External Stiffness Research Articles

Vibration and Stability Analyses of Submarine Fluid-Conveying Pipelines with Local Stiffness Variation Under External Flow Fields

This study analyzes the vibration and stability characteristics of a submarine fluid-conveying pipeline with local variation in stiffness under the influence of external flow fields. Utilizing the absolute nodal coordinate formulation (ANCF), the dynamic equation for the submarine pipeline with local stiffness variation under arbitrary boundary conditions is derived. Through numerical solutions, curves depicting complex frequency variations as a function of the internal flow velocity of the pipeline system are obtained. Additionally, the effects of external flow velocity, geometrical parameters, and local stiffness variation on the vibration and stability characteristics of the submarine pipeline under three different boundary conditions are investigated. Results indicate that the stability of the pipeline system decreases across the three boundary conditions under the influence of the external flow field. Increased external flow velocities lead to further reductions in system stability. Furthermore, as the length-to-diameter ratio increases and the thickness-to-diameter ratio decreases, the first three orders of frequencies of the pipeline gradually diminish. Enhancing local stiffness contributes to improving the stability of the system, whereas reducing local stiffness has the opposite effect.

Detection of fluorescent protein mechanical switching in cellulo

The ability of cells to sense and respond to mechanical forces is critical in many physiological and pathological processes. However, determining the mechanisms by which forces affect protein function inside cells remains challenging. Motivated by invitro demonstrations of fluorescent proteins (FPs) undergoing reversible mechanical switching of fluorescence, we investigated whether force-sensitive changes in FP function could be visualized in cells. Guided by a computational model of FP mechanical switching, we develop a formalism for its detection in Förster resonance energy transfer (FRET)-based biosensors and demonstrate its occurrence in cellulo within a synthetic actin crosslinker and the mechanical linker protein vinculin. We find that in cellulo mechanical switching is reversible and altered by manipulation of cell force generation, external stiffness, and force-sensitive bond dynamics of the biosensor. This work describes a framework for assessing FP mechanical stability and provides a means of probing force-sensitive protein function inside cells.

Resistance training modalities: comparative analysis of effects on physical fitness, isokinetic muscle functions, and core muscle biomechanics.

This study aimed to evaluate the effects of varied resistance training modalities on physical fitness components, body composition, maximal strength assessed by one-repetition maximum (1RM), isokinetic muscle functions of the shoulder and knee joints, and biomechanical properties of core muscles. Forty participants were randomly assigned to four groups: control group (CG, n = 10), compound set training group (CSG, n = 10), pyramid set training group (PSG, n = 10), and superset training group (SSG, n = 10). Excluding the CG, the other three groups underwent an 8-week resistance training program, three sessions per week, at 60%-80% of 1RM intensity for 60-90min per session. Assessments included body composition, physical fitness components, 1RM, isokinetic muscle functions, and biomechanical properties (muscle frequency, stiffness, etc.) of the rectus abdominis and external oblique muscles. The PSG demonstrated the most significant improvement in relative peak torque during isokinetic testing of the shoulder and knee joints. Compared to the CG, all exercise groups exhibited positive effects on back strength, sprint performance, 1RM, and core muscle biomechanics. Notably, the PSG showed superior enhancement in external oblique stiffness. However, no significant differences were observed among the exercise groups for rectus abdominis biomechanical properties. Structured resistance training effectively improved maximal strength, functional performance, and core muscle biomechanics. The pyramidal training modality conferred specific benefits for isokinetic muscle functions and external oblique stiffness, suggesting its efficacy in enhancing force production capabilities and core stability.

An assessment of factors associated with early postoperative stiffness in arthroscopic rotator cuff repair.

