the axial swirler under relight conditions are also made. Experimental data was used as a validation platform for the numerical solver, after a grid sensitivity study and a turbulence model selection process. Boundary conditions for simulating the windmilling environment were extracted from experimental work. The swirler axial and tangential velocity profiles were normalized using the swirler inlet velocity. Results showed that both profiles are only scalable for windmilling conditions of high flight Mach number (≥ 0.5). At low flight Mach numbers, the actual profile had a lower velocity than that predicted through scaling. The swirl number was found to deteriorate significantly with the flight velocity following a linear trend, reducing significantly the expected flame quality. As a consequence the burner is forced to operate at the edge of its stability loop with low certainty regarding its successful relight.

PIV study of the effect of piston position on the in-cylinder swirling flow during the scavenging process in large two-stroke marine diesel engines

A simplified model of a low speed large two-stroke marine diesel engine cylinder is developed. The effect of piston position on the in-cylinder swirling flow during the scavenging process is studied using the stereoscopic particle image velocimetry technique. The measurements are conducted at different cross-sectional planes along the cylinder length and at piston positions covering the air intake port by 0, 25, 50 and 75 %. When the intake port is fully open, the tangential velocity profile is similar to a Burgers vortex, whereas the axial velocity has a wake-like profile. Due to internal wall friction, the swirl decays downstream, and the size of the vortex core increases. For increasing port closures, the tangential velocity profile changes from a Burgers vortex to a forced vortex, and the axial velocity changes correspondingly from a wake-like profile to a jet-like profile. For piston position with 75 % intake port closure, the jet-like axial velocity profile at a cross-sectional plane close to the intake port changes back to a wake-like profile at the adjacent downstream cross-sectional plane. This is characteristic of a vortex breakdown. The non-dimensional velocity profiles show no significant variation with the variation in Reynolds number.

Molecular dynamics study of slip behaviors: Role of a soft attractive tail

The role of soft attractive tails in nano-scale cylindrical Couette flows is investigated by using molecular dynamics computer simulations. The cylindrical Couette flow is generated by rotating an inner wall with a fixed outer wall. By varying the cutoff distance of the Lennard-Jones potential, we can easily control the inclusion or exclusion of an attractive component. We found that the number density and the tangential velocity profiles along the radial direction show rather strikingly different behaviors that can be classified into four distinctive flow types of slip behaviors due to the soft attractive tail.

Helical Flow of Non-Newtonian Fluids in a Concentric and Fully Eccentric Annulus

The laminar and turbulent helical flows of non-Newtonian fluids in concentric and fully eccentric annuli with a rotating inner pipe are numerically simulated using computational fluid dynamics. Pipe rotation speeds are varied from 0 to 400 rpm at different annular flow velocities (0.005–10.05 ft/s). The predicted frictional pressure losses are validated using experimental data obtained from the literature. Then, the effects of pipe rotation on frictional pressure loss and tangential velocity and velocity profile of non-Newtonian fluids in both concentric and fully eccentric annuli are analyzed in detail. It can be observed that as the pipe rotation increases, frictional pressure losses inside the concentric annulus drastically decrease for laminar flow, especially at a low axial Reynolds number. Moreover, pipe rotation effects on pressure loss in concentric annuli for turbulent flow are negligible. Flow regime directly influences change in the pressure gradient due to pipe rotation for the concentric annulus. Pipe rotation increases pressure loss for both the laminar and turbulent regime for fully eccentric annuli. Turbulence significantly raises the pressure gradient for the fully eccentric annulus. Rotating pipe causes a considerable increase in tangential velocity of non-Newtonian fluid inside concentric and fully eccentric annuli. Additionally, eccentricity and turbulent flow exaggerate pipe rotation effects on tangential velocity.

Laminar flow in the gap between two rotating parallel frictional plates in hydro-viscous drive

The velocity, pressure and temperature distributions of the flow in the gap between hydro-viscous drive friction disks are the key parameters in the design of hydro-viscous drive and angular velocity controller. In the previous works dealing with the flow in the gap between disks in hydro-viscous drive, few authors considered the effect of Coriolis force on the flow. The object of this work is to investigate the flow with consideration of the effects of centrifugal force, Coriolis force and variable viscosity. A simplified mathematical model based on steady and laminar flow is presented. An approximate solution to the simplified mathematical model is obtained by using the iteration method assuming that the fluid viscosity remains constant. Then the model considering the effect of variable viscosity is solved by means of computational fluid dynamics code FLUENT. Numerical results of the flow are obtained. It is found that radial velocity profile diverges from the ideal parabolic curve due to inertial forces and tangential velocity profile is nonlinear due to Coriolis force, and pressure has two possible solution branches. In addition, it is found that variable viscosity plays an important role on pressure profiles which are significantly different from those of fluid with constant viscosity. The experimental device designed for this work consists of two disks, and one of them is fixed. Experimental pressure and temperature of the flow within test rig are obtained. It is shown that the trend of numerical results is in agreement with that of experimental ones. The research provides a theoretical foundation for hydro-viscous drive design.

