Fault Identification for Shear-Type Structures Using Low-Frequency Vibration Modes

Shear-type structures are common structural forms in industrial and civil buildings,such as concrete and steel frame structures.Fault diagnosis of shear-type structures is an important topic to ensure the normal use of structures.The main drawback of existing damage assessment methods is that they require accurate structural finite element models for damage assessment.However,for many shear-type structures,it is difficult to obtain accurate FEM.In order to avoid finite elementmodeling,amodel-freemethod for diagnosing shear structure defects is developed in this paper.This method only needs to measure a few low-order vibration modes of the structure.The proposed defect diagnosis method is divided into two stages.In the first stage,the location of defects in the structure is determined based on the difference between the virtual displacements derived from the dynamic flexibility matrices before and after damage.In the second stage,damage severity is evaluated based on an improved frequency sensitivity equation.Themain innovations of this method lie in two aspects.The first innovation is the development of a virtual displacement difference method for determining the location of damage in the shear structure.The second is to improve the existing frequency sensitivity equation to calculate the damage degree without constructing the finite elementmodel.Thismethod has been verified on a numerical example of a 22-story shear frame structure and an experimental example of a three-story steel shear structure.Based on numerical analysis and experimental data validation,it is shown that this method only needs to use the low-order modes of structural vibration to diagnose the defect location and damage degree,and does not require finite element modeling.The proposed method should be a very simple and practical defect diagnosis technique in engineering practice.

Flexible Bio-tensegrity Manipulator with Multi-degree of Freedom and Variable Structure

Conventional manipulators with rigid structures and sti ness actuators have poor flexibility,limited obstacle avoidance capability,and constrained workspace.Some developed flexible or soft manipulators in recent years have the characteristics of infinite degrees of freedom,high flexibility,environmental adaptability,and extended manipulation capability.However,these existing manipulators still cannot achieve the shrinking motion and independent control of specified segments like the animals,which hinders their applications.In this paper,a flexible bio-tensegrity manipulator,inspired by the longitudinal and transversal muscles of octopus tentacles,was proposed to mimic the shrinking behavior and achieve the variable motion patterns of each segment.Such proposed manipulator uses the elastic spring as the backbone,which is driven by four cables and has one variable structure mechanism in each segment to achieve the independent control of each segment.The variable structure mechanism innovatively contains seven lock-release states to independently control the bending and shrinking motion of each segment.After the kinematic modeling and analysis,one prototype of such bionic flexible manipulator was built and the open-loop control method was proposed.Some proof-of-concept experiments,including the shrinking motion,bending motion,and variable structure motion,were carried out by controlling the length of four cables and changing the lock-release states of the variable structure mechanism,which validate the feasibility and validity of our proposed prototype.Meanwhile,the experimental results show the flexible manipulator can accomplish the bending and shrinking motion with the relative error less than 6.8%through the simple independent control of each segment using the variable structure mechanism.This proposed manipulator has the features of controllable degree-of-freedom in each segment,which extend their environmental adaptability,and manipulation capability.

Wake Vortex Structure Characteristics of a Flexible Oscillating Fin

We compute the wake of a two-dimensional and three-dimensional flexible fin in an unsteady flow field with heaving and pitching motions using FLUENT. Deflexion mode is used for a non-uniform cantilever beam with non-uniformly distributed load. The effect of chordwise deflexion length on the characteristics of propulsion is discussed for two-dimensional flexible fin. The thrust coefficient decreases, propulsive efficiency increases and the intensity of turbulence attenuates gradually as the deflexion length increases. For a three-dimensional flexible fin, the intensity of the vortex in the plane of symmetry is higher than that in the plane at 3/4 span length of the caudal fin. But the propulsive perform.ance achieved is not what we expected with the given deflexion mode.

