Fourth Mode Research Articles

Experimental and numerical modal analysis of a reduced scale Kaplan turbine model

This paper presents an experimental modal test of a Kaplan turbine model and provides the corresponding analysis of the results. The modal test of the rotor including the runner, the shaft and the generator was performed using, as exciters, an impact hammer and a shaker and, as sensors, several accelerometers. Additionally, numerical models of the rotor with the runner surrounded by air (dry condition) or submerged in water (wet condition) were also built. By comparing the numerical and experimental results, the main modes of vibration of a runner blade in dry conditions and of the rotor shaft both in dry and wet conditions have been identified and discussed. The most significant deviations between experimental and numerical natural frequencies were found around 10% for the rotor shaft and around 6% for the runner blade. Moreover, it was observed that the fourth mode of vibration presents the highest added mass effect with a Frequency Reduction Ratio of about 6.7% and the second mode of vibration shows the lowest damping ratios in both dry and wet conditions with values of about 1.5 and 2.1%, respectively.

Large eddy simulation of structural characteristics in turbulent flow around a circular cylinder close to a wavy wall

The flow characteristics and vortex evolution behind a circular cylinder near a wavy wall are studied using a large-eddy simulation framework. The Reynolds number based on the cylinder diameter D is ReD = 1500, the gap ratio G/D is fixed to 1, and the slope S = λ/2k varies from 2 to 8 (where G is the distance between the lower surface of the cylinder and the crest, λ is the wavelength, and k is the wave amplitude). The flow field characteristics, hydrodynamic coefficients, pressure distributions, vortex evolution, and three-dimensional flow features are presented and discussed. The phase of the flow field is determined by proper orthogonal decomposition, and the vortex identification method is applied to capture vortex structures. Compared with a smooth wall, the wavy wall changes the pressure distribution of the flow field and decreases (increases) the mean drag (lift) coefficient. As the wall amplitude increases, the Strouhal number increases slightly, attaining values of 0.25 for S = 8, 0.25 for S = 4, and 0.26 for S = 2. The wall pressure coefficient has an approximately periodic distribution, while the wall friction coefficient varies according to the evolution of secondary vortices on the wall. Two small secondary vortices appear either side of the crest before merging into a new secondary vortex that moves downstream with the upper and lower wake vortices. The energy of the first two modes obtained by proper orthogonal decomposition decreases compared with the smooth-wall case, whereas that of the third and fourth modes increases, reflecting the greater large-scale vortex structures between the wavy walls. This is confirmed by examining the instantaneous three-dimensional vortex structures using the Q-criterion.

Stability and contrast in bimodal amplitude modulation atomic force microscopy for different mode combinations in ambient air

Bimodal amplitude modulation atomic force microscopy (AM-AFM) is widely used in nanoscale topography and mechanical property imaging for a variety of materials. In this paper, the stability of the amplitude/phase spectroscopy curves and the imaging contrast in bimodal AM-AFM for different mode combinations are investigated computationally in ambient air. The results show that with the second mode amplitude used for topography feedback on a stiff material, the amplitude/phase spectroscopy would probably undergo volatile fluctuation, leading to unstable imaging. With the third mode amplitude set for topography imaging, it would be difficult for the feedback to maintain the prescribed amplitude since a large cantilever position variation is required for different sample moduli. With the first mode amplitude set for topography feedback, the amplitude and the phase of the second mode vary monotonically with sample modulus or viscosity in comparison with the third or the fourth mode, which is suitable for compositional contrast imaging. These results would provide useful guidelines for optimum imaging in bimodal AFM measurements.

