Divergence Speed Research Articles

Aeroelastic analysis of non-conventional and slender suspension bridges

The aim of this study was to investigate the dynamic effects of wind actions on bridge cross sections, with a goal to propose design charts for non-conventional and slender bridge decks. An eigenvalue analysis was conducted first and the results were validated experimentally. Subsequently, aeroelastic analysis of the bridge deck section was performed. This analysis encompassed the analytical method adhering to the Eurocode and computational fluid dynamics simulations. Both methodologies indicated that the bridge was susceptible to vortex-induced vibrations. To mitigate these vibrations, wind noses provide better stability than the currently used guide vanes. The effect of changing deck width was also studied. Wider and more streamlined sections displayed better aeroelastic performance. The study also revealed that the Eurocode overestimates the derivatives of aerodynamic moment coefficient by 53% to 93%. Consequently, optimized charts are proposed to enhance the accuracy of torsional divergence and flutter speed calculations, facilitating the safe and efficient design of such bridges.

Aeroelastic Structural Analysis to Calculate Symmetrical Divergence Modes of an Aircraft Wing Using Aerodynamic Lifting Line Theory

This work explores the use of numerical matrix iteration to determine an aircraft wing's divergence speed using the aerodynamic span effects approach. The present work begins with the construction of equilibrium equations in differential and integral forms. In this paper, integral formulas are used because it serves as a convenient basis for numerical solutions of complex practical problems. Second, the straight-tapered wing is divided into a number of Multhopp stations. Subsequently, the stations' torsional influence coefficient matrix has been calculated. Third, lifting line theory was used as a suitable choice of aerodynamic theory, and the governing equations were represented in matrix form. Finally, aerodynamic span effects are taken into consideration with induction effects according to Prandtl’s lifting line theory to calculate the symmetrical divergence speed from the lowest eigenvalue of the homogenous governing integral equation. To get the solution to converge, a matrix has been iterated using the MATLAB environment. The obtained results will aid modern aircraft designers in their understanding of wing instability in steady motion.

АНАЛІЗ ВПЛИВУ КУТА СТРІЛОПОДІБНОСТІ НА ХАРАКТЕРИСТИКИ СТАТИЧНОЇ АЕРОПРУЖНОСТІ КРИЛА НАВЧАЛЬНО-ТРЕНУВАЛЬНОГО ЛІТАКА

The article is dedicated to the analysis of static aeroelastic phenomena in the wing of a trainer aircraft and the general influence of wing sweep on critical speeds. Aeroelasticity studies the interaction between aerodynamic and elastic forces and the impact of this interaction on the aircraft's structure. There are two types of aeroelasticity: static and dynamic. The article reviews and analyzes publications related to this issue. The analysis of the research shows that when designing an aircraft, it is necessary to determine the aeroelastic characteristics of its aerodynamic surfaces. In addition to structural rigidity, the sweep angle also influences these phenomena. The scientific novelty of the study lies in the fact that, unlike the analyzed research, the designed wing structure of a trainer aircraft is considered.For the designed trainer aircraft, the critical speeds of static aeroelastic phenomena were determined. The calculation of the influence of the wing sweep angle on the divergence speeds of the trainer aircraft confirms previously obtained results regarding this influence. When the sweep is increased or decreased for wings with the same span, the torsional rigidity of the wing decreases due to the increase in the length of the line of centers of rigidity. However, the most significant impact on the aeroelastic characteristics is made by the shift of the bending center when the sweep angle changes.With forward sweep, the arm of the aerodynamic forces relative to the bending center increases, thereby reducing the critical divergence speeds. For straight sweep, as the sweep increases, the bending center moves forward, and at a certain point, the bending center is located in front of the aerodynamic center. This means that the wing twist angle decreases as the aerodynamic force increases, which, in the considered planar case, eliminates the occurrence of divergence.The preliminarily determined maximum flight speed does not exceed the critical speeds of divergence and aileron reversal. This result represents the practical value of the study. To achieve higher flight speeds, wings with straight sweep should be used. More precise computational or experimental methods for determining aeroelastic characteristics should be used in the subsequent design stages to prevent aeroelastic phenomena across the entire operational range of speeds and altitudes of the trainer aircraft.

