Pressure Loading Conditions Research Articles

Stress Calculation and Analysis of a 600MW Supercritical Boiler’s Steam-water Separator

The steam-water separator of a 600MW boiler has been chosen as the research object. By theoretical analysis’s method and finite element analysis, the stress and secure research has been carried out in the steam-water separator as the thick-walled pressure vessel. For its start-up and normal operation of the working process and features and considering the internal pressure load and thermal stress loading conditions, the initiation of separation stress and security analysis have been carried out about the steam-water separator. The primary stress at the continuum of the cylinder structure can be calculated by the formula, and the calculated results are basically in agreement with the simulated graphic results. And the research work provides a theoretical basis for on-line stress monitoring and life assessment.

Green technique solvent-free fabrication of silver nanoparticle–carbon nanotube flexible films for wearable sensors

Fabricating flexible/stretchable physical sensors has emerged as a topic of interest owing to the huge market demand for wearable medical devices and electronic skins for the regular and continuous monitoring of human health information. Herein, we report a green and efficient strategy for constructing a sensitive polydimethylsiloxane-derived wearable piezoresistive sensor, based on silver nanoparticle (AgNP)@multi-walled carbon nanotube (CNT) nanocomposite films. The developed sensing material exhibits good flexibility and electrical conductivity because of the interfacial effect between AgNPs and CNTs, leading to excellent sensing performances with good sensitivity, fast response time, low operating voltage, and mechanical stability, as measured under different pressure loading, bending angle, and percentage elongation conditions. In addition, finger movement recognition is sampled by testing the exceptional resistance change, and its practicality was further proven. Thus, the developed material has potential for application in wearable electronics. Notably, the entire sensor fabrication process is low-cost, environment-friendly, scalable, and industrially available, which is beneficial for industrial applications.

Generalized Beam Theory formulation for thin-walled pipes with circular axis

In this paper, the linear Generalized Beam Theory (GBT) is formulated for stress and deformation analysis of curved thin-walled circular pipes. In comparison to the analysis of straight pipes, the analysis of pipe bends is a complex problem due to the strong coupling effect of the longitudinal bending, warping and the cross-sectional ovalization. GBT is a beam theory especially formulated for thin-walled sections with the capacity of determining the cross-sectional deformation through the combination of a set of predetermined cross-sectional deformation modes. This nature of GBT makes it suitable to precisely identify and determine possible couplings between the considered GBT deformation modes and to analyze the behavior of pipe bends with high accuracy and computational efficiency. The formulation presented in this paper is based on Kirchhoff’s thin-plate assumption with consideration of additional shear deformation modes to overcome null transverse extension and shear membrane strain assumptions of classical GBT formulations. Here, to illustrate the application and capabilities of the developed GBT formulation, a set of numerical examples with in-plane, out-of-plane and pressure loading conditions involving a combination and coupling of bending, warping, torsional, axisymmetric and local deformations are presented. For the purpose of validation, these examples are compared with refined shell finite element models in both displacement and stress fields.

Compliance of Textile Vascular Prostheses Is a Fleeting Reality

Compliance is considered to be a major property influencing the long term performances of synthetic vascular substitutes that could play a role in anastomotic false aneurysm and intimal hyperplasia stenosis onset. Over the last decades, manufacturers have tried to develop substitutes that mechanically mimic arterial properties and avoid a compliance mismatch at the anastomoses in particular. However, data are missing about how initial compliance properties could change with time. The goal of this study was to evaluate how the compliance of vascular grafts evolves under cyclic loading conditions invitro. The compliance of three different models of commercially available textile polyethylene terephthalate (PET) grafts was evaluated. Tests were performed with and without their original coating. Compliance was assessed with a specific device dedicated to measure the deformations undergone by a graft under cyclic pressure loading conditions, using image analysis software. In each experiment, image analysis was performed under 60 and 140mmHg pressure loading conditions at loading start (H0) and after three, six, and 24h (H3, H6, H24) loading time. Average radial, longitudinal, and volumetric compliance was calculated from the obtained images. Twenty-four samples were tested. Results demonstrate that all values decreased significantly within only a few hours. On average, the loss of compliance after 3h of cyclic loading ranged on average from 35% for longitudinal compliance to 39% for radial compliance and 37% (p<.050) for volume compliance. After 24h, the loss of radial, longitudinal and volume compliance was respectively 63±3%, 60.5±2% and 61±7%. In this invitro model, PET graft compliance has already decreased significantly within 3h. The rapid loss of compliance identified in this experimental study helps explain the mismatch mentioned in clinical observations.