Elements of language in the kalophonic heirmoi of Macarie the Hieromonk and Visarion the Confessor

Abstract The tradition of kalophonic eirmoi has at least two brand representatives in the Romanian Principalities. First of all, Macarie the Hieromonk, but also one of his disciples, Visarion the Confessor. Both lived or worked in the great lavra of the Neamț Monastery, one of the most important spiritual and cultural centers known to the pan-Orthodox world. The intrigue that gives rise to this material is the fact that these kalophonic eirmoi are not only exegeseis or adaptations in Romanian, but also enrichments, melodic processing that reveals individual or common stylistic features, elements of musical language, characteristics of Neamț Monastery tradition and more. The present study therefore intends to identify some of these stylistic elements and compositional techniques of the two composers who deeply marked the Romanian psaltic tradition, in the compositional genre of kalophony, using as study material some kalophonic eirmoi belonging to the plagal of the fourth mode.

A Descriptive Study to Assess the Impact and Perception of Online Classes on Student Community Pan India during COVID-19

Introduction:During the COVID-19 pandemic, online classes in India as in other parts of the world, became a prioritised source for learning. The researchers in the present study attempted to assess the perception of online classes including their impact and challenges amongst the students. Methodology: A quantitative approach using descriptive sample survey research design was incorporated to conduct the study. Subjects were students chosen from school and university. A structured questionnaire as Google Form was used to collect primary data. Descriptive statistics was employed to analyse the data. Results: 97% of students spent 2 to 7 hours daily for online classes. Online classes give the right theoretical and practical experience as expressed by 55.4% and 21% respectively. 62% of students perceive that online grading system is less effective than offline grading system. Half of the subjects prefer face to face learning and one fourth preferred hybrid mode. 67.5% of students opined that online classes do not allow adequate interaction with the teachers. Among health impacts, 68%, 38%, 43% and 59% of the students reported eye, ear, and sleep and socialisation problems respectively. 74% of them reported drastic change in eating habits, while 76% of the subjects reported weight gain; posture problems were reported to be faced by 98 (62%) students; 57 (64.3%) reported pain in the back of the neck, 52 (58.2%) reported low back pain, 42 (42.9%) reported pain during forward bending of shoulders, and 26 (26.5%) complained of stiff shoulders. Conclusion: Online classes at the present time are not considered a preferred mode of learning by students. The students identified various restrictions of online classes towards the understanding of subjects, limiting interaction with teachers and students asserted many negative impacts of prolonged online classes on their health.

Numerical investigation of transonic buffet on a prescribed-pitching OAT15A airfoil

The transonic buffet over a prescribed-pitching OAT15A airfoil was numerically investigated using a well-validated delayed detached eddy simulation approach. The present approach successfully reproduced self-sustained shock wave oscillations. The computational results show that the amplitude of the lift fluctuations in the pitching case is approximately six times that of the fixed case. Compared to the fixed case, the presence of a larger shock motion region, two shock wave interactions, and severe boundary separation give rise to higher pressure and velocity fluctuation levels on the whole upper surface in the pitching case. In particular, the highly disordered flow replaces the periodic vortex shedding in the wake, resulting in the disappearance of the secondary fluctuation in unsteady lift coefficients, which is observed at 2274 Hz in the fixed case. A proper orthogonal decomposition analysis shows that the buffet flow in the fixed case exhibits the feature of regular motion, which is closely related to the coherent flow structure of shock oscillations and Karman vortices. Strong interactions between the Karman vortex structure and the shock oscillations are also observed. Compared to those in the fixed case, the fluctuation amplitudes of the coefficients of the first mode pair and the second to fourth mode pairs in the pitching case are 2.5 times and 5 times larger, respectively, and the energy ratio of the nonlinear component in the total mode energy is significantly increased. Furthermore, the main frequencies of modes 1–10 in the pitching case are all located at the shock buffet frequency or its higher-order harmonics.

Modulated phases of nematic liquid crystals induced by tetrahedral order

Recent theoretical research has developed a general framework to understand director deformations and modulated phases in nematic liquid crystals. In this framework, there are four fundamental director deformation modes: twist, bend, splay, and a fourth mode Δ related to saddle-splay. The first three of these modes are known to induce modulated phases. Here, we consider modulated phases induced by the fourth mode. We develop a theory for tetrahedral order in liquid crystals, and show that it couples to the Δ mode of director deformation. Because of geometric frustration, the Δ mode cannot fill space by itself, but rather must be accompanied by twist or splay. Hence, it may induce a spontaneous cholesteric phase, with either handedness, or a splay nematic phase.

