Axial Support Research Articles

Complex modal analysis of transverse free vibrations for axially moving nanobeams based on the nonlocal strain gradient theory

We investigate the transverse free vibration behaviour of axially moving nanobeams based on the nonlocal strain gradient theory. Considering the geometrical nonlinearity, which takes the form of von Kármán strains, the coupled plane motion equations and related boundary conditions of a new size-dependent beam model of Euler-Bernoulli type are developed using the generalized Hamilton principle. Using the simply supported axially moving nanobeams as an example, the complex modal analysis method is adopted to solve the governing equation; then, the effect of the order of modal truncation on the natural frequencies is discussed. Subsequently, the roles of the nonlocal parameter, material characteristic parameter, axial speed, stiffness and axial support rigidity parameter on the free vibration are comprehensively addressed. The material characteristic parameter induces the stiffness hardening of nanobeams, while the nonlocal parameter induces stiffness softening. In addition, the roles of small-scale parameters on the flutter critical velocity and stability are explained.

Natural Characteristics of The Herringbone Gear Transmission System

According to the structure characteristics of herringbone gear transmission, a more realistic dynamic model of the transmission system is built in consideration of the inner excitation, herringbone gears axial positioning and sliding bearing etc. The natural frequencies of the system are calculated, and the vibration mode is divided into symmetric vibration modes and asymmetric vibration modes. The time history of system dynamic force is obtained by solving the dynamic model. The effects of the connection stiffness of left and right sides of herringbone gears and axial support stiffness on natural characteristics are discussed.

Dynamic Analysis of BTA Deep-Hole Drilling Shaft System

Numerical investigation was conducted into dynamics of deep-hole drilling shaft system. The rotating drilling shaft was modeled as a Rayleigh beam conveying the fluid and subjected to torque, compressive axial force and support constraints. From the viewpoint of rotor dynamics and fluid-structure interaction, the governing equation of the drilling shaft system for lateral vibration was obtained taking into account of the fluid-structure interaction, the rotational inertia, the gyroscopic effect, the effect of the motion constraints and frictional damping generated by the surrounding fluid. The influence of the cutting fluid flow velocity, rotational angular velocity, torque, compressive axial force, and the support constraints on natural frequency and stability of the drilling shaft system was examined. It has been found that the cutting fluid flow velocity, compressive axial force and torque decreases natural frequencies of the drilling shaft system, whereas rotational angular velocity and support constraints can improve the stability of the drilling shaft system.

Design and principle of operation of the HeartMate PHP (percutaneous heart pump).

The HeartMate PHP (percutaneous heart pump) is a second-generation transcatheter axial flow circulatory support system. The collapsible catheter pump is inserted through a 14 Fr sheath, deployed across the aortic valve expanding to 24 Fr and able to deliver up to 5 L/min blood flow at minimum haemolytic risk. As such, this device may be a valuable adjunct to percutaneous coronary intervention (PCI) of challenging lesions in high-risk patients or treatment of cardiogenic shock. This technical report discusses: (i) the HeartMate PHP concept, (ii) the implantation technique, (iii) the haemodynamic performance in an in vitro cardiovascular flow testing set-up, and (iv) preliminary clinical experience. An update on the device, produced by St. Jude Medical/Abbott Laboratories, can be found in the Appendix.

Tip-Tilt Tests by Using Eddy Current Measuring Sensors

Fast-steering Secondary Mirror (FSM) will be installed to the Giant Magellan Telescope (GMT) as a first generation secondary mirror. The FSM implements a tip-tilt mechanism which compensates image degradations caused by wind turbulence and structure jitter. A prototype segment of the FSM has been developed, which comprised of a dummy mirror, a mirror cell, axial and lateral supports, vacuum devices, etc. Several test-bed frames have been developed to hang the segment and to test tip-tilt functionalities. They have been designed, manufactured, assembled, and verified successfully step by step. Tip-tilt measurements were performed mainly by displacement measuring sensors which detect eddy currents precisely. The results proved that the prototype segment worked successfully, by complying the requirements of the FSM for the tip-tilt actuations.

