Maximum Response Amplitude Research Articles

Long-term monitoring of dynamic characteristics of high-rise and super high-rise buildings using strong motion records

Seismic behavior of a structure is directly related to its dynamic characteristics, which include natural frequency, damping ratio, and mode shape. This study focuses on the long-term monitoring of dynamic characteristics of six selected target structures. The covariance-driven stochastic subspace identification (SSI) approach is used to estimate the fundamental natural frequency and damping ratio of target buildings based on long-term motion records in order to examine the temporal variation of dynamic properties. The fundamental natural frequency and damping ratio variations over time are first discussed. It is found that the fundamental natural frequency of some structures reduces dramatically after the 2011 Tohoku Earthquake, accompanied by a rise in damping ratio. Then, regression analysis is used to assess the relationship between dynamic characteristics and ground motion parameters (Peak ground acceleration (PGA), magnitude, focal depth, and epicentral distance) and structural response (root mean square acceleration, maximum response amplitude). It is discovered that the identified natural frequency has no clear correlation with the focal depth, a slight negative correlation with the epicentral distance, and a strong negative correlation with the magnitude and PGA. The root mean square acceleration and the maximum response amplitude are negatively correlated to the target buildings’ natural frequencies. Finally, the influence of environmental factors on dynamic properties is investigated.

An Analytical Method for Elastic Seismic Response of Structures Considering the Effect of Ground Motion Duration

The response to earthquake ground motion is composed of three basic elements, namely, amplitude, frequency, and duration. The seismic response of a structure is controlled by the particular combination of these three elements. The seismic response spectra reflect the earthquake ground motion’s frequency-domain features and provide the maximum response amplitude of a single-degree-of-freedom system to a given earthquake ground motion but do not consider the duration factor. However, the analysis of post-earthquake damage shows that the seismic response duration has a strong impact on the damage to structures. Therefore, it is necessary to develop a simple and practical analytical method to account for the seismic response duration. The present study was conducted based on the response spectra theory. We introduce an analytical method of elastic seismic response, which considers its duration by adding the time-domain dimension of earthquakes. The time-domain spectral matrix is used to solve the time-dependent seismic response through the vibration mode decomposition method. The time-domain vibration mode decomposition reaction spectrum not only takes into account the maximum seismic reaction of each vibration mode but also considers the seismic reaction of different vibration modes occurring at the same time, at each moment. The dynamic time duration of the structure’s seismic reaction is quantified by the time-domain seismic reaction spectrum to obtain a more accurate analysis method for the seismic reaction of the structure.

Vortex-induced vibration of a sphere close to or piercing a free surface

Vortex-induced vibration (VIV) of an elastically mounted sphere placed close to or piercing a free surface (FS) was investigated numerically. The submergence depth ( $h$ ) was systematically varied between $1$ and $-$ 0.75 sphere diameters ( $D$ ) and the response simulated over the reduced velocity range $U^*\in [3.5,14]$ . The incompressible flow was coupled with the sphere motion modelled by a spring–mass–damper system, treating the free-surface boundary as a slip wall. In line with the previous experimental findings, as the submergence depth was decreased from $h^* = h/D =1$ , the maximum response amplitude of the fully submerged sphere decreased; however, as the sphere pierced the FS, the amplitude increased until $h^* = -0.375$ , and then decreased beyond that point. The fluctuating components of the lift and drag coefficients also followed the same pattern. The variation of the near-wake vortex dynamics over this submergence range was examined in detail to understand the effects of $h^*$ on the VIV response. It was found that $h^* = 1$ is a critical submergence depth, beyond which, as $h^*$ is decreased, the vortical structures in the wake vary significantly. For a fully submerged sphere, the influence of the stress-free condition on the VIV response was dominant over the kinematic constraint preventing flow through the surface. For piercing sphere cases, two previously unseen vortical recirculations were formed behind the sphere near times of maximal displacement, enhancing the VIV response. These were strongest at $h^* = -0.375$ , and much weaker for small submergence depths, explaining the observed response-amplitude variation.

Relationship Between Intraoperative Electrocochleography and Hearing Preservation.

