Unequal Diameters Research Articles

Design of test track for accurate calibration of two wheel differential mobile robots

Odometry using incremental wheel encoder sensors provides the relative position of a mobile robot. The major drawback of odometry is the accumulation of kinematic modeling errors when travel distance increases. The major systematic error sources are unequal wheel diameters and erroneous wheelbase. The UMBmark test is a practical and useful calibration scheme for systematic odometry errors of two wheel differential mobile robots. We previously proposed an accurate calibration scheme that extends the conventional UMBmark. A calibration experiment was carried out using the robot’s heading errors, and kinematic parameters were derived by considering the coupled effect of the systematic errors on a test track. In this paper, we propose design guidelines of test tracks for odometry calibration. As non-systematic errors constitute a grave problem in practical applications, the test track shape and size should be determined by considering the distributions of systematic and non-systematic errors. Numerical simulations and experiments clearly demonstrate that the proposed scheme results in more accurate calibration results.

Thermodynamic properties of aqueous solutions of single and multiple salts using the Q-electrolattice equation of state

Thermodynamic property calculations of solutions containing electrolytes are relevant to design and optimize industrial process, among which water desalination. The conventional way of designing such processes relies on specific models or correlations for vapor pressure, density, osmotic coefficient, and mean ionic activity coefficient. Nonetheless, an equation of state (EOS) for electrolyte solutions enables, in principle, the evaluation of all of them. In previous work, the electrolattice EOS was presented, being composed by three terms: the Mattedi–Tavares–Castier (MTC) lattice-based contribution, the Born contribution, and an explicit mean spherical approximation (MSA) for ions of equal diameters. In the present work, an explicit MSA term suitable for ions of unequal diameters is used instead, along with new water parameters and two adjustable parameters per ion. The new expression for the Helmholtz energy, referred to as Q-electrolattice model, is used to correlate mean ionic activity coefficients and densities in strong 78 single-salt aqueous solutions. Additionally, calculations of vapor pressure, osmotic coefficient, and apparent molar volume of salt are performed. Predictions of thermodynamic properties for aqueous solutions containing multiple salts and seawater are also presented without using any additional adjustable parameter.

Oscillatory flow about a cylinder pair with unequal radii

We consider the oscillating flow about a pair of circular cylinders of unequal diameter. In addition to the relative size of the cylinders, the distance between them can be varied, as can the angle that the undisturbed oscillatory flow makes with the line joining the cylinder centres. For small-amplitude vibrations a time-independent, or steady streaming, motion develops that persists beyond the Stokes layer that forms at the solid boundary. This persistent streaming is considered for large values of a suitably defined streaming Reynolds number.

Mathematical Model Establishment of Prefabricated Hole Flange-Forming of Unequal Diameter Tee Pipe

Based on the principle that in the deformation zone the length of bore plain wire does not change, a mathematical model of the prefabricated hole flange-forming of unequal diameter tee pipe is established, for the difficult problem of the flange-forming prefabricated hole size design for tee pipe. To solve the mathematical model, a numerical method and a software system for The solution of the mathematical model is established. In order to verify the reliability of this article to build the mathematical model and its solution, taking engineering for example, apply the method of finite element simulation to verify the mathematical model and the solving system, and the results show that the mathematical model constructed in this paper can relatively accurately make calculation of prefabricated hole size of flange-forming of unequal diameter tee pipe.

Particle image velocimetry technique measurements of the near wake behind a cylinder-pair of unequal diameters

The wake structure behind a circular cylinder-pair of unequal diameters as a function of incident flow angle α (0° ⩽ α ⩽ 180° ) has been investigated using the particle image velocimetry technique. The Reynolds number Re, center-to-center spacing ratio (P/D) and diameter ratio (d/D) are kept constant at 1200, 1.2 and 2/3, respectively. Instantaneous vorticity contours, mean flow fields and Reynolds shear stress contours are presented to elucidate the flow characteristics. The flow patterns behind the cylinder-pair change from that of a single bluff body to two vortex streets with increasing incident angle over the range of 0° ⩽ α ⩽ 90° , while the inverse phenomenon is observed when 90° < α ⩽ 180°.