Postoperative stiffness affects up to 20% of patients following arthroscopic rotator cuff repair. Recent evidence indicates that early postoperative stiffness may associated with lower retear rates. This study aimed to identify the independent predictors of early postoperative stiffness. A retrospective cohort study of 1526 rotator cuff repairs was performed. Range of motion at 6-week postop was used to identify stiff patients. Stiffness was defined as external rotation <27.5o or forward flexion <145o . Multiple logistic regression analysis was used to identify the independent predictors of 6-week stiffness. The independent predictors for external rotation stiffness at 6-week postop were more recent cases (Wald = 60), restricted preoperative external rotation (Wald = 36), younger age (Wald = 21) and poorer surgeon-ranked tissue quality (Wald = 15). The independent predictors for forward flexion stiffness were more recent cases (Wald = 101), restricted preoperative forward flexion (Wald = 16) and external rotation (Wald = 13) and female patients (Wald = 12). All patients that developed early postoperative stiffness had recovered range of motion by 6 months to preoperative levels (P < 0.0001). A significantly greater proportion of younger patients (40-49) developed postoperative stiffness when compared to older patients aged 50-59 (P < 0.0062), 70-79 (P < 0.0126) and 80-89 (P < 0.004). Patients that retore had significantly greater average 6-week postoperative range of motion. Patients earlier in the study were found to have greater postoperative range of motion, which coincided with a more aggressive rehabilitation program with less immobilization. Thus, the data supports the hypothesis that a temporary period of shoulder stiffness facilitates tendon repair and ultimately a better outcome post rotator cuff repair.

Neural network-based variable stiffness impedance control for internal/external forces tracking of dual-arm manipulators under uncertainties

The desired interaction between manipulators, objects, and environments has resulted in the internal/external force control for dual-arm manipulators being in increasing demand. Consequently, this study focused on the internal/external force tracking for dual-arm manipulator systems under external disturbances, geometries, and stiffness uncertainties which continuously lead to unsatisfactory internal force tracking. The proposed scheme is based on a two-level adaptive impedance control scheme, where the stiffness coefficient is adjusted to adapt to uncalibrated objects. An object-level hybrid impedance controller was used to regulate the external disturbance to produce a compliant response. A manipulator-level neural network-based variable stiffness impedance controller (NNVSIC) was proposed to regulate the internal force under various uncertainties. Additionally, an adaptive wavelet neural network was designed to compensate for the geometric estimation errors of the object. The variable stiffness coefficient could automatically adapt to an unknown object during the cooperation process. One advantage of the proposed method is that no prior knowledge was required. The same controller parameters could be adapted to various objects. The asymptotic stability of the proposed NNVSIC was proven via Lyapunov stability analysis. A series of experiments were conducted using two self-developed nine-degrees-of-freedom redundant manipulators. Furthermore, hard and soft objects of various geometries and stiffnesses were used to verify the effectiveness of the algorithm. The experimental results demonstrated the efficiency and superiority of the proposed controller through performance comparison with various algorithms.

Stress analysis of the contact problem in a functionally graded layer loaded with a distributed load and two rigid circular punches resting on an elastic two quarter planes

In this study, the solution of the contact problem in a functionally graded (FG) layer resting on elastic two quarter planes was done using the finite element method (FEM). The contact problem consists of two rigid circular punches loaded FG and two elastic quarter planes. P and Q loads are transmitted to the FG layer by two rigid circular punches. All surfaces in the problem were considered as frictionless and the weight effect is also taken into account. The two-dimensional model of the contact problem was created with the ANSYS package program based on FEM and the stress analyzes were performed. All operations of quarter planes and circular punches are done with standard ANSYS menus. However, defining the material properties of the FG layer and dividing into meshes in finite elements cannot be done with standard menus. For this reason, a special macro was added to the program in order to define the material properties of the FG layer and to perform the mesh division, and the necessary parameters were applied to the layer by this macro. In the study, the effects of external load, stiffness parameter (βh), density parameter (γh) and contact stresses of distributed load change, normal stresses, and stresses along the depth were investigated.

