Frequency Curves Research Articles

Numerical simulation and analysis of fluid-structure interaction on 3D MHKF-180 and NACA4418 cavitating hydrofoils

A numerical investigation of structural and hydrodynamic performance of 3D stainless steel MHKF-180 and NACA4418 cavitating hydrofoils has been carried out using one-way fluid-structure interaction (FSI). Under the application of hydrodynamic load, the structural performance of MHKF-180 is compared with NACA4418 in terms of natural frequency, maximum tip deformation, and von Mises stress, whereas hydrodynamic performance is compared in terms of lift coefficient, drag coefficient, lift to drag ratio, pressure coefficient, and Strouhal number. The simulation is performed at a chord-based Reynolds number, Re = 750000, for different cavitation numbers and angles of attack using ANSYS software. The present result is validated by comparing the natural frequency and pressure coefficient curve of the non-cavitating NACA66 hydrofoil and lift coefficient and drag coefficient of cavitating NACA4412 hydrofoil with the available experimental data. The fluid flow is simulated using the unsteady-Reynolds-averaged-Navier-Stokes (URANS) equations and Realizable k −ε turbulence model. The cavitation effect on the hydrofoil is studied using the Zwart-Gerber-Belamri cavitation model. Comparing the maximum tip deformation under cavitation, the MHKF-180 shows larger tip deformation than NACA4418 hydrofoil. However, the hydrodynamic performance, assessed in terms of lift coefficient, MHKF-180 gives a better than NACA4418 under the cavitating condition at different angles of attack and for different cavitation numbers.

Magnetoelastic simultaneous resonance of axially moving plate strip under a line load in stationary magnetic field

This paper studies the primary-internal simultaneous resonance of the moving ferromagnetic thin plate with the action of an alternating line load in a transverse stationary magnetic field. Based on the theory of thin plates, expressions of strain energy and kinetic energy of the thin plate are given. According to the theoretical magnetoelastic model for ferromagnets, the calculation formula for electromagnetic force is derived. The magnetoelastic coupling nonlinear vibration equation is established by using Hamilton’s principle. Duffing-type nonlinear differential equations are obtained for the clamped-hinged plate strip by applying the Galerkin method. The steady-state response of the system with primary resonance and 1:3 internal resonance is given by using the method of multiple scales, and the stability of steady-state solutions are analyzed according to the theory of Lyapunov stability. The primary-internal simultaneous resonance characteristics of the plate strip are presented through numerical examples. Results show that: energy exchange between the first two modes is available and the first mode dominates; jump phenomena exist in amplitude–frequency curves; both the values of steady solutions and the multi-valued regions of amplitude change with varieties of physical parameters; and numerical results agree with analytical results, which verifies the reliability of analytical research method in this paper.

Application of a Fractional Instantaneous Unit Hydrograph in the TOPMODEL: A Case Study in Chengcun Basin, China

The movement of water flow usually has history and path dependence. Fractional calculus is very suitable for describing the process with memory and hereditary properties. In this study, the order of the differential equation in the Nash confluence system was extended from integer order to fractional order. On the basis of the Laplace transform, the fractional instantaneous unit hydrograph was obtained, which was used to describe the long-term memory of the basin confluence system. Furthermore, the enhanced TOPMODEL (FTOP) model was obtained by applying the fractional instantaneous unit hydrograph as the surface runoff calculation. Taking Chengcun Basin in China as an example, the FTOP model was used to simulate the daily runoff and 22 floods from 1989 to 1996. The simulation results were compared with two original TOPMODEL models (the NTOP and ITOP models). The results show that in the daily runoff simulation, the Nash–Sutcliffe efficiency (NSE), relative error (RE), and root mean square error (RMSE) of the FTOP model were 0.82, −11.14%, and 15.25 m3/s, respectively, being slightly better than the other two TOPMODEL models. According to the hydrologic frequency curve, the measured daily runoff was divided into different flow levels. It was found that the FTOP model can improve the simulation effect of the medium-flow (frequency between 10% and 50%) and low-flow (frequency more than 50%) sections to a certain extent. In the flood simulation, the average runoff depth relative error (RDRE), peak discharge relative error (PDRE), peak occurrence time error (POTE), and NSE of 22 floods were 1.99%, 14.06%, −1.27, and 0.88, respectively, indicating that the simulation effect had been improved. Especially in NSE, the improvement was more prominent, meaning that the FTOP model can better simulate the flooding process. However, the flood peak and runoff depth simulation effect were not significantly improved. These conclusions indicate that the confluence method using the fractional instantaneous unit hydrograph as the TOPMODEL model can improve the simulation effect.

