Reduction Of Fluctuations Research Articles

Modelling of Aggregated Power Output of Photovoltaic Power Generation in Consideration of Smoothing Effect of Power Output Fluctuation around Observation Point

High penetration photovoltaic power generation system (PVS) may cause negative impacts on the frequency control of electric power system. In the impact assessment of high penetration PVS on the system frequency, the proper preparation of time-series data of aggregated PVS power output in electric power system service area is essential. However, the available data points are limited compared to the huge installation points of widely dispersed PVS in a power system service area. Therefore, this study proposes a modelling of aggregated PVS power output based on a low-pass filter (LPF) which is capable to take into account a smoothing effect of power output fluctuation around individual observation point. Then, the proposed model is applied to estimate the spatial average irradiance in the central region (called the Chubu region) in Japan by using the irradiance data observed at 61 points. The reduction in the short-cycle fluctuation is evaluated in comparison to the time-series data calculated by the simple average of 61 points data. Finally, the usefulness of proposed model is discussed in the situation that the aggregated PVS power output in electric power system service area must be curtailed due to the surplus power supply in the electric power system.

Thermal assessment of lightweight building walls integrated with phase change material under various orientations

This paper presents a comparison of four different wall structures aiming to study the impact of using PCM “phase change material” on the thermal performance of lightweight building walls. The comparison was done using simulation based on the weather conditions in Sharjah, UAE, and five different wall orientations were involved in the comparative analysis: horizontal, east-facing, west-facing, south-facing, and north-facing walls. The wall without PCM (with 60 mm insulation) was considered the reference case, while the three other walls included an additional inner layer of 10 mm thickness (insulation, PCM-31, and RT-41). All walls were tested at different orientations to find the influence of PCM and orientation on energy consumption. The results showed that the incorporation of PCM has a significant contribution to stability improvement and inner wall temperature fluctuation reduction. This was more considerable in the case of using PCM-31 as PCM where the inner wall temperature was highly stable with minor fluctuations between 26 °C and 27 °C. Compared to the reference case, PCMs reduced the inner wall temperature peak by more than 2 °C. Similarly, PCM-31 demonstrated the best performance regarding indoor heat flux with a peak reduction of 78.6 %, while the performance of RT-41 was also acceptable with a corresponding percentage of 46.4 %. Furthermore, the greatest amount of energy can be saved by utilizing PCM implemented in the roof of the building and on the south facing surfaces of Sharjah.

Efficacy and Safety of Pharmacist-Managed NSAIDs Deprescribing: A Jordanian Outpatient Study

Background. Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used to manage pain, including chronic pain conditions. However, their prolonged use is associated with significant risks, particularly gastrointestinal (GI) adverse events. This study aimed to evaluate the effectiveness and safety of a pharmacist-managed deprescribing program for NSAIDs in a Jordanian outpatient population. Methods. A convenience sample of 100 participants who had been using NSAIDs for pain management was recruited. Participants underwent a structured deprescribing intervention in collaboration with physicians. Various effectiveness and safety outcomes were assessed before and after deprescribing. Descriptive statistics and chi-square test were used for data analysis. Results. The majority of participants reported chronic pain conditions, with rheumatoid arthritis (24%) and osteoarthritis (22%) being the most prevalent. Ibuprofen (28%) and diclofenac (22%) were the most commonly used NSAIDs. The deprescribing program was associated with a significant reduction in heartburn, stomach ulcer, kidney problems and fluctuation in blood pressure readings (p<0.05), and pain exacerbation. Notably, the reduction in pain exacerbation was evident (p=0.003) in the 4-month follow-up. Conclusion. A pharmacist-managed NSAIDs deprescribing program demonstrated effectiveness in reducing the risk of GI adverse events and fluctuation in blood pressure readings without causing harm during a short-term follow-up. These findings support the feasibility of implementing such programs in outpatient settings. Further long-term investigations are necessary to confirm these results.

