Research Paper
Fluid Mechanics
Miralam Mahdi; Mostafa Shariatnia; Majid Rahimi
Abstract
Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, Etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution ...
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Microbubbles are used in ultrasound imaging, targeted drug delivery, destruction of cancerous tissues, Etc. On the other hand, the demographic behaviors of small bubbles under the influence of Ultrasound have not been fully detected or studied. This study investigates the effect of the radial distribution of Sonazoid microbubbles on frequency response. And it is shown that the optimal subharmonic response is possible by controlling the size distribution. For this reason, the numerical simulation of the dynamic behavior of a coated microbubble is performed using MATLAB coding and the modified Rayleigh-Plesset equation. The Gaussian distribution is then applied, and the frequency response is investigated. It was shown that at a constant excitation pressure of 0.4 MPa and a standard deviation of 0.2, with increasing mean radius, the fundamental response increases. The subharmonic response increases, reach a peak value, and decreases. This peak value occurs for frequencies of 4,6, and 8 MHz in the mean radius of 0.8,1 and 1.6 μm. And by increasing the frequency of excitation, it is transferred to a smaller mean radius. It is also observed that the fundamental and subharmonic responses are amplified by increasing the excitation pressure. Studies show that the optimal subharmonic response can be achieved for various applications by controlling the size distribution of microbubbles.
Research Paper
Biomechanics
Puria Talebi Barmi; Bahman Vahidi
Abstract
Arterial embolism is one of the major causes of brain infarction. Investigating the hemodynamic factors of this phenomenon can help us to get a better understanding of this complication. The carotid artery is one of the primary tracts that emboli can go toward the brain through it. In this study, we ...
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Arterial embolism is one of the major causes of brain infarction. Investigating the hemodynamic factors of this phenomenon can help us to get a better understanding of this complication. The carotid artery is one of the primary tracts that emboli can go toward the brain through it. In this study, we used a 3D model of the carotid bifurcation, and two geometries, elliptical and spherical, were considered for the clots. Hyperelastic and visco-hyperelastic models were used for the mechanical properties of clots. The governing equations of the fluid are Navier-Stokes and continuity equations and have been solved in an Arbitrary Lagrangian-Eulerian (ALE) formulation through the fluid-structure interaction method. The hemodynamic parameters of fluid and shear stress on the wall of the carotid artery were calculated. Besides, by using ADINA software, the effective stress (Von Mises stress) of the clots and shear stress created on them were evaluated as well. Results revealed that the elliptical clot has more effects on the hemodynamic parameters of the fluid and the mechanical property of clots has significant effects on the amount of stress created on the clots. Furthermore, clot fracture will not occur due to this point that the maximum effective stress in this study was 1819 Pa but the creation of crack in clots is more probable, and this probability is more for the elliptical clot.
Research Paper
Heat and Mass Transfer
seyed mostafa moafi madani; Javad Alinejad; yasser rostamiyan; keivan fallah
Abstract
In the present study, the effect of the heating pipe profile on natural convection in a two –phase fluid inside a cavity have been investigated. This geometries has been simulated with the Lattice Boltzmann Method based on D2Q9 model for analyzing stream lines, dimensionless velocity field of fluid ...
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In the present study, the effect of the heating pipe profile on natural convection in a two –phase fluid inside a cavity have been investigated. This geometries has been simulated with the Lattice Boltzmann Method based on D2Q9 model for analyzing stream lines, dimensionless velocity field of fluid flow, solid particles volume fraction, temperature arrangement and Nusselt number. Theseparameters have been investigated in 3 cases of the cavity. The results signified by changing the geometry from a horizontal ellipse to a circular one and a vertical ellipse, the Maximum volume fraction of solid particles decreased. Also, by changing the geometry from a horizontal ellipse to a circular and vertical ellipse, larger velocity vectors have been formed around the geometry. The Nusselt number variations of circular and vertical ellipse geometries in the lower half have a similar behavior. The Nusselt number variation of horizontal ellipse geometry in the lower half is insignificant. Also, the Nusselt number of the circular geometry in the upper half is larger and uniform compared to the other two geometries. The highest average Nusselt number belongs to circular, vertical and horizontal ellipse geometries respectively.
