Damping Strategy Research Articles

On the network of synchronized switch damping for blisks

This paper presents a new semi-active piezoelectric damping strategy for the vibration suppression of integrally bladed disk (blisk). The main novelty is the networking of the synchronized switch damping (SSD). Different from the independently shunted SSD broadly studied in the literature, in our approach the piezoelectric materials distributed to different blade sectors are first connected in few electric networks. The blades in the same network share a single SSD circuit. In this way, additional electrical energy channels are established, and the vibration energy can be thereby dissipated and redistributed globally. In addition, the overall number of the SSD circuits will be drastically reduced, decreasing the complexity of the system. To illustrate and demonstrate such an idea, numerical and experimental studies are conducted. First, We presents the governing equations of a general discrete blisk model with the SSD network and derive a linearization method to solve the steady-state solutions. Next, the optimal topologies of the SSD network for different vibrational modes are summarized through numerical simulation. The proposed network exhibits better performance than other candidates for the mistuned case. Then, through the Mont–Carlo simulation, statistical results prove that the network is also effective for the suppression of the amplitude magnification due to mistuning. Eventually, these findings are validated experimentally through a dummy blisk.

Design of Damping Strategies for LC Filter Applied in Medium Voltage Variable Speed Drive

In recent years, medium-voltage variable-speed drives have become popular in the industry. However, in some applications, the use of long cables can lead to overvoltages at the motor terminals, affecting the motor lifespan. Under such conditions, the use of passive filters is recommended. However, the use of inductive capacitive (LC) filters results in resonances, leading to control stability issues. This issue can be mitigated by introducing a resonance damping strategy. In this work, four damping strategies are implemented and designed: Passive damping, capacitor current feedback, capacitor voltage feedback, and notch filter-based damping. The paper performs a comparative study on the current control phase margin, current and voltage harmonic spectra, and overall changes in the control structure. Then, the effect of the damping strategy on the VSD control is evaluated, creating guidelines to support the selection of the appropriate damping strategy. The results indicate that capacitor voltage feedback stands out, since this strategy presents an interesting dynamic behavior while allowing the elimination of the passive damping losses at a relatively low cost.

Active motor damping strategy for driveline vibrations of a hybrid electric vehicle during ABS operation

Torsional drivetrain vibrations in hybrid and electric drivetrains, which occur during traction and braking control, are commonly encountered. This problem occurs mainly due to the weak damping characteristic of the hybrid/electric drivetrain and the fast time response characteristics of the electric motor. An active motor damping (AMD) control algorithm for a hybrid electric vehicle, considering ABS braking maneuvers on different road conditions, is developed in this work. The control problem is structured such that the control objective is disturbance rejection against the estimated brake torque signal received from the ABS module. Communication delay between the ABS and motor control module is handled within the control strategy. State feedback control strategy is used with the linearized version of the non-linear state-space equations together with an Extended Kalman filter. Gear backlash is taken into account without the need to estimate the mode of backlash. In the development of the controller, state feedback gains are set such that the ABS functionality on tire slip regulation is not altered. Existing studies in the literature feedback only the angle of twist and axle wrap angular speed for damping the vibrations. The structure of the controller in this study is different in that it estimates and feeds back tire slip, in addition to these two. Simulation results show the effectiveness of the controller in reducing the angle of twist without deteriorating ABS tire slip control and braking performance of the vehicle.

On the Jacobian approximation in sea ice models with viscous-plastic rheology

Viscous-plastic rheology is widely used in the sea ice modeling community at increasingly high resolutions. Due to the high degree of non-linearity of the rheological constraints, accurate approximation of the Jacobian is required to improve the efficiency of the implicit solvers of the sea ice momentum equation in pack ice. We consider the analytical Jacobian of the ice momentum equation and assess its approximation errors in the Jacobian-free Newton–Krylov (JFNK) method and in the family of more traditional schemes which neglect the dependence of viscosity coefficients on the deformation tensor. It is shown that this dependence provides a substantial contribution to the Jacobian, especially in the regions enriched by linear kinematic features like ridges and elongated polynyas. Numerical experiments indicate that performance of the Newton solvers is also sensitive to errors associated with inexact computation of the search direction, that may be caused, in particular, by numerical approximations of the Jacobian which violate its dissipative property. Based on this analysis, an improved selective damping strategy for the Newtonian solver of the momentum equation is proposed. A series of numerical experiments conducted in simulated pack ice environment demonstrate faster convergence of the updated solver with analytical Jacobian as compared to the one based on the selectively damped JFNK method with inexact GMRES solver in the inner loop.