Mechano-regulation by clathrin pit-formation and passive cholesterol-dependent tubules during de-adhesion

Adherent cells ensure membrane homeostasis during de-adhesion by various mechanisms, including endocytosis. Although mechano-chemical feedbacks involved in this process have been studied, the step-by-step build-up and resolution of the mechanical changes by endocytosis are poorly understood. To investigate this, we studied the de-adhesion of HeLa cells using a combination of interference reflection microscopy, optical trapping and fluorescence experiments. We found that de-adhesion enhanced membrane height fluctuations of the basal membrane in the presence of an intact cortex. A reduction in the tether force was also noted at the apical side. However, membrane fluctuations reveal phases of an initial drop in effective tension followed by saturation. The area fractions of early (Rab5-labelled) and recycling (Rab4-labelled) endosomes, as well as transferrin-labelled pits close to the basal plasma membrane, also transiently increased. On blocking dynamin-dependent scission of endocytic pits, the regulation of fluctuations was not blocked, but knocking down AP2-dependent pit formation stopped the tension recovery. Interestingly, the regulation could not be suppressed by ATP or cholesterol depletion individually but was arrested by depleting both. The data strongly supports Clathrin and AP2-dependent pit-formation to be central to the reduction in fluctuations confirmed by super-resolution microscopy. Furthermore, we propose that cholesterol-dependent pits spontaneously regulate tension under ATP-depleted conditions.

A Novel Bilevel Electromechanical Compound Braking Coordinated Control Strategy for Electric Vehicles

Due to the difference of response time and braking type between the motor and the pneumatic braking system, it is still difficult to coordinate the motor braking and the pneumatic braking to ensure the vehicle stability and maximal energy regeneration. To address this challenge, a bilevel electromechanical compound braking coordinated control strategy for electric vehicles is proposed considering general and emergency braking state. First, in general braking state, considering the delay characteristics of the pneumatic braking system, a Lagrange quadratic interpolation prediction algorithm is designed to start the pneumatic braking system in advance. Second, in emergency braking state, a model predictive control method is proposed to optimize the braking torque distribution while controlling the wheel slip ratio in a stable range. In order to obtain the optimal control effect, a modified adaptive cuckoo search algorithm is put forward, in which three adaptive impact factors are added. Finally, the proposed control strategy is verified under three road conditions and compared with the conventional control strategy. The results demonstrate significant improvements under gravel road condition, including a 7% increase in energy recovery efficiency, a 92.1% enhancement in the following effect of pneumatic braking torque, and a 43.5% reduction in wheel fluctuation.

Enhancing corrosion resistance of Mg-Li-Zn-Y-Mn alloy containing long period stacking ordered (LPSO) structure through homogenization treatment

This work reported the transformation of (Mg, Zn)24Y5 phase into a long period stacking ordered (LPSO) structure and the reduction of constituent fluctuations induced by massive slender precipitates in α-Mg grains of an as-cast Mg-4Li-4Y–2Zn-0.1Mn (in wt. %) alloy through a simple homogenization treatment. After the treatment, the corrosion resistance of as-homogenized sample significantly improved, primarily attributed to reduced potential differences between LPSO and α-Mg and diminished potential fluctuations in α-Mg compared to the counterparts in the as-cast sample. The corrosion mechanism in both samples was primarily driven by the micro-galvanic effect between (Mg, Zn)24Y5 or LPSO and α-Mg.

New ARMO-based MPPT Technique to Minimize Tracking Time and Fluctuation at Output of PV Systems under Rapidly Changing Shading Conditions

The presence of bypass diodes that mitigate the negative effects of partial shading (PS) conditions produces multiple peak characteristics at the output of a photovoltaic (PV) array. Conventional maximum power point tracking (MPPT) methods develop errors under certain circumstances and detect the local maximum power point (LMPP) instead of the global maximum power point (GMPP). Several artificial intelligence (AI)-based methods have been used to modify the performance of conventional controllers. However, these methods have either not completely solved the PS problem or resulted in considerably complicated and unreliable methodologies, as well as require further development to be used in high-speed applications. This study aims to design, develop, and verify a novel rapid, reliable, and cost-effective method called adaptive radial movement optimization (ARMO) to diminish the effect of the PS problem in the MPP detection for PV systems with additional dynamic applications. The main advantages of ARMO are its improved tracking speed and significant reduction in output fluctuations during the tracking period. An extensive experimental verification has been conducted to provide a fair evaluation of the proposed method compared with conventional and recently developed methods under similar conditions while being applied to a unique PV system and DC/DC converter.

Investigating the mechanistic impact of pork soft tissue preparation techniques on the classification precision of laser-induced breakdown spectroscopy.

