Small Speed Research Articles

Hurricane wind disaster assessment methods on coastal structures based on area and radial distribution integration

Early studies have shown that hurricane disaster assessment indicators that only consider the intensity-related single factor cannot well represent the actual degree of damage caused by hurricanes to coastal structures. In the current study, for hurricane wind damage, in addition to the three wind disaster index formulas (corresponding to the wind resistance characteristics of infrastructures in developed, developing, and underdeveloped regions, respectively) that are related to hurricane intensity, the spatial scale characteristics of hurricanes are also considered. Thus, two kinds of hurricane wind disaster assessment methods by combing the wind disaster index and spatial scale of hurricanes are carried out, area and radial integration, respectively. Compared with the traditional single-factor evaluation index, the method based on area integral can more accurately characterize the degree of hurricane wind disaster. However, the peripheral small wind speed of the hurricane has a greater impact on wind disaster assessment; for medium-strength and intense hurricanes, the highest proportion is up to 61.5–67.7%; and that of weak hurricanes is up to 85.7–94.1%. To solve the challenging problems of hurricanes with small wind speed but the large size and large wind speed but small size, the area integral method with the concept of cut-in wind speed is introduced. The impact of small wind speed on wind disaster assessment is significantly reduced; the highest proportion of medium-strength and intense hurricanes is 14.5–22.5%, and that of weak hurricanes is 27.5–33.3%. Because the three-dimensional wind field is not easy to capture, the structure along the coastline is the most severely damaged, and the linear radial integral is less sensitive to small wind speeds than the quadratic area integral, a hurricane wind disaster assessment method based on radial integral is proposed. The results show that the method has good spatial region insensitivity. Both methods show that the numerical results can accurately represent the hurricane wind disaster when the horizontal grid size is 185 m or 555 m. However, the wind disaster assessment trends of the two methods are not linear because of the asymmetry of the hurricane structure. The two hurricane wind disaster assessment methods proposed in this study can better reflect the degree of disaster. For the comprehensive hurricane wind disaster assessment for large-scale wind farms in the deep sea, the area-based method can be used; for the infrastructure structures along the coastline, the radial-based method is more suitable. Since the measured meteorological data contain different characteristic radius and the corresponding wind speed of hurricanes, the method based on radial integral is more practical.

Existence of traveling wave solutions for a generalized Burgers–Fisher equation with weak convection

The existence of traveling wave solutions for a generalized Burgers–Fisher equation with weak convection term is investigated in current paper. The corresponding traveling wave equation is converted to a regularly perturbed Hamiltonian system by rescaling of the wave speed. Then by using Melnikov’s method, we show that the generalized Burgers–Fisher equation contains kink and anti-kink wave solutions with small wave speeds, and the wave speed selection principle is presented as well. By analyzing the ratio of Abelian integrals, we also prove that the generalized Burgers–Fisher equation admits periodic wave solutions whose rescaled limit wave speed is monotonically increasing. Moreover, the upper and lower bounds of the limit wave speed are given, and the relationship between wave speed and wavelength is established. Numerical simulations are performed to illustrate our theoretical analysis.

Dynamics of He++ Ions at Interplanetary and Earth’s Bow Shocks

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We studied the variations in the parameters of twice-ionized helium ions (4He++ ions or α-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth’s bow shock. We used data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Vα, temperature Tα, absolute density Nα, and helium abundance Nα/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth bow shock crossings. Measurements from the WIND, Cluster, and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Nα/Np with the parameters βi, θBn, and MMS were investigated. The following correlation between Nα/Np and the angle θBn was found: the lower the value of θBn, the greater the drop in helium abundance (Nα/Np) falls behind the IP shock front. For Earth’s bow shock crossings, we found a significant increase in the helium abundance (Nα/Np) in quasi-perpendicular events.

