Dynamic Characteristics Of Structure Research Articles

Study on vehicle-bridge coupling vibration response and impact factor of spatial Y-shaped tied arch bridge

The spatial Y-shaped steel arch bridge adopts a single and double arch rib composite structure, which has a complex spatial structure, and its structural dynamic characteristics are special, resulting in a more complex vehicle-bridge coupling vibration response law. To clarify the dynamic characteristics of the space Y-shaped steel arch bridge structure, this paper takes a space Y-shaped steel arch bridge under construction in China as the research object and uses ABAQUS to establish a vehicle-bridge coupling model. The correctness of the ABAQUS model is verified by the bridge model established by Midas Civil, and four grades of road roughness are established by using the ABAQUS kernel command. The influence of vehicle speed and road roughness on the spatial Y-shaped steel arch bridge is analyzed. The impact factor of the vehicle on the flat bridge deck at the design speed is calculated and compared with the current specification, which provides a reference for the design and maintenance of space Y-shaped steel arch bridge in the future.

Thermal Effects on Dynamic Behavior of CFETR Vacuum Vessel

The vacuum vessel (VV) of the China Fusion Engineering Test Reactor (CFETR) was designed to withstand the variable structural loads resulting from dynamic excitation, such as seismic and plasma disruption. Modal analysis, a powerful tool, was used to evaluate the structural dynamic characteristics, such as frequency and mode shape. In addition, the CFETR VV has three different temperature conditions: room temperature (20°C), normal operation temperature (100°C), and baking temperature (200°C). In this paper, in order to investigate the influence of such different temperature conditions to the dynamic behavior of the VV, three independent finite element analysis with the same modal analysis method were performed. According to analysis results, there are obvious thermal effects on the dynamic behavior, such as nature frequency and mode shape, among the different temperature cases for the CFETR VV. Moreover, the results show that the natural frequency for each order decreases as the temperature increases, and the mode shape of the VV also changed with temperature.

Analysis and improvement of human-induced vibration comfort of articulated steel pedestrian bridges

The effect of different pedestrian densities (0.2, 0.5, 1, 1.5 and 4.6 persons/m2) on a pedestrian bridge is studied, the comfort level is evaluated according to the acceleration peak, and the most sensitive part of the acceleration response employs tuned mass dampers (TMDs) for vibration control. The study shows that the bearing capacity level of the pedestrian bridge with articulated piers meets the standard. Compared with a pier rigid connection system, the structural dynamic characteristics of pier articulation do not change much, and the vertical frequency and peak acceleration in the span are slightly smaller. The comfort evaluation results of the bridge with articulated piers are the same as those of the bridge with a rigid pier. The TMD setting can effectively reduce the human-induced vibration time response, the vibration reduction efficiency can reach 52%, and the comfort level changes from CL2 to CL1 after vibration reduction.

Use of Modal Substructure Method to Improve Wind-Resistance Design of Twin Towers

To provide guidance for the wind-resistant design of super-tall twin towers, this study proposes a new method for the wind-induced response computation and wind-resistant design optimization of twin towers, named the Modal Substructure (MSS) method. The MSS method is established through theoretical deduction, which is utilized to investigate the effects of links on the structural dynamic characteristics of twin towers via parameter analysis. The results show that, in the in-phase mode, the structural link increases the generalized mass of the “linked tower” system but insignificantly affects its stiffness and damping. However, in the out-of-phase mode, the link increases the overall damping and stiffness of the “linked tower” system, with negligible effects on the inertia characteristics of the entire structure. Finally, the accuracy of the MSS method is validated using 570 m-high twin towers as a case study. It was found that although the MSS method is an approximate approach, its results exhibit good accuracy and convenience in exploring the impact of link properties on the dynamic characteristics of twin towers. Therefore, the MSS method can be effectively used to guide the wind-resistant design of linked twin towers.

