Large Parameter Variations Research Articles

BIFURCATIONS AND AMPLITUDE DEATH FROM DISTRIBUTED DELAYS IN COUPLED LANDAU STUART OSCILLATORS AND A CHAOTIC PARAMETRICALLY FORCED VAN DER POL-RAYLEIGH SYSTEM

Distributed delays modeled by 'weak generic kernels' are introduced in the well-known coupled Landau-Stuart system, as well as a chaotic van der Pol-Rayleigh system with parametric forcing. The systems are close via the 'linear chain trick'. Linear stability analysis of the systems and conditions for Hopf bifurcation which initiates oscillations are investigated, including deriving the normal form at bifurcation, and deducing the stability of the resulting limit cycle attractor. The value of the delay parameter $a=a_{Hopf}$ at Hopf bifurcation picks out the onset of Amplitude Death(AD) in all three systems, with oscillations at larger values (corresponding to weaker delay). In the Landau-Stuart system, the Hopf-generated limit cycles for $a>a_{Hopf}$ turn out to be remarkably stable under very large variations of all other system parameters beyond the Hopf bifurcation point, and do not undergo further symmetry breaking, cyclic-fold, flip, transcritical or Neimark-Sacker bifurcations. This is to be expected as the corresponding undelayed systems are robust oscillators over wide ranges of their respective parameters. Numerical simulations reveal strong distortion and rotation of the limit cycles in phase space as the parameters are pushed far into the post-Hopf regime, and reveal other features, such as how the oscillation amplitudes and time periods of the physical variables on the limit cycle attractor change as the delay and other parameters are varied. For the chaotic system, very strong delays may still lead to the cessation of oscillations and the onset of AD (even for relatively large values of the system forcing which tends to oppose this phenomenon). Varying of the other important system parameter, the parametric excitation, leads to a rich sequence of dynamical behaviors, with the bifurcations leading from one regime (or type of attractor) into the next being carefully tracked.

An infraspecific dimension of bioindication? Comparison between genotypes and ecological distribution of Potamogeton coloratus

The role of within-species genetic variability and ecotypes has been poorly documented in research on water bioindication. Some studies already show that macrophytes could present genetic lineages with different optima for specific water parameters. In the present study, we tested this assumption on Potamogeton coloratus Hornem., a macrophyte described as characteristic of oligotrophic waters and threatened by freshwater eutrophication. Species population genetics, water parameters, and macrophyte and macroinvertebrate communities were analysed in 29 sites among three eco-regions of the eastern parts of France: Rhine Plain, Rhône Valley and Provence. The observed diversity of habitats can be divided into two main categories: the lotic hydrosystems such as springs and small watercourses often fed by groundwater, and the lentic waterbodies such as shallow pools or pond sides. Sampling sites were characterised by alkaline (mean pH 7.5 ± 0.4) and cool waters (mean 15.8 ± 4.1 °C) with low N-NH4+ concentration (median value of 20 μg/L), but large variation in other parameters (e.g. nitrates, phosphates). We found two main AFLP genotypic lineages, despite a poor genetic variability mainly distributed between populations, without regional structuring nor within-population diversity. We also sequenced only two ribotypes based on the nrDNA ITS. Genotypes, ribotypes and habitat categories were not correlated, arguing that the divergence of genotypic lineages is not due to ecotypic differentiation for P. coloratus. We highlight a putative event of long-distance dispersal, which illustrates the species ability for recolonization. Finally, we provide some suggestions for its conservation facing global changes.

