Wyniki wyszukiwania - Biblioteka Nauki

1

Stereophotogrammetry measurement of kinematic target effect as speed accuracy benchmark indicator for kicking performance in martial arts

100%

Wąsik J. , Mosler D. , Ortenburger D. , Góra T.

Acta of Bioengineering and Biomechanics

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2021

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tom Vol. 23, no. 4

117--125

EN

Purpose: The development of a motion capture system leads to fast and accessible ways of precise testing of athletes and their motor abilities. The striking performance in martial arts and combat sports requires measuring velocity in the context of successful contact with the target. The aim of this study was to present the novel kinematic target effect coefficient and its possible use as a speed accuracy benchmark of performance based on the example of taekwon-do roundhouse and frontal kicks. Methods: The stereophotogrammetry motion capture setup consists of 10 infrared cameras (NIR Vicon MX-T40). Analysis includes 180 kicks (roundhouse and frontal kicks) performed by 15 adult participants on a master level in taekwon-do. The kinematic target effect comparison includes two targets – a training shield and a table tennis ball hanging from the ceiling. Markers were placed on the lower extremities of participants. Spatial-temporal variables were registered for both kicking legs, techniques, and target types. Results: Both roundhouse and frontal kicks revealed target and marker dependent differences during its execution. The kinematic target effect coefficient values differ for the specific marker and kick type. Conclusion: The wireless motion capture systems could be helpful in the training process and an athlete’s evaluation before sports competitions.

2

Problem with determining the vehicle impact velocity for car bodies breaking apart

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Aleksandrowicz P. , Aleksandrowicz I. , Kukiełka K. , Patyk R. , Stanowski P.

Transport Problems

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2022

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tom T. 17, z. 3

75--86

EN

This article investigates the impact of a passenger car on a tree, which resulted in the car body breaking apart. A side impact of the car on a tree at high driving speeds is not a standard test in the provisions of the applicable Directives of the European Economic Community, even though the impact poses a serious threat to the driver and the passengers. The threat comes from a deep impaction of the barrier into the body which damages the safety cage. For such impacts, it is very difficult for the vehicle speed to be reconstructed. In practice, expert witnesses and appraisers usually disregard the bodybreaking-apart-related energy due to a difficulty in establishing the data for such calculations, which leads to simplifications and speed underestimates. Performing the right simulation of such impacts with accident reconstruction programs without determining the adequate input data for calculations is also impossible to calculate. This paper presents a range of studies and calculations for such incidents and for identifying the input parameters for collision simulations. The approach presented in this article should be used by expert witnesses and researchers. Therefore, this paper provides insights into theory and practice.

3

Weryfikacja możliwości rozpoznania kolizji przy małych prędkościach uderzenia

100%

Treter W.

Paragraf na Drodze

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2020

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tom Nr 2

71--84

PL

Artykuł zawiera analizę możliwości zweryfikowania odczucia przez kierowcę i pasażerów samochodu kolizji przy małych prędkościach uderzenia, wynoszących kilka lub kilkanaście kilometrów w na godzinę. Do takich kolizji dochodzi niejednokrotnie podczas manewrowania na placach parkingowych. Odczucie przez osoby wewnątrz samochodu uderzenia w inny pojazd bywa utrudnione z uwagi na jednoczesne hamowanie pojazdu. Szarpnięcie spowodowane zderzeniem bywa często zbyt słabe, aby osoba je zarejestrowała.

EN

An analysis is performed of the possibility of vehicle driver and occupants to recognize if they are involved in a collision at low impact speeds of a few or several km/h. Such collisions frequently happen during manoeuvres on parking lots. It is difficult for vehicle occupants to feel the impact against another vehicle because braking takes place simultaneously. The jolt caused by the collision is often too slight to be registered by a person.

4

The analytical study on the optimal ballistic performance using interface theory

84%

Hegde G. S. , Narasimha Murthy H. N. , Krishna M.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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tom Vol. 41, nr 1-2

112-123

EN

Purpose: Analytical determination of impact velocity for different combination of target and projectile materials is the objective of this paper. Design/methodology/approach: The penetration efficiency is maximum when the interaction between the projectile and target is hydrodynamic. Considering zero strength for target and projectile the hydrodynamic impact velocities are predicted using hydrodynamic equation of state. Findings: The hydrodynamic equation being an indeterminate equation is solved using interface theory (briefed in the appendix). The indeterminate Johnson-Cook (JC) model and Steinberg-Guinian (SG) model are also solved using interface theory to predict the influence of static strength of projectile and thermal softening effects. It is inferred that the penetration efficiency decreases with increasing static strength of target and also due to thermal softening of the projectile. In the process the plastic strain, the strain rate and the increase in temperature during impact are theoretically predicted. The segmented projectiles have less/more penetration efficiency than the monolithic impactors and hence require higher/lower impact velocities nearing to hydrodynamic state. Research limitations/implications: The analytical results obtained are in fair agreement with experimental results obtained in the reviewed literatures. Some contrasts are also observed. Originality/value: The paper present the analytical study on the optimal ballistic performance using interface theory.

5

New Experimental Technique for Dynamic Bending of Composite Materials

84%

Massaq A. , Rusinek A. , Klósak M.

Engineering Transactions

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2014

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tom Vol. 62, iss. 3

269–-289

EN

The paper is reporting a new experimental technique to study the dynamic behaviour of composite materials subjected to bending direct impact. It is based on the Hopkinson bar system allowing to observe material behaviour at very high impact velocities. The material used to perform the tests is a woven glass-fibre-reinforced Polyamide 6.

