Static Stability Conditions Research Articles

Ionospheric electric potential as an alternative indicator of solar effect on the lower atmosphere

We have explored the possibility of applying the ionospheric electric potential (EP) as a parameter describing the effects of solar activity on the troposphere. We calculated EP, using the semi-empirical model, where the potential spatial distribution is determined by solar wind, interplanetary magnetic field parameters, and the geomagnetic activity index AL. We have carried out a comparative analysis of EP and the commonly used geomagnetic activity indices in a high-latitude region for 1975–2019. It has been shown that EP can be used as an indicator of solar activity since it describes both short-period disturbances and long-term variations. The revealed similar trends in long-term EP variations and near-surface temperature suggest that the changes in climate system parameters are induced by slower changes in the Sun’s large-scale magnetic field. The performed analysis of EP and near-surface temperature correlation maps has revealed that the atmospheric static stability conditions have an effect on spatial distribution of tropospheric response to solar impact.

Электрический потенциал ионосферы — альтернативный индикатор солнечного воздействия на нижнюю атмосферу

We have explored the possibility of applying the ionospheric electric potential (EP) as a parameter describing the effects of solar activity on the troposphere. We calculated EP, using the semi-empirical model, where the potential spatial distribution is determined by solar wind, interplanetary magnetic field parameters, and the geomagnetic activity index AL. We have carried out a comparative analysis of EP and the commonly used geomagnetic activity indices in a high-latitude region for 1975–2019. It has been shown that EP can be used as an indicator of solar activity since it describes both short-period disturbances and long-term variations. The revealed similar trends in long-term EP variations and near-surface temperature suggest that the changes in climate system parameters are induced by slower changes in the Sun’s large-scale magnetic field. The performed analysis of EP and near-surface temperature correlation maps has revealed that the atmospheric static stability conditions have an effect on spatial distribution of tropospheric response to solar impact.

Comparative Study of the Transmission Capacity of Grid-Forming Converters and Grid-Following Converters

The development trend of high shares of renewables and power electronics has increased the demand for new energy converters in the power system, but there is a lack of systematic research on the stability of different types of converters when transmitting power, which is worth exploring in depth. In this study, the power transfer capabilities of grid-forming and grid-following converters are investigated separately through an equivalent circuit diagram and phasor diagram when connected to the grid, and a quantitative relationship between converters’ power transmission limit and short circuit ratio under static stability conditions is obtained, leading to the conclusion that, in terms of power transmission, grid-forming converters are more suitable for weak grids with high damping and low inertia, whereas grid-following converters are more suitable for strong grids with high inertia. The conclusions are further verified by constructing the converter grid-connected models for different grid strengths through the PLECS simulation platform and the real-time simulation RTBOX1 and F28379D launchpad platform.

WheTLHLoc: Small-Scale Hybrid Locomotion Robot With Stair Climbing Capability

AbstractThis paper discusses the theoretical analysis and the experimental validation of the step and stair climbing capability of wheel-track-leg hybrid locomotion (WheTLHLoc), a small-scale hybrid locomotion robot with overall size of 450 × 350 × 130 mm and maximum payload of 0.5 kg. The architecture of this robot combines two tracks, two rotating legs, two actuated wheels, and two passive omni wheels. The robot is capable of performing different locomotion modes: wheeled locomotion on flat and compact grounds with maximum speed of 0.9 m/s, tracked locomotion on soft and yielding terrains with maximum speed of 0.1 m/s, mixed use of tracks, legs, and wheels to overcome obstacles. In particular, the process of step and stair climbing is analyzed considering static stability and non-slipping conditions. The experimental campaign on the first prototype has confirmed the effectiveness of the proposed climbing maneuver for steps up to 165 mm and the operative flexibility of the WheTLHLoc robot.

