Resulting Pressure Force Research Articles

FORCE REQUIRED TO MOVE THE FLEXIBLE STRIP UP SURFACE OF HORIZONTAL CYLINDER

A differential equation of the motion of a flexible incompressible strip with a rectangular cross-section curve along the inner rough surface of a horizontal cylinder has been derived in the article. The strip moves up perpendicularly to the generatrix of the cylinder with a given constant speed, that is, the trajectory of movement is the cross-section curve of the cylinder. The equation takes into account the weight forces of the strip and the friction force from the resulting pressure force of the strip on the surface, as well as the additional friction force depending on the compression of the strip and the angle of its coverage with the cylinder. An example for a circular cylinder is considered. The differential equation is solved, the necessary force for pushing the strip is found. The graphs illustrating the influence of different factors on the pushing force of a strip at a given angle of its coverage are constructed.

A Radial Two-Sector Gas Bearing with Maximum Load Capacity

A variational problem for a radial gas journal bearing with two sectors is considered. The pressure field in the gas layer can be described by the nonlinear Reynolds equation for arbitrary compressibility numbers. The magnitude of the resultant pressure force vector is used as a functional of the variational problem. The system of necessary conditions of the extremum is qualitatively analyzed and, as a result, a computational procedure is constructed. Based on the analysis of the complete system of necessary conditions, it is shown that the profile on each of the sectors is piecewise linear and single-stage; at the same time, one sector provides only gas rarefaction, while the other provides only gas compression.

Multiscale Filtering of Compressible Wave Propagation in Complex Geometry through a Wavelet-Based Approach in the Framework of Pressurized Water Reactors Depressurization Transient Analysis

The proposed research takes place in the framework of the analysis of the mechanical consequences of accidental scenarios for pressurized water reactors (PWR). It is particularly dedicated to the effects of the propagation of a transverse rarefaction wave through the assemblies of the nuclear core, consecutive to a pipe break in the primary circuit of the reactor. This paper focuses on the representation, with a reduced number of well-chosen variables, of a pressure wave propagating through a highly congested medium composed of rod bundles, with the primary objective of accurately evaluating the resulting pressure forces exerted on the rods. To achieve this goal, a description of the fluid domain as a homogenized or porous medium is introduced, yielding the need for a new filtering technique to be applied to the fluid fields. A new homogenized and multiscale representation of the fluid variables, based on continuous wavelet transform (CWT), is thus proposed. The capabilities of CWT to accurately approximate a reference representative unsteady pressure field, corresponding to a wave propagation at microscale, is assessed. The proposed technique is applied to a pressure field obtained numerically at local scale. The number of variables that shall be kept at macroscale to have a meaningful representation of the pressure field is fully evaluated through the comparison of the fluid force applied to the microstructure.

Large-eddy simulation of turbulent flow over the DrivAer fastback vehicle model

Turbulent flow over the DrivAer fastback vehicle model is investigated using large-eddy simulation with particular emphasis on flow separation, vortical structures and unsteady quantities. A systematic and detailed analysis of the flow field is made considering rotating wheels and moving ground floor. Overall features of vortical structures at the cowl top, behind side mirrors, near front and back wheels, at A-, B- and C-pillars and behind the rear end of the vehicle are revealed by investigating velocity and vorticity fields. The rear end is identified to be the main contributor to the pressure force acting on the vehicle, followed by back and front wheels and side mirrors. The resulting pressure force on the upper part of the vehicle, including A-, B-, and C-pillars but excluding the cowl top and side mirrors, is found to be only slightly higher than the contribution of the gap in the cowl top. Flow separation and resulting vortices do not only have an impact on automotive drag, it is also pointed out how unsteadiness in the flow field affects pressure fluctuations. High levels of surface pressure fluctuations are found near side mirrors and front wheels. Similarities in distributions of pressure fluctuations and turbulent kinetic energy are found.

Experimental and CFD investigations of turbulent cross-flow in staggered tube bundle equipped with grooved cylinders

In the present paper, an experimental and numerical simulation of the turbulent cross-flow in a staggered tube bundle with transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively, are performed. The bundle consists of 16 PVC tubes of 40 mm outer diameter arranged in a staggered configuration. Each cylinder has two grooves on the external surface at 90° and 270°. The experiments are carried out using a subsonic wind tunnel. The pressure distributions along the tubes are determined for a variation of the azimuthal angle from 0° to 360°. The drag and lift forces are measured using the TE 81 balance. The drag coefficients are also deduced from the resulting pressure force in order to compare with smooth cylinder configuration. The use of the grooved cylinder shows a reduction on the drag forces. The steady-state Reynolds-averaged Navier–Stokes equations are solved using a finite-volume method where Spalart–Allmaras, k–e realizable and k–ω SST, turbulence models are used to produce a closed system of solvable equations. The staggered tube bundle geometry simulations are performed at steady conditions. An adapted grid using static pressure, pressure coefficient and velocity gradient, furthermore, a second-order upwind scheme were used. The obtained results show that the numerical predictions are in good agreement with the experimental measurements.

