Resonant Period Research Articles

Spatio-Temporal Characteristics of Drought and Its Relationship with El Niño-Southern Oscillation in the Songhua River Basin from 1960 to 2019

Drought is a severe natural hazard all over the world, resulting in enormous losses in many aspects, especially in agriculture. It is essential to analyze the spatio-temporal variation of drought and its relationships with the El Niño-Southern Oscillation under a background of global climate change for better drought prevention. The Songhua River Basin (SHRB), which is an important food base in northeastern China that suffered a severe drought in 2020, was chosen as the research site. The standardized precipitation evapotranspiration index (SPEI) was chosen as the drought index to analyze the spatio-temporal variation of droughts in the SHRB by linear regression analysis and T-test using the meteorological data from 1960 to 2019. The cross-wavelet analysis was adopted to reveal the relationship between the SPEI and El Niño-Southern Oscillation indexes (the Niño 1+2 SST Index (SST1), Niño 3 SST Index (SST2), Niño 3.4 SST Index (SST3), Niño 4 SST Index (SST4), and Southern Oscillation Index (SOI)). The results reveal that the changing trends of yearly, spring, summer, autumn, and winter precipitation were 0.56, 1.47 (p < 0.05), 0.13, 0.04, and 0.16 (p < 0.05) mm/a, respectively; the precipitations were higher in the southeastern regions and lower in the western regions, with extreme values of 831.62 mm and 381.69 mm, respectively. The SPEI was significantly increased (p < 0.05) with a gradient of 0.01/a on a yearly scale and were increased in all seasons (significant in winter (p < 0.05)). The drought probability on a yearly scale was dominated by summer and autumn. The SPEI was positively correlated with SST1, SST2, SST3, and SST4 in a different period with a different resonant period and was negatively correlated with the SOI with a short-term period for 3–4 years from 1986 to 1990 and a long-term period for 9–12 years from 1992 to 2010. These results could provide a scientific guide for drought prevention in the SHRB.

Response of Precipitation in Tianshan to Global Climate Change Based on the Berkeley Earth and ERA5 Reanalysis Products

Global climate change has readjusted a global-scale precipitation distribution in magnitude and timing. In mountainous areas, meteorological stations and observation data are very limited, making it difficult to accurately understand the response of precipitation to global climate change. Based on ECMWF Reanalysis v5 precipitation products, Berkeley Earth global temperature, and typical atmospheric circulation indexes, we integrated a gradient descent-nonlinear regression downscaling model, cross wavelet transform, and wavelet correlation method to analyze the precipitation response in Tianshan to global climate change. This study provides a high-resolution (90 m × 90 m) precipitation dataset in Tianshan and confirms that global warming, the North Pacific Pattern (NP), the Western Hemisphere Warm Pool (WHWP), and the Atlantic Multidecadal Oscillation (AMO) are related to the humidification of Tianshan over the past 40 years. The precipitation in Tianshan and global temperature have a resonance period of 8–15 months, and the correlation coefficient is above 0.9. In Tianshan, spring precipitation is determined mainly by AMO, North Tropical Atlantic Sea Level Temperature, Pacific Interdecadal Oscillation (PDO), Tropical North Atlantic Index, WHWP, NP, summer by NP, North Atlantic Oscillation, and PDO, autumn by AMO, and winter by Arctic Oscillation. This research can serve the precipitation forecast of Tianshan and help in the understanding of the regional response to global climate change.

Frequency of Harmony and the Unified Theory of Everything. Across the Universe towards Human Body and Mind with Discovery of Neuroarchitecture Vinci Power Nap® Pendulum as the Biotechnology of the Future

Science and geometry have always developed parallel and interpenetrated. The orbits of the planets around the Sun can be represented by ellipses as a result of the law of gravity. Simple geometric shapes are associated with simple dynamics because this kind of mathematical representation implies an interwoven relationship between the form of an object and the forces acting on it. The author's pioneering empirical observations and research on the biotechnology patented Vinci Power Nap® neuroarchitecture system, led to the a very important notion that this unique combination of a horizontal pendulum motion with a vertical harmonic oscillator, with a man lying inside as a pendulum lens - all together create harmony in the observed resonant frequency and period by presenting two values of the number Phi. If everything in the universe is made of energy, then maybe that energy can be defined in terms of 0,618Hz frequency, which was found in the Vinci Power Nap® pendulum, as a pattern of incessant space fractal transformation, inner fundamental force of nature and the matrix of creation. Feynman’s fine structure constant can relate this golden ratio to quantum physics, leading to quantum biology, quantum gravity, the general theory of unification and even further to the M-Theory, unified field theory, theory of everything (TOE).