Abrasion test of flexible protective materials on hydraulic structures

In this study, several kinds of flexible protective materials sprayed with polyurea elastomers （hereinafter referred to as polyurea elastomer protective material） were adopted to meet the abrasion resistance requirement of hydraulic structures, and their abrasion resistances against the water flow with suspended load or bed load were studied systematically through tests. Natural basalt stones were adopted as the abrasive for simulation of the abrasion effect of the water flow with bed load, and test results indicate that the basalt stone is suitable for use in the abrasion resistance test of the flexible protective material. The wear process of the polyurea elastomer protective material is stable, and the wear loss is linear with the time of abrasion. If the wear thickness is regarded as the abrasion resistance evaluation factor, the abrasion resistance of the 351 pure polyurea is about twice those of pure polyurea with a high level of hardness and aliphatic polyurea, and over five times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with suspended load. It is also about 50 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load. Overall, the abrasion resistance of pure polyurea presented a decreasing trend with increasing hardness. Pure polyurea with a Shore hardness of D30 has the best abrasion resistance, which is 60 to 70 times that of high-performance abrasion-resistant concrete under the abrasion of the water flow with bed load, and has been recommended, among the five kinds of pure polyurea materials with different hardness, in anti-abrasion protection of hydraulic structures.

Displacement Response Reconstruction of Slender Flexible Structures Based on Cubic Spline Fitting Method

How to reconstruct a dynamic displacement of slender flexible structures is the key technology to develop smart structures and structural health monitoring(SHM), which are beneficial for controlling the structural vibration and protecting the structural safety. In this paper, the displacement reconstruction method based on cubic spline fitting is put forward to reconstruct the dynamic displacement of slender flexible structures without the knowledge of modeshapes and applied loading. The obtained strains and displacements are compared with the results calculated by ABAQUS to check the method's validity. It can be found that the proposed method can accurately identify the strains and displacement of slender flexible structures undergoing linear vibrations, nonlinear vibrations, and parametric vibrations. Under the concentrated force, the strains of slender flexible structures will change suddenly along the axial direction. With locally densified measurement points, the present reconstruction method still works well for the strain concentration problem.

Tailoring the Meso-Structure of Gold Nanoparticles in Keratin-Based Activated Carbon Toward High-Performance Flexible Sensor

Flexible biosensors with high accuracy and reliable operation in detecting pH and uric acid levels in body fluids are fabricated using well-engineered metaldoped porous carbon as electrode material.The gold nanoparticles@N-doped carbon in situ are prepared using wool keratin as both a novel carbon precursor and a stabilizer.The conducting electrode material is fabricated at 500℃ under customized parameters,which mimics A-B type(two different repeating units) polymeric material and displays excellent deprotonation performance(pH sensitivity).The obtained pH sensor exhibits high pH sensitivity of 57 mV/pH unit and insignificant relative standard deviation of 0.088%.Conversely,the composite carbon material with sp^2 structure prepared at 700℃ is doped with nitrogen and gold nanoparticles,which exhibits good conductivity and electrocatalytic activity for uric acid oxidation.The uric acid sensor has linear response over a range of 1-150 μM and a limit of detection 0.1 μM.These results will provide new avenues where biological material will be the best start,which can be useful to target contradictory applications through molecular engineering at mesoscale.

Discrete Element with Flexible Connector for Dynamic Analysis of 3-D Beam Structures

Combined multi-body dynamics with structural dynamics, a new discrete element with flexible connector, which is applicable for 3-D beam structures, is developed in this paper. Both the generalized elastic coefficient matrix of the flexible connector and the mass matrix of discrete element may be off-diagonal in a general case. The zero-length rigid element is introduced to simulate the node at which multiple elements are jointed together. It may also be effective when the axes of adjacent elements are not in the same line. The examples for eigenvalue calculation show that the model is successful. It can be extended to the geometric nonlinear response analysis.

Equivalent continuum modeling of beam-like truss structures with flexible joints

The paper investigated the equivalent continuum modeling of beam-like repetitive truss structures considering the flexibility of joints,which models the contact between the truss member and joint by spring-damper with six directional stiffnesses and dampings.Firstly,a two-node hybrid joint-beam element was derived for modeling the truss member with flexible end joints,and a condensed model for the repeating element with flexible joints was obtained.Then,the energy equivalence method was adopted to equivalently model the truss structure with flexible joints and material damping as a spatial viscoelastic anisotropic beam model.Afterwards,the equations of motion for the equivalent beam model were derived and solved analytically in the frequency domain.In the numerical studies,the correctness of the presented method was verified by comparisons of the natural frequencies and frequency responses evaluated by the equivalent beam model with the results of the finite element method model.

