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numerical simulation

در نشریات گروه پزشکی
تکرار جستجوی کلیدواژه numerical simulation در مقالات مجلات علمی
  • Ali Mohseni, Mohammad Pooyan *, Somayeh Raiesdana, Mohammadbagher Menhaj
    Purpose

    Tumor-induced angiogenesis is a dangerous state of the tumor growth process in which solid tumors have a blood supply. Modeling has been a very important tool in studying tumor growth and angiogenesis. In this paper, we developed a cancer model by introducing tumor angiogenesis agents to better highlight the role of these chemical substances in tumor-induced vascularization. Our model can reconstruct the transition from a pre-angiogenic to a post-angiogenic state.

    Materials and Methods

    The proposed model comprises five variables: host cells (normal cells), immune cells, tumor cells, endothelial cells, and tumor angiogenesis agents. Chaotic behavior in the production of different populations of cells during vascular growth may confer survival advantages to tumors. Our model has a chaotic regime, which is an indication of tumor-induced angiogenesis dynamics. The fixed points are analyzed biologically, and stability analysis is performed via their eigenvalues. We analyzed the model dynamics via observability and bifurcation analysis.

    Results

    The numerical simulations illustrate biological and clinical findings about vascular tumors. The results show that the proposed model with the existence of tumor angiogenesis agents could capture both avascular and vascular stages of tumor growth. There is no effect of tumor cell killing rate via immune cells on the system dynamics. However, the increase of inhibitory factors of tumor angiogenesis agents leads to the termination of chaos.

    Conclusion

    Our results show the ineffectiveness of targeted treatments on the immune system, which has been confirmed by many negative treatment methods in immunotherapies. Tumor-secreted inhibitor factors are essential to regulating the angiogenesis process. However, increasing inhibitor factors via anti-angiogenic drugs would be a more effective therapeutic approach to eradicate metastasis.

    Keywords: Chaos, Angiogenesis, Mathematical Model, Vascular Tumor, Tumor Angiogenesis Agents, Numerical Simulation
  • MohammadAmin Naseri *, Seyed Esmail Razavi
    Introduction

     Vocal folds are responsible for sound generation. In unilateral vocal fold paralysis (UVFP), the recurrent laryngeal nerve, which controls the vocal folds, is paralyzed. Medialization laryngoplasty is a surgery in which an implant is inserted to push the paralyzed vocal fold to the centerline to recover phonation.

    Methods

     Here, a numerical simulation is used to calculate flow-related parameters to give insight into what happens in healthy and treated(implanted) vocal folds and their enhancement. In the present work, airflow over vocal folds is modeled considering fluid-structure interaction (FSI) and varying inlet pressure. The governing equations are discretized for fluid and solid domains and solved using the Galerkin finite element method. The boundary conditions for healthy and unilaterally paralyzed vocal folds were imposed to agree with real cases behavior.

    Results

     The results showed the effectiveness of medialization laryngoplasty in treating unilateral vocal fold paralysis concerning healthy vocal folds.

    Conclusion

     This simulation provided a better insight into treatment results for patient-specific cases.

    Keywords: Phonation recovery, Unilateral vocal fold paralysis, Fluid-structure interaction, Numerical simulation, Navier-stokes equations
  • Mohammad Kashfi, Parisa Fakhri, Ataollah Ghavamian, Payam Pourrabia, Fatemeh Salehi Ghalesefid, Parviz Kahhal
    Background

    Glass ceramic materials have multiple applications in various prosthetic fields. Despite the many advantages of these materials, they still have limitations such as fragility and surface machining and ease of repairing. Crack propagation has been a typical concern in fullceramic crowns, for which many successful numerical simulations have been carried out using the extended finite element method (XFEM). However, XFEM cannot correctly predict a primary crack growth direction under dynamic loading on the implant crown.

    Methods

    In this work, the dental implant crown and abutment were modeled in CATIA V5R19 software using a CT-scan technique based on the human first molar. The crown was approximated with 39514 spherical particles to reach a reasonable convergence in the results. In the present work, glass ceramic was considered the crown material on a titanium abutment. The simulation was performed for an impactor with an initial velocity of 25 m/s in the implant-abutment axis direction. We took advantage of smooth particle hydrodynamics (SPH) such that the burden of defining a primary crack growth direction was suppressed.

    Results

    The simulation results demonstrated that the micro-crack onset due to the impact wave in the ceramic crown first began from the crown incisal edge and then extended to the margin due to increased stress concentration near the contact region. At 23.36 µs, the crack growth was observed in two different directions based on the crown geometry, and at the end of the simulation, some micro-cracks were also initiated from the crown margin. Moreover, the results showed that the SPH algorithm could be considered an alternative robust tool to predict crack propagation in brittle materials, particularly for the implant crown under dynamic loading.

