Specific Dynamic Characteristics Research Articles

Mechanically Interlocked Polyrotaxane Networks with Collective Motions of Multiple Main-Chain Mechanical Bonds.

Type I main-chain polyrotaxanes (PRs) with multiple wheels threaded onto the axle are widely employed to design slide-ring materials. However, Type II main-chain PRs with axles threading into the macrocycles on the polymer backbones have rarely been studied, although they feature special topological structures and dynamic characteristics. Herein, we report the design and preparation of Type II main-chain PR-based mechanically interlocked networks (PRMINs), based on which the relationship between microscopic motion of mechanical bonds on the PRs and macroscopic mechanical performance of materials has been revealed. The representative PRMIN-2 exhibits a robust feature in tensile tests with high stretchability (1680 %) and toughness (47.5 MJ/m3). Moreover, it also has good puncture performance with puncture energy of 22.0 mJ. Detailed rheological measurements and coarse-grained molecular dynamics (CGMD) simulation reveal that the embedded multiple [2]rotaxane mechanical bonds on the PR backbones of PRMINs could undergo a synergistic long-range sliding motion under external force, with the introduction of collective dangling chains into the network. As a result, the synchronized motions of coherent PR chains can be readily activated to accommodate network deformation and efficiently dissipate energy, thereby leading to enhanced mechanical performances of PRMINs.

Mechanically Interlocked Polyrotaxane Networks with Collective Motions of Multiple Main‐Chain Mechanical Bonds

AbstractType I main‐chain polyrotaxanes (PRs) with multiple wheels threaded onto the axle are widely employed to design slide‐ring materials. However, Type II main‐chain PRs with axles threading into the macrocycles on the polymer backbones have rarely been studied, although they feature special topological structures and dynamic characteristics. Herein, we report the design and preparation of Type II main‐chain PR‐based mechanically interlocked networks (PRMINs), based on which the relationship between microscopic motion of mechanical bonds on the PRs and macroscopic mechanical performance of materials has been revealed. The representative PRMIN‐2 exhibits a robust feature in tensile tests with high stretchability (1680 %) and toughness (47.5 MJ/m3). Moreover, it also has good puncture performance with puncture energy of 22.0 mJ. Detailed rheological measurements and coarse‐grained molecular dynamics (CGMD) simulation reveal that the embedded multiple [2]rotaxane mechanical bonds on the PR backbones of PRMINs could undergo a synergistic long‐range sliding motion under external force, with the introduction of collective dangling chains into the network. As a result, the synchronized motions of coherent PR chains can be readily activated to accommodate network deformation and efficiently dissipate energy, thereby leading to enhanced mechanical performances of PRMINs.

In-situ computed tomography and transient dynamic analysis – failure analysis of a single-lap tensile-shear test with clinch points

Clinching is a mechanical joining technology, in which a mainly form-fit joint is created by means of local cold forming. To characterize the load-bearing behavior of such joints, they are typically analyzed destructively, for example by tensile-shear tests in combination with metallographic sections. However, both the initiation and progress of failure can only be described to a limited extent by this method. Furthermore, these tests allow only limited conclusions about clinch points under in-service loading. More purposefully, clinch points can be analyzed nondestructively by combining in-situ computed tomography (CT) and transient dynamic analysis (TDA). The TDA continuously measures the dynamic behavior of the specimen and indicates failure events like crack initiation, which then can be evaluated thoroughly by stopping the test and performing a CT scan. To qualify the TDA for this task, it is necessary to link the observed damage behavior with specific dynamic characteristics. In this work, the complementation of in-situ CT and TDA is investigated by testing a clinched single-lap tensile-shear specimen made of aluminum. The testing procedure is stepwise: at certain displacement levels, the specimen is investigated by in-situ CT and TDA. While the in-situ CT provides the location, extent, and development of the failure phenomena, the TDA uses this information to evaluate the dynamic signal and detect relevant frequency ranges, which indicate damage events. The results demonstrate, that failure initiation and progression can be analyzed efficiently by combining both measuring systems. The TDA reliably detects relevant signal changes in the monitored frequency band. By means of in-situ computed tomography, the corresponding failure phenomena can be described in detail, enhancing the understanding of the load-bearing and deformation behavior of clinch points. The concatenation of characteristic signal changes and observed failure phenomena can henceforth be transferred to analyze complex structures during operation nondestructively by TDA.

