Damped Method Research Articles

An Accelerated Three Term Efficient Algorithm for Numerical Optimization

Background:
 A new optimization algorithm is presented. The method is biased with new non monotone line search an accelerated three term conjugate gradient method damped of Quasi Newton method compared to previews method design efficiency in provident of more than one factor for different optimization problem are more dramatic due to the ability of the technique to utile existing data.
 Materials and Methods:
 New monotone line search, new monotone line search, new modification of Damped Quasi-Newton method, Motivation and New Quasi-Newton Algorithm (MQ) and Global convergence.
 Results:
 In this work, we have n tendency to compare our new algorithm with same classical strategies like [7] by exploiting of unconstrained nonlinear optimization problem the functions obtained from Andrei [5, 6] Waziri and Sabiu (2015)[10] and La couzetul (2004)[3]. The numerical experiments demonstrate the performance of the proposed method. We selected seven relatively unconstrained problems with the size varies from 10 to 100. We consider the three sizes of each problem so that the total number of problem is 21 test problems. We stop the iteration when is satisfied All codes were written in Matlab R2017a and run on a pc with Intel COREi4 with a processor with 4GB of Ram and CPU 2.3GHZ we solved test problems using two different initial starting points.
 Conclusion:
 In this research article, a project on an accelerated three-term efficient algorithm for numerical optimization has presented the method as completely a derivative-free algorithm with less NOI and NOF and CPU time computed to the existing methods .using classical assumption the global convergence was also proved. Numerical results using the three terms efficient algorithm show that the algorithm is promising.

High frequency oscillation damping for the VSC-HVDC connects to a wind farm via a cable transmission line

When a wind farm connects to the grid via a high voltage direct current transmission based on voltage source converter (VSC-HVDC), high frequency oscillation (HFO) is a critical issue that threatens the system stability, this issue has been reported in many HDVC projects all over the world. The current research proved the negative resistance brought by the effect of control delay in VSC-HVDC is a primary cause of instability. This paper ulteriorly analyzes the influence on system stability caused by the long ac cable between the wind farm and the VSC-HVDC, and indicates that the effect of the cable transmission line can contribute to the system instability as well, while the existing damping methods did not consider this effect. Then the control failure of the exiting damming methods when considering the cable transmission line is analyzed and verified by the impedance analysis theory. Thereby, this paper proposed a vector modified resonant controller (VMRC) which can independently and flexibly regulate the magnitude and phase of HVDC impedance, to solve the HFO issue caused by the combined effect of the control delay and the cable transmission line. Also, the design procedure of the proposed control strategy is detailly presented. Finally, experimental results are provided to verify the correctness of the mechanism analysis and the validity of the proposed control strategy.

Geometric modelling of polycrystalline materials: Laguerre tessellations and periodic semi-discrete optimal transport

In this paper we describe a fast algorithm for generating periodic RVEs of polycrystalline materials. In particular, we use the damped Newton method from semi-discrete optimal transport theory to generate 3D periodic Laguerre tessellations (or power diagrams) with cells of given volumes. Complex, polydisperse RVEs with up to 100,000 grains of prescribed volumes can be created in a few minutes on a standard laptop. The damped Newton method relies on the Hessian of the objective function, which we derive by extending recent results in semi-discrete optimal transport theory to the periodic setting.

Direct Power Control of Three-Phase Electric Springs

Three-phase electric spring (TPES) was originally proposed to solve three-phase imbalance issues in power systems. So far, several attempts have been reported on proposing power control methods for it. However, existing solutions on TPES either depend on circuit parameters or have relatively slow dynamic responses. In this article, a novel power control strategy that incorporates the advantages of direct power control (DPC) is proposed to solve the above issues. It might be the first attempt to propose a simple power control strategy with rapid dynamic response and independent with circuit parameters for TPES. Besides, the relationship between power operating range and circuit parameters is well analyzed, which provides a way for parameter optimization. To restrain the resonance phenomenon caused by the TPES topology, the passive and active damping methods are compared, revealing that power quality of the control objective can be greatly improved with the active damping. Finally, the proposed DPC with both damping methods is validated by simulations and experimental results.

