Time Domain Analysis Research Articles

Analysis of unsteady internal flow characteristics in axial pump with varying number of blades using computational modelling and vibration techniques

Axial pumps were extensively applied in many varying applications because of their large flow and low head. In this research investigation, the comparative analysis of the findings unveiled that the predominant source of hydraulic-induced vibration in the pump stemmed from pressure pulsations at the impeller inlet. Notably, similar patterns in amplitude were observed as flow rates increased. Furthermore, time-domain analysis confirmed that pressure pulsations and vibrations are highly correlated under high flow rates. Pressure pulsation's Frequency-domain analysis also revealed that it was a multiple of shaft frequency and changed from one multiple to three multiples of vibration. While analyzing the flow rate characteristics pertaining to pressure pulsation and vibration, it was determined that pressure pulsations at the impeller inlet had the potential to generate frequency components across a broad spectrum, encompassing both low and high flow rates, as well as their respective multiples. This phenomenon was particularly pronounced in regions characterized by unstable and high flow rates. Vibration ingredients likely influenced by pressure pulsation at the impeller inlet could be as low as design flow rates and as high as high flow rates. A vibration frequency with a multiple did not seem to be influenced by pulsating pressure at the impeller entrance. The present study focuses on investigation of flow behaviors in an axial pump with varying numbers of blades. It is an important geometric parameter that significantly affects the pump's performance. Therefore, the dynamic flow patterns in a pump, considering changed flow and impeller blade configurations, are investigated by employing the sliding mesh technique in combination with SST (k-ω) turbulence model. The numerical results exhibit a commendable alignment with the existing experimental data, enhancing the predictive accuracy of pump performance. Qualitative analyses encompass static pressure, shear stress, and various velocity components. Concurrently, quantitative investigations delve into pressure fluctuations and average pressure across a spectrum of operating conditions and impeller blade configurations. These comprehensive findings underscore the substantial influence of the impeller blade on pressure, velocity magnitudes radial, axial, tangential shear stress, average pressure within the system.

Association between obstructive sleep apnea and arrhythmia and heart rate variability among hypertensive patients

BackgroundThe relationship between obstructive sleep apnea (OSA) and the occurrence of arrhythmias and heart rate variability (HRV) in hypertensive patients is not elucidated. Our study investigates the association between OSA, arrhythmias, and HRV in hypertensive patients.MethodsWe conducted a cross-sectional analysis involving hypertensive patients divided based on their apnea-hypopnea index (AHI) into two groups: the AHI ≤ 15 and the AHI > 15. All participants underwent polysomnography (PSG), 24-hour dynamic electrocardiography (DCG), cardiac Doppler ultrasound, and other relevant evaluations.ResultsThe AHI > 15 group showed a significantly higher prevalence of frequent atrial premature beats and atrial tachycardia (P = 0.030 and P = 0.035, respectively) than the AHI ≤ 15 group. Time-domain analysis indicated that the standard deviation of normal-to-normal R-R intervals (SDNN) and the standard deviation of every 5-minute normal-to-normal R-R intervals (SDANN) were significantly higher in the AHI > 15 group (P = 0.020 and P = 0.033, respectively). Frequency domain analysis revealed that the low-frequency (LF), high-frequency (HF) components, and the LF/HF ratio were also significantly elevated in the AHI > 15 group (P < 0.001, P = 0.031, and P = 0.028, respectively). Furthermore, left atrial diameter (LAD) was significantly larger in the AHI > 15 group (P < 0.001). Both univariate and multivariable linear regression analyses confirmed a significant association between PSG-derived independent variables and the dependent HRV parameters SDNN, LF, and LF/HF ratio (F = 8.929, P < 0.001; F = 14.832, P < 0.001; F = 5.917, P = 0.016, respectively).ConclusionsHypertensive patients with AHI > 15 are at an increased risk for atrial arrhythmias and left atrial dilation, with HRV significantly correlating with OSA severity.

