Evaluating Martial Arts Punching Kinematics Using a Vision and Inertial Sensing System

Martial arts has many benefits not only in self-defence, but also in improving physical fitness and mental well-being. In our research we focused on analyzing the velocity, impulse, momentum and impact force of the Taekwondo sine-wave punch and reverse-step punch. We evaluated these techniques in comparison with the martial arts styles of Hapkido and Shaolin Wushu and investigated the kinematic properties. We developed a sensing system which is composed of an ICSensor Model 3140 accelerometer attached to a punching bag for measuring dynamic acceleration, Kinovea motion analysis software and 2 GoPro Hero 3 cameras, one focused on the practitioner’s motion and the other focused on the punching bag’s motion. Our results verified that the motion vectors associated with a Taekwondo practitioner performing a sine-wave punch, uses a unique gravitational potential energy to optimise the impact force of the punch. We demonstrated that the sine-wave punch on average produced an impact force of 6884 N which was higher than the reverse-step punch that produced an average impact force of 5055 N. Our comparison experiment showed that the Taekwondo sine-wave punch produced the highest impact force compared to a Hapkido right cross punch and a Shaolin Wushu right cross, however the Wushu right cross had the highest force to weight ratio at 82:1. The experiments were conducted with high ranking black belt practitioners in Taekwondo, Hapkido and Shaolin Wushu.

Method of graphoanalytical finding borders space-time areas of reachability service spacecraft man-made space objects in geostationary orbit

At the present time at various stages of creation and development there are several projects of service spacecraft. One of the tasks of which is to service orbital objects as soon as possible. During the planning maintenance is needed to perform a large amount of calculations associated with the choice of a rational flight scheme. To reduce the amount of computation, an approach is needed that provides a search for the set of realized flight paths. One of such approaches is the method for determining the boundaries of the spatiotemporal reachability regions, which allows one to evaluate the a priori capabilities of service spacecraft for servicing orbital objects located in circular orbits. To construct spatiotemporal reachable regions, the mathematical apparatus of the hodograph theory is used, which allows, sequentially, based on the analytical solution of the optimization problem of a two-pulse flight, to determine the minimum and maximum duration of the spacecraft’s movement, which is understood as the time required for the flight from the point of maneuvering to the meeting point with the serviced an orbital object under the condition of the application of one velocity impulse. A graphical comparison of the trajectories of the serviced orbital objects and spatiotemporal reachable areas of the service spacecraft makes it possible to determine the potential for service, as well as the time intervals and phase angles at which such service is possible. The proposed methodological apparatus can be used to find a solution providing an initial approximation for the subsequent accurate calculation of the trajectory of motion by numerical methods, as constructing a control program for the spacecraft.

Determining the stability of steady two-dimensional flows through imperfect velocity-impulse diagrams

In 1875, Lord Kelvin stated an energy-based argument for equilibrium and stability in conservative flows. The possibility of building an implementation of Kelvin’s argument, based on the construction of a simple bifurcation diagram, has been the subject of debate in the past. In this paper, we build on work from dynamical systems theory, and show that an essential requirement for constructing a meaningful bifurcation diagram is that families of solutions must be accessed through isovortical (i.e. vorticity-preserving), incompressible rearrangements. We show that, when this is the case, turning points in fluid impulse are linked to changes in the number of the positive-energy modes associated with the equilibria (and therefore in the number of modes likely to be linearly unstable). In addition, the shape of a velocity-impulse diagram, for a family of solutions, determines whether a positive-energy mode is lost or gained at the turning point. Further to this, we detect bifurcations to new solution families by calculating steady flows that have been made ‘imperfect’ through the introduction of asymmetries in the vorticity field. The resulting stability approach, which employs ‘imperfect velocity-impulse’ (IVI) diagrams, can be used to determine the number of positive-energy (likely unstable) modes for each equilibrium flow belonging to a family of steady states. As an illustration of our approach, we construct IVI diagrams for several two-dimensional flows, including elliptical vortices, opposite-signed vortex pairs (of both rotating and translating type), single and double vortex rows, as well as gravity waves. By also considering an example involving the Chaplygin–Lamb dipole, we illustrate how the stability of a specific flow may be determined, by embedding it within a properly constructed solution family. The stability data from our IVI diagrams agree precisely with results in the literature. To the best of our knowledge, for a few of the flows considered here, our work yields the first available stability boundaries. Further to this, for several of the flows that we examine, the IVI diagram methodology leads us to the discovery of new families of steady flows, which exhibit lower symmetry.

Optimal Two-Impulse Trajectories with Moderate Flight Time for Earth-Moon Missions

A study of optimal two-impulse trajectories with moderate flight time for Earth-Moon missions is presented. The optimization criterion is the total characteristic velocity. Three dynamical models are used to describe the motion of the space vehicle: the well-known patched-conic approximation and two versions of the planar circular restricted three-body problem (PCR3BP). In the patched-conic approximation model, the parameters to be optimized are two: initial phase angle of space vehicle and the first velocity impulse. In the PCR3BP models, the parameters to be optimized are four: initial phase angle of space vehicle, flight time, and the first and the second velocity impulses. In all cases, the optimization problem has one degree of freedom and can be solved by means of an algorithm based on gradient method in conjunction with Newton-Raphson method.

Numerical Investigation of Single-Mode Richtmyer-Meshkov Instability

The Richtmyer-Meshkov (RM) instability occurs when a shock passes through a perturbed interface separating fluids of different densities. Similarly, RM instabilities may also occur when a perturbed interface between two incompressible fluids of different density is impulsively accelerated. We report work that investigates RM instabilities between incompressible media by way of numerical simulations that are matched to experiments reported by Niederhaus & Jacobs [1]. We also describe a compact, fractional time-step, two-dimensional, finite-volume numerical algorithm that solves the non-Bousinesq Euler equations explicitly on a Cartesian, co-located grid. Numerical advection of volume fractions and momentum is second-order accurate in space and unphysical oscillations are prevented by using Van Leer flux limiters [2,3]. An initial velocity impulse has been used to model the impulsive acceleration history found in the experiments [1]. We report accurate simulation of the experimentally measured early-, intermediate-, and late-time penetrations of one fluid into another.

Numerical Investigation of Internal Vortex Structure in Two-Dimensional, Incompressible Richtmyer-Meshkov Flows

Richtmyer-Meshkov (RM) instability occurs when one fluid is impulsively accelerated into a second fluid, such that ρ1 ≠ ρ2. This research numerically investigates RM instabilities between incompressible media, similar to the experiments reported by Niederhaus & Jacobs [1]. A two-dimensional, finite-volume numerical algorithm has been developed to solve the variable density Navier-Stokes equations explicitly on a Cartesian, co-located grid. In previous calculations, no physical viscosity was implemented; however, small scale fluctuations were damped by the numerical algorithm. In contrast, current simulations incorporate the physical viscosities reported by Niederhaus & Jacobs [1] and are explicitly used. Calculations of volume fraction and momentum advections are second-order accurate in space. Unphysical oscillations due to the higher-order advection scheme are minimized through the use of a Van Leer flux limiting algorithm. An initial velocity impulse [2] has been used to model the impulsive acceleration history found in the experiments of Niederhaus & Jacobs [1]. Both inviscid and viscous simulations result in similar growth rates for the interpenetration of one fluid into another. However, the inviscid simulations (i.e. no explicit viscosity) are unable to capture the full dynamics of the internal vortex structure that exists between the two fluids due to the absence of viscous effects.