The investigation of the mechanism underlying the impact of biological soft tissue sample preparation methods on laser-induced breakdown spectroscopy (LIBS) signals can enhance the stability of LIBS signals. Our study focused on four specific preparation methods applied to pork samples: rapid freezing, fresh slicing, drying, and pressing. The influence of various preparation techniques on the signal-to-noise ratio and fluctuation of Ca, Na, Mg, and CN bands within the sample spectra was assessed. The signal-to-noise ratios for samples that were dried and pressed notably improved. And the pressing method effectively mitigated the uneven distribution of pork tissue components, displaying superior spectral line stability. To explain this phenomenon, we used the Saha-Boltzmann diagram to estimate the plasma temperature. Remarkably, there was a significant reduction in plasma temperature fluctuations across four pressed samples, with a standard deviation of 108.53. Furthermore, we undertook a classification analysis employing support vector machine models to corroborate the generalization efficacy of the sample preparation technique. Dried and pressed samples demonstrated notably higher classification accuracy, precision, and recall (all >93%) compared to frozen and fresh samples, where these metrics remained below 86%. The performance of the SVM model was ultimately evaluated using Receiver Operating Characteristic (ROC) curves and the Area Under the Curve (AUC). The AUC for the frozen, fresh, dried, and pressed samples was 0.854, 0.907, 0.989, and 0.996, respectively. The findings revealed that the pressing method exhibited superior performance, followed by drying, fresh slicing, and freezing, in descending order of effectiveness.

Squeezing and evolution of single particle by frequency jumping in two-dimensional rotating harmonic

The control of microscopic particle behavior based on a specific external field has always been a research hotspot in the field of physics. Many studies have been exploring various methods to manipulate and control the behavior of particles at a microscopic level. In this work, we investigate the phenomenon of single-particle squeezing induced by frequency jumping in a two-dimensional rotating harmonic oscillator potential. Squeezing, as a quantum mechanical phenomenon, has attracted significant attention due to its potential applications in various fields. It refers to the reduction of fluctuations in certain physical quantities, allowing for more precise measurement results. Squeezing phenomena have been extensively studied in different physical systems, including optics, atomic physics, and solid-state physics. However, there have been few reports on the quantum state squeezing phenomenon induced by frequency jumping in a rotating harmonic oscillator potential. Therefore, our study aims to fill this gap and shed light on this intriguing phenomenon. To explore the squeezing phenomenon induced by frequency jumping, we focus on the fluctuations and squeezing of the single particle’s cyclotron radius coordinate and center-guided coordinate in the two-dimensional rotating harmonic oscillator potential. Through numerical simulations and theoretical analysis, we can understand the influence of frequency jumping on the degree of squeezing and reveal the underlying physical mechanism of squeezing evolution. In this work, we first investigate the influence of frequency jumping on the squeezing evolution of the cyclotron radius mode. By carefully selecting appropriate jumping moments, we analyze the influence of frequency jumping on the degree of squeezing. Our research results show that the degree of squeezing in the cyclotron radius coordinate remains unchanged at the jumping moment. However, we observe a stronger squeezing phenomenon in the subsequent evolution process. This indicates that frequency jumping plays a crucial role in squeezing evolution of the cyclotron radius mode. Furthermore, we focus on the squeezing evolution of the center-guided mode during frequency jumping. By selecting suitable parameters, we analyze the squeezing and evolution of two squeezing modes: the divergent mode and the oscillatory mode. Interestingly, we discover the existence of a critical potential trap aspect ratio, which is determined by the rotation angular velocity of the external potential. When the aspect ratio approaches this critical value, the squeezing mode undergoes a transition, and a significant squeezing phenomenon appears in the oscillatory mode. This finding provides valuable insights into the origin and control of squeezing phenomena. Finally, we discuss the potential applications of these squeezing phenomena. Squeezing has significant implications in the fields of quantum sensing and quantum information processing. Through a deeper understanding of the squeezing evolution process caused by frequency jump, we can better control the microscopic particle behavior through external field. This knowledge opens up new possibilities for future physical research and technical applications.

