Periodic Disturbances Research Articles

Manipulation of Farmed Wetlands Increases use by Migrating Shorebirds and Ducks

The Drift Prairie, in central North America, has been largely converted from grasslands to croplands, but still contains thousands of wetlands used by shorebirds and waterfowl during breeding and migration periods. Consequently, many of the remaining wetlands are situated within cropland where disturbance regimes (i.e., fire, grazing, and water-level dynamics), which occurred naturally prior to agricultural development, have been highly altered by landscape fragmentation from agriculture practices. Currently, smaller wetlands within crop fields are subject to disturbances stemming from agricultural practices (i.e., manipulations), such as burning, disking, harvesting, and mowing. We evaluated vegetation structure of idled (i.e., not recently manipulated by farming practices) and manipulated agricultural wetlands to investigate whether management method or resulting vegetation structure had greater influence on occurrence probabilities and densities of dabbling ducks and shorebirds during spring. All manipulation methods reduced vegetation heights compared to idled wetlands and most manipulations reduced the proportion of vegetation cover in inundated areas. Wetland manipulations generally increased shorebird occurrence compared to idled wetlands, whereas vegetation variables better explained duck occurrence probabilities. Duck occurrence peaked in wetlands with lower vegetation coverage (32%), and duck densities decreased as vegetation coverage increased beyond 10%. While more studies are needed to understand underlying mechanisms driving these outcomes, our results indicate that including periodic disturbances that reduce dense vegetation within wetlands in agricultural fields would increase their use by migrating and breeding shorebirds and dabbling ducks.

Modeling of servo dynamic stiffness for multiple-periodic repetitive learning control system

Servo dynamic stiffness is a pivotal index in characterizing the rejecting performance for the exogenous periodic disturbances of the repetitive learning control system. In this paper, the mathematical modeling of the servo dynamic stiffness for the well-designed repetitive learning control system with multiple-periodic signals is studied by the frequency analysis method. To analysis the complex form of the servo dynamic stiffness, the magnitudes of the direct (real part) and quadrature (imaginary part) servo dynamic stiffness at harmonics of the disturbance are discussed based on the parameters of the repetitive learning controller. An illustrated example of the two linear servomotors with the mechanical coupling is given in this study. Computer simulation are presented to illustrate the effect of the proposed measurement method of the servo dynamic stiffness for the multiple-periodic repetitive learning control system. The proposed servo dynamic stiffness modeling can be used to accurate design the parameters of the repetitive learning control system, such that the batter control performance of the repetitive learning control system at most of the harmonics of the multi-periodic input signal can be achieved.

Global sensitivity analysis of water level response to harmonic aquifer disturbances through a Monte-Carlo based surrogate model with random forest algorithm

Oscillatory water levels are often observed in monitoring wells, when aquifers are disturbed by periodical pressure diffusion (PD) sources, such as oscillatory pumping and ocean tide, and by volumetric strain (VS) sources including the far-field seismic wave and earth tide. The measured water level responses are extensively utilized to interpret aquifer properties and seismic hydrological phenomena. However, owing to wellbore effects, water levels are not always truly representative of pore pressure in aquifers, and can be significantly attenuated or even unobservable in wells. To clarify how water level responds to these disturbances, this study analyzes a global parameter sensitivity of the coupled well-aquifer model based on the assumption of a confined homogeneous aquifer. Parameter uncertainties concerning aquifer properties, source characteristics, and wellbore construction are first analyzed separately for the PD and VS sources. Subsequently, Monte-Carlo based surrogate models linking parameters and response indices are developed using the random forest algorithm. For the PD source, sensitivity results indicate that hydraulic conductivity is the most influential parameter for the yes/no responses. When hydraulic conductivity exceeds 10-4 m/s, water level observations basically represent pore pressure in aquifers. Significant amplitude changes and phase delay occur when the period of disturbances is less than 50 s, majorly due to water column inertia. For VS sources, water level responses are typically observed in aquifers with hydraulic conductivity larger than 10-7 m/s and when disturbed by a source with amplitude greater than 10-3 MPa. However, pronounced amplitude changes and phase shifts occur when the source period varies within 100 s. Consideration of the impact of wellbore effects is recommended, when interpreting water level responses induced by all periodic aquifer disturbances, especially in low-conductivity aquifers with conductivities less than 10-4 m/s.