The intensification of short-duration rainfall extremes due to climate change – Need for a frequent update of intensity–duration–frequency curves

Numerous studies have investigated future changes in extreme precipitation by employing climate models. However, trends in extreme short-duration (20–180 min) rainfall intensities, that is, design storm rainfall intensities used for stormwater infrastructure design, have received considerably less attention despite their importance. This study quantified the effect of climate change on design storm intensity based on observations. Trends were investigated for diverse short-term rainfall durations, ranging from 20 to 180 min, at 11 meteorological stations in Northern Europe, Estonia. The Mann-Kendall test and Sen’s slope estimator were used to detect trends and calculate the trend magnitudes by analyzing a 70 year period of high-resolution temporal observed rainfall data. The Sen’s slope indicated a positive magnitude of slopes for all the durations and stations investigated, and two stations in Northeast Estonia showed significantly increasing trends (p < 0.05). Unsurprisingly, the spatial distribution of trends revealed notable variations from station to station, as extreme rainfall events are heavily localized due to cloudburst. Despite this variety, it can be generalized that the annual maximum rainfall intensities in Estonia have increased at an average rate of 4 % per decade due to changing climate conditions, invariant of the rainfall duration analyzed. The use of decades enables to easily keep the intensity–duration–frequency curves updated, and it is more practical and relatable for engineers as well. The findings of this study provide critical knowledge for urban water management decision-makers, indicating the need to frequently update urban design criteria to design climate resilient urban infrastructure.

The Recycling and Reuse of Natural Materials: Sound Absorbing Box Patterns That Use Waste from Olive Tree Pruning

The agricultural activity of pruning olive trees generates waste which, due to long-standing practices and unawareness of the consequences, are burned on site, thereby producing CO2 emissions in the atmosphere. Therefore, in order to prevent environmental pollution and a waste of resources, the aim of this research investigation was to highlight some alternative uses of the pruning of olive trees waste. This work focuses on recycled and reused by-products as a secondary raw material for the implementation of interior components that can be used for indoor acoustic correction purposes and evaluates their potential as absorbing materials, without overlooking the aesthetic dimension. In this paper, different configurations based on plywood frames with loose olive pruning chips used as a filler, namely, modules and sub-modules, were investigated. Moreover, other technological details, that is, the influence of a Tissue-Non-Tissue (TNT) layer and a spray film coating applied over the external surface of the loose material, were measured. Sound absorption measurements were conducted inside a small-scale reverberation room (SSRR) and the experimental results demonstrated that the samples, for the given thickness, have weighted sound absorption values (αw) of between 0.15 and 0.35 and single third-octave band values that can reach higher values than 0.50 above 500 Hz. The frequency curves and weighted values of the samples in which the influence of TNT and the spray film coating were tested remained unchanged. This is a design aspect that allows absorbing surfaces to be modeled and integrated with existing walls, while maintaining the acoustic performance and the specific aesthetic features of the loose material.

Face Mask Identification Using Spatial and Frequency Features in Depth Image from Time-of-Flight Camera.

Face masks can effectively prevent the spread of viruses. It is necessary to determine the wearing condition of masks in various locations, such as traffic stations, hospitals, and other places with a risk of infection. Therefore, achieving fast and accurate identification in different application scenarios is an urgent problem to be solved. Contactless mask recognition can avoid the waste of human resources and the risk of exposure. We propose a novel method for face mask recognition, which is demonstrated using the spatial and frequency features from the 3D information. A ToF camera with a simple system and robust data are used to capture the depth images. The facial contour of the depth image is extracted accurately by the designed method, which can reduce the dimension of the depth data to improve the recognition speed. Additionally, the classification process is further divided into two parts. The wearing condition of the mask is first identified by features extracted from the facial contour. The types of masks are then classified by new features extracted from the spatial and frequency curves. With appropriate thresholds and a voting method, the total recall accuracy of the proposed algorithm can achieve 96.21%. Especially, the recall accuracy for images without mask can reach 99.21%.