Q-axis Current Reverse Control of Variable Flux Memory Machines With High Salient Ratio During Magnetization Process for Speed Fluctuation Reduction

For variable flux memory machine (VFMM) with high salient ratio, a negative torque occurs when applying a positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_d</i> ) pulse to magnetize the machine under positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> ), causing a large speed drop. Since traditional speed controllers tend to increase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> at this point to increase the speed, unfortunately the higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> will generate stronger negative torque and further exacerbate the speed drop. To deal with this unique problem, a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current reverse control (QCRC) concept is proposed to achieve non-negative torque by reversing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> current during the period of negative torque occurrence. Specifically, based on QCRC concept, three control methods are newly designed, including look-up-table-based QCRC method (Method I), disturbance observer assistance + Method I (Method II) and disturbance-observer-based QCRC method (Method III). A super-twisting sliding mode torque observer (STSMTO) is newly structured as the disturbance observer. Furthermore, a linear active-disturbance-rejection-based feedforward decoupling (LADR-FFD) current controller is utilized to improve the current tracking performance, and the effect of its intrinsic time delay is also investigated. Finally, the effectiveness and feasibility of the proposed three control methods are validated through experimental measurement on a separated series-parallel VFMM (SSP-VFMM).

Comprehensive Analysis and Optimal Control for Capacitor Voltage Fluctuation Reduction in Hybrid MMCs Under Different Over-Modulation Conditions

Comprehensive Analysis and Optimal Control for Capacitor Voltage Fluctuation Reduction in Hybrid MMCs Under Different Over-Modulation Conditions

6PPD-quinone exposure induces neuronal mitochondrial dysfunction to exacerbate Lewy neurites formation induced by α-synuclein preformed fibrils seeding

The emerging toxicant N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q) is of wide concern due to its ubiquitous occurrence and high toxicity. Despite regular human exposure, limited evidence exists about its presence in the body and potential health risks. Herein, we analyzed cerebrospinal fluid (CSF) samples from Parkinson's disease (PD) patients and controls. The CSF levels of 6PPD-Q were twice as high in PD patients compared to controls. Immunostaining assays performed with primary dopaminergic neurons confirm that 6PPD-Q at environmentally relevant concentrations can exacerbate the formation of Lewy neurites induced by α-synuclein preformed fibrils (α-syn PFF). Assessment of cellular respiration reveals a considerable decrease in neuronal spare respiratory and ATP-linked respiration, potentially due to changes in mitochondrial membrane potential. Moreover, 6PPD-Q-induced mitochondrial impairment correlates with an upsurge in mitochondrial reactive oxygen species (mROS), and Mito-TEMPO-driven scavenging of mROS can lessen the amount of pathologic phospho-serine 129 α-synuclein. Untargeted metabolomics provides supporting evidence for the connection between 6PPD-Q exposure and changes in neuronal metabolite profiles. In-depth targeted metabolomics further unveils an overall reduction in glycolysis metabolite pool and fluctuations in the quantity of TCA cycle intermediates. Given its potentially harmful attributes, the presence of 6PPD-Q in human brain could potentially be a risk factor for PD.

Interareal Synaptic Inputs Underlying Whisking-Related Activity in the Primary Somatosensory Barrel Cortex.

Body movements influence brain-wide neuronal activities. In the sensory cortex, thalamocortical bottom-up inputs and motor-sensory top-down inputs are thought to affect the dynamics of membrane potentials (Vm ) of neurons and change their processing of sensory information during movements. However, direct perturbation of the axons projecting to the sensory cortex from other remote areas during movements has remained unassessed, and therefore the interareal circuits generating motor-related signals in sensory cortices remain unclear. Using a Gi/o -coupled opsin, eOPN3, we here inhibited interareal signals incoming to the whisker primary somatosensory barrel cortex (wS1) of awake male mice and tested their effects on whisking-related changes in neuronal activities in wS1. Spontaneous whisking in air induced the changes in spike rates of a subset of wS1 neurons, which were accompanied by depolarization and substantial reduction of slow-wave oscillatory fluctuations of Vm Despite an extensive innervation, inhibition of inputs from the whisker primary motor cortex (wM1) to wS1 did not alter the spike rates and Vm dynamics of wS1 neurons during whisking. In contrast, inhibition of axons from the whisker-related thalamus (wTLM) and the whisker secondary somatosensory cortex (wS2) to wS1 largely attenuated the whisking-related supra- and sub-threshold Vm dynamics of wS1 neurons. Notably, silencing inputs from wTLM markedly decreased the modulation depth of whisking phase-tuned neurons in wS1, while inhibiting wS2 inputs did not impact the whisking variable tuning of wS1 neurons. Thus, sensorimotor integration in wS1 during spontaneous whisking is predominantly facilitated by direct synaptic inputs from wTLM and wS2 rather than from wM1.

