Computational Fluid-structure Interaction Research Articles

Study on flow characteristics and structural properties of vertical axial pump with low guide vane height

Abstract With the full construction of the South to North Water Diversion Project and the renovation of pumping stations, vertical axial flow pump devices have been widely used in various pumping station projects. This article uses the streamlined method to design the impeller and guide vanes of a vertical axial flow pump device. To analyze the hydraulic and structural characteristics, this paper uses CFD numerical simulation and fluid-structure interaction calculation methods. And the trend of output power change under different flow conditions was divided into three stages, elucidating the reasons for the sudden change in output power under flow conditions of 0.8Q-1.0Q. This article focuses on analyzing the internal flow state of the designed lower height guide vane segment to explore the problem of low guide vane height that is prone to occur during the design process. According to the research results, it is found that the lower height guide vane can also play a good role in stabilizing flow and recovering circulation under certain operating conditions. This article also studied the structural characteristics of the impeller and guide vanes, explaining the stress and strain distribution under design flow conditions.

Hydroelastic modelling of a deformable wave energy converter including power take-off

Given the advantages of flexible wave energy converters (FlexWECs), such as deformation-led energy harnessing and structural loading compliance, there has been a significant interest in FlexWECs in both academia and industries. To simulate the FlexWEC interaction with ocean surface waves, a 3D computational fluid-structure interaction approach is developed in this study. The fluid and solid governing equations are discretized using finite difference and finite element methods, respectively. An immersed boundary method is used to couple the two independent grid systems. A novel numerical technique is introduced to model the dielectric elastomer generator (DEG) as the power take-off (PTO). The wave energy capture performance is analysed for different PTO configurations and at various wave conditions. Based on the obtained results, the PTO damping coefficient and the relative wavelength range that maximizes the capture width ratio (CWR) are determined. The wavefield results also reveal the presence of wave-height enhancement and attenuation points around a single FlexWEC, providing potential site selection references when deploying multiple FlexWECs in an array.

Computational Fluid-Structure Interaction in Microfluidics.

Micro elastofluidics is a transformative branch of microfluidics, leveraging the fluid-structure interaction (FSI) at the microscale to enhance the functionality and efficiency of various microdevices. This review paper elucidates the critical role of advanced computational FSI methods in the field of micro elastofluidics. By focusing on the interplay between fluid mechanics and structural responses, these computational methods facilitate the intricate design and optimisation of microdevices such as microvalves, micropumps, and micromixers, which rely on the precise control of fluidic and structural dynamics. In addition, these computational tools extend to the development of biomedical devices, enabling precise particle manipulation and enhancing therapeutic outcomes in cardiovascular applications. Furthermore, this paper addresses the current challenges in computational FSI and highlights the necessity for further development of tools to tackle complex, time-dependent models under microfluidic environments and varying conditions. Our review highlights the expanding potential of FSI in micro elastofluidics, offering a roadmap for future research and development in this promising area.

Elucidating the mechanism of overcuring in microchannels fabricated via vat photopolymerization (VPP) for precise microfluidic chip printing

Vat Photopolymerization (VPP) technology is highly regarded for precision micromachining applications like microfluidic chip fabrication, owing to its fine resolution, adaptability, and rapid prototyping capabilities. However, the challenge of resin over-curing resulting from UV energy penetration poses a significant obstacle in microchannel printing. This study addresses this challenge by investigating the intricate relationship between resin properties and over-curing. Diverse microfluidic chips were printed utilizing VPP technology, and the overall cross-sectional over-curing characteristics of the channels were systematically examined. A novel combination of the classical UV light curing model and computational Fluid-Structure Interaction (FSI) model with the VPP printing process was proposed to examine the complex hydrodynamics and exfoliation dynamics within VPP-printed microchannels. The simulation results suggest that resins with higher viscosities and surface roughness are better suited for microchannel printing. Subsequent experiments using five different resins verified these findings and showed that the microchannels obtained with resins of lower viscosity and surface roughness resins have an irregular trapezoidal cross-section, which is uncontrollable and unpredictable and seriously affects the microchannel printing accuracy. Conversely, resins with higher viscosity and surface roughness have an ideal rectangular cross-section, which can be compensated by the model further refined printing to print microchannel. Finally, microfluidic chips were printed using "high precision 8 K resin" and "8 K-clay resin" with higher viscosity and surface roughness. The results proved that the microchannels printed by these resins had the desired rectangular cross-section, which was consistent with the "DLP light-curing" model. This study elucidates, for the first time, the intricate interplay between resin properties, printing structure, and microchannel over-curing, and this provides a solid groundwork for advancing high-precision microfluidic chip fabrication via DLP printing.