Power draw of the rotor during centrifugal high volume separation of oil and water

Centrifugal separation of oil and water from streams that is concentrated with oil such as the ones from the oil spill disasters is investigated in this study. The existing theories are largely for Stokes settling of oil drops. In this study, two layers, one rich in oil and another rich in water are allowed to spin in a centrifuge. The tangential velocity profile is derived from the equations of continuity and motion. The power drawn at the inner rotor is calculated for a set of parameters for the system and an angular speed w RPM (revolutions per minute). Each simulation required the solution of four simultaneous equations and simultaneous unknowns. The power draw was found to be linear with angular rotor speed on a log-log plot. The viscosity of the oil was increased five times to study the effect on the power draw. An expression of the interlayer thickness ratio (a) was obtained by use of a component mass balance on oil streams that flow in and out of the continuous centrifuge. Key words: Centrifugal separation, polar coordinates, equation of motion, layered flow, matrix inversion, computer simulations, power draw, revolutions per minute (RPM).

Cold experimental investigations into gas/particle flow characteristics of a low-NO x axial swirl burner in a 600-MWe wall-fired pulverized-coal utility boiler

With the use of a three-dimensional particle-dynamics anemometer in conjunction with a gas/particle two-phase test facility, we measured the flow characteristics in the near-burner region of a low-NO x axial swirl burner (LNASB). Mean velocities, root mean square (RMS) velocities and particle volume flux profiles were obtained. The data shows that the central recirculation zone exists only in the region x/ d = 0.1–0.3 between r/d = 0.25–0.4. The central recirculation zone has maximum size at cross-section x/ d = 0.1 located between the primary and secondary air flow zones. Moreover, with a maximum recirculating velocity of 4 m/s, the recirculation zone has a high particle volume flux that can easily result in the slagging and deformation in the burner nozzle. Oxygen concentrations are also high in this zone which can easily lead to NO x formation. In the region x/ d = 0.1–0.5, the primary and secondary air flow zones exhibit two peaks in both axial and radial velocity profiles while a single peak appears in the tangential velocity profiles in the secondary air flow zone.

Simulated Tornadic Vortex Signatures of Tornado-Like Vortices Having One- and Two-Celled Structures

AbstractA tornadic vortex signature (TVS) is a degraded Doppler velocity signature that occurs when the tangential velocity core region of a tornado is smaller than the effective beamwidth of a sampling Doppler radar. Early Doppler radar simulations, which used a uniform reflectivity distribution across an idealized Rankine vortex, showed that the extreme Doppler velocity peaks of a TVS profile are separated by approximately one beamwidth. The simulations also indicated that neither the size nor the strength of the tornado is recoverable from a TVS. The current study was undertaken to investigate how the TVS might change if vortices having more realistic tangential velocity profiles were considered. The one-celled (axial updraft only) Burgers–Rott vortex model and the two-celled (annular updraft with axial downdraft) Sullivan vortex model were selected. Results of the simulations show that the TVS peaks still are separated by approximately one beamwidth—signifying that the TVS not only is unaffected by the size or strength of a tornado but also is unaffected by whether the tornado structure consists of one or two cells.

Smoothness of chewing jaw movements in adults with mandibular prognathism

Indices such as smoothness, movement time, peak velocity, and symmetry of the velocity profile have been shown to be effective in explaining the degree of skilfulness of human saccadic eye, limb, and jaw motions. We investigated whether adult subjects with mandibular prognathism show impaired smoothness of the masticatory jaw movements. Forty-nine adults with skeletal Class III malocclusions and 52 healthy adults with acceptably good occlusions were selected respectively as Test and Control subjects. Subjects of the Test Group were subdivided into two groups: Class III(closed) showed full occlusal contact between the upper and lower teeth at the habitual intercuspal position, whereas Class III(open) showed inability of occlusal contact between the upper and lower anterior teeth. Each subject was asked to chew a piece of chewing gum. The normalised jerk-cost (NJC), movement duration, and tangential velocity profile during jaw-closing movements were compared between groups. Test Groups showed greater NJC (P < 0·01) with longer movement duration (P < 0·01) and lower peak velocity (P < 0·01) than the Control Group did. Class III(closed) showed greater NJC (P < 0·01) with longer movement duration (P < 0·01) and lower peak velocity (P < 0·01) than Class III(open) did. Results show that the mandibular movements made by the Test Groups exhibit lower skilfulness than those made by the Control Group. The jaw movement skilfulness of the prognathic patients decreases most drastically with existence of malocclusal contact between upper and lower anterior teeth.