Transfer Function In Frequency Domain Research Articles

Comparison of Unsteady Low- and Mid-Fidelity Propeller Aerodynamic Methods for Whirl Flutter Applications

Aircraft configurations with propellers have been drawing more attention in recent times, partly due to new propulsion concepts based on hydrogen fuel cells and electric motors. These configurations are prone to whirl flutter, which is an aeroelastic instability affecting airframes with elastically supported propellers. It commonly needs to be mitigated already during the design phase of such configurations, requiring, among other things, unsteady aerodynamic transfer functions for the propeller. However, no comprehensive assessment of unsteady propeller aerodynamics for aeroelastic analysis is available in the literature. This paper provides a detailed comparison of nine different low- to mid-fidelity aerodynamic methods, demonstrating their impact on linear, unsteady aerodynamics, as well as whirl flutter stability prediction. Quasi-steady and unsteady methods for blade lift with or without coupling to blade element momentum theory are evaluated and compared to mid-fidelity potential flow solvers (UPM and DUST) and classical, derivative-based methods. Time-domain identification of frequency-domain transfer functions for the unsteady propeller hub loads is used to compare the different methods. Predictions of the minimum required pylon stiffness for stability show good agreement among the mid-fidelity methods. The differences in the stability predictions for the low-fidelity methods are higher. Most methods studied yield a more unstable system than classical, derivative-based whirl flutter analysis, indicating that the use of more sophisticated aerodynamic modeling techniques might be required for accurate whirl flutter prediction.

Impact of resampling interpolation FIR filter in the practical Kramers-Kronig receiver.

The practical Kramers-Kronig (KK) receiver has been a competitive receiving technique in the data-center, medium reach, and even long-haul metropolitan networks. Nevertheless, an extra digital resampling operation is required at both ends of the KK field reconstruction algorithm due to the spectrum broadening caused by adopting the nonlinear function. Generally, the digital resampling function can be implemented by using linear interpolation (LI-ITP), the Lagrange cubic interpolation (LC-ITP), the spline cubic interpolation (SC-ITP), time-domain anti-aliasing finite impulse response (FIR) filter method (TD-FRM) scheme, and fast Fourier transform (FFT)-based scheme. However, the performance and the computational complexity analysis of different resampling interpolation schemes in the KK receiver have not been thoroughly investigated yet. Different from the interpolation schemes of conventional coherent detection, the interpolation function of the KK system is followed by the nonlinear operation, which will broaden the spectrum significantly. Due to the frequency-domain transfer function of different interpolation schemes, the broadened spectrum will have a potential spectrum aliasing, which will cause serious inter-symbol interference (ISI) and further impair the KK phase retrieval performance. We experimentally investigate the performance of different interpolation schemes under different digital up-sampling rates (i.e. the computational complexity) as well as the cut-off frequency, the tap number of the anti-aliasing filter, and the shape factor of the TD-FRM scheme in a 112-Gbit/s SSB DD 16-QAM system over 1920-km Raman amplification (RFA)-based standard single-mode fiber (SSMF). The experimental results involve that the TD-FRM scheme outperforms other interpolation schemes and the complexity is reduced by at least 49.6%. In fiber transmission results, take 20% soft decision-forward error correction (SD-FEC) of 2×10-2 as the threshold, the LI-ITP and LC-ITP schemes only reach 720-km while others can reach up to 1440-km.

Frequency domain transfer function based multimodal design method for seismic mitigation of building structures

Multiple tuned mass dampers (MTMD) are widely used to mitigate structural seismic response. With the emergence of more and more high-rise buildings, various MTMD design methods applicable to multi degree of freedom (MDOF) model have been developed. However, the existing MTMD design methods for MDOF models often involve complex optimization algorithms. In order to simplify the MTMD design while effectively reducing the seismic response of the structure, this paper proposes an explicit frequency domain transfer function, theoretically showing the mechanism of decomposing the seismic mitigation of MDOF model into simultaneous seismic mitigation of multiple modes, and developed a theoretical design method of MTMD, so that the dynamic parameters and position of each TMD can be directly obtained based on the developed explicit design formula. A benchmark model was used as an example to verify the seismic mitigation performance. It is shown that the developed multimodal control MTMD design method achieves 22.25% reduction rate of acceleration and 18.5% reduction rate of displacement with 3% mass ratio.