Comparative Study of the Seismic Response Characteristics of Three Special Soils

Because of its special material composition, formation environment and special structure, special soil usually shows different seismic response characteristics from general soil, and sometimes causes serious seismic disasters. Therefore, the study of seismic response characteristics of special soil has important practical significance for engineering construction and disaster prevention in special land areas, and a site seismic response analysis is an important way to study the impact of site conditions on ground motions. Based on the existing research work, the uniform and single ideal soil layer profiles of three special soils are established, and the seismic response analysis program of the soilquake soil layer is used to study the effects of the dynamic shear module ratio, damping ratio and shear-wave velocity of soft soil, loess and laterite on the characteristic period and platform value of the design response spectrum under different input ground motion intensities. At the same time, three typical actual drilling data values are selected to establish the calculation model of the site soil layer. On the basis of the seismic response analysis and calculation of the soil layer, three special soil dynamic characteristics are compared from the aspects of peak acceleration and characteristic parameters. Based on the research results of this paper, the recommended values of the dynamic shear module ratio and damping ratio of three special soils are given. This work has important reference value for seismic design in soft soil, loess and laterite areas, and also enriches the research results of soil dynamic parameters.

Dynamic characteristics of sandwich panels with novel improved star-shaped honeycomb

This study proposes a novel sandwich panel with an improved star-shaped honeycomb (SP-ISH) by replacing sharp corners with cubic struts and lengthening inclined ribs of traditional honeycomb. To more effectively analyze its special dynamic characteristics, the bending Poisson’s ratio was derived and effective engineering constants were obtained through asymptotic analysis of the energy functional stored in periodic unit cells. Based on this analysis, a two-dimensional equivalent downscaling model (2D-EDM) was developed to investigate the free vibration of SP-ISH under various boundary conditions, and the influence of initial deformation on free vibration was also discussed. The frequency-domain and time-domain analyses were employed to identify the resonance characteristics of the SP-ISH under harmonic loading. Our findings demonstrate that 2D-EDM can accurately predict the free and forced vibration of SP-ISH and improve computational efficiency by reducing DOFs. The results indicate that the maximum resonance response was obtained by applying excitation at the center of the sandwich panel. Additionally, under cyclic loading, a sharp change in local stress amplitude was observed in the facesheet-core interface region. Compared with traditional star-shaped honeycomb, the incorporation of extended ribs and added struts could significantly reduce the maximum resonance amplitude by 3.8%. Notably, the natural frequencies of SP-ISH were affected by initial compression (up to a 40.6% reduction) and tensile deformation (up to a 26.4% increase).

Numerical analysis of seismic response of rectangular underground structure in coral sand

The underground structure in coral sand is threatened by earthquake. The special dynamic characteristics of coral sand were realized by finite difference program. Specifically, the stress–strain loops, shear modulus attenuation and hysteresis behaviour of coral sand were simulated using hysteresis damping. On this basis, numerical models were established to study the seismic response of the rectangular underground structure in coral sand, and the fluid–solid coupling and soil-structure interaction were considered. The results illustrate that the increasing relative density of coral sand foundation reduces the excess pore water pressure (EPWP), but amplifies the horizontal dynamic soil pressure of the coral sand-underground structure system. The increase in the permeability coefficient of coral sand reduces the EPWP accumulation, which leads to an increase of the stiffness and a decrease of the acceleration amplification of coral sand sites.