Brownian dynamics method for simulation of binding kinetics of patterned colloidal spheres with hydrodynamic interactions

We develop a Brownian dynamics simulation method with full hydrodynamic interactions (HI) to study the recognition kinetics between two patterned colloidal spheres. We use a general resistance matrix (12*12) to describe both the far and near-field hydrodynamics of translation, rotation, and translation-rotation coupling between the two spheres, adopted from Jeffrey and Onishi [J. Fluid Mech. 139, 261 (1984)]. We apply the method to the specific binding of "patchy" spheres, including effects of depletion attraction and orientation-specific binding, as are present in "Janus" spheres whose surfaces contain hydrophobic and hydrophilic faces [Q. Chen, S. C. Bae, and S. Granick, Nature (London) 469, 381 (2011)]. The binding times obtained between two non-patterned spheres (of equal or unequal diameter) with or without HI extrapolated to infinite dilution are shown to be in good agreement with theoretical predictions of the Smoluchowski equation. In addition, the binding times for pairs of spheres for three cases of surface patterning of the two spheres (uniform-uniform, uniform-Janus, and Janus-Janus) are compared with or without rotational motion.

Calibration of omnidirectional wheeled mobile robots: method and experiments

SUMMARYOdometry errors, which occur during wheeled mobile robot movement, are inevitable as they originate from hard-to-avoid imperfections such as unequal wheels diameters, joints misalignment, backlash, slippage in encoder pulses, and much more. This paper extends the method, developed previously by the authors for calibration of differential mobile robots, to reduce positioning errors for the class of mobile robots having omnidirectional wheels. The method is built upon the easy to construct kinematic formulation of omnidirectional wheels, and is capable of compensating both systematic and non-systematic errors. The effectiveness of the method is experimentally investigated on a prototype three-wheeled omnidirectional mobile robot. The validations include tracking unseen trajectories, self-rotation, as well as travelling over surface irregularities. Results show that the method is very effective in improving position errors by at least 68%. Since the method is simple to implement and has no assumption on the sources of errors, it should be considered seriously as a tool for calibrating omnidirectional mobile having any number of wheels.

Interference Between Two Stationary or Elastically Supported Rigid Circular Cylinders of Unequal Diameters in Tandem and Staggered Arrangements

Analysis of model test results was carried out to investigate the hydrodynamic interaction between pairs of fixed or elastically supported rigid cylinders of dissimilar diameters in a water flume. The two cylinders are placed with one situated in the wake of the other. The spacing between the cylinders ranges from 1 to 15 times the larger cylinder diameter. The Reynolds numbers are within the subcritical range. For the vibrating cylinders which are free to oscillate in both the in-line and the cross-flow directions, the reduced velocity ranges from 1 to 13 and the low damping ratio of the test setup at 0.006 gives a combined mass-damping parameter of 0.02. For the fixed cylinders, the downstream cylinder experiences a drag reduction and it was found that this drag reduction also depends upon the diameter ratio. The lift on the fixed downstream cylinder has the frequency components derived from the upstream cylinder's vortex shedding as well as from its own vortex shedding, and the relative importance of the two sources is influenced by the spacing between the two cylinders. This is reflected in the downstream cylinder's vortex induced vibration (VIV) response which appears to be dependent upon the actual reduced velocities of both the cylinders.

The effect of a piggyback cylinder on the flow characteristics in oscillatory flow

Two-dimensional numerical simulations of oscillatory flow around a pair of cylinders of unequal diameters are conducted in order to investigate how the presence of the smaller cylinder affects the hydrodynamic forces acting on the main cylinder. A series of calculations are undertaken in which the frequency of the oscillation is held fixed but its amplitude is varied. Computations are carried out for a range of distances of the secondary cylinder from the primary. In addition, the line joining the two centres is allowed to vary across the whole range from the case when the two centres are aligned with the oncoming oscillatory flow right through till the point when the two cylinders sit side-by-side perpendicular to the far-stream flow. The lift and in-line force coefficients are analysed and reasons for the observed dependence on the relative positions of the two cylinders are discussed in terms of the associated flow structures.

