Normal Pressure Force Research Articles

Conditions for vertical pulling of semi-finished leather products under driving rollers

The conditions for the vertical pulling of a semi-finished leather product laid bent on a transporting base plate between rotating squeezing rollers are theoretically investigated in the article for the first time. At that, an important role is played by the value of the radii of the squeezing rollers, installed in one row in the horizontal plane, and the value of the corner radius of the front part of the transporting base plate. If the value of the corner radius and the thickness of the base plate are large, then when it contacts the squeezing rollers, a significant frontal resistance arises. Thus, to derive the conditions for gripping the semi-finished leather product between the rotating squeezing rollers, the pulling-in force of the traction chains, the normal pressure force of the squeezing rollers, the coefficient of friction between the rotating squeezing rollers and the leather semifinished product are taken into account. The condition for the vertical pulling of the semi-finished leather product laid on the base plate is determined, taking into account the coefficient of friction between the semi-finished leather product and the squeezing rollers when they come into contact.

Flow Dynamics and Acoustics from Glottal Vibrations at Different Frequencies

Glottal vibration is fundamental to breathing-related disorders and respiratory sound generation. However, responses of the flow and acoustics to glottal vibrations of different frequencies are unclear. The objective of this study is to numerically evaluate the influences of glottal vibration frequencies on inspiratory airflow dynamics and flow-induced sound signals; this is different from normal phonation that is driven by controlled expiratory flows. A computational model was developed that comprised an image-based mouth–throat–lung model and a dynamic glottis expanding/contracting following a sinusoidal waveform. Large Eddy simulations were used to solve the temporal and spatial flow evolutions, and pressure signals were analyzed using different transform algorithms (wavelet, Hilbert, Fourier, etc.). Results show that glottal vibrations significantly altered the flows in the glottis and trachea, especially at high frequencies. With increasing vibration frequencies, the vortices decreased in scale and moved from the main flow to the walls. Phase shifts occurred between the glottis motion and glottal flow rates for all frequencies considered. Due to this phase shift, the pressure forces resisted the glottal motion in the first half of contraction/expansion and assisted the glottal motion in the second half of contraction/expansion. The magnitude of the glottal flow fluctuation was approximately linear with the vibration frequency (~f0), while the normal pressure force increased nonlinearly with the frequency (~f01.85). Instantaneous pressure signals were irregular at low vibration frequencies (10 and 20 Hz) but became more regular with increasing frequencies in the pressure profile, periodicity, and wavelet-transformed parameters. The acoustic characteristics specific to the glottal vibration frequency were explored in temporal and frequency domains, which may be used individually or as a combination in diagnosing vocal fold dysfunction, snoring, sleep apnea, or other breathing-related diseases.

STATISTICAL FEATURES OF FIBRE FRICTION IN A ONE-DIMENSIONAL FIBROUS PRODUCT

The article considers a model of plastic deformation for one-dimensional fibrous products based on the ideas of the forces of adhesion and dry friction between the fibres on the surfaces of the areas where the fibres touch in the product. It is proposed to take into account in this model the statistical nature of such factors as the magnitude and direction of the normal pressure forces, the magnitude of the coefficient of friction, the direction of the contact surfaces in the product. The gamma distribution is chosen as the model distribution. The statistical modelling method shows that taking into account the statistical nature of the listed factors leads to a fundamentally new relationship between the rate of plastic deformation and the mechanical stress of forces arising in the product under the action of an external elongating load – the dependence is similar to those acting for viscous materials with Newton's law of viscous friction.

Unidirectional sensitive flexible sensor for bending measurements

The measurement of bending direction and bending angles is essential in the multiaxial servo-controlled system, especially for collaborative robots. However, most flexible sensors developed for bending measurements cannot distinguish bending directions due to their sensitivity to both positive and negative bending. Also, these sensors usually exhibit simultaneous response to normal pressure, which results in additional calibration. Here, a unidirectional-sensitive flexible capacitive sensor is proposed. A simple asymmetric pyramidal microstructure was designed to create uneven responses to positive and negative bending and minimum response to normal pressure based on the fringe effect. The fabricated sensor shows a relative capacitance change of nearly 0.9 in the sensitive direction and only 0.05 in the other direction as the sensor bends from flat to the curvature radius of 10 mm. Also, the sensor shows negligible sensitivity even under a normal pressure force as high as 16 N, either in planar or bending condition.