Active Compliance Control of a Position-Controlled Industrial Robot for Simulating Space Operations

An industrial robot with a six-axis force/torque sensor is usually used to produce a zero-gravity environment for testing space robotic operations. However, using traditional force control methods, such as admittance control, causes position-controlled industrial robots to undergo from force divergence owing to intrinsic time delay. In this paper, a new force control method is proposed to eliminate the force divergence. A hardware-in-the-loop (HIL) simulator with an industrial robot is first presented. The free-floating satellite dynamics and the motion mapping from the satellites to simulator are both established. Thus, the effects of measurement delay and dynamic response delay on contact velocity and force are investigated. After that, a real-time estimation method for contact stiffness and damping is proposed based on the adaptive Kalman filter. The measurement delay is compensated by a phase lead model. Moreover, the identified contact parameters are adopted to modify contact forces, and thus the dynamics response delay can be compensated for. Finally, a co-simulation and experiments were conducted to verify the force control method. The results show that contact stiffness and damping could be identified exactly and that the simulation divergence could be prevented. This paper proposes an active compliance control method that can deal with force constrained tasks of a position-controlled robot in unknown environments.

A novel optimization algorithm for the selective frequency damping parameters

Flow stability analysis is of great importance in flow physics and control. The solution of base flow, achieved as the steady state of the unsteady Navier–Stokes equation (UNSE), counts among keystones in the field of flow stability analysis. To obtain the numerical solution of base flow, the selective frequency damping (SFD) method has been widely used, with the numerical effectivity and computational efficiency being closely related to the selection of a pair of parameters (χ,Δ), where χ represents the control coefficient and Δ denotes the filter width. In the present work, a novel method for calculating the base flow of the unsteady Navier–Stokes equation (UNSE) has been established, by combining the SFD method with the immersed boundary method. Detailed analysis of the influences of the SFD parameters is presented, attempting to establish the relationships between the parameters and eigenvalues for the Jacobian matrix of UNSE. The dynamic mode decomposition method is introduced to calculate the eigenvalues for the velocity field, and several techniques and strategies are applied for improving the solving accuracy. Further, an optimization method of the parameter pair is developed to accelerate the convergence to the steady state, trying to minimize the spectral radius of the Jacobian matrix in the parameter space of (χ,Δ). Two test simulations, that is, flow past a cylinder and flow past two side-by-side cylinders at Re=100, are conducted by applying the optimization method. A faster convergence rate and higher efficiency are demonstrated compared to the results using the previous methods.

An alternative control synthesis for stability enhancement of digital-controlled LCL-filtered grid-connected inverter

• A control synthesis is proposed to damp capacitor current resonance for LCL-filtered GCI. • The stability and performance characteristics are analyzed and compared with methods from the literature. • Intuitive design, wider stable damping region, better dynamic performance, and higher parametric robustness are the potential benefits of the proposed control synthesis. In distributed power generation systems, the inherent resonance phenomena of LCL -filtered grid-connected inverter is one of the major challenges faced by the integration of renewable energy resources with the electric power grid. In this context, the capacitor current based multi-loop active damping method is employed due to lossless resonance damping and flexible control design. However, the damping loop with the feedback compensation design suffers from relatively higher parameters sensitivity unless employed with the reduced digital delays. The filter parameters fluctuation causes a shift in resonance frequency, which leads to ineffective damping at the critical resonance frequency and may risk the control loop stability. Therefore, an alternative linear control synthesis is proposed to design the capacitor current damping loop in order to reduce the filter parameters sensitivity. The proposed design realizes the equivalent virtual impedance in an alternative manner to suppress the resonance peak and enhanced the stability characteristics of the grid-connected inverter. A detailed stability and performance analysis have been done to show the widened stable damping region and high parametric robustness of the suggested design as compared to the literature method. Simulations and experimental results are presented to confirm the theoretical findings.

An Active Damping Control Method for Reduced DC-Link Capacitance PMSM Drives With Low Line Inductance

The power density can be improved and the system cost can be saved in the reduced dc-link capacitance motor drive system. The line inductance can also be diminished to reduce the system volume further. In previous research works, the active damping control methods mainly concentrated on the drive system equipped with a larger line inductor. In this article, a dc-link voltage estimation feedback-based active damping method is proposed to suppress the grid current harmonics and improve the drive system stability with low line inductance. The dc-link voltage ripple caused by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance is analyzed to evaluate the direct dc-link voltage feedback-based active damping control method. To improve the damping performance, the resonant component of the dc-link voltage caused by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance could be obtained through the grid current to establish the feedback control loop. The sampling delay should be compensated to improve the control performance. The stability of the drive system is evaluated by the Nyquist plots of the impedance model, and the grid current is also analyzed, which could satisfy the harmonic requirements of IEC-61000-3-2. Experimental results are performed to verify the effectiveness of the proposed method.