Natural Frequency based delamination estimation in GFRP beams using RSM and ANN

The importance of delamination detection can be understood from aircraft components like Vertical Stabilizer, which is subjected to heavy vibration during the flight movement and it may lead to delamination and finally even flight crash can happen because of that. Any solid structure's vibration behaviour discloses specific dynamic characteristics and property parameters of that structure. This research investigates the detection of delamination in composites using a method based on vibration signals. The composite material's flexural stiffness and strength are reduced as a result of delaminations, and vibration properties such as natural frequency responses are altered. In inverse problems involving vibration response, the response signals such as natural frequencies are utilized to find the location and magnitude of delaminations. For different delaminated beams with varying position and size, inverse approaches such as Response Surface Methodology (RSM) and Artificial Neural Network (ANN) are utilized to address the inverse problem, which aids in the prediction of delamination size and location.

Dynamic prediction of in-situ SO2 emission and operation optimization of combined desulfurization system of 300 MW CFB boiler

As the emission regulation becomes more stringent, in-situ desulfurization and wet flue gas desulfurization have been widely used for circulating fluidized bed (CFB) boilers. However, few studies focus on real-time operation optimization of combined desulfurization system (CDS) in wide-load range based on in-situ SO2 emission prediction. In this work, according to mechanism analysis, a dynamic prediction model of in-situ SO2 emission was developed. Then, closed-loop and step response experiments were conducted to validate the established model, combined with measured data from a 300 MW CFB boiler. Validation results show that the model has satisfactory prediction accuracy in different load conditions and it can capture special dynamic characteristics of in-situ SO2 desulfurization. More importantly, the model can be feasible for building an economical operation strategy of CDS. Thus, a novel control strategy based on dynamic prediction model was designed, which contributes to decrease the SO2 emission fluctuation and operation costs by correcting the limestone-feed rate in advance. The proposed control strategy was applied to actual operation of the 300 MW CFB boiler. In the long-term operation of CDS after optimization, it was easier to reach ultra-low SO2 emission standard and limestone consumption reduces 15.14% compared with before the operation optimization.

Data-driven optimal tracking control of discrete-time linear systems with multiple delays via the value iteration algorithm

In this paper, the optimal tracking problem for discrete-time linear systems with multiple delays is studied without system dynamics. It is known that the total state of a system without specific dynamic characteristics is hard to be measured, unless such a system is equipped with massive sensors, which, however, may lead to an increase in cost and complexity for analysing. To deal with this problem and avoid adverse effects caused by using system state information, a new data-driven value iteration (DDVI) algorithm is proposed by considering three factors: past control inputs, system outputs, and external reference trajectories. Before the algorithm is proposed, a transformation is made to the original system according to the characteristics of the time-delay system, so that the time-delay number can be reduced or become a delay-free system. A novel data-driven state equation is derived from the historical data of the three factors, and then, it is adopted to solve the optimal control of multi-delay systems. Further results show that the proposed DDVI algorithm is convergent and the tracking error is asymptotically stable. Finally, simulations are provided to show the effectiveness of the controller.

Development and application of a numerical analysis method for investigating hydro static and hydrodynamic responses of pocket bearing rotor systems

A numerical tool is presented for simulating the dynamics of a vertical rotor attached with pocket bearing assembly immersed in a liquid pool. The journal of the bearing has a heterogeneous geometry with the presence of pockets and grooves. The fluid pressure supplied to the pockets is a quadratic function of shaft speed. The radial, circumferential and axial flow paths constitute a complex fluid network in the coupled system. The network has been conceived as an assemblage of straight and curved fluid flow paths for the generic applications. An efficient solution strategy has been employed involving both analytical and numerical techniques.A Case study was performed on a representative pocket bearing assembly that is commonly used in the coolant pumps of sodium cooled fast reactor. The study has brought out some specific dynamic characteristics of such bearings. The flow field exhibits both hydrostatic and hydrodynamic effects, thereby hybrid bearing characteristics. The dynamic characteristics are strong function of spinning velocity, eccentricity and angular orientation of the rotor in fluid annulus. Based on an elaborate parametric study, a rotor dynamic stability chart has been established for the practical applications. Interestingly, the dynamic behavior within a limited operating regime exhibits the characteristics of a large eccentric homogeneous rotor rotating in fluid annulus with moderate gaps, predicted by Antunes et al. (1996). Moreover, it is found that the pocket type bearing has better stability control, mainly due to lower added fluid mass. The numerical tool is experimentally validated by comparing the displacements measured on a shaft coupled with pocket bearing assembly, rotating in a water pool.