A reduced smoothed integration scheme of the cell‐based smoothed finite element method for solving fluid–structure interaction on severely distorted meshes

AbstractThis article describes an inexpensive partitioned coupling strategy for computational fluid–structure interaction (FSI) admitting negative‐Jacobian elements. The emphasis is very much on a reduced smoothed integration (RSI) scheme of the cell‐based smoothed finite element method (CSFEM) using four‐node quadrilateral (Q4) elements for a cost‐effective solution to the Navier–Stokes (NS) equations. In the discrete fluid field, each Q4 element is considered as one single smoothing cell so as to diminish the smoothed integration loops substantially. However, the RSI scheme does not respect the stability condition of smoothed Galerkin weak‐form integral in the CSFEM. To tackle this issue, a simple hourglass control is introduced to the under‐integrated formulation of the NS solver. Importantly, the stabilized RSI scheme has an inbuilt advantage of its enormous tolerance towards negative‐Jacobian elements. The developed technique is easy‐to‐implement and has been tested in various FSI examples adopting both fine and distorted meshes.

Analysis of blade noise with different root boundary conditions considering fluid-structure interaction effect

It is of certain importance for noise reduction to investigate the relationship between the aeroacoustic characteristics of blade and root boundary conditions when considering the fluid-structure interaction (FSI) effect. In this study, a set of precise dynamic models and two-way FSI calculation methods are developed to predict the dynamic load and response of blades more accurately. The natural frequency inaccuracy of the blade model is kept within 5% by comparing the results of the modal test using the ploy-reference time domain method and adopting the sensitivity analysis method with the blade beam stiffness as the modification parameter. Besides, based on the numerical results from the computational fluid dynamics method considering the FSI effect, the aeroacoustic characteristics of blades with different root boundary conditions are analyzed by adopting the Ffowcs Williams-Hawkings equations. The aeroacoustic characteristics of the NACA blade in hover are thoroughly discussed, with emphasis on the impact of different root boundary conditions on rotation noise. The result demonstrates that, the sound pressure level (SPL) difference of loading noise can reach 1.4 dB between blades with various root boundary conditions, while the SPL difference of thickness is only 0.4 dB.

Design, control, aerodynamic performances, and structural integrity investigations of compact ducted drone with co-axial propeller for high altitude surveillance

Compact multi-rotor unmanned aerial vehicles (UAVs) can be operated in many challenging environmental conditions. In case the UAV requires certain considerations in designing like lightweight, efficient propulsion system and others depending upon the application, the hybrid UAV comes into play when the usual UAV types cannot be sufficient to meet the requirements. The propulsion system for the UAV was selected to be coaxial rotors because it has a high thrust-to-weight ratio and to increase the efficiency of the propulsion system, a unique propeller was proposed to achieve higher thrust. The proposed propeller was uniquely designed by analyzing various airfoil sections under different Reynolds’s number using X-Foil tool to obtain the optimum airfoil section for the propellers. Since the design with duct increases efficiency, the Hybrid UAV presented in this paper has the modified novel convergent–divergent (C–D)-based duct which is a simplified model of a conventional C–D duct. The yawing and rolling maneuverings of the UAV could be achieved by the thrust vectoring method so that the design is simpler from a structural and mechanical perspective. The use of UAVs has risen in recent years, especially compact UAVs, which can be applied for applications like surveillance, detection and inspection, and monitoring in a narrow region of space. The design of the UAV is modeled in CATIA, and its further performance enactment factors are picked from advanced computational simulations relayed bottom-up approach. The predominant computational fluid dynamics (CFD) and fluid structure interaction (FSI) investigations are imposed and optimized through Computational Analyses using Ansys Workbench 17.2, which includes analysis of structural behaviour of various alloys, CFRP and GFRP based composite materials. From the structural analysis Titanium alloy came out to be the best performing materials among the others by having lower total deformation and other parameters such as normal and equivalent stress. The dynamics control response is obtained using MATLAB Simulink. The validations are carried out on the propeller using a thrust stand for CFD and on the duct through a high-jet facility for structural outcomes to meet the expected outcome.

