Main Frequency Research Articles

Study on pressure pulsations and transient fluid forces in centrifugal pump under different degrees of cavitation

At the early stage of cavitation, the external characteristics and vibration noise of centrifugal pump have not changed significantly, but the flow conditions in the pump have changed markedly. In order to carry out in-depth study on the change characteristics of the flow conditions in centrifugal pump under different degrees of cavitation at the early stage of cavitation, in this paper, the quantitative relation between cavitation degree and pressure pulsation and fluid force was established by means of numerical calculation combined with test and by analyzing the changes in pressure pulsations and fluid forces in the pump under different degrees of cavitation degree. Studies have shown that the pressure pulsation amplitude and range value at the main frequency (shaft frequency and blade frequency) increases with the cavitation degree. The RMS value of pressure pulsation in each frequency band is positively correlated with cavitation development. In case of severe cavitation, the pressure pulsations in high frequency bands are greatly affected by cavitation. The radial force on pump volute and impeller fluctuates more significantly with the increase of cavitation degree.

Associations between education level, blood-lipid measurements and statin treatment in a Danish primary health care population from 2000 to 2018

Objective To examine whether education level influences screening, monitoring, and treatment of hypercholesterolemia. Design Epidemiological cohort study. Setting Department of Clinical Biochemistry, Copenhagen University Hospital Hvidovre. Subjects Cholesterol blood test results ordered by general practitioners in Greater Copenhagen were retrieved from 2000-2018. Using the International Standard Classification of Education classification, the population was categorized by length of education in three groups (basic education; up to 10 years, intermediate education; 11-12 years, advanced education; 13 years or more). The database comprised 13,019,486 blood sample results from 653,903 patients. Main Outcome Measures Frequency of lipid measurement, prevalence of statin treatment, age and comorbidity at treatment initiation, total cholesterol threshold for statin treatment initiation, and achievement of treatment goal. Results The basic education group was measured more frequently (1.46% absolute percentage difference of total population measured [95% CI 0.86%–2.05%] in 2000 and 9.67% [95% CI 9.20%–10.15%] in 2018) over the period compared to the intermediate education group. The advanced education group was younger when receiving first statin prescription (1.87 years younger [95% CI 1.02–2.72] in 2000 and 1.06 years younger [95% CI 0.54–1.58 in 2018) compared to the intermediate education group. All education groups reached the treatment goals equally well when statin treatment was initiated. Conclusion Higher education was associated with earlier statin prescription, although the higher educated group was monitored less frequently. There was no difference in reaching treatment goal between the three education groups. These findings suggest patients with higher education level achieve an earlier dyslipidemia prevention intervention with an equally satisfying result compared to lower education patients. Key Points Little is known about the role of social inequality as a possible barrier for managing hypercholesterolemia in general practice. Increasing education level was associated to less frequent measurement and less frequent statin treatment. Patients with higher education level were younger, and less comorbidity at first statin prescription. Education level had no effect on frequency of statin treatment-initiated patients reaching the treatment goal was found.

Prediction of ground-borne vibration from random traffic flow and road roughness: Theoretical model and experimental validation

With the densification and closer distance to buildings of road traffic network in urban areas, the assessment and control of environmental vibrations becomes the focus of attention, in which the prediction of traffic flow-induced ground vibration is very critical. However, few studies have been reported on the theoretical prediction method of traffic flow-induced ground vibration from the perspective of stochastic theory. The present work contributes to the perfection and innovation of the current methodologies for the prediction of traffic flow-induced ground vibration. In this paper, a semi-analytical and semi-numerical method for predicting traffic flow induced ground vibrations is developed, in which the random effect generated from traffic flow and road roughness is considered by establishing the vehicle-road-soil coupling model. Aiming to predict the long-term vibration and transient vibration induced by road traffic flow, the average and the adverse velocity levels are used as the evaluation indicators. The effectiveness of the proposed method is validated by an on-site experiment, and the characteristics of ground vibrations are investigated in time and frequency domains, respectively. The results demonstrate that the proposed method can effectively predict the road traffic flow-induced ground vibrations, and the randomness of both traffic flow and road roughness cannot be neglected. For the experimental site, the main frequency band of ground vibrations concentrates on 7–25 Hz, and the predominant center frequency is 12.5 Hz, resulting from the resonance between the overlapping dominant frequency bands of the dynamic vehicle loads and the natural frequency of the soil.

