Circumferential Direction Research Articles

Local characterization of collagen architecture and mechanical failure properties of fibrous plaque tissue of atherosclerotic human carotid arteries.

Atherosclerotic plaque rupture in carotid arteries is a major cause of cerebrovascular events. Plaque rupture is the mechanical failure of the heterogeneous fibrous plaque tissue. Local characterization of the tissue's failure properties and the collagen architecture are of great importance to have insights in plaque rupture for clinical event prevention. Previous studies were limited to average rupture properties and global structural characterization, and did not provide the necessary local information. In this study, we assessed the local collagen architecture and failure properties of fibrous plaque tissue, by analyzing 30 tissue strips from 18 carotid plaques. Our study framework entailed second harmonic generation imaging for local collagen orientation and dispersion, and uniaxial tensile testing and digital image correlation for local tissue mechanics. The results showed that 87% of the imaged locations had collagen orientation close to the circumferential direction (0°) of the artery, and substantial dispersion locally. All regions combined, median [Q1:Q3] of the predominant angle measurements was -2° [-16°:16°]. The stretch ratio measurements clearly demonstrated a nonuniform stretch ratio distribution in the tissue under uniaxial loading. The rupture initiation regions had significantly higher stretch ratios (1.26 [1.15-1.40]) than the tissue average stretch ratio (1.11 [1.10-1.16]). No significant difference in collagen direction and dispersion was identified between the rupture regions and the rest of the tissue. The presented study forms an initial step towards gaining better insights into the characterization of local structural and mechanical fingerprints of fibrous plaque tissue in order to aid improved assessment of plaque rupture risk. STATEMENT OF SIGNIFICANCE: Plaque rupture risk assessment, critical to prevent cardiovascular events, requires knowledge on local failure properties and structure of collagenous plaque tissue. Our current knowledge is unfortunately limited to tissue's overall ultimate failure properties with scarce information on collagen architecture. In this study, local failure properties and collagen architecture of fibrous plaque tissue were obtained. We found predominant circumferential alignment of collagen fibers with substantial local dispersion. The tissue showed nonuniform stretch distribution under uniaxial tensile loading, with high stretches at rupture spots. This study highlights the significance of local mechanical and structural assessment for better insights into plaque rupture and the potential use of local stretches as risk marker for plaque rupture for patient-specific clinical applications.

Effects of non-symmetric non-uniformly distributed welding residual stress on fatigue failure initiation and propagation in a hydropower generator shaft

PurposeThis article aims to investigate and model the effects of welding-generated thermal cycle on the resulting residual stress distribution and its role in the initiation and propagation of fatigue failure in thick shaft sections.Design/methodology/approachExperimental and numerical techniques were applied in the present study to explore the relationship(s) between welding residual-stress distribution and fatigue failure characteristics in a hydropower generator shaft. Experimental techniques included stereomicroscopy, optical and scanning electron microscopy (SEM), chemical analysis and mechanical testing. Finite element modelling (FEM) was used to model the shaft welding cycle in terms of thermal (temperature) history and the associated development of residual stresses within the weld joint.FindingsExperimental analyses have confirmed the suitability of the used material for the intended application and confirmed the failure mode to be low cycle fatigue. The observed failure characteristics, however, did not match with the applied loading in terms of design stress levels, directionality and expected crack imitation site(s). FEM results have revealed the presence of a sharp stress peak in excess of 630 MPa (about 74% of material's yield strength) around weld start point and a non-uniform residual stress distribution in both the circumferential and through-thickness directions. The present results have shown very close matching between FEM results and observed failure characteristics.Practical implicationsThe present article considers an actual industrial case of a hydropower generator shaft failure. Present results are valuable in providing insight information regarding such failures as well as some preventive design and fabrication measures for the hydropower and other power generation and transmission sector.Originality/valueThe presence of the aforementioned stress peak around welding start/end location and the non-uniform distribution of residual-stress field are in contrast to almost all published results based on some uniformity assumptions. The present FEM results were, however, the only stress distribution scenario capable of explaining the failure considered in the present research.

