Dynamic State Conditions Research Articles

Whole-body dynamic stability in side cutting: Implications for markers of lower limb injury risk and change of direction performance

Control of the centre of mass (CoM) whilst minimising the use of unnecessary movements is imperative for successful performance of dynamic sports tasks, and may indicate the condition of whole-body dynamic stability. The aims of this study were to express movement strategies that represent whole-body dynamic stability, and to explore their association with potentially injurious joint mechanics and side cutting performance. Twenty recreational soccer players completed 45° unanticipated side cutting. Five distinct whole-body dynamic stability movement strategies were identified, based on factors that influence the medial ground reaction force (GRF) vector during ground contact in the side cutting manoeuvre. Using Statistical Parametric Mapping, the movement strategies were linearly regressed against selected performance outcomes and peak knee abduction moment (peak KAM). Significant relationships were found between each movement strategy and at least one selected performance outcome or peak KAM. Our results suggest excessive medial GRFs were generated through sagittal plane movement strategies, and despite being beneficial for performance aspects, poor sagittal plane efficiency may destabilise control of the CoM. Frontal plane hip acceleration is the key non-sagittal plane movement strategy used in a corrective capacity to moderate excessive medial forces. However, whilst this movement strategy offered a way to retrieve control of the CoM, mitigating reduced whole-body dynamic stability, it also coincided with increased peak KAM. Overall, whole-body dynamic stability movement strategies helped explain the delicate interplay between the mechanics of changing direction and undesirable joint moments, providing insights that might support development of future intervention strategies.

International Outsourcing, Unemployment and Welfare: A Re-Examination

This paper explores the ramifications of international outsourcing on unemployment, income distribution and welfare, which is an important but yet unresolved issue. Using the well-known Harris-Todaro (1970) model of sector-specific unemployment, it shows that the effects of outsourcing on employment, income-distribution and welfare depend on the sector in which the outsourcing occurs, whereby sectoral factor intensities, unemployment-outsourcing response and the dynamic stability condition play crucial roles. In particular, outsourcing in the manufacturing (primary) sector widens (narrows) income inequality by increasing (decreasing) the sectoral wage gap and raising (not affecting) the rental income of the capital owners in the economy. Moreover, outsourcing in the manufacturing (primary) sector can be welfare-decreasing (is always welfare-increasing) due to its negative (positive) employment effect mitigating (reinforcing) the primary gains from the outsourcing.

International Outsourcing, Unemployment and Welfare: A Re-Examination

This paper explores the ramifications of international outsourcing on unemployment, income distribution and welfare, which is an important but yet unresolved issue. Using the well-known Harris-Todaro (1970) model of sector-specific unemployment, it shows that the effects of outsourcing on employment, income-distribution and welfare depend on the sector in which the outsourcing occurs, whereby sectoral factor intensities, unemployment-outsourcing response and the dynamic stability condition play crucial roles. In particular, outsourcing in the manufacturing (primary) sector widens (narrows) income inequality by increasing (decreasing) the sectoral wage gap and raising (not affecting) the rental income of the capital owners in the economy. Moreover, outsourcing in the manufacturing (primary) sector can be welfare-decreasing (is always welfare-increasing) due to its negative (positive) employment effect mitigating (reinforcing) the primary gains from the outsourcing.

Performance evaluation of FPGA‐based predictive current controller for FL‐DSTATCOM in electric distribution system

A four-leg distribution static compensator (FL-DSTATCOM) has been employed for improving the quality of power in electric distribution system using field-programmable gate array (FPGA). A predictive current control technique without any modulation scheme is utilised to generate switching pulses for FL-DSTATCOM using a cost function defining the preferred system behaviour. This technique makes the supply current as balanced and sinusoidal by exactly tracking the reference current, compensating the reactive power, maintaining near unity power factor and nullifies the current flow in neutral conductor during steady and dynamic state conditions. Synchronous reference frame theory is effectively implemented for extracting the reactive and harmonic part of load current which are the primary components in the evaluation of reference currents. The predictive current control scheme implemented in FPGA has been deployed to evaluate the behaviour of the FL-DSTATCOM under multifarious loading conditions.