Bipartite consensus for networked Euler–Lagrange systems with cooperative–competitive interactions and time delays

AbstractThis paper investigates the coordinated behaviour of the multiple Euler–Lagrange systems under diverse interactions with time delays. Specially, in the case of undirected interconnection, the proportional plus damping control strategy is proposed and the sufficient conditions of bipartite consensus are derived via energy function based approach. Subsequently, a velocity‐free controller is further developed by introducing a novel second‐order auxiliary system to each agent. In the case of directed network, by fully investigating the property of the Laplacian matrix associated with the cooperative–competitive interactions, a bipartite consensus controller is devised and the input–output property analysis of the system transfer function in frequency domain is presented. Simulation results are provided to demonstrate the effectiveness of the presented algorithms.

Data Driven prediction of forced nonlinear vibrations using stabilised Autoregressive Neural Networks

AbstractIn this work, we propose a novel approach to the data‐driven prediction of vibration responses of nonlinear systems. The main idea is based on Autoregressive Neural Networks (ARNN) to model the nonlinear transfer behaviour between an external excitation and the system response. We propose an autoregressive network architecture with embedded symmetry using bias‐free tanh activation and guarantee Input‐to‐State‐Stability (ISS) by enforcing a special penalty term to the weights. The resulting training procedure is analysed for the example of a DUFFING oscillator with white noise excitation. In a BAYESian optimisation, it is found that beyond enforcing input‐to‐state‐stability, the stabilising penalty term also decreases sensitivity with respect to other training parameters compared to other classical techniques. Furthermore, we show that the stabilised ARNN is able to give excellent approximations of the nonlinear response of the DUFFING oscillator for a wide range of excitation intensities. In contrast, linear models, such as autoregressive models with exogenous input (ARX) in time domain or linear transfer functions in frequency domain, will only find some linear approximation. In particular, by construction, they will not be able to capture nonlinear effects for arbitrary amplitudes and excitation levels.

Time-domain Analytical Method for Aeroelastic Analysis of High Aspect Ratio Wing Using Unsteady Indicial Aerodynamics

This paper deals with the development of a novel time-domain analytical method to perform an aeroelastic stability analysis of a high aspect ratio wing. The aerodynamic model in this paper is built upon the frequency domain of Theodorsen aerodynamics. An inverse Fourier transform technique is applied to convert the Theodorsen frequency domain transfer function to the Wagner time-domain response function. Later, lift and moment expressions, containing aerodynamic lag states are obtained using the indicial function approach which performs the convolution of the unit step response Wagner lift function with arbitrary input and its time derivative using the principle of superposition. Additional equations containing the derivative of aerodynamic lag states are coupled with previously obtained lift and moment expressions to fully get the complete unsteady aerodynamic model in the time-domain. This time-domain unsteady aerodynamic model is then coupled with a combined bending torsion beam finite element model, using the state space approach. A complex eigenvalue analysis of this state space system is performed, using MATLAB, to determine both the static and dynamic aeroelastic stability boundary. Finally, in this paper, aeroelastic stability analysis of the high aspect ratio wing is performed using the current method and results are validated with MSC Nastran aeroelastic analysis and those available in the literature.

The reciprocal relationship between cardiac baroreceptor sensitivity and cerebral autoregulation during simulated hemorrhage in humans.

A reciprocal relationship between the baroreflex and cerebral autoregulation (CA) has been demonstrated at rest and in response to acute hypotension. We hypothesized that the reciprocal relationship between cardiac baroreflex sensitivity (BRS) and CA would be maintained during sustained central hypovolemia induced by lower body negative pressure (LBNP), and that the strength of this relationship would be greater in subjects with higher tolerance to this stress. Healthy young adults (n=51; 23F/28M) completed a LBNP protocol to presyncope. Subjects were classified as high tolerant (HT; completion of -60mmHg LBNP stage, ≥20-min) or low tolerant (LT; did not complete -60mmHg LBNP stage, <20-min). R-R intervals (RRI), systolic arterial pressure (SAP), mean arterial pressure (MAP), and middle cerebral artery velocity (MCAv) were measured continuously. Cardiac BRS was calculated in the time domain (ΔHR/ΔSAP) and frequency domain (RRI-SAP low frequency (LF) transfer function gain), and CA was calculated in the time domain (ΔMCAv/ΔMAP) and frequency domain (MAP-mean MCAv LF transfer function gain). There was a moderate relationship between cardiac BRS and CA for the group of 51 subjects in both the time (R=-0.54, P<0.0001) and frequency (R=0.61, P<0.001) domains; there was a stronger relationship in the HT group (R=0.73) compared to the LT group (R=0.31) in the frequency domain (P=0.08), but no difference between groups in the time domain (HT: R=-0.73 vs. LT: R=-0.63; P=0.27). These findings suggest that an interaction between BRS and CA may be an important compensatory mechanism that contributes to tolerance to simulated hemorrhage in young healthy adults.

