Fluid Mechanics Analysis Research Articles

Design and Implementation of MDO Integrated System for Valve Products

In view of the demands in multidisciplinary design optimization (MDO) of valve products, the MDO model for valves is established, which takes account of mechanical analysis, fluid mechanics analysis, thermal-mechanical coupled analysis and seismic analysis. On this basis, the MDO integrated system is constructed combined with some new techniques to solve the common and critical problems of optimal design of valves. The system takes interplay and coupling of each discipline into account, applies effective optimization strategy, information transmitting and concurrent design to get the synergistic effect produced by interaction of each discipline, and finally obtains the total optimum solution of valves, which, moreover, could provide technical reference for the practicality and commercialization of the integrated system in valves design optimization.

A framework for parallel computational physics algorithms on multi-core: SPH in parallel

In this paper, a simulation framework that enables distributed numerical computing in multi-core shared-memory environments is presented. Using multiple threads allows a single memory image to be shared concurrently across cores but potentially introduces race conditions. Race conditions can be avoided by ensuring each core operates on an isolated memory block. This is usually achieved by running a different operating system process on each core, such as multiple MPI processes. However, we show that in many computational physics problems, memory isolation can also be enforced within a single process by leveraging spatial sub-division of the physical domain. A new spatial sub-division algorithm is presented that ensures threads operate on different memory blocks, allowing for in-place updates of state, with no message passing or creation of local variables during time stepping. Additionally, the developed framework controls task distribution dynamically ensuring an events based load balance. Results from fluid mechanics analysis using Smoothed Particle Hydrodynamics (SPH) are presented demonstrating linear performance with number of cores.

Design of Valveless Micropump using Preliminary Characteristics from Fluid Flow

The need for cooling in advance thermal systems is ever in demand. The administration of such cooling will need miniaturization of the current pumping system for small-scale use. A valve less pump is one of the methods to create a small microscale flowrate pump. It has intake and outlet on the same side. Advances in fluid mechanics are able to capture the working principles of such pumps and give a close approximation of the pump characteristics. The fundamental aspect that a micropump will endure is analyzed from fluid mechanics analysis, is a key in the development of the model. The sizing and criteria of the pump is set based on fluid equations of mass, momentum and energy. A design is laid out by using computer-aided design (CAD) based on the voltage frequency that will be applied to the piezomaterial. The movement of the material due to current will cause the fluid to move, as the material will act as a diaphragm. The design is then analyzed using computational fluid dynamics (CFD) from the frequency inputs and a steady flow design is simulated. The reading of the small flowrate is analyzed and a proper method of designing the valve less pump is gathered.

Numerical simulation and experimental study of shaft pumping by laser structured shafts with rotary lip seals

A simulation model to predict pumping by shafts with various surface finishes, in combination with a rotary lip seal, has been developed and validated by experiment. The model consists of a fluid mechanics analysis of the flow in the sealing zone coupled with a deformation analysis of the seal. The experimental validation consists of pumping rate measurements with shafts whose surface structures contain laser generated oblique grooves. Plots of pumping rate vs. various parameters show good agreement between the model and experiment. Plots of torque vs. speed, as well, show good agreement between the model and experiment.

