An-Shik Yang

Investigation of Pulsatile Flowfield in Healthy Thoracic Aorta Models

Cardiovascular disease is the primary cause of morbidity and mortality in the western world. Complex hemodynamics plays a critical role in the development of aortic dissection and atherosclerosis, as well as many other diseases. Since fundamental fluid mechanics are important for the understanding of the blood flow in the cardiovascular circulatory system of the human body aspects, a joint experimental and numerical study was conducted in this study to determine the distributions of wall shear stress and pressure and oscillatory WSS index, and to examine their correlation with the aortic disorders, especially dissection. Experimentally, the Phase-Contrast Magnetic Resonance Imaging (PC-MRI) method was used to acquire the true geometry of a normal human thoracic aorta, which was readily converted into a transparent thoracic aorta model by the rapid prototyping (RP) technique. The thoracic aorta model was then used in the in vitro experiments and computations. Simulations were performed using the computational fluid dynamic (CFD) code ACE+® to determine flow characteristics of the three-dimensional, pulsatile, incompressible, and Newtonian fluid in the thoracic aorta model. The unsteady boundary conditions at the inlet and the outlet of the aortic flow were specified from the measured flowrate and pressure results during in vitro experiments. For the code validation, the predicted axial velocity reasonably agrees with the PC-MRI experimental data in the oblique sagittal plane of the thoracic aorta model. The thorough analyses of the thoracic aorta flow, WSSs, WSS index (OSI), and wall pressures are presented. The predicted locations of the maxima of WSS and the wall pressure can be then correlated with that of the thoracic aorta dissection, and thereby may lead to a useful biological significance. The numerical results also suggest that the effects of low WSS and high OSI tend to cause wall thickening occurred along the inferior wall of the aortic arch and the anterior wall of the brachiocephalic artery, similar implication reported in a number of previous studies.

Investigation of Piezoelectrically Generated Synthetic Jet Flow

The purpose of this paper is to investigate the compressible turbulent synthetic jet flow characteristics of a dual diaphragm piezoelectric actuator. Experimentally, a flow visualization system was established to obtain the particle streak images scattered from 10-μm red fluorescent spheres for observing the synthetic jet flowfield produced by a dual diaphragm piezo actuator. The centerline velocity of the synthetic jet was also measured by using a hot-wire anemometry system. In the analysis, the computational approach adopted the transient three-dimensional conservation equations of mass and momentum with the moving boundary specified to represent the piezo diaphragm motion. The standard k-∈ two-equation turbulent model was employed for turbulence closure. For the actuator operating at the frequency of 648 Hz, the particle streakline images in the cross-sectional plane visualized a turbulent jet flow pattern in the far-field area. The hot-wire anemometry data indicated that the measured centerline velocity of synthetic jets reached 3.8 m/s at y/d= 50. The predictions were compared with the visualized particle streak images and centerline velocity of the synthetic jet in order to validate the computer code. The numerical simulation revealed the time-periodic formation and advection of discrete vortex pairs. Caused by the outward movement of the piezo diaphragms, air near the orifice was entrained into the actuator cavity when the vortex pairs were sufficiently distant from the orifice.

Design analysis of a piezoelectrically driven synthetic jet actuator

Technological advancement is being realized by using piezoelectric synthetic jet actuators to generate managing forces and moments with zero-net-mass-flux oscillatory jets for various air flow control applications. This paper firstly explores the synthetic jet flow behavior for a dual-diaphragm piezoelectrically driven synthetic jet actuator. In the experimental study, a flow visualization system was utilized to acquire the particle streak images scattered from red fluorescent spheres for examining the synthetic jet flow. The centerline velocity of the jet was measured with a hot-wire anemometer. For exploring the formation progression of synthetic jets, the numerical analysis implemented unsteady three-dimensional conservation equations of mass and momentum with a standard k?? two-equation turbulent model adopted for turbulence closure. The moving boundary was also treated to represent the motion of the piezo diaphragm under actuation. For a complete sinusoidal actuation cycle at an operating frequency of 648?Hz, the synthetic jet flow pattern was simulated and compared with the visualized image and measured centerline velocity distribution to validate the computer software. In general, the far-field flow structure was fairly similar to a common continuous turbulent air jet; whereas, the?predicted time-recurring formation of a vortex pair was observed in the near field. The surrounding air close to the slot was also drawn into the cavity of the actuator when vortex pairs advected sufficiently downstream. Numerical experiments were then extended to assess the performance of synthetic jet actuators by systematically varying the driving voltage, relative phase delay of frequency, width of the slot and depth of the actuator cavity.