Simulating the Profile of a Radio Altimeter Echo Signal

Introduction. Radio altimeters are used for remote monitoring of the Earth and sea surface based on the signal power profile, i.e. the dependence of echo signal power vs time, averaged over a set of sounding measurements. Calculation of the power profile in the presence of sea waves requires information about the probability distribution density (PDD) of sea surface applicates. The existing applicate PDD models (linear, Gram-Charlier, combined model) are characterized by certain drawbacks leading to errors in assessing sea surface parameters based on the signal power profile. In this work, the echo signal of a radio altimeter is simulated using the nonlinear Creamer model for calculating sea surface applicates.Aim. To test the validity of the non-linear Creamer model for obtaining the PDD of sea surface applicates in the problem of simulating the power profile of a radio altimeter echo signal while providing an unambiguous relationship between the statistical parameters of PDD and wind speed.Materials and methods. A two-dimensional sea surface of finite dimensions with an Elfohaily spatial spectrum was simulated in the MATLAB environment based on both linear and non-linear Creamer models.Results. Under small wind speed values of up to 3 m/s, the PDD of sea surface applicates formed by the non-linear Creamer model obey the Gauss law. For the non-linear model, an increase in the duration of an radio altimeter echo signal along with an increase in the wind speed was shown to be 5.47 % slower on average compared to that for the linear model. The time shift of the leading edge of an echo signal for the nonlinear model relative to the linear model due to the PDD transformation may reach 70 ns, which is equivalent to 10.5 m. The conducted study confirmed the validity of the non-linear Creamer model for obtaining the PDD of sea surface applicates when simulating the power profile of a radio altimeter echo signal.Conclusion. The non-linear Creamer model can be recommended for simulating an echo signal power profile for use as input data when estimating the parameters of a radio altimeter echo signal at the stage of post-processing.

Variations of He++ Ion Parameters at Interplanetary and Earth’s Bow Shock Fronts

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We study the variations in the parameters of twice-ionized helium ions (4He++ ions or {\alpha}-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth's bow shock. We use data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Va, temperature Ta, absolute density Na, and helium abundance Na/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth's bow shock crossings. Measurements from the WIND, Cluster and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Na/Np with the parameters {\beta}_{i}, {\theta}_{Bn} and M_{ms} were investigated. A correlation between Na/Np and the angle {\theta}_{Bn} was found: the lower the value of {\theta}_{Bn}, the greater the drop in helium abundance Na/Np falls behind the IP shock front. For Earth's bow shock crossings, we found a significant increase in the helium abundance Na/Np in quasi-perpendicular events.

Relativistic fluids, hydrodynamic frames and their Galilean versus Carrollian avatars

We comprehensively study Galilean and Carrollian hydrodynamics on arbitrary backgrounds, in the presence of a matter/charge conserved current. For this purpose, we follow two distinct and complementary paths. The first is based on local invariance, be it Galilean or Carrollian diffeomorphism invariance, possibly accompanied by Weyl invariance. The second consists in analyzing the relativistic fluid equations at large or small speed of light, after choosing an adapted gauge, Arnowitt-Deser-Misner-Zermelo for the former and Papapetrou-Randers for the latter. Unsurprisingly, the results agree, but the second approach is superior as it effortlessly captures more elaborate situations with multiple degrees of freedom. It furthermore allows to investigate the fate of hydrodynamic-frame invariance in the two limits at hand, and conclude that its breaking (in the Galilean) or its preservation (in the Carrollian) are fragile consequences of the behaviour of transport attributes at large or small c. Both methods do also agree on the doom of Nœtherian currents generated in the relativistic theory by isometries: conserved currents are not always guaranteed in Newton-Cartan or Carroll spacetimes as a consequence of Galilean or Carrollian isometries. Comparison of Galilean and Carrollian fluid equations exhibits a striking but often superficial resemblance, which we comment in relation to black-hole horizon dynamics, awkwardly akin to Navier-Stokes equations. This congruity is authentic in one instance though and turns out then to describe Aristotelian dynamics, which is the last item in our agenda.

