Showing papers on "Frequency response published in 2022"

Application of Generalized Frequency Response Functions and Improved Convolutional Neural Network to Fault Diagnosis of Heavy-duty Industrial Robot

Abstract: The combination of nonlinear spectrum and convolutional neural network (CNN) is efficient for fault diagnosis of nonlinear system. However, in traditional method, the nonlinear spectrum calculation was accomplished by identification algorithm outside the CNN, which reduced the diagnosis efficiency. To solve this problem, a novel CNN with the function of spectrum calculation and fault diagnosis is designed, in which the spectrum calculation network and the fault diagnosis network are connected in series. By extracting the optimized parameters of network, the nonlinear spectrum based on generalized frequency response function (GFRF) is obtained in the former network. Then, the GFRF spectrum is automatically put into the latter network for feature extraction and diagnosis. Hence, after determining the structure of the CNN, only by system input and output, the fault diagnosis can be realized, which avoids the complex process in traditional method. What's more, a new error cost function model is designed to guide the network parameters optimization in the direction of feature classification, which is conductive to improve the diagnosis accuracy. The proposed network model is applied to the heavy-duty industrial robot system, and the best performance is demonstrated by several experiments.

Experimental characteristics and coupled nonlinear forced vibrations of axially travelling hyperelastic beams

Abstract: Comprehensively investigated in this paper is the coupled nonlinear dynamics of hyperelastic beams. Experimental testing is performed to accurately model the hyperelasticity using different hyperelastic energy density models. Samples were fabricated using 3D printing technique for flexible thermoplastic polyurethane filaments following the ASTM D638 guidance and tested using a tensile testing machine. For a proper hyperelastic energy density model, coupled nonlinear equations of motion are obtained via the von Karman geometrical nonlinearity and Hamilton’s principle. Free natural vibration response of the gyroscopic system is analysed using a generalised modal decomposition method and the influence of different parameters such as the hyperelastic stiffness term and the axial velocity on the natural frequencies is investigated. Complex mode shapes are obtained and the influence of axial velocity on altering the real and imaginary parts is discussed. Furthermore, a comprehensive analysis on the coupled nonlinear dynamics of the system is presented using a combination of Galerkin’s scheme and a dynamic equilibrium technique. The frequency response to different design parameters such as axial speed, axial tension, harmonic external load, hyperelastic parameters and geometrical imperfection is discussed in detail. It is shown that the system shows a wide range of rich nonlinear dynamics including hardening depending on the characteristics of the system.

Vibration and nonlinear dynamic response of temperature-dependent FG-CNTRC laminated double curved shallow shell with positive and negative Poisson’s ratio

Abstract: This paper reports a study on natural frequency, nonlinear dynamic response and frequency amplitude relation of temperature-dependent FG-CNTRC laminated double curved shallow shell with positive and negative Poisson’s ratio. The nonlinear motion equations and the compatibility equation are retrieved from first order shear deformation theory including the effect of von Karman nonlinearity terms, elastic foundations and initial imperfection. The system of dynamic governing equations is obtained by utilizing the Airy stress function and Bubnov–Galerkin procedure. The nonlinear dynamic response is also obtained by applying the 4th-order Runge–Kutta method. The frequency–amplitude relations of the shell is determined by using the assumption of inertia caused by a rotation. Besides, the analytical method and the finite element method are proposed to calculate the vibrational frequencies. Five types of FG-CNTRC laminate shell, three types of the structures and different thermal environments with the shell’s material properties depending on the temperature are also considered in this study. The numerical results are presented, verified with available studies in the literature. Finally, the effects of elastic foundations, initial imperfection, and temperature-dependence, typing double curved shallow shell, angle of lamination against the shell x-axis on the natural frequency and nonlinear dynamic response of FG-CNTRC laminated double curved shallow shell with positive and negative Poisson’s ratio are discussed.

D-Band MUTC Photodiodes With Flat Frequency Response

Abstract: Novel back-illuminated modified uni-traveling- carrier photodiodes (MUTC-PDs) are reported to demonstrate wide bandwidth and high output power performance at D-band (110–170 GHz) regime. A comprehensive design model is employed to predict and tune the frequency response by incorporating coplanar waveguides (CPWs) with different inductive peaking effects. As a demonstration, 4.5-μm-diameter photodiodes with two types of CPWs are fabricated to exhibit different frequency response profiles. Both PDs exhibit a 3-dB bandwidth over 150 GHz and the measured frequency responses are in excellent agreement with simulations. Thanks to the proper design of the CPW electrodes, the two PDs exhibit an output power roll-off of only 4.3 dB and 4.8 dB from dc to 170 GHz, respectively, and high saturation performance is maintained over the broadband frequency range of 130–170 GHz.