Effect of Eight Weeks of Modified Hatha Yoga Exercises on the Balance of Children With Spastic Diplegia Cerebral Palsy Aged 7-14

Background and Aims Cerebral palsy is a common neuromuscular disease with non-progressive symptoms in children. The present study aims to investigate the effect of modified Hatha yoga exercises on the balance of children with spastic diplegia cerebral palsy. Methods This is a quasi-experimental study with a pretest/posttest design. The study population includs all children with spastic diplegia cerebral palsy (with levels 1 to 3 based on the Gross Motor Function Classification System and grades 0 to 3 based on the Modified Ashworth Scale) aged 7-14 years, who were selected from exceptional schools for the disabled students in Isfahan, Iran in 2018. Using a purposive sampling method, 14 eligible children were selected and randomly assigned into two groups of control and exercise. The exercise group performed the modified Hatha yoga exercise for eight weeks at three sessions per week; while the control group did not receive any intervention. The foot plantar center of pressure (COP) was recorded for six seconds (as the balance test) using a foot scanner in the pre-test and post-test phases. Finally, the data were analyzed using repeated measures analysis and independent t-test in SPSS software, version 23. The significance level was set at 0.05. Results The intervention significantly improved the balance of the exercise group compared to the control group. The reduction of COP fluctuations in anterior-posterior (P=0.044), mediolateral (P=0.033), and total directions (P=0.038) in the exercise group were significantly higher than in the control group (P&lt;0.05). Conclusion The modified Hatha Yoga can be a suitable exercise to improve the postural control of children with spastic diplegia cerebral palsy. However, further research is needed to draw a definitive conclusion.

Large-eddy simulations of turbulent flows in arrays of helical- and straight-bladed vertical-axis wind turbines

Effects of helical-shaped blades on the flow characteristics and power production of finite-length wind farms composed of vertical-axis wind turbines (VAWTs) are studied numerically using large-eddy simulation (LES). Two helical-bladed VAWTs (with opposite blade twist angles) are studied against one straight-bladed VAWT in different array configurations with coarse, intermediate, and tight spacings. Statistical analysis of the LES data shows that the helical-bladed VAWTs can improve the mean power production in the fully developed region of the array by about 4.94%–7.33% compared with the corresponding straight-bladed VAWT cases. The helical-bladed VAWTs also cover the azimuth angle more smoothly during the rotation, resulting in about 47.6%–60.1% reduction in the temporal fluctuation of the VAWT power output. Using the helical-bladed VAWTs also reduces the fatigue load on the structure by significantly reducing the spanwise bending moment (relative to the bottom base), which may improve the longevity of the VAWT system to reduce the long-term maintenance cost.

Are patients with GBA–Parkinson disease good candidates for deep brain stimulation? A longitudinal multicentric study on a large Italian cohort

BackgroundGBA variants increase the risk of developing Parkinson disease (PD) and influence its outcome. Deep brain stimulation (DBS) is a recognised therapeutic option for advanced PD. Data on DBS long-term...

Pressure-induced fatigue failures in cast iron water supply pipes

Cast iron pipes have been extensively utilised in water supply networks worldwide. Many of these pipes are either at the onset or within their wear-out phase, during which failure rates rapidly increase, and the pipes should be repaired or replaced. However, the replacement and rehabilitation of these pipes might require extensive resources and time. Therefore, it is essential to investigate the effects of operational practices that might reduce failure rates for ageing cast iron pipes. In this paper, we investigate the conditions under which water pressure fluctuations may impact and accelerate fatigue failures in cast iron pipes. We carried out a systematic review of the mechanical properties of cast iron pipes and conducted sensitivity analyses to estimate fatigue crack propagation using fracture mechanics. Our investigation suggests that cast iron pipes which are affected by reduced wall thickness due to corrosion may experience a significant decrease in their operational life when subjected to water pressure fluctuations. Moreover, this negative influence of pressure fluctuations is exacerbated with an increase in the mean operating pressure. As an example, a 150 mm pipe featuring a corrosion patch of about 7 mm depth could extend its remaining fatigue life by over fourfold through a minor reduction of both mean pressure and pressure fluctuations of approximately 10 mH2O each. The manuscript further explores various pressure reduction combinations and trends, demonstrating the beneficial effects of reducing both mean pressure and pressure fluctuations. Consequently, the presented analysis suggests that water operators should proactively manage (reduce) the magnitude of both pressure components to extend the operating life of ageing cast iron pipes.