Evaluation of tribotechnical parameters of polymer compounds used in machine tool construction

The conducted research of the coefficient of friction of the polymer compound applied by printing on the guides of the grinding machine. The results were obtained using an electromechanical device developed by the authors, when changing the speed of the relative movement of the caliper along the guides, the normal pressure force, and the type of lubricant. It was found that the use of polymer material in the machine guides reduces the coefficient of friction and ensures smooth movement of the calipers at low speeds. The use of solid lubricants based on fluoropolymer allows you to further reduce the coefficient of friction in the machine guides and ensure uniform movement of the calipers throughout the speed range.

Numerical analysis of the ground-mounted solar PV panel array mounting systems subjected to basic wind for optimum design

Comprehensive numerical modeling and investigations have been carried out to analyze the effect of wind loads on various solar array mounting frame structures using ANSYS 18 Workbench (Mechanical). Extensive damages of solar arrays and mounting frames have been reported the world over due to high winds. In this study, six array mounting frame types have been considered, subjected to the basic wind of 55 m/s specified for coastal regions of India. India has six basic wind speed zones ranging from 33 m/s to 55 m/s. Many utility-scale solar farms installed in this region are susceptible to high winds. Solar arrays considered of dimension 6 m × 4 m consisting of 12 photo-voltaic (PV) panels each of size 1 m × 2 m, with panel tilt angle varying from 10° to 50°. Wind load subjected to the PV panels in the solar array considered as normal pressure force over the top and bottom surfaces to simulate forward and backward wind direction. Three different materials with their respective mechanical properties, i.e., structural steel channel for mounting truss members, aluminum casing to encapsulate PV panels, and plexiglass sheet for PV panels, were considered and simulated. Wind pressure forces have been determined, using respective net wind pressure coefficients, induced by respective wind speed and tilt angle. Maximum deformation and maximum stresses were determined by modeling and simulation in ANSYS Workbench and compared the results with various array mounting system arrangements for each case of panel tilt angle subjected to both forward and backward wind incidence.

Justification of instrument parameters for the construction soil strength determination

A portable instrument has been introduced in the construction industry of the Russian Federation for the determination of soil strength grades, which is based on the free weight falling principle. Until the present the theory of such instrument hasn’t yet been completely developed and needs to be improved. In this study on the basis of the theorem on normal stresses on surfaces of a cone to be penetrated into the soil, a logically justified theory of the instrument basic parameter selection has been developed. Stresses on horizontal areas of construction soils are equal to twice the stresses on inclined areas of the cone. At the end of the working section of a rod to be penetrated into the soil there is a round flat punch, which area is A=1 cm2. During the punch penetration into the soil by an impact method, a soil compacted cone body appears before the flat punch, which is affected by normal pressure forces and tangential friction forces. For the first time the equation of normal stresses σ1 has been obtained on inclined areas of the soil cone. The mathematical model of the instrument doesn’t contain soil parameters, that allows to recommend it for any soil and media. The obtained analytical dependences allow to design similar instruments in order to measure the soil strength using any value of the falling weight mass. In this paper the instrument parameter justification has been made with the impact weight mass m 1 = 2.5 kg.

Gas dynamic calculation of detonation in constant-cross-section ducts

The paper presents a computational method with the use of gas-dynamic functions of parameters of detonation in a one-dimensional subsonic flow of ideal gas behind the shock wave propagating in chemically active air-and-fuel mixture in a uniform-cross-section duct, where the resultant of normal pressure forces acting on its side surface is equal to zero. Stabilization of the shock wave is provided by the onset of thermal crisis with the air-and-fuel mixture combustion heat supply to the gas behind the wave. In this case the value of the specific speed of the combustion products is equal to the critical one. The solution of the total-impulse equation considering the above mentioned peculiarities of the flow in a uniform-cross-section duct establishes clear correlation of the specific speed of the stabilized shock wave to the rate of rise of the temperature of the gas behind it, which gives an opportunity to determine all detonation parameters. The shock wave can be initiated by the detonation of an explosive substance and carries a huge amount of energy. It is shown that the shock wave can be obtained only if the source of small disturbances itself moves at the supersonic speed. It is shown that total pressure behind the shock wave decreases significantly and the entropy increases due to the wave losses, whereas the static pressure increases significantly. An explanation of this effect is given. A formula for calculating the rate of gas temperature rise was derived as a function of the specific speed of the shock wave, the air-and-fuel mixture heat value and the heat availability factor that designates the dissociation of the combustion products and heat loss through the duct wall under specified initial conditions. The reliability of the method of calculating detonation was experimentally substantiated. The work is currently important for the evaluation of the detonation engine efficiency.

