Dynamic State Conditions Research Articles

Stability analysis for time-varying WIG craft dynamics in the presence of wavy boundary and gust

Wing-In-Ground (WIG) crafts are special vehicles that operate under particular situation named ground effect. The stability of WIGs in normal situation of ground effect without presence of disturbance is an LTI problem for cruise condition. Wavy surface and gust are undesired conditions which change aerodynamics and stability derivatives of WIGs. Therefore, the WIG dynamics will be time-varying due to wave and gust characteristics. In this article, a fundamental framework is constructed for analytical analysis of WIGs in the presence of disturbance. To meet this aim, the lift and moment coefficients of a WIG according to wave and gust are computed analytically and time-varying dynamics for the vehicle is derived. Since the speed of waves and gust are assumed to be smaller compared to velocity of the vehicle, slowly time-varying method would be an appropriate approach to justify the stability conditions. Consequently, the necessary conditions for longitudinal dynamic stability are addressed via slowly time-varying analysis which is based on norm of system matrix, norm of its derivative and its eigenvalues for all times. Finally, in order to show the effectiveness of the proposed approach, stability analysis of a 20-passenger WIG at different wave and gust specification are illustrated separately and collectively.

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&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.

Dynamic study of milling low depth channels

This paper presents a study of dynamic aspects of the milling cutters used in particular case of low depth channels. A new calculation method was developed, taking into account the high variations of cutting forces during milling small depth channels with peripheral cutting tools. A new formula was established for the minimal value of channel depth that allows cutting process to be performed in conditions of dynamic stability.

Условия динамического состояния сбалансированности рыночного сегмента национальной финансово-экономической системы

Условия динамического состояния сбалансированности рыночного сегмента национальной финансово-экономической системы

Diseño y modelamiento de un aerogenerador Vawt Darrieus tipo H para la zona costera del departamento de Córdoba

Para esta investigación se utilizó el perfil naca 0025 dada las con-diciones de estabilidad dinámica en bajos números de Reynolds. Se eligió el rotor Darrieus tipo H de baja potencia y a través del modelado del rotor (usando el método DMST) se obtuvieron la dimensión óptima del perfil y el diámetro del aerogenerador. Con el software ANSYS se determinó el rendimiento, obteniendo una longitud de cuerda óptima de 0,55 m y un radio del rotor de 1,3 m. En comparación con los resultados obtenidos el DMST, respecto a las simulaciones realizadas en ANSYS, se tuvo como resultado una discrepancia del 15% para el máximo momento a la velocidad de giro nominal.

Elderly Fallers Enhance Dynamic Stability Through Anticipatory Postural Adjustments during a Choice Stepping Reaction Time

In the case of disequilibrium, the capacity to step quickly is critical to avoid falling in elderly. This capacity can be simply assessed through the choice stepping reaction time test (CSRT), where elderly fallers (F) take longer to step than elderly non-fallers (NF). However, the reasons why elderly F elongate their stepping time remain unclear. The purpose of this study is to assess the characteristics of anticipated postural adjustments (APA) that elderly F develop in a stepping context and their consequences on the dynamic stability. Forty-four community-dwelling elderly subjects (20 F and 24 NF) performed a CSRT where kinematics and ground reaction forces were collected. Variables were analyzed using two-way repeated measures ANOVAs. Results for F compared to NF showed that stepping time is elongated, due to a longer APA phase. During APA, they seem to use two distinct balance strategies, depending on the axis: in the anteroposterior direction, we measured a smaller backward movement and slower peak velocity of the center of pressure (CoP); in the mediolateral direction, the CoP movement was similar in amplitude and peak velocity between groups but lasted longer. The biomechanical consequence of both strategies was an increased margin of stability (MoS) at foot-off, in the respective direction. By elongating their APA, elderly F use a safer balance strategy that prioritizes dynamic stability conditions instead of the objective of the task. Such a choice in balance strategy probably comes from muscular limitations and/or a higher fear of falling and paradoxically indicates an increased risk of fall.