Virtual coupling control of photovoltaic-energy storage power generation system for efficient power support

The key to achieving efficient and rapid frequency support and suppression of power oscillations in power grids, especially with increased penetration of new energy sources, lies in accurately assessing the inertia and damping requirements of the photovoltaic energy storage system and establishing a controllable coupling relationship between the virtual synchronous generator and the main network. In this paper, the inertia and damping requirements of the photovoltaic energy storage system are estimated using frequency safety warnings and power oscillation suppression constraints. Furthermore, the oscillation characteristics of the power system, which include photovoltaic and energy storage in the presence of periodic load disturbances, are analyzed. Based on this analysis, a coupled virtual synchronous controller for energy storage is proposed. This controller employs a forced oscillation suppression technique through natural frequency shifting, and establishes a controllable power coupling relationship between the photovoltaic energy storage system and the main network to achieve the desired frequency shift. Finally, a simulation system incorporating conventional generators and a photovoltaic energy storage system controlled with the proposed strategy is built to test the frequency support and power oscillation suppression behaviors of the grid-connected power generation system.

INFLUENCE OF CLIMATE ON THE COUPLED HEAT AND MOISTURE TRANSFER THERMAL CALCULATION IN CHINA

ABSTRACT The climate in China varies substantially across its extensive territory. However, the traditional thermal design of buildings is primarily based on pure heat calculation that considers only heat transfer. Therefore, the heat transfer of a building envelope should be clarified under the action of periodic external disturbance circulation. In this study, four different climatic factors were selected for heat transfer simulation, including season, solar radiation, air temperature, and relative humidity. The results indicate that the outdoor relative humidity has a significant impact on the difference between coupled heat and moisture calculation and pure thermal calculation. This influence becomes evident in the cooling conditions in summer but weakens in the winter heating conditions. Accordingly, the meteorological data of 270 cities in China were statistically analyzed using Python programming language. The concept of “cooling high-humidity days” was proposed as a zoning indicator for coupled heat and humidity thermal calculation zoning. The coupled heat and moisture thermal calculation design zoning map of China is provided, which affords the specific calculation method in building thermal design.

ОЦЕНКА ВЗАИМОСВЯЗИ ПОВЕРХНОСТНЫХ И ПОДЗЕМНЫХ ВОД РЕКИ СЫРДАРИЯ (В ПРЕДЕЛАХ КАЗАХСТАНА)

This study analyzes and evaluates the relationship of surface and groundwater of the Syrdarya River within Kazakhstan. The share of groundwater recharge of the river was calculated by two methods: by genetically partitioning the total runoff hydrograph and by calculating low f low. The difference of groundwater flow into the river between the selected hydrostations is also calculated. A comparison of the obtained results for the quasi-natural and disturbed periods is made. In natural conditions, the infiltration of river runoff into underground horizons prevailed along the length of the Syrdarya River, however, under the influence of anthropogenic activity, the picture changed to the opposite: the discharge of groundwater prevails along the length of the Syrdarya River, including the emergence of filtration waters below the dam of the Shardara HPP, collector-drainage and discharge waters from irrigation f ields of the adjacent territory. Also, apparently, the truncation of spring flood peaks leads to an increase in the groundwater level and an increase in the share of underground river supply. Recommendations for the application of the methods used in the work are given.

Pollinator response to livestock grazing: implications for rangeland conservation in sagebrush ecosystems.

World food supplies rely on pollination, making this plant-animal relationship a highly valued ecosystem service. Bees pollinate flowering plants in rangelands that constitute up to half of global terrestrial vegetation. Livestock grazing is the most widespread rangeland use and can affect insect pollinators through herbivory. We examined management effects on bee abundance and other insect pollinators on grazed and idle sagebrush rangelands in central Montana, USA. From 2016 to 2018, we sampled pollinators on lands enrolled in rest-rotation grazing, unenrolled grazing lands, and geographically separate idle lands without grazing for over a decade. Bare ground covered twice as much area (15% vs. 7) with half the litter (12% vs. 24) on grazed than idle regardless of enrollment. Bee pollinators were 2-3 times more prevalent in grazed than idle in 2016-2017. In 2018, bees were similar among grazed and idled during an unseasonably wet and cool summer that depressed pollinator catches; captures of secondary pollinators was similar among treatments 2 of 3 study years. Ground-nesting bees (94.6% of total bee abundance) were driven by periodic grazing that maintained bare ground and kept litter accumulations in check. In contrast, idle provided fewer nesting opportunities for bees that were mostly solitary, ground-nesting genera requiring unvegetated spaces for reproduction. Managed lands supported higher bee abundance that evolved with bison grazing on the eastern edge of the sagebrush ecosystem. Our findings suggest that periodic disturbance may enhance pollinator habitat, and that rangelands may benefit from periodic grazing by livestock.