Self-Adaptive Obstacle Crossing of an AntiBot From Reconfiguration Control and Mechanical Adaptation

AbstractOne drawback of wheeled robots is their inferiority to conquer large obstacles and perform well on complicated terrains, which limits their application in rescue missions. To provide a solution to this issue, an ant-like six-wheeled reconfigurable robot, called AntiBot, is proposed in this paper. The AntiBot has a Sarrus reconfiguration body, a three-rocker-leg passive suspension, and mechanical adaptable obstacle-climbing wheeled legs. In this paper, we demonstrate through simulations and experiments that this robot can change the position of its center of mass actively to improve its obstacle-crossing capability. The geometric and static stability conditions for obstacle crossing of the robot are derived and formulated, and numerical simulations are conducted to find the feasible region of the robot’s configuration in obstacle crossing. In addition, a self-adaptive obstacle-crossing algorithm is proposed to improve the robot’s obstacle-crossing performance. A physical prototype is developed, and using it, a series of experiments are carried out to verify the effectiveness of the proposed self-adaptive obstacle-crossing algorithm.

До порівняльної оцінки триланкових автобусів різних компонувальних схем за стійкістю руху

The article develops a mathematical model describing the movement of a three-link articulated bus (two-axle bus and two single-axle trailers), further ТAВ, as a four-mass system, taking into account the control wheel module of the bus. The system allows to study the influence of the design parameters of the bus and trailers on the stability of the ТAВ. The object of the study is the stability of the articulated bus with drive either on the axle of the bus or on the axle of the first trailer. The purpose of the work is a comparative evaluation of articulated buses with drive either on the bus axle or on the axle of the trailer in terms of stability. Research methods – mathematical modeling of the stability of the movement of a three-link articulated bus (two-axle bus and two uniaxial trailers) with drive either on the bus axle or on the axle of the first trailer. As a result of the study, it was found that at the selected values of the design parameters of the ТAВ, the critical speed when applying traction to the bus axis was 31.19 m / s, which exceeds the maximum speed of its movement. When implementing traction on the axis of the trailer, the loss of stability of circular stationary modes is realized at values of 0.08 <alpha <0.09 (alpha – coefficient determining the share of normal reaction of the bearing surface on the wheels of the bus or trailer driving wheels), and the loss of stability of rectilinear motion – at alpha = 0,0815. The critical velocity in this case is vkp = 12.34 m / s. Analysis of the conditions of static stability of the ТAВ during the implementation of traction on the axis of the trailer showed that the value of the drag coefficient does not affect the critical speed (not included in the expression of critical speed), and the value of rolling resistance coefficients on the first and second axles slightly affects the critical speed . and a critical value of the alpha parameter that determines the amount of traction. At the same time, even with optimally selected stiffness and layout parameters, the critical speed of articulated buses does not exceed 12.5 m / s, that is, such buses need a special system of opposition. Keywords: articulated bus, stability, critical speed, traction force, driving mode, trailer, support surface reaction.

Seismic Analysis of a Limestone Rock Slope Through Numerical Modelling: Pseudo-Static vs. Non-Linear Dynamic Approach

In the present work, a seismic analysis was performed in advance on a limestone rock slope (height = 150 m) outcropping along the Tagliamento River valley, in the Friuli Venezia Giulia Region, north-eastern Italy. The analysed slope is characterised by strong rock mass damage, thus resulting in a critical stability condition (unstable volume = 110,000–200,000 m3). The seismic analysis was performed adopting the 2D finite difference method (FDM) and employing both a pseudo-static approach and a non-linear dynamic approach. Model outcomes demonstrate that the seismic motion induces internal, localised ruptures within the rock mass. Some important differences in the mechanical behaviour of the rock slope were highlighted, depending on the specific modelling approach assumed. When adopting a pseudo-static approach, the slope failure occurs for PGA values ranging between 0.056 g and 0.124 g, depending on the different initial static stability condition assumed for the slope (Strength Reduction Factor SRF = 1.00–1.15). According to the non-linear dynamic approach, the slope failure is achieved for PGA values varying between 0.056 g and 0.213 g. Pre-collapse slope displacements calculated with the pseudo-static approach (12–15 cm) are much more greater than those obtained through the non-linear dynamic approach (0.5–3 mm). The modelling results obtained through the non-linear dynamic analysis also testify that the seismic topographic amplification is 1.5 times the target acceleration at the slope face and 2.5 times the target acceleration at the slope toe.

