Dimensionless Kinematic Research Articles

Construct Validity of the Gait Deviation Index for People With Incomplete Spinal Cord Injury (GDI-SCI)

Background The Gait Deviation Index for Spinal Cord Injury (SCI-GDI) was recently proposed as a dimensionless multivariate kinematic measure based on 21 gait features derived from 3-dimensional kinematic data which quantifies gait impairment of adult population with incomplete spinal cord injury (iSCI) relative to the normative gait of a healthy group. Nevertheless, no validity studies of the SCI-GDI have been published to date. Objective To assess the construct validity of the SCI-GDI in adult population following iSCI. Methods. SCI-GDI data were obtained from a sample of 50 healthy volunteers and 35 adults with iSCI. iSCI group was also assessed with the following measures: 10-Meter Walk Test (10MWT) at both self-selected (SS) and maximum speeds, Timed Up and Go Test (TUGT), SS and maximum levels of the Walking Index for Spinal Cord Injury (WISCI) II, mobility items of the Spinal Cord Independence Measure III (SCIM IIIIOMob), Lower Extremity Motor Score (LEMS), and Modified Ashworth Scale (MAS). Spearman’s correlation coefficient was used to investigate the relationship with the SCI-GDI. Results SCI-GDI shows strong correlation with the 10MWT (r ≥ −.716) and good correlation with LEMS (r = .638), TUGT (r = −.582), SS WISCI II levels (r = .521), and SCIM IIIIOMob (r = .501). No significant correlations were found with maximum WISCI II levels and MAS (P > .006). Conclusions Construct validity of the SCI-GDI was demonstrated with the 10MWT, TUGT, LEMS, SCIM IIIIOMob, and SS WISCI II levels for independently walking adults with iSCI. Future work will include assessing the psychometric characteristics with a more heterogeneous sample, also considering the pediatric population.

Parameter Scaling of the Aerodynamic Breakup of the Acoustic Levitated Droplets in an Air Jet Flow

The aerodynamic breakup of the droplet has been intensely studied in this paper. We aim to establish a unified relationship between dimensionless kinematic parameters such as displacement, spreading diameter, Weber number, time, and so on. The breakup characteristics of the acoustic levitated ethanol droplet are experimentally investigated when exposed to an air jet flow. The breakup phenomenons were recorded with a high-speed camera. The breakup characteristics were analyzed, and the physical models of the moving and transforming behaviors were established to explain the breakup mechanisms. We found that the displacement of the windward side of the droplet follows free acceleration rule, with the displacement, acceleration, and time in the dimensionless form. The spreading of the diameter during deformation can also be written in a simple equation as a function of Weber number and displacement. We also discussed more details.

Biomechanical Design and Prototyping of a Powered Ankle-Foot Prosthesis

Powered ankle-foot prostheses for walking often have limitations in the range of motion and in push-off power, if compared to a lower limb of a healthy person. A new design of a powered ankle-foot prosthesis is proposed to obtain a wide range of motion and an adequate power for a push-off step. The design methodology for this prosthesis has three points. In the first one, a dimensionless kinematic model of the lower limb in the sagittal plane is built, through an experimental campaign with healthy subjects, to calculate the angles of lower limb during the gait. In the second point a multibody inverse dynamic model of the lower limb is constructed to calculate the foot-ground contact force, its point of application and the ankle torque too, entering as input data the calculated angles of the lower limb in the previous point. The third point requires, as input of the inverse dynamic model, the first dimensioning data of the ankle-foot prosthesis to obtain the load acting on the components of the prosthesis and the angle torque of the actuator during the gait cycle. Finally, an iteration cycle begins with the inverse dynamic model modifying the ankle torque and angle until these quantities during the gait are as close as possible to the physiological quantities. After the mechanical design and the construction of the prototype of the prosthesis, an experimental methodology was used for preliminary validation of the design. The preliminary tests in the laboratory on the prototype alone show that the range of motion of the ankle angle during the gait is close to a healthy person’s: 27.6° vs. 29°. The pushing force of the distal area of the prototype is 1.000 N, instead of 1.600 N, because a budget reduction forced us to choose components for the prototype with lower performance.

