Response Characteristics Of System Research Articles

Dynamic response characteristics of floating offshore photovoltaic systems with anchor position deviations under extreme environmental conditions

Floating offshore photovoltaic (FOPV) systems are key technologies for harnessing offshore solar resources, playing a crucial role in mitigating global climate change. Anchoring systems, essential components of FOPV systems, ensure operational safety by limiting floating body's displacement. However, factors such as positioning errors, uneven seabed, and inhomogeneous loads make it challenging to install anchors exactly at their designed locations. These deviations can significantly alter the system's dynamic responses, particularly under extreme environmental conditions, posing potential safety risks. This study aims to explore the dynamic response characteristics of FOPV systems with varying anchor position deviations under extreme sea states, offering valuable insights for system design. First, a coupled numerical model is developed to capture interactions between multiple modules and their mooring lines. Then, the effects of anchor offset distance, direction, relative position, and the incident direction of sea loads on modules motion and mooring tension are discussed. The results indicate that anchor deviations along the mooring projection direction significantly affect the maximum horizontal motion, maximum mooring tension, and minimum mooring safety coefficient, while the maximum heave motion remains largely unaffected. Additionally, when the displaced anchor and the direction of environmental loads acting on the FOPV system are on the same side, the system's maximum dynamic responses are significantly higher compared to those due to the displaced anchor on the leeward side.

Extreme Characteristics of the Ground Motions Recorded During the 2023 Kahramanmaras Turkiye Earthquakes and Their Effect on Inelastic Seismic Response of RC Frame Buildings

ABSTRACT Two devastating earthquakes occurred on February 6, 2023, in Kahramanmaras Turkiye within 9 h. The epicenter of the first event is in Pazarcik sub-province of Kahramanmaras with a moment magnitude (Mw) of 7.8. Nine hours later the second event occurred with Mw = 7.5, of which the epicenter is close to the Elbistan sub-province of Kahramanmaras. This earthquake sequence caused multiple-fault ruptures with hundreds of kilometers, affecting 11 cities in the near field. The events caused a significant number of casualties along with substantial physical and economic losses. Many different building types in the region suffered damage during the earthquakes but RC frame buildings deserve special attention due to their extremely poor seismic performance. This study examines the inelastic seismic response characteristics of simplified structural systems under the selected ground motions during the 2023 Kahramanmaras Turkiye earthquakes by focusing on the seismic performance of Turkish RC frame buildings. Inelastic seismic demands of this building typology are assessed with idealized SDOF systems in terms of spectral acceleration and displacement. In addition, the effects of multiple wave packets and strong velocity pulses on the inelastic seismic behavior of idealized RC frame-building models are examined. The numerical results of the study verify the extraordinary nature of the selected ground motions in terms of inelastic seismic response. The inferior seismic performance of almost all RC frame-building subclasses, which generally follow field observations after the event, can be attributed to the double effect of the inherent flexibility of frame construction and demanding ground motions with the effects of multiple wave packets and strong velocity pulses.

The Nonlinear Dynamic Response and Vibration Transmission Characteristics of an Unloading System with Granular Materials

The aim of this study is to research the flow property of granular materials under nonlinear vibration, which directly affects the stability of the unloading system and the motion state of granules. According to the mechanical constitutive relation, the coupled suspension–tire model with nonlinear ordinary differential equations is established and the kinematic equations of granules are derived. Furthermore, the amplitude–frequency responses of the coupled system and force transmissibility are obtained by the incremental harmonic balance method (IHBM) with high-order approximation, and then the flow characteristics of granular materials are investigated based on the approximate analytic solution under nonlinear vibration. The theoretical analysis and numerical simulation show that the coupled suspension–tire system presents a softening nonlinear feature and the peaks are significantly smaller than that of the linear system, which further affects the motion rules of granular materials. As a result, different sliding states and flow paths are observed under the same operating conditions. This research not only shows the unloading mechanism and vibration transmission characteristics between the continuum structure and granular material but also theoretically explains the control mechanism of the coupled continuum–granular system. The research is instructive in improving the unloading efficiency of granules in practical engineering.