Research on cumulative effect and diagnosis method of transformer short-circuit impulse

After transformers suffer from short-circuit impact, their mechanical performance decreases significantly. This article establishes a two-wire vibration model to represent the coupling between forces and mechanics and analyzes the transient vibration signals of a 400 V transformer during 22 short-circuits impact. To illustrate the cumulative effect of short-circuits, the vibration entropy, and energy ratio of the main vibration frequency and half frequency are adopted. The results show that transient vibration signals of transformer in short-circuits contain half frequency components, such as 25 Hz and 75, etc., and with the increase of the number of short-circuits, plastic deformation exists in insulation material, which leads to the loss of winding clamping pressure, the reduction of natural frequency, and the upsurge of parametric resonance. With the increase of short circuits, the vibration entropy and half-frequency energy ratio increase, and the main frequency energy ratio decreases. After winding completely lose the axial stability, the vibration entropy and half frequency ratio decrease, and the main frequency ratio increases. The conclusion is of great significance to the analysis of the cumulative effect of short circuits on power transformers.

Nonlinear Vibration of Bolted Rotor Bearing System Accounting for the Bending Stiffness Characteristics of the Connection Interface

This paper considers the discontinuous characteristics of a real aero-engine rotor system, that is, the existence of bolted connection characteristics, and establishes a new bolted connection rotor system model. Taking into account the bending stiffness and the nonlinear Hertzian contact force of the rolling bearing, the Newmark-[Formula: see text] numerical method is used to solve the system response, and the influence of the bending stiffness on the system is studied. Moreover, the effects of bending stiffness and eccentricity on the system dynamics are analyzed. The results show that the nonlinear phenomena of the system are more abundant and the critical speed of the system is higher when the bending stiffness is involved. With the increase of bending stiffness, the critical speed of the system increases, and the frequency component of the system becomes more complex. Then, the influence of eccentricity on the system is studied based on the bending stiffness. It is found that the greater the eccentricity, the greater the critical speed of the rotor and the greater the amplitude of the main frequency. In the case of the same eccentricity, the main frequency increases as the rotational speed increases, and the frequency doubling component appears in the 2-period motion. This paper provides a basis for predicting the nonlinear response of bolted rotor-bearing system.

Variants of the post-COVID syndrome course depending on age, gender, comorbidity and severity of COVID-19