Aerodynamic periodicity of transient aerodynamic forces of flexible plunging airfoils

For flapping micro-air vehicles, periodical aerodynamics in every plunging period is always desired in the design of aircraft controlling system. During the periodic plunges of rigid airfoil, either periodical or non-periodical aerodynamic forces can be generated. Real airfoils are usually flexible so that the effect of flexibility on unsteady characteristics of aerodynamic periodicity should be considered. In this study, a fluid structure interaction analysis is employed to systematically investigate the aerodynamic periodicity of a periodically plunging flexible airfoil. The influences of several dimensionless kinematic and structural parameters on aerodynamic periodicity are investigated. The results show that the aerodynamic periodicity of plunging flexible airfoil qualitatively resembles that of rigid airfoil as the mechanisms contributing to aerodynamic periodicity are kept for airfoil with various flexibilities. However, aerodynamic periodicity at small plunging amplitude and high Reynolds number can be improved as airfoil becomes medium flexible but worsened as airfoil is very flexible. The reason is that the deformation of the airfoil changes the strength and structure of the nearby vortices, thereby leading to weak vortex–vortex and vortex–airfoil interactions. The extent of improvement in aerodynamic periodicity is also found significantly influenced by incoming velocity.

Assessment of dynamic efforts taking into account of inertial and vibrating loads in deaxial pumping units

The choice of rational designs of pumping units for lifting fluid from a well and the modes of their operation is one of the most urgent tasks in oil production. Despite the large amount of theoretical and extreme research, the solution of the problem in this direction cannot be considered complete, given that the dynamic characteristics of the movement of the well product and the kinematics of the well pumping unit are extremely complex. This article discusses the issue of determining the dynamic forces acting at the rod suspension point, in the new constructive solution of a beamless pumping unit depending on the angle of rotation of the crank and dimensionless kinematic parameter characterizing the relationship of the length of the crank to the length of the working part of the rope and the relative eccentric. Analytical dependencies are proposed to determine the maximum load at the rods suspension point depending on inertial and vibration forces.

ИССЛЕДОВАНИЕ ФИЗИЧЕСКИХ ЯВЛЕНИЙ, ПРОИСХОДЯЩИХ В ЗОНЕ КОНТАКТА ЧАСТИЦ СЫПУЧИХ МАТЕРИАЛОВ ПРИ ИХ ДВИЖЕНИИ В ВИНТОВЫХ БАРАБАНАХ, МЕТОДАМИ ТЕОРИИ ПОДОБИЯ, ИНЖЕНЕРНОЙ И КОМПЬЮТЕРНОЙ ГРАФИКИ

In Trubilin State Agricultural University of Kuban there are created machinery working devices as screw drums allowing the assurance of motion of bulk particles at their horizontal location and also promoting the intensity of particles interaction between each other and with the walls of screw drums which widens technological potentialities and decreases dimensions of equipment and its weight. In the paper there are shown various sorts of screw drums and analytical methods of the study of physical phenomena taking place in the contact area of bulk particles. The search of a screw drum design was carried out by the methods of descriptive geometry and engineering graphics with the aid of the “Compass-3D” program complex. The apparatus of dimensionless kinematic functions (similarity invariant) and the analysis of dimensionalities allowing the investigation not one such a case but their infinite number united by the community of properties was used.

Time measurement characterization of stand-to-sit and sit-to-stand transitions by using a smartphone.

The aim of this study is to analyze a common method to measure the acceleration of a daily activity pattern by using a smartphone. In this sense, a numerical approach is proposed to transform the relative acceleration signal, recorded by a triaxial accelerometer, into an acceleration referred to an inertial reference. The integration of this acceleration allows to determine the velocity and position with respect to an inertial reference. Two different kinematic parameters are suggested to characterize the profile of the velocity during the sit-to-stand and stand-to-sit transitions for Parkinson and control subjects. The results show that a dimensionless kinematic parameter, which is linked to the time of sit-to-stand and stand-to-sit transitions, has the potential to differentiate between Parkinson and control subjects.

