Narrow Results

This paper presents a semi-analytical approach to analyze the dynamic response characteristics of lattice composite sandwich plates with varying lattice truss cores. Under the premise of satisfying the classical laminate theory assumptions of Allen, the lattice truss core is considered an equivalent homogenized structure. Then, the displacement equations for the sandwich plate utilize the first-order shear deformation theory (FSDT). The energy equation for the sandwich plate is constructed using the Lagrange energy method and solved through the Rayleigh–Ritz method. To mimic arbitrary boundary conditions, artificial boundary spring techniques are utilized. The spectral geometry method (SGM) is utilized to describe the displacement field of dynamic equations and boundary conditions. Legendre polynomials are chosen to construct admissible displacement functions for the structure, supplemented by auxiliary polynomials to eliminate discontinuities at the boundaries. The method’s validity is verified through comparisons with relevant literature and finite element method (FEM). Based on free vibration analysis, both steady-state and transient displacement responses of laminated composite sandwich plates are examined, considering the influences of structural parameters and boundary conditions on dynamic response characteristics. These works can provide suitable theoretical references for the engineering field.

In this paper, a bolted joint of two prismatic parts subjected to a shear impact force applied in the structure’s longitudinal direction is studied. The base part is made from steel and the connected one is from aluminum alloy. An elastomeric layer is inserted between the assembled parts in order to reduce vibration resulting from external excitation. An equivalent dynamic model is developed to analyze the behavior of bolted structure. The formulation of the problem gives a system of nonlinear equations. Solving differential equations is based on Euler’s method. Dynamic responses which correspond to the two degrees of freedom of the model are shown. The joint nonlinear behavior strongly depends on the interface properties. A cubic stiffness and damping factor are considered for the layer in the model, which gives it more realistic responses. Experimental tests are done for a case study of bolted joint under transient hummer impact. Model results are agreed with those issued from experiments. The damping layer (DL) effect is experimentally observed as well as in the model results.

To study the transient response characteristics of wind turbine structures–extended foundations under wind loads in mountainous areas, this paper develops a simplified analytical model based on soil–structure interaction theory. It explores the effects of constraint conditions, wind speed, and foundation shear wave speed on the transient response behavior. By analyzing the time–domain and frequency–domain trends of tower top displacement, foundation horizontal displacement, and foundation rotation angle, the relationship between foundation shear wave speed and the safe wind speed of the wind turbine is clarified. The results indicate that different constraint conditions lead to variations in the calculated resonance frequency, maximum tower top displacement, and acceleration response spectrum. Furthermore, based on the analysis of the tower top acceleration response curve, the influence interval of frequency can be categorized into three distinct ranges: stable range, small influence range, and large influence range. Wind speed primarily influences the vibration amplitudes of the three displacement components, while the overall trend of the time-displacement waveform remains unchanged. The foundation shear wave speed primarily affects the displacement of the foundation itself, exerting a smaller influence on the displacements of the wind turbine structure. Notably, the total displacement at the tower top decreases as the shear wave speed increases. Moreover, the safe wind speed of the wind turbine shows a positive correlation with the foundation shear wave speed, indicating a linear relationship between the two variables.

A path integral formulation is developed for the transient Brownian motion in response to a sudden change in temperature. Formulae are derived for the time-dependent probability distribution function and for the transient current, employing the negative friction Langevin equation. Numerical implementation of the theory for a double-well system gives a clear illustration of the transient of the transient behaviors of the system.

An ultraviolet (UV) sensor consisting of a zinc oxide (ZnO) nanofiber sensing membrane and a quartz crystal microbalance (QCM) was fabricated. ZnO nanofibers were prepared by electrospinning and calcination. The morphology and structure of the nanofiber sensing membrane were characterized by scanning electron microscopy and X-ray diffraction. The QCM sensor based on ZnO nanofibers was found to be sensitive to 254-nm UV light in nitrogen, oxygen and air atmospheres. When the QCM sensor was placed under UV irradiation, the resonant frequency difference rapidly decreased. When the light was removed, the frequency difference recovered until reaching 0 Hz. The stability and repeatability of the proposed ZnO nanofiber-based QCM sensor were demonstrated, and the sensing mechanism was briefly discussed.