Dynamic stability of rolling missiles employing a two-loop autopilot with consideration for the radome aberration parasitic feedback loop

The dynamic stability of a radar homing rolling missile is extremely complex due to the interaction of the parasitic radome aberration feedback loop and the cross-coupling between the pitch and yaw, which are problems that have not been presented in previous studies. This paper presents mathematical models representative of the parasitic radome aberration feedback loop and proportional navigation guidance (PNG) system with a two-loop autopilot for rolling missile guidance based on reasonable assumptions. A PNG system equation is further proposed in the form of a complex summation. Based on the proposed mathematical models, the sufficient and necessary condition for the dynamic stability of the rolling missile is analytically derived according to the stability criterion of a system with complex coefficients. The proposed dynamic stability condition is verified by numerical simulation. Moreover, the stable region is obtained by solving the dynamic stability condition under different cases. An analysis of the effects of system parameters indicates that the stable region of a rolling missile is smaller than that of a non-rolling missile. Furthermore, it is shown that the stable region is affected by a number of factors, such as the rolling rate and the total delay angle. The dynamic stability condition derived in this paper is useful for evaluating the stability of a rolling missile with consideration for the parasitic radome aberration feedback loop, and the conclusions obtained can provide guidance for the design of PNG systems for rolling missiles.

Controllability analysis and testing of a novel magnetorheological absorber for field gun recoil mitigation

This paper aims to analyze the effects of combined working coils of magnetorheological (MR) absorber on the shock mitigation performance and verify the controllability of MR absorber as applied in the recoil system of a field gun. A physical scale model of the field gun is established and a long-stroke MR recoil absorber with four-stage parallel electromagnetic coils is designed to apply separate current to each stage and generate variable magnetic field distribution in the annular flow channel. Based on dynamic analysis and firing stability conditions of the field gun, ideal recoil force-stroke profiles of MR absorber at different limiting firing angles are obtained. The experimental studies are carried out on an impact test rig under different combinations of current loading: conventional unified control mode, separate control mode and timing control mode. The fullness degree index (FDI) is defined as the quantitative evaluation criterion of the controllability of MR absorber during the whole recoil motion. The results show that the force-stroke profile of the novel MR absorber can approach the ideal curve within 25 degrees of the limiting firing angle through judicious exploitation of the adjustable rheological properties of MR fluid.

A Simplified Synchronous Reference Frame for Indirect Current Controlled Three-level Inverter-based Shunt Active Power Filters

This paper presents a new simplified harmonics extraction algorithm based on the synchronous reference frame (SRF) for an indirect current controlled (ICC) three-level neutral point diode clamped (NPC) inverter-based shunt active power filter (SAPF). The shunt APF is widely accepted as one of the most effective current harmonics mitigation tools due to its superior adaptability in dynamic state conditions. In its controller, the SRF algorithm which is derived based on the direct-quadrature (DQ) theory has played a significant role as a harmonics extraction algorithm due to its simple implementation features. However, it suffers from significant delays due to its dependency on a numerical filter and unnecessary computation workloads. Moreover, the algorithm is mostly implemented for the direct current controlled (DCC) based SAPF which operates based on a non-sinusoidal reference current. This degrades the mitigation performances since the DCC based operation does not possess exact information on the actual source current which suffers from switching ripples problems. Therefore, three major improvements are introduced which include the development of a mathematical based fundamental component identifier to replace the numerical filter, the removal of redundant features, and the generation of a sinusoidal reference current. The proposed algorithm is developed and evaluated in MATLAB / Simulink. A laboratory prototype utilizing a TMS320F28335 digital signal processor (DSP) is also implemented to validate effectiveness of the proposed algorithm. Both simulation and experimental results are presented. They show significant improvements in terms of total harmonic distortion (THD) and dynamic response when compared to a conventional SRF algorithm.