Random Vibration Analysis of the Tip-tilt System in the GMT Fast Steering Secondary Mirror

A random vibration analysis was accomplished on the tip-tilt system of the fast steering secondary mirror (FSM) for the Giant Magellan Telescope (GMT). As the FSM was to be mounted on the top end of the secondary truss and disturbed by the winds, dynamic effects of the FSM disturbances on the tip-tilt correction performance was studied. The coupled dynamic responses of the FSM segments were evaluated with a suggested tip-tilt correction modeling. Dynamic equations for the tip-tilt system were derived from the force and moment equilibrium on the segment mirror and the geometric compatibility conditions with four design parameters. Statically stationary responses for the tip-tilt actuations to correct the wind-induced disturbances were studied with two design parameters based on the spectral density function of the star image errors in the frequency domain. Frequency response functions and root mean square values of the dynamic responses and the residual star image errors were numerically calculated for the off-axis and on-axis segments of the FSM. A prototype of on-axis segment of the FSM was developed for tip-tilt actuation tests to confirm the ratio of tip-tilt force to tip-tilt angle calculated from the suggested dynamic equations of the tip-tilt system. Tip-tilt actuation tests were executed at 4, 8 and 12 Hz by measuring displacements of piezoelectric actuators and reaction forces acting on the axial supports. The derived ratios of rms tip-tilt force to rms tip-tilt angle from tests showed a good correlation with the numerical results. The suggested process of random vibration analysis on the tip-tilt system to correct the wind-induced disturbances of the FSM segments would be useful to advance the FSM design and upgrade the capability to achieve the least residual star image errors by understanding the details of dynamics.

Mechanical Analysis of MgB2 Based Full Body MRI Coils Under Different Winding Conditions

The winding of composite superconducting wire around a mandrel is one of the first stages of manufacturing processes of a superconducting magnet. Depending on the method of mechanical support conditions during winding, the strain development at the final stage in a superconducting magnet may vary significantly. Therefore, proper selection of the winding process is important to increase the feasibility for a conduction cooled full body MRI magnet based on magnesium diboride (MgB 2 ), a strain sensitive high-temperature superconductor. A multiscale multiphysics finite element analysis) model of an 18 filament MgB 2 wire is developed for strain estimation. The computationally homogenized representative volume element of the composite wire is used in the coil bundle in place of the actual MgB2 wire. The simulation considers winding, thermal cool-down and electromagnetic charging to estimate total strain developed at the final step-electromagnetic charging. Four different types of support conditions are studied and strain development is reported. Results suggest that a combination of radial and axial support at the inner radial surface and outermost axial surfaces of the mandrel, respectively, is the most favorable winding condition with a minimum strain development of 0.021%, which is half in comparison to no mandrel support.

大口径望远镜主镜支撑系统装调

According to 1.2 m large aperture telescope primary mirror support system, an effective assembly method was advanced to insure the root-mean-square (RMS) of the surface accuracy. The primary mirror support system was designed following kinematic principle. To achieve excellent performance of the RMS of primary mirror surface accuracy at different ambient temperature (from -20℃ to 60℃) and different elevation(from vertical to horizontal), whiffletree structure were used for axial support,while lateral support mechanisms based on flexible tangent link structure were adopted. Resulting from machining error and installation error of the flexible structures, assembly stress was presented certainly, that could increase primary mirror distortion range evidently. By the finite element analysis(FEA) simulation, the effects of various errors were calculated. According to simulation results, assembly processes were established. After assembly of primary mirror support system, the RMS of primary mirror surface accuracy was measured by compensator and laser interferometer. In measurement, the RMS of surface accuracy was /42 and /31(=632.8 nm), when optical axis of primary mirror was vertical and horizontal.

Effect of Braiding Angle on the Impact and Post-Impact Behavior of 3D Braided Composites

In this study, the impact and post-impact behavior of three-dimensional (3D) four-directional carbon/epoxy braided composites having different braiding angles were investigated. The same impact energy (45 J) was applied to the specimens. The post-impact mechanical properties of the materials were performed by compression after impact (CAI) testing, and the processes were monitored by the acoustic emission (AE) technique. Results showed that the specimens with larger braiding angle sustained higher peak loads, and smaller impact damage area, mainly attributed to a more compact space arrangement. The CAI strength and damage mechanism were found to be mainly dependent on the axial support of the braiding fiber tows. Increasing the braiding angle of the composites, the CAI strength was reduced, and the damage mode of the composites was changed from transverse fracture to shear one. Combining AE parameters and CAI curves allows one to characterize the failure process, thereby enabling fracture analysis of the materials under study.