Static Tactile Sensing for a Robotic Electronic Skin via an Electromechanical Impedance-Based Approach.

Tactile sensing is paramount for robots operating in human-centered environments to help in understanding interaction with objects. To enable robots to have sophisticated tactile sensing capability, researchers have developed different kinds of electronic skins for robotic hands and arms in order to realize the ‘sense of touch’. Recently, Stanford Structures and Composites Laboratory developed a robotic electronic skin based on a network of multi-modal micro-sensors. This skin was able to identify temperature profiles and detect arm strikes through embedded sensors. However, sensing for the static pressure load is yet to be investigated. In this work, an electromechanical impedance-based method is proposed to investigate the response of piezoelectric sensors under static normal pressure loads. The smart skin sample was firstly fabricated by embedding a piezoelectric sensor into the soft silicone. Then, a series of static pressure tests to the skin were conducted. Test results showed that the first peak of the real part impedance signal was sensitive to static pressure load, and by using the proposed diagnostic method, this test setup could detect a resolution of 0.5 N force. Numerical simulation methods were then performed to validate the experimental results. The results of the numerical simulation prove the validity of the experiments, as well as the robustness of the proposed method in detecting static pressure loads using the smart skin.

Monte Carlo simulations of hydrogen adsorption in fullerene pillared graphene nanocomposites

ABSTRACTThe objective of this study is to investigate the hydrogen storage performances of three-dimensional periodic fullerene pillared graphene nanocomposites (FPGNs) consisting of covalently bonded fullerene units between graphene layers. Different forms of fullerenes were used as pillars to adjust porosity and enhance the hydrogen storage capacities of the proposed structures. The gravimetric and volumetric hydrogen uptakes of FPGNs were investigated via grand canonical Monte Carlo calculations under both low- and high -pressure (i.e. 0.01–100 bars) and different thermal (i.e. 77 and 298 K) loading conditions. The simulation results showed that a considerable enhancement in hydrogen adsorption performance could be achieved with the appropriate selection of fullerene size and loading conditions. The simulation results revealed that the FPGNs could uptake 10.3 wt.% hydrogen at 77 K. In addition, the deliverable hydrogen storage capacity of FPGNs could overpass 7.8 wt.% for the charge at 77 K, 100 bar and discharge at 160 K, 5 bar conditions which emphasises the potential of the proposed structures as future ultra-lightweight hydrogen storage media.

P1449 CMR-driven computational modeling of right ventricular flow dynamics

Abstract Introduction The analysis of intracardiac blood flow patterns can significantly contribute to improve the understanding and treatment of cardiovascular disease. In contrast to the substantial literature on the left side of the heart, there is currently a significant lack of knowledge about the fluid mechanics of the right heart – pulmonary circulation unit (RH-PCU), both in healthy and diseased conditions. Purpose It is conjectured that computational modeling can be a key element to enhance current imaging techniques and provide quantitative insights into the unique RH-PCU biomechanics. Here we present a novel methodology that allows personalized numerical simulations of right heart flows, through a proper combination of cardiac magnetic resonance (CMR) with computational fluid dynamics (CFD). Methods and results We developed a patient-specific pipeline from medical images to computational models, as depicted in the figure. First, the RV geometry is reconstructed from time-resolved CMR cine images, comprising short-axis and longitudinal slices of the heart, where feature-tracking techniques are used to extract the motion of the RV endocardium contours. A time-continuous description of the moving geometry is obtained through an image-registration algorithm based on diffeomorphic mappings. The moving model of the RV, including the outflow tract and proximal pulmonary arteries, is finally fed to a dedicated CFD solver. The tool is able to provide a detailed description of the velocity and pressure fields inside the right ventricle and proximal pulmonary arteries during all phases of the cardiac cycle. From these fields, global hemodynamic quantities such as vortex properties, kinetic energy, pressure gradients and hemodynamic forces can be computed. Conclusions CMR-driven computational modeling of intra-ventricular flow enables a promising approach for understanding and evaluating the biomechanical environment of the right heart. This high-fidelity framework can be applied to investigate the RV response and adaptation to abnormal pressure and/or volume load conditions. It can also be used to reproduce the virtual flow that would realize in hypothetical conditions, and therefore adds predictive capabilities to modern flow imaging. The analysis may allow to determine an association between blood flow patterns and disease progression, and ultimately lead to derive and validate imaging biomarkers of clinical significance. Abstract P1449 Figure. Pipeline for patient-specific modeling