Modified TOV in gravity's rainbow:properties of neutron stars and dynamical stability conditions

In this paper, we consider a spherical symmetric metric to extract the hydrostatic equilibrium equation of stars in (3+1)-dimensional gravity's rainbow in the presence of cosmological constant. Then, we generalize the hydrostatic equilibrium equation to d-dimensions and obtain the hydrostatic equilibrium equation for this gravity. Also, we obtain the maximum mass of neutron star using the modern equations of state of neutron star matter derived from the microscopic calculations. It is notable that, in this paper, we consider the effects of rainbow functions on the diagrams related to the mass-central mass density (M-ρc) relation and also the mass-radius (M-R) relation of neutron star. We also study the effects of rainbow functions on the other properties of neutron star such as the Schwarzschild radius, average density, strength of gravity and gravitational redshift. Then, we apply the cosmological constant to this theory to obtain the diagrams of M-ρc (or M-R) and other properties of these stars. Next, we investigate the dynamical stability condition for these stars in gravity's rainbow and show that these stars have dynamical stability. We also obtain a relation between mass of neutron stars and Planck mass. In addition, we compare obtained results of this theory with the observational data.

DC-Link Capacitor Voltage Regulation for Three-Phase Three-Level Inverter-Based Shunt Active Power Filter with Inverted Error Deviation Control

A new control technique known as inverted error deviation (IED) control is incorporated into the main DC-link capacitor voltage regulation algorithm of a three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) to enhance its performance in overall DC-link voltage regulation so as to improve its harmonics mitigation performances. In the SAPF controller, DC-link capacitor voltage regulation algorithms with either the proportional-integral (PI) or fuzzy logic control (FLC) technique have played a significant role in maintaining a constant DC-link voltage across the DC-link capacitors. However, both techniques are mostly operated based on a direct voltage error manipulation approach which is insufficient to address the severe DC-link voltage deviation that occurs during dynamic-state conditions. As a result, the conventional algorithms perform poorly with large overshoot, undershoot, and slow response time. Therefore, the IED control technique is proposed to precisely address the DC-link voltage deviation. To validate effectiveness and feasibility of the proposed algorithm, simulation work in MATLAB-Simulink and experimental implementation utilizing a TMS320F28335 Digital Signal Processor (DSP) are performed. Moreover, conventional algorithms with PI and FLC techniques are tested too for comparison purposes. Both simulation and experimental results are presented, confirming the improvement achieved by the proposed algorithm in terms of accuracy and dynamic response in comparison to the conventional algorithms.

Excitation of parametric resonances in mechanisms with rheonomic constraints subject to the joint effect of fast and slow variations of parameters

As applied to the dynamics of machines with rheonomic constraints, the dynamic stability conditions are studied within the frequency range of parametric resonances, with due account taken of impulse and slow variations of parameters. A modification is suggested for the conditional oscillator method, and the level of dissipation is determined on its basis, which is necessary to suppress parametric resonances and eliminate the amplitude modulation of oscillations within the kinematic cycle. Given properly selected parameters, the stability conditions are demonstrated to be independent of dissipation.

Enhanced Instantaneous Power Theory with Average Algorithm for Indirect Current Controlled Three-Level Inverter-Based Shunt Active Power Filter under Dynamic State Conditions

An enhanced harmonics extraction algorithm based on Instantaneous Power (PQ) Theory is proposed for indirect current controlled (ICC) three-level neutral point diode clamped (NPC) inverter-based shunt active power filter (SAPF). SAPF is famous in current harmonics mitigation for its flexibility in dealing with dynamic state conditions. As for its controller, PQ Theory has served the major role in harmonics extraction algorithm due to its simple implementation features. However, it suffers from serious time delay due to its dependency on sluggish numerical filters. Furthermore, the algorithm is mostly designed to suit the operation of direct current controlled (DCC) SAPF which requires the knowledge of actual SAPF current (injection current). This leads to inaccurate mitigation as the injection current does not possess the exact information on actual source current which suffers from switching ripples problems. Therefore, two major modifications are introduced involving the development of mathematical average algorithm to replace numerical filter for fundamental real power computation and the formation of mathematical current relationship to change DCC to ICC based operation. The proposed algorithm is developed and evaluated in MATLAB/Simulink. From the simulation results, significant improvement in terms of Total Harmonic Distortion (THD) and response time is presented in comparison to conventional algorithm.