Potential sources of atmospheric turbulence estimated using the Thorpe method and operational radiosonde data in the United States

This study estimated the eddy dissipation rate (ε) and the thickness of the turbulence layer (THTL) in the free atmosphere (z = 3–30 km) based on the Thorpe method using high vertical-resolution radiosonde data for 6 years (January 2012–December 2017) at 68 operational stations in the United States and investigated potential sources of turbulence. The results showed that turbulence occurs more frequently in the troposphere than in the stratosphere, with log10ε ranging from −4 to 0 (from −4 to −0.5) m2 s−3 in the troposphere (stratosphere). The mean and median of THTL in the troposphere are 278 m and 205 m, respectively, which are larger than those in the stratosphere of 140 m and 115 m. However, the layer-mean log10ε over 3-km altitude bins is found to be larger in the stratosphere due to there being less turbulence cases than in the troposphere. To better represent the layer-mean turbulence, a new quantity is suggested, named the layer-mean effective ε (EE), by combining ε and THTL. The potential sources of the observed turbulence are examined by analyzing four turbulence indices: squared Brunt-Vaisala frequency (N2), vertical wind shear (VWS), orographic gravity-wave drag (OGWD), and convective precipitation, calculated using the ERA5 reanalysis, which are categorized into cases when there exists at least one turbulence event at the nearby grid and cases without turbulence nearby. Small N2 occurred frequently in the near-turbulence cases at all altitudes, while strong VWS and OGWD occurred more in near-turbulence cases at z = 15–21 km, and strong convective precipitation occurred more in near-turbulence cases at z = 9–15 km. The results demonstrate that the generation of Thorpe-estimated turbulence is favored in conditions of weak static stability at all altitudes, in conditions of strong VWS and OGWD at z = 15–21 km, and in conditions of strong convective precipitation at z = 9–15 km. In addition, the EE and N2 (convective precipitation) are negatively (positively) correlated at all altitudes and in most regions. Contrary, VWS and OGWD are correlated with EE under specific conditions and in specific locations: VWS is positively correlated under the strong static stability condition, and OGWD is positively correlated in western mountainous regions at z = 15–21 km.

A Calculation Method of Power System Static Stability Margin

This paper establishes a hybrid power network equation with node voltage and branch current as state variables. The characteristic equation representing the stable boundary of the system is derived. Then the boundary conditions of static stability of the power system on the critical circle of voltage static stability are formed. Find the closest distance equation between the load point and the corresponding stable boundary through geometric analysis. The introduction of the distance equation avoids artificially setting the direction of load growth. The distance equation and boundary characteristic equation are added to the hybrid power network equations as additional equations for analyzing the minimum load boundary. The equations are solved by Newton's iterative algorithm. In order to avoid the Jacobian matrix singularity near the load boundary, the algorithm adopts the method of replacing the critical point in the Jacobian matrix to calculate. The simulation results show that the method is correct and effective.

A Graphics Processing Unit (GPU) Approach to Large Eddy Simulation (LES) for Transport and Contaminant Dispersion

Recent advances in the development of large eddy simulation (LES) atmospheric models with corresponding atmospheric transport and dispersion (AT&D) modeling capabilities have made it possible to simulate short, time-averaged, single realizations of pollutant dispersion at the spatial and temporal resolution necessary for common atmospheric dispersion needs, such as designing air sampling networks, assessing pollutant sensor system performance, and characterizing the impact of airborne materials on human health. The high computational burden required to form an ensemble of single-realization dispersion solutions using an LES and coupled AT&D model has, until recently, limited its use to a few proof-of-concept studies. An example of an LES model that can meet the temporal and spatial resolution and computational requirements of these applications is the joint outdoor-indoor urban large eddy simulation (JOULES). A key enabling element within JOULES is the computationally efficient graphics processing unit (GPU)-based LES, which is on the order of 150 times faster than if the LES contaminant dispersion simulations were executed on a central processing unit (CPU) computing platform. JOULES is capable of resolving the turbulence components at a suitable scale for both open terrain and urban landscapes, e.g., owing to varying environmental conditions and a diverse building topology. In this paper, we describe the JOULES modeling system, prior efforts to validate the accuracy of its meteorological simulations, and current results from an evaluation that uses ensembles of dispersion solutions for unstable, neutral, and stable static stability conditions in an open terrain environment.