Calculating the Growth of Vascular Cambium in Woody Plants as the Cylindrical Surface

The expansion of the vascular cambium cylinder in the stem of woody plants has been modeled many times, using different approaches and focusing on contributions of different cell events (cell divisions, intrusive cell growth and symplastic cell growth). Although there are many case studies in the literature, a universal model is still lacking. Therefore, the aim of this study is to estimate the quantitative changes in the contribution of symplastic growth of a single cambial cell (a sector of the cambial circumference) to the expansion of the vascular cambium cylinder, as the stem increases in girth. The proposed calculations, using the number π, and considering the actual dimensions of cambial cells, show (a) that the average symplastic increase per one initial cell in the circumferential direction decreases exponentially with the enlargement of cambial circumference, and (b) that the significant difference in the magnitude of symplastic increment of a single initial in the radial and circumferential directions increases proportionally to the increase in the circumference of the cambial cylinder. The proposed mathematical formula helps to understand the general rules that govern the gradual increase of the vascular cambium cylinder during wood production and would further facilitate the description/modeling of stem growth and formation of wood structural patterns.

Transient thermal models of induction machines under Inter‐turn short‐circuit fault conditions

AbstractInduction machines are the working horses in a lot of industries. Inter‐turn short‐circuit (ITSC) fault is one of the most common failure modes taking place in them. It can generate large fault currents that lead to a local temperature rise in the faulty stator slot, which deteriorates the working performance of the machine or even cascades to a complete machine breakdown. This article focuses on developing transient thermal models for an induction machine under ITSC faults. The aim of these thermal models is to understand the thermal behaviour of the induction machine at different ITSC fault propagation stages. The first thermal model is based on finite element method (FEM) simulation that includes a physics‐based model for the thermal contact resistance. The second thermal model is a lumped parameter thermal network that models the stator as inter‐connected slot‐number parts. They are both capable of modelling the characteristic of non‐uniform temperature along the circumferential direction for the induction machine operating under ITSC fault conditions. After area‐weighted averaging the results of the FEM simulation, it is found they are quantitatively consistent, with an average relative error magnitude of 5%, as well.

Numerical Investigation of Gas Dynamic Foil Bearings Conjugated with Contact Friction by Elastic Multi-Leaf Foils

With increasing demand for load capacity and dynamic responses, the new generation of Gas Dynamic Foil Bearings (GDFB), assembled from preloaded elastic multi-leaf foils, has been put forward. It exhibits steady and dynamic characteristics that are more sensitive to the contact friction produced by foil–foil bearings and the housings of foil bearings, distinguishing its response to rigidity from those of classic bearings. This study aims to employ numerical simulations to explore GDFBs conjugated with contact friction using elastic multi-leaf foils. A numerical method with Bidirectional Fluid–Structure Interactions (BFSIs), which strengthens the steady and dynamic characteristics of GDFBs, has been developed. The results showed that the distribution of steady stiffness was closely associated with the configuration of the foil assembly and the state of contact friction. The maximum steady stiffness occurred near the key blocks and was accompanied by the support of bump foils. The contact friction increased the stiffness of the foil assembly, which was unfavorable to its operational stability, and the GDFB was prone to rigidity. The contact friction hindered the pull-back of the top foils near the negative pressure area. An increase in the rotational speed and eccentricity increased the load capacity while decreasing the operational stability. The maximum pressure of the gas film was inconsistent with the maximum deformation along the circumferential direction because of the configuration of the foil assembly. The contact friction induced energy dissipation, whereas increases in the integrated stiffness inhibited loss. The fixed constraint of the key block increased the dynamic cross-stiffness more than the contact constraint did, which was unfavorable to operational stability. The results obtained in this study are significant because they provide a physical basis for GDFBs and can be used to guide their operational optimization.

Three-Dimensional Speckle-Tracking Echocardiography-Derived Tricuspid Annular Dimensions and Right Atrial Strains in Healthy Adults-Is There a Relationship? (Insights from the MAGYAR-Healthy Study).