Research Paper
Energy Systems
Mohammed Ridha Jawad Al-Tameemi; Samir Yahya; Saadoon Abdul Hafedh; Itimad D. J. AZZAWI
Abstract
A thermodynamic evaluation has been conducted on a combined heat and power system integrating a gas turbine (GT), a heat exchanger (HX1) and an organic Rankine cycle ORC. Traditionally, ORC bottoming GT cycle is limited to mechanical power production. The novelty of this study is to recover wasted heat ...
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A thermodynamic evaluation has been conducted on a combined heat and power system integrating a gas turbine (GT), a heat exchanger (HX1) and an organic Rankine cycle ORC. Traditionally, ORC bottoming GT cycle is limited to mechanical power production. The novelty of this study is to recover wasted heat from the GT cycle in multistage, which is used for the simultaneous production of mechanical power and hot water supply. In the first stage, the HX1 recovers heat from the GT cycle compressed air to heat the water stream. In the second stage, the ORC cycle recovers thermal energy from the GT turbine exhaust stream to produce extra mechanical power with the remaining latent heat used to heat the water. Two models have been proposed for comparison using ASPEN Plus software linked with the RAFPROP database. The modelled GT in this study has been adopted from an actual machine. The steady-state results show that the combined system has achieved 51.55% thermal efficiency compared with a standalone GT efficiency of 21% only. The thermal efficiency is divided into 24% mechanical power and 27.55% thermal load. The output hot water temperature is 65 oC. The outcomes of increasing the GT pressure ratio (12-25) are higher combined cycle net power output by up to 16% with a 9.5% reduction in the thermal energy rejected to the environment. Also, the GT efficiency increases from 20-22.5%; however, the final water temperature has declined from 67 to 60 oC, which is still appropriate for various heating applications.
Research Paper
Computational Fluid Dynamics (CFD)
Behnam Dilmaghani Hassanlouei; Nader Pourmahmoud; Pierre Sullivan
Abstract
In this article, an extracorporeal membrane oxygenator (ECMO) is simulated in 2D geometry using computational fluid dynamics (CFD). Momentum and mass transport equations were solved for the laminar flow regime (30 < Re < 130 for the blood channel) using the finite element method. In this study, ...
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In this article, an extracorporeal membrane oxygenator (ECMO) is simulated in 2D geometry using computational fluid dynamics (CFD). Momentum and mass transport equations were solved for the laminar flow regime (30 < Re < 130 for the blood channel) using the finite element method. In this study, the software COMSOL was used as the solver. To this end, the main problem of ECMO devices is the pressure drop and the risk of thrombus formation due to blood stagnation, so to solve this problem, the oxygen transfer rate to the blood should be increased. Therefore, in the present study, to optimize the oxygen transfer rate of the blood, three basic parameters were examined: blood flow velocity, oxygen velocity, and membrane thickness. Blood flow was considered at five different velocities (0.2, 0.4, 0.5, 0.6, and 0.8 mm/s). Results showed that increased blood flow velocity adversely affected oxygen permeability, increasing oxygen permeability from about 60% at 0.2 mm/s to about 24% at 0.9 mm/s. In addition, five different membrane thicknesses (0.04, 0.06, 0.08, 0.2, and 0.3 mm) were investigated, and, as expected, better oxygen exchange occurred as the membrane thickness decreased. We also found that the diffusion rate is about 40% for the 0.4 mm/s thin films and about 25% for the same inlet velocity and larger film thickness. Furthermore, the oxygen diffusivity increases from 28% to 38% as the oxygen gas velocity increases. However, oxygen velocities above 0.8 mm/s should not be used, as the range of oxygen diffusivity variation decreases with higher oxygen gas velocities.
Research Paper
Hydraulic and Pneumatic Systems
Lokesh Kumar; Nimai Pada Mandal
Abstract
This study focused on the flow and pressure fluctuations of a fixed displacement radial piston pump with a valve plate with silencing grooves, and the effect of the number of pistons (5, 6, and 7) has been investigated. Over the manifolds of the pump, valve plate silencing grooves are regarded as Top ...