Adaptive Periodic Disturbance Observer Based on Fuzzy Logic Compensation for Speed Fluctuation Suppression of PMSM Under Periodic Loads

Adaptive Periodic Disturbance Observer Based on Fuzzy Logic Compensation for Speed Fluctuation Suppression of PMSM Under Periodic Loads

Menstrual cycle disorders: a correlation with genetic alterations

The menstrual cycle is considered the fifth vital sign among women. The pituitary, thyroid, pancreas, adrenal, and ovaries are endocrine glands that play a crucial role in governing the menstrual cycle. Endocrine ailments trigger periods of menstruation disturbances throughout a woman's reproductive life. The duration and volume of menstrual bleeding can serve as indicators of endocrine problems. Oligomenorrhea, which refers to monthly periods longer than 35 days, is the most prevalent menstrual disruption observed in endocrine illnesses such as thyrotoxicosis, hypothyroidism, polycystic ovarian syndrome, Cushing's syndrome, and diabetes, based on the existing evidence. The intricate endocrine pathways are crucial in regulating a woman's menstrual cycle.. Menstrual Irregularities are caused due to eating disorders, extreme weight loss or too much exercising, Polycystic ovary syndrome (PCOS), Premature ovarian failure, Pelvic inflammatory disease (PID) and Pregnancy or breast-feeding. Mensesare affected by various factors like junk food, obesity, skipping breakfast lack of physical activity etc. PCOS, Diabetes, Hyperprolactinemia, Hypothyroidism, Thyrotoxicosis, and Cushing’s syndrome are some menstrual disorders which occur due to genetic alterations. All these disorders can be primarily treated by Nutritional Considerations and herbal treatments. In order to achieve a regular menstrual cycle and overcome these diseases, nutritional supplements and lifestyle modifications must be prioritized.

Rejection and Compensation of Periodic Disturbance in Control Systems

in this paper, a brief introduction to the disturbance rejection methods is given in general and to the periodic disturbance rejection methods in particular. Therefore in the following, methods of using only feedback technique to achieve both set point tracking and periodic disturbance rejection are presented. Also, the interaction problem between the set point design demands and the periodic disturbance rejection is discussed. Then, the interaction is minimized by using a separate feed-forward controller to reject the periodic disturbances as an add-on compensator to the pre-existing set point tracking feedback controller. Furthermore, the idea of the disturbance observer is introduced in general as well as the adaptive periodic disturbance cancelation method.

Periodic output regulation for 1-D wave equation subject to non-collocated control

In this paper, we focus on the periodic output regulation for a one-dimensional wave equation where the performance output is non-collocated with the control input. The exosystems considered here are multi-periodic time-varying, capable of generating periodic reference signals and disturbances within the domain and at the boundaries, each with distinct periods. Initially, a backstepping-based state feedback regulator is designed by tackling an ill-posed periodic regulator equation. Subsequently, leveraging an external matrix, we design a novel time-varying observer tailored for the transformed wave equation and the exosystems. An output feedback regulator is then obtained by replacing the states with their estimations. The tracking error is shown to decay exponentially and the closed-loop system is proved to be bounded. Some numerical simulations are presented to validate the results.

Мониторинг околоземного космического пространства, магнитосферы и атмосферы Земли в периоды Форбуш-эффектов в конце августа 2005 г.

We present the results of near-Earth interplanetary space, magnetosphere, and atmosphere monitoring during large-scale solar wind disturbances at the end of August 2005. The monitoring was carried out using ground-level cosmic ray (CR) observations made at the worldwide network of neutron monitors as well as muon telescopes in Yakutsk and Novosibirsk. As a result of the analysis performed by different methods, we have obtained variation properties of CRs of different rigidities in Earth’s orbit, their pitch angle anisotropy, orientation and configuration of the interplanetary magnetic field, changes in the planetary system of geomagnetic cutoff rigidities during geomagnetic disturbances, as well as mass average air temperature over CR stations equipped with muon telescopes. For the periods of geomagnetic disturbances, we have determined parameters of magnetospheric ring current and magnetopause currents.