Capturing spatial variability in the regional Ground Motion Model of Groningen, the Netherlands

Abstract Long-term exploration of the Groningen gas field in the Netherlands led to induced seismicity. Over the past nine years, an increasingly sophisticated Ground Motion Model (GMM) has been developed to assess the site response and the related seismic hazard. The GMM output strongly depends on the shear-wave velocity (V S ), among other input parameters. To date, V S model data from soil profiles (Kruiver et al., Bulletin of Earthquake Engineering, 15(9): 3555–3580, 2017; Netherlands Journal of Geosciences, 96(5): s215–s233, 2017) have been used in the GMM. Recently, new V S profiles above the Groningen gas field were constructed using ambient noise surface wave tomography. These so-called field V S data, even though spatially limited, provide an independent source of V S to check whether the level of spatial variability in the GMM is sufficient. Here, we compared amplification factors (AF) for two sites (Borgsweer and Loppersum) calculated with the model V S and the field V S (Chmiel et al., Geophysical Journal International, 218(3), 1781–1795, 2019 and new data). Our AF results over periods relevant for seismic risk (0.01–1.0 s) show that model and field V S profiles agree within the uncertainty range generally accepted in geo-engineering. In addition, we compared modelled spectral accelerations using either field V S or model V S in Loppersum to the recordings of an earthquake that occurred during the monitoring period (ML 3.4 Zeerijp on 8 January 2018). The modelled spectral accelerations at the surface for both field V S and model V S are coherent with the earthquake data for the resonance periods representative of most buildings in Groningen (T = 0.2 and 0.3 s). These results confirm that the currently used V S model in the GMM captures spatial variability in the site response and represents reliable input for the site response calculations.

Study on the Resonant Behaviors of a Bottom-Hinged Oscillating Wave Surge Converter

This paper studied the resonant behaviors of a bottom-hinged oscillating wave surge converter (OWSC) as well as the relationship of resonance with the response and capture width ratio (CWR). The time-domain dynamic equation of an OWSC in shallow water based on the boundary element method (BEM) was solved by a Python code, considering the corrected wave surface and the nonlinearities of restoring moment, drag, and friction. The unknown factors, such as wave surface corrected factor and drag coefficient, were effectively calibrated with computational fluid dynamics (CFD) method. An intermediate initial angle in free decay is appropriate for use to determine the natural period. Under regular waves, the resonance occurs near the natural period for the uniform wave amplitude, rather than the uniform wave torque amplitude, and can disappear due to the amplification of Power Take-Off (PTO) friction. Under unit-amplitude regular waves, the period of maximum CWR is relatively close to the period of maximum velocity, but far from the resonant period. Under irregular waves, no stable resonance is observed because the maximum equivalent pitch angle appears at different peak periods of wave spectra with the variation in PTO damping. When the period of a regular wave or the peak period of an irregular wave is close to the natural period, a phase hysteresis of velocity relative to wave torque always occurs.

Model tests and numerical simulations on the parametric resonance of the deep draft semi-submersible under regular waves

Parametric resonance of the deep draft semi-submersible (DDS) under regular waves are investigated experimentally and numerically. Special focus is put on the occurrence of parametric resonance under weak or failure mooring condition. Firstly, model tests with and without mooring chains are conducted in wave flume. From results of model without mooring chains, it is observed that parametric resonance occurs when wave period is about the natural period of heave and half of the natural period of pitch or roll. The steady amplitude of parametric resonance is larger under higher wave. In heading waves, parametric resonance occurs in roll direction, while parametric resonance occurs in both roll and pitch direction for beam wave. For the model with 12 mooring chains, parametric resonance does not occur under strong mooring restriction. Whereas for the model with four mooring chains representing a failure mooring condition, parametric resonance occurs in pitch direction. Then, numerical simulations under cases same as experiments are conducted using a potential-theory based weakly nonlinear model. Parametric resonance is successfully reproduced numerically. Furthermore, through comparison with experiments, it is found that the numerical model accurately predicts steady amplitudes and occurring wave periods of parametric resonance except for cases with four mooring chains.