Konzept eines druckgesteuerten Mikrostents für die Glaukomtherapie

A pressure-controlled microstent could permanently normalise the intraocular pressure (IOP) for open-angle glaucoma therapy by drainage into the suprachoroidal space. The complex requirements demand new technical solutions as well as an improved understanding of specific cell biological processes at the implant's surface to develop effective local drug delivery (LDD) concepts and surface modifications. Fluid mechanical requirements were derived from physiological data and the analysis of commercial glaucoma implants. The technological basics for the production of suitable structures are refined ultra-short pulse laser technology and 2-photon polymerisation (2PP). All known glaucoma implants induce unwanted cell proliferation resulting in a loss of function. It is assumed that the activity of fibroblasts is low in the suprachoroidal space. However, it was seen that LDD concepts are required to control cell proliferation. Fibroblasts from sclera and choroidea were isolated und cultured as the most relevant cell types for in vitro investigation. Potential materials and drugs were investigated by cell viability tests for biocompatibility or suppression of cell viability. The fluid mechanical analysis leads to smallest stent lumina (ID = 50 µm) at anatomically suitable implant lengths (7 - 10 mm). Only pressure control can manage the individual conditions with changing IOP. Finite element analysis of valves showed the need for highly flexible structures. This can be achieved by combining basic structures with micromechanically active valves added by 2PP. The potential materials show perfect in vitro and in vivo biocompatibility. Ormocers which are best suited for 2PP are also highly biocompatible. The selected drugs paclitaxel and triamcinolon acetonide open a wide therapeutic window to impair fibroblast growth. The surgical procedure was established by implantation of prototypes in rabbit eyes, connecting the anterior chamber with the suprachoroidal space. Highly flexible implants are required for correct placement within the eye. The new concept of the microstent combines biomechanical approaches, technologies for microfabrication and current LDD concepts and opens new perspectives for glaucoma therapy.

Blade Excitation in Pulse-Charged Mixed-Flow Turbocharger Turbines

In this article, a fully three-dimensional computational modeling approach in the time and frequency domain is presented, which allows to accurately predicting fluid-structure interactions in pulse-charged mixed-flow turbocharger turbines. As part of the approach, a transient computational fluid mechanics analysis is performed based on the compressible inviscid Euler equations covering an entire engine cycle. The resulting harmonic orders of aerodynamic excitation are imposed in a forced response analysis of the respective eigenvector to determine effective stress amplitudes. The modeling approach is validated with experimental results based on various mixed-flow turbine designs. It is shown that the numerical results accurately predict the measured stress levels. The numerical approach can be used in the turbine design and optimization process. Aerodynamic excitation forces are the main reason for high cycle fatigue in turbocharger turbines and therefore a fundamental understanding is of key importance.

Complex chromosomal rearrangements in infertile males: complexity of rearrangement affects spermatogenesis

In this report, we describe 10 male cases of complex chromosome rearrangements (CCRs) with fertility problems: seven of them showed impairment of spermatogenesis, oligoasthenoteratozoospermia or azoospermia; in the other three cases, recurrent abortions were observed. The CCRs were characterized by conventional fluorescence in situ hybridization (FISH) and multicolor FISH methods as well as by the routine G-banding technique. CCRs found in three cases with recurrent abortions were double two-way exchanges, which were the simplest forms of CCRs; three oligoastenoteratozoospermic cases were double two-way exchanges or three-way exchanges. However, the CCRs in four azoospermic cases were much more complicated forms of CCRs. From our results and a review of the literature, we conclude that the complexity of CCRs might affect the severity of spermatogenetic impairment rather than the number of chromosomes involved or the location of breakpoints.

Scaling of coupled heat transfer and plastic deformation around the pin in friction stir welding

This paper presents a coupled phenomenological model of heat transfer and plastic flow around the pin in friction stir welding (FSW). The approach is analogous to the boundary layer analysis in fluid mechanics, and is based on the methodology of scaling. The results are a set of novel closed-form expressions for the maximum temperature reached in the process, the thickness of the shear layer, the shear stress around the pin, the torque and the thermal effect of the shoulder. The model presented focuses on the most common conditions encountered in the practice of FSW, which involve relatively slow translation velocities, relatively high rotation velocities and thin shear layers. The ultimate purpose of this model is to provide simple and accurate expressions useful for providing a temperature and strain rate context for metallurgical analysis of FSW and for the selection of process parameters when using FSW to join novel alloys.

