Effects Of Momentum Exchange Research Articles

Two-Phase Fluid Modeling of Magnetic Drug Targeting in a Permeable Microvessel Implanted With a Toroidal Permanent Magnetic Stent

The key to effective magnetic drug targeting (MDT) is to improve the aggregation of magnetic drug carrier particles (MDCPs) at the target site. Compared to related theoretical models, the novelty of this investigation is mainly reflected in that the microvascular blood is considered as a two-phase fluid composed of a continuous phase (plasma) and a discrete phase (red blood cells (RBCs)). And plasma flow state is quantitatively described based on the Navier–Stokes equation of two-phase flow theory, the effect of momentum exchange between the two-phase interface is considered in the Navier–Stokes equation. Besides, the coupling effect between plasma pressure and tissue fluid pressure is considered. The random motion effects and the collision effects of MDCPs transported in the blood are quantitatively described using the Boltzmann equation. The results show that the capture efficiency (CE) presents a nonlinear increase with the increase of magnetic induction intensity and a nonlinear decrease with the increase of plasma velocity, but an approximately linear increase with the increase of the particle radius. Furthermore, greater permeability of the microvessel wall promotes the aggregation of MDCPs. The CE predicted by the model agrees well with the experimental results.

The one-loop matter bispectrum as a probe of gravity and dark energy

Gravity-induced non-Gaussianity in the large-scale structure of the Universe, characterised by higher-order statistics such as the bispectrum (three-point cumulant), is expected to contain rich cosmological information. A measurement of the bispectrum will not only improve the cosmological constraints, but also give us the possibility to probe gravity on cosmological scales. In this paper, we present a framework to numerically calculate the one-loop matter bispectrum based on standard perturbation theory (SPT). This approach allows general modifications to the standard ΛCDM model to be easily implemented. We demonstrate the performance of the bispectrum calculation in three representative cases, namely the Vainshtein-screened Dvali-Gabadadze-Porrati (DGP) model, the chameleon-screened Hu-Sawicki f(R) model and the phenomenological dark scattering (DS) momentum-exchange model. The predicted bispectra are then compared with measured results from a set of cosmological N-body simulations, and the impact of possible systematics arising from simplified or approximate treatments in the perturbative calculation is studied in detail. We find that the one-loop bispectrum calculation offers significantly more information on general screening and momentum exchange effects than the leading-order bispectrum calculation. Further, the accuracy of the one-loop prediction is shown to be comparable to non-linear fitting formulas over a wide range of wavenumbers (k≲0.3 hMpc−1) even at lower redshifts, z≲ 1.

Modeling two-phase flow of immiscible fluids in porous media: Buckley-Leverett theory with explicit coupling terms

Continuum models that describe two-phase flow of immiscible fluids in porous media often treat momentum exchange between the two phases by simply generalizing the single-phase Darcy law and introducing saturation-dependent permeabilities. Here we study models of creeping flows that include an explicit coupling between both phases via the addition of cross terms in the generalized Darcy law. Using an extension of the Buckley-Leverett theory, we analyze the impact of these cross terms on saturation profiles and pressure drops for different couples of fluids and closure relations of the effective parameters. We show that these cross terms in the macroscale models may significantly impact the flow compared to results obtained with the generalized Darcy laws without cross terms. Analytical solutions, validated against experimental data, suggest that the effect of this coupling on the dynamics of saturation fronts and the steady-state profiles is very sensitive to gravitational effects, the ratio of viscosity between the two phases, and the permeability. Our results indicate that the effects of momentum exchange on two-phase flow may increase with the permeability of the porous medium when the influence of the fluid-fluid interfaces become similar to that of the solid-fluid interfaces.

Comparison Study of Vibration Control Effects between Suspended Tuned Mass Damper and Particle Damper

The vibration control performance and its influencing factors of a tuned mass damper and a particle damper are examined by a single degree of freedom structure with such devices. The vibration control effects between these two dampers are also investigated. Increasing the mass ratio of the damper can improve the damping effects; under the condition of tuning frequency, the damping effects are remarkable. However, the more the deviation from the tuned frequency, the less controlling effects can be obtained. The damping effect of a particle damper is generally better than that of a tuned mass damper. For this test model, the particle damper can improve primary structure’s equivalent damping ratio 19 times to the original one’s, while the tuned mass damper can be 13 times. The reason lies in the fact that the particle damper can dissipate input energy by tuning mass, collision, impact, and friction between particles and the container and the momentum exchange effects between the secondary damper mass and the primary structure.