THE RESONANT STRUCTURE OF SOLAR SYSTEM - HALF A CENTURY OF REFLECTION AND DISCUSSION

The article summarizes ideas of A.M. Molchanov about cooperative property of the Solar system - its “maximum synchronicity”. The general scientific significance of the principle of “maximum synchronicity” is discussed on an interdisciplinary basis. It is noted that the considered theoretical ideas have received numerous observational confirmations. In recent decades, it has been shown that: solar activity are involved in general dynamic of solar system; special resonance periods were found in the dynamics of the solar system; found correlations of variations in the total magnetic field of the Sun and the dynamics of planets; the important role of synchronization in the formation of the fine structure of Saturn's rings is shown. Synchronicity is found in many phenomena in the habitat of our planet.

Energy conversion and hydrodynamic analysis of multi-degree-of-freedom wave energy converters integrated into a semi-submersible platform

The hybrid concept of multi-type wave energy converters provides viable solutions to improve the wave energy exploitation per-unit area and reduce the Levelised Cost of Electricity. In this paper, a multi-degree-of-freedom hybrid system combining an oscillating wave surge converter and two oscillating buoys, is proposed and integrated into a semi-submersible platform to be suitable for both nearshore and offshore zones. The hydrodynamic characteristics of the hybrid system is investigated by establishing a three-dimensional numerical wave tank in the context of computational fluid dynamics theory including dynamic overset grid scheme, with emphasis on its overall characteristic and respective characteristic of each device. The corresponding physical experiments are also performed to cross-check the numerical solutions, and help to further explain un-simulated phenomenons. By comparing with the single-degree-of-freedom wave energy system, the total power capture efficiency of the hybrid system increases over a broader range of wave periods due to the combination of different resonant periods. The optimal power take-off damping for the oscillating buoy and the oscillating wave surge converter decreases and is insensitive with wave height, respectively. The oscillating buoy device with larger radius and deeper draft demonstrates higher energy absorption which reduces wave loads on the platform. Both the total capture efficiency and the effective frequency bandwidth increase initially to maximum values and then decrease with increasing the geometric radius of the oscillating wave surge converter. The findings of this paper validate the feasibility of different-type wave energy converters integrated into floating platforms and show their synergy.

The Gran Sasso fault system: Paleoseismological constraints on the catastrophic 1349 earthquake in Central Italy

We investigated the late Upper Pleistocene activity of the eight main faults that comprise the active, dip-slip Gran Sasso fault system (GSFS) in the Gran Sasso d'Italia Massif (central Italian Apennines; 2912 m a.s.l.). We carried out novel paleoseismological analyses at four sites of three different fault segments, and reviewed the data of the previous results for three other segments. We carried out several topographic profiles across the offset hillslopes, alluvial fans, glacial cirques, moraines, and valley floor. Through the dozen radiocarbon datings that were combined and cross-checked with many other ages published in previous studies, we have provided robust slip-rates and reconstructed the Holocene seismic history of this fault system. Paleoseismic analyses revealed the presence of three consecutive earthquakes since the onset of the Late Holocene, which were separated by 3.3 ky and 2.2 ky, respectively. The last one occurred in the 13th–14th century CE, a time-span that fits with the catastrophic 1349 seismic sequence.Our review of the macroseismic intensity distribution of this sequence indicates the existence of two distinct mesoseismic areas; a southern one that was already related to the Aquae Iuliae fault rupture (Abruzzi-Campania-Molise borders), and a northern one that robustly matches the hanging-wall of the Gran Sasso fault system. Given the length of this fault system, we estimated Mw 7 for its entire rupture, which accounts for the total destruction of L'Aquila and the neighboring villages. This also accounts for the strong effects and severe damage suffered by several settlements in the para-Tyrrhenian far field, especially to buildings characterized by long fundamental resonance periods, as seen for the monuments of Rome.Although characterized by long recurrence times (2.8 ± 0.5 ky), our results suggest that as for all of the main silent faults of the eastern set of active structures in the central Apennines, this fault system has one of the largest seismogenic potentials of the whole Apennine chain, with seismic risk implications extended even to its far-field.