ANALYSIS OF CONVERGENCE BETWEEN PROVINCES IN INDONESIA

<p>Indonesia is one of the developing countries that is always trying to increase its economic growth. Indonesia has a large number of people with various ethnic backgrounds and diverse customs, so this situation has given rise to disparities between regions. This study aims to determine whether or not sigma convergence, to find out whether absolute and conditional convergence occurs or not, and to determine the speed of convergence. This study uses secondary data, namely Gross Regional Domestic Product (GRDP) per capita, poverty, and inequality for each province in Indonesia from 2017-2021. The method used in this study is panel data with a fixed effect approach. The results of the analysis using the sigma convergence (σ) approach show the occurrence of convergence. The results of the absolute convergence analysis explain the divergence of GRDP per capita in Indonesia with a divergence speed of 13.76% per year. The results of the conditional convergence analysis show that there is a divergence of GRDP per capita in Indonesia with a divergence speed of 13.62% per year.</p>

A Jacobi-Ritz Approach for Aeroelastic Analysis of Swept Distributed Propulsion Aircraft Wing

Abstract This paper presents a Jacobi-Ritz approach for conducting flutter and divergence analysis of a complex distributed propulsion aircraft wing like NASA X-57. The general orthogonal Jacobi polynomials are used to approximate the bending displacement and torsional rotation angle in the Ritz method based structural and aeroelastic analysis. The Jacobi polynomials satisfy the orthogonality condition using weight functions which are easily modified to satisfy different essential and natural boundary conditions. Compared to simple polynomials, Jacobi polynomials can eliminate the well-known ill-conditioning numerical issues when considering higher-order polynomials. The Jacobi-Ritz method is also found to alleviate mode switching often encountered in tracking the changes of modes with the varying airspeed. The Jacobi-Ritz method is later used to investigate the flutter and divergence speeds under distributed propulsor mass and their locations, nonuniform aerodynamic model in the presence of multiple propulsors, and the sweep angle. Results show that placing the distributed propulsors on the wing's leading edge increases the flutter speed even though the bending and torsion modal frequencies are decreased compared to those of the wing without propulsors. The presence of pods for the middle high-lift motors causes an extra aerodynamic moment which reduces the flutter speed. Parametric studies also show that the divergence speed is lower than the flutter speed for a uniform and straight distributed propulsor wing. Using swept-back wing configuration and placing the tip propulsor near the wing's leading edge can help to increase both flutter and divergence speeds.

Quantum Speed Limit for States and Observables of Perturbed Open Systems.

Quantum speed limits provide upper bounds on the rate with which a quantum system can move away from its initial state. Here, we provide a different kind of speed limit, describing the divergence of a perturbed open system from its unperturbed trajectory. In the case of weak coupling, we show that the divergence speed is bounded by the quantum Fisher information under a perturbing Hamiltonian, up to an error which can be estimated from system and bath timescales. We give three applications of our speed limit. First, it enables experimental estimation of quantum Fisher information in the presence of decoherence that is not fully characterized. Second, it implies that large quantum work fluctuations are necessary for a thermal system to be driven quickly out of equilibrium under a quench. Moreover, it can be used to bound the response to perturbations of expectation values of observables in open systems.

Flutter and divergence zones of perovskite solar cell-based panels of aircraft wings in subsonic airflow