Research on the characteristics of electro-hydraulic position servo system of RBF neural network under fuzzy rules

A radial basis function neural network PID controller under fuzzy rules (FUZZY-RBF-PID) was designed for the electro-hydraulic position servo system under the influence of uncertain factors such as load mutation, and load stiffness change. Firstly, the mathematical model of the system is established, and the frequency domain and time domain analysis of the system are carried out. Secondly, based on the analysis results, a radial basis function (RBF) neural network PID controller is designed, and fuzzy rules are innovatively used to adjust the learning rate of PID parameters in the RBF neural network learning algorithm in real time. Thirdly, the simulation results show that under the action of the FUZZY-RBF-PID controller, the unit step response of the system has high steady-state accuracy, fast response speed, and under the condition of large load stiffness, the system can recover to the steady-state value faster after being disturbed. At the same time, when the input signal is the sinusoidal signal of 10 HZ, the system under the action of the FUZZY-RBF-PID controller has no obvious phase lag phenomenon, and the tracking error is minimal. The proposed method can effectively improve the comprehensive performance of the electro-hydraulic position servo system under the influence of uncertain factors.

Brillouin expanded time-domain analysis based on dual optical frequency combs

Brillouin Optical Time-Domain Analysis (BOTDA) is a widely-used distributed optical fiber sensing technology employing pulse-modulated pump waves for local information retrieval of the Brillouin gain or loss spectra. The spatial resolution of BOTDA systems is intrinsically linked to pulse duration, so high-resolution measurements demand high electronic bandwidths inversely proportional to the resolution. This paper introduces Brillouin Expanded Time-Domain Analysis (BETDA) as a modified BOTDA system, simultaneously achieving high spatial resolution and low detection bandwidth. Utilizing two optical frequency combs (OFCs) with different frequency intervals as pump and probe, local Brillouin gain spectra are recorded by their spectral beating traces in an expanded time domain. A 2-cm-long hotspot located in a 230 m single-mode fiber is successfully measured in the time domain with a detection bandwidth of less than 100 kHz using dual OFCs with tailored spectral phase, line spacing, and bandwidth.

Utilization and performance comparison of several HESSs with cascade optimal-FOD controller for multi-area multi-source power system under deregulated environment

Electric power system network is evolving rapidly towards a more flexible, robust and secured interconnected network which can provide better power quality within a competitive environment commonly known as deregulated power system (DPS). For safeguarding DPS, energy storage systems (ESSs) and an efficient control method are required to maintain equilibrium between load demand and generated power known as automatic generation control (AGC). This study highlights an attempt of performance comparison of several hybrid ESSs (HESSs) for AGC of multi-area multi-source power system under deregulated scenario. The considered system comprises of thermal, hydro and gas (THG) generating units in each area of a two-area DPS. A cascade optimal controller-fractional order derivative (COC-FOD) is suggested for AGC performance advancement and its performance is compared with optimal controller (OC). A nature inspired salp swarm algorithm (SSA) is utilized to optimise secondary FOD controller gains while primary OC is designed via full state feedback control approach. The time domain analysis and bode plot reveal the eminence of COC-FOD over OC by returning 66 % lower value of cost function, 24 % lower undershoot, 98 % lower overshoot, at least 24 % lesser rise time for area frequency deviation, and 30 % greater stability margins with comparable settling time and lesser number of oscillations. The performances of various HESSs like ultra-capacitor (UC) + redox flow battery (RFB), superconducting magnetic energy storage (SMES) + RFB and flywheel energy storage (FES) + RFB in the attendance of OC and COC-FOD controller are compared and performance of COC-FOD in the presence of SMES+RFB is found superior to other HESS combinations by giving 75 % lesser value of cost function and at least 43 % lesser undershoot for area frequency deviation compared to the scenario where COC-FOD is simulated without ESSs. To present a more realistic scenario, system nonlinearities are considered. Finally, COC-FOD controller proved its resilience and efficacy by providing satisfactory stabilized performance under wide variations in the system parameters.