To compare intraoperative intracochlear electrocochleography (ECochG) with hearing preservation outcomes in cochlear implant (CI) subjects. Intraoperative electrocochleography was performed in adult CI subjects who were recipients of Advanced Bionics' Bionics LLC precurved HiFocus MidScala or straight HiFocus SlimJ electrode arrays. ECochG responses were recorded from the most apical electrode contact during insertion. No changes to the insertions were made due to ECochG monitoring. No information about insertion resistance was collected. ECochG drops were estimated as the change in amplitude from peak (defined as maximum amplitude response) to drop (largest drop) point after the peak during insertion was measured following the peak response. Audiometric thresholds from each subject were obtained before and approximately 1 month after CI surgery. The change in pure tone average for frequencies between 125 Hz and 500 Hz was measured after surgery. No postoperative CT scans were collected as part of this study. A total of 68 subjects from five surgical centers participated in the study. The study sample included 30 MidScala and 38 SlimJ electrodes implanted by approximately 20 surgeons who contributed to the study. Although a wide range of results were observed, there was a moderate positive correlation (Pearson Correlation coefficient, r = 0.56, p < 0.01) between the size of the ECochG drop and the magnitude of pure tone average change. This trend was present for both the MidScala and SlimJ arrays. The SlimJ and MidScala arrays produced significantly different hearing loss after surgery. Large ECochG amplitude drops observed during electrode insertion indicated poorer hearing preservation. Although the outcomes were variable, this information may be helpful to guide surgical decision-making when contemplating full electrode insertion and the likelihood of hearing preservation.

MNP-Enhanced Microwave Medical Imaging by Means of Pseudo-Noise Sensing.

Magnetic nanoparticles have been investigated for microwave imaging over the last decade. The use of functionalized magnetic nanoparticles, which are able to accumulate selectively within tumorous tissue, can increase the diagnostic reliability. This paper deals with the detecting and imaging of magnetic nanoparticles by means of ultra-wideband microwave sensing via pseudo-noise technology. The investigations were based on phantom measurements. In the first experiment, we analyzed the detectability of magnetic nanoparticles depending on the magnetic field intensity of the polarizing magnetic field, as well as the viscosity of the target and the surrounding medium in which the particles were embedded, respectively. The results show a nonlinear behavior of the magnetic nanoparticle response depending on the magnetic field intensity for magnetic nanoparticles diluted in distilled water and for magnetic nanoparticles embedded in a solid medium. Furthermore, the maximum amplitude of the magnetic nanoparticles responses varies for the different surrounding materials of the magnetic nanoparticles. In the second experiment, we investigated the influence of the target position on the three-dimensional imaging of the magnetic nanoparticles in a realistic measurement setup for breast cancer imaging. The results show that the magnetic nanoparticles can be detected successfully. However, the intensity of the particles in the image depends on its position due to the path-dependent attenuation, the inhomogeneous microwave illumination of the breast, and the inhomogeneity of the magnetic field. Regarding the last point, we present an approach to compensate for the inhomogeneity of the magnetic field by computing a position-dependent correction factor based on the measured magnetic field intensity and the magnetic susceptibility of the magnetic particles. Moreover, the results indicate an influence of the polarizing magnetic field on the measured ultra-wideband signals even without magnetic nanoparticles. Such a disturbing influence of the polarizing magnetic field on the measurements should be reduced for a robust magnetic nanoparticles detection. Therefore, we analyzed the two-state (ON/OFF) and the sinusoidal modulation of the external magnetic field concerning the detectability of the magnetic nanoparticles with respect to these spurious effects, as well as their practical application.

