COMPUTER SIMULATION IN SPORT DIDACTICS AND COACHING

Modern athletics and gymnastics are characterized by very complex exercises whose mechanics Is very often difficult to understand by intuition so t h a t some problems may arise in teaching ,and coaching. Moreover, many exercises include an aerial phase composed of different sub-phases; while learning, they are experimented separately by the athlete who rebuilds the whole exercise afterwards: a difficult coaching item concerns. for example. the variations of the movements which allow t o obtain the same sub-phases once they are linked in the full exercise, since the initial conditions of each sub-phase are in fact different. This kind of reasons gave recently impulse t o the development of computer simulation systems, especially oriented to sport biomechanics for teachers and coaches. BACKGROUND Starting from the Denavit(l975) approach to the kinematics of multi-body chains. which is based on the adoption of 4x4 matrices to define the relative position of bodies in 3D space. we introduced a set of six 4x4 special matrices. Our main goal is to face coherently. with the same matrix approach, the whole question of the mathematical analysis and synthesis of human motion: from the position analysis to the direct and inverse dynamics. Three out of those matrices are related t o kinematics (generalized position, velocity and acceleration matrices). while the other ones deal with dynamics (generalized action, momentum and Inertia matrices); all of them feature both linear and rotational components (eg.:linear and angular velocity; forces and couples; momentum and angular momentum). The structure and the properties of those matrices easily allow t o build computer programs for 3D direct and inverse dynamics of human motion. in which the equation structure is quite simple and clear. and efficient for computer handling. APPLICATIONS The system of programs f o r the simulation of sport exercises developed in our Department in connection with the University of Brescia. consists of a set of cooperating modules, each performing a particular task; the basic modules are: SPACE-LIB: a library of routines to perform the operations Involving the described matrices; ANTHROPM: to compute geometrical parameters and to build the Inertia matrix from as many data as they are available; DY-MAN: the main module. for the solution of the direct dynamic problem: from the knowledge of the relative motion of body segments and the external forces applied it calculates the athlete's body trajectory and orientation during an hypothetical exercise; GRAPIIMAN: a graphic 3D post-processor for dy_man output. This kind of software can help to solve some of the teaching problems described in the introduction, showing for instance to the athlete the effect of hypothetical variations of limbs’ movement on the whole body motion. It can also be very useful to plan complex athletic exercises without exposing the athlete to the danger of the preliminary set-up phase

Sections of Coxeter Orbihedra

We study sections of high dimensional polytopes whose vertices form the orbit of a Coxeter group, and create “scans”of such polytopes in order to graphically visualise them for educational and public engagement purposes

Hydrological aspects of the Mesoscale Alpine Programme: finding from field experiments and simulations

Proc. International Conference on Alpine Metorology, Zagreb 23-27 Ma

HIGH JUMP DIRECT DYNAMIC SIMULATION

INTRODUcrION High jumps are composed of a complex sequence of movements whose single contribution to the whole body motion cannot be intuitively predicted. While most of the movements are well learned by the elite athletes in order to reach the result, few are not effective or negative from the mechanical point of view and are probably performed for an erroneous feeling of their effects. The direct dynamic simulation of jumping can be useful in order to more fully understand the mechanics of high jump techniques; to explain to the athletes the consequences of some errors; and to test possible evolution of the exercise. When the external forces and the relative movements of the limbs are known, the calculation of the whole body trajectory and orientation is a direct dynamic problem

HYDROLOGICAL ASPECTS OF THE MESOSCALE ALPINE PROGRAMME: FINDINGS FROM FIELD EXPERIMENTS AND SIMULATIONS

Results of the Mesoscale Alpine Programme provide some answers to basic scientific questions of hydrological relevance posed in its scientific plan i.e: 1. verify the forecasting capabilities of a hydrological flood model, forced by the special measurements or coupled with advanced mesoscale atmospheric prediction models; 2. assess the role of the water storage in reservoirs on the runoff generation during floods in mountainous regions; 3. study the influence of soil moisture conditions prior to flood events in determining the production of runoff and investigate the capabilities and limitations of some soil moisture monitoring techniques over rugged terrain. Summary results from investigations in some areas in the southern (Toce, Ticino, Verzasca and Maggia watersheds) and northern (Ammer watershed) side of the Alps during the Mesoscale Alpine Programme and the 1999 Special Observing Period experiment are presented

Influence of natural surfactants on short wind waves in the coastal Peruvian waters

