Wyniki wyszukiwania - BazTech

1

Development of effective sealing units for oil and gas equipment in the oil and gas production system

Hasanov Ilman I., Guliyev Agali A.

Nafta-Gaz

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2023

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R. 79, nr 7

464--472

EN

The paper presents the results of many years of experience in studying the efficiency of sealing units in the conditions of their operation in the oil and gas production system, as well as the influence of technological parameters that ensure normal operation and protect them from failure due to leakage through the working surface of the seals in the friction zone. In addition, according to the results of practical studies, it has been established that, in order to improve the elastic properties, for example, of cup springs of a direct-flow valve, we calculated heat treatment of the operational values of spring compression for various material thicknesses. The work of the elastic elements of the packer was improved mainly by the design, and the optimal parameters for the development of the elastic element of the packer were determined. The study of the stress-strain state of the sealing element of packers during setting and improving its performance is of both practical and scientific interest. One of the factors that significantly affect operation of pumps is the fluid leakage in valve assemblies in order to identify the effect of the above parameters on tightness based on a preliminary theoretical analysis. Comparison of data during the study showed that the flow rate of work with low viscosities is greater than with high viscosities. The technological processes of hardening the parts of the shut-off assembly of X-mas tree valves, to increase their reliability, are considered. The dependence of the compression force of the spring and its deformation because of geometric parameters of the disk springs has been determined; it has been found that the residual deformation of the disk spring after collapse has a negative effect on tightness. Calculations show that the amount of leakage of the elastic elements in the sealing assembly should not exceed ≤0.309, since the seal at the value of elastic energy deformation provides a self-compacting mode. Thus, the degree of uneven pressing of the seat to the surface of the gate and its regulation to prevent leakage is practically determined.

PL

Artykuł przedstawia wyniki wieloletnich doświadczeń w badaniu skuteczności zespołów uszczelniających, w warunkach ich pracy w systemie wydobywczym ropy i gazu, jak również wpływ parametrów technologicznych zapewniających ich normalną eksploatację i zabezpieczających je przed awarią spowodowaną wyciekiem przez powierzchnię roboczą uszczelnienia w strefie tarcia. Ponadto, zgodnie z wynikami badań o charakterze praktycznym, ustalono, że aby poprawić właściwości sprężyste, np. sprężyn talerzowych zaworu bezpośredniego przepływu, obliczono obróbkę cieplną wartości eksploatacyjnych ściśnięcia sprężyny dla różnych grubości materiału. Praca elementów sprężystych uszczelniacza została poprawiona głównie dzięki projektowi oraz ustalono optymalne parametry dla budowy elementu sprężystego uszczelniacza. Badania stanu naprężenie-odkształcenie elementu uszczelniającego uszczelniacza w czasie posadowienia oraz poprawa jego działania są interesujące zarówno ze względów praktycznych, jak i naukowych. Jednym z czynników znacząco wpływających na pracę pomp jest wyciek płynu w zespołach zaworów, co pozwoliło na określenie wpływu powyższych parametrów na szczelność w oparciu o wstępną analizę teoretyczną. Porównanie danych w czasie badania wykazało, że prędkość przepływu pracy z niskimi lepkościami jest większa niż z wysokimi lepkościami. Rozważane są procesy technologiczne utwardzania części zespołu odcinającego zaworów choinkowych w celu zwiększenia ich niezawodności. Ustalono zależność siły ściskania sprężyny i jej odkształcenia ze względu na parametry geometryczne sprężyn talerzowych; stwierdzono, że odkształcenie resztkowe sprężyny talerzowej po zgnieceniu ma negatywny wpływ na szczelność. Obliczenia wykazują, że wielkość wycieku elementów sprężystych w zespole uszczelniającym nie powinna przekraczać ≤0,309, gdyż uszczelnienie przy wartości odkształcenia energii sprężystej zapewnia tryb samoczynnego zagęszczania. Tak więc stopień nierównomiernego dociśnięcia gniazda do powierzchni zasuwy i jego regulacja w celu przeciwdziałania wyciekowi został praktycznie określony.