Shunt Active Power Filter with Solar Photovoltaic System for Long-Term Harmonic Mitigation

This paper proposes a shunt Active Power Filter (APF), supported by Solar Photovoltaic (SPV) system for a grid-connected application that improves power quality. The reference signal for the shunt APF is obtained from the adaptive Proportional Integrative Derivatives (PID), based on an algorithm of Least Mean Eighth (LME) with Unit Vector Template (UVT). The LME algorithm distinguishes the basic weight sections from load currents and estimates the three phase reference source current. These reference currents are used to generate a gate signal for the shunt APF. The DC-link voltage regulator is used to keep the constant DC-link voltage of the shunt APF with an APID controller. To reduce present distortions of electric power distribution systems, a design of a suitable controller is conducted using an intelligent computational technique for predicting the right reference signals. The SPV scheme is designed to obtain the highest energy output from the SPV panel with the maximum power point tracking algorithm (MPPT) scheme and is connected to the power grid. For long-term harmonic mitigation, the SPV system continuously maintains the DC-link of the shunt APF. Mathematically, the presented current reference signal generation scheme is examined and digital simulation outcomes are displayed under distinct steady and dynamic state conditions. Lastly, the complete scheme is validated by using the hardware prototype.

White dwarfs in de Rham-Gabadadze-Tolley like massive gravity

The existence of possible massive white dwarfs more than the Chandrasekhar limit ($1.45\text{ }{M}_{\ensuremath{\bigodot}}$, in which ${M}_{\ensuremath{\bigodot}}$ is mass of the sun) is a challenging topic. In this regard, and motivated by the important effect of massive graviton on the structure of white dwarfs, we study the white dwarfs in Vegh's massive gravity which is known as one of theories of de Rham, Gabadadze, and Tolley (dRGT) like massive gravity. First, we consider the modified Tolman-Oppenheimer-Volkoff equation in this theory of massive gravity and solve it numerically by using the Chandrasekhar's equation of state. Our results show that the maximum mass of white dwarfs in massive gravity can be more than the Chandrasekhar limit ($M>1.45\text{ }{M}_{\ensuremath{\bigodot}}$), and this result imposes some constraints on parameters of massive gravity. Then, we investigate the effects of various parameters on other properties of the white dwarfs such as mass-radius relation, mass-central density relation, Schwarzschild radius, average density, and Kretschmann scalar. Next, we study dynamical stability condition for super-Chandrasekhar white dwarfs and show that these massive compact objects enjoy dynamical stability. Finally, in order to have a better insight, we compare the super-Chandrasekhar white dwarfs with the obtained massive neutron stars in dRGT like massive theory of gravity.

Stability analysis of spinning missiles induced by seeker disturbance rejection rate parasitical loop

This paper focuses on the dynamic stability of spinning missiles equipped with two-loop autopilot considering the seeker disturbance rejection rate parasitical loop (DRRPL) effect induced by attitude disturbance of projectile. The representative mathematical model of spinning missiles in the non-spinning coordinate system is established, and the cross-coupling effect between the pitch and yaw induced by the rotation motion of missile body is analyzed and decoupled. The two-loop acceleration autopilot for each channel is designed with the conventional design method, and the relationship between the autopilot gains and the expected design indexes is deduced. A proportional navigation guidance (PNG) system model with consideration for the seeker DRRPL is further proposed in the form of complex summation. After strict mathematic deduction, the sufficient and necessary condition of the dynamic stability for spinning missiles is obtained. Numerical simulations and discussions under different cases are conducted to demonstrate the validity of stability condition. The results indicate that the stability of a spinning missile is closely related to the amplitude of the seeker DRR, the rolling rate, and the autopilot design indices. The stable region of the autopilot design frequency is obtained by solving the dynamic stability condition. To meet the requirement of stable controlling at a constant spinning rate, it was found to be effective to decrease the amplitude of the seeker DRR for spinning missiles, employ the lead angle decoupling approach to the commands for the servo system, and guarantee that the autopilot design frequency is lower than the critical value. The dynamic stability condition derived in this paper is useful for evaluating the stability of a spinning missile with consideration for the seeker DRRPL, and the conclusions obtained can provide guidance for the autopilot design of spinning missiles.