Электромагнитное загрязнение околоземного космического пространства излучением ЛЭП

We present an overview, based on satellite observations at low Earth orbits, on electromagnetic radiation from ground power transmission lines at an industrial frequency 50–60 Hz. Particular attention has been given to Chibis-M and DEMETER satellite observations. The electric 40-cm antenna of the micro-satellite often recorded 50–60 Hz radiation (known as Power Line Emission (PLE)) when it flew over industrialized areas of the planet. The PLE spectral amplitude varied from 1.2 to 18 (μV/m)/Hz0.5, which corresponds to the electric field amplitude E~1 μV/m. We report results of numerical calculations of the electromagnetic response of the atmosphere and ionosphere to a large-scale surface emitter at a frequency of 50 Hz. According to simulation results, PLE with an intensity of ~1 μV/m observed on satellites in the nightside ionosphere at midlatitudes can be excited by an unbalanced current 8–10 A in a power transmission line above the earth's crust with conductivity of 10–3 S/m. At middle and low latitudes with an inclined geomagnetic field, the maximum response in the upper ionosphere to the transmission line radiation should be seen shifted equatorward, although this shift is less than that upon guidance by the geomagnetic field. The maximum amplitude of the electromagnetic response of the ionosphere to the power transmission line emission decreases for an inclined geomagnetic field, but insignificantly. To date, the PLE intensity in near-Earth space has turned out to be higher than the intensity of natural radiation in this range (Schumann resonances and ion whistlers), and continues to grow with the technological development of mankind.

Electromagnetic pollution of near-Earth space by power line emission

We present an overview, based on satellite observations at low Earth orbits, on electromagnetic radiation from ground power transmission lines at an industrial frequency 50–60 Hz. Particular attention has been given to Chibis-M and DEMETER satellite observations. The electric 40-cm antenna of the micro-satellite often recorded 50–60 Hz radiation (known as Power Line Emission (PLE)) when it flew over industrialized areas of the planet. The PLE spectral amplitude varied from 1.2 to 18 (μV/m)/Hz0.5, which corresponds to the electric field amplitude E~1 μV/m. We report results of numerical calculations of the electromagnetic response of the atmosphere and ionosphere to a large-scale surface emitter at a frequency of 50 Hz. According to simulation results, PLE with an intensity of ~1 μV/m observed on satellites in the nightside ionosphere at midlatitudes can be excited by an unbalanced current 8–10 A in a power transmission line above the earth's crust with conductivity of 10–3 S/m. At middle and low latitudes with an inclined geomagnetic field, the maximum response in the upper ionosphere to the transmission line radiation should be seen shifted equatorward, although this shift is less than that upon guidance by the geomagnetic field. The maximum amplitude of the electromagnetic response of the ionosphere to the power transmission line emission decreases for an inclined geomagnetic field, but insignificantly. To date, the PLE intensity in near-Earth space has turned out to be higher than the intensity of natural radiation in this range (Schumann resonances and ion whistlers), and continues to grow with the technological development of mankind.

Demand Response Coupled with Dynamic Thermal Rating for Increased Transformer Reserve and Lifetime

(1) Background: This paper proposes a strategy coupling Demand Response Program with Dynamic Thermal Rating to ensure a transformer reserve for the load connection. This solution is an alternative to expensive grid reinforcements. (2) Methods: The proposed methodology firstly considers the N-1 mode under strict assumptions on load and ambient temperature and then identifies critical periods of the year when transformer constraints are violated. For each critical period, the integrated management/sizing problem is solved in YALMIP to find the minimal Demand Response needed to ensure a load connection. However, due to the nonlinear thermal model of transformers, the optimization problem becomes intractable at long periods. To overcome this problem, a validated piece-wise linearization is applied here. (3) Results: It is possible to increase reserve margins significantly compared to conventional approaches. These high reserve margins could be achieved for relatively small Demand Response volumes. For instance, a reserve margin of 75% (of transformer nominal rating) can be ensured if only 1% of the annual energy is curtailed. Moreover, the maximal amplitude of Demand Response (in kW) should be activated only 2–3 h during a year. (4) Conclusions: Improvements for combining Demand Response with Dynamic Thermal Rating are suggested. Results could be used to develop consumer connection agreements with variable network access.