BACKGROUND. Among residents of Chernivtsi region, the main characteristics, frequency and peculiarities of the longterm symptomatic and post-COVID-19 syndrome have not been sufficiently studied.
 OBJECTIVE. To evaluate the variants of the post-COVID syndrome course depending on age, gender, comorbidity and severity course of coronavirus disease (COVID-19).
 MATERIALS AND METHODS. The following research methods were used: electronic questionnaire, epidemiological, clinical and anamnestic, analytical and statistical methods. The study included 214 adult patients infected with SARS-CoV-2 virus (diagnosis was confirmed by polymerase chain reaction) and suffering from COVID-19 of varying severity. The patients were randomized into two groups: the main group included 112 people (63 men – 56.4 % and 49 women – 47.5 %); the comparison group included 102 patients with mild and moderate severity of COVID-19 who were consulted and treated outpatiently (46 men – 45.5 % and 56 women – 54.5 %). Statistical data processing was carried out using the IBM SPSS Statistics v26.0 program.
 RESULTS AND DISCUSSION. It was found that among inpatients, there was a significantly higher number of patients over 60 years of age (p<0.001), whereas among outpatients, people aged 18-29 years prevailed. This indicates the relationship between the age of the respondents and the need for inpatient treatment in case of COVID-19. In the main group, the following symptoms occurred more frequently (p<0.05): cough (odds ratio, OR 2.023; confidence interval, CI 1.105-3.703), fever (OR 6.916; CI 2.061-23.204), shortness of breath – dyspnea (OR 4.421; CI 2.230-8.764). In the comparison group, the following prevailed: loss of smell (OR 0.147; CI 0.077-0.281), fatigue (OR 0.456; CI 0.226-0.920), increased body temperature (OR 2.023; CI 2.061-23.204). In patients who were admitted to the hospital, the following comorbidities prevailed: coronary heart disease (OR 33.088; CI 9.444-115.930), arterial hypertension (OR 13.641; CI 6.547-28.422), diabetes mellitus (OR 4.755; CI 1.915-11.803), heart failure (OR 18.504; CI 8.200-41.752), obesity (OR 4.828; CI 2.433-9.581).
 CONCLUSIONS. 1. Among the patients who were admitted to the hospital, the vast majority are people over 40 years of age; men of a younger age (from 40 years) prevailed in contrast to women (over 60 years). 2. In persons with severe COVID-19, shortness of breath, cough, difficulty breathing, chest pain were registered more often. On outpatient treatment, loss of smell and fatigue prevailed. 3. In patients admitted to the hospital, the following comorbidities prevailed: coronary heart disease (37.5 %), arterial hypertension (57.4 %), diabetes mellitus (21.3 %), heart failure (54.1 %), obesity (41.1 %). Smoking and alcohol abuse did not show significant reliable differences. 4. The most common combination of three pathologies (hypertension, heart failure, obesity) was found in 11 people (10 %).

Analysis of Inner Flow in a Multi-Stage Double-Suction Centrifugal Pump Using the Detached Eddy Simulation Method

In order to analyze the inner flow in a multi-stage double-suction centrifugal pump, which is regarded as a common way of knowing the current characteristics of the pump and as the basis of optimization for better performance, a numerical simulation considering the velocity field distribution characteristics and pressure fluctuation propagation law using the detached eddy simulation method was conducted. Additionally, the principle of entropy generation was put to use to quantify and compare the energy loss of different components. The results reveal that the existence of unstable flow structures in the first-stage impeller and a large number of vortical structures in the back-channel result in reduced operational efficiency of the pump. Furthermore, the pressure fluctuation intensity reaches its maximum with 0.15 at the blade trailing edge, which propagates to the tongue region of the forward flow channel and the double-volute under the low rates condition. Additionally, the main frequency of the monitoring points in the inter-stage flow channel and volute is basically located at a frequency of 198.667 Hz, which is twice the blade frequency. Consequently, the wall entropy production accounting for nearly 25% cannot be ignored and that the loss mainly occurs in the double-volute and the inter-stage flow channel due to the occurrence of irregular flow in the above components with more than 50%. The outcomes of this research present a valuable point of reference for the optimization of structural design in multistage turbomachines with various applications.

Inpatient Understanding of Their Care Team and Receipt of Mixed Messages: a Two-Site Cross-Sectional Study.

