Development of a New Interfacing Strategy for Fluid-Structure Interaction

Transcatheter aortic valve replacement (TAVR) is a minimally invasive procedure that provides an effective alternative to open-heart surgical valve replacement for treating advanced calcific aortic valve disease patients. However, complications, such as valve durability, device migration, paravalvular leakage (PVL), and thrombogenicity may lead to increased overall post-TAVR morbidity and mortality. A series of numerical studies involving a self-expandable TAVR valve were performed to evaluate these complications. Structural studies were performed with finite element (FE) analysis, followed by computational fluid dynamics (CFD) simulations, and fluid-structure interaction (FSI) analysis. The FE analysis was utilized to study the effect of TAVR valve implantation depth on valve anchorage in the Living Heart Human Model, which is capable of simulating beating heart during repeated cardiac cycles. The TAVR deployment cases where no valve migration was observed were then used to calculate the post-deployment thrombogenic potential via CFD simulations. FSI analysis followed to further assess the post-deployment TAVR hemodynamic performance for different implantation depths. The deployed valves PVL, geometric and effective orifice areas, and the leaflets structural and flow stress magnitudes were compared to determine the device optimal landing zone. The combined structural and hemodynamic analysis indicated that with the TAVR valve deployed at an aft ventricle position an optimal performance was achieved in the specific anatomy studied. Given the TAVR's rapid expansion to younger lower-risk patients, the comprehensive numerical methodology proposed here can potentially be used as a predictive tool for both procedural planning and valve design optimization to minimize the reported complications.

<abstract> <bold>Abstract.</bold> Pressure-compensating (PC) emitters can maintain a constant discharge within a wide range of working pressures, thus they have extensive application prospect in mountain regions where the hydraulic pressure in irrigation systems often changes greatly. Although the rapid design method for non-PC emitters based on CFD is quite mature at present, common CFD method is not suitable for the design of PC emitters because there exists a two-way coupling interaction between the fluid flow and elastic diaphragm. In order to improve the design accuracy and efficiency of PC emitters, the fluid-structure interaction (FSI) analysis was studied in this paper. In the FSI analysis procedure, adaptive mesh repair was adopted to refine the distorted fluid mesh. Incremental method and displacement-pressure finite element formula were used for the nonlinear analysis of the incompressible material. In this paper, SST K-ω turbulence model was used for the fluid analysis, while contact analysis method and Neo-Hookean Mooney-Rivlin rubber material model were adopted for the structure analysis. The results showed that the discharge was adjusted by a very small deformation of the diaphragm to reach a steady state. At last, compared with the test results carried out using the test samples made by rapid prototyping, the analyzed values were a little larger while the maximum relative deviation was within 2.5%. This verified that PC emitter's discharge could be predicted by FSI analysis accurately. In conclusion, FSI analysis is an efficient way to improve the design accuracy and reduce the test times for PC emitters.

This paper is an exploration of the numeric and visual properties of a square numerical grid containing 81 elements (“J9 Space”). J9 Space has been derived from the standard multiplication grid through the calculation of digital roots. Nested within J9 Space are eight smaller square grids. A three-dimensional representation of J9 Space has been created from the two-dimensional numerical grid, displaying the highly symmetrical properties contained within it. The three-dimensional representation is fundamentally a collection of two-dimensional triangular polygons that create a surface in three-dimensional space. J9 Space appears to be a fundamental part of the framework of the number system and has some interesting mathematical features. This paper also summarises the recording of a three-dimensional printed model of J9 Space as a denisyuk reflection hologram. This is an artistic impression of the model using a volume holographic technique. The author who has contributed the mathematical concept (Prashant Jadav) suggests that the use of digital roots to develop three-dimensional models from well-known mathematical tools is a new method by which to create and visualise structures within the number system.