The phase space structure in the vicinity of vertical Lyapunov orbits around L1,2 in a barred galaxy model

ABSTRACT We study the phase space structure and the orbital diffusion from the vicinity of the vertical Lyapunov periodic orbits around the unstable Lagrangian points L1,2 in a 3D barred galaxy model. By perturbing the initial conditions of these periodic orbits, we detected the following five types of orbital structures in the 4D spaces of section: (i) Ring-like structures, sticky for large time intervals to the unstable invariant manifolds of the simple and double unstable vertical Lyapunov periodic orbits. (ii) 2D tori belonging to quasi-periodic orbits around stable periodic orbits existing in the region. They are associated either with vertical stable periodic orbits around L4,5 or with ‘stable anomalous’ periodic orbits. (iii) Orbits sticky for large time intervals to these tori, forming ‘sticky tori’, before they slowly depart from them. (iv) Clouds of points that have a strong chaotic behaviour. Such clouds of consequents have slow diffusion speeds, because they are hindered by the presence of the tori around the ‘stable anomalous’ periodic orbits. (v) Toroidal zones consisting of points that stick for long time on the unstable invariant manifolds of the ‘unstable anomalous’ periodic orbits. By continuing the integration, we find that eventually they become strongly chaotic, retaining however small diffusion speeds, due to the presence of the tori around the stable anomalous periodic orbits.

Carroll Expansion of General Relativity

We study the small speed of light expansion of general relativity, utilizing the modern perspective on non-Lorentzian geometry. This is an expansion around the ultra-local Carroll limit, in which light cones close up. To this end, we first rewrite the Einstein--Hilbert action in pre-ultra-local variables, which is closely related to the 3+1 decomposition of general relativity. At leading order in the expansion, these pre-ultra-local variables yield Carroll geometry and the resulting action describes the electric Carroll limit of general relativity. We also obtain the next-to-leading order action in terms of Carroll geometry and next-to-leading order geometric fields. The leading order theory yields constraint and evolution equations, and we can solve the evolution analytically. We furthermore construct a Carroll version of Bowen--York initial data, which has associated conserved boundary linear and angular momentum charges. The notion of mass is not present at leading order and only enters at next-to-leading order. This is illustrated by considering a particular truncation of the next-to-leading order action, corresponding to the magnetic Carroll limit, where we find a solution that describes the Carroll limit of a Schwarzschild black hole. Finally, we comment on how a cosmological constant can be incorporated in our analysis.

Study on output characteristics of Offset Twist-roller Frictional Transmission Mechanism

According to the requirements of high resolution and compact space of a rotational-double-prism system, combined with its practical application characteristics of small load and low speed, an offset twist-roller frictional transmission mechanism is proposed. Compared with the clearance elimination gear transmission mechanism, it has the advantages of high output resolution, adjustable reduction ratio, simple structure and low cost. The influence of twist angle on the output characteristics of offset twist-roller frictional transmission mechanism is studied by experiment. The results show that the larger the twist angle, the smaller the driving torque of the driven wheel, the larger the transmission ratio of the mechanism, the larger the fluctuation range of output angular velocity and transmission ratio, and the more unstable the transmission. The transmission ratio of the mechanism in stable transmission is about 30, which is much higher than that in single-stage cylindrical gear drive. The output angular resolution of the mechanism is better than 0.005°, meeting the system requirements. Through the above analysis, it lays a foundation for the application of offset twist-roller frictional transmission mechanism in rotational double prisms system.

Research on anti leakage construction of building engineering exterior wall based on improved attribute recognition model

Due to the complexity of building shape, the diversification of building materials and the nonstandard construction technology, the seepage channel exists in the outer wall envelope of building engineering, which causes the leakage of the outer wall of the building project to become more and more serious. Therefore, the research on the construction of anti leakage of the exterior wall of the building project based on the improved attribute identification model is proposed. On the basis of the attribute recognition theory subsystem, this paper introduces the grey correlation degree method in the grey system to improve the attribute recognition theory subsystem, and uses the improved attribute recognition model to analyze the influencing factors of the leakage of the building envelope. Based on the porous medium model and numerical simulation method, this paper studies the internal flow of the medium in the external wall of construction engineering, and constructs the micro flow numerical model of fracture water. In this paper, the influence of wind pressure, height and local structure on crack flow is analyzed. The results show that the initial velocity of water is related to wind pressure, building height and the local structure of surrounding retaining structure. The water flowing into the fracture is deep at a small speed, and the velocity inside the fracture has nothing to do with the pressure distribution inside the fracture.