Design and optimization of kinematic lateral support on 2 m SiC primary mirror

The support structure based on kinematic principle had been wildly used in the axial support on large-diameter telescope. But it is not maturely applied in the lateral support system. A lateral support structure based on kinematic principle is explained. Based on a primary mirror with a diameter of 2.04 m, a support structure with more details was designed and analyzed by the ANSYS Parametric Design Language. Selected the Root Mean Square (RMS) of the primary mirror when the optical axis was vertical as the objective function, the support reaction was optimized by the simulated annealing algorithm. Final surface error RMS was 16.67 nm. Surface error with different obliquities were calculated, which meets the requirement that the RMS should be less than λ/3.

Gas film disturbance characteristics analysis of high-speed and high-pressure dry gas seal

The dry gas seal(DGS) has been widely used in high parameters centrifugal compressor, but the intense vibrations of shafting, especially in high-speed condition, usually result in DGS’s failure. So the DGS’s ability of resisting outside interference has become a determining factor of the further development of centrifugal compressor. However, the systematic researches of which about gas film disturbance characteristics of high parameters DGS are very little. In order to study gas film disturbance characteristics of high-speed and high-pressure spiral groove dry gas seal(S-DGS) with a flexibly mounted stator, rotor axial runout and misalignment are taken into consideration, and the finite difference method and analytical method are used to analyze the influence of gas film thickness disturbance on sealing performance parameters, what’s more, the effects of many key factors on gas film thickness disturbance are systematically investigated. The results show that, when sealed pressure is 10.1MPa and seal face average linear velocity is 107.3 m/s, gas film thickness disturbance has a significant effect on leakage rate, but has relatively litter effect on open force; Excessively large excitation amplitude or excessively high excitation frequency can lead to severe gas film thickness disturbance; And it is beneficial to assure a smaller gas film thickness disturbance when the stator material density is between 3.1 g/cm3 to 8.4 g/cm3; Ensuring sealing performance while minimizing support axial stiffness and support axial damping can help to improve dynamic tracking property of dry gas seal. The proposed research provides the instruction to optimize dynamic tracking property of the DGS.

Hybrid optimization methodology of variable densities mesh model for the axial supporting design of wide-field survey telescope

The optimization of a primary mirror support system is one of the most critical problems in the design of large telescopes. Here, we propose a hybrid optimization methodology of variable densities mesh model (HOMVDMM) for the axial supporting design, which has three key steps: (1) creating a variable densities mesh model, which will partition the mirror into several sparse mesh areas and several dense mesh areas; (2) global optimization based on the zero-order optimization method for the support of primary mirror with a large tolerance; (3) based on the optimization results of the second step, further optimization with first-order optimization method in dense mesh areas by a small tolerance. HOMVDMM exploits the complementary merits of both the zero- and first-order optimizations, with the former in global scale and the latter in small scale. As an application, the axial support of the primary mirror of the 2.5-m wide-field survey telescope (WFST) is optimized by HOMVDMM. These three designs are obtained via a comparative study of different supporting points including 27 supporting points, 39 supporting points, and 54 supporting points. Their residual half-path length errors are 28.78, 9.32, and 5.29 nm. The latter two designs both meet the specification of WFST. In each of the three designs, a global optimization value with high accuracy will be obtained in an hour on an ordinary PC. As the results suggest, the overall performance of HOMVDMM is superior to the first-order optimization method as well as the zero-order optimization method.

Stochastic Optimal Control of Stayed Cable Vibrations with Wide-Band Random Wind Excitation Using Axial Support Motion

This paper proposes an optimal control strategy and corresponding method, to use the advantageous characteristics of the axial support motion to control the stayed cable vibrations in plane by wind excitation. Through a thorough investigation of wide-band random wind excitation and spatial relativity of the wind load along the cable, this study derives realistic and accurate motion equations of the control system. These motion equations are simplified into the form of the first four modes using the Galerkin method. The Itô stochastic differential equations of partial average for the system energy are derived using the stochastic averaging method of the quasi-integrable Hamiltonian systems. Furthermore, the dynamic programming equations with performance index are established by the stochastic dynamic programming principle. The random optimal control law is obtained by solving the dynamic programming equations using the approximate method. The numerical results show that, when standard deviations of the axial support motion are the same, the reduction of the standard deviation of the cable acceleration, and the cable displacement under the stochastic optimal control (SOC) law proposed by this paper, is larger than that under bilinear (BL) control. The SOC method proposed in this paper provides better results than the BL method.