An 11.6aF/kPa Mechanical Stress Sensor With 0.808% Temperature-Drift Oscillator for Flip-Chip Packaging

During the package processes, including chip attachment and encapsulation, the stress caused by the thermal and mechanical load is usually generated in integrated circuit chips. This brief developed a mechanical stress sensor in a standard 180nm CMOS process for runtime stress measurement. The contributions done in this brief are summarized as follows: 1) A temperature-compensation RC oscillator circuit converts the warpage of the die induced by the mechanical stress into the frequency output. It even can measure the thermally induced stresses with a wide temperature range. The oscillator has a frequency variation of −0.808% from temperature stability measurements from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 40^{\circ }\text{C}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$120^{\circ }\text{C}$ </tex-math></inline-formula> . 2) Rather than the complicated calibrations and advanced measurement equipment, the frequency can be easily measured with the chip area less than 0.569 mm2 and the power consumption less than 22.9 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> . 3) As for the sensing array, the sensitivity and stability of the metal-insulator-metal (MIM) and metal–oxide–metal (MOM) capacitors are verified. The measured average sensitivity of the test chip using a MIM capacitor with 0.1736 Hz/kPa is more sensitive than that using a MOM capacitor with 0.102 Hz/kPa. The linear fit curves of the output frequency have the coefficient of determination ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}^{2}$ </tex-math></inline-formula> ) of 0.9983 for MIM and 0.9959 for MOM, indicating an excellent linear response of the sensor circuit.

Regionalization of IDF Curves by Interpolating the Intensity and Adjustment Parameters: Application to Boyacá, Colombia, South America

Intensity, duration and frequency (IDF) curves are necessary tools for the design and construction of hydraulic projects. However, the pluviographic records needed to determine the IDF curves do not exist or are scarce. This research presents the regionalization of the IDF curves for the department of Boyacá, Colombia, which is made up of 16 municipalities including the provincial capital, Tunja. For the regionalization, the adjustment parameters (u and α) of the IDF curve stations in the study area were used. In the case of regionalization by the parameters found for the construction of the IDF curves, estimation methods with ordinary moments means and maximum likelihood were used. The regionalization and interpolation of the data were performed with Arcgis software. The resulting isoline maps were made in the case of regionalization intensities, and each map is associated with a different return period and duration to construct the IDF curves in the studied area. In the case of the regionalization maps, the parameters associated with each individual parameter were performed last. The results show that the use of IDF curve data is more accurate and reduces errors in the design. With the methods proposed in this study, IDF curves can be constructed for any site of interest that does not have rainfall stations.

Pre-quake frequency characteristics of Ms ≥7.0 earthquakes in mainland China

In this study, natural orthogonal expansion was performed on earthquake frequencies to compute the pre-quake frequency fields of 9 Ms ≥7.0 earthquakes in mainland China from 1980 to 2020. The temporal and spatial pre-quake anomalies of these earthquakes were extracted from their frequency fields. We found that the majority of pre-quake temporal anomalies (i.e., variations exceeding two-times the absolute mean square error) of a strong earthquake are condensed within the first four frequency fields, and typically comprise multiple components. The temporal factor of the first frequency field usually accounts for the largest proportion of these anomalies (40%–60% of the entire field). Most Ms ≥7.0 earthquakes exhibited long-term anomalies 5–8 years before their occurrence; some presented medium-term anomalies 1–2 years prior to the quake, and only a few presented short-term and imminent anomalies (≤3 months before the quake). Anomalous seismic hazard zones have high-gradient turning points in regional frequency-field contour maps, and the epicenters of strong earthquakes are often located in areas containing active faults that have contour values. Through the comparison of seismic frequency field and the traditional method of regional seismic activity frequency (3 months), it is shown that the frequency-field time factor has the advantages of diversified and rich abnormal information. The slope comparison between the frequency field and the cumulative frequency curve shows that the frequency anomaly time of the two is consistent, and the conclusion is reliable. Therefore, the seismic frequency method can predict the occurrence time and location of strong earthquakes, which is closer to the predictable seismic model.