Temperature- and Frequency-Dependent Nonlinearities of an Integrated Hydro-Pneumatic Suspension with Mixed Gas-Oil Emulsion Flow

Hydro-pneumatic suspension (HPS) systems are increasingly being implemented in commercial vehicles and various industrial equipment, which is mainly attributed to the integration of adaptable nonlinear pneumatic stiffness and hydraulic damping properties. The integrated HPS design with a shared gas-oil chamber, however, leads to gas-oil emulsion flow within the suspension chambers, which intricately affects the internal and external properties of the HPS, especially under variations in temperature and excitation frequency. This study experimentally and analytically investigated the temperature- and frequency-dependent properties of the hydro-pneumatic suspension with the gas-oil emulsion. Laboratory experiments were performed under three different near-constant temperatures (30, 40, and 50 °C) in the 0.5–8 Hz frequency range. An analytical model of the HPS was formulated considering the effects of temperature on internal fluid properties, gas-oil emulsion flow between the coupled chambers, the dynamic seal friction, and polytropic change in the gas state. The internal parameters, including the gas volume fraction, the discharge coefficient of the emulsion, and the dynamic friction components, as well as the external stiffness and damping characteristics, were determined. The relationships between these properties and the system temperature, velocity, and excitation frequency were further investigated. The simulated responses obtained under different excitations showed reasonably good agreement with the experimental results of the HPS. The results suggested that increased temperature yielded greater equivalent stiffness and comparable damping properties of the system. The gas volume fraction, discharge coefficient, and magnitude of seal friction generally tended to increase with increasing temperature. Increased excitation frequency led to greater hysteresis in hydraulic damping force and seal friction, and reduced seal friction magnitude and Stribeck effect.

The biomechanical effect of fibular strut grafts on humeral surgical neck fractures with lateral wall comminution

No studies have evaluated the effect of fibular strut augmentation on the stability of locking plate fixation for osteoporotic proximal humeral fractures with lateral wall comminution. The purpose of this study was to evaluate the stability of locking plate fixation with a fibular strut graft compared with locking plate alone in an osteoporotic two-part surgical neck fracture model with lateral cortex comminution. Ten paired fresh-frozen cadaveric humeri were randomly allocated into two groups, either the locking plate alone (LP group) or locking plate with fibular strut graft augmentation (LPFSG group), with an equal number of right and left osteoporotic surgical neck fractures with lateral wall comminution of the greater tuberosity. Varus, internal/external torsion, and axial compression stiffness as well as single load to failure were measured in plate-bone constructs, and the LPFSG group showed significantly greater values in all metrics. In conclusion, this biomechanical study shows that fibular strut augmentation significantly enhances varus stiffness, internal torsion stiffness, external torsion stiffness, and maximum failure load of a construct compared to locking plate fixation alone in proximal humeral fractures with lateral wall comminution.

Dynamic Load Sharing Behavior for the Pitch Drive in MW Wind Turbines

For a wind energy system, main speed-increasing gearboxes, pitch drives and yaw drives are composed of a multistage planetary gear system. However, inevitable errors in the manufacturing and assembling of the gears lead to uneven load of distribution in the planetary gear system; thus, its service life and reliability decrease greatly, which would eventually affect the normal operation of the whole wind power system. In this study, a dynamic load sharing model of pitch drive is established with a lumped-parameter method. Given the manufacturing and assembly errors and central floating gear, the dynamic equations for each component, the stiffness matrix and damping matrix, the dynamic load sharing coefficient and the floating displacement of the sun gear are obtained according to the dynamic meshing force and damping load. Furthermore, the load sharing coefficient for external and internal meshing of the pitch drive for a 2 MW wind turbine with a three-stage planetary gear are achieved. Then, the floating displacement of the sun gear and the displacement of other gears are also obtained. Moreover, the influence of both external and internal meshing stiffness, the eccentric error and tooth frequency error for all components on the load sharing coefficient of all stages are investigated. Lastly, the theoretical components displacement of this model is compared with experiment results of the pitch drive under 50%, 100% and 150% rated torque in a test rig; the correctness of the model is verified by the experiment results.