Analysis and Design of Digital Injection-Locked Clock Multipliers Using Bang-Bang Phase Detectors

The analysis of injection-locked clock multipliers (ILCMs) using bang-bang phase detectors (BBPDs) is challenging due to the nonlinear BBPD and the multi-rate injected oscillator. This paper presents an explicit analysis of digital ILCMs using BBPDs and proposed an intuitive approach to optimizing parameters with given noise sources. A time-domain analysis in the single-clock domain is presented to solve the closed-form expression of jitter in the ILCM. The proposed approach exhibits good consistency with simulations, for various design parameters and noise cases. With the predicted input-referred jitter, the equivalent BBPD gain is resolved to derive the frequency-domain noise transfer functions in concise forms. To achieve the desired performance with given specifications, recommended design procedures are summarized based on the proposed analysis and verified by simulations.

6G/B5G 네트워크 통신 기반의 스마트팩토리 내 자기부상 물류이송시스템의 시간지연 제어기 설계

Recently, smart factories have been actively introduced in the manufacturing process since the 4th industrial revolution. In particular, research on a logistics transport system using a in-track type magnetic levitational conveyor system is continuing in the semiconductor and display manufacturing industries that require a high-clean environment. This in-track type magnetic levitation system has problems in measuring uncertainty and increasing cost due to the sensors installing to each track. In this paper, we consider a method of installing the sensors to the vehicle and transmitting measurement data using network communication. At this time, end-to-end time latency occurs by using the 6G/B5G communication system in the smart factory. To solve this problem, we propose a controller design method of the magnetic levitation system considering time delay. The proposed controller is designed using the loop shape method for the sensitivity transfer function in frequency domain in order to reduce input disturbance and attenuate sensor noise. The effectiveness of the proposed controller is shown by the simulation.

Determining the cause of incorrect work of bumper paint robot reducer

Industrial robots are used for high-precision tasks and in intensive production. One of the most reliable methods for monitoring robots’ work is vibrodiagnostics, which provides recommendations and maintenance procedures, and also serves as a reliable diagnostic method for determining the causes of industrial robot failures. Connection of robot and the supporting structure is very important and it affects on dynamic behavior of the robot. This paper presents the process of diagnosing dynamic condition of the structure with painting robots, after the failure of the robot motion reducer. To analyze the causes of the failure, a numerical-experimental analysis was performed, which included: static calculation, dynamic calculation, determining transfer function in frequency domain and reinforcement factors and measuring accelerations. Supporting structure has very low eigen-frequencies (3,5 to 9.5 Hz), it cannot accept inertial forces and large deformations and resonant behavior occur. Using FEM analysis is shown that the behavior of the structure is unfavorable because 20 eigen-oscillations had a frequency less than 17 Hz, and all are located in the robots’ working space. Determination of the transfer functions showed that the dynamic gain factor in all three directions of the excitation force is extremely large, while the corresponding frequencies are 5 ÷ 20 Hz. As a part of the experimental analysis, accelerations and displacements at the robots’ locations were measured. Accelerations exceed the standard acceptable limit. It was determined that the main problem was the rigidity of the supporting structure and maintenance omissions observed during the visual inspection. Only a partial and relatively quick repair was done on the structure, and it significantly decreased displacements of most critical zones (robots).

Shifting Method for Identification of TITO Systems using Decentralized Relay Feedback

In this paper, the relay shifting method is extended to identification of systems with two inputs and two outputs (TITO systems) using relay feedback experiments. By means of this approach multiple points of the Nyquist frequency response can be determined from a single experiment. Identification of more frequency points facilitates parameter estimation of more complex models. The proposed procedure is intended for the identification of TITO systems with a sufficiently strong cross-coupling between inputs and outputs. Frequency domain transfer functions of the second order with a time delay are used for modelling individual links. The proposed procedure is intended for controller autotuning and can be extended for multivariable systems.