6

Impact resistance of RC beams under different combinations of mass and velocity: mesoscale numerical analysis

84%

Jin L. , Lan Y. , Zhang R. , Du X.

Archives of Civil and Mechanical Engineering

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2020

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tom Vol. 20, no. 4

308--328

EN

The concrete structures under impact loading duress may be destroyed within an extremely short period of time. The importance and complexity of exploration on the impact resistance of concrete members make this area still open for discussion. In the present study, a 3-D mesoscale numerical model was established to investigate the effect of the combination of impact mass and velocity on the mechanical behavior of reinforced concrete (RC) beams subjected to impact loadings. Heterogeneity of concrete and strain rate effects of concrete and steel bars were taken into account. Furthermore, nonlinear interaction between the concrete and steel bars was considered herein. Results from macroscale and mesoscale simulation were compared with the available physical tests, indicating that the mesoscale numerical model can better represent the influence of heterogeneity of concrete on the mechanical behavior of RC beams. Five different impact energy levels were involved to study the effect of the combination of impact mass and velocity on the impact resistance of RC beams. At last, the residual bearing capacity and natural frequency of impacted RC beams were numerically calculated and their relationship was discussed. It is indicated that the deformation of RC beams is influenced strongly by the impulse, which increases with the increasing impact mass at identical impact energy. Besides, the failure mode of RC beams turns from shear-dominant failure mode to bending shear failure mode with the increase of impact mass, accompanied by the increase of energy dissipation of steel bars and the whole member. Despite this, in the present work, the combination of the impact mass and velocity had little influence on the damage extent (based on the performance) of the RC beams. Moreover, an empirical relationship between the residual bearing capacity and the natural frequency of the impacted RC beams was established as a rough reference for damage evaluation in engineering practice.

7

Teoretyczna analiza wpływu systemu aktywnej pokrywy komory silnika na obliczenia prędkości kolizyjnej samochodu, który potrącił pieszego

84%

Wach K.

Paragraf na Drodze

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2022

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tom Nr 2

63--71

PL

Celem pracy była analiza wpływu systemu aktywnej pokrywy komory silnika na obliczenia prędkości kolizyjnej samochodu, który potrącił pieszego. Jednym z coraz częściej stosowanych tego typu systemów jest tak zwana aktywna pokrywa komory silnika (ang. Active Hood, Pop-up Bonnet). Po wykryciu kontaktu przedniej części nadwozia z pieszym, sterownik systemu generuje sygnał inicjujący uniesienie pokrywy, najczęściej jej tylnej części. Działanie to zapewnia zwiększenie dystansu pomiędzy pokrywą a twardymi elementami znajdującymi się w komorze silnika, redukując obrażenia pieszego (zwłaszcza głowy). Zmiana położenia pokrywy w trakcie zderzenia może mieć wpływ na wartość zmierzonego na samochodzie zasięgu wrzucenia oraz rozwinięcia pieszego, czyli wielkości wykorzystywanych do szacowania prędkości kolizyjnej samochodu. W artykule dokonano teoretycznej analizy wpływu zadziałania systemu na wartość przyrostu rozwinięcia pieszego, a w konsekwencji na szacowaną wartość minimalnej prędkości uderzenia. Uzyskane wyniki wskazują, iż w niektórych przypadkach uniesienie pokrywy komory silnika może nieznacznie wpływać na szacowaną wartość prędkości kolizyjnej, nie powinno to mieć jednak istotnego wpływu na rezultaty prowadzonej analizy.

EN

The aim of the work was an analysis of the currently used solutions that ensure pedestrian protection at the time of collision. Selected systems from the area of external passive safety of a car are presented. One of the increasingly used systems of this type is the so-called Active Hood (Pop-up Bonnet). As a result of detecting the contact of the front part of the car body with a pedestrian, the system controller generates a signal initiating the lifting of the engine cover (usually its rear part) upwards. This increases the distance between the bonnet and the hard components in the engine compartment, reducing the severity of injuries to pedestrians (especially the head). The change of the position of the engine cover during a crash may have an impact on the value of wrap around distance. This quantity is used to estimate the collision speed of the car. The article presents a theoretical analysis of the impact of the Active Hood safety system on the value of the pedestrian wrap around distance increment and, consequently, on the estimated value of the minimum impact velocity. The obtained results indicate that in some cases the lifting of the bonnet may have a slight influence on the estimated value of the collision velocity, however, this should not have significant influence on the results of the analysis.

8

Dynamic splitting tensile performance of new and old concrete after high temperature treatment

67%

Cao H.

Archives of Civil Engineering

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2021

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tom Vol. 67, nr 4

79--89

EN

In order to study the dynamic splitting tensile properties of new and old concrete after high temperature treatment, the effects of different impact velocities and temperatures on failure modes, dynamic splitting strength and energy absorption of new and old concrete were analyzed by impact dynamic splitting tensile test use of variable cross-section Φ 74 mm split Hopkinson pressure bar apparatus. The results show that: Impact velocity and temperature not only affect the dynamic splitting strength of new and old concrete bonding specimens, but also affect the failure modes and degree of breakage. The dynamic splitting strength of new and old concrete increases with the increase of impact velocity, but the increase rate decreased with the increase of temperature. The dynamic splitting strength first increases slowly and then decreases dramatically with the increase of temperature. In the dynamic splitting test of new and old concrete, the energy absorption increases with the increase of impact velocity and decreases with the increase of temperature.