Structures of magnetic excitations in the spin- 12 kagome-lattice antiferromagnets Cs2Cu3SnF12 and Rb2Cu3SnF12

We show the structures of magnetic excitations in spin-1/2 kagome-lattice antiferromagnets Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$ investigated by inelastic neutron scattering in wide energy and momentum ranges. For Cs$_2$Cu$_3$SnF$_{12}$, four single-magnon excitation modes were observed. Low-energy three modes are assigned to be transverse modes and the high-energy fourth mode is suggested to be an amplitude mode. It was found that the broad excitation continuum without a marked structure spreads in a wide energy range from $0.15J$ to approximately $2.5J$ in contrast to the clearly structured excitation continuum observed in the spin-1/2 triangular-lattice Heisenberg antiferromagnet. These findings strongly suggest spinon excitations as elementary excitations in Cs$_2$Cu$_3$SnF$_{12}$. In Rb$_2$Cu$_3$SnF$_{12}$, singlet-triplet excitations from the pinwheel VBS state and their ghost modes caused by the enlargement of the chemical unit cell were clearly confirmed. It was found that the excitation continuum is structured in the low-energy region approximately below $J_{\mathrm{avg}}$ and the almost structureless high-energy excitation continuum extends to approximately $2.6J_{\mathrm{avg}}$. The characteristics of the high-energy excitation continuum are common to both Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$, irrespective of their ground states. The experimental results strongly suggest that the spin liquid component remains in the ground state as quantum fluctuations in Cs$_2$Cu$_3$SnF$_{12}$ and Rb$_2$Cu$_3$SnF$_{12}$.

Observation of Near-Inertial Waves Induced by Typhoon Mitag (2019) on the Southwestern East China Sea Continental Slope

Based on horizontal velocity data recorded by a moored acoustic Doppler current profiler (ADCP) deployed on the southwestern continental slope of the East China Sea (ECS), this study investigates the characteristics of near-inertial waves (NIWs) induced by typhoon Mitag in October 2019. The results indicated that Mitag-induced near-inertial kinetic energy (NIKE) was mainly concentrated above 290 m and was subsurface-intensified; both the maximum velocity and kinetic energy of the NIWs occurred at a depth of 100 m and were 0.21 m/s and 23.01 J/m3, respectively. The rotary vertical wavenumber spectra suggested that both downward and upward energy propagation existed. However, upward energy propagation was much smaller than downward energy propagation, mainly in the 0.007–0.014 cpm wavenumber band. The NIWs had an e-folding timescale of 9.5 days and were red-shifted as a result of the Doppler shift of the Kuroshio. Normal mode analysis suggested that the NIWs were dominated by the first and fourth baroclinic modes, which together accounted for 76.7% of the total NIKE. Spectral analysis showed that although the spectral density of the semidiurnal internal tide (M2) peak overwhelmed that of the NIWs by a factor of approximately 30, the shear strength generated by the NIWs was comparable to that of the semidiurnal internal tide (M2), which plays an important role in upper ocean mixing on the southwestern continental slope of the ECS. In addition, the bicoherence analysis suggested that a harmonic wave (M2–f) was generated via the nonlinear interaction between the NIWs and semidiurnal internal tide (M2), which reflects the energy dissipation mechanism of semidiurnal tides and NIWs on the southwestern continental slope of the ECS.