Topology optimization-based design, development and testing of steel-reinforced epoxy granite vertical machining centre column

The structural vibrations experienced by traditional machine tools made up of cast iron (CI) or cast steel material lead to premature failure of the cutting tool and poor surface finish on the manufactured components. Steel-reinforced epoxy granite (SREG), an alternate material to CI, improves the static and dynamic characteristics of the machine tool structure. However, the addition of steel reinforcement in SREG affects the damping characteristics of epoxy granite (EG). The present work focuses on optimizing both EG and steel reinforcement of the vertical machining centre column to achieve favourable damping characteristics. Initially, parametric analysis is performed to arrive at an optimum configuration of only the EG column. Then, steel reinforcement is integrated into the EG column, and topology optimization is carried out with the objective of maximizing the stiffness and natural frequencies of the SREG column while minimizing the mass of the reinforcement. The multiple design configurations for steel reinforcement evolved from topology optimization are numerically investigated using finite element analysis. The scaled-down prototype of the finalized model was fabricated, after which the dynamic characteristics of the proposed SREG column are measured and compared with that of existing CI and SREG columns. The results revealed six-fold and three-fold improvements in dynamic stiffness along X- and Y-directions, respectively, and a 33% reduction in the mass of steel reinforcement than the existing SREG column.

Modular Dynamic Modeling for On-Orbit Assembly of Large-Scale Space Structures

The large-scale space structure during on-orbit assembly is a time-varying system. The dynamic modeling problem of such incrementally increasing space structure is investigated, and a modular dynamic modeling approach is proposed in this paper. The dynamic model of each substructure is first established, and then, a database is designed to store substructure models, which is used for subsequent dynamic modeling in the assembly process. The fixed connection relationship between adjacent substructures is described by constraint conditions, which lead to the coefficient matrices of adjacent substructures being decoupled. The substructures are assembled in a given sequence, and then, the dynamic modeling, to describe the large-scale space structure on-orbit assembly, is gradually completed via using the proposed modeling approach. The numerical simulation is finally presented. The results demonstrate that the extra calculation resulting from the coefficient matrices coupling of adjacent substructures is avoided. Moreover, the proposed dynamic model can accurately describe the dynamic characteristics of the large-scale space structure during on-orbit assembly.

Influence of the soil liquefaction on dynamic characteristics of a base-isolated structure investigated by the experimental method

Influence of the soil liquefaction on dynamic characteristics of a base-isolated structure investigated by the experimental method

Finite Element Analysis and Optimization of Hydrogen Fuel Cell City Bus Body Frame Structure

Hydrogen fuel cell city bus is a type of new energy public transportation. In this paper, in order to evaluate the safety performance of a newly developed hydrogen fuel cell city bus body frame designed by the collaborating enterprise, finite element analysis is conducted to investigate its structural mechanics and dynamic characteristics under four typical operating conditions, including horizontal bending, ultimate torsion, emergency cornering, and emergency braking. Based on the simulation results, although the body frame of the bus meets the stiffness design requirements and avoids body resonance, it exhibits maximum stresses of 328.9 MPa and 348.6 MPa under emergency cornering and ultimate torsion conditions, respectively, exceeding the material yield strength and failing to satisfy the strength design requirements. Therefore, the size optimization method is employed to optimize the thickness of the body frame components. After optimization, the maximum stresses are reduced to 262.7 MPa and 300.6 MPa, respectively, representing a reduction of up to 20.13%. The optimization significantly improves performance and meets the strength design requirements. Furthermore, the body frame is lightened by 106 kg, achieving the goal of weight reduction.

Dynamic analysis of damping structures considering support stiffness

An analysis method for the random seismic response of viscoelastic damper structures with support is proposed. This method considers the influence of support stiffness and analyzes the dynamic characteristics associated with support stiffness. It also combines the advantages of the complex modal method (CMM) and the pseudo-excitation method (PEM), improving the complex integration operation in calculating the spectral moments and variances of random seismic responses. The support and the viscoelastic damper constitute the equivalent damper. The damper's constitutive relationship and structural dynamic equations are decoupled to calculate conveniently the frequency domain solution of the responses. Second, the quadratic decomposition of the power spectral density function (QD-PSDF) is applied to simplify the power spectrum and obtain the closed-form solution of spectral moments and variances. Finally, the structural dynamic characteristics and the influence of support stiffness on the vibration control effect of the equivalent damper are investigated based on the closed-form solution. The structural dynamic reliability is also discussed according to the first excursion failure criterion. The results demonstrate that the damper's control effect and structural reactions are reduced, while the dynamic reliability is also enhanced when increasing support stiffness. The performance of the structure and damper tends to stabilize when the support coefficient reaches a specific level.