Ideal switched-model dynamic stability conditions for semi-quasi-Z-source inverters

The ideal switched model of the recently introduced semi-quasi-Z-source inverter is a practical example of a switched system where each subsystem is neither asymptotically stable nor detectable from the output, yet asymptotic stability can be ensured by imposing limitations on the load and on how switching is performed. In this paper, we present novel stability conditions for the switched model (i.e. not the averaged model) of the semi-quasi-Z-source inverter connected to different types of loads and operating in both complementary and uncontrolled conduction. These stability conditions give theoretical justification to the standard open-loop inverter operation strategy and are important for the operation of the converter under closed-loop control.

Exact dynamics and squeezing in two harmonic modes coupled through angular momentum

We investigate the exact dynamics of a system of two independent harmonic oscillators coupled through their angular momentum. The exact analytic solution of the equations of motion for the field operators is derived, and the conditions for dynamical stability are obtained. As for the application, we examine the emergence of squeezing and mode entanglement for an arbitrary separable coherent initial state. It is shown that close to instability, the system develops considerable entanglement, which is accompanied with simultaneous squeezing in the coordinate of one oscillator and the momentum of the other oscillator. In contrast, for weak coupling away from instability, the generated entanglement is small, with weak alternating squeezing in the coordinate and momentum of each oscillator. Approximate expressions describing these regimes are also provided.

Growth Rate and Level Effects, the Stability of the Adjustment of Capacity to Demand and the Sraffian Supermultiplier

The paper presents a simple but complete formal version of the Sraffian supermultiplier model in which (i) growth is led by the autonomous components of demand that do not create capacity; (ii) private productive investment is an induced expenditure; and (iii) income distribution is exogenous. We show that the main results of the long-period and fully adjusted versions of the model in terms of growth rate and level effects are quite similar and therefore that such results in no way require the full adjustment of capacity to demand. We then analyze a simple set of sufficient dynamic local stability conditions that allow the long-period positions to gravitate towards the fully adjusted position in which capacity is adjusted to demand and that also provide the upper limit to demand-led growth paths. Finally, we show how some critics of the model have misinterpreted it as being supply-led and how this has led to a further confusion between the analysis of the tendency towards a constant value of the capacity-saving-determined warranted rate of growth and the proper stability analysis of the opposite process of adjusting capacity to demand (which tends to adjust the warranted rate endogenously to the growth rate of autonomous demand).

Stability of persistent currents in open dissipative quantum fluids

The phenomenon of stable persistent currents is central to the studies of superfluidity in a range of physical systems. While most of the previous theoretical studies of superfluid flows in annular geometries concentrated on conservative systems, here we extend the dynamical stability analysis of persistent currents to open dissipative exciton-polariton superfluids. By considering an exciton-polariton condensate in an optically induced annular trap, we determine dynamical stability conditions for an initially imposed flow with a nonzero orbital angular momentum. We show, theoretically and numerically, that the system can sustain metastable persistent currents in a large parameter region, and describe scenarios of the supercurrent decay due to the dynamical instability.