Modeling the performance of a standard single stirred ultrafiltration cell using variable velocity back transport flux

A semi-analytical model based on unsteady state mass transfer has been developed for the prediction of permeate flux, membrane surface concentration and permeate side concentration during ultrafiltration in a standard single stirred cell. Starting from the basic fluid mechanical analysis of the system, stirrer induced back transport flux was evaluated considering the actual non-uniform velocity field and the final expression was incorporated in the fundamental mass balance equation. As a result the obtained partial differential equation (PDE) became associated with variable coefficients. The PDE after taking Laplace transform was reduced to standard confluent hypergeometric equation via a series of appropriate substitutions, which was finally mapped again in the time domain considering only the first four terms of the resulting series solution. Once the analytical form of a concentration field was obtained, permeate flux and the membrane surface concentration were evaluated using polymer solution theory and irreversible thermodynamics. Finally an iterative scheme has been designed to simulate the permeate flux and the membrane surface concentration under specified set of operating parameters. The prediction from this model was found to be in good agreement with experimental data obtained from PEG-6000/water system using cellulose acetate membrane of 5000 Da molecular weight cut-off.

Numerical method and analysis of computational fluid mechanics for photoelectric semiconducting detector

We propose a modified upwind finite difference fractional step scheme for the computational fluid mechanics simulations of a three-dimensional photoelectric semiconductor detector. We obtain the optimal l2-norm error estimates by using the techniques including the calculus of variations, the energy methods, the induction hypothesis, and a priori estimates. The proposed scheme is successfully applied to the simulation of the photoelectric semiconductor detectors.

Transient EHL analysis of an elastomeric hydraulic seal

Recent steady-state numerical analyses of reciprocating hydraulic rod seals have revealed many important details about the operation of such seals, including the fact that they generally operate with mixed lubrication in the sealing interface. However, these seals frequently operate under transient conditions, with the rod speed and sealed pressure undergoing cyclic variations with time. In the present study, a transient numerical model has been developed to take account of the varying rod speed. The model consists of a fluid mechanics analysis of the lubricating film of hydraulic fluid, a contact mechanics analysis of the contacting asperities on the seal lip and a structural analysis of the seal deformations. The fluid mechanics analysis consists of a finite volume solution of the Reynolds equation using a mass-conserving algorithm, which accounts for possible cavitation. The contact mechanics analysis utilizes the Greenwood–Williamson model. The structural analysis consists of a finite element analysis. Typical results are presented for an injection molding application. Of greatest importance is the net leakage per cycle. Also presented are the cyclic histories of such performance characteristics as the lubricating film thickness, contact pressure and fluid pressure distributions, the friction force on the rod and the instantaneous flow rate.

Ceramic foam substrates for automotive catalyst applications: fluid mechanic analysis

Several properties of ceramic foams render them promising substrates for various industrial processes. For automotive applications, the foam properties that need to be further studied include the substrate impact on the exhaust gas flow, in terms of pressure drop and flow uniformity. In this paper, pressure drop measurements are performed with different honeycomb and ceramic foam substrates, and pressure drop correlations are discussed. The flow uniformity upstream and downstream of the substrates is evaluated using particle image velocimetry. The results show that ceramic foam substrates induce higher pressure drop, while increasing the uniformity of the flow. In contrast to honeycomb monoliths, the flow uniformity downstream of ceramic foams does not decrease with increasing flow velocity. The higher flow uniformity of ceramic foams is not only caused by their higher pressure drop, but also by flow homogenization that occurs inside the ceramic foam structure, as a result of the momentum exchange perpendicular to the main flow direction.

The `upstream wake' of swimming and flying animals and its correlation with propulsive efficiency

The interaction between swimming and flying animals and their fluid environments generates downstream wake structures such as vortices. In most studies, the upstream flow in front of the animal is neglected. In this study, we demonstrate the existence of upstream fluid structures even though the upstream flow is quiescent or possesses a uniform incoming velocity. Using a computational model, the flow generated by a swimmer (an oscillating flexible plate) is simulated and a new fluid mechanical analysis is applied to the flow to identify the upstream fluid structures. These upstream structures show the exact portion of fluid that is going to interact with the swimmer. A mass flow rate is then defined based on the upstream structures, and a metric for propulsive efficiency is established using the mass flow rate and the kinematics of the swimmer. We propose that the unsteady mass flow rate defined by the upstream fluid structures can be used as a metric to measure and objectively compare the efficiency of locomotion in water and air.