The tricuspid valve and its annulus (TA) are thought to be integrally related to right atrial (RA) size and function. The present study aimed to assess associations between TA dimensions and RA strains, and quantitative features of its contractility were determined by 3DSTE in healthy adults. The study comprised 145 healthy volunteers with a mean age of 34.4 ± 12.5 years (73 males). Electrocardiographic, two-dimensional Doppler echocardiographic and 3DSTE parameters were in normal reference ranges in all subjects. Enlarged TA areas, regardless of which phase of the cardiac cycle were measured, were not associated with the deterioration of peak RA strains in longitudinal (LS) and circumferential (CS) directions. Increased end-diastolic TA area was associated with reduced RA strain in the radial direction (RS). Dilation of end-diastolic and end-systolic TA areas was related to increased RA volumes. End-diastolic TA area was the smallest in case of increased peak global RA-RS, and other associations between increasing TA areas and peak global strains could not be detected. Peak global RA-CS and RA-LS were not related to TA areas. Increasing peak global RA-RS was not associated with peak global RA-LS and RA-CS, while increasing peak global RA-LS and RA-CS were not associated with peak global RA-RS. Increasing peak global RS did not show associations with RA volumes, Vmin was the smallest in the case of highest peak global RA-CS and RA-LS. Vmax increased with increasing peak global RA-LS. 3DSTE is suitable for simultaneous non-invasive determination of TA dimensions and RA volumes and strains using the same acquired 3D dataset, allowing physiologic studies. RA volumes are associated with end-diastolic and end-systolic TA areas. RA strains in radial direction (RS) show associations with end-diastolic TA area.

Fracture of porcine aorta—Part 1: symconCT fracture testing and DIC

Tissue failure and damage are inherent parts of vascular diseases and tightly linked to clinical events. Additionally, experimental set-ups designed to study classical engineering materials are suboptimal in the exploration of vessel wall fracture properties. The classical Compact Tension (CT) test was augmented to enable stable fracture propagation, resulting in the symmetry-constraint Compact Tension (symconCT) test, a suitable set-up for fracture testing of vascular tissue. The test was combined with Digital Image Correlation (DIC) to study tissue fracture in 45 porcine aorta specimens. Test specimens were loaded in axial and circumferential directions in a physiological solution at 37 °C. Loading the aortic vessel wall in the axial direction resulted in mode I tissue failure and a fracture path aligned with the circumferential vessel direction. Circumferential loading resulted in mode I-dominated failure with multiple deflections of the fracture path. The aorta ruptured at a principal Green-Lagrange strain of approximately 0.7, and strain rate peaks that develop ahead of the crack tip reached nearly 400 times the strain rate on average over the test specimen. It required approximately 70% more external work to fracture the aorta by circumferential than axial load; normalised with the fracture surface, similar energy levels are, however, observed. The symconCT test resulted in a stable fracture propagation, which, combined with DIC, provided a set-up for the in-depth analysis of vascular tissue failure. The high strain rates ahead of the crack tip indicate the significance of rate effects in the constitutive description of vascular tissue fracture. Statement of significanceThis paper represents a significant step forward in understanding the fracture properties of porcine aorta. Inspired by the Compact Tension test, we developed an ad hoc experimental protocol to investigate stable crack propagation in soft materials, providing new insights into the mechanical processes that lead to the rupture of vascular tissue. The set-up enables the assessment of strains and strain rates ahead of the crack tip, and our findings could improve the clinical risk assessment of vascular pathologies as well as optimise medical device design.

Examining heat transfer of a buried pipe heat exchanger in arch tunnel lining with protection engineering

Cooling towers and internal reservoirs are two conventional heat transfer methods used in protection engineering. However, they have the drawbacks of easy exposure and limited capacity. Although the traditional ground source heat pump system can become a new heat transfer method, its high installation cost and space requirements are obstacles to the development of this technology. To address this problem, the heat exchange pipe of the ground source heat pump system being directly laid in the tunnel lining was proposed in this study. A heat transfer performance test platform for a lined buried pipe heat exchanger based on an arch tunnel was built, and the water velocity, wind velocity, and temperature of each measuring point were recorded under appropriate working conditions. The effects of the inlet water temperature, inlet water velocity, ventilation velocity, and initial soil temperature on the heat transfer performance were analyzed. The results have shown that the heat transfer performance of the tunnel reached its maximum when system operation commenced and then decreased gradually with time, and the rate of decrease gradually slowed. Along the radial direction of the tunnel, the shorter the distance to the buried heat exchanger, the greater the increase in soil temperature, and the shorter the time for the temperature to reach the peak value. As the distance increased, the temperature gradient gradually decreased. Along the circumferential direction of the tunnel, the lining temperature on the inlet side of the buried heat exchanger was higher than that on the outlet side. The temperature distribution on both sides of the symmetrical surface of the tunnel was not uniform, resulting in additional temperature stress in the horizontal direction. The time required for the heat transfer capacity of the tunnel to return to its initial value was approximately eight times that of the system. Compared with the ventilation and water velocities, the inlet water temperature and initial soil temperature had a greater impact on heat transfer. The heat-transfer law of an arch tunnel differs from that of a circular tunnel. There were some deviations when comparing the experimental data of the circular tunnel with those of the actual arch tunnel.