Utilizing the synchronous condenser for robust functioning of wind farm implanted electric grid

Abstract Present-day electricity grids are equipped with sophisticated devices that allow to meet various grid code requirements. These include reactive and active power controls to ensure robust functioning of the grid. Robust operation of the electricity grid entails favourable voltage and frequency profile adjustments that can be achieved through reactive and active power controls. This study presents the synchronous condenser capability of providing voltage regulation and reactive power output, and the active power possibility path of a type-3 wind machine for dynamic state conditions and voltage stability issues. Simulations carried out in the MATLAB/Simulink environment prove the efficiency of the proposed methodology.

On the radial stability of ultra-compact Schwarzschild stars beyond the Buchdahl limit

In this paper we used the theory of adiabatic radial oscillations developed by Chandrasekhar to study the conditions for dynamical stability of constant energy-density stars, or Schwarzschild stars, in the unstudied ultra compact regime beyond the Buchdahl limit, that is, for configurations with radius R in the range , where is the Schwarzschild radius of the star. These recently found analytical solutions exhibit a negative pressure region in their centre and, in the limit when , the full interior region of the star becomes filled with negative pressure. Here we present a systematic analysis of the stability of these configurations against radial perturbations. We found that, contrary to the usual expectation found in many classical works, the ultra compact Schwarzschild star is stable against radial oscillations. We computed values of the critical adiabatic index for several stellar models with varying radius and found that it also approaches a finite value as .

Design and test of an astigmatism compensated dynamical stable ring resonator for a subjoule class Nd:YAG laser without external elements

An astigmatism compensated isosceles triangular ring resonator is designed and tested for a subjoule class Nd:YAG laser, considering the thermal lensing effects. The ABCD approach is used and the laser rod is considered as a lens like media whose optical power is induced by dissipated heat in the rod. The beam spot size, divergence angle, and some other parameters were studied for both sagittal and tangential planes and a minimal astigmatic configuration is designed applying dynamic stability condition. It is shown practically that the designed resonator emits a circular TEM00 Gaussian beam (using an aperture). Comparative studies were also done considering a linear resonator especially for alignment sensitivity of the linear and ring resonator.

Modified Dual Output Cuk Converter-Fed Switched Reluctance Motor Drive With Power Factor Correction

The control of a switched reluctance motor (SRM) drive is proposed with a front end power factor correction (PFC) converter. It uses a modified Cuk converter-fed SRM drive to improve power quality at ac mains. The converter configuration consists of two Cuk converters and each of them operates separately for two half-cycles of the supply voltage. The proposed converter generates two identical voltages across two output capacitors to feed a split capacitor converter of a four-phase SRM drive. The proposed pulsewidth modulated ac–dc converter operates in the discontinuous conduction mode to reduce its size and cost by eliminating couple of sensor requirements. The incorporated voltage control loop regulates the dc-link voltage with PFC at ac mains. The SRM is considered for the proposed drive because of its low cost and constructional ease. The motor speed is controlled over a wide range by regulating the PFC converter output dc voltage. The proposed SRM drive is tested for steady-state and dynamic state conditions on a developed prototype in the laboratory. The obtained test results demonstrate good drive performance and line drawn power quality. The input current total harmonic distortion is observed within a limit of a standard.

Generic bifurcations in fractional thermo‐mechanics with peridyamic effects

AbstractIn dynamic stability analysis, mathematical aspects of non‐locality are studied by using the theory of dynamical systems. The set of basic equations describing the behavior of continua is transformed to an abstract dynamical system. Such approach results in conditions for cases, when the differential operators have critical eigenvalues of zero real‐parts (dynamic stability or instability conditions). When the critical eigenvalues have nontrivial eigenspace, the way of loss of stability can be classified as a generic bifurcation. Our experiences show that material non‐locality and the generic nature of bifurcation at instability are connected, and the basic functions of the non‐trivial eigenspace can be used to determine internal length quantities of non‐local mechanics. In the paper, non‐local effects are introduced via fractional stress and strain into the equation of motion and into constitutive relations. Then, by defining dynamical systems, stability and bifurcation are studied for states of thermo‐mechanic solids. Conditions for stability and generic bifurcation are presented for constitutive relations under consideration.