Frequency domain analysis method of tuned liquid damper controlled multi-degree of freedoms system subject to earthquake excitation

Tuned liquid damper (TLD) is a typical passive device to control structural response under wind and earthquake excitation. At present, TLD is often used to control single-mode of structure. Hence, the design theory of TLD is often based on single-degree of freedom (SDOF) system in frequency domain, which is hard to accurately evaluate seismic performance of TLD-installed multi-degree of freedoms (MDOFs) with consideration of higher mode. In this work, a frequency domain transfer function for TLD controlled MDOFs system is established through the concept of substructure to evaluate overall seismic performance of TLD-installed MDOFs. The accuracy of the transfer function is verified by real-time hybrid testing. Using this transfer function, the effect of TLD on the seismic performance of MDOFs was discussed in frequency domain by parametric analysis. The analytical results indicated that, based on the design theory for single-mode, the TLD with large mass ratio cannot enhance the seismic performance effectively comparing with small mass ratio. In order to improve the control efficiency of relatively large mass TLD, a design method for multi-mode control is established based on the developed frequency domain transfer function. The simulation results showed that, with same TLD mass, the multi-mode method performed smaller structural acceleration response and similar displacement response relative to the single mode method.

Prediction method of Ultra-wideband electromagnetic pulse coupling in slotted cavity

With the develofpment of UWB electromagnetic pulse radiation systems, people are paying more and more attention to its serious threat to electronic equipment. The effect of UWB electromagnetic pulse has also become an important content in the field of electromagnetic compatibility. In an UWB radiation system, the distance between the device under test and the transmitting antenna is different, and the radiation field received is also different. Therefore, in actual tests, the test body is often placed at different distances from the antenna to perform multiple measurements to obtain test data as required. Based on this, this article takes the cavity as an example, and proposes a method of using the system transfer function to predict the response of the impulse field inside the cavity to simplify the test and quickly obtain the test data. Firstly, the impulse field response of a certain point with and without a cavity is measured respectively, and then the time domain response is inversely Fourier transformed to obtain the frequency domain transfer function of the test body. Finally, using the transfer function to convolute with the field to be measured, the response of the impulse field inside the cavity can be predicted under the condition of the field to be measured. It is verified by experiments that this method can better predict the response of the impulse field inside the cavity under different distance conditions, and has the characteristics of simple calculation and good prediction effect. At the same time, the transfer function obtained by this method can be used to predict the arbitrary impulse field response of the cavity in its frequency range.

Brain tissue classification from stereoelectroencephalographic recordings

BackgroundStereoelectroencephalographic (SEEG) recordings can be performed before final resective surgery in some drug-resistant patients with focal epilepsies. For good SEEG signal interpretation, it is important to correctly identify the brain tissue in which each contact is inserted. Tissue classification is usually done with the coregistration of CT scan (with implanted SEEG electrodes) with preoperative MRI. New methodBrain tissue classification is done here directly from SEEG signals obtained at rest by a linear discriminant analysis (LDA) classifier using measured SEEG signals. The classification operates on features extracted from Bode plots obtained via non-parametric frequency domain transfer functions of adjacent contacts pairs. Classification results have been compared with classification from T1 MRI following the labelling procedure described in Deman et al. (2018), together with minor corrections by visual inspection by specialists. ResultsWith the data processed from 19 epileptic patients representing 1284 contact pairs, an accuracy of 72 ± 3% was obtained for homogeneous tissue separation. To our knowledge only one previous study conducted brain tissue classification using the power spectra of SEEG signals, and the distance between contacts on a shaft. The features proposed in our article performed better with the LDA classifier. However, the Bayesian classifier proposed in Greene et al. (2020) is more robust and could be used in a future study to enhance the classification performance. Conclusions and significanceOur findings suggest that careful analysis of the transfer function between adjacent contacts measuring resting activity via frequency domain identification, could allow improved interpretation of SEEG data and or their co-registration with subject’s anatomy.

Three-dimensional transfer function of optical microscopes in reflection mode.

Three-dimensional (3D) transfer functions build the basis for a comprehensive characterization of optical imaging systems in the spatial frequency domain. Utilizing the projection-slice theorem, the 2D modulation transfer function of an incoherent imaging system can be derived from a 3D transfer function by integration with respect to the axial spatial frequency. For a diffraction limited microscope with homogeneous incoherent pupil illumination, the modulation transfer function equals the 2D autocorrelation function of a circular disc. However, until now to the best of our knowledge no 3D transfer function has been published, which exactly leads to the 2D modulation transfer function of a diffraction limited microscope in reflection mode. In this article, we derive a formula, which after integration with respect to the axial spatial frequency coordinate perfectly fits to the diffraction limited 2D modulation transfer function. The inverse three-dimensional Fourier transform of the 3D transfer function results in a complex-valued 3D point spread function, from which the depth of field, the lateral resolution and, in addition, the corresponding 3D point spread function of both, a conventional and an interference microscope, can beobtained.

