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Modeling and Analysis of Pregnant Women Uterus Under Vehicle Vibrations

Irannejad Parizi, Mostafa | 2020

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 54181 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi; Firoozbakhsh, Keikhosrow; Mohammadi, Hadi
  7. Abstract:
  8. Nowadays, the use of vehicles is inevitable for all people including pregnant females. Vehicle vibrations during passing road bumps and holes is one of the pregnant females’ concerns. The aim of the present study is to develop a biomechanical model of a Uterus and Fetus Set (UFS) to evaluate its response to the inferior excitation, caused by the vehicle passing over speed bumps. The most important innovation of this research is "Analysis of the effect of vehicle speed and speed bumps characteristics on the risk of injury to the fetus." "Modeling the pregnant uterus complex separately from other abdominal organs", "Biomechanical modeling based on CT scan data from a real subject", "Providing low-risk, medium-risk and high-risk zones for passing over speed bumps", and "Determining safe speed limits for passing over speed bumps" are other innovations of the present study. It is assumed that the vertical excitation, during passing a road bump, causes uterine displacement in the shape of half-sinusoidal pulse of width d, and amplitude u̅. First, a finite element model of a uterus along with a fetus, placenta, amniotic fluid, and two most effective ligament sets is developed. The model geometry is developed based on CT-scan data and validated using anthropometric data. The model relates to the 32nd weeks of gestation, when the fetus is in head-down, occipito-anterior position. Applying Ogden hyper-elastic theory, material properties of uterine wall and placenta are developed and verified. After simulating the “Rigid-Bar” abdominal loading, findings are compared with the experimental abdominal response corridor, previously developed for a non-pregnant abdomen. Based on d, u̅, and vehicle speed, different excitation cases are simulated and the risk of injury in each case is calculated, using Head Injury Criteria (HIC). Second, considering the drag and squeeze effects of the amniotic fluid, a mathematical model representing the fundamental dynamic behaviors of a pregnant UFS is developed. After validating the model, 11544 different excitation cases are investigated, with a much lower computational cost than the finite element model. Three risk zones (Low, Medium, and High) are defined based on the fetal HIC and the effect of different excitation parameters are investigated. Finally, three risk-bounds, corresponding to 25%, 75%, and 100% risk of injury, are developed in the “width-amplitude” and the “frequency-amplitude” planes. As the results show, fetal HIC enhances, sub-exponentially, as the excitation amplitude (width) increases (decreases). The conditions which can push the system to higher risk zones, are investigated. Based on the results, speeds about 10km/h (independent of the bump characteristics) are considered safe speeds. On the other hand, a speed of 30km/h or higher may cause risk of injury to the fetus. Considering a typical speed-bump of width and excitation amplitude of 0.5m and 0.12m, respectively, the driver should not hit the speed-bump at 42km/h or more. We advise hitting such speed-bumps under 25km/h, based on this research findings. The results of this study can help to understand how a pregnant UFS is subjected to injury risk, caused by vehicle vibrations. Consequently, our knowledge can be expanded in order to improve maternal and fetal safety and progress in the field of safety instructions
  9. Keywords:
  10. Biomechanical Models ; Fetuses ; Finite Element Method ; Vehicle Vibration ; Fetal Head ; Pregnant Uterus Health ; Ogden Hyperelastic Material ; Abdominal Response ; Injury

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