Results from measurements of wave slope statistics during the R/V Meteor M91 cruise in the coastal upwelling regions off the coast of Peru are reported. Wave slope probability distributions were measured with an instrument based on the reflection of light at the water surface and a method very similar to the Cox and Munk (1954b) sun glitter technique. During the cruise, the mean square slope (mss) of the waves was found to be very variable, despite the limited range of encountered wind speeds. The Cox and Munk (1954b) parameterization for clean water is found to overestimate mss, but most measurements fall in the range spanned by their clean water and slick parameterizations. The observed variability of mss is attributed to the wave damping effect of surface films, generated by increased biological production in the upwelling zones. The small footprint and high temporal resolution of the measurement allows for tracking abrupt changes in conditions caused by the often patchy structure of the surface films

A COMPOSITE MODEL FOR THE SIMULATION OF SKIING TECHNIQUES

INTRODUCTION In this work we present a model for skiing technique analysis and simulation: it consists of a man model, an equipment model and a contact (ski-snow) model. Such a model is the basis for a deeper understanding of the interaction between skier and equipment and its use will be profitable in various applications such as: equipment optimisation and technique improvement. Moreover this simulation technique can be profitably used for teaching the basic principles of skiing. MATERIAL AND METHODS To build our model we combined the methods used for multibody systems dynamic analysis (man model with finite element techniques (ski model). The human body model consists of 3D chains of rigid bodies: according to the "sophistication" of the simulation we use 16 segments, with 39'internal d.0.f (full man model), or 7 segments, with 6 internal d.0.f . To describe rigid body dynamics and kinematics (man model) we adopt a method based on homogeneous matrices (Casolo 1995): both the absolute and the relative position, velocity and acceleration are described by 4x4 matrices, as well as the inertial properties and the external loads. This approach allows to embed both the linear and angular terms in the same formalism. To derive the equation of motion a Lagrangian approach was adopted, leading to this expression: Mq+C(cf.q.t) = Fl(q.q,t) +Ft(q,q) where M is the mass matrix, C contain the weight, the centrifugal and Coriolis effect, Ft contains joint torques, F2 represent the action exchanged with ski through the bindings and the vector q contains joints laws of motion. The model can be used to perform direct and inverse dynamics analysis of skiing, since it allows the input of joint torques and/or joint relative movements, that can be experimental data or can be generated by scratch, by a law of motion preprocessor. Skis are modelled with Finite Element techniques. The internal structure of a ski is quite complex: different material, with complex arrangement, are employed giving rise to properties (stiffness, damping and mass) which can be determined by experimental measures or by complex FE analysis. These properties can be quite well reproduced by means of a simplified model consisting of 3D beam elements . Some geometrical features, such as camber and sidecut, can be easily reproduced. Ski equations of motion, in matrix form, are: M9+ q v r e l + Kq&f = F,,I +Fnlon-ski f F.+.ki - cn,,wn where M, C, K are, respectively, the ski mass, damping and stiffness matrices. The ski load consists of three terms: weight, action exerted by the skier through the bindings and the contact action exerted by the snow. A simple contact model has been also developed, based on the assumption that the snow reacts both to ski deepening, sliding and skidding. This simple model can take into account, for example, the effect of ski vibration on the ski-snow interaction. RESULTS Some simulations have been performed to test model capabilities: we analysed the effect of ski torsional stiffness, as well as the amount of sidecut, on skier trajectory during traverse and turns. The model is also used to simulate the aerial phase of a free-style jump and the following landing phase. In all of these cases simulation can be an useful tool for predicting the effect of changing joint movements (i.e varying skiing technique) and equipment characteristics. A sensitivity analysis can be a first step toward a technique and equipment optimisation. References Casolo F., Legnani G., Righettini P., Zappa B. "A homogeneous matrix approach to 3D kinematics and dynamics", TMM (in press)