Dynamic response characteristics of molten salt solar power tower plant under rapid load changes

Utilizing molten salt STP plants in grid peak-shaving endeavors is poised to become increasingly pivotal in the forthcoming energy landscape. Investigating the dynamic response characteristics of molten salt STP systems during rapid load fluctuation is paramount for their efficient integration into the grid. In this study, a dynamic simulation model employing a lumped parameters method is present, alongside the proposition of two distinct control strategies tailored to regulate water level and load fluctuation. Moreover, to assess the resilience of STP systems to actual disturbances, three comprehensive closed-loop disturbance scenarios encompassing variations in molten salt temperature, feed water temperature, and main steam valve opening degree are conducted. Subsequently, a three-element water level control strategy is implemented to mitigate feedwater pressure and false-water level effects, and the power generation of the unit is controlled by adjusting the molten salt flow rate. Furthermore, the dynamic response characteristics of STP units during load reduction phases under varying ramp rates (3%, 6%, and 10% Pe/min) employing the two aforementioned control strategies are scrutinized, the delay effects of heat transfer and phase change processes are analyzed, and the adjustment process can be completed within 120 to 280 s, with a maximum water level overshoot of 2.5 mm. The results underscore the efficacy of the combined three-element water level control and load control strategy in ensuring safe and flexible operation during load regulation processes. Additionally, the main factors affecting the change in drum water level and the intricate coupling relationships among critical parameters are analyzed. Ultimately, these findings furnish essential guidelines for optimizing control strategy design and enhancing the flexibility of molten salt STP systems in the context of grid integration and peak load management.

Study on improved control strategy of virtual synchronous generator

Virtual synchronous generator (VSG) control technology for photovoltaic, energy storage, wind power, and other new energy to provide flexibility in the grid interface characteristics, is conducive to improving the stability of the power system, and has been widely considered by many scholars. Firstly, an improved VSG control method is proposed through simulation and analysis, which realizes the complete decoupling of the frequency response time constant and the inertia quantity of the active power control loop and reduces the complexity of the parameter design of the VSG system. Secondly, to avoid the frequent action of the VSG system caused by small-scale frequency change perturbation, this study proposes a VSG frequency optimization control method for VSG frequency control with rated angular velocity ωset feedforward composed of multivariate factors when considering a primary frequency regulation dead zone. Thirdly, the impact of VSG parameter design on the system is investigated through the system response characteristics of power scheduling, primary frequency regulation at the grid connection, and the small-signal dynamic characterization of the improved VSG. Finally, Simulation and experimental verification yielded an active power overshoot of 7% and a maximum frequency deviation of 0.17 Hz for the improved system. The improved control method resulted in an improvement of 0.1 s in the frequency response time and a reduction of 0.15 Hz in the oscillation amplitude. The response speed of the improved control method is much better, while the oscillation amplitude is reduced to meet the grid's regulation requirements. The simulation and experimental analysis verify the feasibility of the improved VSG control method.

Design and experimental study of a semi-active shear-mode vibration absorber using magnetorheological elastomer

This paper presents the design process of a magnetorheological elastomer (MRE) absorber with a shear symmetric structure based on detailed simulation and experiments. First, the MRE materials and dimensional parameters of the MRE absorber are determined, and magnetic field simulation is performed to analyze the magnetic induction performance in the working area. Then, a dynamic simulation model is constructed to analyze the frequency response characteristics of a semi-active vibration system. Finally, a vibration experimental platform is built to test the response performance of the shear-mode MRE absorber. The experimental results showed that the stiffness of the MRE absorber can be effectively adjusted by current. When the applied current changes from 0.5 to 2 A, a vibration reduction frequency band of 8.91 to 14.19 Hz will be formed. The closer the natural frequency in this frequency band is to the external excitation frequency, the better the vibration reduction effect, which verifies the effectiveness of semi-active vibration control for the primary system. These results validate the rationality and feasibility of the semi-active MRE absorber, providing a good reference for the design of MRE absorbers.