Evaluation of the antenna parameters for inspection of hidden defects behind a reinforced shield tunnel using GPR

Ground penetrating radar (GPR), as a recognized non-destructive testing method, has been widely applied to detect hidden defects behind a reinforced shield tunnel. However, the scattering of electromagnetic waves caused by the dense double-layer rebar meshes embedded in a tunnel lining severely influences GPR's detection capabilities. Selecting the appropriate antenna parameters is a crucial step before conducting GPR measurements. In this paper, the penetration capability of GPR waves is evaluated using a shield tunnel model made of two shield tunnel segments. The laboratory experimental results demonstrate that an antenna with a center frequency of 400–600 MHz is appropriate for detecting hidden defects behind the concrete segment. Regarding the antenna polarization direction, it is better to set it in the longitudinal direction of the shield tunnel since the rebar spacing is slightly larger than that in the circumferential direction. The antenna height from the concrete segment should be controlled within a fifth of the wavelength in air to compromise between the data quality and detection efficiency. The results will aid in determining antenna parameters when GPR is applied to inspect hidden defects behind a reinforced shield tunnel.

Finite-element simulation of in-plane tear propagation in the dissected aorta: Implications for the propagation mechanism.

Computer modeling and numerical simulation are essential for understanding the progression of aortic dissection. However, tear propagation has not been properly modeled and simulated. The in-plane dissection propagation between concentrically distributed elastic lamellae is modeled using the cohesive zone method with a bilinear traction-separation law. The parameters of cohesive elements are calibrated for the three modes of interfacial damage in the media, enabling quantitative predictions of in-plane tear propagation. An idealized cylindrical tube-shaped bilayer thick-wall model of the aorta is employed to elucidate the influence of geometrical parameters, loading conditions and residual stress on the tear propagation. While the model is capable of replicating that deeper, larger tears are associated with lower critical pressure, new findings include: (i) Larger axial stretch leads to lower critical pressure; (ii) Increased magnitude of residual stress is associated with higher critical pressure; (iii) Pressure difference between true and false lumen alters the critical pressure; (iv) The interfacial damage is mostly opening mode in the axial direction, but shear-dominated in the circumferential direction; (v) Damage due to the opening mode is associated with smaller fracture energy, which makes it easier to propagate than the shear and the mixed modes. (vi) The deformed shape of the tear, which is related to its geometrical features and loading conditions, modulates the critical pressure via two pathways: (a) deformed shapes are associated with specific modes of damage, which influences the critical pressure, and (b) deformed shapes modulate the critical pressure directly via geometrical constraints.

Validating aortic stiffness parameters by cardiac magnetic resonance against mechanical testing of ex-vivo aortic aneurysms specimens

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Instituto de Salud Carlos III, Sociedad Española de Cardiología Background Aortic stiffness is a predictor of incident cardiovascular events and mortality in the general population (1). Cardiovascular magnetic resonance (CMR) imaging allow to compute a number of parameters, such as pulse wave velocity (PWV), distensibility (AD) and aortic longitudinal strain, theoretically related to aortic wall stiffness, but no formal validation has ever been reported. Purpose To test the correlation between aortic PWV, AD and longitudinal strain and aortic wall stiffness as assessed via ex-vivo mechanical testing of aortic specimens. Methods Patients undergoing ascending aorta (AAo) aneurysms resection underwent a CMR study which included bSSFP images and a 4D flow CMR of the thoracic aorta. At surgery 2 AAo specimens (each 15x5 mm, one oriented in the longitudinal and the other in circumferential aortic direction) were extracted, maintaining a record of their in-vivo position and orientation, and frozen. Specimens were tested under control for extension force (I5558, INSTRON) and elongation was quantifies by laser video extensometer (2663–281, INSTRON). The Young's modulus (E), i.e. tangent of the stress-strain curve, was quantified at the patient’s diastolic pressure during CMR (2). AAo PWV was extracted from 4D flow CMR study and the product of Eh (h being wall thickness) was computed via the Moens-Korteweg equation using the mean AAo diameter(3,4). AD was quantified from cine CMR at the pulmonary artery level using ARTFUN software (INSERM U678, France) while AAo longitudinal strain was assessed as mean deformation of the AAo by tracking the aortic root during the cardiac cycle (5). Results Twenty patients were included: age 52.5 [37.3 – 71.0] years, 13 (65%) male, BSA 1.94 [1.74 – 1.94] m2. Most of patients had AAo aneurysms of degenerative origin and a tricuspid aortic valve, while 2 patients had a bicuspid aortic valve, and 9 patients had connective tissue disorders. Due to missing data, one AD a two PWV could not have been computed while the specimen in circumferential direction of a patient could not be tested. AAo PWV, Eh and AD were strongly associated with circumferential elastic modulus at diastolic blood pressure (R = 0.652, R = 0.602 and R = -0.502, respectively) (Figure 1). Strong association was also obtained between AAo longitudinal strain and longitudinal elastic modulus at diastolic blood pressure (R = -0.513). Conclusion Pulse wave velocity and the derived Eh product, aortic distensibility and aortic longitudinal strain as non-invasively assessed by CMR are reliable representation of aortic wall stiffness.