Search for top squark pair production in compressed-mass-spectrum scenarios in proton–proton collisions at s=8 TeV using the αT variable

An inclusive search is performed for supersymmetry in final states containing jets and an apparent imbalance in transverse momentum, pt[miss], due to the production of unobserved weakly interacting particles in pp collisions at a centre-of-mass energy of 8 TeV. The data, recorded with the CMS detector at the CERN LHC, correspond to an integrated luminosity of 18.5 inverse femtobarns. The dimensionless kinematic variable alpha[T] is used to discriminate between events with genuine pt[miss] associated with unobserved particles and spurious values of pt[miss] arising from jet energy mismeasurements. No excess of event yields above the expected standard model backgrounds is observed. The results are interpreted in terms of constraints on the parameter space of several simplified models of supersymmetry that assume the pair production of top squarks. The search provides sensitivity to a broad range of top squark decay modes, including the two-body decay top squark to c chi0, where c is a charm quark and chi0 is the lightest neutralino, as well as the four-body decay top squark to b f f' chi0, where b is a bottom quark and f and f' are fermions produced in the decay of an intermediate off-shell W boson. These modes dominate in scenarios in which the top squark and lightest neutralino are nearly degenerate in mass. For these modes, top squarks with masses as large as 260 and 230 GeV are excluded, respectively, for the two- and four-body decays.

SELF-DESTRUCTING SPIRAL WAVES: GLOBAL SIMULATIONS OF A SPIRAL-WAVE INSTABILITY IN ACCRETION DISKS

ABSTRACT We present results from a suite of three-dimensional global hydrodynamic simulations that shows that spiral density waves propagating in circumstellar disks are unstable to the growth of a parametric instability that leads to break down of the flow into turbulence. This spiral wave instability (SWI) arises from a resonant interaction between pairs of inertial waves, or inertial-gravity waves, and the background spiral wave. The development of the instability in the linear regime involves the growth of a broad spectrum of inertial modes, with growth rates on the order of the orbital time, and results in a nonlinear saturated state in which turbulent velocity perturbations are of a similar magnitude to those induced by the spiral wave. The turbulence induces angular momentum transport and vertical mixing at a rate that depends locally on the amplitude of the spiral wave (we obtain a stress parameter α ∼ 5 × 10−4 in our reference model). The instability is found to operate in a wide range of disk models, including those with isothermal or adiabatic equations of state, and in viscous disks where the dimensionless kinematic viscosity ν ≤ 10−5. This robustness suggests that the instability will have applications to a broad range of astrophysical disk-related phenomena, including those in close binary systems, planets embedded in protoplanetary disks (including Jupiter in our own solar system) and FU Orionis outburst models. Further work is required to determine the nature of the instability and to evaluate its observational consequences in physically more complete disk models than we have considered in this paper.

A pressure-sensitive kinematic hardening model incorporating Masing’s law

A model is proposed to simulate the stress–strain behavior of sands subjected to cyclic loads in general three-dimensional stress space. A novel formulation is developed using Prager’s kinematic hardening rule and extending the one-dimensional Masing’s rule to general three-dimensional stress space. The hysteretic stress–strain curves are constructed based on skeleton curves. In order to do this, the Masing’s rule is generalized to the proportional rule, which consists of two sets of rules: the internal and external rule. Subsequently, a drag rule is introduced to simulate cyclic stress–strain behavior in which the stress amplitude increases at a decreasing rate during cyclic loading with a constant strain amplitude. The dimensionless kinematic hardening rate is assumed to depend on the current stress value along the stress path. When the direction of loading is reversed, the initial rate of hardening is restored. The rate of variation of hardening is scaled according to an extended Masing’s law. As a result, a closed hysteretic stress–strain loop is obtained during cyclic loading.

Search for supersymmetry in hadronic final states with missing transverse energy using the variables αT and b-quark multiplicity in pp collisions at [Formula: see text

An inclusive search for supersymmetric processes that produce final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of 8 TeV. The data sample corresponds to an integrated luminosity of 11.7 fb−1 collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, α T, is used to discriminate between events with genuine and misreconstructed missing transverse energy. The search is based on an examination of the number of reconstructed jets per event, the scalar sum of transverse energies of these jets, and the number of these jets identified as originating from bottom quarks. No significant excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of simplified models, with a special emphasis on both compressed-spectrum scenarios and direct or gluino-induced production of third-generation squarks. For the case of gluino-mediated squark production, gluino masses up to 950–1125 GeV are excluded depending on the assumed model. For the direct pair-production of squarks, masses up to 450 GeV are excluded for a single light first- or second-generation squark, increasing to 600 GeV for bottom squarks.