Patient understanding of their care, supported by physician involvement and consistent communication, is key to positive health outcomes. However, patient and care team characteristics can hinder this understanding. We aimed to assess inpatients' understanding of their care and their perceived receipt of mixed messages, as well as the associated patient, care team, and hospitalization characteristics. We administered a 30-item survey to inpatients between February 2020 and November 2021 and incorporated other hospitalization data from patients' health records. Randomly selected inpatients at two urban academic hospitals in the USA who were (1) admitted to general medicine services and (2) on or past the third day of their hospitalization. Outcome measures include (1) knowledge of main doctor and (2) frequency of mixed messages. Potential predictors included mean notes per day, number of consultants involved in the patient's care, number of unit transfers, number of attending physicians, length of stay, age, sex, insurance type, and primary race. A total of 172 patients participated in our survey. Most patients were unaware of their main doctor, an issue related to more daily interactions with care team members. Twenty-three percent of patients reported receiving mixed messages at least sometimes, most often between doctors on the primary team and consulting doctors. However, the likelihood of receiving mixed messages decreased with more daily interactions with care team members. Patients were often unaware of their main doctor, and almost a quarter perceived receiving mixed messages about their care. Future research should examine patients' understanding of different aspects of their care, and the nature of interactions that might improveclarity around who's in charge while simultaneously reducing the receipt of mixed messages.

Natural Oscillatory Frequency Slowing in the Premotor Cortex of Early-Course Schizophrenia Patients: A TMS-EEG Study.

Despite the heavy burden of schizophrenia, research on biomarkers associated with its early course is still ongoing. Single-pulse Transcranial Magnetic Stimulation coupled with electroencephalography (TMS-EEG) has revealed that the main oscillatory frequency (or "natural frequency") is reduced in several frontal brain areas, including the premotor cortex, of chronic patients with schizophrenia. However, no study has explored the natural frequency at the beginning of illness. Here, we used TMS-EEG to probe the intrinsic oscillatory properties of the left premotor cortex in early-course schizophrenia patients (<2 years from onset) and age/gender-matched healthy comparison subjects (HCs). State-of-the-art real-time monitoring of EEG responses to TMS and noise-masking procedures were employed to ensure data quality. We found that the natural frequency of the premotor cortex was significantly reduced in early-course schizophrenia compared to HCs. No correlation was found between the natural frequency and age, clinical symptom severity, or dose of antipsychotic medications at the time of TMS-EEG. This finding extends to early-course schizophrenia previous evidence in chronic patients and supports the hypothesis of a deficit in frontal cortical synchronization as a core mechanism underlying this disorder. Future work should further explore the putative role of frontal natural frequencies as early pathophysiological biomarkers for schizophrenia.

Monitoring the dynamic response of a pedestrian bridge by using low-cost GNSS receivers

The development of low-cost GNSS receivers with carrier-phase measurement capacity has led to low-budget GNSS applications of higher accuracy and precision. Recent studies have mainly been carried out with those low-cost receivers for landslide monitoring and achieved promising results. In this study, the performance of two closely-spaced high-rate low-cost GNSS receivers was assessed against the robotic total station (RTS) and geodetic GNSS receiver in monitoring the dynamic response of a major pedestrian suspension bridge at the mid-span. Potential accuracy improvement by the combination of two low-cost GNSS time-series was also examined. It was proved that multi-GNSS solution is required to resolve potential outliers and offsets of the low-cost GNSS time-series, due to cycle slip induced errors. The analysis of the low-cost GNSS time-series showed that the low-cost GNSS receivers can estimate (i) the main dominant frequencies of the bridge with the same accuracy as the geodetic-grade GNSS receiver and (ii) the amplitude of the bridge response with difference of ∼3 mm with respect the geodetic GNSS receiver due to higher noise level. This study revealed the prospect of utilising low-cost GNSS sensors in monitoring dynamic displacement with frequency of 1–3 Hz, corresponding to relatively rigid structures (e.g., short span bridges, etc.).