Flexible electrically pumped random lasing from ZnO nanowires based on metal–insulator–semiconductor structure

Flexible electrically pumped random laser（RL） based on ZnO nanowires is demonstrated for the first time to our knowledge. The ZnO nanowires each with a length of 5 μm and an average diameter of 180 nm are synthesized on flexible substrate（ITO/PET） by a simple hydrothermal method. No obvious visible defect-related-emission band is observed in the photoluminescence（PL） spectrum, indicating that the ZnO nanowires grown on the flexible ITO/PET substrate have few defects. In order to achieve electrically pumped random lasing with a lower threshold, the metal–insulator–semiconductor（MIS） structure of Au/SiO2/ZnO on ITO/PET substrate is fabricated by low temperature process. With sufficient forward bias, the as-fabricated flexible device exhibits random lasing, and a low threshold current of ～ 11.5 m A and high luminous intensity are obtained from the ZnO-based random laser. It is believed that this work offers a case study for developing the flexible electrically pumped random lasing from ZnO nanowires.

Characteristic Model-based Discrete-time Sliding Mode Control for Spacecraft with Variable Tilt of Flexible Structures

In this paper, the finite-time attitude tracking control problem for the spacecrafts with variable tilt of flexible appendages in the conditions of exogenous disturbances and inertia uncertainties is addressed. First the characteristic modeling method is applied to the problem of the spacecraft modeling.Second, a novel adaptive sliding mode surface is designed based on the characteristic model. Furthermore, a discrete-time sliding mode control(DTSMC) law, which makes the tracking error converge into a predefined bound in finite time, is proposed by employing the parameters of characteristic model associated with the sliding mode surface to provide better performances,robustness, faster response, and higher control precision. The designed DTSMC includes the adaptive control architecture and is chattering-free. Finally, digital simulations of a sun synchronous orbit satellite(SSOS) are presented to illustrate effectiveness of the control strategies as well as to verify the practical feasibility of the rapid maneuver mission.

Thermal-Fluid-Structure Coupling Analysis of Flexible Corrugated Cryogenic Hose

This work presents a numerical investigation of the thermal–fluid–structure coupling behavior of the liquid natural gas(LNG)transported in the flexible corrugated cryogenic hose.A three-dimensional model of the corrugated hose structure composed of multiple layers of different materials is established and coupled with turbulent LNG flow and heat transfer models in the commercial software ANSYS Workbench.The flow transport behavior,heat transfer across the hose layers,and structural response caused by the flow are analyzed.Parametric studies are performed to evaluate the impacts of inlet flow rate and thermal conductivity of insulation material on the temperature and structural stress of the corrugated hose.The study found that,compared with a regular operating condition,higher inlet flow velocities not only suppress the heat gain of the LNG but also lower the flow-induced structural stress.The insulation layer exhibits excellent performance in maintaining the temperature at the fluid–structure interface,showing little temperature change with respect to material thermal conductivity and ambient temperature.The simulation results may contribute to the research and design of the flexible corrugated cryogenic hoses and provide guidance for safer and more efficient field operations.

Fluid-Structure Interaction Analysis of Flexible Plate with Partitioned Coupling Method

The development and rapid usage of numerical codes for fluid-structure interaction(FSI) problems are of great relevance to researchers in many engineering fields such as civil engineering and ocean engineering. This multidisciplinary field known as FSI has been expanded to engineering fields such as offshore structures, tall slender structures and other flexible structures applications. The motivation of this paper is to investigate the numerical model of two-way coupling FSI partitioned flexible plate structure under fluid flow. The adopted partitioned method and approach utilized the advantage of the existing numerical algorithms in solving the two-way coupling fluid and structural interactions. The flexible plate was subjected to a fluid flow which causes large deformation on the fluid domain from the oscillation of the flexible plate. Both fluid and flexible plate are subjected to the interaction of load transfer within two physics by using the strong and weak coupling methods of MFS and Load Transfer Physics Environment, respectively. The oscillation and deformation results have been validated which demonstrate the reliability of both strong and weak method in resolving the two-way coupling problem in contribution of knowledge to the feasibility field study of ocean engineering and civil engineering.

