Kahar Osman

Computational Simulation of Boil-Off Gas Formation inside Liquefied Natural Gas Tank Using Evaporation Model in ANSYS Fluent

Research on the waste energy and emission has been quite intensive recently. The formation, venting and flared the Boil-off gas (BOG) considered as one of the contribution to the Greenhouse Gas (GHG) emission nowadays. The current model or method appearing in the literature is unable to analyze the real behavior of the vapor inside Liquefied Natural Gas (LNG) tank and unable to accurately estimate the amount of boil-off gas formation. In this paper, evaporation model is used to estimate LNG Boil-Off rate (BOR) inside LNG tank. Using User Define Function (UDF) hooked to the software ANSYS Fluent. The application enable drag law and alternative heat transfer coefficient to be included. Three dimensional membrane type LNG cargos are simulated with selected boundary condition located in the United States Gulf Coast based on average weather conditions. The result shows that the value of BOR agrees well with the previous study done with another model and with International Marine organization (IMO) standard which is less than 0.15% weight per day. The results also enable us to visualize the LNG evaporation behaviors inside LNG tanks.

The impact of the number of tears in patient-specific Stanford type B aortic dissecting aneurysm: CFD simulation

It is believed that the progression of Stanford type B aortic dissection is closely associated with vascular geometry and hemodynamic parameters. The hemodynamic differences owing to the presence of greater than two tears have not been explored. The focus of the present study is to investigate the impact of an additional re-entry tear on the flow, pressure and wall shear stress distribution in the dissected aorta. A 3D aorta model with one entry and one re-entry tear was generated from computed tomography (CT) angiographic images of a patient with Stanford Type B aortic dissection. To investigate the hemodynamic effect of more than two tear locations, an additional circular re-entry tear was added 24 mm above the original re-entry tear. Our simulation results showed that the presence of an additional re-entry tear provided an extra return path for blood back to the true lumen during systole, and an extra outflow path into the false lumen during diastole. The presence of this additional path led to a decrease in the false lumen pressure, particularly at the distal region. Meanwhile, the presence of this additional tear causes no significant difference on the time average wall shear stress (TAWSS) distribution except at regions adjacent to re-entry tear 2. Moderate and concentrated TAWSS was observed at the bottom region of this additional tear which may lead to further extension of the tear distally.

Boil-Off Gas Formation inside Large Scale Liquefied Natural Gas (LNG) Tank Based on Specific Parameters

Liquefied Natural Gas (LNG) fleets are coasting with various condition and behavior. These variable leads to different type of LNG fleets build every year with unavoidable generated Boil-off Gas (BOG). Estimation of BOG generated inside LNG tank play significant role in determines the ship specification and management method of BOG including venting, propulsion or requalification. Hence, in the present study, the right choices of boundary condition and parameter have been implementing in order to have good estimation amount of BOG evaporates for specific LNG tank. Three dimensional model of cargo with capacity 160000 m3 LNG carrier are simulate using ANSYS Fluent with specific ambient air temperature of 5oC and ambient seawater temperature of 0oC have been chosen as a calculation case, gain the total heat transfer rate and Boil-off Rate (BOR). The result shows that the calculation model and simulation are feasible with typical LNG fleet specification and International Marine Organization (IMO) standard.

Comparative analysis of realistic CT-scan and simplified human airway models in airflow simulation

Efforts to model the human upper respiratory system have undergone many phases. Geometrical proximity to the realistic shape has been the subject of many research projects. In this study, three different geometries of the trachea and main bronchus were modelled, which were reconstructed from computed tomography (CT) scan images. The geometrical variations were named realistic, simplified and oversimplified. Realistic refers to the lifelike image taken from digital imaging and communications in medicine format CT scan images, simplified refers to the reconstructed image based on natural images without realistic details pertaining to the rough surfaces, and oversimplified describes the straight wall geometry of the airway. The characteristics of steady state flows with different flow rates were investigated, simulating three varied physical activities and passing through each model. The results agree with previous studies where simplified models are sufficient for providing comparable results for airflow in human airways. This work further suggests that, under most exercise conditions, the idealised oversimplified model is not favourable for simulating either airflow regimes or airflow with particle depositions. However, in terms of immediate analysis for the prediction of abnormalities of various dimensions of human airways, the oversimplified techniques may be used.

Prediction on Behaviour of Blood Velocity and Mitral Leaflet Displacement in the Different Shapes of Heart Valve during Cardiac Cycle

The number of cases for heart diseases is increasing every day, even though medication technologies are always improving and moving forward. In this paper, the objectives of the study are to investigate the effect of blood flow velocity and leaflet displacement using different shapes of simplified two dimensional heart valve leaflets in the diastole condition. Four different shapes of heart valve were created and the simulation was performed by using Fluid Structure Interaction (FSI). From the results obtained, the triangle shaped leaflet showed it had the highest blood velocity changes and leaflets displacement changes in a one second period when compared to the other three shapes. The outcome simulation result shows that a large vortex formed behind the leaflet and leaflet deformed when the blood flow into left ventricle is agreed with the results in literature. In conclusion, four different shapes of two dimensional model of mitral valve has been developed and investigated for applying the most suitable shape in future artificial valve design.

