Smooth Pressure Research Articles

Improvement of stability in moving particle semi‐implicit method

AbstractMoving particle semi‐implicit (MPS) method is one of the particle methods, which can be used to analyze incompressible free surface flow without surface tracking by a mesh or a scalar quantity. However, MPS causes unphysical numerical oscillation of pressure with high frequencies. We proposed a new formulation for the source term of Poisson equation of pressure. The proposed source term consists of three parts, one main part and two error‐compensating parts. With proper selection of the coefficients for the error‐compensating parts, we can suppress the unphysical pressure oscillation. Smoother pressure distributions are obtained in hydrostatic pressure and dam break problems. Copyright © 2010 John Wiley & Sons, Ltd.

Treatment of Checkerboard Pressure in the Collocated Unstructured Finite-Volume Scheme

In this article, a new concept, “local triangle,” is described. A smoother pressure field is then obtained through the utilization of local triangles in a multiblock local triangulation method. The cell face velocity is corrected with a pressure-correction term which is usually underrelaxed. It is demonstrated that this relaxation factor has to be one, and it cannot be the general relaxation factor. It is indicated that the checkerboard oscillations are more significant at higher cell Reynolds numbers and, in turn, in this article, numerical simulations are mainly performed in turbulent flow.

Pressure corrected SPH for fluid animation

AbstractWe present a novel pressure correction scheme for the Smoothed Particle Hydrodynamics (SPH) for fluid animation. In the conventional SPH method, equations of state (EOS) are employed to relate the pressure to the particle density. To enforce the volume conservation, high speeds of sound are usually required, which leads to very small time steps and noisy pressure distribution. The problem remains one of the main reasons of numerical instability in SPH. In the paper, a new extra pressure correction scheme is proposed to transport the local pressure disturbance to the neighboring area and no solution of the Poisson equation is required. As a result, smoother pressure distribution and more efficient simulation are achieved. The proposed method has been used to simulate free surface problems. The results demonstrate the validation of the present SPH method. Surface tension and fluid fragmentation can be well handled. Copyright © 2009 John Wiley & Sons, Ltd.

Comparative high pressure Raman study of individual and bundled single‐wall carbon nanotubes

AbstractIn this work, individual single‐wall carbon nanotubes (i‐SWCNTs) and their parent bundled material (b‐SWCNTs) are investigated by means of high pressure Raman spectroscopy. Pressure application results in the broadening and intensity redistribution of the radial breathing modes (RBMs) in both materials. These changes are more pronounced in the case of bundled SWCNTs as it is also evident by the abrupt increase of the G+ bandwidth at ∼5.5 GPa, in contrast to the smoother pressure response of the individual tubes. Our experimental findings reflect the size dependent cross‐section deformation of carbon nanotubes which evolves differently in the two materials investigated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improved Maneuverability of Power Plants for Better Grid Stability and Economic Dispatch

Abstract The interaction between power systems and power plant becomes more and more important as power system operators look at the properties of power plants with respect to their primary and secondary control capabilities whereas plant operators look at the expenses that are incurred with frequency support operation. The New Unit Control method presented guarantees an exceptionally careful operation of the plant. Scheduled load variations will be realized according to the natural transfer response. Because there are less movements of the actuators you have less wear and tear on the plant. The smoother pressure and temperature control reduces the thermal stress of the plant thus increasing lifetime. The firing will become even more smooth if Condensate Throttling (C.T.) is used. C.T. is used not only on major frequency drops, but also during normal operation. Overfirring with the fuel controller can then to a large extend be reduced and replaced by the load reserves of the condensate throttling circuit. The New Unit Control has been proven over several years. It can be installed instead of any conventional unit control in any fossil-frred power plant. Experimental results are presented demonstrating the validity of the approach.

Plunging Wave Pressures on Semicylindrical Tube

Laboratory measurements of wave pressures due to plunging breakers were made on a 6-in. diam semicylindrical tube simulating a prototype concrete structure designed to be placed parallel to the coastline in the surf zone to intercept offshore transport of bean materials and thus preserve the beach. It was found during the wave uprush, that an impact pressure of short duration was recorded at the front of the tube, followed by smoother pressure variations in time. During the wave downrush, the volume of water transported across the tube flowed back under gravity. The pressure distribution on the beach side of the tube was relatively steady in the flow reversing process. The impulse-momentum theory was applied to investigate the behavior of impact pressures. The pressure distribution on the tube surface during the wave downrush was treated as a quasisteady case in which the Bernoulli principle for steady state condition applies.

Effect of Engine Structure on Noise of Diesel Engines

The objectionable noise of a diesel engine or ‘diesel knock’ is produced by the abrupt rise of cylinder pressure resulting from initial inflammation of the injected fuel. Worth-while reductions of this noise have been achieved by the control of the fuel injection characteristics producing a smoother pressure rise, but these are limited by performance considerations. Further reductions can only be obtained by structural changes of the engine and these are considered here. This has led to the construction of a number of structure research engines using two basically different principles for controlling vibration of the outer surfaces, namely, control by damping and control by stiffness. In each case conventional cylinder heads, pistons, connecting rods and crankshafts are used but with different crankcase cylinder-block constructions. The first principle, employing control by damping, entails a skeleton load carrying structure arranged so that it exposes to the sides of the engine only narrow edges which do not radiate much noise because of their small exposed surface area. Highly damped panels, which cannot be set into resonant vibrations, are attached to this load carrying framework. Using the second principle, i.e. control by increased stiffness, an engine with a cast magnesium crankcase having a wall thickness of about 1 1/4 in was constructed. Magnesium was chosen so that the thickness of the crankcase walls could be increased to 5 or 6 times that of a normal cast-iron crankcase of the same weight. In subjective units these engines are about half as noisy as a normal engine using the same working parts. There are distinct differences in the characteristics of the noise of the two engines. The magnesium engine shows a tendency to be less noisy in the low and middle frequency range and is a little noisier from about 4000 c/s upwards.