Unsteady, three-dimensional fluid mechanic analysis of blood flow in plaque-narrowed and plaque-freed arteries

Fluid mechanic analysis is used to create and implement a metric to quantify the effectiveness of plaque removal (i.e., debulking) modalities in small arteries. The quantification is based on a three-dimensional, unsteady model of blood flow in complex tubular geometries which characterizes plaque-narrowed arteries. Blood flow unsteadiness is due to the heart-imposed temporal variations which occur during the cardiac cycle. The arterial geometries used for the analysis were determined by the reconstruction of ultrasonic images which were captured before and after debulking. Numerical simulation was used to implement the fluid mechanic model, and separate consideration is given to Newtonian and non-Newtonian constitutive equations. The results of the analysis indicates that the removal of the plaque led to an increase in the rate of blood flow of approximately 2.5, both during the systole and diastole portions of the cardiac cycle. This increase corresponds to the application of the same time-varying, end-to-end pressure difference across the artery segments. The shear stress on the artery wall, a major determinant of the buildup of plaque, is found to be higher for a debulked artery than for a plaque-narrowed artery. This outcome is favorable in that the higher the wall shear, the lower the rate of plaque formation.

Development and fluidic simulation of microneedles for painless pathological interfacing with living systems

In this paper, we investigate the development and fluidic analysis of microneedles integrated with painless blood extraction systems that aim to mimic the female mosquito’s blood sampling techniques in certain respects. The microneedles are fabricated by employing the sputtering deposition method. A fluid mechanical analysis is presented toward predicting the transport mechanisms inside the microneedle as dynamically evolving consequences of the resistive forces and the aiding surface tension influences. The theoretical predictions are comprehensively compared to experimental data, and excellent agreements are found for all cases.

Simulation and design of planarizing materials for reverse-tone step and flash imprint lithography

Reverse-tone step and flash imprint lithography SFIL-R shows promise as a cost-efficient, high-resolution patterning technique; however, the generation of satisfactory patterns requires the successful application of a planarizing topcoat over topography through spincoating. Photopolymerizable nonvolatile fluids are ideal topcoat materials because they planarize better than volatile fluids during spincoating and can continue to level after spincoating. Fluid mechanics analyses indicate that complete planarization using capillary force is slow. Therefore, defining the acceptable or critical degree of planarization DOPcrit becomes necessary. Finite difference simulation of the spincoat and postspin leveling processes was used to determine the planarization time for various topographic and material property combinations. A new material, Si-14, was designed to have ideal planarization characteristics low viscosity-15.1 cP; low shrinkage-5.1% and satisfy SFIL-R processing requirements oxygen etch resistance-33 wt% silicon, photocurable and was used to validate our models through profilometry and interferometry experiments. During spincoating, minimizing the spin speed generates more planar films; however, this increases the spin time. To rectify this problem, a two-stage spincoating process-a first step with high spin speeds to achieve the target thickness quickly and a second step with low spin speeds to improve planarization-was proposed and experimentally demonstrated.

Energy consideration for designing supercharged ram jet engines

The present work investigates the energy considerations and performance characteristics of a newly proposed supercharged ram jet engine. Thermodynamics and fluid mechanics analyses were developed to predict specific thrust, thrust-specific fuel consumption (TSFC), overall efficiency, and thrust-to-weight ratio of the engine. Compressor pressure ratio and efficiency, combustor temperature, and pressure losses in the burner and nozzle are considered as primary variables in the engine performance analysis. Performance characteristics are calculated to illustrate the effect of each parameter independently at different flight speeds. This is done while maintaining other parameters at given typical operating values. A computer program was developed to perform the iterative calculations. Results indicate that the compressor pressure ratio and the combustion product temperature are the most critical parameters in determining the performance of the engine. At compressor pressure ratio of 1.15–1.2, the typical static thrust-to-weight ratio is at maximum. Increasing combustion product temperature increases the thrust-to-weight ratio as well as TSFC. Finally, newly developed high power-to-weight ratio IC engine makes it possible for the supercharged ram jet engine to achieve high performance, in terms of thrust-to-weight ratio and TSFC. Copyright © 2007 John Wiley & Sons, Ltd.