Analysis of vibration characteristics of ship propeller spindle

In order to obtain the vibration response characteristics of the propeller spindle system effectively and accurately, and provide the basis for the subsequent fault diagnosis, the modal simulation and test of the spindle model were carried out. With the propeller set as eccentric mass, the amplitude and torsion angle of the spindle model were simulated under the condition of excited vibration and unexcited vibration respectively, and the frequency response of bending and torsion under the coupled condition was obtained. The newmark-β method was used to solve the transient response of the bent-torsional coupling model. The results shows that when the propeller spindle system undergoes rotation at a specific frequency and experiences bending vibration excitation force, the latter will induce torsional vibration response. Moreover, the amplitude of the torsional vibration response varies with changes in the frequency of the bending vibration excitation force.

Experimental investigation of particle impact dampers: Vibration reduction and noise levels with varied particle numbers

Structural vibrations present significant challenges in engineering systems, and particle impact dampers (PIDs) have emerged as a promising solution for vibration control. This paper presents a comprehensive experimental investigation on the damping performance of PIDs with varying numbers of particles. The experimental setup involves subjecting a single-degree-of-freedom (SDOF) structure to base motion excitations. Frequency response analysis is conducted to assess the dynamic behavior of the primary system using different PID designs. PIDs with one mass, two masses, three masses and multiple particles are designed and analyzed using the same mass ratio. Additionally, time domain displacement responses of the top of the structure and the base are measured to capture the system's response characteristics. The frequency response analysis reveals the influence of different particle configurations on the system's response amplitude at various frequencies. Interestingly, the results show that a PID with multiple particles exhibits reduced damping performance due to excessive particle-particle collisions. These collisions decrease the energy of the particles, leading to lower velocity before impact. This highlights that the impact itself is the primary source of damping in PIDs, and any other phenomena, such as particle-particle collisions, directly affect the relative velocity before impact. The outcomes demonstrate that an optimal design of PID can reduce vibration amplitude by approximately 85 % with single mass, two masses, and three masses configurations. Conversely, the best-case scenario of PID with multiple particles provides a vibration amplitude reduction of 75 % compared to the absence of a damper. Furthermore, noise data is recorded for all cases, as noise generation is a significant concern associated with PIDs. The results indicate noise magnitudes of 62.5 dB, 70.60 dB, 73.24 dB and 78.64 dB for PIDs with single mass, two masses, three masses, and multiple particles, respectively. Overall, the relationship between the number of particles and damping performance provides valuable insights for optimizing PID designs and ensuring comfortable operation. The findings have broad implications for diverse engineering systems, leading to improved structural performance, reduced noise, and enhanced safety. This study could serve as the basis for several potential applications of PID in structural vibration control with enhanced performance and reduced noise.

Coordinated control algorithm of hydrogen production-battery based hybrid energy storage system for suppressing fluctuation of PV power

Photovoltaic (PV) power generation has issues of volatility and intermittency. Currently, PV plants are generally equipped with 10% rated capacity lithium-ion (Li) battery energy storage systems in China, who often fail to suppress fluctuation in the output power of PV plants effectively and meet the grid-connected standard. The hybrid energy storage system (HESS) combining with hydrogen production and Li battery system can produce hydrogen by water electrolysis during the peak period of PV power generation, effectively improving PV utilization efficiency, while smoothing PV power fluctuation and improving grid connection electricity quality. Firstly, models of the solid oxide electrolysis cell (SOEC) and alkaline electrolysis cell (AEC) systems for hydrogen production, and Li battery energy storage system are established, and the transient response characteristics of each system are analyzed. Secondly, an adaptive wavelet packet decomposition (AWPD) method for PV power signal decomposition is proposed based on the wavelet packet decomposition (WPD) method. Thirdly, a capacity configuration method for HESS are proposed based on the APWD method. Fourthly, a coordinated control strategy for HESS is proposed with the transient response characteristics of different energy storage systems and the state of charge for Li battery system. Finally, the proposed method is validated through simulation experiments based on the actual power data of the PV plant. The results show that the developed methods can effectively utilize partial PV power generation to produce hydrogen, improve PV utilization, and the combined output power of PV plant and HESS can fulfill the grid-connected standard.