The combination of thin-walled steel structure with concrete infill can be used as the alternative material properties in the building in Indonesia. This composite material is suitable for seismic-resistant building because it has more ductility than conventional material. In the tsunami event, some tsunami debris strikes the building and induced partial or full collapse of the building. The loading tip shape of tsunami debris which contacts to a tubular surface affects the local deformation or buckling mode of the thin-walled structures. In order to investigate the effects, we conducted three-dimensional nonlinear finite element analyses of concrete filled square steel tubular members subjected to concentrated lateral loads by using the finite element analysis (FEM) program MSC Marc/Mentat. The fiber element analysis is also performed to reduce the analysis time of FEM and simplify the analysis. The accuracy of the FEM and fiber element analysis is verified by the experiment. Being based on the parametric numerical study, it discusses the effect of axial load on the load-deflection relations. It shows that the higher the axial load, the more degradation the ductility of the structure.

Field investigation and finite element analysis on expansion and shrinkage strains of expansive concrete structures

This paper proposes the distributed collaborative information entropy adaptive Kriging (DC-IE-AK) method for evaluating high-cycle fatigue reliability of tuned turbo-fan blisk with circumferential inlet distortion. Based on information entropy adaptive Kriging (IE-AK), it incorporates a distributed collaboration strategy to build a multi-level Kriging model and an information entropy-driven iterative sampling strategy, using maximum vibration stress as the main failure criterion. Validated via an integrated wide-chord turbo-fan blisk case, with modeling in finite element analysis and fluid-structure interaction analysis considering circumferential inlet distortion, the method shows excellent performance, providing a feasible approach for high-cycle fatigue reliability evaluation of key aero-engine components.

In this study, 3D model of the bio-inspired blow fly wing Callphere Erytrocephala is created and aeroelastic analysis is performed to calculate its aerodynamical characateristic by use of numerical methods. In order to perform the flapping motion, a sinusoidal input function is created. The scope of this study is to perform aeroelastic analysis by syncronizing computational fluid dynamics (CFD) and structural dynamic analysis model and to investigate the unsteady lift formation on the aeroelastic flapping wing. Keywords: Micro air vehicle, Fluid-structure interaction analysis, Computational Fluid Dynamics, Structural dynamic analysis, Finite element analysis

Hemodynamic factors, induced by pulsatile blood flow, play a crucial role in vascular health and diseases, such as the initiation and progression of atherosclerosis. Computational fluid dynamics, finite element analysis, and fluid-structure interaction simulations have been widely used to quantify detailed hemodynamic forces based on vascular images commonly obtained from computed tomography angiography, magnetic resonance imaging, ultrasound, and optical coherence tomography. In this review, we focus on methods for obtaining accurate hemodynamic factors that regulate the structure and function of vascular endothelial and smooth muscle cells. We describe the multiple steps and recent advances in a typical patient-specific simulation pipeline, including medical imaging, image processing, spatial discretization to generate computational mesh, setting up boundary conditions and solver parameters, visualization and extraction of hemodynamic factors, and statistical analysis. These steps have not been standardized and thus have unavoidable uncertainties that should be thoroughly evaluated. We also discuss the recent development of combining patient-specific models with machine-learning methods to obtain hemodynamic factors faster and cheaper than conventional methods. These critical advances widen the use of biomechanical simulation tools in the research and potential personalized care of vascular diseases.

A non-linear analysis procedure has been developed to investigate the plastic behavior of the divider (or partition) plate in Steam Generators (SG) of Pressurized Water Reactors (PWRs). The integrity of the divider plate in the primary channel head of a Steam Generator of a Pressurized Water Reactor has to be verified for a postulated loss of coolant accident (LOCA). Primary stresses due to differential pressure Δp have to be analyzed for faulted conditions. A static elastic-plastic finite element analysis for the divider plate was performed showing unrealistically high plastic deformation due to the high differential pressure loading resulting from the assumption of rigid walls in the fluid analysis. Therefore the LOCA is analyzed in a Fluid Structure Interaction Analysis (FSIA), representing the divider plate as a single degree of freedom system (SDOFS) acting like a piston. The present paper explains how the Δp across the plate was correlated with an equivalent displacement ve and how the mass of the plate is considered. In the FSIA a realistic dynamic response of the divider plate is considered now, with a significant reduction of differential pressure Δp. The analysis results proved the resistance of the divider plate with sufficient margin.