Distributed dynamic strain sensing of very long period and long period events on telecom fiber-optic cables at Vulcano, Italy

Volcano-seismic signals can help for volcanic hazard estimation and eruption forecasting. However, the underlying mechanism for their low frequency components is still a matter of debate. Here, we show signatures of dynamic strain records from Distributed Acoustic Sensing in the low frequencies of volcanic signals at Vulcano Island, Italy. Signs of unrest have been observed since September 2021, with CO2 degassing and occurrence of long period and very long period events. We interrogated a fiber-optic telecommunication cable on-shore and off-shore linking Vulcano Island to Sicily. We explore various approaches to automatically detect seismo-volcanic events both adapting conventional algorithms and using machine learning techniques. During one month of acquisition, we found 1488 events with a great variety of waveforms composed of two main frequency bands (from 0.1 to 0.2 Hz and from 3 to 5 Hz) with various relative amplitudes. On the basis of spectral signature and family classification, we propose a model in which gas accumulates in the hydrothermal system and is released through a series of resonating fractures until the surface. Our findings demonstrate that fiber optic telecom cables in association with cutting-edge machine learning algorithms contribute to a better understanding and monitoring of volcanic hydrothermal systems.

Dynamic Service Mechanism of Double-Row Spherical Roller Bearings Due to Self-Aligning Behavior

Spherical roller bearings (SRBs) are widely used under self-aligning operating conditions, such as rotor bending or an angular misalignment between inner and outer rings due to their self-aligning function. However, the characterization of SRBs’ self-aligning function is often ignored in the present models. The reason for this is that the self-aligning condition is essentially a fault condition, and many scholars have assumed SRBs are in an ideal operating condition. Although there is nothing wrong with this analysis theoretically, it is incapable of characterizing SRBs’ service behavior comprehensively. In this work, the Lagrange equation was introduced to model the relationship among the rollers and the inner and outer rings. The contact region in particular was characterized in detail in order to solve the problems of undetermined contact status (UCS) and the varying law of the self-aligning contact angle (SAC angle). For the experiment, a novel SRBs pedestal with a self-aligning operating condition was designed, and the relevant self-aligning function testing was carried out. A good agreement was shown between the theoretical and experimental results. The results pointed out that, if taking no account of the self-aligning function, SRBs can be regarded as angular contact ball bearings or cylinder roller bearings. The amplitude of the inner-ring motion orbit is determined by the external load, but the shape is influenced by the direction and magnitude of the SAC angle. In the example of this paper, the values of the main frequency equal 136.8 Hz. Some additional frequencies are clearly aroused under the self-aligning operating condition, whose value is approximately equal to 8.3 Hz or its integer multiples. The dynamic performance of SRBs will be substantially improved by a light axial load plus an anticlockwise self-aligning contact angle rather than a large axial preload.

Impedance eduction experiments covering higher frequencies based on the multimodal straightforward method

The multimodal straightforward method is developed further, validated and applied experimentally. The trust-region algorithm is introduced to reduce the eduction time, a flow duct setup with a cross section of 51 × 51 mm2 is built for the impedance eduction, and several single- and multi-layer perforated liners are tested from 0.5 kHz up to 6.0 kHz at two average Mach numbers under several types of modal sound sources. It is validated that, this method, by utilizing a diagonal microphone array and improving Prony’s algorithm, enables the automatic match between axial and transverse wavenumbers, and thus realizes the full decomposition to three-dimension multimodal sound fields. By introducing the trust-region algorithm, it can educe the impedance with a good consistency and a higher time efficiency. Generally, this method is applicable to the practical impedance eduction in multimodal aeroacoustic environments on a real flow duct, with the upper frequency extended from 3.0 to 6.0 kHz covering the main frequency range of aeroengine fan noises. For multilayer liners, the educed impedance spectrum is considerably flatter than the prediction by an existing impedance model in some cases especially near the antiresonance, and the grazing flow magnifies such a flatting trend accompanied by more evident predicting deviations. The spectra of educed impedance and transmission loss show that the multilayer liner possesses more resonant frequencies within the concerned range and broadband absorption potentials if well designed.