Design of a Real‐Time Wireless Sensing Monitoring System Based on Acoustic Emission Power GIS Equipment

In this paper, real‐time monitoring of acoustic emission power GIS equipment is studied and analyzed, and a real‐time wireless sensing monitoring system is designed. The overall design of the wireless sensing monitoring system for acoustic emission power GIS equipment is as follows: the model of the system is constructed, the design of the system module function is proposed, the platform of the system is built, the hardware and software solutions are configured, the operating system is optimized, the graphics and data are input into the GIS distribution network system, the editing function is optimized, the fast positioning function of the equipment is improved, and the automatic generation of the system diagram is improved. By using ZigBee technology to establish a wireless sensor network and realize wireless transmission of monitoring signals, it can avoid many disadvantages, such as cumbersome cable laying, troublesome changes, inconvenient expansion, and daily maintenance in wired transmission, and save various resources and reduce monitoring costs, which is well worth promoting in the system. In this paper, for the actual situation of GIS equipment, combined with the characteristics of the wireless sensor network structure and the design needs of the monitoring system (the overall design of the monitoring system, OFS maximum response amplitude of 19.9 mV, to be reached 40 dB), the signal will be uploaded to the high‐speed collection system, and the efficiency is increased by more than 10%. The feasibility test of the monitoring system, the test results, and the related data show that the UHF sensor can accurately collect the UHF signal, the wireless network formed by ZigBee can reliably transmit the signal, the monitoring interface is correctly displayed, and the whole monitoring system operates stably and meets the requirements of the initial design.

The Optimization and Stabilization of Pump Light Frequency in the Minimized Atomic Magnetometer

In this article, we found an appropriate operating frequency of pump light for stabilizing the light frequency based on the atomic absorption of the vapor cell in the minimized atomic magnetometer. The traditional way to apply this stabilizing method is to stabilize the laser frequency at the absorption peak because its derivative is always zero and not affected by the cell temperature if the pressure shift is suppressed. However, it is observed experimentally that the response amplitude has a drop of up to 40% from the maximum at the absorption peak. It is due to the hyperfine optical pumping, and we explored the applicable condition to obtain the maximum response amplitude by solving the Liouville equation and proved it experimentally as well. Furthermore, we found that under the appropriate pressure, the frequency to obtain maximum response is close to the zero points of the second-order derivative which are not affected by cell temperature as well. Therefore, it is purposed to stabilize the pump laser frequency at these points. It is demonstrated experimentally that the frequency stabilization is the same, while the response amplitude is increased by more than 40% compared to stabilizing at the absorption peak. These results are instructive in improving the performance of minimized atomic magnetometers.

Estrogenic activity of capsule coffee using the VM7Luc4E2 assay

Coffee brewed from capsule machines may contain estrogenic chemicals migrated from plastic, but the estrogenic activity of capsule coffee has not been evaluated. This study evaluated the estrogenic activity of capsule coffee using the VM7Luc4E2 estrogen receptor transcriptional activation assay. Estrogenic potentials of six capsule coffee samples were calculated using relative maximum amplitude response of E2 (>15%RME2 indicative of estrogenic activity) and estradiol equivalent factor (EEF). Estrogenic chemical content was determined using ultra-performance liquid chromatography with tandem mass spectrometry. All capsule coffee samples possessed estrogenic activity (48–56%RME2). EEFs were 6–7 orders of magnitude lower than that of E2, (1.2 × 10−7−1.7 × 10−6), indicating substantially weaker estrogenic potencies. Bisphenol A, bisphenol F, benzophenone, 4-nonylphenol, dibutyl phthalate, and dimethyl terephthalate were detected in capsule coffee. Capsule coffee exhibited estrogenic activity in vitro, and its estrogenic chemical content is likely driving its estrogenicity, warranting further investigations to fully understand the degree to which they are related and to predict the estrogenic potential based on the concentration of estrogenic chemicals.

Evaluation of Impulse-Oscillometric Extravasation Prevention

Infusion liquid extravasation occurs in up to 6% of all intensive care patients and up to 78% for neonates. Currently, emerging extravasation cannot be detected. An impulse-oscillometric method to detect the onset of extravasation is tested and evaluated in vitro.A pinch valve compresses the infusion line, an impulse is formed, and the pressure response is recorded at the peripheral vein catheter. The response of this catheter-sensor-system is analysed by measuring the transient-step response (n = 10) for an opened and closed pinch valve. Trials utilising porcine shanks (n = 15) are performed with venous and extravasational catheter placement. The fundamental frequency, maximum amplitude, damping and decay constant of the pressure response are tested for differences between venous and extravasational placement.The response of the catheter-sensor-system shows no significant differences between an opened or closed pinch valve. The maximum amplitude, frequency, damping and decay constant of the pressure response differ highly significant for venous and extravasational catheter placement (p < .001). The parameters also differ depending on the presence of infusion liquid flow (p < .001).The method enables the detection of the onset of extravasation. Further tests are performed to investigate the relationships between impulse response and hydraulic impedance.