Distributed Delay Effects on Coupled van der Pol Oscillators, and a Chaotic van der Pol-Rayleigh System

Distributed delays modeled by `weak generic kernels' are introduced in two well-known coupled van der Pol systems, as well as a chaotic van der Pol-Rayleigh system with parametric forcing. The systems are closed via the `linear chain trick'. Linear stability analysis of the systems and conditions for Hopf bifurcation that initiates oscillations are investigated, including deriving the normal form at bifurcation, and deducing the stability of the resulting limit cycle attractor. The value of the delay parameter $a = a_{Hopf}$ at Hopf bifurcation picks out the onset of Amplitude Death(AD) in all three systems, with oscillations at larger values (corresponding to weaker delay). In both van der Pol systems, the Hopf-generated limit cycles for $a > a_{Hopf}$ turn out to be remarkably stable under very large variations of all other system parameters beyond the Hopf bifurcation point, and do not undergo further symmetry breaking, cyclic-fold, flip, transcritical or Neimark-Sacker bifurcations. Numerical simulations reveal strong distortion and rotation of the limit cycles in phase space as the parameters are pushed far into the post-Hopf regime, and also reveal other features, such as how the oscillation amplitudes and time periods of the physical variables on the limit cycle attractor change as the delay and other parameters are varied. For the chaotic system, very strong delays may still lead to the cessation of oscillations and the onset of AD. Varying of the other important system parameter, the parametric excitation, leads to a rich sequence of dynamical behaviors, with the bifurcations leading from one regime (or type of attractor) into the next being carefully tracked.

Near-surface full-waveform inversion in a transmission surface-consistent scheme

Land seismic velocity modeling is a difficult task largely related to the description of the near-surface complexities. Full-waveform inversion (FWI) is the method of choice for achieving high-resolution velocity mapping, but its application to land seismic data faces difficulties related to the complex physics, unknown and spatially varying source signatures, and low signal-to-noise ratio (S/N) in the data. Large parameter variations occur in the near surface at various scales causing severe kinematic and dynamic distortions of the recorded wavefield. Some of the parameters can be incorporated in the inversion model, whereas others, due to subresolution dimensions or unmodeled physics, need to be corrected through data preconditioning; a topic not well described for land data FWI applications. We have developed novel algorithms and workflows for surface-consistent data preconditioning using the transmitted portion of the wavefield, S/N enhancement by generation of common midpoint (CMP)-based virtual supershot gathers (VSGs), and robust 1.5D Laplace-Fourier full-waveform inversion (LF-FWI). Our surface-consistent scheme solves residual kinematic corrections and amplitude anomalies via scalar compensation or deconvolution of the near-surface response. S/N enhancement is obtained through the statistical evaluation of volumetric prestack responses at the CMP position, or VSGs. These are inverted via a novel 1.5D acoustic LF-FWI scheme using the Helmholtz wave equation and Hankel domain forward modeling. Inversion is performed with nonlinear conjugate gradients. The method is applied to a complex structure-controlled wadi area exhibiting faults, dissolution, collapse, and subsidence in which the high-resolution FWI velocity modeling helps clarify the geologic interpretation. The developed algorithms and automated workflows provide an effective solution for massive FWI of land seismic data that can be embedded in typical near-surface velocity analysis procedures.

Design of a model reference adaptive PID control algorithm for a tank system

This paper describes the design of an adaptive controller based on model reference adaptive PID control (MRAPIDC) to stabilize a two-tank process when large variations of parameters and external disturbances affect the closed-loop system. To achieve that, an innovative structure of the adaptive PID controller is defined, an additional PI is designed to make sure that the reference model produces stable output signals and three adaptive gains are included to guarantee stability and robustness of the closed-loop system. Then, the performance of the model reference adaptive PID controller on the behaviour of the closed-loop system is compared to a PI controller designed on MATLAB when both closed-loop systems are under various conditions. The results demonstrate that the MRAPIDC performs significantly better than the conventional PI controller.