Crystal Structure of Dimeric Units Cd_2(ncpo)_2(phen)_2(H_2O)_2 Constructed by Flexible Dicarboxylic Acid with Fluorescent Emission

A dimeric coordination complex Cd2（ncpo）2（phen）2（H2O）2 was constructed by a flexible dicarboxylic acid, 2-nitro-4-carboxylphenoxyacetic acid. Its crystal structure was determined by X-ray single-crystal diffraction analysis. The crystal is of monoclinic system, space group P21/n with a = 17.2616（3）, b = 12.7460（2）, c = 18.4041（3） A^°, β= 94.432（1）°, C42H30Cd2N6O16, Mr = 1099.52, V = 4037.09（12）A^°^3 Dc = 1.809 g/cm^3, F（000） = 2192, μ = 1.139 cm^-1 and Z = 4. The final R = 0.0218 and wR = 0.0703 for 8288 observed reflections with I 〉 2σ（I）. There are two crystallographically independent but structurally very similar molecules in the unit cell of the title complex. It is noticeable that the ligand ncpo^2- displays a good flexibility, demonstrating different modes from the rigid ligands. The luminescence property has been investigated, which shows photoluminescence at 465, 490 and 574 nm upon excitation at 320 nm in the solid state at room temperature.

Syntheses and Crystal Structures of Three Cadmium（II） Coordination Complexes Based on Flexible 1,2-Bis（imidazol-1~ˊ-yl）ethane

Three Cd（II） coordination complexes,{[Cd（bime）3]（NO3）2·（H2O）3}n（1）,[Cd（bime）Br2]n（2） and [（H2bime）（CdBr4）（H2O）]n（3）（bime = 1,2-bis（imidazol-1-yl）ethane）,have been prepared and characterized.Single-crystal X-ray diffraction analysis reveals that 1~3 crystallize in the trigonal space group P-3,monoclinic space group C2/c and triclinic space group P1,respectively.In 1,bime bridges six-coordinated Cd（II） to generate a two-fold interpenetrating 3D coordination polymer,in which NO3- is not involved in coordination,but serves as a void filler to balance the charge of the 3D framework.The six NO3- and six uncoordinated water molecules form an unprecedented 24-membered macrocycle through hydrogen bonding interaction.In 2,bime in an anti-conformation links the CdBr2 units into a zigzag chain.In 3,bime does not take part in coordination,but is protonated to act as a counter cation of [CdBr4 ]2-.The hydrogen bonds between H2bime and [CdBr4]2- result in the formation of a supramolecular chain.

Vibration control of flexible spacecraft actuated by piezoceramics via variable structure strategy

This paper presented a hybrid control scheme to vibration reduction of flexible spacecraft during rotational maneuver by using variable structure output feedback control (VSOFC) and piezoelectric materials. The control configuration included the attitude controller based on VSOFC method and vibration attenuator designed by constant-gain negative velocity feedback control. The attitude controller consisted of a linear feedback term and a discontinuous feedback term. With the presence of this attitude controller, an additional flexible control system acting on the flexible parts can be designed for vibration control. Compared with conventional proportional-derivative (PD) control, the developed control scheme guarantees not only the stability of the closed-loop system, but also yields better performance and robustness in the presence of parametric uncertainties and external disturbance. Simulation results are presented for the spacecraft model to show the effectiveness of the proposed control techniques.

Syntheses and Crystal Structures of Two One-dimensional Cobalt(Ⅱ) Compounds with the Flexible Dipyridyl Ligan

