Damping Of Fluctuations Research Articles

Sensitivity of creep parameters to pressure fluctuation of transient flow in viscoelastic pipes

ABSTRACT A stepwise method is one of the efficient approaches in the calibration of transient flow in viscoelastic pipes. However, there is the lack of comprehensive research on the calibration method for retarded time and creep compliance. Therefore, the sensitivity of the order of magnitude of the creep parameters in the presence of interactions to transient flow pressure damping and phase in the case of the two-element Kelvin–Voigt model is investigated. Also, the calibration methods of retarded time and creep compliance in the stepwise method of transient flow parameter calibration for viscoelastic pipes are proposed. The results indicate that the creep compliances do not affect the phase of the pressure fluctuations when the selected retarded times are greater than the order of magnitude 10−1. For the first Kelvin–Voigt element, when the order of magnitude of the retarded time exceeds 10−2, an increase in creep compliance results in an increase in the degree of damping of pressure fluctuations. When the order of magnitude of the retarded time is less than 10−2, the rule is reversed. For the second Kelvin–Voigt element, an increase in creep compliance results in an increase in the degree of damping of transient flow pressure fluctuations independent of the retarded time.

Predictor-Based ADRC for Dynamic Wireless Power Transfer System with Voltage Fluctuation Damping and Measurement Noise Filtering

Predictor-Based ADRC for Dynamic Wireless Power Transfer System with Voltage Fluctuation Damping and Measurement Noise Filtering

Parametric Damping of Microgrid Frequency Fluctuations at Synchronous Machines with Using Lyapunov Theory for Exciter Regulation

In synchronous machines, electromechanical swinging can be damped by parametric control of the excitation current. This is possible only in case the excitation time constant is much smaller than the mechanical constant of the machine. The method described in this paper is effective for damping oscillations caused by oscillations in the grid frequency, grid voltage, and mechanical torque fluctuations. The method is based on the Lyapunov stability theory and demonstrated on a real synchronous machine. This machine operates as a noninterruptible backup power system. The original power fluctuations were up to 50% of the nominal power of the machine. With the described control, a sevenfold increase in the damping of fluctuations caused by grid frequency variations has been achieved.

Linear interaction approximation for shock/disturbance interaction in a Noble–Abel stiffened gas

When departure from the ideal gas equation of state is considered, the Noble–Abel stiffened gas model is an appealing and versatile candidate due to its simple form. The linear interaction approximation formalism is extended to consider non-ideal gas effects introduced by this equation of state. Kovásznay decomposition and adequate definition of the energy of disturbances are provided in the context of this equation of state. Changes with respect to ideal gas are investigated on transfer functions, critical angle, and compression factor. Those differences yield concrete effects on the damping and transfer of fluctuations across shock waves. Those changes are further illustrated by considering the interaction of an entropy spot with a Mach 3 stationary shock wave.

Load-Frequency Control in a Two-Area Power System Using the Fuzzy-PID Method

Power systems are plant units connected to each other, with the electrical power flow constantly moving between them and the load. All systems must be implemented in such a way that they remain stable not only under normal conditions but also after the implementation of unwanted inputs or malfunctions and should be able to return to stable nominal conditions as soon as possible. The basic factors of stability control in a power system are the frequency of different areas and the amount of power flow between them. Now that the main goals of stability control in a power system have been stated, these indicators must be kept at their desired levels through the design and implementation of controllers. This paper first describes the mechanism of load frequency control (LFC). The parameters of several types of complementary controllers are then designed based on the proposed algorithm. The controllers designed on the simulated power system are finally applied, and the effect of each controller on faster damping of frequency fluctuations is discussed. In this study, a multi-area power system is simulated and the effect of disturbance in each area and the performance of the proposed controller in controlling the frequency of the whole network are investigated. The case studies show that the share of active and reactive power generation sources in each region have the greatest impact on frequency control, given that the proposed control coefficients are determined using fuzzy logic in the shortest possible time and the number of transient oscillations eliminated, resulting in a steady system.