The transient voltage response of the charge density wave (CDW) to current pulses in Tl_0.3MoO₃ and K_0.15Tl_0.15MoO₃ have been studied. Contrasted with the data reported previously for other blue bronze systems, a kind of superimposed (overshoot and sluggish) response waveform is observed for the first time. These results are discussed in analogy with the coexisting of "inductive" and "capacitive" effects at the onset of the CDW depinning.

With higher operating frequencies, transmission lines are required to model global on-chip interconnects. In this paper, an accurate and efficient solution for the transient response at the far end of a transmission line based on a direct pole extraction of the system is proposed. Closed form expressions of the poles are developed for two special interconnect systems: an RC interconnect and an RLC interconnect with zero driver resistance. By performing a system conversion, the poles of an interconnect system with general circuit parameters are solved. The Newton–Raphson method is used to further improve the accuracy of the poles. Based on these poles, closed form expressions for the step and ramp response are determined. Higher accuracy can be obtained with additional pairs of poles. The computational complexity of the model is proportional to the number of pole pairs. With two pairs of poles, the average error of the 50% delay is 1% as compared with Spectre simulations. With ten pairs of poles, the average error of the 10%-to-90% rise time and the overshoots is 2% and 1.9%, respectively. Frequency dependent effects are also successfully included in the proposed method and excellent match is observed between the proposed model and Spectre simulations.

This paper proposes a realistic model of magnetizing branches for transient calculation of electric power circuits. The model represents the nonlinear relationship between flux linkage and exciting current of magnetizing branches with a major loop and a family of minor loop trajectories, which has the capability of simulating the multi-valued hysteresis behavior. By applying the proposed model to transient calculation, an efficient algorithm is developed for obtaining the transient responses in electric power circuits. In the algorithm, the electric power circuit is divided into the magnetizing branches and the remaining linear part. The nonlinear differential equations are set up for the magnetizing branches and solved by the semi-explicit Runge–Kutta method. The transient calculation for the remaining linear part is performed on the basis of the solution to the magnetizing branches. Then, a laboratory measurement is made with a reduced-scale experimental arrangement. The measured results are compared with the calculated ones and a reasonable agreement is shown between them.

This paper proposes an output-capacitorless low-dropout (LDO) regulator with ultra-low quiescent power. It applies an adaptive error amplifier to improve the bandwidth and transient response during heavy load, and a second gain stage to improve the stability during light load. Furthermore, an overshoot and undershoot reduction circuit is used to shorten the settling time when output load is changed. The LDO is fabricated in 0.18$\mu$m CMOS process and occupies a chip area of 0.06mm². The LDO is measured to output a stable voltage at 1.6V with a quiescent power of 1.8$\mu$W. The experimental results also show a good transient response.

A cap-less voltage spike detection and correction circuit for flipped voltage follower (FVF)-based low dropout regulator (LDO) is proposed in this paper. The transients in the output voltage are controlled by the pull-up currents $I_{\mathrm{\text{UP1}}}$ and $I_{\mathrm{\text{UP2}}}$ and pull-down currents $I_{\mathrm{\text{DN1}}}$ and $I_{\mathrm{\text{DN2}}}$. These currents are dynamic current sources which are activated only during transient period and noise contributed by these current sources at steady state is zero. These currents increase/decrease based on the intermediate FVF node voltage $V_X$. The proposed circuit detects the output voltage via $V_X$ and controls the power MOSFET gate and output capacitances by changing the pull-up and pull-down currents whenever the load changes. The proposed circuit consumes small additional bias current in the steady state and achieves less settling time and output spike voltage. This LDO is simulated using 180nm technology and the simulation result shows that the LDO has good load transient response with 190ns settling time and 170mV voltage spike over 1mA to 100mA load current range.

This paper proposes a three-stage coarse-fine-tuning analog-assisted digital low dropout regulator (AAD-LDO) without digital ripple. The digital regulation consists of two stages, which break the accuracy-speed-power trade-off. To further improve transient response, a step-variable counter used in the first stage is designed, which makes sure that the output current can track the load current rapidly. The ripple caused by the digital regulation disappears due to the existence of the analog-assistant stage (in the proposed AAD-LDO). As a result, the AAD-LDO achieves the output voltage with high accuracy. Designed in a 0.18$\mu$m CMOS process, the proposed AAD-LDO has a layout area of 0.133mm. For the input range of 1.2–1.8V, the output voltage is 1V. The maximum load current is 10mA at the input voltage of 1.2V. The linear regulation and load regulation are 0.061mV/V and 0.0082mV/mA, respectively. The over/undershoot is suppressed effectively for a 9.5mA load step. The peak current efficiency is 99.78%.