Suppressing stick–slip oscillations in drill-strings by Modified Integral Resonant Control

This paper presents development of a novel control scheme for suppressing stick–slip oscillations of drill-strings. This scheme utilises a Modified Integral Resonant Control (MIRC) with tracking in order to meet a desired drilling velocity. A low-dimensional two degrees-of-freedom drill-string model incorporating bit-rock interactions adopted for an open-loop control, clearly demonstrate presence of unwanted stick–slip responses. Next a detailed design of the MIRC-based damping scheme (without tracking) capable of eliminating this undesired behaviour is presented. Then in order to enhance efficacy, the MIRC-based scheme is combined with an integral tracking controller to show that this combined damping and integral tracking control scheme is not only capable of eliminating stick–slip oscillations but also maintaining the desired drill-bit angular velocity. To highlight the benefits of the proposed combined scheme, it is compared with the recently proposed Sliding-Mode Controller (SMC). Its inherent simplicity, robustness to parameter uncertainty and excellent performance of the proposed combined scheme propels it to be a leading candidate for stick–slip mitigation in drill-strings. To further showcase the efficacy of the proposed control scheme, its closed-loop performance when implemented on an 8-DOF system, has also been discussed.

Impacts of Land Surface Parameterizations on Simulations over the Arid and Semiarid Regions: The Case of the Loess Plateau in China

Abstract The arid and semiarid areas of the Loess Plateau are extremely sensitive to climate change. Land–atmosphere interactions of these regions play an important role in the regional climate. However, most present land surface models (LSMs) are not reasonable and accurate enough to describe the surface characteristics in these regions. In this study, we investigate the effects of three key land surface parameters including surface albedo, soil thermal conductivity, and additional damping on the Noah LSM in simulating the land surface characteristics. The observational data from June to September from 2007 to 2009 collected at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL) station in northwest China are used to validate the Noah LSM simulations. The results suggest that the retrieved values of surface albedo, soil thermal conductivity, and additional damping based on observations are in closer agreement with those of the MULT scheme for surface albedo, the J75_NOAH scheme for soil thermal conductivity, and the Y08 scheme for additional damping, respectively. Furthermore, the model performance is not obviously affected by surface albedo parameterization schemes, while the scheme of soil thermal conductivity is vital to simulations of latent heat flux and soil temperature and the scheme of additional damping is crucial for simulating net radiation flux, sensible heat flux, and surface soil temperature. A set of optimal parameterizations is proposed for the offline Noah LSM at the SACOL station when the MULT scheme for surface albedo, the J75_NOAH scheme for soil thermal conductivity, and the Y08 scheme for additional damping are combined simultaneously, especially in the case of sensible heat flux and surface soil temperature simulations.

Transient Stability Analysis and Improved Control Strategy for DC-Link Voltage of DFIG-Based WT During LVRT

In this paper, the transient stability for dc-link voltage of doubly-fed induction generator (DFIG)-based wind turbine (WT) is studied in detail during low voltage ride-through (LVRT). Firstly, referring to the rotor swing equation of synchronous generator (SG), the nonlinear large-signal model of dc-link voltage is established. In addition, the damping power, static slip power, and dynamic slip power are derived. Consequently, the transient performance of dc-link voltage under the different operation conditions of DFIG is revealed during LVRT. Furthermore, the instability form of dc-link voltage with the moving process of equivalent power angle is analyzed by the energy function of dc-link voltage. In addition, the impacts of dc voltage control loop's parameter, the active current of the stator, and the slip on the stabilization process of dc-link voltage are studied. Analysis result indicates that the insufficient damping and large unbalanced power would deteriorate the transient behavior and steady-state level of dc-link voltage. Therefore, an additional damping and slip power feedforward control strategy is proposed, which can make the transition process of dc-link voltage smoother and significantly improve the voltage steady-state level. Finally, simulation and experimental results validate the effectiveness of theoretical analysis.

Transient Acoustic Wave Propagation Problems in Multilayered Pavement Using a Time Discontinuous Galerkin Finite Element Method

This paper presents a modified time discontinuous Galerkin finite element method (MDGFEM) for transient acoustic wave propagation problem of multilayered pavement. The pavement consists of cement concrete pavement, semi-rigid base, and natural soil. The multilayered pavement is modeled as poroelastic mediums and assumed to be water-saturated. The well-known generalized Biot’s theory is employed to describe the wave propagation problem. The present MDGFEM, based on the artificial damping scheme, employs the Hermite (P3) functions and the linear (P1) shape functions to interpolate the global nodal vector and its temporal gradient respectively in a time step. Numerical results of 1D and 2D problems show that the MDGFEM can filter out spurious numerical oscillations before and after waves, boundaries of the hole, and the interface between the layers more effectively for the propagation of acoustic waves in multilayered pavement. Compared with widely used time-continuous methods such as the Newmark method, the method proposed in this paper presents better capabilities in the fluid–structure interaction behavior of multilayer pavements and provides a more accurate solution, which contributes to the further development of non-destructive testing of multilayer pavement structures.