Spectral Methods for Response Enhancement of Microwave Resonant Sensors in Continuous Non-Invasive Blood Glucose Monitoring

Abstract: In this paper, the performance of three recent algorithms for the frequency-response enhancement of microwave resonant sensors are compared. The first one, a single-step algorithm, is based on a couple of direct-inverse Fourier transforms, giving a densely sampled response as a result. The second algorithm exploits an iterative procedure to progressively restricts the frequency response. The final one is based on the super-resolution MUSIC algorithm. The comparison is carried out through a Monte Carlo analysis. In particular, synthetic signals are firstly exploited to mimic the frequency response of a resonant microwave sensor. Then, experimental data collected from water-glucose solutions are adopted as validation test for potential applications in noninvasive blood-glucose monitoring.

Encoding Frequency Constraints in Preventive Unit Commitment Using Deep Learning With Region-of-Interest Active Sampling

Abstract: With the increasing penetration of renewable energy, frequency response and its security are of significant concerns for reliable power system operations. Frequency-constrained unit commitment (FCUC) is proposed to address this challenge. Despite existing efforts in modeling frequency characteristics in unit commitment (UC), current strategies can only handle oversimplified low-order frequency response models and do not consider wide-range operating conditions. This paper presents a generic data-driven framework for FCUC under high renewable penetration. Deep neural networks (DNNs) are trained to predict the frequency response using real data or high-fidelity simulation data. Next, the DNN is reformulated as a set of mixed-integer linear constraints to be incorporated into the ordinary UC formulation. In the data generation phase, all possible power injections are considered, and a region-of-interest active sampling is proposed to include power injection samples with frequency nadirs closer to the UFLC threshold, which enhances the accuracy of frequency constraints in FCUC. The proposed FCUC is investigated on the IEEE 39-bus system. Then, a full-order dynamic model simulation using PSS/E verifies the effectiveness of FCUC in frequency-secure generator commitments.

A High-sensitivity FBG Accelerometer Based on a Bearing

Abstract: We present the modelling, design, and characterization of a novel fiber Bragg grating (FBG) accelerometer based on a bearing. A cantilevered mechanical structure with bearings can effectively decrease energy loss during vibration and enhance sensitivity. The principle of the accelerometer is analysed by a simplified model. The influence of the structural parameters of the proposed sensor on its sensitivity and resonance frequency is further analysed for structural optimization. Meanwhile, its dynamic behaviour and frequency response characteristics are analysed by numerical simulations. In addition, dual-FBG not only enables temperature compensation but also enhances sensitivity. Experimental results indicate that the FBG accelerometer provides a linear response over a broad frequency range from 0.5 Hz to 40 Hz, with a high sensitivity of 575.8 pm/g. This FBG accelerometer with low frequency and high sensitivity provides effective support for the design of sensors of the same type.

Real-Time Structural Health Monitoring and Damage Identification Using Frequency Response Functions along with Finite Element Model Updating Technique

Abstract: Throughout service, damage can arise in the structure of buildings; hence, their dynamic testing becomes essential to verify that such buildings possess sufficient strength to withstand disturbances, particularly in the event of an earthquake. Dynamic testing, being uneconomical, requires proof of concept; for this, a model of a structure can be dynamically tested, and the results are used to update its finite element model. This can be used for damage detection in the prototype and aids in predicting its behavior during an earthquake. In this instance, a wireless MEMS accelerometer was used, which can measure the vibration signals emanating from the building and transfer these signals to a remote workstation. The base of the structure is excited using a shaking table to induce an earthquake-like situation. Four natural frequencies have been considered and six different types of damage conditions have been identified in this work. For each damage condition, the experimental responses are measured and the finite element model is updated using the Berman and Nagy method. It is seen that the updated models can predict the dynamic responses of the building accurately. Thus, depending on these responses, the damage condition can be identified by using the updated finite element models.

D-Band MUTC Photodiodes With Flat Frequency Response

Abstract: Novel back-illuminated modified uni-traveling- carrier photodiodes (MUTC-PDs) are reported to demonstrate wide bandwidth and high output power performance at D-band (110–170 GHz) regime. A comprehensive design model is employed to predict and tune the frequency response by incorporating coplanar waveguides (CPWs) with different inductive peaking effects. As a demonstration, 4.5-μm-diameter photodiodes with two types of CPWs are fabricated to exhibit different frequency response profiles. Both PDs exhibit a 3-dB bandwidth over 150 GHz and the measured frequency responses are in excellent agreement with simulations. Thanks to the proper design of the CPW electrodes, the two PDs exhibit an output power roll-off of only 4.3 dB and 4.8 dB from dc to 170 GHz, respectively, and high saturation performance is maintained over the broadband frequency range of 130–170 GHz.