Robust linear parameter varying frequency control for islanded hybrid AC/DC microgrids

• The LPV representation of a nonlinear isolated hybrid microgrid model is investigated. • The intermittent nature of the wind speed, solar irradiation, and loads, and several parameter uncertainties are considered in the frequency control design procedure. • A dynamic robust LPV controller synthesis based on the three-step algorithm is proposed for the nonlinear model. • The proposed secondary frequency control approach suggests a practical dynamic output feedback controller with lower order than the IHMG model. • The algorithm superiority is verified in various disturbance-based and uncertain parameter-based scenarios. The applicability of a robust linear parameter varying (LPV) control for frequency fluctuation damping in an islanded hybrid microgrid (IHMG) system (DEG/WTG /PV/FC/ESSs) is investigated in this paper. Due to the erratic behavior of the majority of the renewable energy sources (RESs) and the varying time nature of loads, frequency deviation from the nominal value is inevitable, especially in the islanded mode. Load variation, solar irradiation, and wind power disturbance, as well as system parametric uncertainties, can significantly disturb the system frequency operation. In this paper, the wind speed and rotated speed of the nonlinear wind turbine are highlighted as scheduling parameters, and the nonlinearity of the wind turbine is hidden by the LPV approach. In the proposed method, a dynamic output feedback controller is obtained based on the power balance equation, by solving three LMIs to minimize the upper bound of the L 2 -Norm of the uncertain IHMG in an algorithmic approach. For better evaluation, the ultimate LPV control approach is compared with two other methods on the understudy IHMG model. The result represents a noticeable advantage of the proposed robust method compared to other methods in terms of frequency stability based on time-domain and norms characteristics in presence of the simultaneous disturbances and parametric uncertainties.

Simulating long-term responses of soil organic matter turnover to substrate stoichiometry by abstracting fast and small-scale microbial processes: the Soil Enzyme Steady Allocation Model (SESAM; v3.0)

Abstract. Understanding the coupling of nitrogen (N) and carbon (C) cycles of land ecosystems requires understanding microbial element use efficiencies of soil organic matter (SOM) decomposition. Whereas important controls of those efficiencies by microbial community adaptations have been shown at the scale of a soil pore, a simplified representation of those controls is needed at the ecosystem scale. However, without abstracting from the many details, models are not identifiable; i.e. they cannot be fitted without ambiguities to observations. There is a need to find, implement, and validate abstract simplified formulations of theses processes. Therefore, we developed the Soil Enzyme Allocation Model (SEAM). The model explicitly represents community adaptation strategies of resource allocation to extracellular enzymes and enzyme limitations on SOM decomposition. They thus provide an abstraction from several microbial functional groups to a single holistic microbial community. Here we further simplify SEAM using a quasi-steady-state assumption for extracellular enzyme pools to derive the Soil Enzyme Steady Allocation Model (SESAM) and test whether SESAM can provide the same decadal-term predictions as SEAM. SESAM reproduced the priming effect, the SOM banking mechanism, and the damping of fluctuations in carbon use efficiency with microbial competition as predicted by SEAM and other more detailed models. This development is an important step towards a more parsimonious representation of soil microbial effects in global land surface models.

Energy dissipation in synchronous binary asteroids

Synchronous binary asteroids can experience libration about their tidally-locked equilibrium, which will result in energy dissipation. This is an important topic to the Asteroid Impact and Deflection Assessment, where excitation caused by the DART kinetic impact in the Didymos binary asteroid system may be reduced through dissipation before Hera arrives to survey the effects of the impact. We develop a numeric model for energy dissipation in binary asteroids to explore how different system configurations affect the rate of energy dissipation. We find tumbling within the synchronous state eliminates a systematic trend in libration damping on short timescales (several years), but not over long times (hundreds of years) depending on the material conditions. Furthermore, damping of libration, eccentricity, and fluctuations in the semimajor axis are primarily dependent on the stiffness of the secondary, whereas the semimajor axis secular expansion rate is dictated by the stiffness of the primary, as expected. Systems experiencing stable planar libration in the secondary can see a noticeable reduction in libration amplitude after only a few years depending on the stiffness of the secondary, and thus dissipation should be considered during Hera’s survey of Didymos. For a very dissipative secondary undergoing stable libration, Hera may be able to calculate the rate of libration damping in Dimorphos and therefore constrain its tidal parameters.