Performance analysis of IMC-PID controller on PCT-14 air pressure control system

This research presents a comprehensive performance analysis of the IMC-PID controller implemented in the PCT-14 air pressure control system, a platform ideal for experimenting with various control methodologies. The study aims to compare the effectiveness of the IMC-PID controller with IMC-PIDF, Good Gain - PID and Skogestad's - PI controllers, focusing on response time characteristics based on the simulation of the PCT-14′s transfer function. Performance analysis is conducted by comparing system response characteristics to set point changes, including rise time, overshoot, settling time, peak time, and steady-state error. To validate the controller's effectiveness, performance index value such as Integrated Absolute Error (IAE) was calculated. The research findings indicate that the IMC-based PID controller outperforms the Good Gain – PID, Skogestad-PI, and IMC-PIDF controllers in handling set point changes.•Simulating the transfer function of the PCT-14 air pressure control system to examine the response time characteristics of the IMC-PID, IMC-PIDF, Good Gain - PID, and Skogestad's - PI controllers.•Conducting a performance analysis by comparing system response characteristics in response to changes in set point values.•Calculating performance index value, IAE to assess the controllers' effectiveness.

Research on Energy-Saving Control Strategies for Single-Effect Absorption Refrigeration Systems

The automatic control device is a critical component of absorption refrigeration systems. Its functional enhancement can reduce operating costs, improve energy efficiency, and ensure long-term stable unit operation. Given that absorption refrigeration systems operate under various dynamic conditions, the rational design of control strategies is particularly important. This study analyzes the influence of changes in the cooling water and heat source water flow rates on the outlet temperature of chilled water in the unit based on the open-loop response characteristics of absorption refrigeration systems. It proposes a dual-loop energy-saving control strategy for single-effect hot water lithium bromide absorption refrigeration systems based on the setpoint comprehensive optimization algorithm. Considering the multiple variables, strong coupling, large inertia, long time delay, and nonlinear characteristics of absorption refrigeration systems, as well as the difficulties in modeling these systems, this study applies a model-free adaptive control algorithm to the system’s control. It derives both SISO and MIMO model-free control algorithms with time-delay components. Through simulations comparing MFAC, improved MFAC, and traditional PID control, the dual-loop energy-saving control strategy is demonstrated to effectively reduce system heat consumption by approximately 20%, decrease power consumption by about 10%, and enhance the system’s SCOP by approximately 19.3%.

Proposal of a Nonlinear Spring Model on Piping Support Structures for an Elasto-Plastic Response Analysis Method

Abstract In probabilistic risk assessment against earthquakes (seismic PRA) for nuclear power plants, the development of a realistic response analysis method for the fragility assessment of piping systems considering input seismic motions exceeding design assumptions is one of the important issues. Usually, piping systems exhibit complex three-dimensional shapes. The arrangement and stiffness of the piping support structures significantly affect the response characteristics of the entire piping system. Therefore, it is necessary to develop a realistic response analysis method of piping systems including piping support structures. In this study, a method for modeling the elasto-plastic hysteresis characteristics of piping support structures is developed to establish a seismic response analysis method of piping systems including piping support structures. First, we formulate an elatsto-plastic spring model that can express the elasto-plastic hysteresis characteristics of a piping support structure. Subsequently, we perform a simulation analysis for the loading test of a piping support structure using this model. As the analysis results and test results were in good agreement, we confirmed the effectiveness of the formulation of the model. The main contents, such as the formulation of the elasto-plastic spring model, the simulation analysis of the loading test, and the comparison between the analysis results and the test results, and the results of this study are reported in this paper.