2

Zmiany niwelety stalowego przęsła mostu podwieszonego

Machelski Czesław, Hildebrand Maciej

Inżynieria i Budownictwo

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2023

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R. 79, nr 3-4

165--169

PL

W niniejszej pracy skupiono się na analizie zmiany niwelety mostu. Do tego celu wykorzystano wyniki pomiarów geodezyjnych. Z uwagi na złożony kształt wykresów ugięć konieczne było stosowanie korekty, w której korzystano z pomiaru sił w wantach. Jest to jeden ze stosowanych algorytmów wygładzania funkcji ugięcia uzyskanych z pomiarów geodezyjnych. Do analizy skuteczny jest globalny model konstrukcji 2D z wykorzystaniem elementów prętowych. Jest on szczególnie efektywny w zastosowaniu MRS, gdy występuje regularny układ punktów pomiarowych. Zaletą algorytmu jest wybór dowolnego wycinka przęsła i niezależność od warunków podporowych.

EN

The alterations of bridge gradeline is a main subject of the paper. For this purpose, the results of geodetic survey were used. Due to the complex shape of the deflection lines, it was necessary to apply a correction procedure, using the results of measurement of forces in the stays. This is one of the algorithms used to smooth the deflection function obtained from geodetic measurements. A global 2D numerical model with bar elements is effective for the analysis. It is especially effective in MRS applications when there is a regular arrangement of measurement points. The advantage of the algorithm is the selection of any section of the span and independence from the support conditions.

3

Evaluation of forces in a racing simulator based on a Stewart platform

Tytuła Jakub, Zaremba Arnold, Nitkiewicz Szymon

Diagnostyka

|

2023

|

Vol. 24, No. 4

art. no. 2023405

EN

This paper presents how forces are perceived in a racing simulator based on a Stewart Platform. By retrieving calculated forces in a racing game by its physics engine and comparing them to real-life measurements during the platforms motions it is possible to evaluate the platforms immersiveness. Virtual values extracted from the game engine are deemed satisfactory to their real life counterparts and serve as a baseline. In order to evaluate forces created by the simulator, a lap around a virtual test track is recorded and played back while an accelerometer and gyroscope record its movements. Overall, accelerations recorded in the direction of X and Y axis along with angular speed of rotation around the aforementioned those axis. To accurately comparing every derived force, the recorded virtual lap is divided into sections representing the five most common manoeuvres during racing. These comparisons serve as an evaluation method to measure the immersiveness of the simulator.

4

Leading-edge polymer/carbonaceous nano-reinforcement nanocomposites — opportunities for space sector

Kausar Ayesha, Ahmad Ishaq

Advances in Materials Science

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2023

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Vol. 23, nr 4(78)

99--122

EN

Carbonaceous or nanocarbon nano-reinforcement nanocomposites have been found as emergent candidates for aerospace industry. Consequently, the multifunctional nanocomposites have been fabricated using marvelous nanocarbon nanostructures like graphene, carbon nanotube, fullerene, carbon black, etc. Manufacturing techniques have also been engrossed for the formation of high performance engineering nanocomposites having fine strength, heat stability, flame resistance, and other space desired features. These practices include solution, in situ, and melt procedures, on top of specific space structural design techniques, for the formation of aerospace structures. The aerospace related material property enhancements using various carbonaceous nano-reinforcements depends upon the type of nanocarbon, dimensionality, as well as inherent features of these nanostructures (in addition to the choice of manufacturing methods). Furthermore, carbon nano-reinforcements have been filled, besides carbon fibers, in the epoxy matrices. Nanocarbon coated carbon fibers have been filled in epoxy resins to form the high performance nanomaterials for space structures. The engineering features of these materials have been experiential appropriate for the aerospace structures. Further research on these nanomaterials may be a key towards future opportunities in the aero systems. Additionally, the explorations on structure-property relationships of the carbonaceous nanocomposites have been found indispensable for the development of advanced aerospace structures.

5

Porównanie wybranych parametrów biomechanicznych osób po upadku oraz osób, które nie uległy upadkowi