Estimating the Shear-Wave Velocities of Shallow Sediments in the Yellow Sea Using Ocean-Bottom-Seismometer Multicomponent Scholte-Wave Data

Scholte-wave dispersion analysis is effective at imaging the relatively low shear-wave velocity of shallow marine sediments in marginal seas. The combination of a four-component ocean-bottom-seismometer (OBS) and a towed air-gun source can economically and effectively acquire the marine dispersive seismic data. Extracting higher-order dispersive Scholte wave modes is the most critical problem in the dispersion analysis method. The extremely low shear-wave velocity and severe attenuation in the top hundreds of meters of marginal sea sediment provide an uneven dispersive energy distribution for the four components of the Scholte wave data. The fundamental mode dispersive energy dominates in the vertical component and higher-order modes dominate in the horizontal component. We developed the method of the four-component OBS Scholte velocity-spectra stacking, which can effectively, rapidly, and robustly extract higher-order modes. We imaged the shear-wave velocity structure of complicated shallow marine sediment in the North Yellow Sea using an active OBS seismic profile with a large-volume air-gun array. The fourth higher-order Scholte wave mode can be imaged with the four-component velocity-spectra stacking method with a lower frequency range of 1.0–7.0 Hz. Only the second-order mode can be recognized from the dispersion energy image of the single vertical component. The joint inversion of multimode dispersion curves can provide more accuracy and deeper constraints for the inverted model; thus, the constraint depth with five modes increases by a factor of 1.9 compared with single fundamental mode inversion. The inverted profile suggests a low shear-wave velocity of 123–670 m/s and strong lateral variations within 350 m. The main regional geological structures are shown by the inverted shear-wave velocity structure.

Research Progress on Spread Through Air Spaces of Lung Cancer

气腔扩散（spread through air spaces, STAS）是2015版世界卫生组织（World Health Organization, WHO）肺癌病理分类中首次提出的概念，是指在主瘤体边界外的气腔内出现微乳头状细胞簇、实性细胞巢或单个肿瘤细胞。除传统观念的肺腺癌浸润方式（间质、脉管及胸膜侵犯）外，STAS被确定为第四种肺浸润性腺癌的侵袭模式。近年来，关于STAS的研究成为热点，STAS的存在不仅与肺癌病理组织学、基因突变等因素相关，诸多研究也证实其可作为肿瘤复发及预后的独立相关因素。但是，也有研究认为人为因素可以造成STAS的形态学假象，需在临床工作中注意甄别。本文就STAS的分类、相关病理学特征、基因状态改变以及可能造成STAS假象的人为因素等方面的研究进展予以综述。

Design of a colorless transmitter based on a low-resonant Fabry–Perot Laser for applications in WDM-PON

In this paper, we propose and numerically analyze a colorless transmitter based on a Fabry–Perot Laser Diode (FPLD) with an emission wavelength that is externally tuned using a spectral sliced super luminescent diode. The Fabry–Perot based colorless transmitter is designed to support 100 GHz spaced longitudinal modes with a central wavelength of 1552.525 nm. We study the cavity’s end-facets reflectivity, in order to determine a configuration that allows a low injection power requirement with high transmission performance. Finally, we analyze the transmission performance of the colorless transmitter in a Passive Optical Network (PON) at 2.5 Gbps bit rate with a Non-Return-to-Zero (NRZ) using the following configuration: transmission distances up to 120 km, seeding carrier with 3-dB bandwidths (12.5 GHz, 25 GHz and 50 GHz), two optical channels at 1552.525 nm (central mode) and 1550.125 nm (fourth side mode). The results show that reflectivities of 10% and 90% for the front-facet and the end-facet, respectively, allow a good trade-off between the injection power requirement for tuning the colorless source avoiding the inter-channel interference, and the transmission performance in terms of Bit Error Rate (BER). Thus, in all scenarios, it is possible to obtain Side Mode Suppression Ratios (SMSR) above 30 dB using injection power below to 0.3 mW. Besides, an error-free transmission is achieved for distances over 25 km, in the case with the injection carrier is less than 25 GHz 3-dB bandwidth. Hence, the proposed colorless source can be a suitable feasible solution to implement optical access networks.