Chatter and Surface Waviness Analysis in Oerlikon Face Hobbing of Spiral Bevel Gears

A vectorized analytical model for the cutting dynamics in the spiral bevel gear face hobbing process has been developed, which is based on machine tool kinematics and vibration vectorization. The structural modal parameters of the cutter head spindle system are obtained through experimental modal analysis with hammer impact testing. The analytical model is utilized to simulate the generation of simulated vibration acceleration signals during spiral bevel gear hobbing. A wavelet threshold denoising method is applied to process the simulated vibration signals of the spiral bevel gear face hobbing with added white noise. Signal processing methods, including short-time Fourier transform are employed for time-domain analysis, frequency-domain analysis, and time–frequency-domain analysis of measured signals and simulated signals, thereby extracting the corresponding statistical features. In addition to the results of the experimental modal analysis, the causes of chatter in spiral bevel gear hobbing are discussed in detail, revealing that the main factor is cutter head vibration in the Y direction of the Hunan ZDCY CNC EQUIPMENT YKA2260 machine tool used in this research. The error in the time-domain characteristic parameters between simulated signals and measured vibration acceleration signals is within 15%, with a difference of 3.5% in spectral peak values. The predicted tooth surface morphology from simulation matches the actual morphology on the workpiece, comprehensively validating the reliability of the cutting dynamics model for the spiral bevel gear face hobbing process. Another conclusion drawn from numerical simulation experiments is that the amount of tooth surface waviness of the spiral bevel gears is the ratio of tool chatter frequency to cutting fundamental frequency.

A Wear Debris Signal Processing Method Based on Inductive Monitoring for Aero-Engine

In view of the high false alarm rate in the oil debris monitoring results of the triple-coil inductive sensor in the transmission lubrication system of the aero-engine, a new debris signal processing method based on inductive monitoring is proposed. A time domain analysis is carried out first, and the signal energy is the most effective index to distinguish the debris signature from the noise signature. On this basis, signal energy values within a fixed-length sliding window is processed through the histogram. Finally, a threshold is set for the detection of the debris signature, which is based on the distribution of data within the histogram. This method is applied to the experimental data from a test run of an aero-engine, and the results show that all the debris is detected even if part of it appears during a change in the working condition of the aero-engine. Therefore, this method shows satisfactory results in debris detection accuracy and especially the inhibition of false alarms. It is also applicable for real-time monitoring due to the similarity between the movement of the sliding window and real-time data acquisition. In addition, it is applicable for various sensing principles, including but not limited to the inductive sensor signal, since the detection performance is only related to the signal itself.

A hexagonal shape fractal flexible UWB antenna based on jeans material for healthcare applications

This work aims to provide a compact, flexible, lightweight ultra-wideband antenna design with enhanced bandwidth for medical applications. The proposed antenna features fractal geometry and is made by iterating a hexagonal slot within a circular copper construction. The basic radiator’s partial ground plane is defective with a slit at the centre and a down ramp on both sides of the plane. A stub in the feed line improves impedance matching and provides enhanced −10dB bandwidth of 10.6 GHz (1.9 GHz to 12.5 GHz). The antenna is built on a black jeans textile substrate of dielectric constant 1.7 and size of 48 mm × 36 mm × 1.7 mm . The maximum gain of 6.75 dB at the frequency of 2.3 GHz is reported. In the operational band, the developed antenna provides steady radiation properties. Furthermore, the antenna has been verified for use in practical applications by setting up the proposed antenna as a receiver with an NRF24L01 wireless transceiver module and given coverage up to 50 feet in an open environment. The designed prototype is analysed for flexibility with different bending radii. A SAR analysis is also carried out for 1 gram and 10-gram of tissue along with the extensive time domain analysis for wearable UWB applications.

Radial artery pulse wave age-related assessment for diabetic patients based on multiple linear regression time domain analysis method

The global incidence of diabetes increases yearly. About 10 % of adults are affected. This study established a multiple linear regression (MLR) time domain analysis model of radial artery pulse wave characteristic parameters in CUN, GUAN and CHI based on traditional Chinese medicine (TCM) to assess diabetes. Pulse signals of diabetic subjects were collected by a pulse instrument. The locations of CUN, GUAN and CHI were determined by a TCM practitioner, and all pulse signals were normalized. Measurement data from 100 male and 100 female patients were used to establish a new time domain analysis method for extracting pulse wave characteristic parameters called equal pressure pulse transit time (EP-PTT). For these mentioned samples, the EP-PTT is different for male and female diabetic subjects, it was smaller for male diabetic subjects than those of female diabetic subjects. EP-PTT1 and EP-PTT6 are relevant to predicting age based on CUN, GUAN and CHI signals, which showed a linear negative correlation (P < 0.05). The EP-PTTi (i = 2, 3, 4) of female diabetic subjects are linearly correlated with age, and all of these are positively correlated (P < 0.05). These observations were clearly different from observations in healthy controls. The pulse waveform of CUN, GUAN and CHI of diabetic subjects can explore the relationship between the age of diabetic subjects and EP-PTT. The preliminary findings will provide foundational data for type 2 diabetes assessment based on CUN, GUAN and CHI pulse signals of radial artery, and the proposed new analysis method can be used for assessing type 2 diabetes.