Accurate determination of viscosity and surface tension by surface light scattering in the presence of a contribution from the rotational flow in the bulk of the fluid

HypothesisNear the critical damping of surface fluctuations, surface light scattering (SLS) signals are affected by the rotational flow in the bulk of the fluid. The adequate consideration of this bulk shear mode is essential for a reliable determination of viscosity and surface tension, yet not fully resolved so far. ExperimentsTo elucidate the influence of the bulk shear mode on the recorded correlation functions related to surface fluctuations with an oscillatory behavior, different evaluation procedures are compared. A new evaluation approach is suggested, which makes use of the entire signal information and represents the contribution of the bulk shear mode to the signal in a convenient and physically meaningful way. This allows to unambiguously access the dynamics of the probed surface fluctuations, i.e. their mean lifetime and frequency as well as their response to the rotational flow in the bulk of the fluid. FindingsBy applying the evaluation approach to SLS signals for eight different vapor–liquid systems corresponding to reduced capillary numbers between about 0.4 and 15, it is demonstrated that the developed strategy allows for an accurate determination of viscosity and surface tension. This strategy facilitates the thermophysical property research on fluids by SLS experiments performed close to the critical damping.

Підвищення ефективності використання транспортних машин у агропромисловому виробництві узгодженням їх експлуатаційних характеристик та умов функціонування

This paper examines the issue of increasing the efficiency of the use of transport vehicles in agro-industrial production by harmonizing their operational characteristics and operating conditions. The approach of matching the operational characteristics of machines with the conditions of operation is proposed, which is based on structural and simulation models of the "transport machine-conditions of its operation" system. An iterative solution of the simulation model with the search for optimal parameters is proposed. The specific fuel consumption for carrying out transport work is taken as an integral criterion for the efficiency of the use of a transport vehicle at an agro-industrial production enterprise. The specificity of the operating conditions of transport vehicles is proposed to be characterized by the consistency coefficient, which reflects the influence of operating conditions on the specific fuel consumption during transport operations. This coefficient takes into account the influence of the characteristics of the engine, cargo and external load. the corresponding system of equations is given as a mathematical model, which was supplemented with auxiliary dependencies that determine the boundary conditions of the operation of individual subsystems of transport machines, their control conditions and transitions of the model from a dynamic state based on a simulation model, the characteristics of machines and their structural elements in time are calculated for cases of partial high-speed and loading modes and transitions between them. Matching the characteristics of transport vehicles with the operating conditions, justifying their optimal design parameters, was carried out by selecting the transmission parameters, which ensure the improvement of conditions by partial damping of load fluctuations. The results of the parameters of the damping assembly of the transmission of the KamAZ-4308 car for different driving modes are presented. For these conditions, basic, theoretical, and experimental evaluations of the consistency coefficient were carried out, as well as recommended driving modes of transport vehicles when removing grain from the КамАЗ-4308 combine for cars and МТЗ-82+2ПТС4 tractor units.

Multi-level direct crystal plasticity model of polycrystalline specimen: representative volume determination

Since the origination of solid mechanics as a scientific discipline, full-scale experiments on loading (deformation) of macro samples of shape and size corresponding to accepted standards have been used as the main tool to establish the laws of material behavior and determine certain physical and mechanical properties of materials. With the development of technologies and widespread miniaturization, experiments begin to be carried out on samples of meso- and micro scales. This leads to the question: below what sample sizes does a significant deviation of the average response of the samples begin? Therefore, authors introduce the definition of a sample representative volume as the minimum volume, when exceeding which the possible deviation of the mean response of the sample to the same load does not exceed the predetermined value. In order to determine representative volume of polycrystalline specimen numerical experiments on compression of polycrystalline specimens were carried out. The initial grain structure of the sample was formed by cutting cube into set of equal cubes, where each represented a grain. Then the grains were approximated by a set of finite elements using the Gmsh software package. In order to directly solve the boundary-value problem, a software package was used to implement an algorithm for solving the crystal elastoviscoplastic problem formulated in the rate-form by the finite element method. The resulting curve of the relative (relative to the mean values) standard deviation of stresses monotonously decreases with an increase in the number of grains, and the curve of the mean value has a complex shape with a rapid damping of fluctuations and also seem to reach a constant value.