Dynamic response and damage characteristics of special blast-resistant door structure subjected to underwater explosion

The blast resistance and protection of underwater special blast-resistant door structures were essential research elements for the safety of underwater facilities. This paper aimed to research the dynamic response and damage mode of the plate blast-resistant door structure under the impact load of an underwater explosion. First, a three-dimensional free-field shock wave numerical model was established through LS-DYNA based on the arbitrary lagrangian–eulerian (ALE) algorithm, and the obtained shock wave loads were compared with empirical values to verify the validity and accuracy of the finite element model. Then, to further explore the damage characteristics of the underwater explosion on the plate blast-resistant door structure, a three-dimensional numerical model of the plate blast-resistant door structure under an underwater explosion load was established. The dynamic response and damage of the blast-resistant door structure under different explosive equivalents, propagation medium, explosion distance, hydrostatic pressure and geometric dimensions of structural elements were also analyzed. The results revealed that the damage mode of the blast-resistant door structure was related to its dynamic characteristics and depended on the explosive equivalents, propagation medium, explosive distance, hydrostatic pressure and member size. As the frame beams on both sides were the weak part of the blast resistance, the blast-resistant door structure might cause bending deformation and warpage on both sides of the frame beam and overall structure bending. The research results can provide the characteristics of the underwater explosion load and the mechanism and law of fluid–solid coupling damage of the load on the special blast-resistant door structure, providing a reference for the damage power assessment and blast-resistant door structure design.

Nonlinear Dynamic Analysis of Pilotis Structures Supported by Drift-Hardening Concrete Columns.

Pilotis structures consisting of upper concrete bearing-walls and a soft first story have been well used in residential and office buildings in urban areas to primarily accommodate parking lots. In this research, drift-hardening concrete (DHC) columns developed by the authors are proposed to form the pilotis story with the aims of reducing its excessive residual drift caused by stronger earthquakes than anticipated in current seismic codes, mitigating damage degree, and enhancing resilience of the pilotis story. Nonlinear dynamic analysis was conducted to investigate the dynamic response characteristics of the wall structures supported by DHC columns. To this end, two sample six-story one-bay pilotis structures were designed following the current Japanese seismic design codes and analyzed. One sample structure is supported by ductile concrete (DC) columns, while the other is supported by DHC columns, which have the same dimensions, steel amount, and concrete strength as DC columns. Three representative ground motions were adopted for the nonlinear dynamic analysis. The analytical parameter was the amplitude of peak ground acceleration (PGA), scaled by the peak ground velocity (PGV) ranging between 12.5 cm/s and 100 cm/s with an interval of 12.5 cm/s. The analytical results have revealed that the residual drift of the pilotis story composed of DHC columns could be reduced to nearly zero under selected earthquakes scaled up to PGV = 100 cm/s, owing to not only the inherent self-centering ability of DHC columns but also the shake-down effect, which implies that the use of DHC columns can greatly enhance resilience of pilotis structures under strong earthquake inputs and promote its application in the buildings located in strong earthquake-prone regions. The maximum inter-story shear forces (MISFs) along the building height of the two models are also compared.

Dynamic Feature Identification of Carbon-Fiber-Reinforced Polymer Laminates Based on Fiber Bragg Grating Sensing Technology

Carbon-fiber-reinforced polymer (CFRP) composites have many advantages, and have been widely used in aerospace structures, buildings, bridges, etc. The analysis of dynamic response characteristics of CFRP composite structures is of great significance for promoting the development of smart composite structures. For this reason, vibration experiments of CFRP laminates with surface-attached fiber Bragg grating (FBG) sensors under various dynamic loading conditions were carried out. Time- and frequency-domain analyses were conducted on the FBG testing signals to check the dynamic characteristics of the CFRP structure and the sensing performance of the installed sensors. The results show that the FBG sensors attached to the surface of the CFRP laminates can accurately measure the dynamic response and determine the excited position of the CFRP laminates, as well as invert the strain distribution of the CFRP laminates through the FBG sensors at different positions. By performing Fourier transform, short-time Fourier transform, and frequency domain decomposition (FDD) on the FBG sensing signals, the time–frequency information and the first eight modal frequencies of the excited CFRP structure can be obtained. The modal frequencies obtained by different excitation types are similar, which can be used for structural damage identification. The research in this paper clarifies the effectiveness and accuracy of FBG sensors in sensing the dynamic characteristics of CFRP structures, which can be used for performance evaluation of CFRP structures and will effectively promote the design and development of intelligent composite material structures.