Fuzzy PID control method for damping of electronically controlled air suspension shock absorbers for vehicles

A damping fuzzy proportional-integral-derivative (PID) control method for electronically controlled air suspension shock absorbers was proposed to reduce the RMS values of the body vibration acceleration and improve vehicle ride comfort. Depending on the operating mode of the electronically controlled air suspension shock absorber, a mechanical model of the air suspension shock absorber was established. A fuzzy PID control technology for damping control of the shock absorber is designed by combining a PID control algorithm with the fuzzy control concept. The adaptive expansion factor of the cybernetics domain for the fuzzy PID controller is calculated by considering nonlinear characteristics and time delay to improve the controller’s adaptability. Then, the control parameters are adjusted based on the control deviation and deviation rate parameters. The nonlinear detection platform produced by an enterprise is selected to build an experimental environment for analysis. Simulation results reveal that when the vehicle speed is 30 km h−1, the RMS values of the body vibration acceleration upon applying the proposed method is approximately 0.02 and 0.05 km h−2, respectively, on Class B and C road surfaces. Furthermore, the RMS values of the body vibration acceleration using the proposed method has little fluctuation; when the vehicle speed is 60 km h−1, the RMS values of the body vibration acceleration is 0.022 and 0.028 km h−2, respectively, on Class B and C road surfaces, indicating that the proposed method can effectively reduce the RMS values of the body vibration acceleration and improve rider comfort.

Development of a Novel Seat Suspension Based on the Cubic Stewart Parallel Mechanism and Magnetorheological Fluid Damper

To alleviate the impact and vibrations to a driver in multiple directions during the driving of non-road vehicles, the authors of this paper proposed a multi-degree-of-freedom (MDOF) seat damping suspension that was based on the cubic Stewart mechanism and magnetorheological fluid (MRF) damper. A kinematics analysis of the cubic Stewart mechanism was carried out. The relative motion velocity of each leg of the Stewart mechanism was calculated from the center velocity of the upper and lower platforms, according to a reverse kinematics equation. Furthermore, forward and inverse dynamic models of the MRF damper were established, which laid the foundation for semi-active control of the seat suspension. Finally, a semi-active control method for multidimensional damping based on the optimized fuzzy skyhook control method was proposed. The research results showed that using this method could simultaneously improve the vibration damping performance of a seat suspension in the vertical, horizontal, and roll directions.

Damped AC Testing and Diagnosis of Wind Farm HVAC Long-Length Cable Circuits

Many new HVAC power cable installations on wind farms, both on- and offshore, have long lengths. In contrast to traditional power cable connections of a few kilometers, the failures of those systems usually result in much higher repair and unsupplied energy costs. To support the quality assurance of newly installed cable systems as well as to create a sound basis for condition-based maintenance, this paper discusses the technical challenges of the field testing of long-length power cable systems using a damped AC testing method and also discusses the best practical applications for the testing and diagnosis of these wind farm HVAC cable systems.

The Dynamics of a Continuous Newton-like Method

The objective of the current work is to invent and introduce the continuous version of Newton’s method. This scheme is used to establish some interesting properties with examples. We have plotted the fractal pattern graphs for a Newton-like method and a Damped Newton-like method in the discrete case and hence we have introduced a new concept of streamline for the continuous version of the Newton-like method. The graph and streamlines of these patterns are in agreement with numerical results and describe the convergence and stability of the proposed method to different roots when the Newton method fails.

Influence of bottom slope on gap resonance behavior between fixed body and back wall in close proximity

Narrow gap resonances ubiquitously presenting in coastal and offshore engineering domain may provoke unexpected structure damages and threaten operation safety, especially those occurring between floating bodies and vertical walls. While most of the existing studies assume a flat bottom, effects of the real-world sloping bottom are still unclarified and may probably change gap resonance behavior. By combining the advantages of CFD based model and modified potential flow model, this study focuses on variations of gap resonance height with the presence of a sloping bottom and the capacity of potential flow model with artificial damping method in predicting resonant patterns. For the incident wave heights from minimal ones to relatively larger ones, empirical relationship between gap resonance amplitude and incident wave amplitude is re-examined and found to be similar to that obtained from a flat bottom but with geometry-specific parameters. The potential flow model is interestingly revealed to possibly perform even better in dealing with larger incident wave amplitude and steeper bottom slope once the damping term is well-tuned. Origin of the better performance is qualitatively found to be related to the turbulence patterns inside the fluid domain beneath the narrow gap.