Effect of Nonlinear Hyperelastic Property of Arterial Tissues on the Pulse Wave Velocity Based on the Unified-Fiber-Distribution (UFD) Model.

Pulse wave velocity (PWV) is a key, independent risk factor for future cardiovascular events. The Moens-Korteweg equation describes the relation between PWV and the stiffness of arterial tissue with an assumption of isotopic linear elastic property of the arterial wall. However, the arterial tissue exhibits highly nonlinear and anisotropic mechanical behaviors. There is a limited study regarding the effect of arterial nonlinear and anisotropic properties on the PWV. In this study, we investigated the impact of the arterial nonlinear hyperelastic properties on the PWV, based on our recently developed unified-fiber-distribution (UFD) model. The UFD model considers the fibers (embedded in the matrix of the tissue) as a unified distribution, which expects to be more physically consistent with the real fiber distribution than existing models that separate the fiber distribution into two/several fiber families. With the UFD model, we fitted the measured relation between the PWV and blood pressure which obtained a good accuracy. We also modeled the aging effect on the PWV based on observations that the stiffening of arterial tissue increases with aging, and the results agree well with experimental data. In addition, we did parameter studies on the dependence of the PWV on the arterial properties of fiber initial stiffness, fiber distribution, and matrix stiffness. The results indicate the PWV increases with increasing overall fiber component in the circumferential direction. The dependences of the PWV on the fiber initial stiffness, and matrix stiffness are not monotonic and change with different blood pressure. The results of this study could provide new insights into arterial property changes and disease information from the clinical measured PWV data.

Exploding wire method for the characterization of dynamic tensile strength of composite materials

In the presented study a wire electric explosion method is adopted for the shock loading test of wound T700/LY113 carbon/epoxy composite. The advantage of the proposed test method is a possibility to reach strain rate ∼104 s−1, exceeding upper limit of split Hopkinson pressure bar, but matching lower limits of plate impact test. Compared to the latter test method, a promising feature is a capability to measure in-plane tensile strength of the laminated composite. To implement the proposed method, test samples were fabricated by winding of carbon fiber layers over a polymethyl methacrylate (PMMA) cylinder. Electric explosion of wire inserted in the channel inside the cylinder generates a shock wave, which propagates towards the outer composite shell, and free surface velocity history is recorded using a laser interferometer. It allows estimation of failure strain and tensile strength of the composite in circumferential direction. However, incident shock wave and reverberations are also critical for out-of-plane strength, including delamination, so finite element analysis is used to elaborate what type of failure mode is critical.

Automation of the procedure for determining the admissibility of erosion- corrosion wear in pipelines of nuclear power plants made of carbon steels

Many pipelines in Ukrainian nuclear power plants have been in operation for over 30 years, and the determination of the admissibility of erosion-corrosion wear (ECW) defects in the pipeline wall metal is currently one of the pressing issues in the nuclear energy sector of Ukraine. A comparative analysis of determining the admissibility of pipe wall thinning due to ECW was conducted using the adopted methodology “MT-T.0.03.224-18” by the State Enterprise “Energoatom” and the guidance based on the use of regulatory documents for designing pipeline elements. The use of the methodology demonstrated significant advantages in terms of reducing the conservatism of ECW assessment, especially for small-scale thinning and pipelines operating at pressures below 60-80 kgf/cm2, which allows for a substantial reduction in repair work. However, the implementation of the methodology in practice may encounter difficulties due to the complexity and labor-intensiveness of the calculation assessment procedure for nuclear power plant personnel. Therefore, to automate the ECW admissibility assessment in accordance with the methodology requirements, software (SW) was developed for use by nuclear power plant personnel, enabling the prompt generation of a protocol for the express assessment procedure of ECW admissibility for a straight section of the pipeline based on the measurement results of wall thinning parameters in the axial direction. The software allows for concluding whether the section can be put into operation, sent for repair, or requires further refined assessment. Additionally, software based on the finite element method (FEM) was developed, which, when necessary, allows for a refined assessment of a straight section, taking into account the depth and angle of thinning in the circumferential direction, and calculates the stress of the limit plastic state of the pipeline section with ECW from the perspective of viscous fracture. The devel- opment is applicable in the field of nuclear energy in Ukraine.