A detailed study of the parametric excitation of a vertical heavy rod using the method of multiple scales

An analytical solution for the problem of an immersed flexible and vertical heavy rod subjected to a vertical top motion is developed using the multiple scales method directly applied to the partial differential equations of motion. The obtained results show good agreement with a numerical solution obtained using the finite element method for a study case. The analytical solution is then used to carry out some sensitivity studies. The effects of the structural nonlinearities, hydrodynamic and structural damping terms are investigated. It is shown that the nonlinearities play a role in defining the frequency of the top motion that causes the maximum amplitude of response, but not the value of the amplitude itself. In turn, the major role played by the hydrodynamic damping in defining the response amplitude is addressed. It is also shown that the structural damping have an important effect on the response amplitude even in the case of small damping ratio. This occurs due to the combined effect of the structural with the hydrodynamic damping. Finally, it is pointed out that small differences in the structural damping ratio can lead to significant differences in the response amplitude.

Impact of nanostructures on the superharmonic resonance characteristics of nanobeam-based capacitors: Analytical approach

In this paper, the nonlinear vibration of a size-dependent doubly clamped NEMS has been investigated based on the consistent couple-stress theory and Euler-Bernoulli beam theory. The impact of surface elasticity, dispersion Casimir force, and fringing field effect are considered in the nonlinear model. Here, the nanobeam is supposed to be under a single-side electrostatic actuation, which is a combination of DC and AC voltages. The governing differential equation of motion is derived using the extended Hamilton’s principle and discretized to a nonlinear ODE using Galerkin’s procedure. The multiple time scales method is applied to the reduced-order model in order to analytically obtain the nanobeam frequency–response curves under hard AC load. The influence of the small-scale parameter, Casimir force, and surface effect are investigated on both the static pull-in and the superharmonic resonance characteristics of the system. It is shown that the application of non-classical continuum theory effectively shifts the saddle-node bifurcation point’s loci to lower frequencies, and diminishes the maximum amplitude of the system response without changing the system stiffness. Moreover, it is concluded that the influence of surface energy on the system dynamic behavior depends on the value of DC voltage load. To validate the results obtained from perturbation analysis, the shooting method is schemed through numerical integration of the reduced-order model equation.

Flow induced vibration of two rigidly connected circular cylinders in different arrangements at a low Reynolds number

The flow induced vibration (FIV) responses of two rigidly connected cylinders in various arrangements have been studied numerically using the two-dimensional incompressible Navier-Stokes equations coupling with a fourth-order Runge-Kutta method. Four different values of the angle of incidence (α) and two different values of center-to-center pitch (P) between the two cylinders have been selected for the study. The FIV response amplitudes, lock-in regions, hydrodynamic force coefficients, phase portraits, and flow fields have been systematically compared. The numerical results demonstrate that for P = 4D and increasing α, the maximum value of the total mean drag coefficient tentatively increases, however, the maximum response amplitude shows a decreasing tendency. Furthermore, the maximum amplitude for P = 4D occurs when α = 0° at Vr = 7. For P = 4D and α = 0°, the response amplitude remains a certain value during the large Vr range, which is caused by the participation of the wake-induced vibration. For P = 2D, the maximum amplitude happens when α = 30° at Vr = 12. For P = 2D when α = 90°, owing to the proximity-induced galloping, during the large Vr range, the response amplitude increases slightly with increased Vr, displaying no desynchronization characteristics.