Transitions Between Austenite and Martensite Structures in Ni <sub>50</sub>Mn <sub>25</sub>Ga <sub>20</sub>Fe <sub>5</sub> Thin Foil

Using common and high resolution transmission electron microscopy, we study the evolution of crystal structure with increasing thickness in a thin Ni50Mn25Ga20Fe5 foil. Iron alloying enables to observe the complete spectrum of known martensitic phases and respective transitions simultaneously. Starting from cubic austenite at about 30 nm foil thickness, the structure evolves via interleaved stripes of austenite and five-layered modulated 10M martensite to pure 10M phase with low density of stacking faults. With increasing thickness the 10M phase transforms gradually to seven-layered modulated 14M by increasing density of stacking faults. Finally the non-modulated tetragonal NM phase appears within the 14M phase by detwinning of nanotwins. We found large local variation of lattice parameters, which is ascribed to elastically very soft austenite and 10M phase and faulty 14M lattice. Our experiments show clearly that nanotwinning and stacking faults are inherent structure features tightly connected with lattice modulation and intermartensite transformations. This is important finding in broader attempt to bridge the gap between the nanotwinning and modulation period development with temperature and composition. From the application point of view, the observed instability of modulation or of particular phases in thin films imposes certain limits on the use of material on microscale.

Quantifying the Environmental Design Trades for a State-of-the-Art Turbofan Engine

Aircraft and engine technology have continuously evolved since their introduction and significant improvement has been made in fuel efficiency, emissions, and noise reduction. One of the major issues that the aviation industry is facing today is pollution around the airports, which has an effect both on human health and on the climate. Although noise emissions do not have a direct impact on climate, variations in departure and arrival procedures influence both CO2 and non-CO2 emissions. In addition, design choices made to curb noise might increase CO2 and vice versa. Thus, multidisciplinary modeling is required for the assessment of these interdependencies for new aircraft and flight procedures. A particular aspect that has received little attention is the quantification of the extent to which early design choices influence the trades of CO2, NOx, and noise. In this study, a single aisle thrust class turbofan engine is optimized for minimum installed SFC (Specific Fuel Consumption). The installed SFC metric includes the effect of engine nacelle drag and engine weight. Close to optimal cycles are then studied to establish how variation in engine cycle parameters trade with noise certification and LTO (Landing and Take-Off) emissions. It is demonstrated that around the optimum a relatively large variation in cycle parameters is allowed with only a modest effect on the installed SFC metric. This freedom in choosing cycle parameters allows the designer to trade noise and emissions. Around the optimal point of a state-of-the-art single aisle thrust class propulsion system, a 1.7 dB reduction in cumulative noise and a 12% reduction in EINOx could be accomplished with a 0.5% penalty in installed SFC.

A Generalized Interpretation of Three Types of Disturbance-Based Controllers for Perturbed Integral Systems in Frequency Domain

It is well recognized that two-degree-of-freedom controllers are more proficient than one-degree-of-freedom controllers in overcoming uncertainty and large parameter variation. Establishing the equivalence analysis criterion among different classes of two-degree-of-freedom controllers to evaluate or compare the performance of controllers can stimulate more advanced two-degree-of-freedom controllers. We establish the equivalence analysis criterion by exploring the equivalence among proportional (P) with full-order extended state observer (FESO), P with reduced-order extended state observer (RESO) and proportional-integral (PI) with reduced-order proportional-integral observer (RPIO) in the context of a class of second-order, cascade integral systems. The equivalence analysis results are also suitable for high-order cascade integral systems. Moreover, P with FESO, P with RESO and PI with RPIO can be interpreted as a class of the generalized PI controllers, which can provide parameter tuning guidelines for the traditional PI controllers. Furthermore, the parameters of PI with RPIO cascade control can be entirely applied to tune the parameters of P with FESO cascade control and P with RESO cascade control and vice versa. Lastly, simulations in high speed permanent magnetic synchronous machine starter are provided to illustrate the theoretical results in this brief.

Pressure fluctuation characteristics of a model pump-turbine during runaway transient

The runaway transient of pump-turbine usually goes in an oscillating mode with large variations of flow parameters. In this work, dynamic flow characteristics during the runaway are numerically investigated, focusing on the variations of rotation speed, flow rate, torque, and the corresponding pressure fluctuations. The time-frequency relationship of pressure pulsations in major flow passage components is analyzed using fast Fourier transform (FFT) and short-time Fourier transform (STFT), where a few special frequency bands related to rotational frequency are presented. Low-frequency components of pressure oscillations are universal in the flow passage, and mainly due to the temporal changing of flow rate. Runner-stator interaction induced frequency bands show highest magnitude in the runner, accompanying with reversed flow.