Effects on Frequency Stability of Power System for Photovoltaic High-Penetration Ratio Grid-Connected Power Generation

In this paper, the effects of three typical operation modes, namely short-circuit fault, load change, and chemical energy storage on the frequency of a regional power grid after photovoltaic asynchronous interconnection were studied with different penetration ratios, taking the power grid in Northern Henan Province as the research object. It was found that with an increase in the photovoltaic penetration ratio, the maximum value of the system frequency and the fluctuation amplitude gradually increased, and the power grid system in Northern Henan became less and less stable. With an increase in the penetration ratio, the peak value of the system frequency at the corresponding node gradually increased, and the valley value gradually decreased. With an increase in load, the peak value of the frequency curve gradually increased, and the valley value gradually decreased. When photoelectricity was connected to the grid through chemical energy storage, the system stability during a short-circuit fault and load change operation was significantly improved. Compared with that before energy storage, the frequency amplitude of the system after energy storage was reduced to approximately one tenth of the original. Compared with the case before energy storage, when the load changed, the frequency amplitude of the system decreased to approximately a quarter of the original.

Performance evaluation of Standardized Copula‐based Drought Index with Reconnaissance Drought Index and Standardized Precipitation Temperature Index using severity–duration frequency curves over Balochistan, Pakistan

AbstractDrought and aridity are good measures to study climate change that are measured using several indices. In this study, the performance of Standardized Copula‐based Drought Index (SCDI) is compared with Standardized Precipitation Temperature Index (SPTI) and Reconnaissance Drought Index (RDI) for measuring drought in Balochistan province of Pakistan. These standardized drought indices combine the outcomes of De‐Martone Aridity Index (DAI) and UNEP Aridity Index (UAI). SCDI is calculated using probability distributions and copula models that combine the outcomes of UAI and DAI utilizing data of precipitation, potential evapotranspiration (PE), and temperature. Climate data from nine including arid and humid metrological stations are used to study drought conditions in Balochistan province. SCDI outcomes are graphically and numerically compared with SPTI and RDI. Selected drought indices are compared based on frequency of drought and wet events occurred in moderate, severe, and extreme drought categories, which indicate that SCDI has maximum number of events in these categories. It gives better results due to the utilization of more climate data as compared to RDI and SPTI. Severity–duration frequency curves are used to find future projections which shows that drought severity and drought duration have increasing trend with the passage of time. The indices have more differences in results of arid stations. The results indicate that there are no significant chances of drought at lower time scales, but the chances increase with the increase in time scale. The SCDI may also be more useful for agricultural and hydrological droughts due to temperature and PE variables. This study's results will be helpful for climate planning in Balochistan province.

Correction to: Regionalization of rainfall intensity–duration–frequency (IDF) curves with L-moments method using neural gas networks

Correction to: Regionalization of rainfall intensity–duration–frequency (IDF) curves with L-moments method using neural gas networks

General Method Based on Regressive Relationships to Parameterize the Three-Parameter Depth–Duration–Frequency Curve

This paper aims to present simple regressive equations to estimate the parameters of the three-parameter depth–duration–frequency (DDF) curve (3p-DDF), which accurately expresses, for a preassigned return period, the relationship between the rainfall depth and the rainfall duration over large duration ranges, from below 1 h (i.e., tens of minutes) to above 1 h (up to 24 h). These equations are developed to relate their parameters to those of the two-parameter DDF curve (2p-DDF), which can be estimated more easily being based on more readily available data related to rainfall durations above 1 h. In the applications, the regressive equations are first calibrated using recent pluviographic data in northern Italy, Germany, and Sweden. Two validation steps are then carried out to test the equations in terms of estimated rainfall depths using the same data as those used in the calibration step and data of stations from other geographic areas, i.e., Sicily in southern Italy, and from the past century, respectively. The results obtained prove this methodology capable of providing reliable estimation of short-duration rainfalls with various return periods in the absence of measurements with fine temporal resolution.