Aerodynamic and static stability investigation into aircraft coupled system to suborbital space flights

PurposeThe aim of the research is to conduct a study into a configuration of an aircraft system with a focus on aerodynamics. In addition, trim condition and static stability constraints were included. The main application of this system is suborbital space flights. The presented concept of a modular airplane system (MAS) consists of two vehicles: a Rocket Plane and a Carrier. Both are designed in tailless configurations but coupled formed a classic tail aircraft configuration, where the Rocket Plane works as the empennage. The most important challenge is to define the mutual position of those two tailless vehicles under the assumption that each vehicle will be operating alone in different flight conditions while joined in one object create a conventional aircraft. Each vehicle configuration (separated and coupled) must fulfil static stability and trim requirements.Design/methodology/approachAircrafts’ aerodynamic characteristics were obtained using the MGAERO software which is a commercial computing fluid dynamics tool created by AMI Aero. This software uses the Euler flow model. Results from this software were used in the static stability and trim condition analysis.FindingsThe main outcome of this investigation is a mutual position of the Rocket Plane and the Carrier that fulfils project requirements. Also, the final configuration of both separated vehicles (Rocket Plane and Carrier) and the complete MAS were defined. In addition, it was observed that in the case of classic aircraft configuration which is created by connecting two tailless vehicles increasing horizontal tail arm reduces static stability. This is related to a significantly higher mass ratio of the horizontal tail (the Rocket Plane) with respect to the whole system. Moving backward, the Rocket Plane has a notable effect on a position of a centre of gravity of the whole system static stability. Moreover, the impact of the mutual vehicles’ position (horizontal tail arm) and inclination angle on the coupled vehicle lift to drag ratio was analysed.Research limitations/implicationsIn terms of aerodynamic computation, MGAERO software using an inviscid flow model, therefore, both a friction drag and breakdown of vortex are not considered. But the presented research is for the computation stage of the design, and the MGAERO software guarantees satisfactory accuracy with respect to the relatively low time of computations. The second limitation is that the presented results are for the conceptual stage of the design and dynamic stability constraints were not taken into account.Practical implicationsThe ultimate goal of the coupled aircraft project is to conduct flying tests and the presented result is one of the milestones to achieve this goal.Originality/valueA design process for a conventional aircraft configuration is well known however, there are not many examples of vehicles that consist of two coupled aircrafts where both vehicles have similar mass. The unique part of this paper includes results of the investigation of the mutual position of the vehicles that can fly alone, as well as in coupled form. The impact of the position of the centre of gravity on trim conditions and static stability of the coupled configuration was investigated.

Precipitation Diurnal Cycle over the Maritime Continent Modulated by the Climatological Annual Cycle

AbstractThe modulation of the diurnal cycle (DC) of precipitation over the Maritime Continent (MC) by the background annual cycle mean state was studied for the period of 1998–2014 through observational analyses and high-resolution simulations using the Weather Research and Forecasting (WRF) Model. The observational analyses reveal that there are statistically significant differences in the DC amplitude between boreal winter and summer. The amplitude of precipitation DC reduces by about 35% during boreal summer compared to boreal winter, especially over the MC major islands and adjacent oceans. A precipitation budget analysis indicates that the DC amplitude difference is primarily attributed to vertically integrated convergence of the mean moisture by diurnal winds. The relative roles of the background dynamic and thermodynamic states in causing the enhanced diurnal wind activity in boreal winter are further investigated through idealized WRF simulations. The results show that the seasonal mean background moisture condition is most critical in inducing the winter–summer difference of the precipitation DC over the MC, followed by atmospheric static stability (i.e., vertical temperature gradient) and circulation conditions.

Stable Balance Adjustment Structure of the Quadruped Robot Based on the Bionic Lateral Swing Posture

Aiming at the problem that the stability of the quadruped robot is decreased as its leg momentum is too high, a stable balance adjustment structure of the quadruped robot based on the bionic lateral swing posture is proposed. First, the leg structure of the quadruped robot is improved and designed by using the mechanism of the lateral swing posture of the leg of the hoof animal. Then, the D-H method is used to construct the corresponding leg kinematics model and determine the generalized coordinates of the leg joints in the lateral swing posture. The torque expression of the quadruped robot when it is tilted is established. Based on the differential equation of momentum of the hip joint and its static stability analysis, the static stability conditions in the upright posture and the bionic lateral swing posture are given. Finally, the experimental simulation and comparative analysis of the upright posture and the lateral swing posture of the quadruped robot are proposed by using the Adams virtual prototype technology. The simulation results show that as the angle of lateral swing increases, the peak value of the positive flip torque of the quadruped robot body increases accordingly, while the degree of tilt decreases accordingly, which shows that the bionic lateral swing posture of the quadruped robot has higher static stability than the traditional upright posture. This research provides a technical reference for the design and optimization of the offline continuous gait of the robot and the improvement of stability.