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This study focused on the flow and pressure fluctuations of a fixed displacement radial piston pump with a valve plate with silencing grooves, and the effect of the number of pistons (5, 6, and 7) has been investigated. Over the manifolds of the pump, valve plate silencing grooves are regarded as Top Dead Center (TDC) and Bottom Dead Center (BDC). The mathematical modelling is run in MATLAB Simulink. Analysing the flow characteristics and volumetric efficiency of the pump with and without silencing groove valve plate configuration of pump. The opening and closing area pattern of the kidney port is also analyzed.The percentage reduction of flow and pressure fluctuation with the silencing groove is 19% and 16.16%, respectively, for Z = 7, as compared to the model without silencing groove valve plate. The volumetric efficiency of the model with silencing groove valve plate is improved from 1% to 2% as compared to the model without silencing groove valve plate. The lower the flow and pressure fluctuation coefficients, higher the flow rate and volumetric efficiency of the pump for the model with silencing groove valve plate.
Research Paper
Nonlinear Solution
Wah Yen Tey; Yu Maan Kong
Abstract
The theory of superposition of waves has been widely deployed in many engineering applications such as medical imaging, engineering measurements, and wave propagation in structures. However, these applications are prone to the interference of unwanted waves. The root cause of the weakness could be ascribable ...
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The theory of superposition of waves has been widely deployed in many engineering applications such as medical imaging, engineering measurements, and wave propagation in structures. However, these applications are prone to the interference of unwanted waves. The root cause of the weakness could be ascribable to the wave propagation pattern, which is not actively controlled. A new concept of imposing a time-lagging effect on the source of the wave as an active wave emission strategy is introduced and discussed in this paper. A numerical solver has been developed based on the finite volume Euler explicit method to investigate the wave propagation pattern when there is a time-lagged effect and frequency difference at the source of the wave. Our results reveal that time-lagged wave propagation will be more immune to the disturbance of other waves. The larger the time lag, the more resilient the wave is to resist the interference of other waves, even at a higher frequency. Time-lagged waves can be regarded as a promising active wave emission method that has many potential and robust engineering applications to be explored in the future.
Research Paper
Production Methods
Mohammad Ali Farsi
Abstract
Manufacturing systems are one of the complex systems for modelling and analysis, different types of structures may be utilized for this. Their behaviour is similar to Multi-state systems. Multi-state system configurations, possibly with load sharing and other structural dependencies are designed to provide ...
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Manufacturing systems are one of the complex systems for modelling and analysis, different types of structures may be utilized for this. Their behaviour is similar to Multi-state systems. Multi-state system configurations, possibly with load sharing and other structural dependencies are designed to provide high reliability/availability. Consequently, this scheme can help companies to improve efficiency and reduce operation cost. During operation and utilization, maintenance and part replacement contribute to keeping their performance. Decision-making about spares ordering is difficult because of the interconnection between spare parts inventory and maintenance strategy. In this paper, the characteristic parameters of spare parts inventory management and maintenance policies are jointly considered for multi-machines systems (manufacturing systems) with different types of dependencies among them (economic, load-sharing, and multi-state configuration). Two maintenance policies are considered: condition-based and preventive maintenance. The interactions among maintenance policies and spare parts management are considered for determining system cost and availability of a manufacturing system. These factors influences are investigated. load sharing factor and ordering time are more important and their influence are higher then others.
Research Paper
Optimization
ehsanolah Assareh; Iman poultangari; Afshin ghanbarzadeh
Abstract
A common method utilized in wind turbines is pitch angle control whereby via varying the angle of wind turbine blades around their own axis, power generated at high speeds of wind is held around maximum amount and is kept away from the severe mechanical stress on wind turbine. In current study, in order ...
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A common method utilized in wind turbines is pitch angle control whereby via varying the angle of wind turbine blades around their own axis, power generated at high speeds of wind is held around maximum amount and is kept away from the severe mechanical stress on wind turbine. In current study, in order to control pitch angle, a control method based on using PI controller is suggested. Therefore, gains of the PI controller are regulated through combining the Firefly evolutionary algorithm and MLP neural network in such a way that the controller at its output sends a suitable controlling signal to the pitch actuator to set the pitch angle and so by varying the blades pitch angle suitably at high speeds of wind, the produced generator power remains around its nominal value. A wind turbine 5MW made by NREL (National Renewable Energy Laboratory) has been utilized based on FAST software code to simulate and analyze the results. The simulation results show that proposed method has a good performance.
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