On thin gaps between rigid bodies two-way coupled to incompressible flow

Two-way solid fluid coupling techniques typically calculate fluid pressure forces that in turn drive the solid motion. However, when solids are in close proximity (e.g. touching or in contact), the fluid in the thin gap region between the solids is difficult to resolve with a background fluid grid. Although one might attempt to address this difficulty using an adaptive, body-fitted, or ALE fluid grid, the size of the fluid cells can shrink to zero as the bodies collide. The inability to apply pressure forces in a thin lubricated gap tends to make the solids stick together, since collision forces stop interpenetration but vanish when the solids are separating leaving the fluid pressure forces on the surface of the solid unbalanced in regard to the gap region. We address this problem by adding pressure degrees of freedom onto surfaces of rigid bodies, and subsequently using the resulting pressure forces to provide solid fluid coupling in the thin gap region. These pressure degrees of freedom readily resolve the tangential flow along the solid surface inside the gap and are two-way coupled to the pressure degrees of freedom on the grid allowing the fluid to freely flow into and out of the gap region. The two-way coupled system is formulated as a symmetric positive-definite matrix which is solved using the preconditioned conjugate gradient method. Additionally, we provide a mechanism for advecting tangential velocities on solid surfaces in the gap region by extending semi-Lagrangian advection onto a curved surface mesh where a codimension-one velocity field tangential to the surface is defined. We demonstrate the convergence of our method on a number of examples, such as underwater rigid body separation and collision in both two and three spatial dimensions where typical methods do not converge. Finally, we demonstrate that our method not only works for the aforementioned “wet” contact, but also works in conjunction with “dry” contact where there is no fluid in the gap between the solids.

Method of Sliding Bearings Static Characteristics Calculation

The direct problem of researching the load capacity of segment gas-static bearing is being discussed. In calculation the movement of the shaft in the bearing is considered slow comparing than the rotational velocity. Vibrations and the influence of non-stationarity are neglected. The given geometry of the bearing and the pressure of lubrication supply in the gap between the bearing and the shaft are considered initial data. The result of the calculation is the value of the resultant pressure force, applied to the bearing segments. Summing the forces the value of the static load capacity can be found. For segments that may spontaneously rotate about the joint axis, described a method of calculating the rotation angle, at which the main moment of pressure forces applied to the segment is equal to zero and the segment's position is stable.

Retinale Schäden durch flüssige Perfluorkarbone – eine Frage des spezifischen Gewichts? Intraokulare Druckspitzen und Scherkräfte

Perfluorocarbon liquids (PFCL) cause retinal damage when used as long-term ocular endotamponades. Whether these changes are related to the mechanical or to the chemical properties of PFCL is unclear. The purpose of this study was to evaluate pressure spikes or shearing forces during endotamponade with PFCL and standardised eye movements. Part 1: In an eye model the resulting pressure forces of 6 PFCL were measured at four different sites during standardised eye movements. Part 2: Shearing forces were determined in a plexiglass eye model and the resulting tangential forces at the PFCL-retina interface were calculated. Part 3: Rabbit eyes were vitrectomised and filled with light and heavy fluorocarbons for 6 weeks. Subsequently, the retina were examined histologically and by immunohistochemistry. With increasing filling of the eye model, the maximum of the pressure peaks moved from the inferior wall of the eye model to the lateral eye walls. For perfluorodecalin (PFD) the highest pressure peak was 407 Pa with a 75 % filling of the vitreous cavity. The lowest pressure peak was 314 Pa with a 50 % filling of hexafluoropropene oxide. Shearing forces for standardised accelerations were dependent on viscosity and ranged between 0.87 mN/m(2) (perfluorohexyloctane) and 8055 mN/m(2) (hexafluoropropene oxide). Part 3: Histological and immunohistochemical analyses did not reveal pressure-related damage or any difference between the effects of the different tamponades in vivo. In comparison with physiological dynamic and static pressure peaks, the measured mechanical forces induced by intraocular PFCL tamponades are low. Specific gravity and mechanical damage by intraocular PFCL as a cause of retinal damage seem unlikely. Animal studies underline these findings.

Second-Order Diffraction in Short Waves

Asymptotic approximations are derived for the second-order potential and the result-ing pressure forces acting on fixed vessels in monochromatic or bichromatic incident waves. These approximations are based on the short-wavelength assumption, with respect to the first-order incident waves. Comparisons are made with computations based on the second-order panel code WAMIT, to indicate the domains where the approximate results are useful.