Water Level Control in Coupled Tank System with PLC and IoT-Based PID Method

There are many advanced technological discoveries in industry, including the coupled tank. Coupled tanks are several tanks connected to each other. One of the quantities that is often controlled in the industry is the control of water levels. Water level control in a PLC and IoT-based coupled tank system is a medium for controlling and monitoring water levels remotely in real-time. The sensor used is a Differential Pressure Transmitter (DPT) with a pump motor actuator which is connected to an Omron PLC using an inverter. There is a disturbance in the form of setting the control valve opening. The control method used is the PID method with Ziegler-Nichols tuning and trial and error. Both methods analyzed which performance of the system response characteristics was better. It is proven that PID tuning is suitable for water level control of coupled tank systems.

A piezoelectric cantilever-beam-spring-pendulum oscillator for multi-directional vibration energy harvesting

Harvesting energy from environmental vibrations holds significance for powering wireless sensors and transducers. However, the current vibration energy harvesting methods still have room for improvement, especially in the field of low-frequency vibration, where the performance of output voltage is relatively insufficient. This paper proposes a novel piezoelectric energy harvester consisting of a piezoelectric cantilever beam and a spring pendulum in order to address this challenge. Under external excitation, energy exchange is generated between the internal parts of the system, so that the swinging of the pendulum is interchanged with the extension and contraction motion of the spring and the bending motion of the cantilever beam to realize multidirectional energy harvesting. Firstly, the energy equation of system is obtained and the dynamics model of system is derived based on Lagrange's theorem. In addition, the response characteristics of system under harmonic excitation and the effects of different parameters on the system performance are investigated by simulation. With proper parameter selection, the system can produce higher output voltages. Compared to a piezoelectric cantilever-single-pendulum, the proposed structure demonstrates superior performance, especially in low-frequency vibration. The maximum voltage amplitudes in the x- and z-directions were 106.6% and 187.3% of those of the piezoelectric cantilever-single-pendulum, respectively. This paper proves the superior energy harvesting performance of the proposed structure.

Modeling and dynamic characteristics analysis of bearing pedestal early looseness in dual-rotor system

In order to study the dynamics in a dual-rotor system in the presence of a bearing pedestal early looseness fault, a 12-degree-of-freedom dual-rotor system bearing pedestal looseness fault dynamic model considering gyroscopic moments is developed. The Newmark-β method is used to solve the developed model. The dynamic response characteristics of the dual-rotor system when the bearing pedestal is loosened are analyzed. A dual-rotor fault simulation test bench is built to carry out bearing pedestal looseness fault simulation experiments. The comparative results show that the fault frequency distribution pattern in the simulation analysis envelope spectrum is consistent with the experimental results, which proves the validity of the proposed dynamics model. It is found that there is clippings in the rotor vibration signal when there is a bearing pedestal early looseness fault in the dual-rotor system. In the envelope spectrum there are high and low pressure rotor rotation frequency, the sum of frequencies and 2-fold the characteristic frequency of rotor rotation frequency. With the increase of rotational speed ratio, the amplitude of envelope spectrum characteristic frequency increases. When the bearing pedestal is loose, the loose rotor axis trajectory is elliptical-like, and the rotor axis trajectory has a tendency to be more chaotic. Capturing the vibration signal characteristics of a dual-rotor system at very small loosening angles is necessary for preventing larger looseness, which is crucial for fault prediction.

Research on Simulation and Power Regulation Control Strategy of Fengning Variable-Speed Pumped Storage Unit

Abstract Variable-speed pumped storage unit demonstrates rapid power response and flexible adjustment of unit speed, significantly enhancing unit operational efficiency and the power system’s stability. This paper focuses on simulating the control strategy of the Fengning variable-speed pumped storage unit. First, the water pump/turbine and motor models are established based on the relevant parameters of the Fengning variable-speed pumped storage unit. Second, according to the distinct responsibilities of the governor and the excitation system, the control strategies of the unit in the power priority mode and speed priority mode are designed. Finally, we compare and analyze the power response characteristics of a single-machine infinite bus system under various operating conditions and control strategies. We also summarize the applicable scope and existing problems under different operating conditions.