Study of fracture behaviour of a composite laminate with central circular hole subjected to thermo-mechanical loading with Temperature fall

Abstract There is an increased usage of advanced composite structures due to several inherent benefits that they offer in comparison with the monolithic materials. But the application of these materials is being limited by the fact that the knowledge about the crack propagation and strength behaviour under application of loads and environmental conditions is not extensive. So, undertaking research in this direction is still very much important. In this paper, a circular crack which is present in the middle of a composite laminate was modelled and then subjected to combined (temperature + pressure) loading conditions where the temperature was considered to be falling and pressure remaining constant to study the fracture behaviour. The fracture behaviour of the composite laminate was studied using the strain energy release rate (SERR) value calculated using Virtual crack closure technique (VCCT). The effect of temperature fall, fiber angle and the combined thermo-mechanical loading conditions on the SERR value in the 3 different modes of fracture with a circular crack located in the middle of the composite laminate was studied and the influence of these parameter was discussed in this paper

Growth pattern and physiological characteristics of the temporomandibular joint studied by histological analysis and static mechanical pressure loading testing

ObjectiveThe aim of this study was to investigate the age-related changes in the articular disc, condyle, condylar fibrocartilage, and subchondral bone of the temporomandibular joint (TMJ) in rabbits. MethodsFemale New Zealand white rabbit aged 1, 4, 12, and 32 weeks were obtained. Each age group comprised 5 rabbits and was subjected to chondrocyte culture, histological assessment of the articular disc length, assessment of the anteroposterior diameter of the condyle, measurement of the fibrocartilage thickness, and assessment of the subchondral bone architecture. The production of Collagen, type II, alpha1 (COL2A1); SOX9; Collagen, type X, alpha1 (COL10A1); and Runt-related transcription factor 2 (Runx2) was detected via western blot. Six rabbits at the ages of 12 and 32 weeks were sacrificed for the mechanical pressure loading test (75 kPa, 3 days). Changes in the condyles after pressurization were observed via scanning electron microscopy and evaluated by micro-CT. ResultsSignificant enlargement of the condyle occurred from 4 to 12 weeks of age (p = 0.003); however, the length of the articular disc increased significantly from 1 to 12 weeks of age (p < 0.005). A rapid decrease in the cartilage thickness but an increase in the subchondral bone density occurred from 1 to 4 weeks of age and from 4 to 32 weeks of age in rabbit, respectively (p < 0.05). The expressions of COL2A1 and SOX9 gradually decreased from 1 to 32 weeks of age. The protein expressions of COL10A1 and Runx2 were maintained at a high level at 4–12 weeks of age. After static mechanical pressure loading, the damage and reduction in the bone mineral density (BMD) in the12-week-old group was greater than those in the 32-week-old group. ConclusionsAn inconsistency between the condyle and articular disc during growth and development may be a causal factor for temporomandibular disorders TMDs in adolescents. Our findings suggest that the response of the adult condyle to the mechanical pressure is significantly greater than that of the adolescent condyle; however, with regard to reconstruction, the situation is reversed, which may influence the pathological progress of TMDs.

Effects of pulse wave on the variation of coal pore structure in pulsating hydraulic fracturing process of coal seam

Coal pore structure is not only closely related to gas adsorption, but also affect the dynamic characteristics of gas desorption and diffusion. In order to understand the influence of pulsating hydraulic fracturing on the variation of coal pore structure, in this paper, the mercury intrusion method and liquid nitrogen adsorption method were used to quantitatively analyze the changes of coal porosity and pore size distribution under the action of pulse wave. And combined with scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) test to study the variation of minerals on the surface of coal samples. The results show that the influence of pulsating load on coal porosity is greater than that of static pressure load. The cumulative volume of micropores and their proportion decrease with the increase of pulsating frequency and pressure; the cumulative volume and proportion of macropores show an increasing trend; the cumulative volume of mesopores increases with increasing frequency, but the proportion increases in the low frequency phase, and decreases in the high frequency phase. There are two types of pores in the coal sample affected by the pulse waves: one is the expansion of the original pores, and the other is the new pores because the mineral crystals embedded in the coal body are washed out. The results have an important theoretical basis for the analysis of gas microscopic dynamics during pulsating hydraulic fracturing.