EVALUATION OF TRAINING METHODS BY MEANS OF KINEMATIC MEASUREMENTS

INTRODUCTIONAim of this work is the evaluation of different training techniques developed for increasing the hip joint range of motion.The standard technique has been comparedwith a training program based on PNF(Proprioceptive Neuromuscolar Facilitation).The experimental data were acquired by using an electrogoniometer system for its easy application in sport exercices, for its reduced dimensions and weight and for its high sample rate (up to 1000 Hz).The quality of the results has been critically analysed and compared with experimental tests made by using both electrogoniometer and optoelectronic system. MATERIAL AND METHODS The flexion extension movement of hip joint of101 male volunteer students, aged between19 and 23 years, was evaluated before and after a training with PNF. The subjects, fastened to an experimental table in supine position, were asked top erform the maximum hip flexion. The tests consist also on passive movements. Preliminary 'results seem to confirm the adequacy of the training technique but the high dispersion of the results leads the authors to analyse the possible causes related to the phenomena. With this aim further tests have been acquired both with electrogoniometer and with an automated optoelectronic system. The experimental analysis included both planar motion of two hinged bar and athletes movement during the standard test. For these analysis reflective markers where rigidly fixed on the electrogonio meter bases. From the 3Dmarker coordinates the angle (a*) between the electrogoniometer bases has been evaluated and compared with that one obtained by the electrogoniometer output. RESULTS The results of the training program showed that the range of motion of the subjects increases after the PNF technique both for passive and active movements The angle between the bases is evaluated in[1.11in which RCHA and RCHB are the electrogoniometer output data representing the two active channels, a and 8 the angles represented in Fig. I.Fig.I In the evaluation of athlete movements the analysis of the result differences of the two systems adopted leads to these following considerations. For the analysed movement the effect of the goniometer cable torsion seems to be negligible while an incorrect calibration procedure seems to be the main source of errors. In fact in the evaluation of athlete movement the gauges have been zeroed at the initial movement position and not with the basis perfectly aligned. This error can be easily corrected if the relative position of the bases is known by using the [ I .2]where k~ and k~ are the output of the electrogoniometer previously correctly calibrated and then placed on the subjects. Another source of errors may be due to the skin where the bases and consequently the markers are fixed. This effect can be partially solved by using rigid cluster linked to the moving body segment. CONCLUSION This study leads to consider new aspects of the movement evaluation by using electrogoniometer and suggest some practical rules to correct the electrogoniometer acquired data

A Multisensor Comparison of Ocean Wave Frequency Spectra from a Research Vessel during the Southern Ocean Gas Exchange Experiment

Obtaining accurate measurements of wave statistics from research vessels remains a challenge due to the platform motion. One principal correction is the removal of ship heave and Doppler effects from point measurements. Here, open-ocean wave measurements were collected using a laser altimeter, a Doppler radar microwave sensor, a radar-based system, and inertial measurement units. Multiple instruments were deployed to capture the low- and high-frequency sea surface displacements. Doppler and motion correction algorithms were applied to obtain a full 1D (0.035–1.3 ± 0.2 Hz) wave spectrum. The radar-based system combined with the laser altimeter provided the optimal low- and high-frequency combination, producing a frequency spectrum in the range from 0.035 to 1.2 Hz for cruising speeds ≤3 m s−1 with a spectral rolloff of f−4 Hz and noise floor of −20/−30 dB. While on station, the significant wave height estimates were comparable within 10%–15% among instrumentation. Discrepancies in the total energy and in the spectral shape between instruments arise when the ship is in motion. These differences can be quantified using the spectral behavior of the measurements, accounting for aliasing and Doppler corrections. The inertial sensors provided information on the amplitude of the ship’s modulation transfer function, which was estimated to be ~1.3 ± 0.2 while on station and increased while underway [2.1 at ship-over-ground (SOG) speed; 4.3 m s−1]. The correction scheme presented here is adequate for measurements collected at cruising speeds of 3 m s−1 or less. At speeds greater than 5 m s−1, the motion and Doppler corrections are not sufficient to correct the observed spectral degradation

HYDROLOGICAL ASPECTS OF THE MESOSCALE ALPINE PROGRAMME: FINDINGS FROM FIELD EXPERIMENTS AND SIMULATIONS

Results of the Mesoscale Alpine Programme provide some answers to basic scientific questions of hydrological relevance posed in its scientific plan i.e: 1. verify the forecasting capabilities of a hydrological flood model, forced by the special measurements or coupled with advanced mesoscale atmospheric prediction models; 2. assess the role of the water storage in reservoirs on the runoff generation during floods in mountainous regions; 3. study the influence of soil moisture conditions prior to flood events in determining the production of runoff and investigate the capabilities and limitations of some soil moisture monitoring techniques over rugged terrain. Summary results from investigations in some areas in the southern (Toce, Ticino, Verzasca and Maggia watersheds) and northern (Ammer watershed) side of the Alps during the Mesoscale Alpine Programme and the 1999 Special Observing Period experiment are presented