Parametric and internal resonance of axially accelerating viscoelastic beams with the recognition of longitudinally varying tensions

In this paper, parametric and 3:1 internal resonance of axially moving viscoelastic beams on elastic foundation are analytically and numerically investigated. The beam is restricted by viscous damping force. The beam’s material obeys the Kelvin model in which the material time derivative is used. The governing equations of coupled planar vibration and the associated boundary conditions are derived from the generalized Hamilton principle. The effects of the nonhomogeneous boundary conditions due to the viscoelasticity are highlighted, while the boundary conditions are assumed to be homogeneous in previous studies. In small but finite stretching problems, the equation is simplified into a governing equation of transverse nonlinear vibration. It is a nonlinear integro-partial differential equation with time-dependent and space-dependent coefficients. The dependence of the tension on the finite axial support rigidity is also modeled. The method of multiple scales is directly applied to establish the solvability conditions. The nonlinear steady-state oscillating response along with the stability and bifurcation of the beam is investigated. A detailed study is carried out to determine the influence of the viscoelastic coefficient and the viscous damping coefficient on dynamic behavior of the system. The numerical calculations by the differential quadrature scheme confirm the approximate analytical results.

Nonlinear dynamics of axially moving viscoelastic Timoshenko beam under parametric and external excitations

This investigation focuses on the nonlinear dynamic behaviors in the transverse vibration of an axially accelerating viscoelastic Timoshenko beam with the external harmonic excitation. The parametric excitation is caused by the harmonic fluctuations of the axial moving speed. An integro-partial-differential equation governing the transverse vibration of the Timoshenko beam is established. Many factors are considered, such as viscoelasticity, the finite axial support rigidity, and the longitudinally varying tension due to the axial acceleration. With the Galerkin truncation method, a set of nonlinear ordinary differential equations are derived by discretizing the governing equation. Based on the numerical solutions, the bifurcation diagrams are presented to study the effect of the external transverse excitation. Moreover, the frequencies of the two excitations are assumed to be multiple. Further, five different tools, including the time history, the Poincare map, and the sensitivity to initial conditions, are used to identify the motion form of the nonlinear vibration. Numerical results also show the characteristics of the quasiperiodic motion of the translating Timoshenko beam under an incommensurable relationship between the dual-frequency excitations.

Development of somites and their derivatives in amphioxus, and implications for the evolution of vertebrate somites.

BackgroundVertebrate somites are subdivided into lineage compartments, each with distinct cell fates and evolutionary histories. Insights into somite evolution can come from studying amphioxus, the best extant approximation of the chordate ancestor. Amphioxus somites have myotome and non-myotome compartments, but development and fates of the latter are incompletely described. Further, while epithelial to mesenchymal transition (EMT) is important for most vertebrate somitic lineages, amphioxus somites generally have been thought to remain entirely epithelial. Here, we examined amphioxus somites and derivatives, as well as extracellular matrix of the axial support system, in a series of developmental stages by transmission electron microscopy (TEM) and in situ hybridization for collagen expression.ResultsThe amphioxus somite differentiates medially into myotome, laterally into the external cell layer (a sub-dermal mesothelium), ventrally into a bud that forms mesothelia of the perivisceral coelom, and ventro-medially into the sclerotome. The sclerotome forms initially as a monolayered cell sheet that migrates between the myotome and the notochord and neural tube; subsequently, this cell sheet becomes double layered and encloses the sclerocoel. Other late developments include formation of the fin box mesothelia from lateral somites and the advent of isolated fibroblasts, likely somite derived, along the myosepta. Throughout development, all cells originating from the non-myotome regions of somites strongly express a fibrillar collagen gene, ColA, and thus likely contribute to extracellular matrix of the dermal and axial connective tissue system.ConclusionsWe provide a revised model for the development of amphioxus sclerotome and fin boxes and confirm previous reports of development of the myotome and lateral somite. In addition, while somite derivatives remain almost entirely epithelial, limited de-epithelialization likely converts some somitic cells into fibroblasts of the myosepta and dermis. Ultrastructure and collagen expression suggest that all non-myotome somite derivatives contribute to extracellular matrix of the dermal and axial support systems. Although amphioxus sclerotome lacks vertebrate-like EMT, it resembles that of vertebrates in position, movement to surround midline structures and into myosepta, and contribution to extracellular matrix of the axial support system. Thus, many aspects of the sclerotome developmental program evolved prior to the origin of the vertebrate mineralized skeleton.

Dipteran wing motor-inspired flapping flight versatility and effectiveness enhancement.