A finite element based method for estimating natural frequencies of locally damaged homogeneous beams

Lower envelopes are fundamental structures in computational geometry, which have many applications, such as computing general Voronoi diagrams and performing hidden surface removal in computer graphics. We present a generic, robust and efficient implementation of the divide-and-conquer algorithm for computing the envelopes of surfaces in IR3. To the best of our knowledge, this is the first exact implementation that computes envelopes in three-dimensional space. Our implementation is based on CGAL (the Computational Geometry Algorithms Library) and is designated as a CGAL package. The separation of topology and geometry in our solution allows for the reuse of the algorithm with different families of surfaces, provided that a small set of geometric objects and operations on them is supplied. We used our algorithm to compute the lower and upper envelope for several types of surfaces. Exact arithmetic is typically slower than floating-point arithmetic, especially when higher order surfaces are involved. Since our implementation follows the exact geometric computation paradigm, we minimize the number of geometric operations, and by that significantly improve the performance of the algorithm in practice. Our experiments show interesting phenomena in the behavior of the divide-and-conquer algorithm and the combinatorics of lower envelopes of random surfaces.

This paper focuses on three-dimensional grasping and manipulation by robotic fingers with soft fingertips. The authors have proposed two-dimensional parallel-distributed model of a soft fingertip to describe the dependency of its potential energy to the relative orientation between the fingertip and the object. Here we extend the previous two-dimensional model to three-dimensional model, incorporating the rotation in three-dimensional space. We formulate the elastic potential energy stored in a soft fingertip due to the contact with the planar surface in three-dimensional space. We sketch the Lagrangian of the system consisting of a rigid prism grasped by three fingers with soft fingertips.

Modern ceramic femoral head components of total hip implants offer improved tribology and wear rates in comparison to traditional bearing materials. However, their brittle nature leaves them susceptible to fracture. As a result, manufacturers test their product lines with experiments designed to prove the mechanical failure strength of these components. These destructive proof tests apply a load to the ceramic samples in a manner that models in vivo conditions. The fracture strength is therefore determined to ensure the implants will withstand physiological loads. Finite element analyses (FEAs) are used to model these experiments and determine the mechanical effects on the heads. The standard method used in these experiments is adequate for new ceramic components, but is undesirable for testing surgically retrieved samples. This test has been recognized to damage the surface of the head's tapered cone which complicates finite element and fracture analysis. The goal of this thesis was to develop a destructive proof test that would minimize taper surface damage by loading ceramic heads in a physiological manner with water pressure, and to create an FEA model of the testing conditions. This concept originated in a patent held by CeramTec GmbH, and was built using a high pressure system that pressurized the inside of ceramic samples until failure. Specifically, this pressure was localized along the region that would be in contact with a metal femoral stem during implantation. The pressure applied to the heads was digitally recorded in ADMET's MTestQuattro software, and was used to select a constant rate of pressure increase. In all, two new alumina components from CeramTec's BIOLOX Forte product line were tested. No retrieval heads were tested, as this experiment was used as a pilot for determining the functionality of the designed experiment. Also, five FEA models were produced to simulate this experiment. Two modeled the conditions experienced by the two new alumina samples, whereas the other models were used for a material comparison. The comparison models were created by applying the maximum possible system pressure to heads made of the three most common ceramic materials: alumina, zirconia (Y-TZP), and zirconia toughened alumina (ZTA). The alumina samples fractured under pressures of 191.86 MPa applied at a rate of 1.96 MPa per second, and 192.60 MPa applied at 1.80 MPa per second. Based on the FEAs, the heads experienced maximum tensile principal stresses of 167.69 MPa and 168.33 MPa respectively. From these stress values, the critical depth for an edge crack to cause material failure along the pressurized region was calculated as 92.41 [mu]m and 91.70 [mu]m. Despite having a significantly lower burst strength than zirconia or ZTA, the two alumina samples required 93% of the test system's pressure capacity to cause failure. The results of the three remaining FEAs displayed similar magnitudes of stress between the modeled materials, and for this reason, no other ceramics were tested. Although there were limitations to this study, the test and FEA performed as required. During the testing procedure, one primary source of error was introduced by the equipment that was used to fixate the ceramic samples. Due to this, the stress values calculated for the fractured heads in the FEAs were likely underestimated. However, the designed test was capable of fracturing ceramic heads in a controlled and repeatable manner without causing significant damage to the surface of the taper. As such, this test should be considered a viable means for evaluating the strength of both new and retrieved ceramic heads.