Effect of process parameters on the phase transformation behavior and tensile properties of NiTi shape memory alloys fabricated by selective laser melting

Abstract In this work, we show that selective laser melting (SLM), apart from producing complex structures, can also act as a metallurgical method to modify the Ni/Ti ratio of NiTi shape memory alloys, and thus providing a feasible approach to tailor the transformation temperatures and to modify the mechanical performance of NiTi alloys. NiTi samples were fabricated by SLM with a large variation of process parameters, e.g. scanning speed (v) from 400 to 1200 mm s−1, hatch spacing (h) from 40 to 110 μm, and laser power (P) from 60 to 200 W. It is found that the martensite transformation temperature changes monotonously with the respective change of v, h or P. The composition analysis suggests that the different amount of Ni-loss under various SLM process conditions is the main reason for the evolution of transformation temperatures. Most importantly, good mechanical (total elongation >10 %) and functional properties under tensile mode have been obtained despite of the large variation of SLM process parameters and the presence of extensive defects. The good tensile properties and tailorable phase transformation temperatures will provide great potential to make novel NiTi smart structures.

Enhancing load frequency control of multi-area multi-sources power system including conventional and renewable energy units with nonlinearities

The foremost aims the Load Frequency Control (LFC) is to maintain the frequency at nominal value and minimize the unscheduled tie line power flow between different control areas. The penetration of renewable energy sources into the grid is a recent challenge to the power system operators due to their different modelling rather than conventional units. In this paper, enhancing load frequency control of multi-area multi-sources power system including renewable units system with nonlinearities is proposed using a new application of proportional–integral–derivative controller with proportional controller in the inner feedback loop, which is called as PID-P controller. To investigate the performance of the proposed controller, a thermal with reheater, hydro, wind and diesel power generation units with physical constraints such as governor dead band, generation rate constraint, time delay and boiler dynamics are considered. The proposed controller parameters are optimized using different heuristic optimization techniques such: Linearized Biogeography-Based Optimization technique, Biogeography-Based Optimization technique and Genetic Algorithm. The ability of the system to handle the large variation in load conditions, time delay, participation factors, and system parameters has been verified comprehensively.

Bayesian inference of particle source and sink in a closed-divertor using Balmer line spectroscopy

A new analysis technique for Balmer line spectroscopy that enables recombination rate (particle sink) and ionization rate (particle source) inference in a closed divertor configuration is reported. Bayesian inference is employed to systematically utilize all available information from multiple Balmer lines and constrain parameter ranges by using prior knowledge about plasmas. While a closed-divertor facilitates detachment, neutral plugging typically leads to large spatial variations in plasma parameters. A forward model is developed to take into account non-uniformity in the plasma parameters and applied to test data generated by divertor plasma simulations. It is shown that the forward model robustly provides particle source and sink inference over a wide parameter range. In addition, the precision improves as more Balmer lines are resolved simultaneously. The new analysis technique is also applied to an L-mode ASDEX Upgrade plasma in the high-recycling regime. The inferred quantities and their profiles are consistent with the expectations of a high-recycling divertor plasma. The further insight into the detachment physics will be provided by using this new analysis technique.

A systematic review on diagnostic test accuracy of magnetic resonance neurography versus clinical neurosensory assessment for post-traumatic trigeminal neuropathy in patients reporting neurosensory disturbance.