Effects of clearances on dynamic response and nonlinear characteristics of the planar multibody mechanical system

Effects of clearances on dynamic response and nonlinear characteristics of the planar multibody mechanical system

Hydrodynamic characteristics of coral nursery buoyancy system and prediction using machine learning methods under wave action

The buoyancy system is a critical structure that ensures the safety and stability of the floating coral nursery and reduces the rate of coral shedding. Firstly, experiments in a wave tank were conducted on the motion response characteristics of the buoyancy system with four different structural types and submerged states, using the buoyancy system as the experiment object. The experimental results showed that the submerged state of the floating sphere was an essential element in affecting the hydrodynamic characteristics of the buoyancy system. The variation trends of the maximum oscillating tension of mooring cable with increase in period, and of the floating sphere motion amplitude with increase in Kc number under different submerged states were significantly different. Subject to experiment conditions, it was hard to judge the change tendency of the floating sphere motion amplitude under the large Kc number. Machine learning models trained through experiment data samples can quickly and accurately predict physical phenomena over a broader parameter range. Secondly, the prediction results of various machine learning models were compared and analyzed. Then the traditional machine learning model was optimized based on the particle swarm algorithm, which can improve the accuracy by about 20%. Finally, the optimal PSO-RBF model was employed to predict the floating sphere motion amplitude under the large Kc number. The predicted results showed that Kc = 6 was the demarcation point where the motion amplitude of the floating sphere varies with the Kc number. In addition, the fully submerged single floating sphere of buoyancy system is the best choice for floating coral nurseries under the four experiment cases in this paper, which can effectively reduce the damage of extreme waves with large wave heights and periods to floating coral nurseries.

Numerical modeling and dynamic response analysis of an integrated semi-submersible floating wind and aquaculture system

Floating wind turbines (FWT) are facing the challenges of high cost of energy. Integrating floating wind with offshore aquaculture cages presents a mutually beneficial approach to address cost concerns and maximize overall benefits. This study introduces and numerically models an integrated system, encompassing a self-designed semi-submersible FWT coupled and an aquaculture cage (FWT + AC). Comprehensive, fully coupled aero-hydro-servo-elastic-mooring models for this integrated system are established. Subsequently, the numerical model of the FWT is validated against wave basin model tests. The research further discusses the coupled dynamic response characteristics of the integrated system for both the FWT with and without the aquaculture cage. The results highlight that integrating aquaculture cages leads to an increase in the mean surge response by up to 12.6%, while significantly reducing pitch motion by as much as 7.69% under combined wind, wave, and current conditions. Moreover, the mean mooring loads, particularly for line 4 which faces the direction of wind, wave, and current, do not exhibit an increase of more than 15%. This integration not only enhances the stability of wind power generation under different wind degree, but also minimally impacts the average power generation efficiency, showing a variation of only about 2% under rated wind speed. The findings provide beneficial theoretical support for the design of the integrated FWT + AC system, demonstrating the potential of such integrated systems in promoting offshore sustainable development and enhancing wind energy utilization efficiency.

High-temperature molten salt circulating cold salt pump shaft system prestress response analysis research

To investigate the response characteristics of the rotor system in a high-temperature molten salt pump, a specific model of a cold salt pump was selected as the research object. The natural frequencies and mode shapes, critical speeds, and harmonic response analysis based on modal analysis of the rotor system with and without prestress were computed. The results indicate that with prestress, the natural frequencies of the rotor are higher compared to the rotor without prestress, and there is no clear pattern among the various vibration modes. The calculated critical speed for the second mode is much higher than the rotor’s operating speed. This suggests that the rotor system will not experience resonance at its operating speed, meeting design requirements and ensuring stable operation. When the rotor of the cold salt pump is subjected to unbalanced forces, vibrations occur in the x, y, and z directions. The region with the largest vibration amplitude is located at the fifth-stage impeller. At a frequency of 52 Hz, the corresponding harmonic response displacement reaches its maximum value, and this frequency remains unchanged with variations in the magnitude and position of the unbalanced force. Therefore, it is advisable to avoid operating the rotor system at the critical speeds corresponding to the first and second modes. Furthermore, the operating speed of the rotor system is much lower than the critical speeds corresponding to the first and second modes, so axial unbalanced forces generally do not affect the normal operation of the rotor system.