A slow rotary dynamic motion of a disc under the influence of torque with the concept of a large parameter

A rotary motion is studied, which is used as a paradigm in both mathematics and dynamics. In this motion, the body moves around its axis. Important examples of this motion are the earth, wheels for cars or bicycles, cooling fans, airplanes, radars, and motion of the discs. In this article, we consider one of these motions such as the slow rotational motion of a disc of high natural frequency around a fixed point different from its center of mass. Suppose a constant gyrostatic couple acts on the body about the axis of symmetry. Let us consider the axis of symmetry coincide with one of the main axes of inertia. The controlled nonlinear independent system of equations of motion is obtained in the form of six nonlinear differential equations in the presence of three independent first integrals. This system is reduced to an alternative independent quasi-linear system consisting of two differential equations with only one integral. At first, when the body rotates slowly with a small angular speed about the axis of the symmetry, we achieve a large parameter for the motion which is proportional to the inverse of the angular velocity component. Then, we use the large parameter technique to obtain approximate and high-frequency analytic solutions for this motion. This technique enables us to introduce new conditions of the motion, save a lot of energy required to move the disc, and obtain new approximated solutions in a new domain of the disc parameters. We present a digital example of the problem to clarify the inferences of the motion depending on the parameters of the body. On the other hand, we use the Runge–Kutta algorithmic method to obtain the numerical solutions corresponding to the approximate solutions of the considered independent system. We investigate the inaccuracies and errors of analytic and numerical solutions by comparing them. This problem offers many applications in gyroscope dynamics, industrial engineering, astrophysics, navigation, satellites, and space engineering.

A finite control set model predictive direct speed controller for PMSM application with improved parameter robustness

Model predictive control (MPC) is an advanced control method that relies on a mathematical model containing the motor parameters in the field of Permanent Magnet Synchronous Motor (PMSM) application. However, the internal parameters of the motor and external load characteristic parameters are uncertain, and their actual values ​​may be inconsistent with the nominal values, resulting in prediction errors, which in turn affect the performance of the control algorithm. Based on the analysis of the parameter sensitivity of the motor prediction model, traditional finite control set model predictive direct speed controller (FCS-MPDSC) predicts state parameters based on a mathematical model, and there is a problem that the parameters of the motor model are uncertain, which will lead to prediction errors. In order to improve the robustness of FCS-MPDSC parameters, this paper proposes an improved FCS-MPDSC for PMSM application, which abandons the traditional PMSM control cascade structure and has the advantages of fast speed response performance, small speed error and strong parameter robustness. In order to solve the problem of load characteristic parameter uncertainty, Luenberger observer and the Model Reference Adaptive System (MRAS) algorithm are used to estimate the variation of load characteristic parameters in this paper. Moreover, a proportional-integral (PI) control term of speed error is introduced into the cost function to achieve the zero steady state error of speed and torque, which make full use of the robustness of integral action and also a faster dynamic response of direct speed control is maintained. In this paper, the HIL experimental platform is built according to the simulation. The proposed method reduces the steady-state error of the traditional method under the parameter mismatch. When the inductance parameter and the permanent magnet flux parameters deviate two times larger than nominal values, the steady-state error of the motor speed are 0.1125% and 0.8725%, respectively, demonstrating the effectiveness of the proposed method.

