George P. Huang

Plasma excitation dependence on voltage slew rates in 10–200 Torr argon–nitrogen gas mixture DBD

An argon–nitrogen gas mixture dielectric barrier discharge (DBD) excited by fast rise time (~20 ns) and slow rise time (~100 ns) 3–5 kV high-voltage pulses was investigated in the pressure range 10–200 Torr. Time resolved emission intensities of Ar (2p1–1s2), Ar (2p9–1s5), N2 (C 3Πu–B 3Πg) and were recorded while the applied voltage was kept constant during measurements. The influence of different applied voltages and nitrogen concentrations on the observed emission spectra was also obtained. The reduced electric field, E/n, was derived from the ratio of the measured emission intensities by comparing excitation rates calculated using the BOLSIG+ code. The corresponding electron excitation energies, , were obtained. For the fast-pulse excited DBD, was in the range 6–8 eV and it decreased by about 0.5 eV for the lower voltage slew rate excitation under the same experimental conditions. The ionization rates were also derived from the corresponding E/n. The pulsed DBD plasma processes with different voltage slew rates were analyzed based on the dependence of the observed emission spectra and on the discharge operating parameters. The discharge voltage, current and power deposition were also estimated from applied voltage and current measurements.

Hovering Hinge-Connected Flapping Plate with Passive Deflection

T IS undoubtedly important to understand the aerodynamics offlexible wings of insects and birds to improve micro air vehicle(MAV) design. The flexibility mechanism and its effects onaerodynamic performance are not fully understood yet and stillattract a lot of attention, ranging from chordwise flexibility [1,2], tospanwise flexibility [3]. It is also worthy to note the study onpropulsion properties of flexible flapping wing by Yang et al. [4], inwhich flow and body interaction are handled by a strong-couplingapproach. However, why there is remarkable diversity of wingrigidity and flexibility across insect taxa and how the animalspassively or actively control their wing flexibility to obtainaerodynamically favorable kinematics at various phases of flappingare still mysteries. The underlying active or passive controlmechanism may be helpful from a design point of view, in terms ofreduced size of control surface, number of actuators, weight ofMAVs, and so on. Among the literatures on completely passiverotation of flapping wing, Ishihara et al. [5] investigated the passivepitching due to wing torsional flexibility and lift generation indipteranflight,anddemonstratedthatenoughliftcanbeproducedtosupport the weight of some diptera. The significance of passiverotationisfurtherconfirmedbyBergouetal.[6].Theydemonstratedthat aerodynamic and inertial forces are sufficient to pitch the wingwithout the aid of the muscles. Recently, Granlund et al. [7]experimentallystudiedpassivepitchingofhoveringflatplateswithafree-to-pivot hinge at the leading edge. They found that the plateproduces a motion akin to normal–hover, but with delayed rotation.However, there has been very limited study of the stroke amplitudeeffect on a flapping wing with passive rotation. Also, there is still alack of parametric studies on the aerodynamic performance offlapping wings with partial flexibility. In this paper, numericalsimulationsareconducted tostudytheaerodynamic performance ofa completely and partially rigid plate with passive rotation undervarious stroke amplitudes. Optimal aerodynamic performance andinput power are then obtained from these studies.

Numerical simulation of sloshing motion inside a two dimensional rectangular tank by level set method

Purpose – The purpose of this paper is to develop the numerical simulated methodology for sloshing motion of fluid inside a two dimension rectangular tank, and parametric studies were performed for three parameters – excitation frequency, excitation amplitude, and liquid depth.Design/methodology/approach – A numerically simulated methodology by using the cell‐centered pressure‐based SIMPLE scheme and level set method for the sloshing motion of fluid in a rectangular tank has been developed. The convection term in the Navier‐Stokes equations and the equations used in the level set method were treated by the second‐order upwind scheme. The temporal derivative terms were solved by the three‐level second order scheme. The diffusion term in the Navier‐Stokes equations alone was solved by the central‐difference scheme. All algebraic equations were solved by the point Gauss‐Seidel method. A fully implicit scheme to treat the level set distancing equation, written as the advection equation, was developed. In addi...

The Influence of Normal and Early Vascular Aging on Hemodynamic Characteristics in Cardio- and Cerebrovascular Systems

Age-associated alterations in cardiovascular structure and function induce cardiovascular disease in elderly subjects. To investigate the effects of normal vascular aging (NVA) and early vascular aging (EVA) on hemodynamic characteristics in the circle of Willis (CoW), a closed-loop one-dimensional computational model was developed based on fluid mechanics in the vascular system. The numerical simulations revealed that higher central pulse pressure and augmentation index (AIx) appear in the EVA subjects due to early arrival of reflected waves, resulted in the increase of cardiac afterload compared with the NVA subjects. Moreover, the hemodynamic characteristics in the CoW show that the EVA subjects in an older age display a higher blood pressure than that of the NVA with a complete CoW. Herein, the increased blood pressure and flow rate coexist in the subjects with an incomplete CoW. In conclusion, the hemodynamic characteristics in the aortic tree and CoW related to aging appear to play an important role in causing cardiovascular and intravascular disease.