Numerical analysis of wave\u2013structure interaction of regular waves with surface-piercing inclined plates

The Mocean wave energy converter consists of two sections, hinged at a central location, allowing the device to convert energy from the relative pitching motion of the sections. In a simplified form, the scattering problem for the device can be modelled as monochromatic waves incident upon a thin, inclined, surface-piercing plate of length L' in a finite depth d' of water. In this paper, the flow past such a plate is solved using a Boundary Element Method (BEM) and Computational Fluid Dynamics (CFD). While the BEM solution is based on linear potential flow theory, CFD directly solves the Navier–Stokes equations. Problems of this type are known to exhibit near-perfect reflection (indicated by a reflection coefficient |R|approx 1) of waves at specific wavenumbers k'. In this paper, we show that the resonant motion of the fluid induces large hydrodynamic forces on the plate. Furthermore, we argue that this low-frequency resonance resembles Helmholtz resonance, and that Mocean’s device being able to tune to these low frequencies does not act like an attenuator. For the case where the water is deep (d'>lambda '/2, where lambda '=2pi /k'), we find excellent agreement between our simulations and previous semi-analytical studies on the value of the resonant wave periods in deep water. We also find excellent agreement between the excitation forces on the plate computed using the BEM model, analytical results, and CFD for large inclination angles (alpha > 45^circ ). For alpha le 15^circ , both methods show the same trend, but the CFD predicts a significantly smaller peak in the excitation force compared with BEM, which we attribute to non-linear effects such as the non-linear Froude–Krylov force

An effective resonant wave absorber for long regular water waves

A new type of resonant wave absorber is proposed to absorb long regular waves more effectively in physical wave flume based on the mechanism of gap resonance. The wave absorber is designed by placing a fixed box in front of the end of a physical wave flume, thereby forming a gap between the box and the end wall. To achieve optimal performance, both resonant and damping conditions for the wave absorber should be matched. The resonant condition requires that the resonant period of the fluid confined in the wave absorber closely mirrors the incident wave period, and the damping condition requires the introduction of appropriate damping into the absorber. The experimental results show that the present short-length resonant wave absorber performs well within a wide range of wave period T ∈ [1.37 s, 3.63 s], which is difficult to be achieved with traditional passive wave absorbers. The reflection coefficient Cr, ratio of wave heights of reflected to incident, remained smaller than 0.1 for the present wave absorber when encountering long waves with 7.04 m in experiments with a typical water depth h = 0.4 m. The working principle of resonant wave absorber is further clarified by revealing the wave components outside the wave absorber.

Occurrence of pressure-forced meteotsunami events in the eastern Yellow Sea during 2010–2019

Abstract. This study examined the occurrence of meteotsunamis in the eastern Yellow Sea and the conceptual framework of a monitoring/warning system. Using 1 min intervals of mean-sea-level pressure and sea-level observations from 89 meteorological stations and 16 tide gauges between 2010 and 2019, a total of 42 pressure-forced meteotsunami events were classified. Most meteotsunamis (71 %) displayed a distinct seasonal pattern occurring from March to June, and intense meteotsunamis typically occurred at harbor tide gauges. The occurrence characteristics of the meteotsunamis were examined to improve the meteotsunami monitoring/warning system. Air pressure disturbances with speeds of 11–26 m s−1 and NNW–SW directions were conducive to meteotsunami generation. Most meteotsunamis (88 %), as well as strong meteotsunamis with a wave height exceeding 40 cm (19 %), had dominant period bands of less than 30 min, containing the resonant periods of harbors in the eastern Yellow Sea. Thus, the eastern Yellow Sea is a harbor-meteotsunami-dominated environment, characterized by frequent meteotsunami occurrences and local amplification in multiple harbors. This study can provide practical guidance on operation periods, potential hot spots, and risk levels to monitoring/warning system operators in the eastern Yellow Sea.

