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In order to ensure the reliability of the structural design, it is necessary to know the external loads acting on the structure. In this paper, we propose a novel method to identify the dynamic loads based on function principles in the time domain. Assuming the external load remains constant within one micro segment, we establish a linear relationship between external load and structural response in the micro segments based on the mechanical energy conservation law. Next, the external load is obtained by solving the inverse problem in each micro-segment. Finally, the external load in the whole time domain is achieved by fitting the load-identification results in each micro segment. In order to verify the effectiveness and accuracy, single-force and two-force identification, and load identification with noise simulations, are performed on the structures, and the identification results are compared to the ones of the traditional time-domain method with a deviation of less than 5%. The proposed method can effectively solve the problem of cumulative errors in the time-domain method, while its resistance to noise interference is also strong. At last, we verify the experimental performance of the proposed method. The experimental results show the effectiveness and high accuracy of the proposed method. This work presents a first attempt to solve the structural dynamic load with an approach based on a function principle.

To explore the spectral radiation characteristics of carbon nanofibers, a finite-difference time-domain method has been applied to study and calculate the scattering/absorption factors of carbon nanofibers with various arrangements, while the filler contents are 61.15%, 53.81%, 48.92%, 44.03% and 39.13% in the spectrum band of 2.5–15 µm. The effects of the nanofiber content, 2D/3D random arrangement and nanofiber radius on scattering/absorption characteristics have been analyzed. The analytical results show that the spectral radiation characteristics of carbon nanofibers have been significantly increased with an increase in the filler content. When the nanofiber content reduced to 48.92%, the random arrangement structure of carbon nanofiber plays an essential role in determining the spectral radiation characteristics. Analytical results prove that the prediction accuracy has been significantly improved by 30.12% by sing the 3D random arrangement model than by using the 2D uniform arrangement model. This study proposed a 3D model to predict the spectral radiation characteristics of carbon nanofibers and their aggregates in engineering nanocomposites.

A method of assessing equivalent static wind loads that can represent all the real ultimate states of a high-rise building and towering structure has still not been fully determined in wind engineering. Based on random vibration theory, the wind-induced response and equivalent static wind loading of high-rise buildings and towering structures are investigated using the vibration decomposition method. Firstly, the structural wind-induced mean response, background response, resonant response and background and resonant coupled response are studied in the time and frequency domains. Secondly, a new gust load factor (GLF) assessment method suitable for wind-induced displacement, bending moment and shear force response at any height of the structure is proposed, and a typical high-rise building is used as an example for comparison with the previous research results, in order to verify the effectiveness of the method in this paper. The results show the following: for high-rise buildings and towering structures, the percentage of the coupled components in the total pulsation response is less than 2%, and the influence can be ignored; the GLF based on bending moment (MGLF) and the GLF based on shear force (QGLF) increase significantly with height, and the traditional GLF methods underestimate the maximum wind effects.

Wave attenuation is a widespread physical phenomenon in most acoustic tests, but there is a scarcity of quantitative investigations into the influence of wave attenuation on the determination of shear wave travel time in bender element tests. To ascertain this attenuation effect, a series of bender element tests were conducted on clay samples with different lengths under unconfined conditions. The experimental results suggest that the real first peak of the received signal attenuates gradually with the increase of the sample length and even becomes undistinguished when the sample length exceeds a limit. This phenomenon results in misinterpretation of the wave travel time using the time domain method. In this study, the shear wave travel time is misinterpreted when wave travel distance over approximately 80 mm, leading to underestimation of the VS by 17% for the peak-to-peak approach and 10% for the arrival-to-arrival method. Therefore, besides the near field effect and boundary reflection, the wave attenuation effect turned out to be an important factor influencing the determination of VS using the time domain method. Accordingly, it is advisable to predetermine the limit test distance for a specific testing system under conditions, particularly for long distance testing.

$LLC$ resonant converter is utilized for a 3.3-kW on-board charger (OBC), where high efficiency and wide output voltage are required. In this paper, the resonant frequency and the magnetizing inductor of the converter are first optimized based on the required efficiency. Then, the resonant inductor and the resonant capacitor are designed considering the required maximum output voltage. The energy equations and the KCL and KVL equations about the converter are established by the time domain method to find out the information about peak resonant current, peak magnetizing current, and minimum switching frequency. The above-mentioned information is used to accurately design the converter’s magnetic components. A 3.3-kW prototype applied for OBC is developed. Its output voltage ranges from 230 to 430 V. Its peak efficiency is higher than 97.6%. The experimental results verify that the proposed method can accurately design the efficiency, the voltage gain, and the magnetic components of $LLC$ resonant converter in a wide output voltage range.