Stability Analysis of the Bat Algorithm Described as a Stochastic Discrete-Time State-Space System

The main problem with the soft-computing algorithms is a determination of their parameters. The tuning rules are very general and need experiments during a trial and error method. The equations describing the bat algorithm have the form of difference equations, and the algorithm can be treated as a stochastic discrete-time system. The behaviour of this system depends on its dynamic and preservation stability conditions. The paper presents the stability analysis of the bat algorithm described as a stochastic discrete-time state-space system. The observability and controllability analyses were made in order to verify the correctness of the model describing the dynamic of BA. Sufficient conditions for stability are derived based on the Lyapunov stability theory. They indicate the recommended areas of the location of the parameters. The analysis of the position of eigenvalues of the state matrix shows how the different values of parameters affect the behaviour of the algorithm. They indicate the recommended area of the location of the parameters. Simulation results confirm the theory-based analysis.

Model of Power System Stabilizer Adapting to Multi-Operating Conditions of Local Power Grid and Parameter Tuning

The rapid development of the modern power grid has resulted in significant changes to the dynamic characteristics of regional power grids. Moreover, the operating conditions of power grids are increasingly complex, and uncertainty factors are on the rise, which makes it difficult for a conventional power system stabilizer (PSS) to provide enough damping for the power system. To solve the problem where the conventional model and parameter-tuning method of a PSS cannot adapt to the multi-operating conditions of the modern power system, a new emergency control model of PSS (E-PSS) that can adapt to the multi-operating conditions of the local power grid and a method of parameter tuning based on probabilistic eigenvalue are proposed in this paper. An emergency control channel is also installed on the PSS2B. The conventional channel is used to control the system under normal operating conditions, which ensures that the system meets the conditions of dynamic stability in 99% of operating conditions, and the emergency control is adopted immediately in extreme conditions. Through the process of parameter tuning, the adaptability of the PSS to multi-operating conditions and damping coupling are both considered. Finally, it is verified that the emergency control model of the PSS and the parameter tuning method are effective and robust by a series of simulations based on MATLAB and its Power system analysis toolbox (PSAT). The rapidity of the emergency control can guarantee its effectiveness.

Dynamic stability and bifurcation analysis in fractional thermodynamics

In mechanics, viscoelasticity was the first field of applications in studying geomaterials. Further possibilities arise in spatial non-locality. Non-local materials were already studied in the 1960s by several authors as a part of continuum mechanics and are still in focus of interest because of the rising importance of materials with internal micro- and nano-structure. When material instability gained more interest, non-local behavior appeared in a different aspect. The problem was concerned to numerical analysis, because then instability zones exhibited singular properties for local constitutive equations. In dynamic stability analysis, mathematical aspects of non-locality were studied by using the theory of dynamic systems. There the basic set of equations describing the behavior of continua was transformed to an abstract dynamic system consisting of differential operators acting on the perturbation field variables. Such functions should satisfy homogeneous boundary conditions and act as indicators of stability of a selected state of the body under consideration. Dynamic systems approach results in conditions for cases, when the differential operators have critical eigenvalues of zero real parts (dynamic stability or instability conditions). When the critical eigenvalues have non-trivial eigenspace, the way of loss of stability is classified as a typical (or generic) bifurcation. Our experiences show that material non-locality and the generic nature of bifurcation at instability are connected, and the basic functions of the non-trivial eigenspace can be used to determine internal length quantities of non-local mechanics. Fractional calculus is already successfully used in thermo-elasticity. In the paper, non-locality is introduced via fractional strain into the constitutive relations of various conventional types. Then, by defining dynamic systems, stability and bifurcation are studied for states of thermo-mechanical solids. Stability conditions and genericity conditions are presented for constitutive relations under consideration.

Voltage Sensorless Controller for Photovoltaic Integrated Shunt Active Power Filter for Enhancement of Power Quality

Abstract The shunt active power filter (APF) is one of the most effective custom power devices that provide compensation to current-based disturbances. The shunt APF topology consists of a voltage source inverter and a dc link capacitor. The current-based compensation ability of the shunt APF is influenced by the control technique, which is used to estimate the reference source current signal. Moreover, the controller decides the required number of devices and measurement practices; therefore, it determines the corresponding costs. In this paper, second order generalized integrator (SOGI) with a fuzzy logic controller (FLC) is utilized to estimate the reference source current of shunt APF. The proposed control algorithm makes use of the details about the converter and load currents; therefore, it does not require voltage-related information and sensors. The proposed topology employs a photovoltaic (PV) system with a supplementary energy storage unit to supply the active power requirement of the utility grid and provides the continuous compensation of current-based disturbances and voltage interruption in the power distribution system. The PV integrated shunt APF is tested with different load conditions and the performance of the system is investigated under steady and dynamic state conditions. To ensure the effectiveness of the proposed control algorithm for the PV integrated shunt APF, the simulation and experimental results are presented.