In this paper, a method is presented for the mathematical modeling and analysis of the DC–DC Buck Converter output voltage. This paper consists of the demonstration of a mathematical model for the converter transient response submitted to a pulse width modulated (PWM) input voltage, resulting in accurate symbolic expressions for the output voltage. The novelty of the method is the capability of the expressions derived to describe correctly the behavior of the converter submitted to time-varying control reference input signals modulating the switch pulse width. The mathematical model was then validated by comparing it with the responses obtained using the Runge–Kutta numerical method. By using different circuit parameters and PWM input signals with constant and time-varying duty cycles, it was possible to validate the model for different cases, showing the effectiveness of the approach.

As an important unit of power management system, traditional analog low-dropout regulator (ALDO) is widely used in System-on-Chip (SoC) design to provide stable and pure power for each sub-circuit block. However, in ultra-low-power design applications, low quiescent current greatly affects the loop gain of ALDO. Digital low-dropout regulator (DLDO) has good low-voltage working ability, process scalability and diversified control schemes, which is more suitable for low-power SoC design. However, a large number of digital circuits with fast switching devices will produce large load current changes, so DLDO needs fast transient response speed to adjust load changes. In recent years, DLDO can be divided into synchronous DLDO and asynchronous DLDO according to different control methods. Among them, the design structure of synchronous DLDO is relatively simple. It depends on an independent global clock, and there is a tradeoff between speed, accuracy and power consumption. When the clock frequency increases, the system needs fast transient response, but the power consumption will increase proportionally, and the current efficiency and loop stability will decrease. Using large output capacitor to deal with load transient is not conducive to improve chip integration. Although asynchronous DLDO can improve the response speed based on the advantages of asynchronous control scheme, the stability of DLDO will face greater risks. Therefore, this paper will introduce several transient response enhancement technologies that do not sacrifice system power consumption, accuracy or stability. It includes adaptive frequency technology and fast response algorithm to improve the transient response speed of synchronous DLDO, event-driven solution and coarse and fine adjustment technology to improve the transient response speed of asynchronous DLDO. On this basis, a typical DLDO structure with excellent performance in the recent 10 years is given.

In this paper, an idea of evolving probabilistic vector (EPV) is introduced into the Generalized Cell Mapping (GCM) method to replace the classical fix-sized probabilistic vector in order to efficiently capture the transient behaviors in noise-induced bifurcations, by which an initial localized probability distribution around a deterministic attracting set of a nonlinear dynamical system may expand abruptly or escape with a jump as the noise intensity increases and exceeds some critical values. A Mathieu–Duffing oscillator under excitation of both additive and multiplicative noise is studied as an example of application to show the validity of the proposed method and the interesting phenomena in noise-induced explosive and dangerous bifurcations of the oscillator that are characterized respectively by an abrupt enlargement and a sudden fast jump of the response probability distribution. The insight into the roles of deterministic global structure and noise as well as their interplay is gained.

The linear, viscoelastic, integral constitutive law is employed to model the viscoelastic characteristic of belt materials. By assuming the translating eigenfunctions instead of stationary eigenfunctions to be the spatial solutions, the governing equation is reduced to differential-integral equations in time, which are then solved by the block-by-block method. The transient amplitudes of parametrically excited viscoelastic moving belts with uniform and non-uniform travelling speed are obtained. The effects of viscoelastic parameters and perturbed axial velocity on the system response are also investigated.

Steady-state and transient acoustic radiation characteristics of clamped-free annular plate with tuned mass damper (TMD) device is studied. Galerkin’s procedure is employed to obtain the transverse vibration of the annular disk. Based on the Rayleigh integral approach, acoustic pressure radiation is obtained and subsequently the modal sound power and modal radiation efficiency are obtained. A new formulation for the transient acoustic pressure in Laplace domain is presented for the first time in this paper. Durbin’s numerical Laplace transform inversion scheme is employed to obtain the response spectrum. The optimum parameters of vibration absorbers are proposed for suppressing the dynamic vibration and acoustic pressure. A parametric study is carried out and the effects of vibration absorber characteristics are investigated using the analytical procedure. Limiting cases are considered and good agreements with the finite element solution, as well as with those available in the literature, are achieved.