A dynamic model for supercritical once-through circulating fluidized bed boiler-turbine units

It is urgent to establish a dynamic model of once-through supercritical circulating fluidized bed (SCFB) power generation units in order to explore the flexible operation mode. This study aims to establish such a dynamic model with the balance between model complexity and accuracy. Within the analysis on operation characteristics of SCFB units, some reasonable assumptions and simplifications were introduced. Then, a dynamic model structure was derived from mass, energy balance laws as well as thermodynamic principles. And the unknown parameters in the model were identified by regression analysis and quantum genetic algorithm, combined with running data from a 350 MW SCFB unit. After this, the open-loop step responses and closed-loop experiments were developed to further validate the established model. The simulation results show that all model outputs can track the dynamic trends of running data in different load conditions with the satisfactory accuracy. More importantly, the model captures the special dynamic characteristics of the SCFB unit. Therefore, the model can be feasible and applicable for advanced control algorithms test and flexible operation control system design of SCFB units.

Monte Carlo Tree Search as an intelligent search tool in structural design problems

Monte Carlo Tree Search (MCTS) is a search technique that in the last decade emerged as a major breakthrough for Artificial Intelligence applications regarding board- and video-games. In 2016, AlphaGo, an MCTS-based software agent, outperformed the human world champion of the board game Go. This game was for long considered almost infeasible for machines, due to its immense search space and the need for a long-term strategy. Since this historical success, MCTS is considered as an effective new approach for many other scientific and technical problems. Interestingly, civil structural engineering, as a discipline, offers many tasks whose solution may benefit from intelligent search and in particular from adopting MCTS as a search tool. In this work, we show how MCTS can be adapted to search for suitable solutions of a structural engineering design problem. The problem consists of choosing the load-bearing elements in a reference reinforced concrete structure, so to achieve a set of specific dynamic characteristics. In the paper, we report the results obtained by applying both a plain and a hybrid version of single-agent MCTS. The hybrid approach consists of an integration of both MCTS and classic Genetic Algorithm (GA), the latter also serving as a term of comparison for the results. The study’s outcomes may open new perspectives for the adoption of MCTS as a design tool for civil engineers.

Binary coded cantilevers for enhancing multi-harmonic atomic force microscopy

Harmonic atomic force microscopy (AFM) has been widely applied to characterize local mechanical properties of the specimens under imaging. However, the harmonic amplitude is commonly quite weak owing to the fast decay at an off-resonance state for a conventional cantilever and the internal resonance between eigenfrequencies and higher harmonics can amplify the harmonic response. Therefore, specific dynamic characteristics of AFM cantilevers are frequently required. Here, we proposed a coding scheme of a cantilever where the structure is described by a two-dimensional binary matrix to tailor its dynamic characteristics. Genetic algorithms combined with finite element analysis were used to optimize the code configuration. Cantilever properties including eigenfrequencies, stiffness and quality factor can be conveniently tuned to satisfy multiple requirements. AFM cantilevers were then re-designed with the second and the third resonance frequencies being moved to integer multiples of the fundamental one for higher harmonic enhancement, yet with minor stiffness alteration. Harmonic AFM imaging on a polymer mixture demonstrated that the amplitude difference between two material phases was increased up to at least 2.7 times for the 6th harmonic and 1.6 folds for the 18th harmonic using the optimized cantilevers. The enhancement of harmonic contrast can benefit the discrimination of different materials. The proposed binary coding method has advantages such as flexible tailoring of dynamic characteristics, multiple outputs of optimal structures, and automatic optimization. Consequently, it could be a promising way to design cantilevers for enhanced performances in various dynamic AFM imaging applications and also cantilever-based sensing.