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

Theoretical research of dynamic characteristics of Tc bearing of measurement while drilling

In this paper, through analyzing Tc bearing by the theory of Hydrodynamic lubrication, the unsteady Reynolds equation of Tc bearing under the dynamic-state condition is initially established. The formula of Tc bearing’s liquid-film dimensionless stiffness coefficient and damping coefficient is derived. Furthermore, two kinds of the distribution curves of Tc bearing’s liquid-film dimensionless stiffness coefficient, damping coefficient against Tc bearing’s eccentricity ratio and width-diameter ratio are displayed respectively, and the stability criterion of liquid film is worked out and the angular speed of instability of bearing shaft is calculated. Overall, conclusions are drawn: downhole system improves the entire system’s stability by enhancing the stiffness of bearing shaft itself. The improvement of the stability of bearing shaft itself, which can be done by altering the structure of Tc bearing and adopting better spiral flutes and ellipse groove can strengthen the whole system’s stability. The high width-diameter ratio of Tc bearing increases the liquid film’s stiffness coefficient and damping coefficient of Tc bearing. The rotational rate of rotary table is lower than half of that of the supporting system of Tc bearing.

Performance Evaluation of PV Interfaced Z-Source-Network-Based Shunt Active Power Filter

Abstract In this paper, a photovoltaic supported Z-source-inverter (ZSI)-based shunt active power filter (SAPF) is proposed for power-quality improvement. The topology has a voltage source inverter (VSI), which is connected in parallel with the point of common coupling (PCC), and is assisted by an impedance network. The Z-source network is really a distinct impedance network to facilitate interconnection between the photovoltaic (PV) power-generating system and VSI. The key features of ZSI can boost up the changeable dc voltage into any specified AC output voltage, decrease the components required, and mitigate harmonic content. The compensation capability of the SAPF mainly depends on the control scheme utilized to reference current generations. In addition, the control scheme decides a number of sensor essential and measurement practices; thus, it also estimates the cost of the topology. In this proposed system, second-order generalized integrator (SOGI) is employed to extract the reference current of SAPF. The SOGI-based control scheme uses only the measurement of the converter, and load current as the feedback signals therefore does not need voltage measurement and sensors. The proposed SAPF topology utilizes an alternative energy source having an energy storage unit to compensate the long-term current disturbances and voltage interruption and mete out the active power requirement of the utility grid. The PV-supported ZSI-based SAPF tested with various kinds of loads can examine the performance of the system under steady and dynamic state conditions. To verify the effectiveness of the proposed control scheme and PV-supported SAPF topology, the simulation and experimental results are presented.

Phase stability, elastic, anisotropic properties, lattice dynamical and thermodynamic properties of B12M (M=Th, U, Np, Pu) dodecaborides

Dodecaborides are promising high strength ceramic and refractory materials, due to the excellent physical properties. However, the scarce systematic investigations of physical properties of B12M (M=Th, U, Np, Pu) dodecaborides hinder the better applications of these dodecaborides. By means of the first-principles approach, we systemically investigated the phase stability, elastic, anisotropic properties, dynamical stability and thermodynamic properties of B12M (M=Th, U, Np, Pu) dodecaborides. The optimized structure constants are consistent with available experimental data. The values of formation enthalpies and V/V0 under pressure indicate B12M have good phase stability. The elastic parameters and modulus indicate that B12M dodecaborides are all brittle and superhard materials. The results of anisotropic factors, 3D surface contours and 2D projections of B12M indicate that they are all anisotropic, but the extent of anisotropy is relatively small. Anisotropy of acoustic velocities and the 2D planar projections of the minimum thermal conductivity are also calculated and discussed. The lattice dynamic properties indicate that four dodecaborides are all satisfied with the dynamic stability conditions. The relationship between thermodynamic quantity and temperature was calculated and discussed for four dodecaborides.