Three-dimensional stability of non-thin anisotropic cylindrical shells under axial pressure

Based on the modified Hu-Washizu variational principle, a three-dimensional system of homogeneous linearized differential equations of stability of non-thin anisotropic cylindrical shells is obtained. The anisotropy type of shells is characterized by one plane of elastic symmetry. Reducing the system to a one-dimensional one is carried out using the Bubnov-Gal'orkin method, which approximates the functions of unknown systems of equations along the generatrix and takes into account their periodicity in the circumferential direction. The numerical solution of the obtained one-dimensional system of equations is carried out using the discrete orthogonalization method. 
 The problem of stability of a non-thin anisotropic cylindrical shell for a different number of cross-laid composite layers against the action of axial pressure is solved. The nature of the dependence of critical forces on the number of layers is analyzed.

Morphological study of the arterial supply to the menisci in pigs with special reference to creating meniscus injury model.

Some reports have used pigs to establish models of meniscus injury. However, accurate information on the origin, course, and access of the arteries supplying the menisci remains unclear. This information is important to avoid damaging vital arteries when creating the meniscus injury model. In this study, fetal and adult pigs were employed to investigate the arterial supply of the menisci in pigs using gross anatomical and histological methods. Macro-anatomically, the anterior horn, body, and posterior horn of the medial meniscus were found to be supplied by the medial superior genicular artery, medial inferior genicular artery, and posterior middle genicular artery. The anterior and posterior horns of the lateral meniscus were supplied by the cranial tibial recurrent artery and the middle genicular artery, respectively. Anastomosis was observed in some cases, but appeared to be infrequent and too thin to expect the anastomotic branches to provide adequate blood flow. The histological examination showed that the arteries entered the meniscus along the tie-fiber. The access process of the artery was the same irrespective of whether it was in fetal or mature pigs, the medial or lateral meniscus, or the anterior horn or body or posterior horn. The medial inferior genicular artery ran along the medial meniscus in the circumferential direction. Therefore, the clinical longitudinal incision should take into account the characteristics of the vessel course in order to protect the blood vessels from damage. Based on the results of this study, the protocol for creating a pig meniscus injury model should be reconsidered.

Application of a semi-analytical method to the dynamic analysis of functionally graded porous conical–conical–cylindrical shell

The dynamic response characteristics of a coupled, functionally graded porous conical–conical–cylindrical shell (FGP-CCCS) with arbitrary boundary conditions are investigated using a semi-analytical method in this research. The individual shells are firmly connected at the interface. It is assumed that FGP-CCCS is made of three types of FGP materials with uniform or non-uniform distribution of porosity along the thickness direction. The overall theoretical model for the dynamic response analysis of FGP-CCCS is established based on the first-order shear deformation theory. All the displacement components of individual shells, including boundary conditions, are expanded along the meridian direction into the Chebyshev polynomial and along the circumferential direction into the standard Fourier series. By applying the Rayleigh–Ritz method to the determination of the expansion coefficient, a unified solution for a FGP-CCCS with arbitrary boundary conditions is derived directly without the need to change the equation of motion or the displacement functions. The reliability and accuracy of this method is verified in comparison with the results in the literature and finite element method. New numerical examples are presented to illustrate the dynamic response characteristics of FGP-CCCS, and the effects of the geometrical, material parameters and external forces on the dynamic response of FGP-CCCS with different boundary conditions are reported.

Three-dimensional analysis of hydrogel-imbedded aortic valve interstitial cell shape and its relation to contractile behavior.