THE EFFECT OF DIFFERENT LOCATIONS OF TRACHEAL STENOSIS TO THE FLOW CHARACTERISTICS USING RECONSTRUCTED CT-SCANNED IMAGE

The presence of tracheal stenosis would alter the flow path of the inhaled and exhaled air and subsequently changed the flow behavior inside the trachea and main bronchi. Therefore, it was our aim to investigate and predict the changes of flow behavior along with the pressure distribution with respect to the presence of stenosis on the tracheal lumen. In this study, actual CT scan images were extracted for flow modeling purposes. The images were then reconstructed to mimic the effect of different stenosis locations. This method overcomes the problem of the absence of actual images for different tracheal stenosis locations. The flow was subjected to different breathing situations corresponding to low, moderate and rigorous activities. The results showed that for flow over the stenosis farthest from the bifurcation, the pressure drop was insignificant for all breathing situations. At the same time, the inlet flow rate at the bifurcation showed less air flows into the right lung as compared to healthy flow conditions. On the other hand, for the flow over stenosis closest to the bifurcation, the pressure drop near the bifurcation area was very significant at high flow rate.

Gravitational Effect Formulation on In-House Air-Particle Flow Solver

Conventional efforts on the design of air-particle related environments are merely on heuristic and experience basis. Distribution control of particles in air such as dust, soot, smoke, chemical aerosol or any other pollutants are only simulated in current years when computational power is slowly fading from being an issue. Most commercial engineering software already equipped with the features but in-house solvers are always developed by institutions of related fields in order to fulfil their research needs. This work is preformed specifically to analyse the effect of additional gravitational effect feature in our newly developed in-house fluid-particle software. The effect is included in the Eulerian-Lagrangian solver so that it capable of simulating heavy particles in environmental air flows. Flow distributions of heavy particles such as liquid aerosol, sand or granular fertilizer are greatly affected by gravitational effect as compared to relatively buoyant particles such as smoke and light dust. Transient particle distribution in a ventilated room is simulated in this work. 10,000 particles that represent homogenous 2 mm Hemlock wood dust were randomly distributed in 3.3x2.8x5.9 m3 ventilated room that consist of two ceiling air intake and four bottom wall ventilation outlets. Homogeneous Hemlock wood solid sphere particles with diameter of 2 mm is simulated while the air intake is equivalent to 0.0944 m3/s. Simulation without the particle gravitational effect shows physically irrational results where 26 % of particles stayed at the top half of the room. Simulation with particle gravitational effect shows otherwise where 92 % of the particles settled at the bottom half of the room when measures at the same transient duration. This finding agrees well with distribution patters of previous experiments and simulation works. The introduction of gravitational effect in the newly developed in-house air-particle solver can be considered as the turning point where simulations of environmental air-particle related studies such as dust ventilation, aerosol control or even granular fertilizer distributions out of boom sprayer are possible.

Comparison of simplified and actual model of trachea and main bronchi in airflow simulation

Understanding of airflow in human airways is beneficial to medical field. Through the understanding, assessment on severity of airway disease and efficiency of medical inhalation drugs delivery can be assessed. For this purpose, an accurate and realistic human lung model is needed. With the variability in the outcomes based on both models notified, the reliability of the simplified models is questionable. It is the aim of this paper to determine the accuracy of the simplified models against actual human airways. Two models of trachea and main bronchi with different conditions; actual model and simplified were developed for comparison purpose. Different conditions of inspiratory breathing, 5 l/min, 9 l/min, 12 l/min and 15 l/min were imposed at the outlet with different ratio, 55% for right bronchus and another 45% for left. The results showed that the simplified model is reliable to provide accurate result on airflow in the airways. However, the level of accuracy diminished in regions with complex geometry i.e. highly irregular cross-sectional shape, rapid change in cross-sectional area, and around small radius curvature.

The Use of Mechanical Interlock in Dental Prosthesis

Good long term outcomes in prosthetic dentistry depends on the stability of its abutment-implant construct. One of the abutment designs normally used is a cylindrical taper where interference fit is achieved on large contact pressure and frictional resistance at the interface. Other designs include the screw and a combination of screw and taper. The stability of the implant body relative to the bone is also crucial because inadequate fixation would prevent bone integration. This study analysed a concept design where the abutment is locked mechanically once inserted into the dental implant body. Non-linear finite element contact analysis was carried out on the new design, as well as on a design based on a simple taper for comparison. Three dimensional model of the mandible was reconstructed from CT dataset and a section of the mandible was chosen for analysis. Pressure was applied on the top surface of the abutment simulating the normal biting force. Results showed that the mechanical interlock design was 5 times more stable than the simple taper design. However, the threshold limit for osseointegration was not exceeded for both implants. Stresses exerted on the distal region of the abutment for the taper design was an order of magnitude higher than the one found on the mechanical interlock.

Bio-based lubricants for numerical solution of elastohydrodynamic lubrication

This paper presents a programming code to provide numerical solution of elastohydrodynamic lubrication problem in line contacts which is modeled through an infinite cylinder on a plane to represent the application of roller bearing. In this simulation, vegetable oils will be used as bio-based lubricants. Temperature is assumed to be constant at 40°C. The results show that the EHL pressure for all vegetable oils was increasing from inlet flow until the center, then decrease a bit and rise to the peak pressure. The shapes of EHL film thickness for all tested vegetable oils are almost flat at contact region.