Broadband non-reciprocal wave suppression and frequency conversion by active metabeams

Non-reciprocal wave propagation has recently attracted considerable attention as it is potentially beneficial to many applications, ranging from waveguiding, sensing, and communication to vibration control. Here, we propose the design of an active metabeam for broadband non-reciprocal wave suppression, that can strongly suppress the transmitted wave for forward incidence and amplify the transmitted wave for backward incidence. The metabeam consists of piezoelectric sensors and actuators connected by a feedforward control loop. We find that the broadband non-reciprocal wave suppression can be realized by making the second forward transmission dip close to the first one, which can be controlled by the distance between the piezoelectric actuators. The broadband non-reciprocal wave suppression of the metabeam is demonstrated via a set of time domain analyses. We further study the frequency conversion effects of the metabeam based on a time-varying transfer function. In particular, we show that among the frequency converted harmonics, those at high frequencies can be eliminated by destructive interference, resulting in an approximate single-frequency conversion in the transmitted wave. Our study advances the field of non-reciprocal mechanics and offers a reliable platform for designing active broadband elastic wave devices, providing a feasible way for asymmetrical energy control, broadband vibration attenuation, and signal processing.

Understanding stiffness degradation of composite helical springs with multi-braided layers under impact

Understanding stiffness degradation and developing suitable damage detection method for composite helical springs (CHSs) are important for their application and further development. In this study, a coupled plasticity-damage model for capturing stiffness degradation of CHSs with multi-braided layers (MBLs-CHS) is developed. Experimental results show that there is minor damage that only happens in the resin component of MBLs-CHS during impact. The element removal fraction in the simulation result is used to evaluate the damage severity, which is suggested to increase with impact energy (Ei) and decrease sequentially for CHSs with single, double, and triple braided layers (i.e., SCHS, DCHS, and TCHS). Specifically, damage severity of TCHS decreases by 51.3 % under 60 J impaction compared to that of SCHS. Finally, the time domain analysis method is introduced to monitor damage in real time. The amplitude intensity profiles under various Ei of CHSs have been fitted to predict the global stiffness degradation of CHSs in real time.

Design and analysis of grid mooring system for gravity net cage with a comprehensive optimization method

The design of gravity net cage mooring systems is a complex endeavor, which is critical for preventing major accidents caused by mooring system failures. A comprehensive optimization method is proposed to enhance the reliability and performance of the net cage mooring system by integrating static and dynamic phases. The proposed method initiates static simulations based on the catenary theory to refine the initial range of parameters. This preparatory step ensures the subsequent dynamic analysis is carried out based on feasible initial conditions with the lumped mass method. The dynamic simulation captures the complex interactions and behavior of the mooring systems under various environmental conditions. The multi-objective optimization provides feasible solutions with simultaneous consideration of both processes. Three different scenarios are optimized with the forces and motions compared after the time domain analysis, resulting in a satisfactory set of solutions. The results show that variations in the angle of the mooring line of the net cage primarily impact the net cage's movement and volume in different environments.

Probabilistic method for risk analysis of unintentional islanding of distributed generators

Unintentional islanding can be a harmful event, requiring the fast actuation of the anti-islanding protection to disconnect the distributed generators. Although passive techniques are mostly used, they have non-detection zones and fail to detect islanding under specific conditions. Therefore, knowing in advance such operative conditions and the risks associated with the islanding occurrence can be a strategic information to support grid operators in the decision-making process regarding the effectiveness of distributed generators interconnection protection. In this context, this paper proposes a probabilistic method to assess the risk of energized island formation by combining the probability of breaker (or recloser) opening with the probability of anti-islanding protection failure. The method employs probabilistic short circuit associated with overcurrent protection actuation by using Monte Carlo simulation and time-domain analysis to obtain the cases of unintentional islanding and to calculate the risk of distributed generator islanded operation. The results drove more realistic and less conservative conclusions than previous literature. Additionally, it is shown that faults as the cause of breaker opening do play a relevant role in the performance of the anti-islanding protection.