Monitoring of near-Earth space, Earth’s magnetosphere and atmosphere during Forbush decreases in August 2005

We present the results of near-Earth interplanetary space, magnetosphere, and atmosphere monitoring during large-scale solar wind disturbances at the end of August 2005. The monitoring was carried out using ground-level cosmic ray (CR) observations made at the worldwide network of neutron monitors as well as muon telescopes in Yakutsk and Novosibirsk. As a result of the analysis performed by different methods, we have obtained variation properties of CRs of different rigidities in Earth’s orbit, their pitch angle anisotropy, orientation and configuration of the interplanetary magnetic field, changes in the planetary system of geomagnetic cutoff rigidities during geomagnetic disturbances, as well as mass average air temperature over CR stations equipped with muon telescopes. For the periods of geomagnetic disturbances, we have determined parameters of magnetospheric ring current and magnetopause currents.

Frequency-adaptive odd-harmonic repetitive control scheme for three-phase shunt active power filters

Repetitive control (RC), which can track the periodic input or suppress the periodic disturbance with a zero steady-state error, is a promising control strategy for shunt active power filters (SAPF). However, the conventional RC (CRC) scheme will suffer a severe performance degradation caused by the grid frequency variations. In this article, a frequency-adaptive odd-harmonic repetitive control scheme with a single and fixed sampling rate is proposed for SAPF to deal with grid frequency variations and provide fast transient response for RC system. The frequency-adaptability of proposed repetitive control scheme can be implemented by updating the coefficients of the approximate expression for the delay unit in repetitive controller. The FIR filter based on Lagrange linear interpolation is used to transform the multirate repetitive control system into single-rate repetitive control system to address the problems caused by the multirate repetitive control system. Moreover, a fractional-order linear compensator with a simple structure is designed to compensate the magnitude and phase of the system accurately. Compared with other classical repetitive control strategies, the proposed repetitive control scheme can provide a better adaptation to the steady-state deviation and dynamic variation of grid frequency and ensure the control performance of SAPF system. Simulation and experimental results verify the effectiveness of the proposed control scheme.

Assessment of Tunnel Lining Stability through Integrated Monitoring of Fiber Bragg Grating Strain and Structural Deformation.

Tunnel excavation induces the stress redistribution of the surrounding rock. Structural cracks may develop in the secondary lining due to this stress redistribution and bias pressure, consequently affecting the overall construction safety of the tunnel. This paper aims to achieve real-time monitoring of the excavation stability of the lining structure by integrating two monitoring technologies: structural deformation monitoring and fiber grating strain monitoring. Additionally, it proposes a method to simultaneously measure the thermal strain and applied stress-strain of the structure. By analyzing the displacement and deformation of the lining structure, its stability can be preliminarily evaluated in the short term. To achieve long-term real-time monitoring and a more accurate assessment of the tunnel structure's stability, the paper introduces fiber Bragg grating (FBG) strain sensor monitoring technology. First, based on the geological stratigraphy information obtained from the exploration, a simulation model of the tunnel under different section bias angles is established. The displacement and stress concentration areas of the lining structure are then analyzed to optimize the sensor deployment array and provide a theoretical basis for the sensor arrangement. FBG strain sensors are installed on the surface of the structure to measure thermal strain and loading stress-strain, whereas FBG temperature sensors measure local temperature. The findings indicate that following tunnel excavation, the maximum daily strain differences at K107+043 and K107+240 were 126.87 µε and 209.38 µε, respectively. After a period of rock disturbance, the average daily strain differences due to applied stress-strain were 16.8 µε and 12.65 µε, respectively. The thermal strain was close to the daily strain difference. Therefore, after the rock disturbance subsided, the strain fluctuations in the lining structure were mainly caused by local temperature changes, and the surrounding rock tended to stabilize. This offers a viable method for evaluating structural stability post-tunnel excavation.

Analysis of reservoir permeability evolution and influencing factors during CO2-Enhanced coalbed methane recovery

CO2-ECBM is an effective energy saving and emission reduction technology. Among them, the permeability of coal seam will affect the CO2 injection efficiency, which is the key factor affecting the CH4 production. In order to reveal the evolution of reservoir permeability, effective stress, adsorption/desorption effect, and binary gas seepage and diffusion are considered. The research results indicate that the evolution of permeability can be summarized into two stages. The permeability during the CO2 undisturbed period is mainly controlled by the effective stress, which exhibits a parabolic relationship with permeability. The CO2 disturbed period is mainly controlled by the strain, which exhibits a negative correlation with permeability. Increasing the injection pressure, during the CO2 undisturbed period, the effective stress increases, the strain decreases, and the higher the permeability. During the CO2 disturbed period, the lower the effective stress, the higher the strain, and the lower the permeability. Increasing the injection temperature, the greater the effective stress and permeability in the undisturbed period. In the CO2 disturbed period, the competitive adsorption intensifies, the larger the strain, and the faster the permeability decreases. Increasing the initial water saturation, the slower the gas transportation rate. The slower the effective stress rises in the CO2 undisturbed period, the lower the permeability. In the CO2 disturbed period, the smaller the strain, and the higher the permeability. In summary, injection pressure, temperature, initial water saturation will have an impact on the permeability, in engineering practice, it is not the case that the higher the injection pressure, the higher the injection temperature, the smaller the initial water saturation is the better.