Elastic Wave Field Neural Networks for Structural Health Monitoring: An Analytical and Numerical Study of Multiple Neurons

The purpose of this study is to develop a novel concept of smart structural systems recognizing their own structural integrity by an embodied high density sensor network. In our concept, a number of sensor nodes are embedded in the host structure, each of which reacts point-wise to the structural vibration with a simple rule. This allows the whole nodes to be mutually coupled through the elastic field, forming a neural network that incorporates the dynamic characteristics of the host structure as the coupling weights. In the previous study, we presented that a single-neuron network as its minimum configuration can exhibit a bifurcation of its dynamics behavior, which can be used to detect the change of the network due to damages. In this study, the formulation of networks with multiple neurons deployed in a structure with single-mode approximation is presented particularly focusing on the bi- furcation analysis to reveal how the behavior of the network is drastically altered depending of the network and structural parameters. Numerical analysis is conducted to examine the validity of the bifurcation analysis.

A comparison of modal parameter identification tests in laboratory conditions

AbstractModal parameter evaluation is widely used for structural health monitoring, damage detection, and numerical model calibration. This study benchmarks two methods for modal identification under controlled laboratory conditions using operational modal analysis to compare dynamic parameters from ambient vibrations and shaker tests. A 2‐storey 3D spatial steel frame equipped with 3‐axial accelerometers is used as a case study. The identified dynamic parameters are benchmarked against a preliminary finite element model by computing Auto‐MAC and MAC matrices. It can be concluded that the preliminary FEM approach performs better in the prediction of modes shapes than natural frequencies. It was found that analysing the structural response to both ambient and artificially induced excitations provide a more complete understanding of a structure's dynamic characteristics. An additional mode shape was identified from the artificially induced excitation that was not previously captured from the ambient excitation.

Modal analysis of a lattice type metamaterial by modeling cell structures using Euler–Bernoulli beams

Metamaterials have superior properties compared to materials found in nature and allow the tailoring of static and dynamic characteristics of the cell structures. In this study, the vibration characteristics of the sandwich plate systems composed of lattice beam structures are investigated and their behavior under various loading conditions is determined. In this context, a matrix-based solution method is developed to calculate the natural frequencies of the structure by assuming lattice elements as individual Euler–Bernoulli beams. The same structures are also analyzed with a commercial finite-element solver (ANSYS) to compare the results. In order to verify the results and determine the applicability of the proposed approach, an experimental study is conducted. Unit cell structures are additively manufactured with Stereolithography (SLA) and experimental modal analysis is performed using impact testing. Also, the amount of deflections on the structures under various loading conditions is determined experimentally by performing three-point bending tests on the plates. It has been concluded that approximate vibration characteristics of lattice-type metamaterial structures with various unit cell geometries can be determined in a short time by utilizing the matrix-based method without the need for any commercial software or performing complex experiments.

Dynamic characteristics of the ring gear structure of two-stage plastic planetary reducers

Dynamic characteristics of the ring gear structure of two-stage plastic planetary reducers

Reliable modal estimation of high-rise structures via synergistic usage of multiple stabilization diagram-based operational modal analysis techniques

In operational modal analysis, typically only structural responses are available. Errors and uncertainties may exist in modal estimates, thereby leading to discrepancies in the results by different modal identification approaches even analyzing the same data set. To this end, a synergistic usage of multiple stabilization diagram-based modal identification techniques is presented in this paper to reduce the errors and uncertainties in modal estimates associated with modal identification techniques or modeling ideas. The effectiveness and noise robustness of the synergistic strategy are validated via numerical simulation study of a frame structure. Additionally, the synergistic strategy is further utilized to evaluate the dynamic characteristics of a supertall building with 600 m height during a typhoon event. The application of the synergistic strategy to field measurements reveal that the building natural frequencies varied during the typhoon and exhibited significant amplitude-dependent features. Meanwhile, the damping ratios of the skyscraper for all concerned modes remained roughly stable within a range of [0.16%, 0.94%]. This paper aims to provide a practical way or effective tool to enhance the accuracy and confidence in modal estimation of high-rise buildings, thus further revealing the dynamic characteristics of large-scale structures under severe wind excitations.