Introduction and Objectives: The electromagnetic fields which are emitted by cellular telephones may influence the autonomic tone which modifies the functioning of the circulatory system. The present research work was taken up to study the long term impact of mobile phone usage on the heart rate variability (HRV) in healthy, young, adult males. Methods: A total of 37 healthy, volunteered males (18 -24 years) were included in the study and they were grouped in to mobile users who had been using the mobile phones for more than one year (n=21) and non-mobile users (n=16). The HRV was analyzed both by the time domain and the frequency domain methods during normal breathing. Statistical analysis was done by using the Students unpaired t-test. A two tailed p value less than 0.05 was considered to be significant. The present study was completed in two months. Results: In the time domain analysis, the HRV showed no statistically significant difference in between the two groups. But in the frequency domain analysis, the total power (TP), the very low density frequency (VLF) power and the low frequency (LF) power were found to be statistically significantly high in the mobile users. The high frequency normalized unit ( HF nu) was low and the LF normalized unit (LF nu) and the LF: HF ratio were high in the mobile users. Conclusion: The present study showed that the mobile users had a higher sympathetic tone and a lower parasympathetic tone as compared to the mobile non users.

International audience; The development of wireless technologies arises important questions about the effects of the wave propagation in the human body. To study accurately these effects, we have to use rigorous numerical methods. In this paper, we present and analyze the One-Step time domain method. This method, which was proposed by De Raedt [Phys Rev E 67(056706):1-12, 2003] for lossless media, is known to be unconditionally stable and so it can be used for applications for which the Courant-Friedrich-Levy (CFL) stability condition can be a limiting factor, e.g., for bioelectromagnetic applications. The numerical dispersion and the insertion of lossy media in the One-Step method are evaluated. The perfectly matched layer (PML) absorbing conditions are also introduced in our study.

The aeroelastic behaviour of vibrating blade assemblies is usually investigated in the frequency domain where the determination of aeroelastic stability boundaries is separated from the computation of linearized unsteady aerodynamic forces. However, nonlinear fluid-structure interaction caused by oscillating shocks or strong flow separation may significantly influence the aerodynamic damping and hence effect a shift of stability boundaries. In order to investigate such aeroelastic phenomena, the governing equations of structural and fluid motion have to be simultaneously integrated in time. In this paper a technique is presented which analyzes the aeroelastic behaviour of an oscillating compressor cascade in the time domain. The structural part of the governing aeroelastic equations is time-integrated according to the algorithm of Newmark, while the unsteady airloads are computed at every time step by an Euler upwind code, The link between the two time integrations is an automatic grid generation in which the used mesh is dynamically deformed as such that it conforms with the deflected blades at every time step. The computed time series of the aeroelastic simulation of an assembly of twenty compressor blades performing torsional vibrations in transonic flow are presented. For subsonic flow, the differences between time domain and frequency domain results are of negligible order. For transonic flow, however, where vibrating shocks and a temporarily choked flow in the blade channel dominate the unsteady flow, the energy transfer between fluid and structure is no longer comparable to that of a linear system. It is demonstrated that the application of the time domain method leads to a significantly different aeroelastic behaviour of the blade assembly including a shift of the stability boundary.

Linear time invariant (LTI) systems like linear elastic structures are characterized by modal parameters i.e. natural frequencies, natural modes and modal damping. For the given mathematical models there are number of well established procedures that calculate modal parameters (Ljung, 2006, Ewins, 2000). When the structure is given as real system, experiment is employed to detect modal parameters. The experiment comprises excitation of the structure, data acquisition, data processing and finally modal parameters extraction. During last decades a number of very sophisticated methods for modal parameters detection have been and still are being developed (Zhou, 2008). All these methods can be divided in two groups: frequency domain and time domain methods. The frequency domain methods are typically based on modal parameters detection from the frequency response functions (FRF) while time domain methods typically rely on impulse response function. So we can conclude that the most of the methods detect the modal parameters in two steps: FRF or impulse response function has to be calculated first and then modal parameter detection techniques applied.

Virtually all traditional signal quality analysis procedures operate on data in the frequency domain, and therefore require steady-state signals. However, real-life signals are, typically, not steady-state. In order to be able to measure the conversion quality of a sigma-delta modulator under non-steady-state excitation, in this chapter a time domain SINAD measurement method is introduced. The operation of this time domain method is first verified with steady-state signal measurements, and finally applied to non-steady-state signals. The simulations on various non-steady-state signals indicate that no significant conversion errors are generated, and that the traditional signal quality analysis procedures are adequate.

This paper investigates the flutter mechanism of a high loaded transonic compressor rotor by applying different numerical methods. For predictions of the stability in the frequency domain, harmonic fluid forces are calculated with a linearized Euler method and with a nonlinear time domain Navier-Stokes solver for forced motion. To include nonlinear effects in the stability prediction, the time domain method is applied in a fluid-structure coupled mode of operation. The results of this 3D viscous aeroelastic computations in the time domain for the whole annulus of the rotor are compared to the frequency domain solutions.