Uni-axial behaviour of steel slag concrete-filled-steel-tube columns with external confinement

Using steel slag, a waste by-product in the steel industry to replace natural aggregates to produce concrete can offer a sustainable solution in mitigating the environmental problems due to huge depletion of natural aggregates and disposal of abundant slag. Extensive research studies revealed that steel slag concrete has superior strength and stiffness but may also cause unsoundness to concrete. To solve the problem, steel slag concrete-filled-steel-tube (SSCFST) column was proposed, in which the concrete’s expansion would activate larger confining stress, and thereby enhancing the overall behaviour of the column. A total of 18 traditional concrete-filled-steel-tube (CFST) and SSCFST column specimens with and without external confinement were prepared and tested under uni-axial compression. The major testing parameters were the steel tube diameter to thickness ratio, steel slag coarse/fine aggregate replacement ratio and spacing of external confinement. Results revealed that by replacing 50% natural coarse aggregate with steel slag coarse aggregate or 50% natural fine aggregate with steel slag fine aggregate, the compressive strength of steel slag concrete increased but the flowability decreased. Besides, SSCFST columns showed superior mechanical behaviour than traditional CFST columns. With external confinement, the strength and stiffness were further improved. Lastly, a load–strain model developed previously by the authors was adopted to predict the mechanical behaviour of traditional CFST and SSCFST columns. Good agreement has been obtained between predicted and experimental results for traditional CFST column while for SSCFST columns, the model under-estimated the axial load and over-estimated the absolute hoop strain at a given axial strain attributed to the change in the packing structure and possible expansion of steel slag concrete.

Free vibration of a taut cable with internal high damping rubber dampers and an external negative stiffness damper

Frequent vibration events on the long stay cables highlight the need to control their multi-mode vibrations. Compared to commonly used viscous dampers for cable vibration control, the negative stiffness damper (NSD) demonstrates its superior performance. However, a single NSD is incapable of providing sufficient supplemental damping for a super-long cable, especially for the multi-mode vibration mitigation. The combined internal high damping rubber (HDR) dampers and the external NSD for cable vibration control is proposed to achieve better multi-mode control performance in this study. First, the complex modal analysis of a taut cable coupled with an external NSD and two internal HDR dampers is conducted to reveal the coupling performance of the damping system. The asymptotic and iterative solutions of transcendental equation obtained in complex modal analysis are derived, respectively. Subsequently, the comparison of asymptotic and iterative solutions verifies the applicability of asymptotic solutions. Finally, parametric studies are performed to investigate the effect of the parameters of NSD and the coupling configuration on their combined control performance. Results show that the coupling schemes with different configurations can possess a wider effective modal range or a better damping effect in the narrower modal ranges according to different damping targets. It provides a diversified solution for multi-mode damping enhancement of stay cables.

An exact solution for vibration analysis of pipe coupled with conical-ring stiffened cylindrical shells with arbitrary boundary condition

In this paper, an analytical impedance synthesis method (ISM) is proposed to analyze the vibration characteristics of a pipe-hull coupled system, in which the hull of a submarine can be simplified to a combined conical-stiffened cylindrical-hemisphere shell. Wave solution and power series solution are used to describe the displacement of cylindrical and conical shell respectively. Rib stiffened and bulkhead are modeled as annular plate and circular plate. Based on exact general solutions, the impedance matrix of each segment is established separately and assembled in the global coordinate by displacement continuity and force balance boundary conditions. Natural frequency and forced responses are compared with open literature and FEM results to verify the correctness of the method. In the numerical examples, the effects of direction of external force and stiffness of support on the forced vibration characteristics are discussed, which can provide some guides for acoustic design of pipe in submarine.