Mechanisms responsible for interdecadal variation of the thermodynamic component of East Asian summer monsoon moisture transport

AbstractIn this study, the East Asian summer (June–July–August) monsoon (EASM) atmospheric moisture transport variability under global warming are examined using ERA‐Interim reanalysis data from 1979 to 2019. The total EASM atmospheric moisture transport is decomposed into the thermodynamic (δTH) and dynamic (δMCD) components, which are related to specific humidity and wind velocity, respectively. Based on empirical orthogonal function (EOF) analysis, both the second and the fourth modes of δTH are linked to δMCD, indicating that δMCD can impact the moisture distribution and consequently influence δTH indirectly. Both the first (δTH_EOF1) and the third (δTH_EOF3) modes of δTH show considerable interdecadal changes. It is noted that their principal components exhibit significant increasing trends in recent decades. The response of EASM moisture transport to global warming is probably reflected in these two modes. δTH_EOF1 is associated with negative phases of the Interdecadal Pacific Oscillation (IPO)/Pacific Decadal Oscillation (PDO). This causes the western North Pacific subtropical high (WNPSH) to extend westward and the strengthening of Pacific trade winds. As a result, positive precipitable water anomalies dominate East Asia and δTH_EOF1 is characterized by anomalous southwesterly moisture transport along the East China Sea to southern Japan. δTH_EOF3 corresponds to anomalous moisture transport over the Indochina Peninsula and Japan. The precipitable water associated with δTH_EOF3 in general represents a meridional dipole. Anomalous southward wind induced by the eastward extension of the WNPSH is the main reason for positive (negative) precipitable water anomalies in southern (northern) East Asian. The anomalous circulation associated with the anomalous east–west sea surface temperature gradient over the Indian Ocean affects atmospheric moisture in southern East Asian and can dramatically impact δTH_EOF3.

ТРАНСФОРМАЦИЯ ТЕХНОЛОГИЧЕСКИХ УКЛАДОВ: ТЕОРЕТИЧЕСКИЕ АСПЕКТЫ И СОВРЕМЕННОЕ СОСТОЯНИЕ В АГРАРНОМ СЕКТОРЕ РОССИИ

The problems of development and implementation of high technologies in the manufacturing sector are currently in the spotlight. In our country, the issues of technical and technological modernization, digitalization of the agrarian sector of the economy, the dissemination of the achievements of the fifth technological mode and the transition to the sixth mode, which is based on high technologies, have acquired particular relevance. As part of the scientific study, the economic categories "technological mode" and "techno-economic paradigm" are analyzed, a variety of approaches to the definition of the concept of "technological mode" is established, which indicates both the existing differences in the theoretical knowledge bases of researchers, and the complexity of the concept itself. The author's definition of the category "technological mode" is given in relation to the agricultural sector, taking into account the multi-structural nature of agricultural production that has developed in our country. The properties of the technological mode as a complex socio-economic and technological system are considered, the characteristics of technological modes are presented, the approaches of economists to their periodization, manifestations of technological modes in the agricultural sector of the economy are considered. It has been established that in the domestic agricultural sector, production is carried out within the framework of the second, third, fourth and fifth technological modes with a predominance of the third and fourth. It has been determined that the multi-structural organizational and economic structure of the agro-industrial production in Russia, based on a combination of various forms of management, is a factor that significantly complicates the widespread use of scientific achievements of the fifth technological order and complicates the transition to the "rails" of the breakthrough sixth technological order, and therefore, in our opinion opinion, the implementation of a unified comprehensive state policy for the modernization of the agricultural sector of the domestic economy is required.