Bandgap tunability and impact mitigation enhancement of hybrid graded origami-inspired metamaterials with multiple resonators

Origami structure has become an important design source of metamaterials because of its extremely rich form and infinite design space. In order to improve the wave attenuation and impact mitigation ability of origami structure, a hybrid graded origami-inspired metamaterials with multiple resonators is proposed. The bandgap characteristics, transmission spectrum and impact resistance of the proposed metamaterials are analyzed in detail by numerical simulation. The results show that multiple local resonance mechanisms can open two new bandgaps compared to the single local resonance case, and the bandgap boundary is very sensitive to the dimension of resonance units. In particular, the resonance peaks of the origami metamaterials are substantially weakened due to the presence of dimensional gradients, which allows multiple bandgaps to merge into an ultra-wide bandgap (bandwidth up to 8.9 kHz), about five times than the original bandwidth. According to the time domain and frequency domain analysis results, it can be found that the amplitude of reaction force is significantly reduced in the bandgap range, and the ultra-wide frequency domain (2.9–10 kHz) with sustainable-low peak appears. Moreover, the asymmetry and graded design of unit-cell also affects the ability of dissipate and attenuate wave energy and delay the wave transmission time. In addition, the local-resonant origami metamaterials are fabricated by 3D printing technology, and the experimental results are in good agreement with the numerical simulation results. This study is expected to provide valuable ideas in crashworthiness design and impact wave protection of important equipments.

Model based control of dissolved oxygen in paper mill effluent using response surface methodology

In this work, for analysis, one and half liters of (effluent) waste water from paper mill industry was used in batch reactor, to study the variations in DO values under three operating conditions are speed, concentration of effluent in water and time with respect to step change in oxygen feed. The experiment was done 270 trails under specified operating conditions. Experimental data were collected, many trials were done using response surface method (RSM) and respective optimum values of three operating parameters were obtained for DO value ranging from 5 to 6 ppm. In trials, RSM predicted 82.732 % effluent to water concentration, stirrer speed at 150 rpm and at 0.091 min predicted DO is 5.7 ppm, from obtained experimental results shown in figure 3 for 80 % and 90 % concentration. RSM predicted optimal conditions are considered for experimental study and three control strategies such as particle swarm optimization (PSO) based PID control and state feedback controller with Integral action and state observer were used to achieve desired DO value. A comparative study was done among three controllers and it was concluded that state feedback controller with Integral action based control strategy yield better closed loop results in-terms of time-domain and stability analysis.

Ultra-Compact 4-Port MIMO Antenna with Defected Ground Structure and SAR Analysis for 28/38 GHz 5G Mobile Devices

To tackle the challenge of keeping 5G mobile devices compact while supporting millimeter-wave bands, we've created an ultra-compact 4-port dual-band MIMO antenna with a defected ground structure (DGS). This design minimizes mutual coupling and covers a broad frequency range. Built on a Rogers TMM4 substrate with dimensions of 17.76×17.76 mm2, the antenna includes four planar patch antennas positioned perpendicularly at the corners. Each antenna operates at 28/38 GHz and features a rectangular patch with four rectangular slots and a full ground plane. The patches are separated by 0.5 λo, with the DGS further reducing mutual coupling. Both simulations and measurements indicate a significant reduction in mutual coupling (−39 to −60 dB), improving ECC, TARC, MEG, and DG. Time-domain and SAR analyses confirm the antenna's efficiency and its suitability for 5G devices.