Solar-powered aircraft have advantages such as quite long flight time and resource conservation. In recent years, with the improvements in solar cell efficiency, lightweight structural design, microelectronics, and automation control technology, more and more countries and organizations have conducted research on solar-powered aircraft. Solar cells are an important component of solar-powered aircraft systems. Perovskite solar cells have the advantages of high flexibility, lightweight, and high specific power, making them the ideal material for solar-powered aircraft wings. To receive as much sunlight radiation as possible and improve the lift-to-drag ratio of the entire aircraft, solar-powered aircraft have a high aspect ratio, making them more sensitive to changes in airflow. Therefore, the stability zones and vibration of perovskite solar cell (PSC) panels in subsonic airflow were studied for the first time. Additionally, to enhance the novelty of the paper and present more comprehensive results, the effect of the nanomaterial properties of one-layered perovskite solar cell substrates reinforced by carbon nanotubes and graphene platelets on the flutter and divergence phenomenon was investigated. To accurately simulate the displacement field after the composite perovskite panel is bent, Reddy's high-order shear deformation theory was adopted. The PSC panel's aerodynamic-elastic coupling motion equations were established by combining Hamilton's principle with the linear potential flow theory and the Bernoulli equation. The dynamic equations were discretized using a meshless numerical method to obtain the generalized multi-parameter characteristic equations. The obtained natural frequencies and critical divergence speeds were compared with published literature to validate the correctness of the aerodynamic model and laminated board model. The divergence instability and flutter instability of the PSC nanocomposite panel were investigated for changing the thickness, nano-fillers, porosity, laying angle, and aspect ratio of the substrate. We showed, that the PSC panel has a divergence instability state first, and then flutter instability appears. Additionally, the substrate nanomaterial parameters of the PSC panel significantly affect shifting divergence and flutter zones. Interestingly, the corresponding natural frequency increases when flutter occurs with an increase in the porosity volume.

Assessing the mechanical and static aeroelastic performance of cellular Kirigami wingbox designs

Adaptive wings configurations have been evaluated for morphing airframe applications during the last two decades. Constructions with flexible hinges can be in particular a solution for small top medium-scale air vehicles, while novel Kirigami technologies help to produce flexible and complex structures by enabling novel geometric paradigms. In this study, a cellular Kirigami wingbox with an adaptive hinge is designed and manufactured. The mechanical properties of the wingbox are numerically evaluated, considering the shear modulus of the cellular elements patterning the wingbox. Thus, the equivalent torsional, flexural stiffness, as well as the shear center location of the whole wingbox structure are calculated. The analysis is parametrized against various possible internal cell angles and cell thickness values that define the Kirigami cellular tessellation of the wingbox. The static divergence speed is also evaluated by means of the same parametrization. This study shows the feasibility of using a Kirigami wingbox concept for morphing/adaptive small to medium-scale from a structural and aeroelastic perspective.

Divergence Structural Analysis of an Aircraft Tapered-Unswept Wing Using Aerodynamic Strip Theory for the Case of Flight at Sea Level

This study investigates the utilize of the iteration of matrix numerically to get the divergence speed of an aircraft tapered-unswept wing via using method of strip theory (without finite span correction and with finite span correction). The 2-D fluid flow across the wing airfoil section is assumed by the aerodynamic strip theory and then integrated over wing span. In the present work, first the tapered unswept wing is divided into four Multhopp’s stations. Then, elastic properties of this wing in relation to torsional influence coefficients related with this four Multhopp’s stations have been evaluated. Second, equations for equilibrium are constructed as integral equations. Then, an appropriate aerodynamic theory in the form of strip theory was addressed, as well as the technique of solution for determining the divergence speed. Finally, using strip theory, the integral equation has been expressed in matrix form. Iteration of matrix has been done using MATLAB environment to reach for the solution to converge. Also, an increase of 15% in torsional stiffness of aircraft wing has been considered to illustrate its effects on torsional divergence speed of aircraft wing. The attained results are going to be helpful in understanding of wing instability for modern aircraft designer.

Dynamics of functionally graded porous rotating Rayleigh microbeams with longitudinal movement in complex fields

As a first attempt, the vibration of rotating functionally graded porous Rayleigh beams under longitudinal motion in hygro-thermo-magnetic fields is scrutinized numerically and analytically based on the scale-dependent strain gradient theory. Also, parametric studies are performed to diagnose the impacts of critical factors such as the functionally graded index, rotary inertia parameter, porosity distribution, foundation characteristics, environmental loads, boundary conditions, axial and tangential follower forces on the microbeam stability. It is assumed that the material properties of the microbeam are graded across the thickness according to a power-law function with six different porosity models. The dynamical equations of the functionally graded microbeam are derived based on the extended Hamilton’s principle. Then, backward and forward vibrational frequencies are computed with the aid of the Galerkin discretization scheme and eigenvalue analysis. For validation purposes, the results are compared with published reports. Furthermore, the instability border of the microbeam is determined via an analytical approach. Critical rotational and longitudinal speeds as well as Campbell and stability diagrams are obtained to identify the stability evolution. The results declared that as the functionally graded index and rotary inertia parameter ascend, divergence and flutter speeds of the microbeam descend. The presented outcomes could be helpful in the optimum design of inhomogeneous gyroscopic microsystems.