Численное моделирование взаимодействия еловых балансов неодинакового диаметра в корообдирочном барабане

Interaction type and intensity are the main factors that influence the efficiency of pulpwood debarking in debarking drum. This technological process is a scantily known complex subject. That is why new decisions on improvement of pulpwood debarking process have met difficulties. The article deals with computer simulation, which explains the pulpwood diameter (mass) effect on its collision characteristics in debarking process by means of drum. Work goal: the determination of maximum interaction force at collisions of pulpwood of unequal diameter (or mass). Earlier offered mathematical simulation for numerical determination of this force is applied. The experimental data for spruce pulpwood stiffness were used as initial data for calculation. A simulation application has been demonstrated by six case-studies. In all of them pulpwood 1.2 m length was taken into account. Two different diameters of spruce pulpwood (0.12 m with a mass of 9 kg and 0.20 m with a mass of 31 kg) were used to reconstruct pulpwood collisions in the numerical experiment. As a result of the work, it was established that pulpwood diameter decrease leads to the increase of collisions number in the unit of time. The forces of contact interaction reach maximum more quickly. However, the maximum of pulpwood collisions force is decreased in the considered cases.

Density anomaly of charged hard spheres of different diameters in a mixture with core-softened model solvent. Monte Carlo simulation results

Very recently the effect of equisized charged hard sphere solutes in a mixture with core-softened fluid model on the structural and thermodynamic anomalies of the system has been explored in detail by using Monte Carlo simulations and integral equations theory [J. Chem. Phys., 2012, 137, 244502]. Our objective of the present short work is to complement this study by considering univalent ions of unequal diameters in a mixture with the same soft-core fluid model. Specifically, we are interested in the analysis of changes of the temperature of maximum density (TMD) lines with ion concentration for three model salt solutes, namely sodium chloride, potassium chloride and rubidium chloride models. We resort to Monte Carlo simulations for this purpose. Our discussion also involves the dependences of the pair contribution to excess entropy and of constant volume heat capacity on the temperature of maximum density line. Some examples of the microscopic structure of mixtures in question in terms of pair distribution functions are given in addition.

Optimization of a Y-Graft Design for Improved Hepatic Flow Distribution in the Fontan Circulation

Single ventricle heart defects are among the most serious congenital heart diseases, and are uniformly fatal if left untreated. Typically, a three-staged surgical course, consisting of the Norwood, Glenn, and Fontan surgeries is performed, after which the superior vena cava (SVC) and inferior vena cava (IVC) are directly connected to the pulmonary arteries (PA). In an attempt to improve hemodynamic performance and hepatic flow distribution (HFD) of Fontan patients, a novel Y-shaped graft has recently been proposed to replace the traditional tube-shaped extracardiac grafts. Previous studies have demonstrated that the Y-graft is a promising design with the potential to reduce energy loss and improve HFD. However these studies also found suboptimal Y-graft performance in some patient models. The goal of this work is to determine whether performance can be improved in these models through further design optimization. Geometric and hemodynamic factors that influence the HFD have not been sufficiently investigated in previous work, particularly for the Y-graft. In this work, we couple Lagrangian particle tracking to an optimal design framework to study the effects of boundary conditions and geometry on HFD. Specifically, we investigate the potential of using a Y-graft design with unequal branch diameters to improve hepatic distribution under a highly uneven RPA/LPA flow split. As expected, the resulting optimal Y-graft geometry largely depends on the pulmonary flow split for a particular patient. The unequal branch design is demonstrated to be unnecessary under most conditions, as it is possible to achieve the same or better performance with equal-sized branches. Two patient-specific examples show that optimization-derived Y-grafts effectively improve the HFD, compared to initial nonoptimized designs using equal branch diameters. An instance of constrained optimization shows that energy efficiency slightly increases with increasing branch size for the Y-graft, but that a smaller branch size is preferred when a proximal anastomosis is needed to achieve optimal HFD.