Frictional Characteristics of Metal Friction Pairs and the Amontons and Coulomb Friction Laws

Based on the interpretation of the laws of friction of Amontons and Coulomb as equations of linear regression of the friction force on the normal pressure force corresponding to the statistical processing of the experimental results, the values of the friction coefficients for six metal pairs are calculated. The principal difference between the values of the friction coefficient calculated in this way and the values calculated by simply dividing the friction force by the normal force is emphasized. Quantitatively, the difference can be more than twofold.

О некоторых механизмах предельного трения с разрушением

A model of the process leading to formation of the third body elements at fracture of material in a dry friction contact zone was suggested. A variant of a plane element of the third body evolution was analyzed for the regime of an intensive shear action on its contact surfaces. A separated fragment can form an rolling element or remain to be a plane slipping element in dependence on a relation between normal pressure forces and shear forces in the contact zone. A criterion for twisting a plane element into a rolling element was obtained (within the framework of the plane elasticity)

Modelling of static aerodynamics of helicopter underslung loads

AbstractThe complex aerodynamics of rectangular underslung helicopter loads can lead to severe stability problems, but are difficult to represent in flight dynamics models. Current models for box aerodynamics are highly unsatisfactory, being entirely empirical and requiring large amounts of experimental data to generate. This paper presents a new modelling approach, which takes account of the bluff-body nature of the flow, where loads are dominated by normal pressure forces. Existing experimental data is recast in body-axes form, with α and β replaced by velocity components perpendicular and parallel to the box faces. Force and moment data for a wide range of boxes then collapse onto a set of simple generic characteristics, with features that can be related directly to the underlying flow physics. Modelling of container aerodynamics is greatly simplified, and allowance for effects of turbulence, Reynolds Number, wind tunnel interference and geometry modifications becomes possible.

Controlled rolling of a disc along a plane curve

The plane-parallel rolling of a disc along a fairly smooth curve under the action of perturbing and controlling forces and moments of forces is investigated. Models of the controlled motion corresponding to an explicit or implicit coordinate specification of the curve are constructed. The requirements imposed on the values of the sliding friction force and the normal pressure force, which ensure that the disc rolls without slipping and without loss of contact are determined. The problem of bringing the disc into the required state of motion in a time-optimal way by the action of the force of gravity and a limited axial moment of forces are considered. The situation when the reference curve contains a linear component (inclined upwards or downwards) and a periodic (wavy) component is investigated. Problems of optimal synthesis for a relatively large and relatively small controlling moment are considered.Investigations of the rolling of bodies of different geometrical shape on surfaces, both flat and curved (see Refs 1-4, etc.), are important for applications in modern machine construction, transport, mobile robot systems, 5–7 etc. However, there are no results of systematic investigations of the problems of the dynamics and control of rolling of bodies on curved surfaces, including comparatively simple bodies (cylinders, discs and spheres). From the applied point of view, the problem of controlled rolling of a disc under gravitational forces on a curve containing a linear incline and periodic smooth changes in the slope is of interest as a model of the motion of a wheel along a path with a curvilinear profile. The solution of problems of the control of the motion of a disc along a closed curve, for example, inside or outside a circle, surmounting obstacles or “rolling out” from hollows of different shapes etc. is of fundamental importance.