Design flood hydrographs: a regional analysis based on flood reduction functions

ABSTRACT Modern flood hazard mapping techniques and water infrastructure design require the entire flood hydrograph. However, statistical methods for flood hydrograph estimation in ungauged basins have not received the same attention as the models used to predict the peak flow value. Here the design hydrograph of an ungauged basin is reconstructed in a parsimonious way through the estimation of a non-dimensional flood reduction function (FRF). Based on data from 87 basins (763 station-years of flood hydrographs), we show that a two-parameter FRF can be efficiently estimated by multiple linear regression from the longest drainage path length and slope of the basin, the average basin elevation, the width function kurtosis and the mean value of the scaling exponent of the intensity–duration–frequency curve. Reasonable similarities between the estimated flood hydrograph and the original ones make the method suitable for extension into other areas to estimate design hydrographs in ungauged basins.

A nested bistable module within a negative feedback loop ensures different types of oscillations in signaling systems

In this article, we consider a double phosphorylation cycle, a ubiquitous signaling component, having the ability to display bistability, a behavior strongly related to the existence of positive feedback loops. If this component is connected to other signaling elements, it very likely undergoes some sort of protein–protein interaction. In several cases, these interactions result in a non-explicit negative feedback effect, leading to interlinked positive and negative feedbacks. This combination was studied in the literature as a way to generate relaxation-type oscillations. Here, we show that the two feedbacks together ensure two types of oscillations, the relaxation-type ones and a smoother type of oscillations functioning in a very narrow range of frequencies, in such a way that outside that range, the amplitude of the oscillations is severely compromised. Even more, we show that the two feedbacks are essential for both oscillatory types to emerge, and it is their hierarchy what determines the type of oscillation at work. We used bifurcation analyses and amplitude vs. frequency curves to characterize and classify the oscillations. We also applied the same ideas to another simple model, with the goal of generalizing what we learned from signaling models. The results obtained display the wealth of oscillatory dynamics that exists in a system with a bistable module nested within a negative feedback loop, showing how to transition between different types of oscillations and other dynamical behaviors such as excitability. Our work provides a framework for the study of other oscillatory systems based on bistable modules, from simple two-component models to more complex examples like the MAPK cascade and experimental cases like cell cycle oscillators.

Use of the Modified Ramberg-Osgood Material Model to Predict Dynamic Modulus Master Curves of Asphalt Mixtures.

Dynamic modulus master curves are usually constructed by using sigmoid functions, but the coefficients of these functions are not independent of each other. For this reason, it is not possible to clearly identify their physical mean. Another way of describing the dynamic modulus master curves is to choose the Ramberg-Osgood (RAMBO) material model, which is also well-suited for modelling the cyclic behaviour of soils. The Ramberg-Osgood model coefficients are completely independent of each other, so the evaluation of the fitted curve is simple and straightforward. This paper deals with the application of the Ramberg-Osgood material model compared to the usual techniques for constructing a master curve, determining the accuracy in describing the material behaviour of asphalt mixtures, and seeking any surplus information that cannot be derived by traditional techniques. Because the dynamic modulus and phase angle master curves are strictly related, in the present study, the asymmetric bell-shaped frequency curve of Toranzos was used to describe the phase angle for four types of asphalt mixtures (RmB, PmB, RA, and NB). The results show that the RAMBO model is a good alternative to the sigmoid function in describing the master curve of the dynamic modulus. We successfully used the Toranzos asymmetric bell-shaped frequency curve to describe the phase angle master curve. We also found a promising relationship between the independent RAMBO model parameters and the physical properties of the investigated binders, but this requires further research.

Deriving of Intensity–Duration–Frequency (IDF) curves for precipitation at Hanoi, Vietnam

The rainfall Intensity-Duration-Frequency (IDF) relationship is one of the most commonly used tools in establishing rain intensity formulas for urban stormwater drainage design. Currently, the rain formulas being applied in Vietnam according to the design standard TCVN 7957-2008 are mostly Soviet formulas with climate parameters dating back to the 80s of the twentieth century. Therefore, it is no longer suitable for the calculation of the current stormwater drainage system, especially in the context of climate change. In this paper, we used statistical methods to process rain gauge data from 1960 to 2021 to build the IDF curve for the inner city of Hanoi (Vietnam). The results show that the new IDF curves are more suitable for the current climate situation than the IDF curves according to TCVN 7957-2008.