Biofouling Removal Using a Novel Electronic System for Driving an Array of High Power Marinised Transducers

This paper explains producing a novel ultrasonic system to remove/prevent biofouling growth from wind turbines’ access ladders by means of producing local ultrasound cavitation. Using bespoke hardware, an array of high-power ultrasound transducers (HPUTS) and optimally synthesized signal types to remove/prevent biofouling growth from the ladder without violating the standard noise level in the sea is explained. This is a non-toxic and non-invasive solution to detach biofouling and prevent biofilm initiation on offshore structures. It is shown that the marinisation of the HPUT slightly shifts the main resonance frequency from 28.1 to 27.5 kHz. The vibration output from the HPUTs with different mounting systems showed that the transducer with the horn could vibrate the plate at 20 cm from the excitation point, with 300 pm, six times higher than the vibration output from the marinised HPUT. A transducer array and attachment are proposed to make the ultrasound noise below the standard underwater noise limits. The produced sound pressure level (SPL) and sound equivalent level (SEL) from the proposed ultrasonic system was measured. It was specified that the SPL came below 120 dB at 25 m from the excitation point and the SEL value below the 173 dB limit. Finally, the effectiveness of the marinised HPUTS on biofouling removal has been demonstrated with an in-situ measurement, and it was indicated that local biofouling removal could be achieved.

Four Subbands from Dual Mismatched Wideband Bandpass Filter for 5G/WAS/Wi-Fi/WiMAX/WLAN Applications

Based on the simplicity of the design method, this paper presents a new approach for developing matched subbands when splitting two mismatched dual-wideband bandpass filters (BPFs) for the fifth generation (5G), wireless access systems (WAS), wireless fidelity (Wi-Fi), worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN), radar, and other communication devices. The method’s novelty involves using identical quarter-wavelength resonators terminated by alternated short-and-open stub configurations. Both configurations alternate and describe a perfect symmetry by their location from each other to make the subbands possible in the low-frequency and its harmonic (high-frequency) bandwidths (BW). A stub admittance Y 1 is defined and associated with the mainline section characteristic impedance Z 0 and an operating frequency f 0 . A quality factor Q a p is connected to Y 1 and f 0 to approach the BPF global quality factor Q g initially fixed. The stub characteristic impedance and the mainline one differ, while electric lengths (stub and mainline section) are identical. Using the operating frequency determines physical dimensions, creates harmonic frequencies and the rejected BW, mismatches the main frequency BW, matches the subbands, and creates transmission zero (TZ). Hence, a 28.118-dB stopband that separates the two bandpasses at 9.373 GHz is made. At the same time, the unmatched dual ultrawideband (UWB) covers a large panel of communication systems. The lowest (3.146–5.431) and highest (11.891–14.749) GHz BW exhibit a minimum insertion loss (IL) of 0.656 dB and 3.027 dB. The subbands return losses (RL) are better than 28 dB and 19 dB, respectively, and a flat group delay of 0.205 ns is obtained in the upper band. All subbands adaptation methodology is read from 10 dB of the RL. In that case, the four matched subbands in its lower wideband are 3.327–3.709 GHz and 4.442–5.048 GHz, and in its higher wideband are 11.922–12.486 GHz and 14.281–14.653 GHz. The 2275/2858 MHz is the dual-wideband with a fractional BW 53.282/21.456%. The fabricated prototype has validated the EM-simulations, and Anritsu MS4642B 20 GHz vector network analyzer (VNA) has been used for experimental results by scanning the frequency range 3 GHz–15 GHz. The tested prototype is made with a 1 mm FR4 HTG-175 thickness by considering a dielectric constant of 4.4, and its overall size occupies 22.45 × 5.72 m m 2 ( 0.32 λ 0 × 0.082 λ 0 mm 2 ).