Growth of power spectrum due to decrease of sound speed during inflation

We study the amplification of the curvature perturbations due to a small sound speed and find that its origin is different completely from that due to the ultraslow-roll inflation. This is because when the sound speed is very small the enhancement of the power spectrum comes from the fact that the curvature perturbations at the scales smaller than the cosmic microwave background (CMB) scale become scale variant, rather than growing that leads to the amplification of the curvature perturbations during the ultraslow-roll inflation. At large scales, the power spectrum of the curvature perturbations remains to be scale invariant, which is consistent with the CMB observations, and then it will have a transient ${k}^{2}$ growth and finally approach a ${k}^{4}$ growth as the scale becomes smaller and smaller. Thus, the power spectrum can be enhanced to generate a sizable amount of primordial black holes. Furthermore, when the high order correction in the dispersion relation of the curvature perturbations is considered, the growth of the power spectrum of the curvature perturbations has the same origin as that in the case without this correction.

Deep Reinforcement Learning for Stability Enhancement of a Variable Wind Speed DFIG System

Low-frequency oscillations are a primary issue for integrating a renewable source into the grid. The objective of this study was to find sensitive parameters that cause low-frequency oscillations and design a Twin Delayed Deep Deterministic Policy Gradient (TD3) agent controller to damp the oscillations without requiring an accurate system model. In this work, a Q-learning (QL)-based model-free wind speed DFIG was designed on the rotor-side converter (RSC), and a QL-based model-free DC-link voltage regulator was designed on the grid-side converter (GSC) to enhance the stability of the system. In the next step, the TD3 agent was trained to learn the system dynamics by replacing the inner current controllers of the RSC, which replaced the QL-based model. In the first stage, the conventional PSS and Proportional–Integral (PI) controllers were introduced to both the RSC and GSC. Then, the system was trained to become model-free by replacing the PSS and the PI controller with a QL algorithm under very small wind speed variations. In the second stage, the QL algorithm was replaced with the TD3 agent by introducing large variations in wind speed. The results reveal that the TD3 agent can sustain the stability of the DFIG system under large variations in wind speed without assuming a detailed control structure beforehand, while QL-based controllers can stabilize the doubly fed induction generator (DFIG)-equipped wind energy conversion system (WECS) under small variations in wind speed.

Dynamic characteristics of elastic ring squeeze film damper coupled high-speed ball bearings

This paper explores an elastic ring squeeze film damper (ERSFD) model incorporating high-speed ball bearings to study the journal dynamics at different rotor operating speeds and squirrel cage stiffness. Firstly, dynamic model of the ERSFD is established. The journal works under ball-outer raceway excitation rather than rotor unbalance force. Bearing high-speed characteristics including ball centrifugal force, contact angle change and heavy thrust-applied load are outlined in quasi-static model when deriving bearing force. Oil film pressure is governed by the Reynolds equation and solved iteratively using the central finite difference scheme. Flow performance through the orifice and its effect on the oil film pressure are analyzed using computational fluid dynamics (CFD) technique. Elastic ring deformation is addressed using a thin-walled ring model. Secondly, squirrel cage stiffness and rotor operating speeds were chosen as influence parameters to numerically examine the journal steady-state and transient dynamics, and finally the center orbit and vibration of the journal were experimentally measured. The results demonstrate that an increase in squirrel cage stiffness enables the journal to orbit at small size but leads to higher transmissibility. Small squirrel cage stiffness and rotor operating speed result in high amplitude and velocity oscillations and destabilize the journal; alternatively, higher squirrel cage stiffness is ineffective in transmissibility attenuation regardless of rotor operating speed. It was concluded that a small squirrel cage stiffness cooperating with high rotor operating speed contributes to stabilize journal and attenuate vibration effectively.

Stationary states in two-lane traffic: Insights from kinetic theory.