Influence of pitch control method of offshore medium speed wind power based on lateral damping strategy on blade vibration

The operating conditions of offshore wind turbines are complex due to the coupling effects of wind waves and other factors. The blade is subjected to uneven load for a long time, which not only increases the difficulty of control and causes fatigue damage, but also leads to the vibration of the tower and affects the service life of the wind turbine. This article mainly GH simulation software was used to simulate sea under variable load condition, based on join the lateral damping strategy, by comparing the independent variable pitch and variable pitch unified control method, analyzed the low frequency vibration of blade root and spindle hub, verified the effectiveness and control advantages of the independent variable pitch control method with lateral damping. It provides effective control measures to solve the vibration problems of the unit and improves the operation reliability.

Hydrodynamic Analysis of a Breakwater-Integrated Heaving-Buoy-Type Wave Energy Converter with an Optimal Artificial Damping Scheme

A three-dimensional frequency-domain numerical wave tank (FR-NWT) based on the Rankine panel method was developed. An optimal artificial damping zone (ADZ) scheme was first applied to the FR-NWT to prevent reflection waves from the end walls. Parametric studies of ramp function shape with artificial damping coefficients and damping zone length were conducted to find a proper damping scheme for the frequency domain program. Applying both the Sommerfeld radiation condition and the ADZ scheme to the frequency domain program can reduce the length of the ADZ to less than one wavelength. The FR-NWT developed by the authors was used to calculate the hydrodynamic response of a hemispherical-heaving buoy wave energy converter (WEC) integrated with a seawall-type breakwater of infinite length. A linear power take-off system was used to calculate power generation of the WEC. The global motion of the WEC combined with the breakwater was up to 1.85 times greater than that of the WEC without the breakwater. Moreover, the capture width ratio of the WEC increased approximately 3.67 times more than that of the WEC without the breakwater.

Selective LQ wide area damping of power networks based on the spectral decomposition of Gramians

Inter-area oscillations in large power network are poorly controlled via local decentralized control. One promising strategy for wide-area damping of these oscillations is to minimize the quadratic state and control cost function for a linearized system model. In this paper, we improve this linear-quadratic method by introducing novel selective approach. Namely, instead of using the full state we minimize in the cost function only the selected spectral part of the state. The proposed selective LQ optimal problem is reformulated via the selected spectral part of the closed-loop observability Gramian. This spectral part is a solution to the modal Lyapunov equation specially designed for a chosen spectral range. Novel approach allows to take into account in global optimization only the selected set of oscillations and therefore to improve flexibility and accuracy of controllers setting. Numerical experiments with the IEEE New England test system confirm that the selective approach improves the performance of the conventional LQ method for suppressing low frequency inter-area oscillations.

Active damping strategy with differential feedback of grid-side inductor voltage for LCL-filtered grid-connected inverters

Active damping strategy with differential feedback of grid-side inductor voltage for LCL-filtered grid-connected inverters

Guided wave propagation analysis in stiffened panel using time-domain spectral finite element method

Stiffened panels have been widely utilized in fuselages and wings as critical load-bearing components. These structures are prone to be damaged under long-term and extreme loads, and their health monitoring has been a common concern. The guided wave-based monitoring method is regarded as an efficient approach to detect the damage in stiffened plates because of its wide monitoring range and high sensitivity to micro-damage. Efficient simulation of wave propagation can theoretically demonstrate the detection mechanism of the method. In this study, a Time-Domain Spectral Finite Element Method (TD-SFEM) is adopted to study the wavefield in stiffened plates, where continuous Absorbing Layers with Increasing Damping (ALID) strategy is proposed to circumvent the disturbance of reflected waves on boundaries. After the convergence analysis, the developed TD-SFEM with ALID is validated by the finite element method first. Then, wave scattering and the influence of the stiffener are investigated in detail by comparing the results with the non-stiffened structure. Finally, the effects of the parameters of the stiffener, such as the height and width, on wave propagation are studied, respectively. The results illustrate that the proposed TD-SFEM with ALID is an efficient approach to study the wave propagation in the stiffened plate and can reveal the mechanism of influence of the stiffener. It is found that the height of the stiffener changes the interference of wavefield in the plate, while the effects of the width are mainly in wave scattering and mode conversion.