    Conclusion

    The main achievement of the present study was that the SPH algorithm is a helpful tool to predict the crack growth pattern in brittle materials, especially for ceramic crowns under dynamic loading. The predicted crack direction showed that the initial crack was divided into two branches after its impact, leading to the crown fracture. The micro-crack initiated from the crown incisal edge and then extended to the crown margin due to the stress concentration near the contact area.

    Keywords: Crack propagation, Mechanical properties, Monolithic crowns, Numerical simulation, Smooth particle, Hydrodynamics
  • محمدرضا سلطانی صدرآبادی، بهمن وحیدی*، روزبه ریاضی
    مقدمه

    تحلیل جریان خون در شریان های مغزی از موضوعات دارای کاربردهای بالینی پر اهمیت است. بررسی سوابق تحقیقاتی نشان می دهد که تاکنون در خصوص بررسی جریان خون در رگ های حلقه ویلیس با بررسی تنش برشی روی دیواره و هم چنین با در نظر گرفتن اثرات هایپرالاستیک بودن دیواره رگ و برهم کنش سیال و سازه(Fluid-Structure Interaction) در شرایط مختلف گرانش، ارائه نشده است. این مطالعه در حوزه طب هوا-فضا دارای کاربرد می باشد.

    مواد و روش ها: 

    برای بررسی جریان خون در شریان های مغزی و هم چنین تنش روی دیواره آن ها در شرایط مختلف گرانش از روش های دینامیک سیالات محاسباتی (Computational Fluid Dynamics) استفاده شده است. حلقه ویلیس به عنوان مجاری انعطاف پذیرمعرفی و رفتار دیواره رگ هایپرالاستیک فرض شد. حل جریان به روش برهم کنش سیال و سازه در دو شتاب گرانشی صفر و 8/9 متر بر مجذور ثانیه مورد بررسی قرار گرفت. برای طراحی هندسه، تعداد 248 تصویر سی تی آنژیوگرافی استفاده شده است. شرایط مرزی با احتساب چندشاخگی و خودتنظیمی، در ورودی و خروجی شریان ها اعمال شد.

    یافته های پژوهش:

     در حالت گرانش 8/9 متر بر مجذور ثانیه، مقدار حداکثر تنش برشی روی دیواره برابر 9/3 پاسکال و در حالتی که از گرانش صرف نظر شد، مقدار آن برابر با 5/6 پاسکال به دست آمد. با بررسی نتایج جریان خون در گرانش 8/9 متر بر مجذور ثانیه، فشارخون در رگ های بالایی حلقه ویلیس نسبت به فشارخون خروجی از قلب، کاهش چشم گیری داشته است.

    بحث و نتیجه گیری: 

    با توجه به این که نرخ تولید مواد بیوشیمیایی در پاسخ به محرک مکانیکی رابطه مستقیمی با تنش برشی دارد، پیش بینی می شود که در رگ های ارتباطی خلفی و قدامی (Anterior and posterior communication arteries) آن نوع واکنش های بیوشیمیایی بیشتر از دیگر رگ های مورد بررسی رخ دهد. از نتایج به دست آمده از این پژوهش می توان در آزمایش های فیزیولوژی فضانوردان و مطالعات مکانوبیولوژیکی عروق مغزی در شرایط پاتولوژیکی و نیز در مطالعات رشد و ترمیم در پزشکی بازساختی استفاده نمود.

    کلید واژگان: سیالات زیستی، عروق مغزی، گرانش، شبیه سازی عددی، تنش برشی
    Mohammad Reza Soltany Sadrabadi, Bahman Vahidi*, Rouzbeh Riazi
    Introduction

    Investigation of the blood flow in the cerebral arteries has important clinical applications. There is a dearth of research on fluid flow in the circle of Willis, analysis of shear stress on the arterial wall, and the effect of hyperelasticity of the arterial wall and fluid-structure interactions in different gravities. This study has practical implications in aerospace medicine.

     Materials & Methods

    In this study, computational fluid dynamics methods were used to study the blood flow in the cerebral arteries and the stresses on the arterial walls through alternations in gravity. The circle of Willis was introduced as a flexible tube with hyperelastic material properties. The solution of the flow was evaluated using the method of fluid-structure interactions in two gravitational accelerations of zero and 9.8 m/s2. A total number of 248 computed tomography angiography images were used to design the geometry. The boundary conditions considering the multi-branching and autoregulation were assumed at the inlet and outlet of the arteries.

    Findings

    Regarding the 9.8 m/s2 gravity, the maximum stress was equal to 3.9 Pascal. On the other hand, when gravity was neglected, the corresponding value was equal to 6.5 Pascal. Considering the results of blood flow in 9.8 m/s2 gravity, the blood pressure in the upper arteries and the circle of Willis was significantly reduced, compared to the blood pressure output from the heart.