Laser induced flexural wave analysis: an aluminum element in steel substrate

Laser non-conduction limited heating is involved with evaporation at the surface, which in turn results in a recoil pressure generated at the vapor liquid interface. Depending on the magnitude of interface pressure, a pressure force acting normal to the workpiece surface occurs. This generates flexural waves propagating in the substrate material. When the material contains some impurities or defects, the flexural wave characteristic changes. On the detection of the wave characteristics, it becomes possible to identify the location and size of the impurities and defects in the substrate material. In the present study, laser induced evaporation of the steel substrate is considered. The interface pressure and normal pressure force acting at the workpiece surface is determined. Three-dimensional flexural wave analyses is carried out. An aluminum element is considered as impurity in the steel substrate. The effect of location of an element aluminum on the flexural wave motion is investigated. It is found that the flexural wave amplitude is influenced considerably by the presence of aluminum element. Temporal behavior of aluminum element changes the displacement characteristics considerably in the axial direction while characteristics of displacement difference do not alter considerably.

Flexural wave generation and stress analysis during laser evaporative heating of steel

Flexural waves are generated during the laser evaporative heating process. In this case, vapour pressure developed at the workpiece surface generates a pressure force acting normal to the surface. This, in turn, results in waves in the workpiece. Moreover, a stress field arises in the substrate material during the flexural motion. Consequently, investigation into the flexural waves and stress levels developed in the substrate material on account of the laser evaporative heating process becomes necessary. In the present study, laser evaporative heating of steel is considered. The flexural waves generated by teh normal pressure force are formulated and the stress levels inside the substrate material are computed numerically using the finite element method (FEM). To investigate the effect of an additional element, as an impurity in the substrate material, on the stress levels, aluminium is added to the steel substrate. It is found that a displacement of the surface of the order of 2μm occurs, and that the maximum stress level is of the order of 105 Pa during the heating process. The additional aluminium lowers the displacement and stress levels in the substrate material.

Computing ship wave resistance from wave amplitude with a non-local absorbing boundary condition

A method for computing ship wave resistance from a momentum flux balance is presented. It is based on computing the momentum flux carried by the gravity waves that exit the computational domain through the outlet plane. It can be shown that this method ensures a non-negative wave-resistance, in contrast with straightforward integration of the normal pressure forces. However, this calculation should be performed on a transverse plane located far behind the ship. Traditional Dawson-like methods add a numerical viscosity that dampens the wave pattern so that some amount of momentum flux is lost, and resulting in an error in the momentum balance. The flow field is computed, then, with a centred scheme with absorbing boundary conditions. Copyright © 1998 John Wiley & Sons, Ltd.

Atmospheric angular momentum fluctuations during 1979–1988 simulated by global circulation models

This note summarizes the main findings of an investigation described in detail in a recently-published paper (Hide et al. 1997) and presented at a symposium on “Modelling of global change phenomena with observational geodetic and geophysical constraints” held during the 1997 Congress in Vienna of the European Geophysical Society. Changes in major global dynamical phenomena in the Earth's atmosphere are manifested in the time series of atmospheric angular momentum (AAM), as determined directly from meteorological observations and indirectly from geodetic observations of small fluctuations in the rotation of the solid Earth which are proportional to length of day. AAM fluctuations are intimately linked with energetic processes throughout the whole atmosphere and also with the stresses at the Earth's surface produced largely by turbulent momentum transport in the oceanic and continental boundary layers and by the action of normal pressure forces on orographic features. A stringent test of any numerical global circulation model (GCM) is therefore provided by a quantitative assessment of its ability to represent AAM fluctuations on all relevant timescales, ranging from months to several years. From monthly data provided by the Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme, we have investigated seasonal and interannual fluctuations and the decadal mean in the axial component of AAM in 23 AMIP GCMs over the period 1979–1988. The decadal means are generally well simulated, with the model median value (1.58 × 10 26 kg m 2 s −1) being only 3.5% larger than the observed mean and with 10 of the models being within 5% of the observed. The seasonal cycle is well reproduced, with the median amplitude of the models' seasonal standard deviations being only 2.4% larger than observed. Half the seasonal amplitudes lie within 15% of the observed, and the median correlation found between the observed and model seasonal cycles is 0.95. The dominant seasonal error is an underestimation of AAM during northern hemisphere winter associated with errors in the position of subtropical jets. Less robust are the modeled interannual variations, although the median correlation of 0.61 between model simulations and observed AAM is statistically significant. The two El Niño-Southern Oscillation events that occurred during the AMIP decade 1979–1988 have the expected positive AAM anomalies, although the AAM signature of the 1982–1983 event tends to be underestimated and that of the 1986–1987 event overestimated.