Strip Casting of 6061 Aluminum Alloy by Unequal Diameter Twin Roll Caster and Properties of Its Sheet

Strip Casting of 6061 Aluminum Alloy by Unequal Diameter Twin Roll Caster and Properties of Its Sheet

Numerical study of two side-by-side cylinders with unequal diameters at low Reynolds number

Two-dimensional laminar flow about two side-by-side unequal cylinders with different diameter ratios d/D and centre-to-centre spacing ratios T/D at Re=300 (based on the larger cylinder diameter) was simulated using a CFD software. Comparisons of experimental and numerical results were made to elucidate the degree of interference due to d/D and T/D and their effects on the flow patterns and vortex shedding frequencies. The findings showed that the flow patterns behind two unequal cylinders were distinctly different from that behind two equal side-by-side cylinders, with distinct in-phase and anti-phase vortex shedding, and random switching of modes of vortex shedding.

Interactions of lock-on wake behind side-by-side cylinders of unequal diameter at Reynolds number 600

The flow characteristics, mutual interactions and downstream evolutions of the wakes behind the side-by-side cylinders of unequal diameter are illustrated by flow visualization and Laser Doppler Anemometry. All the experiments are conducted in a recirculating water channel at Reynolds number 600. The gap ratio is 0.75 and the diameter ratio is 2.0. Periodic excitations are applied to the large cylinder with constant excitation amplitude. Within the excitation frequency range studied, the wake behind the large cylinder experiences the primary and the one third sub-harmonics lock-on; whereas the wakes behind the small cylinder are not locked-on. For the wake behind the large cylinder experiencing the primary lock-on, the gap flow becomes unbiased and the gap vortices are observed to interact and shed alternately into the wake behind each cylinder in synchronization with the excitation frequency (the natural vortex shedding frequency of large cylinder). The synchronized flow patterns exist only in the near wake region; in the downstream region, only one wider wake dominated by the excitation frequency is detected. While the wake behind large cylinder is locked-on at the one third sub-harmonics of the excitation frequency, the gap vortices are observed to entrain alternately into the wake behind each cylinder in synchronization with the one third of the excitation frequency (e.g., natural vortex shedding frequency of large cylinder). The synchronized flow patterns exist only in the near wake region; in the downstream region, the wake is relatively weak, less organized and turbulent. For both lock-on cases, the near and the far wake structures change suddenly within a short distance.

L’hyperparathyroïdie primaire étude de dix cas

In this research a 3-D two phase CFD model in Eulerian–Eulerian framework was developed to study sieve trays efficiency, hydraulics and mass transfer. To estimate the efficiency of the sieve trays, two trays with similar geometry but unequal hole diameters were used while the effects of the holes and bubbles diameters were observed. The results were compared with the available experimental data for distillation of methanol and n-propanol mixture. Mass transfer coefficients were estimated by the Higbie and surface renewal stretch (SRS) mass transfer models. It has been found that the liquid flow pattern on the tray which had smaller hole diameter is closer to the plug flow pattern and tends to have a larger mass transfer rate. In addition, while comparing the SRS model theory with the Higbie model, it has been found that using the SRS model reduces the sensitivity of the simulation results to the bubble diameters.

Lock-on characteristics behind two side-by-side cylinders of diameter ratio two at small gap ratio

The lock-on characteristics, the detailed interactions and downstream evolutions of the wakes behind side-by-side cylinders of unequal diameter (D/d = 2), spaced by a gap ratio 0.75 (G/D = 0.75), are investigated at Reynolds number 600 by the dye flow visualization, laser Doppler anemometry (LDA) and particle image velocimeter (PIV) velocity measurements. The lock-on frequency bands are studied by LDA and PIV at Reynolds number 2,000. The D, d and G are the diameters of the large, the small cylinders and the net gap between two cylinders, respectively. Periodic excitations, in form of rotary oscillation about the cylinder center, are applied to the large cylinder with the same amplitude. It is found that while the large cylinder is excited, two lock-on frequency bands of the wake behind the large cylinder are detected. These two lock-on frequency bands correspond to the primary and the one-third sub-harmonic lock-on of the wake behind large cylinder, respectively. These two lock-on frequency bands distribute symmetrically about the fundamental and the third superharmonic of the natural shedding frequency behind a single cylinder at the same Reynolds number. The left-shifted frequency band (1.8 ≤ fe/fos ≤ 2.0) is not considered as a locked-on frequency band because the phase difference between two excitation frequencies across fe/fos = 2.0 vary significantly. While the wake behind the large cylinder is locked-on at fe/3 (or fos), the gap flow becomes unbiased and the frequency of the wake behind small cylinder remains around the natural shedding frequency. Thus, the frequency band of 3.0 ≤ fe/fos ≤ 3.22 is also not locked-on because the phase difference in the narrow wake excited at fe/fos = 2.93 and 3.07 changes significantly. Note fe and fos denote the excitation frequency and the natural shedding frequency behind a single large cylinder, respectively.