Continuous mixing technology: Validation of a DEM model

Continuous powder mixing is an important technology used in the development and manufacturing of solid oral dosage forms. Since critical quality attributes of the final product greatly depend on the performance of the mixing step, an analysis of such a process using the Discrete Element Method (DEM) is of crucial importance. On one hand, the number of expensive experimental runs can be reduced dramatically. On the other hand, numerical simulations can provide information that is very difficult to obtain experimentally. In order to apply such a simulation technology in product development and to replace experimental runs, an intensive model validation step is required. This paper presents a DEM model of the vertical continuous mixing device termed CMT (continuous mixing technology) and an extensive validation workflow. First, a cohesive contact model was calibrated in two small-scale characterization experiments: a compression test with spring-back and a shear cell test. An improved, quicker calibration procedure utilizing the previously calibrated contact models is presented. The calibration procedure is able to differentiate between the blend properties caused by different API particle sizes in the same formulation. Second, DEM simulations of the CMT were carried out to determine the residence time distribution (RTD) of the material inside the mixer. After that, the predicted RTDs were compared with the results of tracer spike experiments conducted with two blend material properties at two mass throughputs of 15 kg/h and 30 kg/h. Additionally, three hold-up masses (500, 730 and 850 g) and three impeller speeds (400, 440 and 650 rpms) were considered. Finally, both RTD datasets from DEM and tracer experiments were used to predict the damping behavior of incoming feeder fluctuations and the funnel of maximum duration and magnitude of incoming deviations that do not require a control action. The results for both tools in terms of enabling a control strategy (the fluctuation damping and the funnel plot) are in excellent agreement, indicating that DEM simulations are well suited to replace process-scale tracer spike experiments to determine the RTD.

Flow features and thermal stress evaluation in turbulent mixing flows

The present paper depicts a numerical study of flow and thermal features in T-junctions with circular cross-section. The numerical simulation is based on the experimental validated wall-resolved Large-Eddy Simulation method. The Reynolds number in the warm main pipe flow covers a range of Rem=27000 to Rem=134000 and the temperature difference of the mixing fluids is up to ΔT=249 K. The location of maximum fluctuations does not change due to a nearly identical flow pattern type in all simulations. This condition allows the investigation of the flow evolution, mixing process and heat transfer for the same thermal flow pattern type. The numerical simulations are coupled with the heat conduction in the structure due to the thermal fluid-structure-interaction. Further, this study offers a deeper insight into the hidden physics of turbulent mixing flows and the transport as well as damping of thermal fluctuations in the near-wall fluid/solid region. Our study considers also thermal stress analysis by Finite-Element Method by utilizing the wall temperature distribution of previously performed numerical simulations. Therefore, fatigue damage is evaluated based on the stress received from the Finite-Element analysis. The results show that the highest Reynolds number case corresponds to the highest flux intensity and turbulence. This affects the flow field and the thermal features in the core flow and the transport of fluctuations close to the wall. The locations with peak fluctuation intensity in the fluid generates also high fluctuating temperature areas in the structure. The finite element analysis demonstrates that the highest temperature difference case leads to the highest alternating stress intensity which has potential for thermal fatigue. The generated maximal alternating stress is coupled with the flow conditions of the mixing fluids. With an increasing Reynolds number of the main and branch pipe flow as well as temperature difference raises also the resulting maximum alternating stress intensity.

Spatial Active Damping of Vibrations, Vibration Forces, and Pressure Fluctuations Transferred via Expansion Joints in Liquid-Filled Pipelines

Spatial Active Damping of Vibrations, Vibration Forces, and Pressure Fluctuations Transferred via Expansion Joints in Liquid-Filled Pipelines

Activity of Small-Scale Internal Waves in the Northern Polar Atmosphere of Venus by Radio Occultation Measurements of Signal Intensity (Λ = 32 cm) from Venera-15 and -16 Satellites

The radio occultation measurements of the signal intensity (λ = 32 cm) of the Venera-15 and -16 satellites, carried out from October 16 to October 31, 1983, are used to analyze the activity of internal waves in the northern polar atmosphere of Venus. Observations of the intensity of radio waves provide important information about the fine-scale structure of the planet’s atmosphere. Comparison of radio occultation measurements and the results of the standard wave theory shows that small-scale fluctuations of the received signal intensity are caused by the spectrum of vertically propagating internal gravity waves. The vertical length of these fluctuations at altitudes of more than 61.5 km is about ~1 km. The model developed for the radiative damping of intensity fluctuations with altitude in the atmosphere of Venus assumes that the intrinsic frequencies of the identified internal waves (measured in a frame of reference moving together with the undisturbed flow) in the sessions under study vary from 3.5 × 10–4 to 9.5 × 10–4 rad/s, and the ratio of horizontal and vertical wavelengths is in the range from 57 to 21.