Insects are a prime source of inspiration towards the development of small-scale, engineered, flapping wing flight systems. To help interpret the possible energy transformation strategies observed in Diptera as inspiration for mechanical flapping flight systems, we revisit the perspective of the dipteran wing motor as a bistable click mechanism and take a new, and more flexible, outlook to the architectural composition previously considered. Using a representative structural model alongside biological insights and cues from nonlinear dynamics, our analyses and experimental results reveal that a flight mechanism able to adjust motor axial support stiffness and compression characteristics may dramatically modulate the amplitude range and type of wing stroke dynamics achievable. This corresponds to significantly more versatile aerodynamic force generation without otherwise changing flapping frequency or driving force amplitude. Whether monostable or bistable, the axial stiffness is key to enhance compressed motor load bearing ability and aerodynamic efficiency, particularly compared with uncompressed linear motors. These findings provide new foundation to guide future development of bioinspired, flapping wing mechanisms for micro air vehicle applications, and may be used to provide insight to the dipteran muscle-to-wing interface.

Hemodynamic Assessment Using Pressure-Volume (PV) During Mechanical Circulatory Support

Mechanical circulatory support devices (MCS), namely percutaneous ventricular assist devices (pVAD) are temporarily introduced to support circulation in hemodynamically compromised patients and also during mid to high risk coronary artery procedures. Their multiple responsibilities include maintaining an adequate systemic blood pressure and cardiac output to provide satisfactory end-organ perfusion in unloading of the failing ventricle, and to temporary lower myocardial contractility while reducing myocardial oxygen demand supporting favorable ventricular remodeling. To timely and quantitatively assess hemodynamics during pVAD circulatory support post-cardiogenic shock or acute myocardial infarction (MI), pressure-volume (PV) measurements are becoming progressively more appreciated as they can longitudinally evaluate the status of the support. Hemodynamically, importance of constant circulatory interrogations by PV during pVAD support lies in its capacity to “fine-tune” the device for a specific patient to work in synergy with the ailing organ. In this review basic characteristics of a diagnostic value of pressure-volume during pVAD hemodynamic support will be discussed fostering conversation about the necessity of e.g. combining pump flow with load-independent indices creating indexes that can be used to further characterize pump unloading in relation to innate cardiac contractility during axial or centrifugal flow support. Additionally, discussion about central hemodynamics during different flow support will be provided evaluating pVADs to assess its ability to work in synergy and to anticipate potential difficulties that might occur during the procedure. Brief description of recent efforts to combine PV exam with pump flow during circulatory support using pVAD and the concept of pressure-volume area (PVA) and myocardial oxygen consumption (mVO2) during unloading will be also discussed.

Fluid–structure interaction with viscoelastic supports during waterhammer in a pipeline

Waterhammer modeling with fluid–structure interaction (FSI) in a pipeline with axial viscoelastic supports is the aim of this research. The viscoelastic materials of supports (or the pipe wall) were described using the generalized Kelvin–Voigt model. Hydraulic governing equations were solved by the method of characteristic (MOC) and axial vibration equation of the pipe wall was solved using the finite element method (FEM) in the time domain. For a typical case study, four different types for supporting the pipeline in the axial direction: fully free to move; fixed (rigid support); elastic and viscoelastic supports, subject to a waterhammer are analyzed and the results are scrutinized. The results quantitatively confirm that the use of supports with viscoelastic behavior in the axial direction of the pipeline can significantly reduce axial-pipe vibrations (displacements and stresses). The consequences of this structural damping on the attenuation of the internal fluid pressure are further demonstrated.

Periodic responses and chaotic behaviors of an axially accelerating viscoelastic Timoshenko beam

This paper investigates the steady-state periodic response and the chaos and bifurcation of an axially accelerating viscoelastic Timoshenko beam. For the first time, the nonlinear dynamic behaviors in the transverse parametric vibration of an axially moving Timoshenko beam are studied. The axial speed of the system is assumed as a harmonic variation over a constant mean speed. The transverse motion of the beam is governed by nonlinear integro-partial-differential equations, including the finite axial support rigidity and the longitudinally varying tension due to the axial acceleration. The Galerkin truncation is applied to discretize the governing equations into a set of nonlinear ordinary differential equations. Based on the solutions obtained by the fourth-order Runge–Kutta algorithm, the stable steady-state periodic response is examined. Besides, the bifurcation diagrams of different bifurcation parameters are presented in the subcritical and supercritical regime. Furthermore, the nonlinear dynamical behaviors are identified in the forms of time histories, phase portraits, Poincare maps, amplitude spectra, and sensitivity to initial conditions. Moreover, numerical examples reveal the effects of various terms Galerkin truncation on the amplitude–frequency responses, as well as bifurcation diagrams.