Analysis of a flexural wave due to a laser heating pulse: The two-layer assembly case

In the present study laser ablation of a two-layer assembly with a cantilever arrangement is considered. The recoil pressure generated at the vapour front-workpiece interface is formulated and the resulting pressure force (loading force) is computed. The flexural motion of the workpiece due to the loading force is formulated. The first layer of the workpiece is Inconel 625 with a thickness on the order of 200 μm, which may resemble the HVOF (high-velocity oxygen fuel) coating, while the second layer is 1 mm thick stainless steel plate. The simulations are repeated for four values of the first layer thickness and the relation between the magnitude of the displacement and the first layer thickness is discussed. It is found that the displacement of the workpiece reaches as high as 2 μm in the region close to the free end, while the equivalent stress level is high in the region close to the fixed end. The temporal behaviour of the equivalent stress almost follows the displacement behaviour of the workpiece. As the first layer thickness increases, the displacement reduces. The variation of displacement with the first layer thickness is almost linear and the slope of this variation attains high values for certain time periods in the flexural motion.

Flexural waves generated due to pressure force during the laser induced evaporation process

During the laser ablating of surfaces, the pressure is generated at the interface between the vapor front and the solid substrate. In some cases, the magnitude of the pressure attains considerably high values, which in turn develops a pressure force acting normal to the workpiece surface. The magnitude of the pressure force is sufficient to generate flexural waves propagating along the workpiece. In the present study, a flexural wave generation during laser ablation of steel surface is modeled. The pressure rise at the interface is predicted and the resulting pressure force is determined. The flexural wave characteristics are examined at different locations at the workpiece surface. In order to examine the effect of reflected waves, from the free ends of the workpiece, on the traveling waves radiating boundary conditions on the element sides is considered. It is found that the flexural wave amplitude decays as the location at the surface moves towards the workpiece end. The radiating conditions on the element sides show that the reflected waves have significant effect on the traveling wave characteristics.

Dynamic Response and Stability of Pressurized Gas Squeeze-Film Dampers

Compressible squeeze films, an important and interesting area in gas lubrication, have been relatively neglected in recent times. Aircraft engines are being designed with light weight flexible rotors operating at high speeds and temperatures that may eventually eliminate the use of oil lubrication. A gas or air SFD might be a viable alternative to a conventional oil damper, in high temperature applications that preclude the use of oil lubrication. Oil squeeze-film dampers currently being used for rotordynamic control will not be viable at temperatures above 350°F, due to limitations on lubricant oil temperature. A good example of gas SFD application is in conjunction with high temperature gas lubricated foil bearings, which inherently have low damping. This paper presents an analysis of pressurized air dampers, similar to a hydrostatic gas bearing. Pressurized air is supplied through a series of orifices in the bearing midplane. Airflows through the orifices and the resulting pressure forces are calculated using a simple gas-flow model, as in orifice compensated hydrostatic bearings. A small perturbation analysis of the shaft center yields the stiffness and damping coefficients, for centered circular orbits. Damping characteristics are studied for a range of parameters such as supply pressure, orifice diameter, pocket volume, orbit size, number of orifices and shaft speed. Results show that maximum damping forces are generated for near choking flow conditions. The damping coefficient becomes negligible at frequencies above 350 Hz. For damping force to be present, the gas pressurization has to exert a force on the rotor opposing the instantaneous velocity, or, 90 degrees out of phase with displacement. Linear stability of unbalanced dampers undergoing centered circular orbits, is also investigated, in view of their relevance to rotordynamics. Damper design curves are presented for various parameters.

Intralaryngeal Pressure Conditions and a Membranophonic Interpretation of Voice Production

The article gives one of the possible explanations of the complex event which may be registered when recording the vibrations from the thyroid cartilage in ventral-dorsal direction during phonation and approximately in two octaves of the modal voice. The alternating displacement of the vibrating thyroid cartilage is caused apparently by the alternating increase and decrease in the resulting pressure force acting upon the vocal folds. For the time being the adduced hypothesis does not take into consideration specific reflex activity, in spite of the fact that it can probably be expected with lesions of the nervous system on the basis of the typically changed manifestations.

Wave‐Induced Forces on Buried Pipelines

Ocean waves induce dynamic pressure responses in permeable seabeds which result in dynamic loads on buried pipelines. An analytical model is developed for estimating the pore pressure in the soil and the resulting pressure force on buried pipelines. It is assumed that the seabed is rigid, homogeneous, and porous with isotropic permeability, that the pore water is incompressible, that fluid flow in the soil is modeled by Darcy's Law, and that the seabed is infinitely deep. A solution is developed for a circular, rigid pipeline using conformal mapping techniques. The solution is compared with the results of both small and large‐scale tests; reasonable agreement is obtained for the small‐scale tests. Wave‐induced seepage forces are evaluated by integrating the pressure distribution over the pipe surface. The magnitude of the force remains constant but the direction rotates around the cylinder once with the passage of each wave. This force may be of sufficient magnitude to be an important consideration in the design of buried marine pipelines.