The effects of anterior cruciate ligament sacrifice on the behavior of the knee joint, tested through the use of a musculoskeletal model

In usual knee joint arthroplasty, the insertion of the prosthetic components requires the removal of the anterior cruciate ligament (ACL), while the posterior cruciate (PCL) is retained. Since the balance of the knee joint ligaments is fundamental for a good functionality of the joint, it is important to know the effects of the ACL sacrifice. In a previous study [1] the tension of the knee joint ligaments was tested by simulating the typical maneuvers (anterior/posterior drawers, varus/valgus and internal/external rotation forcing) applied to a musculoskeletal model. In the present work the tests were repeated in the absence of the ACL, and the changes with respect to the ‘all ligaments’ condition were analyzed. The dynamic musculoskeletal model was described in previous publications [1,2]. Briefly, it included femur, tibia and rotula, all collateral ligaments, subdivided in several bundles, and the two cruciate ligaments subdivided in their respective anterior and posterior components. The femoral condyles and the tibial plateaus were in contact and could slide one relatively to the other without penetration. External forces were applied to the tibial tuberosity to reproduce the anterior/posterior drawer. In this case the rotation of the tibia was constrained so that it could only translate. External torques were instead applied to reproduce the varus/valgus and the internal/external rotation maneuvers. The tests were conducted at different knee flexion angles: 0°, 20°, 60°, 90° and 135°. The force/displacement and the moment/angle curves were analyzed in relation to respectively the anterior/posterior drawer test and the varus/valgus and internal/external rotation maneuvers. According to [3] the curves were separated into three portions: the central one corresponding to ‘laxity’, and the two extreme parts corresponding to ‘stiffening’. In each portion the stiffness (slope of the curve) was computed and compared in the two modelling conditions: ‘All ligaments’ and ‘ACL sacrificed’. Table 1 reports an example of how the stiffness of the extreme portion of the curve changes during the anterior drawer test. In all the tested conditions the joint stiffness appeared less affected by the lack of the ACL when the knee was either fully extended (0°) or flexed to around 90°. During the drawer test, for angles of 20°, 60° and 135° the anterior stiffness was markedly reduced. Moreover, the laxity of the knee at 135° was about more than doubled during drawer test and doubled in internal/external maneuvers, in which also a strong reduction of the external terminal stiffness was obtained. In terms of medial-lateral stability the major impact of the severed ACL was recorded on valgus and varus terminal stiffness for flexion angles of 90° and 135° respectively. Our results are in a good agreement with those obtained on cadaver studies by [3], and this further demonstrates the validity of the model implemented. The possibility to simulate a complete gait cycle by our musculoskeletal model will permit to extend the analysis to a dynamic condition which, of course, is impossible to reproduce in vitro with anatomical specimens.

Mathematical Problems in Engineering Joint Structure Stiffness Analysis of an Automotive Body in White with the Finite Element Method

The finite element model of the seven connection heads of an automotive body in white is established, and the stiffness calculation is carried out by taking the lower joint of the B pillar as an example. Nine stiffness values were obtained for each branch, which can be written as a 3 × 3 symmetric matrix. The front and back bending stiffness, torsional stiffness, and internal and external bending stiffness are obtained with the decoupling method. Based on this, the finite element model for unrigid and rigid joints is established, and the three stiffness ratio coefficients of each branch of the joint are calculated and evaluated. Finally, the effects of the thickness and stiffness of the sheet metal parts on the bending condition, torsion condition, first-order bending, and torsion frequency of the body in white are discussed using the regional sensitivity analysis and strain energy calculation.

An analytical prediction method for the bifurcation of an asymmetric rotor system partially filled with viscous incompressible fluid

Instability of a rotor partially filled with viscous incompressible fluid will cause the amplitudes of perturbations to increase exponentially. Many models of an isotropic rotor partially filled with fluid have been proposed to investigate its stability. However, the bifurcation of an anisotropic rotor partially filled with viscous incompressible fluid is complicated, which has rarely been studied. To investigate this problem, a continuous model is first established for the isotropic case and the hydrodynamic forces are calculated. The D-decomposition method is then used to determine the stable and unstable regions of the isotropic rotor. An analytical prediction method is then proposed in this paper, and the results for stable and unstable regions are the same as those obtained with the D-decomposition method. Then, this novel analytical prediction model is applied to an anisotropic rotor partially filled with viscous incompressible fluid, and the stable and unstable regions are analyzed. One isotropic and two anisotropic conditions are compared to verify the correctness of the proposed analytical method. The results show that the dimensionless damping and stiffness have significant effects on the stability of an anisotropic rotor partially filled with viscous incompressible fluid; in particular, it is found that there exists a single stable region for low values of the dimensionless damping coefficient and stiffness. Furthermore, the bifurcation law of different anisotropic parameters is first explored, which can provide theoretical guidance for the chosen external stiffness and damping coefficients.