Is varicocele prevalence increasing with age?

Varicocele is a bilateral vascular disease which occurs when the one-way valves in the internal spermatic veins, the testicular venous drainage system, malfunction. Based on new findings and fluid-mechanics analysis we showed that this process results in vertical blood columns, which cause pathological hydrostatic pressure in the testicular venous microcirculatory system. Ultimately, these pressures exceed the pressure in the arteriolar system. This unique phenomenon of reversal of pressures gradient between the arteriolar and venular systems leads to persistent hypoxia in the testosterone production site, namely, the Leydig cells. The result of bilateral varicocele is decreased testosterone production. Adequate treatment of bilateral varicocele significantly elevates the testosterone production. We found that the prevalence of varicocele increases with age with a rise of about 10% for each decade of life with the incidence reaching 75% in the eight decade of life. Based on our findings the following statements can be made: (1) varicocele prevalence is increased over time. (2) The rise of the incidence is about 10% for each decade of life. (3) 75% of men in the eight decade of their life have varicocele. As varicocele decreases testosterone production and it is reversible by appropriate treatment, it raises two interesting and important issues to be studied: (i) it is possible that varicocele accelerates the process of the ageing male. (ii) It is possible to retard, at least partially, the process of ageing in men by adequate treatment of bilateral varicocele.

Spatio-temporal Flow Analysis in Bileaflet Heart Valve Hinge Regions: Potential Analysis for Blood Element Damage

Point-wise velocity measurements have been traditionally acquired to estimate blood damage potential induced by prosthetic heart valves with emphasis on peak values of velocity magnitude and Reynolds stresses. However, the inherently Lagrangian nature of platelet activation and hemolysis makes such measurements of limited predictive value. This study provides a refined fluid mechanical analysis, including blood element paths and stress exposure times, of the hinge flows of a CarboMedics bileaflet mechanical heart valve placed under both mitral and aortic conditions and a St Jude Medical bileaflet valve placed under aortic conditions. The hinge area was partitioned into characteristic regions based on dominant flow structures and spatio-temporal averaging was performed on the measured velocities and Reynolds shear stresses to estimate the average bulk stresses acting on blood elements transiting through the hinge. A first-order estimate of viscous stress levels and exposure times were computed. Both forward and leakage flow phases were characterized in each partition by dynamic flows dependent on subtle leaflet movements and transvalvular pressure fluctuations. Blood elements trapped in recirculation regions may experience exposure times as long as the entire forward flow phase duration. Most calculated stresses were below the accepted blood damage threshold. Estimates of the stress levels indicate that the flow conditions within the boundary layers near the hinge and leaflet walls may be more detrimental to blood cells than bulk flow conditions, while recirculation regions may promote thrombus buildup.

Poincaré sphere representation for the anisotropy of phase singularities and its applications to optical vortex metrology for fluid mechanical analysis

A new technique for fluid mechanics measurement is proposed that makes use of the elliptic anisotropy of phase singularities in the complex signal representation of a speckle-like pattern. Based on the formal analogy between the polarization field of a vector wave and the gradient field of the complex signal, the Poincaré sphere representation has been used to characterize the phase singularities that serve as unique fingerprints attached to the seeding particles moving with the flow. Experimental results for flow velocity and acceleration measurement are presented that demonstrate the validity of the proposed optical vortex metrology for fluid mechanics measurement.