    Discussion & Conclusions

    The rate of production of biochemical materials due to a mechanical stimulation had a direct relationship with shear stress. Therefore, it is anticipated that those chemical reactions occurred more in the anterior and posterior communicating arteries. The results of this study can be used in physiological experiments on the astronauts, mechanobiological studies of the cerebral arteries in pathological conditions, and investigations of tissue growth and repair in regenerative medicine.

    Keywords: Bifluids, Cerebral arteries, Gravity, Numerical simulation, Shear stress
  • حسن رجبی وردنجانی، حسن اصیلیان مهابادی*، مرتضی بیاره، مرتضی سدهی
    مقدمه
    معمولا در مطالعات سم شناسی ذرات آلاینده هوابرد، از اتاقکهای مواجهه تنفسی استفاده می شود که مسئولیت تامین و توزیع یکنواخت و پایدار اتمسفر آزمایشی را در منطقه تنفسی حیوانات آزمایشگاهی برعهده دارند. مطالعه حاضر با هدف طراحی، ارزیابی و بهینه سازی یک اتاقک مواجهه تمام بدن، ویژه مواجهه حیوانات آزمایشگاهی کوچک با آلاینده های ذره ای انجام شد.
    روش کار
    ابتدا مقالات و منابع علمی که جزئیات فنی و عملکرد اتاقک های مواجهه را بیان کرده بودند استخراج شد و مزایا، معایب و عوامل موثر بر عملکرد آنها تعیین گردید. سپس با لحاظ اصول دینامیک سیالات و شرایط استاندارد نگهداری حیوانات آزمایشگاهی، فرضیات طرح اولیه اتاقک تهیه شد. برای ایجاد توزیع یکنواخت ذرات در داخل اتاقک، از صفحات هدایت کننده جریان در مخروط فوقانی استفاده شد. به منظور بهینه سازی طرح اولیه از روش شبیه سازی عددی و نرم افزار ANSYS Fluent استفاده شد. ترسیم هندسه اتاقکها با استفاده از نرم افزار  Design modeler و شبکه بندی میدان محاسباتی با استفاده از نرم افزار ANSYS meshing انجام شد. ذرات استفاده شده دارای میانگین قطر آئرودینامیکی 10 میکرومتر، کروی، بدون بار و دارای چگالی 1400 کیلوگرم بر متر مکعب بوده و با سرعت گاز حامل وارد اتاقک شد. نمونه برداری غلظت ذرات در اتاقکها، در راستای شعاع استوانه و در فواصل 10 سانتی متری بر روی محور x انجام شد. سپس درصد ضریب تغییرات غلظت برای هر خط محاسبه شد. در تحلیل نهایی نتایج، طرح هندسه ای که دارای کمترین مقدار ضریب تغییرات غلظت ذرات در طول خط منتخب نمونه برداری بود، به عنوان بهترین طرح اتاقک انتخاب شد.  
    یافته ها
    اتاقک مواجهه تنفسی بهینه سازی شده در این مطالعه، دارای جریان دینامیک و شامل یک استوانه با دو مخروط فوقانی و تحتانی است. جریان دو فازی گاز و ذرات معلق از دهانه مخروط فوقانی وارد و ضمن گذر از صفحات هدایت کننده، در محیط داخلی اتاقک توزیع و از مخروط تحتانی خارج میگردد. مدلهای پیش فرض آشفتگی k- ε و Discrete Phase Model توانایی مدل کردن این مساله را داشته و در نهایت طرح شماره 7 با کمترین ضریب تغییرات غلظت معادل  08/4 درصد طرح بهینه بدست آمد.
    نتیجه گیری
    روش شبیه سازی عددی که برای طراحی و بهینه سازی این اتاقک استفاده شد، توانست با صرف هزینه بسیار کمتری نسبت به روش های تجربی، اطلاعات جامعی از میدان حل را فراهم نماید. تحلیل این اطلاعات منجر به انتخاب بهترین طرح اتاقک مواجهه برای تامین غلظت یکنواخت و پایدار ذرات آزمایشی در منطقه تنفسی حیوان شد.
    کلید واژگان: اتاقک مواجهه، شبیه سازی عددی، ذرات معلق، مواجهه تنفسی، شبیه سازی عددی
    Hassan Rajabi, Vardanjani, Hassan Asilian, Mahabadi*, Morteza Bayareh, Morteza Sedehi
    Introduction
    Usually, in the toxicological studies of airborne particulate pollutants, inhalation exposure chambers are used for providing and distributing the test atmosphere uniformly and stability in the respiratory zone of laboratory animals. The purpose of this study was to design, evaluate and optimize a whole-body exposure chamber, specifically for small laboratory animals exposed to particulate matter.
    Material and Methods
    In the first, the papers and scientific resources which had provided the technical details and performance of the inhalation exposure chambers were studied, and the advantages, disadvantages and those factors affecting their performance were extracted. Then the assumptions of the initial design of the chamber were prepared with regard to the principles of fluid dynamics and the standard conditions of lab animal housing. To create a uniform distribution of particles inside the chamber, guide plates of flow were used in the upper cone. Numerical simulation and ANSYS Fluent software were used to optimize the initial design. Drawing geometry of the chambers was done using Design modeler software and meshing of the computational field using ANSYS meshing software. The particles used had a mean aerodynamic diameter of 10 μm, spherical, inert, and a density of 1,400 kg. m^-3 and entered the chamber at the carrier gas velocity. Particle concentration was measured in the chambers along the cylindrical radius at 10 cm intervals on the x-axis. Then the percentage of variation coefficient of the particle concentration for each line was calculated. In the final analysis of the results, the geometry design with the lowest coefficient of variation of particle concentration along the selected sampling line was selected as the best chamber design.
    Results
    The optimized inhalation chamber has a dynamical flow and consists of a cylinder with two upper and lower cones. The flow enters from the upper cone and after passes through the guide plates, distributes in the interior of the chamber and exits from the lower cone. The k-ε turbulence and Discrete Phase Models could have modeled this problem. Design No. 7 was optimal design with the lowest coefficient of variation of the concentration (4.08%).
    Conclusion
    The numerical simulation method for planning and optimizing of the chambers, at a much lower cost than the empirical methods, was able to provide comprehensive information on the solution field. The analysis of this information led to the selection of the best chamber design to provide uniform concentration of the particles in the respiratory region of the animals.
    Keywords: Exposure chamber, Numerical simulation, Particulate matters, Inhalation exposure
  • Alireza Rezvani, sharif, Malikeh Nabaei *
    Introduction
    Endovenous laser treatment (ELT) is a new treatment method for the reflux of the great saphenous vein. A successful ELT is dependent on the selection of optimum parameters required to achieve optimal vein damage while avoiding side effects including skin burns. The mathematical modeling of ELT can be used to understand the process of ELT. This study was conducted to examine the effect of laser pullback speed and the distance between the vein and skin on the performance of ELT.
    Material and
    Methods
    The finite element method was used to develop optical-thermal damage models and simulate the process of ELT process. Firstly, light distribution was modeled using the diffusion approximation of the transport theory. On the second step, temperature rise was determined by solving the bioheat equation. Considering the temperature field, the extension of laser-induced tissue damage was estimated using Arrhenius model.
    Results
    Regarding the results, pullback speed and the distance between the vein and the skin distance can affect the process of ELT. Moreover, the pullback speed of 1 mm/s, 2 mm/s, and 4mm/s were suitable for the treatment of varicose veins located in a depth of 15 mm, 10 mm, and 5 mm, respectively.
    Conclusion
    In the ELT method, the pullback speed should be determined considering the geometry of the varicose vein segments, especially the distance between the skin and vein.
    Keywords: Endovenous laser treatment, Varicose vein, Bioheat transfer, Thermal damage, Numerical simulation
  • Morteza Asghari *, Mostafa Dehghani, Hossein Riasat Harami, AmirHossein Mohammadi