Design and characterization of novel bi-directional auxetic cubic and cylindrical metamaterials

Traditional auxetic structures only exhibit lateral contraction when axially compressed. In this paper, a strategy of bi-directional auxetic metamaterials with tunable effective Poisson's ratio is proposed. The bi-directional auxetic metamaterials based on two-dimensional double arrow structures are designed and then fabricated through additive manufacturing. The deformation mechanisms of the proposed structures are investigated through numerical simulations combined with experiments in the present study. The results show that the relative specific stiffness and the effective Poisson’s ratios of the proposed structures depend on geometrical parameters and geometrical configuration. The relative specific stiffness of the three-dimensional cubic structure (TCU) is between the internal and external stiffness of the structure, as is the case of the effective Poisson’s ratio. The axisymmetric deformation mechanism of the three-dimensional cylindrical structure (TCY) generates transversely isotropic Poisson’s ratio and enhances stiffness compared to the TCU with the same geometric parameters. This work systematically characterizes the deformation mechanism of innovatively designed structures and widens the potential applications of metamaterials in the fields of machinery, encompassing biomedicine, and electronic devices.

Design and analysis of the optimal spinning top-shaped buoy for wave energy harvesting in low energy density seas for sustainable marine aquaculture

The floating buoys are an emerging source for renewable energy harvesting using ocean waves. Various point absorbers have been developed based on multi-freedom oscillating structures to capture wave energy. However, the choice of geometrical parameters for buoy design is still a critical problem. This paper presents a novel method to develop new geometries of floating buoy for wave energy harvester (WEH) in heave motion and aims to maximize WEH absorbed power and performance. Fives shapes (Cyl-Cone, Cyl-HS, Cyl-TCC, Cyl-AS and Cyl-SP) were derived from a cylinder buoy based on identical parameters (radius, draft, mass, water-plane area, volume and natural frequency). The Cyl-HS buoy was selected as a reference buoy for comparative analysis. The effects of shape change on the performance and output power were investigated for regular and irregular wave conditions in ANSYS AQWA at an incident wave frequency of 0.22 Hz (low energy density seas). The optimal resonant buoy was identified employing optimal and sub-optimal modes of the PTO system at external stiffness and damping parameters. Moreover, the performance of resonant buoys in optimal and suboptimal working modes was validated statistically using the F-test for variances of two samples in Origin Pro (2019). The energy conversion efficiencies of Cyl-AS buoy were examined as highest among others, with a maximum of 8.4% and 7.4% rise in optimal and suboptimal PTO modes for regular waves, respectively. For irregular waves, the Cyl-AS buoy resulted in maximum output power of 33.9% higher than the Cyl-HS buoy (reference buoy) with a maximum conversion efficiency of 90%. Finally, the simulation and experimental results for the scaled model were compared for RAO and average power and found a good agreement. The findings of this research agree with the UN-2030 Agenda for Sustainable Development Goals (in particular, SDG-7 and SDG-14 goals) while providing a path towards clean energy and blue economy developments.

A new dynamic stiffness model with hysteresis of air springs based on thermodynamics

A new theoretical model of the dynamic stiffness of air springs based on thermodynamics is proposed for determining the precise algorithm for air suspension control systems. The complex stiffness formula comprehensively considers the external heat exchange equivalent damping characteristics and air spring stiffness and damping characteristics with clear physical meaning and precise mathematical expressions for each contribution. Compared with the traditional air spring model, this model is universal because it does not restrict the gas change process inside air springs. Based on the new model, a set of identification methods for key nonlinear parameters are given. The indicator experiment was carried out to validate the dynamic stiffness model and parameter identification methods under various frequencies and strokes. Finally, the influence of key parameters and their dynamic characteristics are analysed. This theory and experiment identify air spring nonlinear parameter frequency dependence and change characteristics.