Numerical Simulation of the Tip Leakage Vortex Characteristics in a Semi-Open Centrifugal Pump

Tip leakage vortex has an important influence on the performance of semi-open centrifugal pumps. Simulations based on the three-dimensional Reynolds-Averaged Navier–Stokes were conducted to study the structural characteristics of tip leakage vortex and its effects on the internal flow field, and the Shear Stress Transport k-ω turbulence model was used to simulate the whole flow passage of centrifugal pumps with tip clearances of 0 mm and 1 mm. Then, the tip leakage vortex was analyzed using the relative vorticity transport equation. The numerical data and experimental results agreed well. The leakage vortex formed in the tip clearance led to 18.7% and 14.4% decrease in head and efficiency under design condition, respectively, and the bigger the flow rate, the fast the performance decreased. Tip leakage vortex formed at the leading edge of the blade moved along the suction surface. Whereas the tip leakage vortex formed near the middle of the blade extended to the pressure surface of the adjacent blade. This phenomenon deteriorated the flow field and induced passage vortex, thereby reducing the static pressure and blade load and changing the static pressure distribution law. The formation and development of leakage vortex could be attributed to the relative vortex stretching the term. The Coriolis force term could reflect the change of vorticity caused by leakage flow, and the viscous diffusion term served as the vorticity source.

Prediction of Failure Pressure in Pipelines with Localized Defects Repaired by Composite Patches

In recent years, fibrous composite materials have been used to repair pipelines in combination with commonly employed standards such as ASTM B31G and ASTM PCC2. Reinforcement and repair of pipelines without interruption are the advantages of these new methods. Pipe repair by composite patches with considering various types of surface damages and crack has been investigated in many previous works. In the present paper, a comprehensive model has been developed to predict the critical pressure for several defect types in static pressure loading condition using the ABAQUS finite element software. The effect of various defect patterns in API X65 Grade steel pipes is investigated by a ductile damage criterion. The obtained results are assessed using available experimental data. The first ply failure theory is employed to predict failure in composite patches. The effects of boundary conditions are considered using a semi-infinite element. The results generated from finite element simulations are compared with those from ASTM PCC2 standard. Moreover, the required minimum patch thickness for different live internal pressures is proposed. The extended finite element method is also applied to study the effect of patch layer thickness on crack propagation. The effect of initial crack angle on the critical internal pressure with and without patch is investigated too. The results indicate that the z symmetric boundary conditions are appropriate for pipelines. The estimation of the burst pressure using a ductile damage criterion is shown to be in good agreement with experimental data and ASME B31G. Furthermore, the estimated values for patch layer thickness obtained by the present approach agree well with ASME PCC2 standard. The obtained results also clearly indicate that using composite patches has no considerable influence on prevention of crack propagation.

Dynamic seal at the aortic neck-endograft interface studied using a novel method of cohesive zone modeling

BackgroundEndovascular aortic stent graft technology radically altered aortic aneurysm repair from a maximally invasive procedure to a minimally invasive approach. Whereas the overall principle of the repair remained the same, the surgeon ceded control of the proximal seal when suturing was eliminated. In endovascular aneurysm repair (EVAR), no longer does the surgeon control the precise placement of mechanical fasteners (sutures) between graft and tissue; rather, the graft is kept in place by creation of a seal zone that often lacks any mechanical fastening. The kinematic coupling condition is replaced by contact mechanics between the outer graft surface and the aorta. MethodsWe develop a novel computational methodology to fully model and characterize the aorta-endograft seal zone within a fully integrated aorta-EVAR model. The aorta, endograft, and intraluminal thrombus are modeled by standard finite element analysis in the limit of elastic response under pressure loading conditions. The seal zone in our simulations is fully dynamic and modeled using the cohesive zone method. Our methodology allows full separation of the aorta and endograft, simulating loss of seal and endoleak. ResultsUsing patient-specific geometry, we show that our approach is capable of predicting the location of rupture in an index patient who presented with a ruptured juxtarenal aneurysm. Applying our novel cohesive zone method analysis to the post-EVAR geometry, we studied the stability of the endograft under several seal zone strengths correlating to very weak, standard, and very strong seal. Loss of seal is shown to correlate to the propagation of an elastic front in the aortic neck. We propose that aortic neck dilation, which develops from graft deployment and pressurization, provides an energy release mechanism that drives seal zone failure: the elasto-adhesive seal model. ConclusionsWe develop the first ever fully integrated computational model of aorta-endograft seal. Our elasto-adhesive seal model provides the first biomechanical model to evaluate seal loss. We hope that our method will provide a rich tool set with which to study the vexing problems of type I endoleak and help guide the development of technologies to optimize seal.