Cell-shape is a conglomerate of mechanical, chemical, and biological mechanisms that reflects the cell biophysical state. In a specific application, we consider aortic valve interstitial cells (AVICs), which maintain the structure and function of aortic heart valve leaflets. Actomyosin stress fibers help determine AVIC shape and facilitate processes such as adhesion, contraction, and mechanosensing. However, detailed 3D assessment of stress fiber architecture and function is currently impractical. Herein, we assessed AVIC shape and contractile behaviors using hydrogel-based 3D traction force microscopy to intuit the orientation and behavior of AVIC stress fibers. We utilized spherical harmonics (SPHARM) to quantify AVIC geometries through three days of incubation, which demonstrated a shift from a spherical shape to forming substantial protrusions. Furthermore, we assessed changes in post-three day AVIC shape and contractile function within two testing regimes: (1) normal contractile level to relaxation (cytochalasin D), and (2) normal contractile level to hyper-contraction (endothelin-1). In both scenarios, AVICs underwent isovolumic shape changes and produced complex displacement fields within the hydrogel. AVICs were more elongated when relaxed and more spherical in hyper-contraction. Locally, AVIC protrusions contracted along their long axis and expanded in their circumferential direction, indicating predominately axially aligned stress fibers. Furthermore, the magnitude of protrusion displacements was correlated with protrusion length and approached a consistent displacement plateau at a similar critical length across all AVICs. This implied that stress fiber behavior is conserved, despite great variations in AVIC shapes. We anticipate our findings will bolster future investigations into AVIC stress fiber architecture and function. STATEMENT OF SIGNIFICANCE: Within the aortic valve there exists a population of aortic valve interstitial cells, which orchestrate the turnover, secretion, and remodeling of its extracellular matrix, maintaining tissue integrity and ultimately sustaining the proper mechanical function. Alterations in these processes are thought to underlie diseases of the aortic valve, which affect hundreds of thousands domestically and world-wide. Yet, to date, there are no non-surgical treatments for aortic heart valve disease, in part due to our limited understanding of the underlying disease processes. In the present study, we built upon our previous study to include a full 3D analysis of aortic valve interstitial cell shapes at differing contractile levels. The resulting detailed shape and deformation analysis provided insight into the underlying stress-fiber structures and mechanical behaviors.

Influence of bearing waviness on the lubrication performances of coupled journal-thrust water-lubricated bearings

The purpose of this study is to discuss the effect of the bearing waviness on the lubrication performances of coupled journal-thrust water-lubricated bearings using an elastohydrodynamic lubrication model. The results of the numerical model are compared to the published experimental data to verify the validity of the numerical model. The load capacity and maximum fluid pressure under different parameters of waviness of coupled journal-thrust bearings are calculated by numerical model, and then the influence of the bearing waviness on the performance of coupled journal-thrust water-lubricated bearings is analyzed. The simulation results show that the waviness amplitude has great influence on the bearing performances and the effect becomes increasingly pronounced with the growth of waviness amplitude. For the waviness of journal bearings, the performances are more sensitive to the waviness arranged in bearing circumferential direction than radial direction. For the waviness of thrust bearings, the presence of circumferential waviness can improve the load capacity, while radial waviness can reduce the load capacity. With the increase of wavelength, the load capacity and maximum fluid pressure have similar periodic changes, but the change is irregular. More investigations are required regarding the influence of geometrical shape of the waviness and its wavelength on the performance of the bearing.

Acoustic scattering mechanism and noise attenuation of circumferentially non-uniform liner with spectral-wave guide method

In this paper, a model is established with application of the spectral-wave guide method, which has higher accuracy and can serve as a rapid calculation tool for sound transmission calculations. Based on this calculation model, some numerical results of circumferentially non-uniform lined annular/circular ducts are carried out, and some physical mechanisms can be discovered. The numerical results show that periodical impedance distributions along the circumferential direction will lead to discontinuous scattered modes with regular spacing; and mirror-symmetric structure liner will converge the energy of opposite modes. Relying on this mechanism, the potential of acoustic scattering can be further developed by suppressing lower or enhancing higher order modes with expressly designed segmented liner configurations. In particular, the intrinsic mechanism of mode redistribution brought about by the non-uniform liner can be subtly utilized to attenuate broadband noise. The present work indeed shows that circumferentially non-uniform liner is conducive to the reduction of the practical broadband sound source. Furthermore, the effects of non-uniform flow are considered in the model, then distinction of noise attenuation and scattered modes energy in different flows is shown. A possible mechanism is proposed that refraction effects in complex flows lead to the distinction. These works show that the current model has profound potential and availability for the research and designs of circumferentially non-uniform liner.