Two-degree-of-freedom flow-induced vibration suppression of a circular cylinder via externally forced rotational oscillations: comparison of active open-loop and closed-loop control systems

In the current work, both active open-loop and closed-loop control approaches are considered to reduce two-degree-of-freedom vortex-induced vibration (VIV) of a circular-section cylinder, by means of externally imposed rotational oscillations. The open-loop control method utilizes pre-specified rotary oscillations, while the active closed-loop controller computes the proper angular velocity depending on the feedback signal of lift coefficient. The interactions between fluid and structure are realized by utilizing of the moving mesh methodology by means of user-defined function, which incorporated into the central code of computational fluid dynamic solver. According to the numerous set of numerical simulations, three optimum open-loop control systems for appropriate suppression of cylinder vibration are selected. In particular, it is observed that the VIV suppression capability of the closed-loop control strategy in comparison with optimum open-loop systems is more desirable despite the lower level of consuming control effort. Moreover, it is detected the excellent performance of selected closed-loop controller with constant proportional control gain in the entire range of reduced velocities, while the optimum open-loop systems are executable mainly near their corresponding reduced velocities. In particular, the selected closed-loop VIV control system (Kp = 10) is found to suppress the maximum transverse response amplitudes by 99.6%, 99.5%, and 99.3% for reduced velocities Vr = 5, 6, and 7, respectively, while the associated in-line displacement amplitudes decrease by 99.2%, 98.3%, and 96.2%. Also, the closed-loop controller does not require to find the “lock-on” frequency to execute appropriate de-synchronization type action and can effectively shift the C(2S)-mode vortices to the typical von Karman 2S-mode vortex shedding.

The effect of inclination on vortex-induced vibration of a circular cylinder with a base column

The vortex-induced vibration (VIV) of an inclined cylinder can be affected by its end condition. This paper numerically investigates the effect of inclination on the VIV of an elastically mounted rigid cylinder with a base column, which derives from a floating offshore wind turbine (FOWT). The numerical methods are validated against an existing VIV study of a finite-length cylinder. Two inclination angles, i.e. −5° and −10°, are studied to simulate the relatively small wind-induced inclination experienced by FOWTs. Results from stationary simulations show that differences between the force coefficients of inclined and upright cylinders are rather small. Nevertheless, contrary to the finding from previous VIV studies that the effect of inclination on the response of a cylinder with small inclination angles is limited, the present investigation reveals that the maximum response amplitude of the cylinder increases by about 20% when the inclination angle grows to −10° due to the presence of the base column. Meanwhile, the inclination leads to a reduction in the width of the lock-in regime. The impacts of inclination are further discussed via forced vibration studies with same oscillation parameters, which show that the upper part of the cylinder is more affected by the inclination compared to the base column with a considerable decrease in the amplitude of lift coefficient. The discrepancies in fluid forces are substantiated by analysing the pressure distribution on specified spanwise sections of the cylinder surface.

Retinal toxicity study of intravitreal ganciclovir in albino rabbit

Objective: To elevated the retinal toxicity of intravitreal ganciclovir in albino rabbit eyes. Methods: Experimental study. Twenty-four New Zealand albino rabbits (forty-eight eyes) were divided into four groups by random. Three groups were prepared for ganciclovir experiment, named A, B, C. Each group received intravitreal injection ganciclovir dose at 400 μg/0.05 ml, 2 mg/0.05 ml and 5 mg/0.05 ml respectively. The other group named D served as a control accepted intravitreal injection 0.9% normal saline 0.1 ml. Before and after 1, 2 and 4 weeks, flicker full field electroretina gram (ERG) was recorded. After 1, 2 and 4 weeks light and electron microscopic tests were recorded for further toxicity study. Results: There was significant difference in amplitude of maximal combined response a wave in one week(χ(2)=8.319, P=0.04), and pairwise comparison the 5 mg group (140.50 μV) was significantly lower than the control group (165.00 μV) (χ(2)=-2.830, P=0.028). Maximal combined response b wave in four weeks(χ(2)=-10.626, P=0.014), and pairwise comparison the 5 mg group (261.50 μV) was significantly lower than the control group (398.00 μV) (χ(2)=-2.973, P=0.018). 30 Hz flicker response in one, two and four weeks(χ(2)=17.589, 8.225, 8.997, P=0.001, 0.042, 0.02), and pairwise comparison the 5 mg group (71.3μV, 106.00μV, 63.60μV) was significantly lower than the control group (118.50μV, 129.00μV, 116.50μV) (χ(2)=-4.142, -2.826, -2.713, P=0.000, 0.028, 0.040). There was no histologic retinal toxicity evidence of group 400 μg and control group observed by light microscopy in any stage of the study. Histologic changes of group 2 mg four week later, group 5 mg two and four week later include inner nuclear layer loose arranged, nuclear of ganglia were widened and outer plexiform layer stained less in four week later. By electron microscopic observation, the ultrastructure of retina changed to different degrees and became worse in each experimental group with significant mitochondrial swelling and hydropic changes were seen in the inner segments of photoreceptors, loosely arranged and disordered in the outer segment of photoreceptors four weeks later. Conclusions: The retinal function and morphology were normal in group 400 μg. Group 2 mg and 5 mg had retinal toxicity, and 5 mg was more severe. Therefore, the clinical application of ganciclovir in the treatment of acute retinal necrosis (ARN) should select the minimum effective dose to avoid the occurrence of retinal toxicity. (Chin J Ophthalmol, 2020, 56:279-285).