Computational Fluid-Body Interaction of Hinge Connected Flapping Plate in Hover

Direct Numerical Simulation (DNS) is conducted on hinged plates to model the effects of passive deflection on aerodynamic performance of a flexible wing in hover. The plate is actively controlled by prescribed motion either at the leading edge only, or on part of the body; the rest of it is subjected to passive deflection due to fluid-body interaction. The influences of stroke-to-chord ratio are studied using one-link plate. Both the averaged lift-todrag ratio and the Root Mean Square (RMS) of lift and drag are deteriorated as the stroke amplitude gets shorter. Using a model of two-link plate, the hinge location is varied along chord to investigate the optimal aerodynamic performance obtained by passive deflection. In the range we have studied, the plate with mid-chord hinge and ±45∞ incidence limiter generates close lift-to-drag ratio, and smaller RMS lift and drag values, compared with its rigid counterpart.

1D simulation of blood flow characteristics in the circle of Willis using THINkS

Abstract One-dimensional (1D) simulation of the complete vascular network, so called THINkS (Total Human Intravascular Network Simulation) is developed to investigate changes of blood flow characteristics caused by the variation of CoW. THINkS contains 158 major veins, 85 major arteries, and 77 venous and 43 arterial junctions. THINkS is validated with available in vivo blood flow waveform data. The overall trends of flow rates in variations of the CoW, such as the missing anterior cerebral artery (missing-A1) or missing posterior cerebral artery (missing-P1), are confirmed by in vivo experimental data. It is demonstrated that the CoW has the ability to shunt blood flow to different areas in the brain. Flow rates in efferent arteries remain unaffected under the variation of CoW, while the flow rates in afferent vessels can be subject to substantial changes. The redistribution of blood flow can cause particular vessels to undergo extra flow rate and hemodynamic stresses.

A multiscale computational modeling for cerebral blood flow with aneurysms and/or stenoses

A 1-dimensional (1D)-3-dimensional (3D) multiscale model for the human vascular network was proposed by combining a low-fidelity 1D modeling of blood circulation to account for the global hemodynamics with a detailed 3D simulation of a zonal vascular segment. The coupling approach involves a direct exchange of flow and pressure information at interfaces between the 1D and 3D models and thus enables patient-specific morphological models to be inserted into flow network with minimum computational efforts. The proposed method was validated with good agreements against 3 simplified test cases where experimental data and/or full 3D numerical solution were available. The application of the method in aneurysm and stenosis studies indicated that the deformation of the geometry caused by the diseases may change local pressure loss and as a consequence lead to an alteration of flow rate to the vessel segment.

Experimental investigation on flow characteristics of a four-wing micro air vehicle

The aim of current research work on micro air vehicles is to realize their autonomous control, i.e. building a library for a lookup table that would apply to micro electronics. In doing so, comprehensive flight tests need to be carried out. In this study, a four-wing flapping MAV is built and a multi-discipline approach is used to design the MAV model. Precision manufacturing technology is introduced here. The finished micro air vehicle has a weight of 8 g and is tested for flight by remote control. The micro air vehicle can perform both hovering and forward flight with high maneuverability. Forward flight is investigated first in this paper. Particle image velocimetry system is employed to examine unsteady aerodynamic performance in selected flight conditions. The study reveals that the micro air vehicle model will provide enough lift at a 30° angle of attack and flapping frequency of 12 Hz, which is consistent with real-life forward flight observations.

Biological Flow Measurement using Optical Flow Method

The physics based optical flow method (OFM) was explored and applied to the blood flow measurement based on the digital subtraction angiography X-ray images. The objective of the present study is to examine the applicability of the physics-based OFM in the biological flow and evaluate the accuracy of OFM in recovering the velocity of blood flow in cerebral arteries. In order to examine the algorithm and conduct the error analysis, simulations are conducted on synthetic grid images (640×480 piexiels and 8 bits), where the intensity profiles across a grid line is Gaussian. The recovered velocity from OFM agrees well with the exact velocity distribution. Then, the improved OFM algorithm was applied on the DSA images of cerebral arteries including the cerebral arterial aneurysm and the parent internal cerebral artery. Again, synthetic parabolic velocity distribution and Oseen vortices were imposed to the vessel image and aneurysm image respectively to examine the accuracy of the current method. Compared to the grid image, the DSA image featured as low-intensity and isotropic distribution challenges the OFM algorithm. Appropriate intensification process combined with Gaussian filtering are applied to improve the accuracy of the OFM estimation. Finally the improved OFM was applied to the in-vivo measurement of the blood flow in the aneurysm to analyze the blood velocity distribution and hemodynamics.

An Experimental Investigation on Wing Optimization for a Four-Wing Flapper

An experimental investigation was conducted to study the flow characteristics of the flow around the flapping wings of a four-wing flapper as well as its lift and thrust coefficients. In the present study, a clap-and-fling type of four-wing flapper was designed and manufactured by using several flexible materials, such as PET film, latex and aluminized Mylar. Different cross-strut patterns and dimensions of wings were manufactured and tested for the optimization of wing designs. In addition to the lift and thrust measurements using a high sensitive force moment sensor unit, a high-resolution Particle Image Velocimetry (PIV) system was employed to achieve detailed flow field measurements to quantify the evolution of the unsteady vortex flow structure around wings and in the downstream of the flapper. The force measurements were analyzed in correlation with the detailed flow measurements to elucidate underlying physics in order to improve our understanding for an optimized flexible wing design and better performance for flapping-wing micro air vehicle.