Analysis and Control of Critical Conduction Mode High-Frequency Single-Phase Transformerless PV Inverter

This article presents a critical conduction mode (CRM) single-phase transformerless full-bridge inverter in a residential photovoltaic system. The CRM full-bridge inverter in bipolar mode features zero-voltage switching capability for the whole line cycle. This enables the inverter to push switching frequency up to hundreds of kHz and achieve high power density with high efficiency. However, CRM operation incurs nonconstant common mode (CM) voltage during the resonant period, causing high frequency leakage current. To minimize the leakage current, a new switching modulation strategy is proposed introducing triangular current mode (TCM) near the ac voltage zero crossing. The switching modulation scheme alleviates the CM voltage by shortening the resonant period and consequently reduces the leakage current. Then, discontinuous conduction mode is inserted between the CRM and TCM operation regions to improve light load efficiency. In this article, the basic operation principle of the CRM full-bridge inverter, impacts of CRM operation on the leakage current, and details of the proposed switching modulation method are discussed. Experimental results with a 2.4-kW prototype built with GaN devices validate its performance.

Low-threshold wavelength-tunable ultraviolet vertical-cavity surface-emitting lasers from 376 to 409 nm

Optically pumped wavelength-tunable vertical-cavity surface-emitting lasers (VCSELs) operating in the ultraviolet A (UVA) spectrum were demonstrated. The VCSELs feature double dielectric distributed brag reflectors and a wedge-shaped cavity fabricated using the substrate transfer technique and laser lift off, resulting in a graded cavity length in one device. A resonant period gain structure is used in the InGaN/GaN multi-quantum well active region to enhance the coupling between the cavity mode field and the active layers. The optical field inside the cavity is modulated by the cavity length; thus, tunable lasing at different wavelengths is realized at different points of a single VCSEL chip. The lasing wavelength extends from 376 to 409 nm, covering most of the UVA band below the band gap of GaN. The threshold pumping power density of the UVA VCSELs at different wavelengths ranges from 383 to 466 kW/cm2, which is among the lowest values for ultraviolet (UV) VCSELs. This study is promising for the development of small-footprint, power-efficient UV light sources.

Temporal Variations in Karst Spring Flow and Its Response to Climate Change in the Taihang Mountains, China

The variation in flow for the Xiaonanhai spring and its main controlling factors were statistically examined using Mann-Kendall trend analysis, rescaled range (R/S) analysis, Morlet wavelet analysis, and cross-wavelet analysis. The annual spring flow has exhibited a continuous and significant downward trend since 1997, which varies temporally, with main periods of 14–17 years and 25–28 years. There is a positive correlation between the spring flow and precipitation (p<0.01). The results of the cross-wavelet analysis and the wavelet coherence analysis show that the main resonance periods of the precipitation and spring flow were present in 1983–1995 and 1998–2015, respectively. A stepwise regression model and a back propagation neural network model were established based on the analysis of the flow changes in order to predict the spring flow under the expected changes in precipitation. The simulation precision of the neural network structure is better than that of the stepwise regression model. Therefore, the neural network model can be used to predict the dynamic flow of the Xiaonanhai spring under the effects of future climate change.

Partial Series Resonance Pulse Commutated Current-Fed Three-Phase Current Sharing DC–DC Converter: ZCS Analysis, Design, and Experimental Results

A three-inductor current-fed converter leveraging short pulse series resonance to facilitate zero-current switching (ZCS) and voltage clamping of the semiconductor devices is proposed and investigated in detail. The circuit exploits series resonance characteristics during conduction overlap of any two switching signals that naturally reduce the current in outgoing switch to zero accomplishing zero-current turn- off . It succeeds in natural switch voltage clamping eliminating the traditional snubber requirement. Owing to the short resonance period, circulating current through the converter limits the conduction losses particularly at light load, thus improving the light-load efficiency. In addition, current-sharing topology offers reduced current stresses through the primary side devices and simpler gate driving requirements because of common source grounded with power supply. Detailed analysis and design are reported. Experimental results from 1-kW proof-of-concept hardware prototype are established to validate the projected claims and confirm the performance and the efficacy of proposed converter. This concept has been verified in single-phase topologies and first time studied for three-phase current-fed circuit.