Vortex-induced vibration of elastically connected multiple circular cylinders in a side-by-side arrangement in steady flow

Vortex-induced vibration (VIV) of multiple circular cylinders elastically connected together in a side-by-side arrangement subject to steady flow is investigated numerically at a low Reynolds number of 150 and a mass ratio of 2. Simulations are conducted for two-, five- and ten-cylinder systems over a wide range of reduced velocities. The aim of the study is to identify the high-amplitude response range of the reduced velocity for the multiple degree of freedom vibration system and identify the difference between the responses of the single- and multiple-degree-of-freedom vibrations. Unlike the single cylinder case, distinct lock-in between the response frequency and any of the structural natural frequencies in a wide range of reduced velocity is not observed in the multiple-cylinder cases. Instead, the response frequency increases continuously with increasing reduced velocity. High response amplitudes are found when the response frequency is between the first and the highest modal frequencies. In a multiple-cylinder system, the single-mode response, where the vibration is dominated by one mode, can be only found in low reduced velocity range. In the single-mode branch, the dominance of a single mode shape in the response can be clearly identified except at the boundary reduced velocity between two modes. The maximum response amplitude occurs in the multiple-mode response and interaction between the vortices in the wake of the cylinders is strong when the response amplitudes are high.

Design of dry friction and piezoelectric hybrid ring dampers for integrally bladed disks based on complex nonlinear modes

This paper investigates a new passive damper coupling the energy dissipative mechanisms of dry friction and piezoelectric shunting circuit for Integrally Bladed Disks (blisks). The idea is to distribute piezoelectric material to the dry friction ring so that the elastic deformation of the dry friction ring is utilized to generate additional damping. Mounting piezoelectric material on the additional structure instead of the host structure is a more practical alternative to install piezoelectric damping devices to realistic mechanical systems. This improves the reliability and maintainability of both dampers and host structures. Based on the concept of Complex Nonlinear Modes (CNMs), the dry friction damping effect of the proposed damper is measured through the modal damping ratio for target modes. Modal Electromechanical Coupling Factor (MEMCF) is extended to nonlinear electromechanical coupling systems in order to quantify the additional piezoelectric damping ratio. The damping effect of the hybrid damper is also evaluated by the maximal response amplitude in the frequency domain by the forced response analysis. On one hand, it validates the results from the nonlinear modal analysis, on the other hand, it serves as a reference to choose the optimum design parameters of the hybrid damper. Steady-state response of the cyclic symmetric structure under engine-order excitation is calculated by the Multi-Harmonic Balance Method (MHBM). A phenomenological lumped parameter model representing a blisk with a hybrid ring damper is firstly studied to demonstrate the methodology. Then a blisk finite element model is used as a demonstrator to quantitatively verify the effectiveness of the idea. It is shown that for those modes that can be damped by the dry friction damper, the addition of piezoelectric material further enhances the damping effect.