Measuring tube structure optimization of coriolis mass flowmeter with liquid hydrogen

To improve the sensitivity of the Coriolis mass flowmeter (CMF) when measuring the mass flow rate of liquid hydrogen (LH2), this study investigates and compares the performance of measuring tubes with various shapes but identical lengths. The aim is to elucidate the mechanisms how the tube shapes affect the sensitivity of the CMF. An iterative fluid-structure interaction (FSI) calculation framework is developed on the ANSYS 2021R1 platform and validated using experimental results of water on a dual U-tube CMF. By employing the orthogonal test method in conjunction with numerical analysis, the tube structure is optimized. The variables considered for optimization include the length of the vertical and horizontal tubes, as well as the radius of the curved tube. Modal characteristics are analyzed, and their influence on the measurement performance of CMF is summarized. Additionally, the Coriolis force acting along the measuring tube, which is the primary factor causing the phase difference, is extracted to explore its impact. The results demonstrate that optimizing the measuring tube structure significantly increases measurement sensitivity, resulting in a larger phase difference. Furthermore, a dimensionless parameter is identified, exhibiting a strong correlation with measurement sensitivity. This parameter can serve as an approximation method for preliminary optimization of the measuring tube, effectively reducing the complexity of fluid-structure coupling calculations. More interestingly, the results of this research also indicated that the structural optimization results of the CMF with water and LH2 as the working fluids are the same.

Dynamics of settling disks in a cross-flow

Physical properties of rocks depend strongly on its grain packing which is determined by the natural process involving fluid-structure interaction during deposition. Here, we address the dynamics of settling solids with different sizes in a cross-flow numerically. This is an important aspect in rock formation process. Computational fluid-structure interaction usually involves the use of body-conformed grid. For the case of solid moving in a viscous fluid, the body-conformed grid has to be reconstructed in every time iteration which can be time consuming. The so-called Immersed Boundary method can be used to eliminate this grid reconstruction process. In this study, we use the couple of Immersed Boundary and Lattice Boltzmann Method (usually termed as IBLBM). In lattice Boltzmann, one does not require solving Poisson equation for pressure and a computation of intermediate field as in the usual fractional step procedure since velocity and pressure field can be obtained from the locally solved distribution function. These advantages make IBLBM can be easily employed. In this study, we perform simulations on the dynamics of a cluster of disks with two different values of diameter in a cross-flow. We compute the velocity distribution of the disks to study the sedimentation dynamics and we compare the results with a sedimentation process in a quiescent fluid. For the solid-fluid density ratio of 5 and incoming flow Reynolds number of 12, the velocity distribution is close to the normal distribution as also observed in the case of sedimentation in quiescent fluid.

Experimental and computational fluid-structure interaction analysis and optimization of Deep-V planing-hull grillage panels subject to slamming loads – Part II: Irregular waves

The paper presents a comprehensive experimental and numerical study of the structural response of a planing hull in irregular waves. Two grillage panels are investigated: a traditionally designed grillage panel based on current structural design methods and an optimized grillage panel based on loads evaluated by computational fluid dynamics (CFD) in regular waves and mathematical optimization methods. The structural response of these two grillage panels in irregular waves is investigated both experimentally and numerically. Experiments and numerical simulations show that the largest impacts do not necessarily occur when the wave height is largest, but rather when there is a deep trough and the wave height is low. Comparing the structural response in irregular waves with the structural response in regular waves shows a reasonable correlation. Nevertheless, a more severe regular wave condition is needed to capture the wave impacts needed for structural design. Numerical simulations show that they can better predict the vertical acceleration of the center of gravity than current structural design methods. It is discussed how American Bureau of Shipping practices lead to safe but conservative structural designs and how current computational methods lead to more efficient design solutions.