Thermal-aero-elastic analysis of a typical all-moving control surface

• A thermal interpolation method is proposed, which can easily load thermal field onto FEM models. This method can decouple thermal computation and basic structure dynamic mode computation. • Thermal dynamic characteristics of a typical all-moving control surface for hypersonic vehicle were investigated. • Mach number effects on flutter computation of the present all-moving control surface were studied via thermal effects or not. At present, thermal-fluid–structure coupling problems always need to be considered for the design of hypersonic flight vehicle. This work proposes numerical analysis of thermal-aero-elastic characteristic of a typical all-moving control surface for hypersonic flight vehicle. Basic aerodynamic and aero-thermal analysis of the model were gotten through finite volume simulations. By adopted transient temperature distribution of the control surface, thermal effects were interpolated to structural stiffness which could change modes of the control surface. Material nonlinearity of it due to thermal effect was included. Aeroelasticity analysis of the control surface was presented to find the difference of divergence speed between the usage of ‘thermal mode’ and ‘normal mode’. Flutter boundary was investigated to present the influence due to thermal effects. Different Mach numbers were used in flutter computations. It was seen from the results that thermal effects could obviously influence aeroelastic characteristic of the all-moving control surface. The proposed numerical process can provide a useful engineering method for aeroelastic studies on hypersonic flight vehicles.

Active and passive hybrid detection method for power CPS false data injection attacks with improved AKF and GRU‐CNN

Influenced by deep penetration of the new generation of information technology, power systems have gradually evolved into highly coupled cyber-physical systems (CPS). Among many possible power CPS network attacks, a false data injection attacks (FDIAs) is the most serious. Taking account of the fact that the existing knowledge-driven detection process for FDIAs has been in a passive detection state for a long time and ignores the advantages of data-driven active capture of features, an active and passive hybrid detection method for power CPS FDIAs with improved adaptive Kalman filter (AKF) and convolutional neural networks (CNN) is proposed in this paper. First, we analyze the shortcomings of the traditional AKF algorithm in terms of filtering divergence and calculation speed. The state estimation algorithm based on non-negative positive-definite adaptive Kalman filter (NDAKF) is improved, and a passive detection method of FDIAs is constructed, with similarity Euclidean distance detection and residual detection at its core. Then, combined with the advantages of gate recurrent unit (GRU) and CNN in terms of temporal memory and feature-expression ability, an active detection method of FDIAs based on a GRU-CNN hybrid neural network is proposed. Finally, the results of joint knowledge-driven and data-driven parallel detection are used to define a mixed fixed-calculation formula, and an active and passive hybrid detection method of FDIAs is established, considering the characteristic constraints of the parallel mode. A simulation system example of power CPS FDIAs verifies the effectiveness and accuracy of the method proposed in this paper.

Optimum Design of Aft-swept Composite Wings for Aeroelastic Characteristics with Structural Damping

The present paper deals with the aeroelastic characteristics of aft-swept composite plate wings with structural damping. Based on the complex modulus approach, a minimum weight design of cantilevered laminated plates with a sweep-back angle under the flutter and divergence speed constraints is conducted by using a differential evolution in which lamination parameters are used as design variables.

Modern Economic System: Evaluation Index System, Regional Inequality and Temporal-Spatial Evolution