Objectives:To perform a systematic review of published studies on diagnostic accuracy of magnetic resonance neurography (MRN) vs clinical neurosensory testing (NST) for post-traumatic trigeminal neuropathy (PTTN) in patients reporting neurosensory disturbances (NSD).Methods:Human studies except case reports, reviews, systematic reviews and meta-analyses were included. PubMed, Embase, Web of Science and Cochrane Library were consulted. Risk of bias assessment was conducted using the Quality Assessment of Diagnostic Accuracy Studies 2 tool. Predetermined data extraction parameters were noted and summarized.Results:8 studies met eligibility criteria of which 7 were retrospective, representing 444 subjects. Most studies were at high risk of bias with low applicability concerns. Populations and objectives were divergent with a large variation in timing (3 days–17 years post injury) and parameters (multiple coil designs, fat suppression techniques, additional contrast agent) of MRI acquisition. T2 weighted 3 T imaging with short echo times (2.2–100 ms) and fat suppression was applied in seven studies, techniques varied. Determination of sensitivity and specificity could not be performed due to the methodological variation between studies and lacking comparative data between index and reference tests. Based on limited data, PTTN correlated reasonably well between clinical assessment, intraoperative findings and MRN abnormalities (k = 0.57). Increased signal intensity correlated with persistency of neurosensory disturbances in one study. Intra- (ICC 0.914–0.927) and interobserver (k = 0.70–0.891) MRN variability was considered good to excellent. One retrospective study showed substantial impact of MRN on clinical decision making in one-third of patients.Conclusion:Currently, there is insufficient scientific knowledge to support or refute the use of MRN. Based on limited data, MRN seems promising and reliable in detection and grading of PTTN. Methodological issues underline the importance for prospective blinded studies with standardization of signal intensity calculation and rigorous reporting of MRI acquisition parameters.

Fractional-Order Sliding Mode Control of Overhead Cranes

We constitute a control system for overhead crane with simultaneous motion of trolley and payload hoist to destinations and suppression of payload swing. Controller core made by sliding mode control (SMC) assures the robustness. This control structure is inflexible since using fixed gains. For overcoming this weakness, we integrate variable fractional-order derivative into SMC that leads to an adaptive system with adjustable parameters. We use Mittag–Leffler stability, an enhanced version of Lyapunov theory, to analyze the convergence of closed-loop system. Applying the controller to a practical crane shows the efficiency of proposed control approach. The controller works well and keeps the output responses consistent despite the large variation of crane parameters.

A Globally Optimal Robust Design Method for Complex Systems

The uncertainty of the engineering system increases with the growing complexity of the engineering system; therefore, the tolerance to the uncertainty is essential. In the design phase, the output performance should reach the design criterion, even under large variations of design parameters. The tolerance to design parameter variations may be measured by the size of a solution space in which the output performance is guaranteed to deliver the required performance. In order to decouple dimensions, a maximum solution hyperbox, expressed by intervals with respect to each design parameter, is sought. The proposed approach combines the metaheuristic algorithm with the DIRECT algorithm where the former is used to seek the maximum size of hyperbox, and the latter is used as a checking technique that guarantees the obtained hyperbox is indeed a solution hyperbox. There are three advantages of the proposed approach. First, it is a global search and has a considerable high possibility to produce the globally maximum solution hyperbox. Second, it can be used for both analytically known and black-box performance functions. Third, it guarantees that any point selected within the obtained hyperbox satisfies the performance criterion as long as the performance function is continuous. Furthermore, the proposed approach is illustrated by numerical examples and real examples of complex systems. Results show that the proposed approach outperforms the GHZ and CES-IA methods in the literature.