Numerical study on the effect of baffle structure on the heat transfer performance of elastic tube bundle heat exchanger

To make up for the research gaps in the existing literature on the effect of baffle structural parameters on the vibration and heat transfer of elastic tube bundle (ETB) heat exchangers, and improve the comprehensive heat transfer performance (HTP) of heat exchangers, based on an improved elastic tube bundle (I-ETB) heat exchanger used in previous studies, using the bi-directional fluid-structure interaction calculation method, the effects of the baffle structure improvement (height and curvature) on the comprehensive HTP of the I-ETB heat exchanger at different inlet velocities (Uin) were numerically studied. The results show that: while the height factor increases from 0.70 to 0.80, the vibration amplitude of I-ETBs decreases maximum by 10.05 %, and the heat transfer coefficient (h) of I-ETB increases maximum by 5.50 %. Increasing the baffle height improves the comprehensive HTP while suppressing the vibration of the I-ETBs. While the baffle curvature is 10°, the vibration of I-ETBs is the most intense, with the amplitude of the I-ETBs improving maximum by 10.79 %. The Nusselt number per unit pressure drop Nu/ΔP and performance evaluation criteria PEC and JF (a dimensionless number related to Colburn factor j and Fanning friction factor f) values of the heat exchanger all reach the maximum while the baffle curvature is 10°. The increase of baffle curvature has a positive effect on the vibration-enhanced HTP of the I-ETBs, and when the curvature is 10°, the comprehensive HTP of the heat exchanger is better.

Computational fluid–structure interaction framework for passive feathering and cambering in flapping insect wings

AbstractIn flapping insect wings, veins support flexible wing membranes such that the wings form feathering and cambering motions passively from large elastic deformations. These motions are essentially important in unsteady aerodynamics of insect flapping flight. Hence, the underlying mechanism of this phenomenon is an important issue in studies on insect flight. Systematic parametric studies on strong coupling between a model wing describing these elastic deformations and the surrounding fluid, which is a direct formulation of this phenomenon, will be effective for solving this issue. The purpose of this study is to develop a robust numerical framework for these systematic parametric studies. The proposed framework consists of two novel numerical methods: (1) A fully parallelized solution method using both algebraic splitting and semi‐implicit scheme for monolithic fluid–structure interaction (FSI) equation systems, which is numerically stable for a wide range of properties such as solid‐to‐fluid mass ratios and large body motions, and large elastic deformations. (2) A structural mechanics model for insect flapping wings using pixel modeling (pixel model wing), which is combined with explicit node‐positioning to reduce computational costs significantly in controlling fluid meshes. The validity of the proposed framework is demonstrated for some benchmark problems and a dynamically scaled model incorporating actual insect data. Finally, from a parametric study for the pixel model wing flapped in fluid with a wide range of solid‐to‐fluid mass ratios, we find a FSI mechanism of feathering and cambering motions in flapping insect wings.

Effect of TAVR commissural alignment on coronary flow: A fluid-structure interaction analysis

Background and ObjectivesCoronary obstruction is a complication that may affect patients receiving Transcatheter Aortic Valve Replacement (TAVR), with catastrophic consequences and long-term negative effects. To enable healthy coronary perfusion, it is fundamental to appropriately position the device with respect to the coronary ostia. Nonetheless, most TAVR delivery systems do not control commissural alignment to do so. Moreover, no in silico study has directly assessed the effect of commissural alignment on coronary perfusion. This work aims to evaluate the effect of TAVR commissural alignment on coronary perfusion and device performance. MethodsA two-way computational fluid-structure interaction model is used to predict coronary perfusion at different commissural alignments. Moreover, in each scenario, hemodynamic biomarkers are evaluated to assess device performance. ResultsCommissural misalignment is shown to reduce the total coronary perfusion by −3.2% and the flow rate to a single coronary branch by −6.8%. It is also observed to impair valvular function by reducing the systolic geometric orifice area by −2.5% and increasing the systolic transvalvular pressure gradients by +5.3% and the diastolic leaflet stresses by +16.0%. ConclusionsThe present TAVR patient model indicates that coronary perfusion, hemodynamic and structural performance are minimized when the prosthesis commissures are fully misaligned with the native ones. These results support the importance of enabling axial control in new TAVR delivery catheter systems and defining recommended values of commissural alignment in upcoming clinical treatment guidelines.

Simulating the mechanical stimulation of cells on a porous hydrogel scaffold using an FSI model to predict cell differentiation.