МОДАЛЬНЫЙ АНАЛИЗ ШПИНДЕЛЬНОГО УЗЛА НА ОПОРАХ С АНИЗОТРОПНЫМИ УПРУГИМИ ХАРАКТЕРИСТИКАМИ

The article deals with issues related to the influence of options for the design of the spindle assembly (SA), the anisotropy of the radial rigidity of the bearing supports, as well as the spindle speed on the dynamic quality of the machine. The problem statement is formulated as follows: it is necessary to determine the degree of influence of each of the above parameters on the eigen frequencies and vibration modes of the SA. To identify patterns, numerical finite element modeling was carried out in the ANSYS Workbench environment. Variants of the spindle assembly were considered on the example of four models of the CNC lathe model 16B16T1, which differ in the number of structural elements and their location along the length of the spindle. When modeling, the spindle bearings were represented as solid rings with certain elastic properties, varying which the anisotropy of the stiffness of the bearings was realized. During the numerical experiment, the spindle speed was taken into account in the range from 0 to 20,000 rpm. When analyzing the results, the values of six natural frequencies and modes of vibration were considered for each of the models with a change in the rigidity of the front support; Campbell diagrams were obtained, illustrating the dependence of the dynamic characteristics of the spindle on the rotational speed in the specified range. As a result of the research, it was found that design factors have a significant impact on the vibration modes and natural frequencies of the spindle assembly. The simulation showed that when machining in the centers, the fourth natural frequency and modes of vibration will affect the accuracy, and when using a chuck, the first one. Taking into account the fact that the difference between them is more than 2.5 times, then machining in the centers can be carried out at significantly higher cutting speeds. Changing the stiffness of the front support results in a range of natural frequencies for each waveform, which can be up to 200 Hz. Within the specified range, natural frequencies change depending on the spindle speed.

Behavior of precast hollow slabs with different ratios of shear span to effective depth

This study presents an experimental work to examine the effect of shear span to effective depth (a/d) ratio on the behavior of precast hollow slab. For this purpose, tests were performed under the effect of four lines loading of different shear span values to effective depth (a/d) ratios (1.5, 2, 3.5 and 5). This test program involved four full-scale precast prestressed hollow core slabs, with width of 1200 mm, length of 2000 mm, and thickness of 160 mm. The entire set of hollow-core slabs was cast using a high compressive strength concrete of about 79.5 MPa at the age of 28 days. Based on the experimental results, the four failure mode patterns were highly dependent on the (a/d) ratio. These modes include, shear compression failure, flexural failure, and flexure-shear failure. While the fourth failure mode was represented as a combination of anchorage failure and tension shear, this failure pattern was accompanied by slippage of strand reinforcement in concrete. It has been found that a decrement percentage of 19.58% was recorded for different failure loads, whereas the percentage of (a/d) ratio was increased by 233.3%. In addition, the highest first crack load of 110 kN was obtained by sample HCS 1.5 that had the lower (a/d) ratio.

Design of an ultrasonic elliptical vibration device with two stationary points for ultra-precision cutting

Ultrasonic elliptical vibration cutting (UEVC) is a promising hybrid machining technique for ultra-precision cutting. In this paper, an available and propagable design of the UEVC device is proposed through detailed mechanism analysis. The one-dimensional longitudinal vibration theory and Timoshenko beam theory are utilized and the frequency equations of the designed structure are proposed and solved by analytical solution. Thus, the preliminary size parameters of the proposed structure are obtained according to theoretical analysis, and then appropriate structural adjustment and dimensional parameters optimization are performed based on the modal analysis. The resonance frequencies of the longitudinal and bending vibrations can be adjusted to be the same, and two installation holes are determined near the wave node of the second longitudinal vibration mode and the fourth bending mode. Then the resonant frequency and tool trajectory of the manufactured prototype are verified by laser vibrometer, which are consistent with the design. Cutting experiments on pure iron with the proposed device shows that the mirror surface is achieved with nearly no tool wear. Therefore, the proposed design of the device which works in these two resonant modes can be applied for ultra-precision elliptical vibration cutting.