Combining time varying filtering based empirical mode decomposition and machine learning to predict precipitation from nonlinear series

In recent years, due to the influence of human activities and changing climate conditions, precipitation time series have had increasing non-stationarity and randomness. Therefore, the scientific and accurate prediction of precipitation has become increasingly difficult. To improve precipitation prediction accuracy, nonlinear precipitation data was decomposed into several subcomponents via three decomposition methods (time varying filtering based empirical mode decomposition (TVF-EMD), wavelet transform (WT), and complementary ensemble empirical mode decomposition (CEEMD)). Then, the Elman neural network (ENN) was used to construct TVF-EMD-ENN, WT-ENN, and CEEMD-ENN models to predict the subcomponents of precipitation. Finally, these three models were applied to the monthly and daily precipitation series from different meteorological stations. The results showed that TVF-EMD-ENN made relatively stable predictions for monthly and daily precipitation, and was better than WT-ENN, CEEMD-ENN, and other models. Predictions for Turpan station were generally poor, likely due to the discontinuous resonance periods and abnormal resonance periods between precipitation and climate indices. Overall, the predictions by TVF-EMD-ENN were better, which was clearly reflected in the variance contribution rates (VCR) of high-frequency subcomponents, which were lower than those of WT and CEEMD. Parameter sensitivities of TVF-EMD indicated that the bandwidth threshold (BT) and the b-spline order (BSO) had a strong influence on model performance, and that BT and BSO should remain within 0.15–0.50 and 15–65, respectively. This study has provided a new approach to precipitation prediction that is better equipped to handle non-stationarity and randomness.

Rotational Seismology with a Quartz Rotation Sensor

Abstract We describe the construction and performance of a new high-precision ground- or platform-rotation sensor called the Quartz Rotation Sensor (QRS). The QRS is a mechanical angular accelerometer that senses rotational torque with an inherently digital, load-sensitive resonant quartz crystal. The noise floor is measured to be ∼45 pico-radians/root (Hz) near 1 Hz, and the resonant period of the sensor is about 10 s, making it a broadband sensor. Among similarly sized broadband rotation sensors, this represents more than two orders of magnitude improvement in noise floor near 0.1 Hz. We present measurements of rotational components of teleseismic waves recorded with the sensor at a vault. The QRS is useful for rotational seismology and for improving low-frequency seismic isolation in demanding applications such as the Laser Interferometer Gravitational-Wave Observatories.

The solution of the long-wave equation for various nonlinear depth and breadth profiles in the power-law form

Long waves bring many important challenges in the ocean and coastal engineering, including but are not limited to harbor resonance and run-up. Therefore, understanding and modeling their dynamics is crucially important. Although their dynamics over various types of geometries are well-studied in the literature, the study of the geometries with power-law variations remains an open problem in this setting. With this motivation, in this paper, we derive the exact analytical solutions of the long-wave equation over nonlinear depth and breadth profiles having power-law forms given by h(x)=c1xa and b(x)=c2xc, where the parameters c1,c2,a,c are some constants. We show that for these types of power-law forms of depth and breadth profiles, the long-wave equation admits solutions in terms of Bessel functions and Cauchy–Euler series. We also derive the seiching periods and resonance conditions for these forms of depth and breadth variations. Our results can be used to investigate the long-wave dynamics and their envelope characteristics over equilibrium beach profiles, the effects of nonlinear harbor entrances and angled nonlinear seawall breadth variations in the power-law forms on these dynamics, and the effects of reconstruction, geomorphological changes, sedimentation, and dredging to harbor resonance, to the shift in resonance periods and to the seiching characteristics in lakes and barrages.

Spatiotemporal Response of Hydrological Drought to Meteorological Drought on Multi-Time Scales Concerning Endorheic Basin.

Under the controversial background of “Northwestern China is gradually developing towards warm and humid”, how hydrological drought responds to meteorological drought at the endorheic basin is of great significance. To address this problem, we first analyzed the spatiotemporal variation of meteorological and hydrological droughts at Tarim Basin River from 1960 to 2014 by using the daily standardized precipitation index (SPI) and daily standardized terrestrial water storage index (SWSI) based on the reanalysis data. Thereafter, we explored the spatiotemporal response of hydrological drought to meteorological drought on the multi-time scale by using the cross-wavelet transform method, Ensemble Empirical Mode Decomposition (EEMD), and correlation analysis. We find that: (1) both meteorological and hydrological droughts signified a gradually weakened trend in time; (2) meteorological and hydrological drought have significant resonance periods on the 10-month time scale and the 8-year time scale; (3) hydrological drought generally lags behind the meteorological drought by 7 days in plains areas, while it can last as long as several months or even a year in mountainous areas.