Active suspension control using novel HB3C optimized LQR controller for vibration suppression and ride comfort enhancement

This article addresses the optimization of a Vehicle Active Suspension System (VASS) through the application of a Linear Quadratic Regulator (LQR) controller. The primary objective is to enhance ride comfort and ensure vehicle stability by addressing the divergent needs of vibration control. The research identifies key issues in existing optimization algorithms, namely, the exploration stage inefficiency in Big Bang Big Crunch Optimization (B3C) and the slow convergence rate in Coyote Optimization (CO). To overcome these challenges, a novel hybrid algorithm, Hybrid Coyote optimization based Big Bang Big Crunch (HB3C), is proposed. The research objective is to optimize the LQR weighting matrices using the HB3C algorithm, aiming for improved ride comfort and vehicle safety. The problem statement involves the inadequacies of existing algorithms in addressing the exploration and convergence issues. The motivation lies in enhancing the efficiency of VASS through optimal control, leading to better ride comfort and safety. The methodology involves integrating CO within a loop with B3C to compute the optimum reduction rate for the algorithm. Since, B3C algorithm’s success is highly dependent on selecting the ideal reduction rate. This hybrid approach is then applied to optimize the existing LQR weighting matrices. The results are evaluated in terms of time domain and frequency domain response analysis, with a focus on ride comfort based on ISO 2631-1 standards. The study demonstrates a maximum reduction of approximately 74% achieved by the optimized HB3C-LQR controllers.

SPICE-Compatible Circuit Models of Multiports Described by Scattering Parameters with Arbitrary Reference Impedances

New SPICE-compatible circuit models of a multiport are presented here that are suitable for the frequency-domain and time-domain analyses of hybrid systems containing linear distributed elements and possibly non-linear lumped elements. Distributed elements models are based on scattering parameters with potentially complex reference impedances, which are not necessarily equal for all ports. Both exact and approximated (lumped) models are proposed. The scattering parameters are directly taken as the model element values in the former case. In the latter case, the model element values are equal to the real and imaginary parts of the poles and residues of the rational approximation. The models comprise a multiport (with an admittance matrix numerically equal to the modeled scattering matrix or approximating it) equipped with a pair of coupled impedances at each port. A few examples validate the proposed approach and prove its efficiency in terms of matrix size and analysis time compared to some selected commercial counterparts.

Irregular ANCF model and experimental investigations of the irregular membrane structures with variable cross-section

The membrane spacecraft structures are widely used for deep space exploration and on-orbit operation, but the dynamic responses of them is more complex. To advance the state of membrane structures, in this paper, a new ANCF membrane element is established to model dynamic equations of the membrane structure precisely and efficiently. Firstly, the irregular ANCF membrane element is studied by considering anomalistic boundary and variable cross-section. The mapping relations between the sub-ANCF element and the parent-ANCF element are illuminated by the Jacobian matrix, which makes the strain of each irregular element accurately calculated with the same shape functions. It is helpful to improve the description accuracy of inherent attributes and reduce the element number of dynamic systems. Further, the nonlinear dynamic model for membrane spacecraft system is established by the virtual work principle. Finally, the numerical examples and experiments are analyzed to verify the correctness of the proposed method and discuss the influence of nonlinear geometry and distortion on the dynamic behaviors. The results from the time domain and frequency domain analyses demonstrate that the distinct irregular geometric boundary of the irregular spacecraft can be more accurately modeled using the presented method. However, the difference becomes more pronounced when the distortion is too large. The research outcomes of this paper can provide theoretical guidance for the irregular spacecraft system, which is of great significance and urgently needs to be studied.

Reduced-order modeling for time domain analysis of finite periodic structures with absorbing boundary conditions

A reduced-order model of finite periodic structures with absorbing boundary conditions (ABCs) and localized time-dependent excitations is proposed. 1D-periodic structures whose cells can represent any 2D or 3D arbitrary substructures are considered. The key steps for modeling an ABC in the time domain are: (i) expression of the impedance matrix with the wave finite element (WFE) method; (ii) partial rational decomposition of the impedance matrix; (iii) introduction of vectors of supplementary variables to describe the ABC in the time domain. In this paper, a model reduction approach is proposed to speed up the computation of the ABCs. The focus is on the reduction of the number of internal degrees of freedom of substructures, and the reduction of the number of degrees of freedom at the substructure interfaces. The approach allows the consideration of complex substructures with large FE models, and the computation of the time response of periodic structures at a low computational cost. Numerical experiments are carried out to highlight the relevance of the proposed approach. Specifically, the analysis of a metamaterial structure containing nonlinear resonant substructures is carried out with the proposed approach. Results show that, when compared to the linear case, band gaps in periodic structures with nonlinear substructures can be significantly improved.