Effects of temporal constraints on medio-lateral stability when negotiating obstacles

If an obstacle suddenly appears during walking, either the crossing step can be lengthened or the precrossing step shortened to avoid the obstacle. We investigated the effects of temporal constraints on dynamic stability during step adjustments. Twelve healthy young adults avoided a virtual white planar obstacle by lengthening or shortening their steps under free or constrained conditions. When constrained, participants had only one step to avoid the obstacle. The results indicated that center of mass (COM) displacement in the mediolateral (ML) direction and the COM velocity toward the swing-leg side during the crossing step were significantly increased in the long-constraint compared with the long-free condition. Consequently, the extrapolated COM (XcoM) position at the swing foot contact was also located further toward the swing-leg side. However, the distances between the XcoM and base of support (BOS) at the swing foot contact in the ML direction was unchanged because of greater lateral foot placement. In the anteriorposterior (AP) direction, temporal constraints led to greater AP COM displacement. The XcoM–BOS distance in the AP direction was unchanged in the long-constraint condition because of greater step length. However, the value became negative in the short-constraint condition, violating the conditions for dynamic stability, because step length adjustments were obstructed by the spatial constraints of the obstacles. These results suggest that temporal constraints affect postural stability in the AP and ML directions during step adjustments. AP and ML stability at swing foot contact are maintained through adjustments of step length and lateral foot placement, respectively.

Dynamic stability conditions for a rolling flight vehicle applying continuous actuator

The conditions for dynamic stability of coning motion for a rolling missile are proposed. Considering dynamics of fin actuator, a Proportional–Derivative (PD) controller is applied to the servomechanism employing a permanent magnet DC motor. The necessary and sufficient conditions of dynamic stability are analytically derived. Both steady state and transient responses of actuator are considered in this paper. The differential equation of a whole system for steady state response of actuator leads to a second order differential equation with complex coefficients. A theorem based on Routh–Hurwitz stability criterion is proposed that gives a triple inequality to determine the stability region of PD controller and consequentially, the stability of coning motion. For transient response, the feasibility of a linear matrix inequality should be checked for each PD coefficient. It is shown that considering the transient response of actuator can change the stability region. The controller coefficients that stabilize the coning motion in steady state response may cause instability in transient response of actuator. Finally, validation of this investigation is examined through simulation. Because of continually rolling motion of missile, the cross coupling that is caused by phase lag angle, will occur, so the effect of PD controller coefficients on static phase lag angle is discussed and some technical notes to reduce the cross coupling effect are explained. Furthermore, the influence of roll rate frequency on the region of PD controller coefficients is presented and a safe region for design is recommended.

The blow-off mechanism of a bluff-body stabilized laminar premixed flame

The objective of this work is to investigate the dynamics leading to blow-off of a laminar premixed flame stabilized on a confined bluff-body using high fidelity numerical simulations. We used unsteady, fully resolved, two-dimensional simulations with detailed chemical kinetics and species transport for methane–air combustion. The flame–wall interaction between the hot reactants and the heat conducting bluff-body was accurately captured by incorporating the conjugate heat exchange between them. Simulations showed a shear-layer stabilized flame just downstream of the bluff-body, with a recirculation zone formed by the products of combustion. The flame was negatively stretched along its entire length, primarily dominated by the normal component of the strain. Blow-off was approached by decreasing the mixture equivalence ratio, at a fixed Reynolds number, of the incoming flow. A flame is stable (does not undergo blow-off) when (1) flame displacement speed is equal to the flow speed and (2) the gradient of the flame displacement speed normal to its surface is higher than the gradient of the flow speed along the same direction. As the equivalence ratio is reduced, the difference between the former and the latter shrinks until the dynamic stability condition (2) is violated, leading to blow-off. Blow-off initiates at a location where this is first violated along the flame. Our results showed that this location was far downstream from the flame anchoring zone, near the end of the recirculation zone. Blow-off started by flame pinching separating the flame into an upstream moving (carried within the recirculation zone) and a downstream convecting (detached from the recirculation zone) flame piece. Within the range of operating conditions investigated, the conjugate heat exchange with the bluff-body had no impact on the flame blow-off.