CFD-Based Optimization of a Diamond-Obstacles Inserted Micromixer with Boundary Protrusions

Abstract: Effective mixing is vitally important to many microfluidic devices with applications in the areas of biotechnical industries, analytic chemistry and medical industries. In practice, passive micromixers are dependent on the proper layout of channel geometric configurations with obstacles deposited in microchannels to break-up and recombine the flow and reduce the diffusion path to improve the mixing performance. This study aims to investigate the mixing behavior of two different fluids in a passive micromixer with protruded boundary structures. The predicted mixing indexes at different longitudinal locations and Reynolds numbers achieved a good approximation of the experimental data in the literature for numerical simulations. The simulation results also indicated that intense vortices and secondary flows in spanwise planes were induced near the boundary protrusion regions to augment mixing efficiency along the flow course. In order to attain the optimal micromixer design, numerical calculations were attempted for the first time to thoroughly examine the effects of shape, length, width and placement of boundary protrusion structures on the mixing efficiency of a diamond-obstacles inserted micromixer.

Investigation of a piezoelectric valveless micropump with an integrated stainless-steel diffuser/nozzle bulge-piece design

To meet a growing need in biological and medical applications, innovative micro-electro-mechanical system (MEMS) technologies have realized important progress on the micropump as one of the essential fluid handling devices to deliver and control precise amounts of fluid flowing along a specific direction. This research proposes a piezoelectric (PZT) valveless micropump adopting an integrated diffuser/nozzle bulge-piece design. The pump mainly consisted of a stainless-steel structured chamber with dimensions of 8 mm in diameter and 70 μm in depth to enhance its long-term reliability, low-cost production, and maximized liquid compatibility. A PZT diaphragm was also used as a driving source to propel the liquid stream under actuation. As commonly used indices to describe pump operation, the delivered volumetric flow rates and pressures were determined at bulge-piece diameters of 2, 4 and 6 mm, with a driving voltage of 160 Vpp and frequency ranging from 50 to 550 Hz. Measurements and simulations have successfully shown that this micropump is capable of operating at a greater volumetric flow rate of up to 1.2 ml min−1 with a maximum back pressure of 5.3 kPa. In addition, the time-recurring flow behavior in the chamber and its relationship to the pumping performance were examined in detail.

A real-time convective PCR machine in a capillary tube instrumented with a CCD-based fluorometer

Abstract This research reports the design, analysis, integration, and test of a prototype of a real-time convective polymerase chain reaction (RT-cPCR) machine that uses a color charged coupled device (CCD) for detecting the emission of fluorescence intensity from an RT-cPCR mix in a microliter volume glass capillary. Because of its simple mechanism, DNA amplification involves employing the cPCR technique with no need for thermocycling control. The flow pattern and temperature distribution can greatly affect the cPCR process in the capillary tube, a computational fluid dynamics (CFD) simulation was conducted in this study for the first time to estimate the required period of an RT-cPCR cycle. This study also tested the PCR mix containing hepatitis B virus (HBV) plasmid samples by using SYBR Green I fluorescence labeling dye to assess the prototype performance. The measured results from the image-processing scheme indicate that the RT-cPCR prototype with a CCD-based fluorometer can achieve similar DNA quantification reproducibility compared to commercial machines, even when the initial DNA concentration in the test PCR mix is reduced to 10copies/μL