Atmospheric angular momentum fluctuations during 1979–1988 simulated by global circulation models

Changes in major global dynamical phenomena in the Earth's atmosphere are manifested in the time series of atmospheric angular momentum (AAM), as determined directly from meteorological observations and indirectly from geodetic observations of small fluctuations in the rotation of the solid Earth which are proportional to length of day. AAM fluctuations are intimately linked with energetic processes throughout the whole atmosphere and also with the stresses at the Earth's surface produced largely by turbulent momentum transport in the oceanic and continental boundary layers and by the action of normal pressure forces on orographie features. A stringent test of any numerical global circulation model (GCM) is therefore provided by a quantitative assessment of its ability to represent AAM fluctuations on all relevant timescales, ranging from months to several years. From monthly data provided by the Atmospheric Model Intercomparison Project (AMIP) of the World Climate Research Programme, we have investigated seasonal and interannual fluctuations and the decadal mean in the axial component of AAM in 23 AMIP GCMs over the period 1979–1988. The decadal means are generally well simulated, with the model median value (1.58×1026 kg m2 s−1) being only 3.5% larger than the observed mean and with 10 of the models being within 5% of the observed. The seasonal cycle is well reproduced, with the median amplitude of the models' seasonal standard deviations being only 2.4% larger than observed. Half the seasonal amplitudes lie within 15% of the observed, and the median correlation found between the observed and model seasonal cycles is 0.95. The dominant seasonal error is an underestimation of AAM during northern hemisphere winter associated with errors in the position of subtropical jets. Less robust are the modeled interannual variations, although the median correlation of 0.61 between model simulations and observed AAM is statistically significant. The two El Niño‐Southern Oscillation events that occurred during the AMIP decade 1979–1988 have the expected positive AAM anomalies, although the AAM signature of the 1982–1983 event tends to be underestimated and that of the 1986–1987 event overestimated.

Numerical simulation and experimental results of the metal armature acceleration

A numerical model for calculating the contact pressure in EM rail launchers is developed. The calculation code is based on the solution of steady, axis-symmetrical contact springiness problem utilizing the finite element method. An experimental investigation was also carried out with the following parameters: (1) the power supply system was based on 5 MJ capacitor banks charged to 4.3 kV; (2) the rail accelerator had a bore length of 4.2 m and a bore diameter of 30 mm; (3) the rail material was bronze and the insulator material was fiberglass STB-3 (G-10 type); and (4) the preaccelerator was a conventional powder gun. The experimental results agree with the authors' understanding of armature physics at velocities of 2.1 to 2.7 km/s. The results can be improved with correct calculation of balancing forces that provide the necessary contact in the conducting part of the armature, and the normal pressure force, which is responsible for friction. The problem of 2-D and 3-D distribution of nonsteady electromagnetic heat and force fields in the fixed contact zone should then be solved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of belt velocity on flat belt drive behavior

Belt drive behavior is investigated theoretically to determine the effect of (1) belt velocity on normal and tangential belt forces and (2) centrifugal forces on belt tension. The tangential belt force is found to increase with belt velocity for positive λ and decrease with negative λ. The active angles and the distribution of normal pressure forces change to balance the applied torque load.

Double layer mediated energy conversion with a protein membrane using an imposed frequency and wavelength

A mechanical excitation of known temporal frequency and fixed spatial wavelength is imposed on a collagen membrane in a homogeneous aqueous electrolyte environment. An electrical response is measured at the same frequency as the imposed mechanical excitation. A quasi-one dimensional model is developed which includes the effects of electrolyte viscous shear and normal forces as well as inertial and normal pressure forces. Experimental parameters examined include collagen membrane tension, amplitude of the mechanical excitation, system geometry and the electrolyte bath pH. The objective of this work is to model and evaluate electromechanical transductive coupling with charged membranes at the device or system level as well as at the macromolecular level. The results are also directly relevant to physiological electromechanical processes occurring in connective tissue structures such as cartilage.