Performance of sequence batch moving bed biofilm reactor under different operation cycle modes for domestic wastewater treatment

Because of the rapid urbanization, the rate of surface water pollution is increasing daily due to the disposal of different wastewater in the water bodies leading to creating major impacts on humans and wildlife. Therefore, there is an urgent need to find a new treatment technology that can meet the challenges of increased sewage discharges and strictness in standard specifications for treated water and the lowest possible construction, maintenance, and operation costs while avoiding all the problems that arise from the use of the traditional technique of active sludge. Sequence Batch Moving Bed Biofilm Reactors (SBMBBR) technology has been developed to overcome these challenges, (SBMBBR) process is one of the most efficient and economical wastewater treatment systems. in our research. the Lab-scale of SBMBBR technology is constructed to treat domestic wastewater. The SBR unit is consist of; Primary clarifier of (150 L), an SBR reactor of (96 L) which were used to treated 80 L/d, at the MBB which used Kaldnes media, was utilized as a carrier in reactor at a media fill ratio equal to 50%. We Was optimize of five operations cyclic mode and choose The fourth cyclic mode is the best for the average efficiency of removal (COD, NH4+-N, TN, TP) was (98.132%), (97.642%), (82.255%), and (92.107%) respectively. Â

On the Optimal Modes for Glucose Droplet Sensing Based on Multi-Modes

In this paper, we demonstrate the optimal multi-modes for glucose droplet (GD) sensing depending on sample (glucose droplet) positions in a half-wavelength ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula> /2) microstrip resonator. Using two different GD positions, i.e., an edge and a center position, in the resonator, the resonant behavior of microwave multi-modes for GD sensing was investigated. GDs with three different concentrations, i.e., 0.1, 0.2, and 0.3 g/ml, were tested in the present experiment. With increasing GD concentration, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{21}$ </tex-math></inline-formula> -level of the edge-positional GD gradually was declined at all resonant modes. For a center-positional GD, the frequency not only was deviated into the high-frequency region, but its <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{21}$ </tex-math></inline-formula> -level also gradually was declined for the second and fourth modes. Based on the experimental results, the resonant behavior indicated the edge-(center-) positional GD had the resolution (~0.01/gmL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> or ~0.05 dB/gmL <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) at the second (second) and third (fourth) modes, respectively. Furthermore, we showed that the edge-positional GD sensing is more suitable when the resonator is associated with an active circuit system, and simultaneous sensing is also possible for different positions in multi-modes.

A study on resonance characteristics of hydraulic structures and buildings conducted using small-size models

Introduction. The study focuses on resonance characteristics of a hydraulic engineering structure, such as a groin, land retention works on an artificial island, and a school building. Any structure, exposed to dynamic effects of natural or man-induced origin, can be validly simulated as a mechanical resonator. Models are made of materials that have electro-elastic properties allowing to measure responses to induced oscillations, or changes in an alternating electric field, and reevaluate the physical characteristics later.&#x0D; Materials and methods. Small-size physical models of structures are made of electro-elastic materials, such as organic glass and ABS plastic, used for 3D printing. A laboratory test bench, composed of an oscillator and a personal computer, used as an oscillograph, was applied to conduct the testing. Mathematical modeling was performed using SolidWorks software packages. Oscillation modes and structural responses, featuring different response amplitudes, were identified. Models of structures were studied in different contexts, including restraint and free bearing.&#x0D; Results. It has been found that frequencies of the first mode of oscillations in a restrained model correspond to the fourth mode of a model in case of free bearing. Mutual correlation of eigenfrequencies of oscillations in small-size models, made of ABS plastic and organic glass, is demonstrated.&#x0D; Conclusions. The applicability of ABS plastic as the material of small-size physical models of buildings and structures has been proven for the purpose of identifying resonance frequencies of the prototypes. The co-authors have developed an integrated physical and mathematical modeling method that entails the use of SolidWorks software packages. This method allows to identify resonance frequencies, which are most dangerous for structures. Different structure support patterns allow to apply the geometric scale to obtain resonance frequencies when translating small-size model results to natural values and, hence, identify the vulnerability of structures to dynamic effects.