Use of cervical elastography at 18 to 22 weeks’ gestation in the prediction of spontaneous preterm birth

Accurate identification of the women who will have spontaneous preterm birth continues to be a great challenge. The use of cervical elastography for prediction of preterm birth is promising, but several limitations exist. Newer cervical elastography technology has been developed that may prove useful in evaluation of risk of preterm birth. This study aimed to develop standard cervical elastography nomograms for singleton pregnancies at 18 to 22 weeks' gestation using the E-Cervix ultrasound application, assess intraobserver reliability of the E-Cervix elastography parameters, and determine whether these cervical elastography measurements can be used in the prediction of spontaneous preterm birth. This was a prospective cohort study of pregnant women undergoing cervical length screening assessment via transvaginal ultrasound examination at 18 to 22 weeks' gestation. A semiautomatic, cervical elastography application (E-Cervix) was used during the transvaginal examination to calculate 5 quantitative parameters (internal os stiffness, external os stiffness, internal -to -external os stiffness ratio, hardness ratio, and elasticity contrast index) and create a standard nomogram for each one of them. The intraobserver reliability was calculated using Shrout-Fleiss reliability. Cervical elastography parameters were compared between those who delivered preterm (<37 weeks) spontaneously and those who delivered full term. A multivariable logistic regression model was performed to determine the ability of the cervical elastography parameters to predict spontaneous preterm birth. A total of 742 women were included, of which 49 (6.6%) had a spontaneous preterm delivery. A standard nomogram was created for each of the cervical elastography parameters from those who had a full-term birth in the index pregnancy (n=693). Intraobserver reliability was good or excellent (intraclass correlation, 0.757-0.887) for each of the cervical elastography parameters except external os stiffness which was poor (intraclass correlation, 0.441). In univariate analysis, none of the cervical elastography parameters were associated with a statistically significant increased risk of spontaneous preterm birth. In a multivariable model adjusting for history of preterm birth, gravidity, ethnicity, cervical cerclage, and vaginal progesterone use, increasing elasticity contrast index was significantly associated with an increased risk of spontaneous preterm birth (odds ratio, 1.15; 95% confidence interval, 1.02-1.30; P=.02). Cervical elastography parameters are reliably measured and are stable across 18 to 22 weeks' gestation. Based on our findings, the elasticity contrast index was associated with an increased risk of spontaneous preterm birth and may be a useful parameter for future research.

Experimental research on the seismic properties of shear wall reinforced with high‐strength bars and magnetorheological dampers

Magnetorheological (MR) damper was a kind of smart instrument, and it was very suitable for the semi-active control. In this research, a large-scale MR damper working in the shear mode of the MR fluid was developed to enhance the mechanical properties of the shear wall. The influence of MR damper on the mechanical properties of the shear walls, such as stiffness, strength, ductility, and the energy dissipation capacity, had been researched. Firstly, both the model of MR damper and shear wall were established to optimize the properties of the MR damper and shear wall. Then, three different concrete shear walls were fabricated, which were reinforced by carbon fiber-reinforced polymer (CFRP) bars (W-1), CFRP bars and MR dampers (W-2), and steel strands and MR dampers (W-3), respectively. The mechanical properties of the specimens were experimentally researched and analyzed. The experimental results showed that the ductility, the ability to bear external loads, stiffness, and energy dissipation capacity of the shear walls could be enhanced by the MR damper simultaneously. Compared with W-1, the ductility, the ability to bear external loads, ultimate deformation, and energy-dissipation capacity of W-2 increased by 4.1%, 26.8%, 83.9%, and 35.8%, respectively. The residual deformation of the three shear walls was almost the same. The results indicated that the MR damper could enhance the mechanical properties of the shear walls and had no influence on the self-centering capacity of the shear walls at the same time.