Comparison of damping performance of an aluminum bridge via material damping, support damping and external damping methods

Damping property is the basic energy dissipation mechanism that widely exists in almost all kinds of structures or components. This paper presents an experimental study on three different measures including rubber sheet pavements, rubber bearings and external passive damper to increase the damping of a lightly damped aluminum bridge. These methods are conventional treatments in engineering practice, and they aim to take effect through the aspects of material damping, support damping and external damping, respectively. The performance of these methods in damping increment is compared, and the possible damping mechanism of each measure is discussed. The external damper is found to be most effective in damping increment, followed by rubber bearings. The method of rubber sheet pavement is inefficient in damping increment owing to the huge difference in elastic modulus between aluminium and rubber. The rubber sheet keeps in tiny strain state during structural vibration and fails to generate effective internal friction between particles, and thus contributes little to the overall material damping. This indicates that the damping material method can take effect only if the damping layer has not only remarkable loss factor but also comparable elastic modulus with the target structure. In addition, the external damper generally follows the linear viscous damping law. The external damper having liquid viscosity of 3.05 Pa·s can increase the system damping to 1.5 %, which is almost one order greater than the performance of rubber sheet pavement and rubber bearing methods. Moreover, the external damping method is found to be sensitive to the installation location of the damper. The greater the modal displacement, the larger the system damping is. Furthermore, the system damping is not sensitive to structural frequency, whereas it slightly increases with the structural strain in small strain levels.

A combined GA and DLS parallel algorithm for multimode Rayleigh wave inversion

Multichannel analysis of surface waves (MASW) is a vital method in near-surface exploration. Linear algorithms, such as damped least square method (DLS), are highly dependent on the initial model and are prone to trapping in local minima. While nonlinear algorithms such as genetic algorithm (GA) are globally optimal but inefficient, they are not very practical for complex calculations.In this paper, we propose a combined GA and DLS parallel algorithm (GA-DLS), which has a global search capability due to the GA framework, and has a quick local search capability due to the DLS parallel computing. To simulate the earth model in complex near-surface conditions, we set a low-velocity layer among a layered earth model (LVL) and a high-velocity layer among a layered earth model (HVL), we perform the inversion with DLS, GA, and GA-DLS, respectively. The comparison shows that the GA-DLS inversion gets an efficient and accurate result. Finally, we use the GA-DLS algorithm to invert the field data and achieve good results, verifying the effectiveness of the algorithm.

Robust damping and decoupling controller for interconnected power network based on distributed energy resources

Converter based distributed energy resource (DER) units are intended to be integrated into the power system using grid-forming converters (GFCs). It proposes to emulate the synchronous machines dynamics and forms the grid voltage/frequency by instantaneously balance the load changes without peer-to-peer coordination. However, the damping and coupling characteristics of GFCs in multi-vendor interoperability-based network have not yet been fully explored. The paper proposes a step-by-step analytic method based on participation factor analysis to efficiently analyze the oscillatory modes and the coupling characteristics in the GFCs-based network, especially where the GFCs are controlled by different control techniques. Moreover, to efficiently damp these oscillatory modes and such control coupling, a hybrid damping method based on an oscillation damper and a decoupling controller is proposed. A mathematical modelling is derived to confirm the role of the proposed decoupling controller especially during transient periods. Design guidelines using pattern search algorithm are presented to identify the optimum parameters of the proposed hybrid damping method. Finally, the experimental results using Controller-hardware-in-the-loop (CHiL) verify the theoretical analysis and the efficient damping against large disturbances. © 2017 Elsevier Inc. All rights reserved.

Sensorless passivity based control of doubly-fed induction generators in variable-speed wind turbine systems based on high gain observer

The current study presents a robust sensorless control using passivity based control (PBC) combined with high gain observer (HGO). The proposed controller is applied to control the generated doubly-fed induction generator (DFIG) active and reactive power installed on a variable speed wind energy conversion system. The control objective is used to regulate independently the DFIG stator active and reactive power, which are decoupled by using the field oriented control technique. Additionally, this process leads to reduce the cost of control scheme by eliminating the speed sensor. Firstly, the DFIG is modeled under the port controlled Hamiltonian (PCH) model, as well as the method of simultaneous injection damping. Then, the DFIG is further modeled by assignment passivity based on the simultaneous injection damping and assignment (SIDA-PBC) control of the obtained model under such conditions and a comparison with the fuzzy sliding mode controller is carried out. Furthermore, the HGO is selected in order to estimate the rotor position and the speed from the measurement of the DFIG currents and voltages, and compared with fuzzy sliding mode observer. For testing the proposed control scheme performance, a 1.5 MW DFIG system is developed and simulated using MATLAB/Simulink. The obtained results demonstrate the effectiveness of the proposed control scheme in the presence of various DFIG parameters variation. Additionally, the control objective is achieved without speed sensor.