Dynamic Modeling of Multiple Microgrid Clusters Using Regional Demand Response Programs

Preserving the frequency stability of multiple microgrid clusters is a serious challenge. This work presents a dynamic model of multiple microgrid clusters with different types of distributed energy resources (DERs) and energy storage systems (ESSs) that was used to examine the load frequency control (LFC) of microgrids. The classical proportional integral derivative (PID) controllers were designed to tune the frequency of microgrids. Furthermore, an imperialist competitive algorithm (ICA) was proposed to investigate the frequency deviations of microgrids by considering renewable energy resources (RERs) and their load uncertainties. The simulation results confirmed the performance of the optimized PID controllers under different disturbances. Furthermore, the frequency control of the microgrids was evaluated by applying regional demand response programs (RDRPs). The simulation results showed that applying the RDRPs caused the damping of frequency fluctuations.

High-speed volumetric imaging of formaldehyde in a lifted turbulent jet flame using an acousto-optic deflector

The development of high-speed volumetric laser-induced fluorescence measurements of formaldehyde ($$\hbox {CH}_2\hbox {O}$$-LIF) using a pulse-burst laser operated at a repetition rate of $${100} \hbox { kHz}$$ is presented. A novel laser scanning system employing an acousto-optic deflector (AOD) enables quasi-4D $$\hbox {CH}_2\hbox {O}$$-LIF imaging at a scan frequency of $${10}\hbox { kHz}$$. The diagnostic capability of time-resolved volumetric imaging is demonstrated in a partially premixed DME/air lifted turbulent jet flame near the flame base. Simultaneous imaging of laser beam profiles is performed to account for the laser pulse energy fluctuation and laser sheet inhomogeneity. With the accurate registration of laser sheet positions, the volumetric reconstruction of $$\hbox {CH}_2\hbox {O}$$-LIF signals is performed within a detection volume of $$17.3 \times 11.9 \times {2.3}\, \hbox { mm}^3$$ with an average out-of-plane spatial resolution of $${250}\,\upmu \hbox {m}$$. A surface detection algorithm with adaptive thresholding is used to determine the global maximum intensity gradient by calculating gradient percentiles. The flame topology characteristics are investigated by evaluating the 3D curvatures of $$\hbox {CH}_2\hbox {O}$$ surfaces. Curvatures calculated using 2D data systematically underestimate the full 3D curvature due to the lack of out-of-plane information. The inner surfaces near the turbulent fuel jet exhibit higher probabilities of large mean curvature than the outer surfaces. The saddle and cylindrical structures are dominant on both the inner and outer surfaces and the elliptic structures occur with lower probability. The results suggest that the damping of turbulent fluctuations by the temperature increase through the $$\hbox {CH}_2\hbox {O}$$ region reduces the curvature, but the local structure topology remains self-similar.

On the damping intensity of the odd Fourier impulse loading the boundary of the periodic composite

Investigated in the paper boundary effect behaviour for a single odd amplitude which loads rectangular boundary of the two-phased periodic composite layer confirms the common view through the prism of the expected strong suppression of the boundary impulses of the physical field near the boundary of the region occupied by the composite. There is no presence of a composite reaction to the boundary loadings mentioned here different than the exponential damping effect. However, the presence in the general equation describing the boundary effect equations the component 2?ssurf pqz?q with the first space derivative responsible for suppression of the solution along the axis Oz should cause not only exponential type of boundary temperature fluctuation damping. This component disappears in principle for the boundary effect analysed for a single impulse.

Power fluctuation damping of the thermostatically controlled loads based on state estimation

As a kind of important demand side resource, the thermostatically controlled loads (TCLs) play an important role in the peak load shifting and load balancing programs. This paper establishes a state-queuing (SQ) model for the large-scale TCLs, and estimates the system states based on the Kalman-filtering. Based on state estimation, the control strategy, whose parameters are optimized by the genetic algorithm (GA), is designed to damp the power fluctuation of the TCLs. Finally, the effectiveness of the proposed method is verified.

Damping of Frequency Fluctuations of Hybrid Power System by Variable Deloaded Operation of PMSG Based Offshore Wind Farm

Damping of Frequency Fluctuations of Hybrid Power System by Variable Deloaded Operation of PMSG Based Offshore Wind Farm