3D-structured hydrogel scaffolds are frequently used in tissue engineering applications as they can provide a supportive and biocompatible environment for the growth and regeneration of new tissue. Hydrogel scaffolds seeded with human mesenchymal stem cells (MSCs) can be mechanically stimulated in bioreactors to promote the formation of cartilage or bone tissue. Although in vitro and in vivo experiments are necessary to understand the biological response of cells and tissues to mechanical stimulation, in silico methods are cost-effective and powerful approaches that can support these experimental investigations. In this study, we simulated the fluid-structure interaction (FSI) to predict cell differentiation on the entire surface of a 3D-structured hydrogel scaffold seeded with cells due to dynamic compressive load stimulation. The computational FSI model made it possible to simultaneously investigate the influence of both mechanical deformation and flow of the culture medium on the cells on the scaffold surface during stimulation. The transient one-way FSI model thus opens up significantly more possibilities for predicting cell differentiation in mechanically stimulated scaffolds than previous static microscale computational approaches used in mechanobiology. In a first parameter study, the impact of the amplitude of a sinusoidal compression ranging from 1% to 10% on the phenotype of cells seeded on a porous hydrogel scaffold was analyzed. The simulation results show that the number of cells differentiating into bone tissue gradually decreases with increasing compression amplitude, while differentiation into cartilage cells initially multiplied with increasing compression amplitude in the range of 2% up to 7% and then decreased. Fibrous cell differentiation was predicted from a compression of 5% and increased moderately up to a compression of 10%. At high compression amplitudes of 9% and 10%, negligible areas on the scaffold surface experienced high stimuli where no cell differentiation could occur. In summary, this study shows that simulation of the FSI system is a versatile approach in computational mechanobiology that can be used to study the effects of, for example, different scaffold designs and stimulation parameters on cell differentiation in mechanically stimulated 3D-structured scaffolds.

Static aeroelasticity analysis of a rotor blade using a Gauss-Seidel fluid-structure interaction method

The present study introduces a Gauss-Seidel fluid-structure interaction (FSI) method including the flow solver, structural statics solver and a fast data transfer technique, for the research of structural deformation and flow field variation of rotor blades under the combined influence of steady aerodynamic and centrifugal forces. The FSI method is illustrated and validated by the static aeroelasticity analysis of a transonic compressor rotor blade, NASA Rotor 37. An improved local interpolation with data reduction (LIWDR) algorithm is introduced for fast data transfer on the fluid-solid interface of blade. The results of FSI calculation of NASA Rotor 37 show that when compared with the radial basis function (RBF) based interpolation algorithm, LIWDR meets the interpolation accuracy requirements, while the calculation cost can be greatly improved. The data transmission time is only about 1% of that of RBF. Moreover, the iteration step of steady flow computation within one single FSI has little impact on the converged aerodynamic and structural results. The aerodynamic load-caused deformation accounts for nearly 50% of the total. The effects of blade deformation on the variations of aerodynamic performance are given, demonstrating that when static aeroelasticity is taken into account, the choke mass flow rate increases and the peak adiabatic efficiency slightly decreases. The impact mechanisms on performance variations are presented in detail.

Mechanism of blood flow energy loss in real healthy aorta using computational fluid-structure interaction framework

Blood flow energy loss may correlate with the occurrence of vascular diseases. However, the mechanism of blood flow energy loss is still not fully explored. The objective of the present study is to reveal the mechanism of energy loss of blood flow in the healthy aorta. Two patients without aortic diseases are retrospectively screened from a clinical hospital. The computed tomography image is used to inversely reconstruct a three-dimensional geometric model of the healthy aorta. Non-invasive clinical measurements are applied to determine patient-specific boundary conditions. The fluid-structure interaction method is adopted to acquire high-resolution hemodynamics. A novel method is proposed to calculate the blood flow energy loss caused by aortic wall deformation. The distribution of blood flow validates the accuracy of the above computational framework, which could capture more than 90% of blood flow energy loss. Viscous friction of blood flow is the primary cause of energy loss, followed by aortic wall deformation, and finally turbulent dissipation. Energy loss due to viscous friction and wall deformation mainly occurs on the aortic vessel wall. The sum of these two energy losses approximates the total energy loss and may be associated with the initiation of aortic lesions. Besides, we find that the buffering efficiency of the real healthy aorta is about 80%. The mechanism of aortic blood flow energy loss is uncovered and these findings would inform the new hemodynamic markers and clinical assessment tool for the vascular wall.

Deciphering the connection between upstream obstacles, wake structures, and root signals in seal whisker array sensing using interpretable neural networks.