복단면 개수로흐름에서 홍수터 식생의 흐름저항을 반영한 1차원 모형

본 연구에서는 식생이 포설된 홍수터를 포함하는 복단면 개수로 흐름의 수위를 예측하기 위하여 유효 전단응력기법에 근거한 일차원 모형을 제시하였다. 제안된 모형은 주수로와 홍수터 접합부에서 발생하는 운동량 교환효과를 와점성계수 개념을 이용하여 반영할 수 있다. 주수로와 홍수터의 경계에서 발생하는 경계와점성계수는 3차원 레이놀즈 응력 모형을 이용하여 결정하였다. 경계와점성계수의 영향을 파악하기 위하여 민감도분석을 수행하였다. 경계와점성계수의 변화에 대하여 배수곡선의 변화는 크지 않았으나, 홍수터에서 부담하는 유량은 경계와점성계수에 비례하여 증가하였다. 마지막으로 식생된 홍수터의 식생밀도 및 침수비에 따른 경계와점성계수의 변화를 살펴보았다. 계산된 경계와점성계수는 식생밀도와 침수비에 비례하며, 대략<TEX>$(2-5){\times}\;10^{-4}$</TEX> 정도의 값을 갖는 것으로 나타났다. In this study, the 1D apparent shear stress model for vegetated compound open-channel flows was suggested. To consider the effect of momentum exchange between main channel and floodplain, the eddy viscosity concept was used in the present model. The interfacial eddy viscosity in the interface of main channel and floodplain was determined from the 3D Reynolds stress model. The evaluated interfacial eddy viscosity appears to be good agreement with those proposed previously. To investigate the effect of interfacial eddy viscosity, sensitive analysis was carried out. the computed backwater profiles are nearly identical with respect to the value of the interfacial eddy viscosity. However, the discharge conveyed by the floodplain changes is proportional to the interfacial eddy viscosity. Finally, the changes of the interfacial eddy viscosity due to the vegetation density and vegetation height were examined. The computed results of interfacial eddy viscosity are in proportion to the vegetation density and vegetation height, and the interfacial eddy viscosity has a range of <TEX>$(2-5)\;{\times}\;10^{-4}$</TEX>.

Effects of Velocity Head and Momentum Exchange on Critical Stable Sectional Area of Downstream Throttled Surge Tank

The velocity head and momentum exchange at the T-junction between the surge tank with a riser and the tail water tunnel of hydroelectric powerplants have been introduced by using the Gardel’s head-loss formula. The effects of the velocity head and momentum exchange on the critical sectional area of the downstream tank have been analyzed. With Thoma’s assumption, the critical stable sectional area of the downstream throttled surge tank is derived theoretically. The study shows that the velocity head has an unfavorable effect on water level stability in the downstream surge tank while the effect of the momentum exchange is positive. These two effects counteract. Thus, the critical sectional area of a downstream throttled surge tank is close to that of a corresponding simple surge tank. However, if the size and shape of a riser are optimized, the area of the downstream surge tank may be further reduced. It is also demonstrated that a downstream throttled surge tank can reduce electricity loss and easily meet...

Prediction of Cross Flow Due to Coolant Channel Blockages

Computer programs such as COBRA IIIC, which handle flow blockages, use a transverse momentum balance on a control volume of uniform width connecting any two subchannels to evaluate cross flow and momentum exchange effects on axial flow distribution. The transverse momentum balance employed has several constants that need to be determined empirically. This Note describes the method to develop such a correlation for three blockage configurations. It was found that with a constant width control volume, the data could not be satisfactorily correlated. A variable width control volume was therefore used to correlate the data behind flow blockage. A similar correlation could be developed ahead of the blockage but is not completed yet. Although the applicability of the correlation is limited to the blockage configurations analyzed, the variable width control volume method of correlating data that has evolved from this study is of general use in correlating such data.

Effect of Momentum-Exchange on the Fall Velocity of an Accreting Hydrometeor

Effect of Momentum-Exchange on the Fall Velocity of an Accreting Hydrometeor