A Lego®-like swappable fluidic module for bio-chem applications

Abstract A Lego®-like swappable fluidic module (SFM) is proposed in this research. We designed and fabricated selected modular fluidic components, including functional and auxiliary types that can be effortlessly swapped and integrated into a variety of modular devices to rapidly assemble a fully-portable, disposable fluidic system. In practice, an integrated SFM uses finger-operated, electricity-free pumps to deliver fluids. Using a swirling mechanism, the vortex mixer can rapidly mix two liquids in a one-shot mixing event. We demonstrate the successful application of this SFM in several microfluidic applications, such as the synthesis of gold nanoparticles (AuNPs) from chloroauric acid (HAuCl4), and nucleic acid amplification from the Hepatitis B virus (HBV) with a capillary convective polymerase chain reaction (ccPCR).

Optimization of lift force for a bio-inspired flapping wing model in hovering flight

The lift force is an important component that affects the aerodynamic performance of bio-inspired flapping-wing micro aerial vehicles. However, there is a lack of endeavors in the optimization of the flapping wing parameters that affect the lift force of micro aerial vehicles. This research is therefore to establish a methodology that combines computational fluid dynamic simulation for the evaluation of the lift generation and wing parameters. The Taguchi’s framework for design of experiments, combined with the computational fluid dynamics simulations, is performed on a simplified robotic fly wing model used in the experiment found in Dickinson et al. (1999), under the hovering flight mode, to identify the most influential parameters on the lift generation of micro aerial vehicles. A commercial computational fluid dynamics code, ANSYS/FLUENT, along with a three-dimensional Navier–Stokes solver is used to simulate the unsteady flow field. With the optimization of the time-averaged lift force as the optimization objective, five typical parameters (flapping frequency, maximum angle of attacks during the upstroke and downstroke motions, stroke amplitude, and rotation type) in the flapping trajectory equation are selected as the input factors with each having four levels. Specific computational fluid dynamics cases are simulated in accordance with the chosen orthogonal arrays. By conducting statistical analyses with analyses of means and variance, the flapping frequency and the stroke amplitude are determined to be the two most influential parameters. The response surface of the time-averaged lift force and the power consumption contour are constructed with respect to these two parameters to determine the optimal combination for the generation of lift forces under a specific power constrain and provide a guideline for bio-inspired micro aerial vehicle designs.

Investigation of flow and heat transfer around internal channels of an air ventilation vest

The effects of a fabric’s ventilation and cooling are important to human comfort in the design of clothes. Persons in a high-temperature situation can experience imbalance of thermoregulation, which in turn results in the symptoms of heat exhaustion and heat stroke. The purpose of this research was to achieve cooling enhancement by designing air ventilation vests as an effective measure to control human thermoregulation in hot environs. In this study, the Taiwan Textile Research Institute devised a new air ventilation vest characterized by seven internal flow channels. The computational fluid dynamics software ANSYS/Fluent® was applied using the three-dimensional conservation equations of mass, momentum and energy to simulate the airflow and heat transfer phenomena within the internal channels. The incompressible turbulent flow was also treated with a standard k-ɛ two-equation model for turbulence closure. We compared the predicted steady axial velocities at the centers of channel exits with the measured data for software validation. The simulated results were employed to investigate the complicated flowfield and heat transfer phenomena around internal channels of the air ventilation vest. In practice, the design with the outlet arranged along the airflow direction produces a higher flow rate due to a relatively lower flow resistance, and thereby achieves better air-cooling outcomes. To enhance the cooling performance, simulations were also conducted to examine the influences of channel outlet design, inlet temperature and velocity on the convective heat transfer coefficient distributions over the inner channel surface of the vest.

Hybrid motion planning of a planar robot for a tracking problem with singularity

A motion planning problem for a planar robot on a path with singularity is studied in this paper. The motion planning problem is solved by a proposed hybrid motion planning method to guarantee the robustness of singularity and to reduce the computing load of the optimal-perturbation problem. To verify the proposed method, a tracking path with singularity is studied to compare the proposed method from the inverse Jacobin method. Moreover, a planar robot is designed and controlled via the PC-base architecture to implement the proposed method.