A Novel Demodulation Analysis Technique for Bearing Fault Diagnosis via Energy Separation and Local Low-Rank Matrix Approximation.

Bearing fault diagnosis is of utmost importance in the maintenance of mechanical equipment. The collected fault vibration signal generally presents a modulated nature due to the special structure and dynamic characteristics of the bearings. This paper introduces a novel demodulation analysis technique via energy separation and local low-rank matrix approximation (LLORMA) to address this type of signal. The amplitude envelope and instantaneous frequency of the signal can be calculated via an energy separation algorithm based on the Teager energy operator. We can confirm the bearing faults by comparing the peak frequencies of the Fourier spectrum of the amplitude envelope and instantaneous frequency with the theoretical bearing fault-related frequencies. However, this algorithm is only suitable for handling single-component signals. In addition, the powerful background noise has a serious effect on the demodulation results. To tackle these problems, a new signal decomposition method based on LLORMA is proposed to decompose the signal into several single-components and eliminate the noise simultaneously. After that, the single-component signal representing the fault characteristics can be identified via the high frequency feature of the modulated signal. The analysis of the simulated signal and the bearing outer race fault signal collected from a bearing-gear fault test rig indicate that the proposed technique has an excellent diagnostic performance for bearing fault signals.

A new hybrid modeling and optimization algorithm for improving carbon efficiency based on different time scales in sintering process

Sintering process is a major energy-consumption process in steel making processes. Carbon efficiency, which reflects the level of the energy-consumption, is affected by the raw material variables and the operating variables. This situation makes the process with special dynamic characteristics, especially with different operation periods. However, there is seldom research on carbon efficiency with the multiple time-scale property taken into account. This paper introduces an optimization method for carbon efficiency based on an intelligent multiple time-scale model, which is able to optimize process variables in both long and short time scales. As the comprehensive carbon ratio (CCR) and the ratio between CO and CO2 in exhaust gas (CO/CO2) are taken as the carbon efficiency indexes, a predictive model consisting of two sub-models is developed, one for predicting the state variables with a single neural network (NN), and the other for predicting carbon efficiency indexes with a linear combination of NNs. Then a multi-objective, multi-time-scale optimization framework is designed, which is able to optimize carbon efficiency in two time scales, according to the optimization variables available encountered at different operation periods. Finally, the experimental results based on actual process data shows its feasibility and improvement in carbon efficiency optimization.

Experimental Study on Dynamic Characteristics of Marine Soft Clay in North China

Marine soft clay is a modern sediment dominated by fine particles in the hydrostatic or slow flow. Because of its special dynamic characteristics, it has been widely applied in the construction of major projects such as highways, railways and airport runways. It greatly reduces the possibility of catastrophic deformation and instability caused by long term use and avoids huge economic losses.In the construction of engineering, it is urgent to analyze the dynamic characteristics of soft clay and solve the difficulties in the project.Based on the GDS vibration triaxial test, the dynamic characteristics of soft clay, namely dynamic modulus and damping ratio, are studied with marine soft clay produced by a practical engineering site in North China.The test results show that with the increase of cycle times, the dynamic modulus of soil gradually decreases, and the damping ratio increases, but the increase in amplitude is related to the level of cyclic stress. The increase of the cyclic stress level and the application of the initial deviatoric stress will accelerate the attenuation of the dynamic modulus, which leads to the increase of the damping ratio. In contrast to the dynamic modulus, the deviatoric stress has a more significant influence on the damping ratio.Zhao, Y.; Du, X.; Xiong, B., and Zhang, D., 2018. Experimental study on dynamic characteristics of marine soft clay in North China. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 474–478. Coconut Creek (Florida), ISSN 0749-0208.