Search for supersymmetry in final states with missing transverse energy and 0, 1, 2, or ≥3 b-quark jets in 7 TeV pp collisions using the variable α T

Abstract A search for supersymmetry in final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of $ \sqrt{s}=7 $ TeV. The data sample corresponds to an integrated luminosity of 4.98 fb−1 collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, α T, is used as the main discriminator between events with genuine and misreconstructed missing transverse energy. The search is performed in a signal region that is binned in the scalar sum of the transverse energy of jets and the number of jets identified as originating from a bottom quark. No excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of the constrained minimal supersymmetric extension of the standard model, and also in simplified models, with a special emphasis on compressed spectra and third-generation scenarios.

一类平转耦合并联机构运动学性能的评价方法

The parallel mechanisms having mixed degrees-of-freedom (DoFs) of one translation and two rotations have been used in manufacturing the extra large structural aircraft components with complex geometries. This statement can be demonstrated practically by very successful applications of the Sprint Z3 head to aircraft industry. However, to evaluate the kinematic performance of these parallel mechanisms is a challenging issue because serious problems may occur due to dimensional inconsistencies of the Jacobian matrix. By taking a 3-PRS parallel mechanism as an example, this paper presents an approach to formulate a set of local dimensionless kinematic performance indices on the basis of the overall Jacobian developed by screw theory. The merits of these indices are that they can be represented by the instantaneous virtual power transmission ratios within one limb and amongst limbs, leading to the global ones represented by their mean values and standard deviations throughout the entire workspace. In-depth discussion is made via the example to illustrate the validity of these brand new indices. The outcome may provide with the designers a powerful tool for the kinematic performance evaluation and optimal design of the parallel mechanisms having combined DoFs in terms of translations and rotations.

On the Effects of Rotation on the Passive Scalar and Kinematic Fields of Homogeneous Sheared Turbulence

In this work, the effect of rotation on the evolution of kinematic and passive scalar fields in two dimensional homogeneous sheared turbulence is studied using two different approaches. The first one is analytical and it consists on the resolution of differential linear equations governing the turbulence at high shear when the non linear effects are neglected. The second one is numerical and it consists on the modeling of governing equations using the most known second order models of turbulence and their numerical integration using the fourth order Runge-kutta method. In this second approach, the classic Launder Reece Rodi model, the Speziale Sarkar Gatski and the Shih Lumley models are retained for the pressure-strain correlation, pressure-scalar gradient correlation and for the time evolution equations of the kinematic and scalar dissipations. The evolution of turbulence is studied according to the dimensionless rotation number R which is varied from -0.75 to 0.5. The obtained results are compared to the recent results of the DNS of Brethouwer. Both methods have confirmed the existence of asymptotic equilibrium states for dimensionless kinematic and scalar parameters.

Storm-Water Predictions by Dimensionless Unit Hydrograph

This paper presents a theoretical derivation of a dimensionless unit hydrograph using the kinematic wave approach. The dimensionless kinematic wave unit hydrograph (KWUH) is normalized by the parameters associated with the equilibrium condition and can be generated according to the selected rainfall duration. For comparison, a KWUH whose rainfall duration is equal to the time of equilibrium produces good agreement with the Soil Conservation Service dimensionless unit graph (SCSUH). Both the KWUH and SCSUH are kinematic in nature and have a 37.5% runoff volume that occurred before the time to peak. To verify the applicability of the KWUH derived in this study, a set of hypothetical rectangular watersheds ranging from 20 to 200 acres was investigated. The predicted 100-year peak flow rates from these five hypothetical rectangular watersheds are compared with the SCSUH method and the Colorado Unit Hydrograph Procedures (CUHP). In general, the KWUH produces good agreement with the CUHP when the catchment has an area between 60 and 120 acres. Based on the study of hypothetical rectangular watersheds, it is recommended that the KWUH be applicable to urban catchments with a drainage area of up to 120 acres.