Based on grasping the scientific connotation and basic framework of the modern economic system, this paper selects 52 indicators from four parts: motive force system, resource allocation, industrial system and growth quality to build an evaluation index system of modern economic system, and uses time-space range entropy weigh to measure the development level of the modern economic system of 31 provinces in China from 2013 to 2018, using Dagum Gini coefficient, Kernel density estimation, and temporal-spatial convergence model to analyze the spatial-temporal distribution pattern and evolution trend of the development of modern economic system in China from the perspectives of different regions. The results show that the development level of China’s modern economic system is showing an upward trend, and the development level of different regions differs significantly. The development level and speed of the southern region is higher than that of the northern region. The eastern region has the highest level of development, followed by the central and northeastern regions, and the western region has the lowest level of development. The central region develops faster, followed by the western and eastern regions, and the northeastern region is slower. The development level of Beijing and Shanghai is much higher than that of other provinces, forming the first echelon of the development of modern economic system. During the sample period, the overall regional gap shows a trend of narrowing. The gap between the northern region and the southern region is constantly narrowing, and the gap between the regions first narrows and then widens. In the four major regions, the disparity in descending order is east, west, northeast, and central, and the disparity among regions is in descending order of east-west, east-northeast, east-middle, middle-west, west-northeast, and middle-northeast. The gap between the northern region and the southern region mainly comes from the gap within the region, and the four major regional gaps mainly come from the gap between regions. The center of the density function of the development level of modern economic system in China and various regions shifts to the right, but its temporal and spatial distribution characteristics are different. The eastern region shows a significant trend of multi-polarization, while the southern region shows a slight trend of polarization. The number of wave crests in other regions is all single peaks, and there is no polarization phenomenon. The development performance of modern economic system in China and various regions is in a divergent state. The divergence rate in the later period of China is higher than that in the early period. The divergence rate in the north-south region shows an upward trend, and the overall divergence rate in the south is higher than that in the north. The divergence speed of the four major regions is sorted from high to low into the western, central, northeastern and eastern regions. The polarization trend in the east and west regions is more pronounced in the later period of the investigation, the development of the central region is relatively stable, and the divergence rate of the northeast region shows a downward trend. This paper measures the development level of the modern economic system of various provinces in different periods, reveals the development and evolution trend of modern economic system in China, and provides foundations for accelerating the construction of a modern economic system and promoting high-quality development.

How does the magnitude of genetic variation affect ecological and reproductive character displacement?

AbstractWhile previous studies on character displacement tended to focus on trait divergence and convergence as a result of long‐term evolution, recent studies suggest that character displacement can be a special case of evolutionary rescue, where rapid evolution prevents species extinction by weakening interspecific competition. Here we analyzed a simple model to examine how the magnitude of genetic variation affects evolutionary rescue via ecological and reproductive character displacement that weakens interspecific competition in exploitation of shared resources (i.e., resource competition) and in the mating process caused by incomplete species recognition (i.e., reproductive interference), respectively. We found that slow trait divergence due to small genetic variance results in species extinction in reproductive character displacement but not in ecological character displacement. This is because one species becomes rare in slow character displacement, and this causes deterministic extinction due to minority disadvantage of reproductive interference. On the other hand, there is no deterministic extinction in the process of ecological character displacement. Furthermore, species extinction becomes less likely in the case of positive covariance between ecological and reproductive traits as divergence of the ecological trait (e.g., root depths) increases the divergence speed of the reproductive trait (e.g., flower colors) and vice versa. It will be interesting to compare intraspecific genetic (co)variance of ecological and reproductive traits in future studies for understanding how ecological and reproductive character displacement occur without extinction.

Suppression of the G-sensitive drift of laser gyro in dual-axis rotational inertial navigation system

The dual-axis rotational inertial navigation system (INS) with dithered ring laser gyro (DRLG) is widely used in high precision navigation. The major inertial sensor errors such as drift errors of gyro and accelerometer can be averaged out, but the G-sensitive drifts of laser gyro cannot be averaged out by indexing. A 16-position rotational simulation experiment proves the G-sensitive drift will affect the long-term navigation error for the rotational INS quantitatively. The vibration coupling and asymmetric structure of the DRLG are the main errors. A new dithered mechanism and optimized DRLG is designed. The validity and efficiency of the optimized design are conformed by 1 g sinusoidal vibration experiments. An optimized inertial measurement unit (IMU) is formulated and measured experimentally. Laboratory and vehicle experimental results show that the divergence speed of longitude errors can be effectively slowed down in the optimized IMU. In long term independent navigation, the position accuracy of dual-axis rotational INS is improved close to 50%, and the G-sensitive drifts of laser gyro in the optimized IMU are less than 0.000 2 °/h. These results have important theoretical significance and practical value for improving the structural dynamic characteristics of DRLG INS, especially the high-precision inertial system.