The effect of support surface and footwear condition on postural sway and lower limb muscle action of the older women.

Diminished somatosensory function is a critical age-related change which is related to postural instability in the older population. Footwear is a cost-effective way to modulate the postural stability by altering sensorimotor inputs via mechanoreceptors on the plantar surface of the feet. Compared to insoles with indentions in the entire surface, we innovatively developed a textured insole with site-specific nodulous protrudous. This study thus aimed to investigate the immediate effect of the nodulous insole and supporting surface condition on static postural stability and lower limb muscle activation for healthy older women. This is a single-session study with repeated measurements. Twenty-three healthy older women stood on the firm (i.e., concrete floor) and foam surfaces with their eyes open in the three footwear conditions, namely barefoot, plain shoes and shoes with an innovative textured insole, for 30 seconds. Static postural sway and muscle activation of biceps femoris (BF), vastus lateralis (VL), tibialis anterior (TA), and lateral gastrocnemius (LG) of the dominant leg were measured during each testing condition. Compared to a firm surface, standing on the foam could significantly increase the body sway and lower limb muscle activation (p<0.05). When standing on the foam, compared to barefoot, wearing footwear significantly decreased the VL and TA muscle activation and minimize the postural sway in medial-lateral and anterior-posterior direction, while the influence is larger for the shoes with nodulous insloe compared to the plain shoes. No significant differences between the footwear conditions for static stability and muscle activation were observed on firm surface condition. For older women, footwear could improve the postural stability in the unstable surface, particularly the footwear with nodulous insole, with the underlying mechanism as enhancing the mechanoreceptors on the plantar surface of the feet.

3D-simulation of sound propagation through the wake of a wind turbine: Impact of the diurnal variability

Coupled three-dimensional numerical flow and sound propagation simulations were performed for four different times of a diurnal cycle in the area downwind of a wind energy converter with a hub height of 100 m and a rotor radius of 50 m. The sound propagation from the turbine is subject to vertical and lateral refraction in the wind speed deficit of the wake. The latter is influenced by the varying static stability and turbulence condition of the atmospheric boundary layer. The sound level near the ground is significantly increased by the atmospheric and wake-induced refraction for distances larger than eight times the rotor diameter. This increase is strongest in the morning and evening hours when it locally amounts up to 18 dB. Three-dimensional propagation effects are evident and cannot be neglected. A significant sound-level variation during the turbine revolution is simulated for the evening situation in the far field.

Phase Transition Effects on the Dynamical Stability of Hybrid Neutron Stars

We study radial oscillations of hybrid non-rotating neutron stars composed by a quark matter core and hadronic external layers. At first, we physically deduce the junction conditions that should be imposed between two any phases in these systems when perturbations take place. Then we compute the oscillation spectrum focusing on the effects of slow and rapid phase transitions at the quark-hadron interface. We use a generic MIT bag model for quark matter and a relativistic mean field theory for hadronic matter. In the case of rapid transitions at the interface we find a general relativistic version of the reaction mode which has similar properties as its classical counterpart. We also show that the usual static stability condition $\partial M/\partial \rho_c\geq 0$, where $\rho_c$ is the central density of a star whose total mass is $M$, remains always true for rapid transitions but breaks down in general for slow transitions. In fact, for slow transitions we find that the frequency of the fundamental mode can be a real number (indicating stability) even for some branches of stellar models that verify $\partial M/\partial \rho_c \leq 0$. Thus, when secular instabilities are suppressed, as expected below some critical stellar rotation rate, it would be possible the existence of twin or even triplet stars with the same gravitational mass but different radii, with one of the counterparts having $\partial M/\partial \rho_c \leq 0$. We explore some astrophysical consequences of these results.