An efficient finite element iterative method for solving a nonuniform size modified Poisson-Boltzmann ion channel model

In this paper, a nonuniform size modified Poisson-Boltzmann ion channel (nuSMPBIC) model is presented as a nonlinear system of an electrostatic potential and multiple ionic concentrations. It mixes nonlinear algebraic equations with a Poisson boundary value problem involving Dirichlet-Neumann mixed boundary value conditions and a membrane surface charge density to reflect the effects of ion sizes and membrane charges on electrostatics and ionic concentrations. To overcome the difficulties of strong singularities and exponential nonlinearities, it is split into three submodels with a solution of Model 1 collecting all the singular points and Models 2 and 3 much easier to solve numerically than the original nuSMPBIC model. A damped two-block iterative method is then presented to solve Model 3, along with a novel modified Newton iterative scheme for solving each related nonlinear algebraic system. To this end, an effective nuSMPBIC finite element solver is derived and then implemented as a program package that works for an ion channel protein with a three-dimensional molecular structure and a mixture of multiple ionic species. Numerical results for a voltage-dependent anion channel (VDAC) in a mixture of four ionic species demonstrate a fast convergence rate of the damped two-block iterative method, the high performance of the software package, and the importance of considering nonuniform ion sizes. Moreover, the nuSMPBIC model is validated by the anion selectivity property of VDAC.

Artificial compressibility approaches in flux reconstruction for incompressible viscous flow simulations

Artificial compressibility methods intend to offer divergence-free free velocity fields at the incompressible limit for compressible solvers. Three major approaches for this are compared within a high-order flux reconstruction framework: the established method (ACM) of Chorin (1967) and a new entropically damped method (EDAC) of Clausen (2013) which can keep velocity divergence sufficiently low to be run explicitly without the non-linear solver required by ACM. Furthermore, the ACM approach with hyperbolised diffusion is investigated. The accuracy and computational efficiency of these methods is investigated for a series of turbulent test cases over a range of Reynolds numbers. It is found for EDAC that velocity divergence scales linearly with the square root of compressibility, whereas for ACM a clear relation is not observed. EDAC is found to accurately resolve the low Reynolds number Taylor–Green vortex case; however, for the circular cylinder at Reynolds number 3900, earlier transition of the free shear-layer is observed due to an over-production of the turbulence kinetic energy. This over production of turbulent kinetic energy is attributed to the increased spatial pressure gradients of the EDAC method, and similar behaviour is observed for an aerofoil at Reynolds number 60 000 with an attached transitional boundary layer. These issues were not observed for the other ACM approaches. It is concluded that hyperbolic diffusion of ACM can be beneficial in terms of convergence but at the cost of case setup time, and EDAC can be a time efficient method for unsteady incompressible flows. However, care must be taken when reducing the stiffness of EDAC as the resulting pressure fluctuations can have a significant impact on transition.

On the onset of breathing mode in Hall thrusters and the role of electron mobility fluctuations

Breathing mode is an ionization instability which is observed ubiquitously in the operation of Hall thrusters. It is recognized as a relatively low frequency (10–30 kHz) longitudinal oscillation of the discharge current and the plasma parameters. Although breathing instability is widely studied in the literature, the conditions for its origin are not fully understood. In this work we investigate the mechanisms responsible for the origin of the breathing mode in Hall thrusters by using a numerical model, allowing us to highlight the importance of electron mobility fluctuations for the onset and self-sustenance of the instability. Our one-dimensional, fully fluid model of the thruster channel is calibrated against the measured discharge current signal for a 5 kW-class Hall thruster operating in a condition where breathing mode is fully developed. The corresponding steady, unstable configuration (base state) is numerically computed by applying the Selective Frequency Damping (SFD) method. Then, a series of numerical tests is performed to show the existence of a feedback loop involving fluctuations around the base state of the neutral density, electron mobility, and electric field. We show that oscillations of the electron mobility are mainly caused by variations of the neutral density and are in phase with them; this, in turn, induces oscillations of the electric field, which are in phase opposition. The electric field acts simultaneously on the electron temperature and on the ion dynamics, promoting the depletion and replenishment of neutrals in the chamber.