DIMENSIONLESS ANALYSIS OF HUMAN LOWER LIMB

This study derives a dimensionless kinematic model using a coordinate transformation matrix to analyze the kinematic characteristics of human lower limb. The lower limb model in this study considers three segments including the thigh, shank and foot, and three joints, namely the hip, knee, ankle and the two extremes of the foot, namely the heel and toe. Based on the dimensionless analysis model ignoring human stature, the kinematic characteristics of lower limb can be described by the relationships of the dimensionless displacements, velocities and accelerations with respect to dimensionless time. The results of an experimental data have shown that dimensionless kinematic characteristics follow the same trends as current gait analysis. This study proposed a dimensionless kinematic model that is capable of analyzing kinematic characteristics of lower limb joints. In the future, this model is anticipated to investigate the dynamics of gait and clinical application.

Liquid−Solid Mass Transfer at a Fixed Bed of Lessing Rings, in Relation to Electrochemical Reactor Design

The mass-transfer behavior of a fixed bed of Lessing rings, under single- and two-phase flow, was studied by measuring the limiting current of the cathodic reduction of the ferricyanide ion. Variables studied included ring diameter (d), solution flow rate, gas flow rate, physical properties of the solution, and the effect of drag-reducing polymers. The single-phase mass-transfer data were correlated for the conditions of 1390 < Sc < 4763 (where Sc is the Schmidt number, which represents a dimensionless kinematic viscosity/molecular diffusivity coefficient), 166 < Re < 722 (where Re is the solution Reynolds number, which represents a dimensionless flow parameter), and 1 cm < d < 1.4 cm by the equation Sh = 1.57Sc0.33Re0.46 (where Sh is the Sherwood number, which represents a dimensionless mass-transfer coefficient). The two-phase mass-transfer data were correlated for the conditions 1390 < Sc < 4763, 144 < Re < 748, 60 < Reg < 818 (where Reg is the gas Reynolds number), and 1 cm < d < 1.4 cm by the equation Sh = 1.93Sc0.33Re0.34Reg0.11. Polyox WSR-301 drag-reducing polymer was found to reduce the rate of mass transfer by an amount of 17.2%−32.7% for single-phase flow; for two-phase flow, the decrease in the rate of mass transfer was 27%−34%. Implication of the present results for the design and operation of electrochemical reactorsespecially those involving gas absorptionwas noted.

Kinematic Pile Response to Vertical P-wave Seismic Excitation

An analytical solution based on a rod-on-dynamic-Winkler-foundation model is developed for the response of piles in a soil layer subjected to vertical seismic excitation consisting of harmonic compressional waves. Closed-form solutions are derived for: (1) the motion of the pile head; (2) the peak normal strain in the pile, and (3) the group effect between neighboring piles. The solutions are expressed in terms of a dimensionless kinematic response factor Iv, relating pile-head motion and free-field soil surface motion, a dimensionless strain transmissibility factor Ie, relating pile and soil peak normal strains, and a pile-to-pile interaction factor α measuring group effects. It is shown that a pile foundation may significantly reduce the vertical seismic excitation transmitted to the base of a structure.

A mathematical modeling of rotating waves in axial and radial compressors

A comparison between meteorological systems and fluid motions through compressors is proposed. A mathematical analysis analogous to the geophysical one emphasizes characteristic dimensions. A dimensionless kinematic parameter, akin to the Rossby number, emerges, and thus leads to the study of different cases. Two kinds of solutions of rotating waves are presented here. The first describes a Rossby wave propagation in compressors, and the second depicts a limit form of part-span stall.

Collisional viscosity of FCC particles in a CFB

AbstractParticle velocity distributions were measured for a flow of 75‐μm FCC particles in a CFB using a new video‐digital camera technique. From the spread of particle histograms, a random oscillating particle velocity was determined. This random velocity was used to compute the powder viscosity with the help of dense‐phase kinetic theory of granular flow. There was excellent agreement between this kinetic‐theory measurement and previous macroscopic viscosity measurements. The dimensionless group kinematic viscosity divided by the oscillating velocity and particle diameter correlated all available data as a function of particle volume fraction.