A Comprehensive Review of Small-Signal Stability and Power Oscillation Damping through Photovoltaic Inverters

This paper focuses on the methods that ensure the rotor angle stability of electric power systems, which is most frequently analyzed with small-signal models. Over the past several decades, power system stabilizers (PSSs) for conventional excitation systems were the main tools for improving the small-signal stability of electromechanical oscillatory modes. In the last decade, power oscillation damping (POD) control implemented in photovoltaic (PV) inverters has been considered an alternative to PSSs. As PV generation undergoes massive rollout due to policy directions and renewable energy source integration activities, it could potentially be used as a source of damping, which is crucial for sustaining the rotor angle stability of the remaining in-service synchronous generators. Several studies have already been dedicated to the development of different damping strategies. This paper contributes to the existing research in power system stability by providing a comprehensive review of the effects of PV generation on small-signal stability, as well as the recent evolution of POD control through PV inverters. The features and impacts of the various ways to realize POD controllers are assessed and summarized in this paper. Currently, detailed information and discussions on the practical application of PV inverter PODs are not available. This paper is, thus, intended to initiate a relevant discussion and propose possible implementation approaches concerning the topic under study.

A Non-Compact Effective Impedance Model for Can-to-Can Acoustic Communication: Analysis and Optimization of Damping Mechanisms

Abstract Can-annular combustors can feature azimuthal instabilities even if the acoustic coupling between the individual cans is weak. Recently, various studies have focused on modeling the acoustic communication between adjacent cans in can-annular systems. In this study, a coupling model is presented that, in contrast to previous models, includes the effect of density fluctuations, mean flow, and dissipative effects at the connection gaps. By assuming plane acoustic waves inside each can and exploiting the discrete rotational symmetry of the can-annular system, the acoustic can-to-can interaction can be represented by an effective Bloch-type impedance. A single can modeled with the effective impedance at the downstream end emulates the acoustic response of the entire can-annular arrangement. We then propose the idea of installing a liner just upstream of the first turbine stage to damp azimuthal instabilities. By using the proposed can-to-can coupling model, we discuss in detail the effect that the impedance of the liner has on the effective reflection coefficient for different Bloch wavenumbers. In the low-frequency limit, we derive an analytical condition for achieving maximum damping at a specific Bloch-number. We show that the damping of azimuthal modes depends on the porosity of the liner, mean flow parameters and the Bloch-structure of the mode. These results suggest the possibility of targeting the damping of modes of certain azimuthal order by geometric variations of the liner or of the connection gap. As an exemplary application of the theory, we setup a network model of a generic industrial 12-can combustor and investigate a cluster of acoustic and thermoacoustic eigenvalues for a varying liner porosity. The findings of this study provide a deeper understanding of the mechanisms that drive the can-to-can acoustic communication, and open the path for devising passive damping strategies aimed at stabilizing specific modes in can-annular combustors.

Approximate Message Passing Algorithms for Low Complexity OFDM-IM Detection

Low complexity approximate message passing (AMP) orthogonal frequency division multiplexing combined with index modulation (OFDM-IM) detection algorithms are proposed, which exploit the sparse structure of the frequency domain (FD) OFDM-IM symbols. To circumvent the high root mean square error (RMSE) in the conventional AMP algorithm, a minimum mean square error (MMSE) denoiser is proposed based on the classic Bayesian approach and on the state evolution of AMP. Our simulation results demonstrate that it is capable of improving both the RMSE as well as the convergence rate. However, in practice, the channel's diagonal FD matrix may be a non-Gaussian sensing matrix, hence a damping strategy is conceived. In conclusion, the proposed MMSE denoiser based damping-assisted AMP-aided detector strikes a compelling bit error ratio vs. complexity trade-off.

Model Predictive Control of the Input Current and Output Voltage of a Matrix Converter as a Ground Power Unit for Airplane Servicing

This paper deals with the design, control, and implementation of a three-phase ac–ac mobile utility power supply using a matrix converter for airplane servicing applications. Using a matrix converter as a compact direct ac-to-ac converter can provide savings in terms of the size and cost of a mobile power supply compared to common back-to-back converters. Furthermore, using the proposed direct matrix converter eliminates the need for bulky electrolytic capacitors and increases the system’s reliability and lifetime. A finite control set model predictive control is used to generate a high-quality 115 V/400 Hz output voltage and a low-harmonic-distortion source current with a unity input power factor for various load conditions, including balanced, unbalanced, linear, and nonlinear loads. The predictive strategy is used to control the output voltage and source current for each possible switching state in order to simultaneously track the references. To achieve a further reduction in the system’s size and cost, an active damping strategy is used to compensate for the instability caused by the input filter in contrast to the passive method. Experimental tests were conducted on a prototype matrix converter to validate the performance of the proposed control strategy.