The influence of blade trailing edge modification on the pressure pulsation inside a two-stage centrifugal pump

Adjusting the clearance between the rotor and the stator in the centrifugal pump is an effective measure to reduce the pressure pulsation. In this paper, we investigated the influence of blade trailing edge modification on the internal unsteady flow and the performance of a two-stage centrifugal pump with the V-type trailing edge (VTE) and elliptic trailing edge (ETE). The pressure pulsation on the spherical casing and the performance were analyzed based on the experimental results for the pump with the modified blade trailing edges of the cutting depths 1 mm, 2 mm and 2.5 mm. Also the unsteady flow in the pump was numerically simulated, and the velocity and the axial vorticity intensity were analyzed to evaluate the influence of the flow on the pressure pulsation and the performance of the pump. The results show that cutting the blade trailing edge will reduce the head and efficiency of the two-stage pump, and different outlet shapes under the same cutting depth have little effect on the performance. The modified impeller makes the high velocity areas at the blade outlet away from the spherical casing wall and reduces the pressure pulsation amplitude at the main frequency. At the design flow rate, the heads decrease by 7.3%, 9.8% and 11.3%, the efficiencies decrease by 2.8%, 3.5% and 4.0%, and the pressure pulsation amplitudes at the main frequency are reduced by 29%, 10.1% and 28.7% for the ETE1, ETE2, ETE2.5 blade compared with that of original impeller. Also, the heads decrease by 6.3%, 8.0% and 9.1%, the efficiencies decrease by 3.5%, 3.9% and 4.1%, and the pressure pulsation amplitudes at the main frequency are reduced by 3.2%, 11.7% and 38.1% for VTE1, VTE2, VTE2.5 blade. When the cutting depth is large, the trailing edge of the blade has a large vortex intensity. This may cause the energy loss and lead to the decrease of the efficiency and head. Considering the performance and unsteady pressure pulsation of the two-stage pump, the impeller with VTE1 blade has certain reference significance for engineering application.

Development and Field Validation of Wireless Sensors for Railway Bridge Modal Identification

Bridges are strategic infrastructures which are subject to degradation during their lifetime. Therefore, structural health monitoring is becoming an essential tool in this field to drive maintenance activities. Conventional vibration monitoring systems relying on wired sensors present several limitations for continuous monitoring projects on a huge number of structures. In this work, a smart wireless monitoring system is developed for bridge modal identification with the aim of providing an alternative tool to wired sensors in this field. The main peculiarities of the designed wireless accelerometers are the low cost, the ease of installation on the structure, and the long-term autonomy granted by the use of energy harvesting techniques. To assess their measurement performance, some prototypes were installed for a field test on a railway bridge and significant data were acquired. Through the processing of the collected data, bridge main natural frequencies were estimated, and their values were in good agreement with the reference ones obtained with a conventional system. The assessment of the developed solution paves the way to the instrumentation of many bridges with the aim of performing continuous monitoring activities using simple diagnostic indicators, such as the variation of frequencies in time.

Time–frequency signal analysis of flow pulsation in siphon outlet conduit based on HHT considering the pump‐conduit interaction

AbstractThe unsteady three‐dimensional numerical simulation calculation of the vertical axial flow pump device is performed based on CFD to examine the pressure pulsation and energy distribution features of the water flow within the siphon outlet conduit (SOC) under the hydraulic coupling of the pump and the flow conduit. The pressure pulsation signals (PPS) of monitoring points are decomposed using the Hilbert–Huang approach via empirical mode decomposition (EMD) and Hilbert spectrum analysis. The results show that the PPS of monitoring points of the SOC has no obvious periodicity. The low‐frequency range below 20 Hz serves as the primary frequency, and the energy ratio of the high‐frequency signal above 700 Hz is less than 1%. Under the condition of a small flow rate 0.3Qbep, there is obvious high‐frequency pulsation above 500 Hz at the inlet of the upstream section of the SOC, and there are periodic components distributed around 200 Hz. The energy of the pressure pulsation is primarily focused in the low‐frequency range below 40 Hz at the SOC outlet section. The PPS at the top and bottom monitoring points of the hump section are consistent, and the pressure pulsation energy (PPE) is mainly concentrated in the low frequency below 40 Hz. In both the big flow condition (1.2Qbep) and the optimal flow condition (1.0Qbep), the PPE of the monitoring points at the top of the hump section is distributed in the middle and low‐frequency band below 40 Hz, and the energy of monitoring points at the bottom of the hump section is concentrated in the low‐frequency band below 20 Hz, accounting for more than 70%. When the flow rate increases from 0.3Qbep to 1.2Qbep, the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the top of the hump section changes little, and the peak value of the pressure pulsation coefficient at the main frequency of each monitoring point at the bottom increases first and then decreases. From the upstream section to the hump section of the SOC, the average frequency of each intrinsic mode function (IMF) of the PPS under different flow conditions shows an overall increasing trend. From the hump section of the SOC to its outlet, the average frequency of each IMF of the PPS decreases under the conditions of 1.0Qbep and 1.2Qbep, and there is no obvious change under the condition of 0.3Qbep.