Iterative-learning-based tracking control of a two-wheeled mobile robot with model uncertainties and unknown periodic disturbances

In this paper, we develop an adaptive iterative learning approach to investigate the trajectory tracking control issue for a class of two-wheeled mobile robots subject to model uncertainties and unknown disturbances. First, we derive the nonlinear velocity error dynamics. Then a parameterization-based adaptive iterative learning control scheme is adopted to achieve precise tracking, along with logic-based update law for the estimated period and bound of the disturbance. Moreover, the boundness of all the closed-loop signals is rigorously analyzed based on the Lyapunov stability theory to provide the theoretical foundation for the proposed method. The experimental results show the efficacy and viability of our results.

Characterization of the Endwall Flow in a Low-Pressure Turbine Cascade Perturbed by Periodically Incoming Wakes, Part 1: Flow Field Investigations with Phase-Locked Particle Image Velocimetry

Particle image velocimetry (PIV) measurements were performed inside a low-pressure turbine cascade operating at engine-relevant high-speed and low-Re conditions to investigate the near-endwall flow. Of particular research interest was the dominant periodic disturbance of the flow field by incoming wakes, which were generated by moving cylindrical bars at a frequency of 500 Hz. Two PIV setups were utilized to resolve both (1) a large blade-to-blade plane close to the endwall as well as midspan and (2) the wake effects in an axial flow field downstream of the blade passage. The measurements were performed using a phase-locked approach in order to align and compare the results with comprehensive CFD data that are also available for this test case. The experimental results not only support a better understanding and even a quantification of the wake-induced over/under-turning inside and downstream of the passage, they also enable the tracing of the ‘negative-jet-effect’, which is widely known in the CFD branch of the turbomachinery community but is seldom visualized in experiments. The results also reveal that the bar wake periodically widens the blade wake by up to 165%, while the secondary flow is less affected and exhibits a phase lag with respect to the 2D-flow effects. The results presented here are an essential basis for the subsequent investigation of the near-endwall blade suction surface effects using unsteady pressure-sensitive paint in the second part of this two-part publication.

Adaptive containment fault‐tolerant control for saturated nonlinear multiagent systems with multiple faults and periodic disturbances

AbstractThis paper addresses the problem of adaptive containment fault‐tolerant control for nonlinear multiagent systems with periodic disturbances. Different from most existing fault‐tolerant control schemes, the form of multiple faults is explicitly considered in this paper, including actuator faults and sensor faults. By combining the Fourier series expansion with neural networks, the unknown nonlinear dynamics subject to time‐dependent periodic disturbances are approximated. Then, the “complexity of explosion” issue that exists in traditional backstepping‐based results is avoided by introducing a first‐order sliding‐mode differentiator. It is proved that the developed containment control policies can ensure that all signals of the close‐loop systems are uniformly ultimately bounded, and all followers can converge to a convex area formed by multiple leaders. Simulation results verify the validity of the proposed scheme.

Repetitive dynamic matrix control for systems with periodic specifications

This paper proposes a Repetitive Dynamic Matrix Control (RDMC) for systems with periodic specifications. The new algorithm is able to track periodic references and reject repetitive disturbances with a known period based on a modified prediction error. A repetitive version of the Generalized DMC (GDMC) is also proposed such that it can be applied to control open-loop unstable systems. Only the step-response coefficients are required to describe the dynamical system such that the RDMC preserves the modeling simplicity of the Dynamic Matrix Control (DMC). The proposed solution can be interpreted as an extension of the DMC for repetitive control applications. A data-driven filter design is proposed in order to ensure null prediction steady-state error in the presence of periodic disturbances even for unstable open-loop systems. Two case studies are presented to show the usefulness of the proposed strategy for control systems with periodic specification and to illustrate the typical advantages and drawbacks of the proposed repetitive control extension of the DMC algorithm.