Flow over a circular cylinder with a flexible splitter plate

In the present work, we study the flow field around, and forces acting on, a circular cylinder with an attached flexible splitter plate/flap. Two cases of flap length ( $L/D$ ), namely, $L/D = 5$ and $L/D = 2$ have been investigated focusing on the effect of variations in flap flexural rigidity, $EI$ . We find that for a range of $EI$ and Reynolds numbers $Re = UD/\nu$ , a non-dimensional bending stiffness $K^{\ast }=EI/((1/2)\rho U^2 L^3)$ collapses flap motion and forces on the system well, as long as $Re&gt;5000$ . In the $L/D = 5$ flap case, two periodic flap deformation regimes in the form of travelling waves are identified (modes I and II), with mode I occurring at $K^{\ast } \approx 1.5\times 10^{-3}$ and mode II at lower $K^{\ast }$ values ( $K^{\ast }&lt;3\times 10^{-5}$ ). In the $L/D = 2$ flap case, we find a richer set of flapping modes (modes A, B, C and D) that are differentiated by their flapping characteristics (symmetric/asymmetric and amplitude). Force measurements show that the largest drag reduction occurs in mode I ( $L/D = 5$ ) and mode C ( $L/D = 2$ ), which also correspond to the lowest lift and wake fluctuations, with the mode C wake fluctuations being lower than even the rigid splitter plate case. In contrast, the highest fluctuating lift, in both $L/D$ cases, occurs at higher $K^{\ast }$ , when the wake frequency is close to the first structural bending mode frequency of the flap. The observed rich range of flap/splitter plate dynamics could be useful for applications such as drag reduction, vibration suppression, reduction of wake fluctuations and energy harvesting.

The Stochastic Climate Model helps reveal the role of memory in internal variability in the Bohai and Yellow Sea

Hasselmann’s theory elucidates how short-term random noise leads to longer-term unprovoked variations, i.e., red spectra. Here, we study ensembles of numerical model simulations of the hydrodynamics of the Bohai and Yellow Sea concerning internal variability formation. Short(/long) term variations are associated with small(/large) spatial scales, and the internal variability of long-term temporal and large-scale variations is markedly enhanced, even without external forcing on these scales, when the tides are turned off. This pattern is well explained by Hasselmann’s theory. A critical element in this theory is the concept of memory, which in our ensembles exhibits a scale dependence that aligns with the scale-dependent nature of redness. Additionally, this framework clarifies why there is a significant reduction of long-term fluctuations during winter and when tides are active: the system’s memory is notably diminished under these conditions.

Surrogate model-based deep reinforcement learning for experimental study of active flow control of circular cylinder

The flow around a circular cylinder is a classical problem in fluid mechanics, and the reduction of drag and lift has been a long-standing research focus in flow control. In this study, we apply deep reinforcement learning (DRL) to intelligently determine suction flow rate on a circular cylinder model in wind tunnel, aiming to minimize aerodynamic forces while considering energy dissipation efficiency. However, DRL has been criticized for its low data utilization rate and long training period, leading to high experimental training cost. To address these issues, this study employs a surrogate model to optimize the reward function and hyperparameters, and this method is called SM-DRL. This SM-DRL method efficiently expedites the DRL training process, significantly reducing the experimental training cost. In addition, DRL training was conducted in a variable flow field, and the robustness of the obtained DRL model was tested. The results indicate that the DRL agent can determine the optimal control strategy, i.e., automatically select the optimal suction flow rate in terms of the incoming wind velocity, resulting in a significant reduction in lift fluctuations. For Reynolds number of 1.65×104, the reduction in lift fluctuations of the circular cylinder exceeds 50%.