Optimizing Ballistic Motion of Partially Coherent Multiple Airy Beams by Quadratic and Linear Phases

AbstractBy applying quadratic and linear phase modulations (QPM and LPM), the propagation properties of the partially coherent dual and quad Airy beams which maintain acceleration in free space are studied. They are generated by superimposing two and four partially coherent Airy beams whose phase is modulated in the source field. It is demonstrated that the trajectories of the partially coherent light beams and the location and number of focal points, along with maximum altitude and range of the trajectories can be easily dominated by adjusting the appropriate values of QPM p and LPM l. Furthermore, for the quad case, the transverse spectral density distribution of lacking side lobes exhibits the structure of the optical frame which may be flipped under certain conditions. Both the peak intensity of the beams and the divergence speed of the optical frame can be managed by choosing the different characteristic transverse width of the beams. These results show an energizing new idea in the manipulation of partially coherent multiple fields of accelerating beams.

Delamination effects on the unsteady aero-elastic behavior of composite wing by modal analysis

This article deals with the investigation of delamination effects on the flutter behavior of a composite wing subjected to unsteady aerodynamic loads by providing an integrated procedure using exact methods. For this purpose, an undamaged wing structure is modeled as a cantilevered Bernoulli–Euler beam with coupled bending–torsion and delaminated wing structure is modeled as three interconnected intact beams. The modal analysis of the intact and delaminated beams is performed and mode shapes are obtained based on the development of the dynamic stiffness matrix, a computer code and an iterative method. The fundamental modes of the intact and delaminated beam derived from the free vibration analysis are used in Galerkin’s method and the flutter and divergence speeds are obtained with aerodynamic forces applied. In fact, modified shape functions were developed to reflect the delamination effect in the aeroelastic analysis. Also, for the unsteady aeroelastic analysis, an iterative algorithm is developed. It was found that the delamination location and its length can have a positive or a negative influence on the flutter behavior of the wing which depends on the fiber angle.

Partially Coherent Dual and Quad Airy‐Like Beams

AbstractPartially coherent multi‐Airy‐like beams are investigated by introducing coordinate transformation parameters and combining them with the theory of multi‐beam superposition under symmetrical conditions, for the case of dual and quad as examples. The accurate propagation position of the mutual‐focusing point is obtained by analyzing the normalized spectral density (SD) curves at different planes. The outcomes show that both the optical frame and the interference pattern can be changed by means of adjusting the coordinate transformation parameters. For a special circumstance, the transverse SD overlapping profile is presented in a rotational four‐square grid. In addition, the coordinate transformation parameters periodically affect the distance between the two main lobes, which provides us a new idea with adjusting the width of the optical frame edges. Moreover, both the peak intensity of the SD and the divergence speed can be controlled by tuning the value of the equivalent beam width. These results may provide new inspiration for applications of partially coherent Airy‐like beams in optical propagation, capture, and communication.

Observations and high‐resolution simulations of convective precipitation organization over the tropical Atlantic

AbstractHigh‐resolution simulations (grid spacing 2.5 km) are performed with ICON‐LEM to characterize convective organization in the Tropics during August 2016 over a large domain ranging from northeastern South America, along the tropical Atlantic to Africa (8,000×3,000 km). The degree of organization is measured by a refined version of the wavelet‐based organization index (WOI), which is able to characterize the scale, the intensity and anisotropy of convection based on rain rates alone. Exploiting the localization of wavelets both in space and time, we define a localized version of the convective organization index (LWOI). We compare convection observed in satellite‐derived rain rates with the corresponding processes simulated by ICON‐LEM. Model and observations indicate three regions with different kinds of convective organization. Continental convection over West Africa has a predominantly meridional orientation and is more organized than over South America, because it acts on larger scales and is more intense. Convection over the tropical Atlantic is zonally oriented along the ITCZ and less intense. ICON and observations agree on the number and intensity of the African easterly waves during the simulation period. The waves are associated with strong vorticity anomalies and are clearly visible in a spatiotemporal wavelet analysis. The central speed and the wavelength of the waves is simulated well. Both the scale and intensity components of LWOI in ICON are significantly correlated with environmental variables. The scale of precipitation is related to wind shear, CAPE and its tendency, while the intensity strongly correlates with column‐integrated humidity, upper‐level divergence and maximum vertical wind speed. This demonstrates that the LWOI components capture important characteristics of convective precipitation.