This study presents a novel method that combines a computational fluid-structure interaction model with an interpretable deep-learning model to explore the fundamental mechanisms of seal whisker sensing. By establishing connections between crucial signal patterns, flow characteristics, and attributes of upstream obstacles, the method has the potential to enhance our understanding of the intricate sensing mechanisms. The effectiveness of the method is demonstrated through its accurate prediction of the location and orientation of a circular plate placed in front of seal whisker arrays. The model also generates temporal and spatial importance values of the signals, enabling the identification of significant temporal-spatial signal patterns crucial for the network's predictions. These signal patterns are further correlated with flow structures, allowing for the identification of important flow features relevant for accurate prediction. The study provides insights into seal whiskers' perception of complex underwater environments, inspiring advancements in underwater sensing technologies.

Fluid-structure interaction study of hemodynamics and its biomechanical influence on carotid artery atherosclerotic plaque deposits

Atherosclerotic plaque deposits are common causes of blood flow disruption in the carotid artery bifurcation and the associated fluid mechanics has been extensively studied using Computational Fluid Dynamics (CFD) and Fluid Structure Interaction (FSI). However, the elastic responses of plaques to hemodynamics in the carotid artery bifurcation has not been deeply studied using either of the above-mentioned numerical techniques. In this study, a two-way FSI study was coupled with CFD technique, using Arbitrary-Lagrangian-Eulerian method, to study the biomechanics of blood flow on nonlinear and hyperelastic calcified plaque deposits in a realistic geometry of the carotid sinus. FSI parameters such as total mesh displacement and von Misses stress on the plaque, as well as flow velocity and blood pressure around the plaques, were analyzed and compared to variables such as velocity streamline, pressure and wall shear stress obtained from CFD simulation in a healthy model. The blood flow simulations reveal complete reversed blood flow behavior in the internal carotid artery, ICAs and external carotid artery, ECAs for both cases. In particular, this study suggests that plaques, irrespective of the masses, possess a high yielding response to hemodynamic forces at the attaching edges, while the surfaces are vulnerable to rupture.

Research on the heat transfer performance of an improved elastic tube bundle heat exchanger under fluid-induced vibration

The heat transfer performance (HTP) of an improved elastic tube bundle (IETB) was analyzed using a bi-directional fluid-structure interaction calculation method. The vibration-enhanced HTP of heat exchangers with different inlet velocities (Uin) and row number N were studied. The results show that the amplitude gradually increases as the Uin increase with a maximum increase of 309.98%. The amplitude with fixed shell side length (FL-heat exchanger) is generally higher than that with variable shell side length (VL-heat exchanger) under different row numbers. The average amplitude of the three directions increased by 4.55%, 11.54%, and 7.41%, respectively. The heat transfer coefficient (h) is directly proportional to Uin, and the comprehensive HTP gradually decreases with the increase of Uin. With the increase in the row numbers, h generally showed a downward trend. For the VL-heat exchanger, h decreases as the row number increases, which increases from N=6 to N=9, and h decreases by 13.85%. For the FL-heat exchanger, h first increases and then gradually decreases. The comprehensive HTP also maintained the same trend. Compared VL-heat exchanger and FL-heat exchanger, reducing the spacing between tube rows increases heat transfer per unit volume, leading to improved comprehensive HTP of the IETB heat exchanger.

Fluid-structure interaction analysis of amniotic fluid with fetus and placenta inside uterus exposed to military blasts

Introduction: Pregnancy-related trauma is one of the leading causes of morbidity and mortality in pregnant women and fetuses. The fetal response to injury is largely dependent on the timing of fetal presentation and the underlying pathophysiology of the trauma. The optimal management of pregnant patients who have suffered an obstetric emergency depends on clinical assessment and understanding of the placental implantation process, which can be difficult to perform during an emergency. Understanding the mechanisms of traumatic injuries to the fetus is crucial for developing next-generation protective devices. Methods: This study aimed to investigate the effect of amniotic fluid on mine blast on the uterus, fetus, and placenta via computational analysis. Finite element models were developed to analyze the effects of explosion forces on the uterus, fetus, and placenta, based on cadaveric data obtained from the literature. This study uses computational fluid-structure interaction simulations to study the effect of external loading on the fetus submerged in amniotic fluid inside of the uterus. Results: Computational fluid-structure interaction simulations are used to study the effect of external loading on the fetus/placenta submerged in amniotic fluid inside the uterus. Cushioning function of the amniotic fluid on the fetus and placenta is demonstrated. The mechanism of traumatic injuries to the fetus/placenta is shown. Discussion: The intention of this research is to understand the cushioning function of the amniotic fluid on the fetus. Further, it is important to make use of this knowledge in order to ensure the safety of pregnant women and their fetuses.