Objective To explore the establishment of 3D thoracic model by finite element methods, and study the mechanical mechanism of minimally invasive surgery for correcting the chest wall deformity, and provide personalized surgery solution in the future. Methods According to admission and exclusion criteria, we selected 10 cases of pectus carinatum that received chest CT scan. The finite element model of pectus carinatum was established and analyzed by Mimics, ABAQUS, etc. The validity of finite element method for chest wall was verified by comparing the sternal displacement between the simulated values and actual values with the same force. Results The 3D finite element model of pectus carinatum was successfully established and analyzed. The stress distribution of the 10 cases in the posterior ribs was mainly in the 1-6 ribs on both sides, mostly concentrated in the 4th to 6th ribs, and the stress was symmetrical on both sides. Statistical analysis showed that the displacement value of the sternum was correlated, and the validity of the model was verified. Conclusion Mimics, ABAQUS and other finite element modeling and analysis software can effectively establish the thoracic 3D finite element model and mechanical analysis, which can help the further development of personalized minimally invasive surgery for correcting chest wall deformities. Key words: Pectus carinatum; Chest wall deformity; Finite element analysis

ObjectiveDual‐plate fixation was thought to be the gold standard for treating complicated bicondylar tibial plateau fractures, yet it was found to be hard to accommodate the posterior column in three‐column fractures. Currently, column‐specific fixation is becoming more and more recognized, but no comprehensive investigation has been performed to back it up. Therefore, the objective of this study was to validate the importance of posterior column fixation in the three‐column tibial fractures by a finite element (FE) analysis and clinical study.MethodsIn FE analysis, three models were developed: the longitudinal triple‐plate group (LTPG), the oblique triple‐plate group (OTPG), and the dual‐plate group (DPG). Three loading scenarios were simulated. The distribution of the displacement and the equivalent von Mises stress (VMS) in each structure was calculated. The comparative measurements including the maximum posterior column collapse (MPCC), the maximum total displacement of the model (MTD), the maximum VMS of cortical posterior column (MPC‐VMS), and the maximum VMS located on each group of plates and screws (MPS‐VMS). The clinical study evaluated the indicators between the groups with or without the posterior plate, including operation time, blood loss volume, full‐weight bearing period, Hospital for Special Surgery Knee Scoring system (HSS), Rasmussen score, and common postoperative complications.ResultsIn the FE analysis, the MPCC, the MPC‐VMS, and the MTD were detected in much lower amounts in LTPG and OTPG than in DPG. In comparison with DPG, the LTPG and OTPG had larger MPS‐VMS. In the clinical study, 35 cases were included. In the triple‐plate (14) and dual‐plate (21) groups, the operation took 115.6 min and 100.5 min (p < 0.05), respectively. Blood loss in both groups was 287.0 mL and 206.6 mL (p < 0.05), and the full‐weight bearing period was 14.5 weeks and 16.2 weeks (p < 0.05). At the final follow‐up, the HSS score was 85.0 in the triple‐plate group and 77.5 in the dual‐plate (p < 0.05), the Rasmussen score was 24.1 and 21.6 (p < 0.05), there were two cases with reduction loss (9.5%) in the dual‐plate group and one case of superficial incision infection found in the triple‐plate group.ConclusionThe posterior implant was beneficial in optimizing the biomechanical stability and functional outcomes in the three‐column tibial plateau fractures.