EFFECT OF A SCALED CANTILEVER BEAM ON NATURAL FREQUENCY

This paper deals with the scaling factor's effect on the cantilever beam's natural frequency. Scaling a prototype dimension will make it easier to manufacture and test the dynamic characteristics of structures with enormous sizes. Natural frequency is one of the essential parameters of the vibration characteristics of the system. The phenomenon that often occurs in vibrating structures is the resonance phenomenon. Resonance is a system state in which an abnormally large vibration is generated in response to an external stimulus, happening when the frequency of the disturbance is equal to, or nearly identical to, the natural frequency of the system. This research investigates the scale factor on natural frequency using the analytical method using Euler-Bernoulli beam theory, the MSC Nastran/Patran software, and experimental testing using an impact hammer on a cantilever beam. The three methods were applied to beams with four scaling variations: 1:1, 1:2.04, 1:2.85, and 1:3.48. Based on the results, the natural frequencies increase by the size scale reduction value in the modeling. The natural frequency value in the actual structure has a value equivalent to 1/S of the natural frequency value of the scale, whereas S is defined as the downgrade scale value. This result follows the Similitude theory.

Dynamic characteristics of rockbolt anchorage structure under radial cylindrical P wave

The anchorage structure formed of rockbolt, anchoring agent and surrounding rock plays a significant role in supporting underground engineering, however, there are still damage and failure cases of rockbolt supporting systems under blasting load. Therefore, it is important to clarify the mechanical behavior of rockbolt anchorage structure subjected to dynamic load. In this paper, we derive the analytical solution of dynamic response around anchorage structure subjected to radial cylindrical P wave based on the wave function expansion method, and the transient response is obtained by using Fourier transform. Two cases with and without anchoring agent are taken into consideration, and the elastic-slip model is introduced into describing the interaction between the surrounding rock and rockbolt without anchoring agent. The influence of multiple parameters such as thickness, stiffness and distance from the disturbance source on dynamic response is investigated in detail. The steady-state results demonstrates that the alternating tensile and compressive stress concentration is generated with the increase of wavenumber. The dynamic stress concentration can be reduced by appropriately decreasing the thickness and stiffness of anchoring agent, and the optimal values are obtained. The dynamic stress distribution in rock is opposite to that in anchoring agent under transient incidence and the tensile damage in rock along the incident direction and that in anchoring agent at the vertical direction of propagation must be alert. The novelty of the manuscript consists in studying the dynamic mechanical behaviors of anchorage structure subjected to radial dynamic load. The implications of these investigations for practical engineering will serve as a reference to design supporting methods and improve anchoring agent parameters.

Seismic response analysis of submerged floating tunnel considering non-uniform excitation and flexible-support boundary effect

In order to ensure the safety of submerged floating tunnel(SFT) during operation, it is necessary to carry out SFT response analysis under environmental loads. Given that SFTs are often constructed in valley areas situated in seismic zones, the aseismic performance of SFT needs to be investigated. However, there are important factors of non-uniform excitation and flexible-support boundary which have not been explored thoroughly. Non-uniform excitation affects the load input characteristics while flexible-support boundary affects the dynamic characteristics of structure itself. In this paper, we built a multi-point seismic wave synthesis model which fits well with the target power spectrum and a numerical response analysis model which reflects the dynamic characteristics of SFT structure well. The results based on the proposed model show that vertical non-uniform excitation can significantly increase the peak value of SFT tether tension and tube displacement with flexible-support boundary under whether artificial or natural seismic wave series input. While flexible-support boundary can availably produce vibration control effect on peak value of tether tension and tube response of whether displacement or stress indices under non-uniform wave series input. This work can provide reference for dynamic safety assessment and vibration control design of SFT to improve the development of ocean space.