Reinforced concrete (RC) beams under the impact loading are typically prone to suffer shear failure in the local response phase. In order to enhance the understanding of the mechanical behavior of the RC beams, their dynamic response and shear demand are numerically investigated in this paper. A 3D finite-element model is developed and validated against the experimental data available in the literature. Taking advantage of the above calibrated numerical model, an intensive parametric study is performed to identify the effect of different factors including the impact velocity, impact mass and beam span-to-depth ratio on the impact response of the RC beams. It is found that, due to the inertial effect, a linear relationship exists between the maximum reverse support force and the peak impact force, while negative bending moments also appear in the shear span. In addition, the local response of the RC beams can be divided into a first impact stage and a separation stage. A shear plug is likely to be formed near the impact point at the first impact stage and a shear failure may be triggered near the support by large support forces. Based on the simulation results, simplified methods are proposed for predicting the shear demand for the two failure modes, whereas physical models are also established to illustrate the resistance mechanism of the RC beams at the peak impact force. By comparing with the results of the parametric study, it is concluded that the shear demand of the RC beams under the impact loading can be predicted by the proposed empirical formulas with reasonable accuracy.

This paper studies the nonlinear dynamic responses of graphene-reinforced composite (GRC) beams in a thermal environment. It is assumed that a laminated beam rests on a Pasternak foundation with viscosity and consists of GRC layers with various volume fractions of graphene reinforcement to construct a functionally graded (FG) pattern along the transverse direction of the beam. An extended Halpin–Tsai model which is calibrated against the results from molecular dynamics (MD) simulations is used to evaluate the material properties of GRC layers. The mechanical model of the beam is on the establishment of a third-order shear deformation beam theory and includes the von-Kármán nonlinearity effect. The model also considers the foundation support and the temperature variation. The two-step perturbation technique is first applied to solve the beam motion equations and to derive the nonlinear dynamic load–deflection equation of the beam. Then a Runge–Kutta numerical method is applied and the solutions for this nonlinear equation are obtained. The influence of FG patterns, visco-elastic foundation, ambient temperature and applied load on transient response behaviors of simply supported FG-GRC laminated beams is revealed and examined in detail.

This paper deals with the stability and dynamic evolution of a sliding pipe conveying fluid in the three-dimensional sense. The pipe is assumed to slide out from a fixed channel so that its free end is moving at the same time, a problem often associated with instabilities in applications of aerial refueling operation. To tackle this problem, the nonlinear governing equations of motion are derived by using the Hamilton’s principle and then reduced to a set of ordinary differential equations by the Galerkin’s method. A parametric study is performed to explore the transient vibration responses of the pipe for different values of flow velocity and sliding rate. Various dynamic behaviors are detected for the pipe in sliding and conveying fluid. The results show that 3-D oscillations of the pipe occur when the flow velocity exceeds a certain value, which can be affected by the sliding rate. For various flow velocities, the evolution of the dynamic characteristics of the sliding pipe can be classified into three typical types of motion. When at low flow velocity, the pipe is mainly subjected to a single type of 3-D motion. When the flow speed increases to high values, multi-type of 3-D motion consisting of three typical types occurs on the pipe. In addition, the pipe can display planar motions, transferring from one plane to the other. The result presented herein is helpful to understand the stabilities and dynamic behaviors of sliding-pipe systems used in aerial refueling applications.

Aiming at the poor transient convergence and real-time performance of the horizontal vibration state variables of the high-speed elevator car system, and the low control accuracy and stability, this paper proposes an adaptive control strategy to ensure the transient response of the elevator car system. First, a prescribed preset transient performance function is introduced into the controller design to control the variation range of the state variables and ensure the steady transient performance of the elevator car; Second, representing the information of observation error/control error through algebraic operations, designing an adaptive law based on e-correction, estimating unknown parameters in the elevator car system, and achieving online parameter updates; Then, using neural networks to learn and compensate for unknown dynamics in the elevator car system, and solving the online estimation problem of neural network weights through adaptive laws, so that the tracking error and weight estimation error converge to a tight set near zero; Finally, using MATLAB/SIMULINK to compare and analyze the four control algorithms of passive control, PID control, adaptive control based on gradient descent method and transient response adaptive control proposed in this paper under two different rail excitations: Random excitation and pulse excitation. The simulation results show that the adaptive control strategy proposed in this paper effectively suppresses the horizontal vibration of the elevator car, makes the state variables have faster convergence speed and smaller convergence error, and ensures the stable and transient performance of the elevator car system.