Kinetics of dilute heterogeneous traffic on a two-lane road is formulated in the framework of Ben-Naim-Krapivsky model and stationary state properties are analytically derived in the asymptotic limit. The heterogeneity is introduced into the model as a quenched disorder in desired speeds of vehicles. The two-lane model assumes that each vehicle or platoon in a lane moves ballistically until it approaches a slow-moving vehicle or platoon and then joins it. Vehicles in a platoon are assumed to escape the platoon at a constant rate by changing lanes after which they continue to move at their desired speeds. Each lane is assumed to have a different escape rate. As the stationary state is approached, the platoon densities in the two lanes become equal, whereas the vehicle densities and fluxes are higher in the lane with lower escape rate. A majority of the vehicles enjoy a free flow if the harmonic mean of the escape rates of the lanes is comparable to average initial flux on the road. The average platoon size is close to unity in the free-flow regime. If the harmonic mean is lower than the average initial flux, then vehicles with desired speeds lower than a characteristic speed v^{*} still enjoy free flow while those vehicles with desired speeds that are greater than v^{*} experience congestion and form platoons behind the slower vehicles. The characteristic speed depends on the mean of escape times [R=(R_{1}+R_{-1})/2] of the two lanes (represented by 1 and -1) as v^{*}∼R^{-1/μ+2}, where μ is the exponent of the quenched disorder distribution for desired speed in the small speed limit. The average platoon size in a lane, when v^{*}≪1, is proportional to R^{μ+1/μ+2} plus a lane-dependent correction. Equationsfor the kinetics of platoon size distribution for two-lane traffic are also studied. It is shown that a stationary state with platoons as large as road length can occur only if the mean escape rate is independent of platoon size.

Thermal suppression of bubble nucleation at first-order phase transitions in the early Universe

One of the key observables in a gravitational wave power spectrum from a first order phase transition in the early Universe is the mean bubble spacing, which depends on the rate of nucleation of bubbles of the stable phase, as well as the bubble wall speed. When the bubbles expand as deflagrations, it is expected that the heating of the fluid in front of the phase boundary suppresses the nucleation rate. We quantify the effect, showing that it increases the mean bubble separation, and acts to enhance the gravitational wave signal by a factor of up to order 10. The effect is largest for small wall speeds and strong transitions.

MS-DNet: A mobile neural network for plant disease identification

Plant disease identification has recently attracted immense attention from the perspective of food security. Owing to the complexity and diversity of plant diseases, plant disease recognition using image processing techniques is a challenging task. Although the widely applied deep neural networks are promising for recognizing diverse plant diseases, they have certain drawbacks such as their requirement for a large number of parameters, which necessitates a large amount of annotation data for training models. To overcome this challenge, this study proposes a novel lightweight network architecture called MS-DNet for the recognition of crop diseases; the network has a small model size and high computation speed. The proposed method has attained a satisfactory performance in comparative experiments, with the highest average accuracy of 98.32% in recognizing different crop disease types. The experimental results further show that the proposed method outperforms other state-of-the-art methods and also demonstrate its efficiency and extensibility. Our code is available at https://github.com/xtu502/Automatic-crop-disease-identification-under-field-conditions.

Small Diameter, Lower Speed, and Laminar Flow Are Protective Factors Against Atherosclerosis In Distal Coronary Arteries

Small Diameter, Lower Speed, and Laminar Flow Are Protective Factors Against Atherosclerosis In Distal Coronary Arteries

The effect of plyometric exercises to develop some physical and skill abilities and functional measurements of beach soccer players

Importance of research was revealed in the plyometric training method And its impact on the variables under study, which are among the essential pillars to provide a reasonable level for the team, the speed of moving, jumping, receiving, and handing over. Scoring offset continuation with the performance of skills throughout the match time, and as it's known that the beach soccer game needs the speed of execution and to repeat those skills in a way Fast and repetitive throughout the game and the privacy of the game due to the small area and speed of movement in the stadium.The research problem was in the following question: Do plyometric exercises affect some of the physical abilities, skills, and functional measurements of Qalaat Saleh players in beach soccer?The research aims to identify the effect of plyometric exercises on the level of some physical abilities, skills, and functional measurements of Qalaat Saleh players in beach soccer. The researcher relied on the experimental method for the nature of solving the research (problem, and the research sample of (12 players from Qalaat Saleh Club for the first degree included The beach, where the researcher concluded through this study an improvement in the level of physical abilities, skills, and functional measurements.