A comparative study of circular and rectangular bended plunging jets

In the present work we study the topology, mixing properties, turbulence quantities, dependence on the outlet geometry of a sharp-edged orifice plunging jet which first issues horizontally in air and then plunges in a water pool. The investigated orifices shapes are circular and rectangular. Data are acquired at different Reynolds numbers in the range 11000–25000, based on the orifice diameter (equal to 2 cm) and on the average exit velocity, as derived from flow rate measurements. Velocity fields in vertical and horizontal planes are measured using planar time-resolved Particle Image Velocimetry. Results show a clear asymmetry of the cross-velocity profiles both in circular and rectangular cases, with the latter that revealed a shape which is Reynolds number dependent. Axial velocity decays, potential core lengths and spreading rates highlight an opposite trend between the two jet geometries, thus suggesting a higher mixing for the lowest Reynolds number circular jet and the highest rectangular one. Plunging angle shows a dependency on Reynolds number. Moreover, it seems to play a role in the evolution of the upper and lower side of the jet due to the onset of a co-flow. Ambient mass entrainment points out the different interactions of the two plunging jets with the ambient flow: in circular case, it entrains fluid from the surroundings, from horizontal to vertical planes in streamwise direction, while in rectangular one it ejects flow from vertical to horizontal planes. Finally, Strouhal numbers are derived for main vortices frequencies along jet centerline, other than upper and lower sides.

Smartphone-based cough monitoring as a near real-time digital pneumonia biomarker.

Cough represents a cardinal symptom of acute respiratory tract infections. Generally associated with disease activity, cough holds biomarker potential and might be harnessed for prognosis and personalised treatment decisions. Here, we tested the suitability of cough as a digital biomarker for disease activity in coronavirus disease 2019 (COVID-19) and other lower respiratory tract infections. We conducted a single-centre, exploratory, observational cohort study on automated cough detection in patients hospitalised for COVID-19 (n=32) and non-COVID-19 pneumonia (n=14) between April and November 2020 at the Cantonal Hospital St Gallen, Switzerland. Cough detection was achieved using smartphone-based audio recordings coupled to an ensemble of convolutional neural networks. Cough levels were correlated to established markers of inflammation and oxygenation. Cough frequency was highest upon hospital admission and declined steadily with recovery. There was a characteristic pattern of daily cough fluctuations, with little activity during the night and two coughing peaks during the day. Hourly cough counts were strongly correlated with clinical markers of disease activity and laboratory markers of inflammation, suggesting cough as a surrogate of disease in acute respiratory tract infections. No apparent differences in cough evolution were observed between COVID-19 and non-COVID-19 pneumonia. Automated, quantitative, smartphone-based detection of cough is feasible in hospitalised patients and correlates with disease activity in lower respiratory tract infections. Our approach allows for near real-time telemonitoring of individuals in aerosol isolation. Larger trials are warranted to decipher the use of cough as a digital biomarker for prognosis and tailored treatment in lower respiratory tract infections.