Modeling the mitral valve.

This work is concerned with modeling and simulation of the mitral valve, one of the four valves in the human heart. The valve is composed of leaflets, the free edges of which are supported by a system of chordae, which themselves are anchored to the papillary muscles inside the left ventricle. First, we examine valve anatomy and present the results of original dissections. These display the gross anatomy and information on fiber structure of the mitral valve. Next, we build a model valve following a design-based methodology, meaning that we derive the model geometry and the forces that are needed to support a given load and construct the model accordingly. We incorporate information from the dissections to specify the fiber topology of this model. We assume the valve achieves mechanical equilibrium while supporting a static pressure load. The solution to the resulting differential equations determines the pressurized configuration of the valve model. To complete the model, we then specify a constitutive law based on a stress-strain relation consistent with experimental data that achieves the necessary forces computed in previous steps. Finally, using the immersed boundary method, we simulate the model valve in fluid in a computer test chamber. The model opens easily and closes without leak when driven by physiological pressures over multiple beats. Further, its closure is robust to driving pressures that lack atrial systole or are much lower or higher than normal.

Progressive Multifocal Liquid Lenses Based on Asymmetric Freeform Surface Structure of Nonuniform Thickness Elastic Membranes with Different Constraints

For a progressive multifocal liquid lens with an elastic membrane deformed by liquid pressure, to realize a reasonably power distribution, asymmetric deformation characteristics of the membrane surface are needed. Based on the asymmetric freeform surface structure, this paper proposed progressive multifocal liquid lenses focused by liquid with nonuniform thickness membranes. The structure and mathematical model of power distribution for the lens are introduced. The membrane deformation and the corresponding power distribution of the lenses with asymmetric freeform surface are predicted and compared under uniform pressure load and different boundary conditions using the finite element method. An optical testing system is constructed to analyze the optical characteristics of the fabricated lenses through observing the focusing performance of the F target image at different regions of the lenses. Experimental results show that the liquid lenses can realize as asymmetrical progressive multifocal liquid lenses after liquid accommodation; meanwhile, the trends of power distribution of the lenses generally agree well with simulations.

Self‐Powered Flexible Sensor Based on the Graphene Modified P(VDF‐TrFE) Electrospun Fibers for Pressure Detection

AbstractPolymer P(VDF‐TrFE) has been extensively applied in modern flexible electronics, such as nanogenerators and pressure sensors. In this study, a repolarization method is proposed to exploit the piezoelectric properties of the P(VDF‐TrFE) electrospinning film modified by the reduced graphene oxide (rGO). Then, the repolarized composite film is applied as the self‐powered flexible pressure sensor. Notably, the piezoelectric output voltage and current of the repolarized composite film are up to 1.5 V and 0.125 µA, respectively. Typically, the piezoelectric voltage of the composite film is three times as high as that of the pure spinning film. Meanwhile, this composite film also exhibits piezoresistive effect, which is ascribed to the 3D network structure of the electrospun nanofibers. In addition, the highest piezoresistive sensitivity of the pressure sensor is 0.072 kPa−1. To sum up, the pressure sensor fabricated in this study allows to simultaneously detect the static and dynamic pressure loads, which thereby has great application potentials in electronic skins (e‐skins) for human motion monitoring, such as motion state and finger bending.