Dynamic Analysis and Experiment of a Space Mirror Based on a Linear State Space Expression

Dynamic analysis of the optical–mechanical structure based on the linear state space expression is performed for a three-point flexural mount lightweight space mirror with a diameter of ϕ740 mm. Using linear structure dynamics and linear state space theories, the state space model of the mirror assembly is established based on modal information. The DC gain method is used to reduce modes and a frequency response analysis of the reduced modes is performed to obtain the frequency domain transfer function between the excitation input and response output points and determine the contribution of each mode to the total frequency response. The frequency response curve is plotted. A mechanical vibration test is performed to verify the accuracy and rationality of simulation analysis. The dynamic analysis method based on state space theory provides a new method of investigating optical and mechanical structures, which can help efficiently and accurately analyze the frequency response characteristics of complex linear systems.

FPAA Implementations of Fractional-Order Chaotic Systems

In this paper, fractional-order chaotic systems in an analog-based platform are realized using field programmable analog arrays (FPAA) hardware. With the help of this work, we aim to increase the complexity of chaotic systems. Approximated transfer functions in frequency domain are obtained by analyzing different values of fractional-order integrator with the Charef approximation method. In this study, fractional-order numerical calculation of Rssler and Sprott type-H chaotic systems is carried out. MATLAB Simulink model for chaotic systems that satisfy the conditions of chaos in the boundaries of fractional order value is schematically presented. Moreover, CAM designs and analysis that facilitate the realization of fractional-order transfer functions in FPAA platforms are introduced. The analog-based FPAA experimental and numerical outcomes for fractional order chaotic systems are demonstrated. The comparison of the results obtained in the numerical analysis and simulation study with the experimental results is given. This study confirms that the unpredictability of the chaos carrier signals realized by digital-based can be increased with analog-based FPAA hardware and fractional-order structures so as to provide safer transfer of information signals.

Direct approach to realizing quantum filters for high-precision measurements

Quantum noise sets a fundamental limit to the sensitivity of high-precision measurements. Suppressing it can be achieved by using nonclassical states and quantum filters, which modify both the noise and signal response. We find an approach to realizing quantum filters directly from their frequency-domain transfer functions, utilizing techniques developed by the quantum control community. It not only allows us to construct quantum filters that defy intuition, but also opens a path towards the systematic design of optimal quantum measurement devices. As an illustration, we show an optical realization of an active unstable filter with anomalous dispersion, proposed for improving the quantum-limited sensitivity of gravitational-wave detectors.

Multitone Multiharmonic Scattering Parameters for the Characterization of Nonlinear Networks

This work describes a generalized multitone multiharmonic scattering parameters ( $\mathbf {M^{2}S}$ -parameters) measurement approach suitable for multiport nonlinear network characterization in the wave-variable domain. Based on the incommensurate (or offset) frequency concept, the $\mathbf {M^{2}S}$ -parameters are directly measurable quantities independent of the incident wave phases and display a mild nonlinear dependence on the incident wave amplitudes. They feature a well-defined relationship with the frequency-domain nonlinear transfer functions derived from the Volterra theory, representing a generalization to the multiinput multiharmonic case of the widely used single-input single-frequency describing function approach. The proposed framework allows to capture the nonlinear steady-state behavior from a reduced set of measurements and can be effectively exploited for performance prediction in application-like scenarios. The approach is here applied to RF transistor and power amplifier load-pull measurements, as well as to the case of broadband modulation, showing that the performance assessment of the device can be obtained in a straightforward way from the $\mathbf {M^{2}S}$ -parameters description.

A frequency domain transfer function methodology for thermal characterization and design for energy flexibility of zones with radiant systems

This paper presents a frequency domain transfer function methodology for thermal characterization and design for energy flexibility of zones with hydronic radiant heating/cooling systems and significant thermal mass. The modeling methodology is validated with experiments in an environmental chamber. Using the developed frequency domain model of the zone, key transfer functions are calculated for a case study. By means of transfer functions, the effect of different levels of thermal mass on the zone thermal response and quantification of the energy flexibility in response to grid signals is studied. The model is used to evaluate different design and operation options on a relative basis to enhance energy flexibility for different scenarios. It is shown how transfer function analysis provides insight into the building thermal dynamics without the need for simulations. The transfer function that relates the radiant floor heat source at the bottom of the slab to the zone air temperature is derived and the delay between the heat input of the radiant slab and zone air temperature is calculated. Experimental measurements in an environmental chamber are used to validate the key design parameters obtained from the frequency domain transfer function regarding the operational strategies for energy flexibility of the thermal zone. Finally, it is shown how to utilize the quantified energy flexibility that is possible with the floor thermal mass through application of appropriate control strategies while maintaining satisfactory comfort conditions.