Improving survival of inter-generic grafts of nematode-susceptible watermelon cultivars and nematode-resistant Cucumis species

Inter-generic grafting of highly nematode susceptible watermelon (Citrullus lanatus) cultivars onto nematode-resistant wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myricoarpus) had on average 36% graft survival ratios, which was attributed to unequal stem diameters at the graft union. Cucumis species had smaller stem diameters at the graft union, whereas Citrullus had bigger ones. The objective of the study was to improve inter-generic graft compatibility of Citrullus and Cucumis through optimizing the sizes of stem diameters during grafting. Cucumis species were raised in a 160-hole seedling tray and primed seeds of Citrullus were raised in a 200-hole seedling tray seven days after emergence of Cucumis in order to reduce the stem diameters. At grafting, stem diameter ratios in various treatments were equal to one, whereas at 66 days after grafting the ratios were grater than one, with the exception of those of intact plants. Survival of grafts from grafting to 66 days after grafting was 100%, translating into relative improvement of 186%. Improved survival of grafts would invariably promote the potential uses of inter-generic grafting among wild and cultivated watermelon in management of soil-borne pathogens.

Numerical study of an oscillating smaller cylinder in the wake of an upstream larger cylinder

A numerical study of flow around two tandem cylinders with unequal diameters was carried out. The upstream larger cylinder was fixed and the downstream smaller cylinder was allowed to oscillate in the transverse direction only. Comparisons of the experimental and numerical results were made to investigate the effects of the gap ratio on the maximum vibration amplitude and vortex shedding frequency. The results showed that the vibration response of the smaller cylinder was significantly affected by the presence of the upstream larger cylinder, and resulted in greatly reduced vibration amplitudes. With an increasing gap ratio, the vibration amplitude increased. However, the magnitude was lower than that corresponding to a single cylinder (with the same diameter as that of the downstream smaller cylinder) under the same flow conditions.

Effect of the Transient Nature of Flow on Annular Parachute Drag Prediction

The aerodynamics of parachute systems are highly unsteady, resulting from separated ∞ows, vortex shedding, etc., caused by complex interactions between a ∞exible canopy and its payload. However, when dynamically permitted, the ∞owflelds and resulting surface forces have often been approximated using the assumptions and characteristics of rigid bodies and steady-state simulations. For example, results from steady-state simulations have been used successfully to assist the determination of parachute loading and trajectory. They have even been used in the estimation of peak drag and canopy fllling times sustained by in∞ating parachutes. This paper compares ∞ow characteristics and canopy drag obtained from solving the steady-state equations with those calculated with the unsteady equations, using a Reynolds Reynolds-Averaged Navier Stokes ∞ow solver on a rigid concentric annular parachute geometry comprised of two concentric fabric rings. The rings have unequal diameters and are vertically ofiset. Under load, the in∞ated rings not only yield a canopy that is highly porous but one that is characterized by high drag, a result of the cambered proflle formed by the billowing of the rings. The simulations have been performed at two Reynolds numbers of 8:03 ¢ 10 6 and 10:04 ¢ 10 6 . In particular, drag forces and wake characteristics observed in the steady simulations are compared to the unsteady simulations in order to judge the ability of the steady-state equations to capture the behavior noted in the transient cases. Results also include velocity, vorticity, and turbulence contours to help clarify the ∞ow physics resulting from steady and unsteady simulations.