Stress Analysis of IBS Molding Machine

Home is a place for shelter and survival for every living thing. These residential buildings are made using materials, one of which is brick. The technology of making bricks continues to grow over time. At present, bricks have been made using machines that use modern methods with the Interlocking Brick System (IBS) model. This molding machine using pneumatic to press the clay in the mold to becomes an IBS. This study aimed to determine the structural strength of the IBS printing press when given a load when printing is carried out. This research also serves to determine the most vulnerable locations on the machine structure as a concern when the load capacity will be increased. The analysis was carried out using the finite element method by using the finite element software. The simulation results obtained are, this IBS brick molding machine is safely operated for static pressure loads of 100 bar (10MPa).

FINITE ELEMENT ANALYSIS OF URINARY BLADDER WALL THICKNESS AT DIFFERENT PRESSURE CONDITION

In this work, a 3D urinary bladder was subjected to various pressure loading conditions mimicking the bladder filling volume. The bladder layer consisting of adventitia, detrusor and mucosa layer having different mechanical properties produced different deformation and stresses when subjected to the varying loads. The volume of the bladder changed to 231.34[Formula: see text]ml which was 128.91% higher than the assumed initial volume of 50[Formula: see text]ml on application of 18[Formula: see text]kPa of pressure. The detrusor layer which is thickest of the bladder wall reduced to 1.312[Formula: see text]mm from 4.4[Formula: see text]mm, recording a 108% change in its thickness at 18[Formula: see text]kPa pressure. The maximum von-Mises stress obtained were significantly higher in case of the Mucosa layer when compared to the detrusor and adventia layer. The unique layup of the bladder wall having different properties plays a major role in sustaining adverse pressure gradients and absorbing high stresses.

ДЕФЕКТИ ПРИ ВИГОТОВЛЕННІ БУРОІН’ЄКЦІЙНОЇ ПАЛІ В СКЛАДНИХ ІНЖЕНЕРНО-ГЕОЛОГІЧНИХ УМОВАХ, ЩО ВПЛИВАЮТЬ НА ЇЇ НЕСУЧУ ЗДАТНІСТЬ, ЗА ВЛАСТИВОСТЯМИ ҐРУНТОВОЇ ОСНОВИ

У роботі представлено основні дефекти при виготовленні буроін’єкційної палі, що впливають на її несучу здатність за властивостями ґрунтової основи. Систематизовано умови, за яких можливе виникнення дефектів палі при виготовленні та надано загальні рекомендації щодо усунення таких умов. Найбільш впливовою умовою, що спричинює появу дефектів, є така геологічна будова, коли у верхній частині інженерно-геологічного розрізу розташовані водонасичені піщані ґрунти та/або пилувато-глинисті ґрунти з показником текучості більше 0,5, а в нижній частині - пилувато-глинисті ґрунти з показником текучості менше 0,1 - 0,2.

Bidirectional Ultrasound Elastographic Imaging Framework for Non-invasive Assessment of the Non-linear Behavior of a Physiologically Pressurized Artery

Studies of non-destructive bidirectional ultrasound assessment of non-linear mechanical behavior of the artery are scarce in the literature. We hereby propose derivation of a strain–shear modulus relationship as a new graphical diagnostic index using an ultrasound elastographic imaging framework, which encompasses our in-house bidirectional vascular guided wave imaging (VGWI) and ultrasound strain imaging (USI). This framework is used to assess arterial non-linearity in two orthogonal (i.e., longitudinal and circumferential) directions in the absence of non-invasive pressure measurement. Bidirectional VGWI estimates longitudinal (μL) and transverse (μT) shear moduli, whereas USI estimates radial strain (ɛr). Vessel-mimicking phantoms (with and without longitudinal pre-stretch) and in vitro porcine aortas under static and/or dynamic physiologic intraluminal pressure loads were examined. ɛr was found to be a suitable alternative to intraluminal pressure for representation of cyclic loading on the artery wall. Results revealed that μT values of all samples examined increased non-linearly with εr magnitude and more drastically than μL, whereas μL values of only the pre-stretched phantoms and aortas increased with ɛr magnitude. As a new graphical representation of arterial non-linearity and function, strain–shear modulus loops derived by the proposed framework over two consecutive dynamic loading cycles differentiated sample pre-conditions and corroborated direction-dependent non-linear mechanical behaviors of the aorta with high estimation repeatability.