    In this communication, an advanced, simultaneous mass and heat transfer model has been developed to take a meticulous glance on the influences of different parameters on Persian Gulf seawater desalination using Sweeping Gas Membrane Distillation (SGMD) technique. This essay focuses on the increasing the distillate flux by investigation of the physical properties and feed temperature of the sweeping gas membrane distillation on the seawater desalination. The effects of operating parameters, including feed temperature, salt concentration, sweeping gas temperature, and heat transfer coefficient on the distillate flux of the Persian Gulf seawater have been investigated. The effect of feed temperature on temperature polarization has also been studied. By increasing the feed temperature from 25 oC to 60 oC, the temperature polarization increases and the polarization coefficient (TPC) decreases; for instance, for membranes with PP, the TPC decreases from 0.95 to 0.905. By increasing the feed temperature, higher fluxes are achieved for both the gas velocities. Therefore, by increasing the feed temperature from 50 oC up to 80 oC, the distillate flux grows 9 times. Also, the distillate flux for membrane with PVDF as polymer increased from 0 to 4.2 by increasing the feed temperature from 40 oC to 70 oC. The model predictions show a small error of 3.6% with the experimental data reported in literature which indicates the reliability of simulated results.

    Keywords: Distillate flux, numerical simulation, Seawater, Sweeping gas membrane distillation (SGMD), Temperature polarization
نکته
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