Methodology for Identification of Areas with Possible Risk for Sturgeon Species Migration Disruption on The Lower Danube

In the context of the continuing decline of the species belonging to the order Acipenseriformes on a global level, the anadromous sturgeon species sturgeon species in the Lower Danube have been affected by a significant reduction in historical migration routes and fragmentation of breeding habitats. This paper presents the stages of the methodology for identifying areas that present a possible risk of interruption of sturgeon migration in correlation with satellite images and daily values for discharge/water level databases. In order to determine the two ranges of values that characterize the extreme phenomena (high/low flows), a hydrological statistical analysis was carried out for the most extensive period of time covered by recorded data (January 2011 – May 2023) in the hydrometric station located in Calarasi, Romania. Based on the 4524 values from the series of average daily discharge values, the discharge hydrograph, the empirical curve of insurance/exceedance probability and the frequency and duration curves using 200 m3/s discharge steps were determined and represented. Correlated with satellite imagery recorded during the determined time intervals with extreme phenomena, there were identified areas with possible risk for sturgeon species migration disruption.

Identification of the relationship between rainfall intensity and the probability of urban flooding in Nganjuk District

Floods are hydrometeorological disasters that often occur in various regions, including in Nganjuk Regency. From 2019 to 2022, there were urban floods that inundated highways, markets and hospitals and disrupted community and government activities. Heavy rain is one of the causes of flooding. Rain intensity, duration and frequency (IDF) curves were constructed using rainfall data from six rain gauge stations. This curve is used to determine the 10-year and 25-year probabilities of PUH intensity and the probability of causing flooding in Nganjuk District. Rain intensity in Nganjuk Regency is PUH 10 and 25 with an average rain duration of 15-60 minutes which is included in the moderate rain category, namely 20-50 mm/day. The results of this analysis will become the basis for consideration in formulating policies and strategies for urban flood disaster prevention and management in Nganjuk Regency. Therefore, coordination between the city government and the government is needed to reduce the risk of urban flooding in Nganjuk Regency.

Rainfall Intensity Duration Frequency Curve Statistical Analysis and Modeling for Patna, Bihar

Using data from 41 years in Patna, India, the study’s goal is to analyze the trends of how often it rains on a weekly, seasonal, and annual basis (1981–2020). First, utilizing the intensity-duration-frequency (IDF) curve and the relationship by statistically analyzing rainfall, the historical rainfall data set for Patna, India, during a 41-year period (1981–2020), was evaluated for its quality. Changes in the hydrologic cycle as a result of increased greenhouse gas emissions are expected to induce variations in the intensity, length, and frequency of precipitation events. One strategy to lessen vulnerability is to quantify probable changes and adapt to them. Techniques such as log-normal, normal, and Gumbel are used (EV-I). Distributions were created with durations of 1, 2, 3, 6, and 24 hours and return times of 2, 5, 10, 25, and 100 years. There were also mathematical correlations discovered between rainfall and recurrence interval. Findings: Based on findings, the Gumbel approach produced the highest intensity values, whereas the other approaches produced values that were close to each other. The data indicates that 461.9 mm of rain fell during the monsoon season’s 301st week. However, it was found that the 29th week had the greatest average rainfall, 92.6 mm. With 952.6 mm on average, the monsoon season saw the highest rainfall. Calculations revealed that the yearly rainfall averaged 1171.1 mm. Using Weibull’s method, the study was subsequently expanded to examine rainfall distribution at different recurrence intervals of 2, 5, 10, and 25 years. Rainfall and recurrence interval mathematical correlations were also developed. Further regression analysis revealed that short wave irrigation, wind direction, wind speed, pressure, relative humidity, and temperature all had a substantial influence on rainfall. Originality and Value: The results of the rainfall IDF curves can provide useful information to policymakers in making appropriate decisions in managing and minimizing floods in the study area.