Reliability and Performance Changes with the Addition of a Cognitive Task to Static and Dynamic Postural Stability Testing

Concussions are an unfortunate consequence of sports participation. They affect motor control, neurocognitive performance, and recent reports indicate they increase the risk of lower extremity musculoskeletal injury (LEMI) upon return to sport. The increased risk of secondary LEMI may indicate the need to establish a test that is predictive of LEMI risk following return to sport. PURPOSE: Assess the between-session reliability and the effects of adding a cognitive task to static and dynamic postural stability testing. METHODS: Twelve healthy, physically active subjects (Age: 22.3 ± 2.9 years, Height: 174.4 ± 7.5 cm, Weight: 154.5 ± 28.0 lbs) participated. Subjects underwent static and dynamic postural stability testing with and without the addition of a cognitive task (Stroop task) on two separate days. Static postural stability was assessed with a single-leg balance task under eyes open (with and without the addition of the Stroop task) and eyes closed conditions. Variability of each ground reaction force component was averaged across three trials for each of the static postural stability conditions. Dynamic postural stability testing consisted of forward jump over a hurdle with a one-legged landing performed with and without the addition of the Stroop task. A stability index was calculated based on the resultant ground reaction force and each of its components. Interclass correlation coefficients (ICC, 2,1) were calculated to determine the between-session reliability of each testing condition. Comparisons were made across the static conditions and between the dynamic postural stability tasks. RESULTS: The addition of a cognitive load proved to have moderate to excellent between-session reliability for the majority of variables calculated during static (ICC values 0.74 – 0.81) and dynamic postural stability testing (ICC values 0.77 – 0.80; ML=0.800, V=0.774, DPSI=0.781). No significant differences were observed between the postural stability tasks (with or without the Stroop task). CONCLUSION: Postural stability tasks with the addition of a cognitive load prove to have moderate to excellent reliability in a healthy population. These results provide new evidence on the feasibility of dual-task postural stability testing when examining risk of LEMI following return to sport.

Основи практичної методології формування навичок регуляції пози в умовах статодинамічної стійкості тіла спортсмена

Основи практичної методології формування навичок регуляції пози в умовах статодинамічної стійкості тіла спортсмена

PERANCANGAN AWAL SCALE MODEL GLIDER STTA-25-02_SAILPLANE

The knowledge and experience in aircraft design, especially for glider or sailplane are very important to have. Today, process of designing glider developed so rapidly, especially in America and Europe, one of the significant achievement is the performance aspect of glider. For example, the German-built Eta has a wingspan 30.78 m, aspect ratio 51 and wing loading 50.97 kg/m2, with glide angle of 0.8 degree and 3 km altitude, the glider able to fly 213 km in horizontal direction. Therefore, as the first step to understand the preliminary design of glider, it is important to start with designing a scale model glider STTA-25-02_Sailplane. The goals of this design are to get geometry and configuration of the glider, to obtained stability of glider and to gain performance data that meet with design requirements and objectives data (DR&amp;O). The conclusions from the preliminary design of scale model glider STTA-25-02_Sailplane are the geometry and configuration are good, for example the achivement in performance, the minimum sink rate 0.52 m/s, the glide ratio more than 20 at a cruising speed over 13 m/s, stall speed 11.45 m/s at angle of attack 0 degree. In addition glider STTA-25-02_Sailplane has static and dynamic stability, the static stability condition is indicated by the value of trim angle is positive 1 degree, curve of Cma and Clfi has negative slope, Cnfi curve has positive slope. The dynamic stability condition is indicated by the eigen value for each mode o f movement are negative except on phugoid and spiral mode, eigen value for short period -5.7681 ± 7.0010, phugoid 0.0403 ± 1.1136, rool damping -32.6243, dutch roll -1.0468 ± 3.4891 and spiral 0.1467. Positive eigen value on phugoid and spiral mode can be solved by adding a control parameter of the controlsurfaces.

A Methodology for Determining Permissible Operating Region of Power Systems According to Conditions of Static Stability Limit

For power systems with long-distance ultra-high-voltage (UHV) transmission lines, power transmission limits are often determined by static stability limits. Therefore, the assessment of stability and finding solutions to improve the stability reserve are essential for the operation of the system. This article presents an analytical approach to construct limit characteristics according to static stability conditions on a power plane. Based on the approach proposed, a program is developed and tested on a system with long-distance UHV transmission lines, showing a good performance.