Bayesian Elastic Full‐Waveform Inversion Using Hamiltonian Monte Carlo

AbstractWe present a proof of concept for Bayesian elastic full‐waveform inversion in 2‐D. This is based on (1) Hamiltonian Monte Carlo sampling of the posterior distribution, (2) the computation of misfit derivatives using adjoint techniques, and (3) a mass matrix tuning of the Hamiltonian Monte Carlo algorithm that accounts for the different sensitivities of seismic velocities and density. We apply our method to two synthetic end‐member scenarios with different dimension that are particularly relevant in the context of full‐waveform inversion: low‐dimensional models ( ) with potentially large variations in material parameters and high‐dimensional models ( > 30,000) describing smaller‐scale variations of lower amplitude relative to some background. For both end members, the Hamiltonian Monte Carlo sampling reliably recovers important aspects of the posterior, including means, covariances, skewness, and 1‐D and 2‐D marginals. Depending on the strength of material variations, the posterior can be significantly non‐Gaussian. This suggests to replace local methods for uncertainty quantification based on Gaussian assumptions by proper sampling of the posterior. In addition to P wave and S wave velocity, the sampling provides constraints on density structure that are free from subjective regularization artifacts.

Robust Control Facing a Large Scale Parameter Variation in a Sensorless Vector Controlled Induction Motor Drive

In vector control systems using the slip frequency control method, the rotor resistance of induction motors is used to calculate a slip frequency. Thus the change in temperature and saturation levels cause the variation of rotor resistance value and hence the deterioration of the whole torque control characteristic. This paper presents a simulation of induction motor behavior facing a sudden parameter variation in very low speed basing on fuzzy logic perturbation rejection controllers, the rotor flux and speed are observed by an adaptive Luenberger observer based fuzzy adaptation mechanism. Simulation results show that the proposed control with the proposed fuzzy regulation provide good performance dynamic characteristics for a large scale parameter variation. All simulations have been realized in MatLab/Simulink.

Optimal endoatmospheric ascent phase guidance with load constraint

Closed loop guidance issues generates commands during flight to meet mission specifications and constraints. During atmospheric ascent phase, guidance has to honour constraints on structural loads due to aerodynamic forces and winds. During the flight regimes where the structural loads are not dominant, vehicle has to be steered optimally to meet desired final states, maximizing the payload. An algorithm to guide the launch vehicle optimally, meeting the desired end states and satisfying the structural load constraint is presented. A novel approach which guides the vehicle along the constraint boundary is developed. The effect of winds is incorpoarated in load computations assuming angle of attack measurements are available. The guidance algorithm is validated with wind profiles of different seasons. Dispersions in propulsion parameters are also considered. It is observed that the guidance algorithm meets the targets and the structural load constraint even under large parameter variations.

THE 1991 SEISMIC CRISIS IN THE WEST OF ROMANIA AND ITS IMPACT ON SEISMIC RISK AND HAZARD ASSESSMENT

The paper represents a multidisciplinary investigation of the relation between seismicity, active stress field and geological structure for the West of Romania. The study is based on revised and updated catalogues of earthquakes (3572 events) and focal mechanisms (89 solutions). The large spatio-temporal variations of the stress tensor parameters, b-value (b=0.74-0.81) and fractal dimensions of seismicity (D=1.05-2.34) highlight both clustering patterns along active fault systems and scattered epicentres within planes or volumes. A tectonic model with at least three blocks bordered by active faults is proposed controlling SHmax trend: it rotates clockwise in time and 3D space by up to 900 along with the changes of the stress regime from the compressional to extensional and activity migration between two major and complex fault systems. Low b-values characterize the regardless of the size of data source, but the smaller source/dataset, with or without aftershocks included, ensures a more realistic estimation of seismic hazard that is confirmed by seismic history (Tr_Mw5.5 = 76 years).

Stability of spin XOR gate operation in silicon based lateral spin device with large variations in spin transport parameters

We investigate stability of the spin exclusive or (XOR) gate operation in silicon(Si) -based lateral spin devices whose spin transport properties have large variations. The optimum charge current, I0, for the spin XOR gate operation is calculated by using the one dimensional spin-drift-diffusion model with variable spin polarization, interface resistance of the ferromagnetic contact, channel length and channel conductivity. I0 is strongly modulated by changing the spin transport parameters particularly under the condition with small spin polarization and short channel length. In contrast, I0 shows constant value irrespective of the interface resistance of one ferromagnetic contact under spin extraction condition. Our results provide a device design guideline for the robust spin XOR gate operation.