Semitrailer Steering Control for Improved Articulated Vehicle Manoeuvrability and Stability

Abstract Articulated heavy vehicles have some specific performance limitations and safety risks due to their special dynamic characteristics. They show poor manoeuvrability at low speeds and may lose their stability in different manners at high speeds. In this study, the potential of active steering control of the semitrailer on manoeuvrability and stability of tractor-semitrailer combinations is investigated. A linear bicycle model and a nonlinear version are used for controller design and vehicle dynamic simulation in MATLAB environment. The Linear Quadratic Regulator optimal state feedback control is used to minimise the tracking error at low-speed, and regulate Rearward Amplification ratio and roll at high-speed. Quantum Particle Swarm Optimisation is used for optimising the weighting factors. Three different control algorithms are introduced and it is demonstrated through simulations that the vehicle with the proposed steering control exhibits desirable improvements compared to the baseline vehicle.

Adjustment of Pole Placement Algorithm Based on Vulnerability Reduction of Skewed Bridges

Skewed bridges due to the specific dynamic characteristics have shown vulnerability in recent strong earthquakes. In this study, an active control strategy is employed to optimize the seismic performance of a typical model of such structures. As the control algorithm, the pole placement method has been used, of which the key factor is selection of desired poles to achieve desired dynamic responses. A performance index (PI) was defined as a function of displacement and rotation of a bridge deck. The desired poles for the algorithm were extracted by optimizing this index. A previously presented and approved simplified model of a skewed bridge with the three degrees of freedom was selected as a typical model, and the methodology was applied on this model. The optimization of PI was carried out by a series of time-history analysis. Ten far-field ground-motion records presented in FEMA-P695 were used for this purpose. The PI was calculated for a range of damping ratio and frequency of the system, and the desired poles were selected for the optimum values of PI. The results show that the control of the model using the selected pole by this method could effectively reduce the displacement and rotation of the bridge model.

Dynamic Water Electrolysis in Cross‐Sectoral Processes

AbstractA simulation‐based optimization for water electrolysis is performed to identify preferable scenarios with respect to economic as well as ecological aspects. As the electrolyzer interacts with the wholesale electricity market and with the production of bulk chemicals implying each specific dynamic characteristics, various and partly counteracting relevant impulses result in a multi‐objective optimization approach. In order to demonstrate the capability of alkaline electrolytic systems to meet these dynamic demands, a 20‐kW lab‐scale electrolyzer and a 2‐MW large‐scale electrolyzer are commissioned and tested.

Seismic design of passive tuned mass damper parameters using active control algorithm

Tuned mass dampers are a widely-accepted control method to effectively reduce the vibrations of tall buildings. A tuned mass damper employs a damped harmonic oscillator with specific dynamic characteristics, thus the response of structures can be regulated by the additive dynamics. The additive dynamics are, however, similar to the feedback control system in active control. Therefore, the objective of this study is to develop a new tuned mass damper design procedure based on the active control algorithm, i.e., the H2/LQG control. This design facilitates the similarity of feedback control in the active control algorithm to determine the spring and damper in a tuned mass damper. Given a mass ratio between the damper and structure, the stiffness and damping coefficient of the tuned mass damper are derived by minimizing the response objective function of the primary structure, where the structural properties are known. Varying a single weighting in this objective function yields the optimal TMD design when the minimum peak in the displacement transfer function of the structure with the TMD is met. This study examines various objective functions as well as derives the associated equations to compute the stiffness and damping coefficient. The relationship between the primary structure and optimal tuned mass damper is parametrically studied. Performance is evaluated by exploring the h2-and h∞-norms of displacements and accelerations of the primary structure. In time-domain analysis, the damping effectiveness of the tune mass damper controlled structures is investigated under impulse excitation. Structures with the optimal tuned mass dampers are also assessed under seismic excitation. As a result, the proposed design procedure produces an effective tuned mass damper to be employed in a structure against earthquakes.