Validation of a morphology adaptive multi-field two-fluid model considering counter-current stratified flow with interfacial turbulence damping

Stratified flows are one of the most important multiphase flow regimes for safety analyses of the loss-of-coolant accident in pressurized water reactors. The present paper considers simulations of an isothermal counter-current stratified flow case in the channel of the WENKA (Water Entrainment Channel Karlsruhe) experiment using a morphology adaptive multi-field two-fluid modelling framework. A consistent momentum interpolation approach is applied together with the partial elimination algorithm, as it is required for strong momentum coupling, which enforces the no-slip condition at the interface and mirrors the behaviour of a homogeneous model. To model the turbulent flow conditions near an interface, the framework is extended with a turbulence damping model based on the damping scale formulation from the literature, which is introduced into the k-ω SST (Shear Stress Transport) turbulence model. The presented modelling approach is validated with experimental data for the pressure difference and vertical profiles of volume fraction, velocity and turbulent kinetic energy. Results of a mesh sensitivity study of the model are presented. Simulations were performed on two- and three-dimensional models of the channel geometry. Two turbulence damping strategies are investigated: symmetric, with damping in both phases, and asymmetric with damping only in the gas phase. The comparison shows that the asymmetric approach offers improved prediction of turbulent kinetic energy on the liquid side of the interface, but with a cost of diminished accuracy of the predicted velocity profiles on the gas side.

Active Damping and Passive Control Strategy for Three-Phase LCL Grid-Connected Inverter

Compared with traditional controllers such as PI based on classic control theory, the article applies passive control (PBC) theory to the design of three-phase LCL grid-connected inverter controllers. The mathematical model of the system based on Euler-Lagrange (EL) is established, and the damping method of the trap is used to suppress the resonance spikes generated by the system, so that the system meets the requirements of grid connection. The simulation results verify the feasibility of the scheme.

Robust Multiobjective Nonlinear Constrained Optimization with Ensemble Stochastic Gradient Sequential Quadratic Programming-Filter Algorithm

Summary As the crucial step in closed-loop reservoir management, robust life-cycle production optimization is defined as maximizing/minimizing the expected value of a predefined objective (cost) function over geological uncertainties (i.e., uncertainties in the reservoir permeability, porosity, endpoint relative permeability, etc.). However, with robust optimization, there is no control over downside risk defined as the minimum net present value (NPV) among the individual NPVs of the different reservoir models. Yet, field operators generally wish to keep this minimum NPV reasonably large to try to ensure that the reservoir is commercially viable. In addition, the field operator may desire to maximize the NPV of production over a much shorter time period than the life of the reservoir under the limitation of surface facilities (e.g., field liquid and water production rates). Thus, it is important to consider multiobjective robust production optimization with nonlinear constraints and when geological uncertainties are incorporated. The three objectives considered in this paper are; to maximize the average life-cycle NPV, to maximize the average short-term NPV, and to maximize the minimum NPV of the set of realizations. Generally, these objectives are in conflict; for example, the well controls that give a global maximum for robust life-cycle production optimization do not usually correspond to the controls that maximize the short-term average NPV of production. Moreover, handling the nonlinear state constraints (e.g., field liquid production rates and field water production rates for the bottom-hole pressure controlled producers in the robust production optimization) is also a challenge because those nonlinear constraints should be satisfied at each control steps for each geological realization. To provide potential solutions to the multiobjective robust optimization problem with state constraints, we developed a modified lexicographic method with a minimizing-maximum scheme to attempt to obtain a set of Pareto optimal solutions and to satisfy all nonlinear constraints. We apply the sequential quadratic programming filter with modified stochastic gradients to solve a sequence of optimization problems, where each solution is designed to generate a single point on the Pareto front. In the modified lexicographic method, the objective is always considered to be the primary objective, and the other objectives are considered by specifying bounds on them to convert them to state constraints. The temporal damping and truncation schemes are applied to improve the quality of the stochastic gradient on nonlinear constraints, and the minimizing–maximum procedure is applied to enforce constraints on the normal state constraints. The main advantage that the modified lexicographic method has over the standard lexicographic method is that it allows for the generation of potential Pareto optimal points, which are uniformly spaced in the values of the second and/or third objective that one wishes to improve by multiobjective optimization.