Two one-dimensional cobalt（II） compounds {[Co（Hbpma）（H20）4]2·3SO4·4.5H2O}n 1 and {[Co（Hbpma）（NCS）3（H20）]·2.85H2O}n 2 （bpma = N,N＇-bis（3-pyridylmethyl）amine） have been synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 crystallizes in triclinic, space group Pi with a = 15.8780（5）, b = 16.2187（5）, c = 16.4858（5） A, α = 91.0420（10）,β = 94.5190（10）, γ = 101.4360（10）°, V = 4145.7（2） A3, C24H53Co2N6024.5083, Mr = 1031.76, Z = 4, Dc = 1.653 g/cm3, p（MoKa） = 1.046 mm-1, F（000） = 2148, S = 1.017, the final R = 0.0269 and wR = 0.0644 for 13032 observed reflections （I 〉 2a（/））. For complex 2, it belongs to triclinic, space group Pi with a = 9.3761（11）, b = 10.5814（13）, c = 11.2972（14）A, α= 85.472（2）,β = 88.058（2）,γ = 76.203（2）°, V= 1085.0（2） A3, C15Hzl.v0CoN603.85S3, Mr= 502.79, Z = 2, Dc = 1.539 g/cm3, p（MoKa） = 1.112 mm-1, F（000） = 519, S = 1.070, the final R = 0.0358 and wR = 0.0899 for 3466 observed reflections （I 〉 2σ（I））. Two complexes 1 and 2 are both found to be one-dimensional coordination polymers bridged by the protonated bpma ligands, which are assembled into three-dimensional supramolecular structures through the hydrogen bonding interactions and π-π packing interactions.

A Neural Fuzzy System for Vibration Control in Flexible Structures

An adaptive neural fuzzy (NF) controller is developed in this paper for active vibration suppression in flexible structures. A recurrent identification network (RIN) is developed to adaptively identify system dynamics of the plant. A novel recurrent training (RT) technique is suggested to train the RIN so as to optimize nonlinear input-output mapping and to enhance convergence. The effectiveness of the developed controller and the related techniques has been verified experimentally corresponding to different control scenarios. Test results show that the proposed RIN can effectively recognize the time-varying dynamics of the plant. The RT-based hybrid training technique can improve the adaptive capability of the control system to accommodate different system conditions and enhance the training convergence. The developed NF controller is a robust and stable vibration suppression system, and it outperforms other related NF controllers.

Out-of-plane (SH) soil-structure interaction： a shear wall with rigid and flexible ring foundation

Soil-structure interaction （SSI） of a building and shear wall above a foundation in an elastic half-space has long been an important research subject for earthquake engineers and strong-motion seismologists. Numerous papers have been published since the early 1970s; however, very few of these papers have analytic closed-form solu- tions available. The soil-structure interaction problem is one of the most classic problems connecting the two dis- ciplines of earthquake engineering and civil engineering. The interaction effect represents the mechanism of energy transfer and dissipation among the elements of the dynamic system, namely the soil subgrade, foundation, and super- structure. This interaction effect is important across many structure, foundation, and subgrade types but is most pro- nounced when a rigid superstructure is founded on a rela- tively soft lower foundation and subgrade. This effect may only be ignored when the subgrade is much harder than a flexible superstructure： for instance a flexible moment frame superstructure founded on a thin compacted soil layer on top of very stiff bedrock below. This paper will study the interaction effect of the subgrade and the super- structure. The analytical solution of the interaction of a shear wall, flexible-rigid foundation, and an elastic half- space is derived for incident SH waves with various angles of incidence. It found that the flexible ring （soft layer） cannot be used as an isolation mechanism to decouple asuperstructure from its substructure resting on a shaking half-space.

Variable structure attitude maneuver and vibration control of flexible spacecraft

A dual-stage control system design method is presented for the three-axis-rotational maneuver and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator. In this design approach, the attitude control and the vibration suppression sub-systems are designed separately using the lower order model. The design of attitude controller is based on the variable structure control (VSC) theory leading to a discontinuous control law. This controller accomplishes asymptotic attitude maneuvering in the closed-loop system and is insensitive to the interaction of elastic modes and uncertainty in the system. To actively suppress the flexible vibrations, the modal velocity feedback control method is presented by using piezoelectric materials as additional sensor and actuator bonded on the surface of the flexible appendages. In addition, a special configuration of actuators for three-axis attitude control is also investigated: the pitch attitude controlled by a momentum wheel, and the roll/yaw control achieved by on-off thrusters, which is modulated by pulse width pulse frequency modulation technique to construct the proper control torque history. Numerical simulations performed show that the rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque and parameter uncertainty.