Tokarski Tomasz

Bezpieczeństwo Pracy : nauka i praktyka

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2021

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nr 9

17-21

PL

Upadek, spowodowany na przykład utratą równowagi, stanowi bardzo częstą przyczynę wypadków przy pracy. Problem ten dotyczy zwłaszcza pracowników starszych. Okazuje się, że każdego roku blisko 1/3 osób po 65. roku życia ulega upadkom. Narażone są m.in. osoby o pogorszonych parametrach fizycznych. Do tych niekorzystnych zmian dochodzi wraz z postępującym procesem starzenia, a także na skutek uszkodzeń układu ruchu. Wraz z wiekiem rośnie więc częstość upadków, a ich skutki dla zdrowia stają się coraz poważniejsze. W artykule opisano badania nad osobami z grupy wiekowej 60-67 lat. Ich celem było: po pierwsze – porównanie wybranych parametrów biomechanicznych (tj. parametrów chodu, koordynacji wzrokowo ruchowej, siły mięśniowej oraz zdolności utrzymywania równowagi) osób po upadku oraz osób, które nie uległy upadkowi, a po drugie – wskazanie tych parametrów, które mogą mieć wpływ na większą skłonność do upadku. Tymczasem różnice pomiędzy parametrami uzyskanymi dla obu badanych grup okazały się niewielkie i statystycznie nieistotne.

EN

Falling out of balance is a very common cause of accidents at work. Older workers are particularly affected by this problem. It turns out that each year nearly 1/3 of people over 65 experience a fall. Particularly vulnerable are, inter alia, people with impaired physical parameters. These unfavourable changes occur along with the progressive aging process and as a result of damage to the locomotor system. Thus, the frequency of falls increases with age, and the effects on health become more severe. The article describes research on people in the 60-67 age group. Their aim was: firstly – to compare selected biomechanical parameters (i.e. parameters of walking, eye-hand coordination, muscle strength and the ability to maintain balance) of people after a fall and people who did not fall, and secondly – to indicate those parameters that may have an influence on a greater tendency to fall. Meanwhile, the differences between the parameters obtained for both studied groups turned out to be small and statistically insignificant.

6

Destruction of the Structure of Boiling Emulsions

Pavlenko Anatoliy, Melnyk Viktor

Rocznik Ochrona Środowiska

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2020

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Tom 22, cz. 1

70--81

EN

In this paper we consider the processes of dynamic interaction between the boiling particles of the dispersed phase of the emulsion leading to the large droplet breakup. It is indicated the differences in the consideration of forces that determine the crushing of non-boiling and boiling drops. It is determined the possibility of using the model to define the processes of displacement, deformation or fragmentation of the inclusion of the dispersed phase under the influence of a set of neighboring particles. The proposed method allows us to determine the main energy parameters of the homogenization process by boiling the emulsion.

PL

W tym artykule rozważamy procesy dynamicznej interakcji między wrzącymi cząsteczkami zdyspergowanej fazy emulsji, prowadzące do rozpadu dużych kropel. Wskazano na różnice w uwzględnianiu sił, które determinują kruszenie kropli niewrzących i wrzących. Określono możliwość wykorzystania modelu do zdefiniowania procesów przemieszczenia, deformacji lub fragmentacji włączenia fazy rozproszonej pod wpływem zestawu sąsiednich cząstek. Proponowana metoda pozwala określić główne parametry energetyczne procesu homogenizacji podczas ogrzewania i wrzenia emulsji.

7

O precyzji sondowania statycznego na przykładzie badań gruntów przejściowych poletka badawczego AMU Morasko

Wierzbicki Jędrzej, Młynarek Zbigniew, Wołyński Waldemar

Przegląd Geologiczny

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2020

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Vol. 68, Nr 8

655--662

EN

The Cone Penetration Test is one of the most versatile and widely used geotechnical tests over the world. Some differences in technical solutions between the equipment manufactured by different producers and the relatively quick wear of the penetrometer itself make the issue of quality and comparability of the CPTU results very actual. The tests were conducted in the testing ground of Adam Mickiewicz University in Poznań. The test site is located in the northern part of Poznań, within a marginal zone of the Poznań Phase of the Weichselian (Vistulian) glaciation. The subsoil consists of glacial till of the Riss glaciation and glacial till of the Vistulian glaciation, separated by fluvioglacial sandy sediments and covered with fine and medium sands with single gravel grains. The quality of geotechnical parameters of the tested subsoil was assessed for the initial constrained modulus and undrained shear strength. To determine these parameters, static penetrometers produced by two different manufacturers were used. The tests and the results of analysis were performed in three stages. In the first stage, each penetrometer was used to investigate homogeneity and diversity of the subsoil structure in the test sites. The subsoil structure diversity was examined by grouping statistically similar Rf coefficient values along the profile. In the second stage, the level of accuracy and precision in the assessment of the corrected cone resistance - qt, friction on the friction sleeve-fs, and pore pressure - u2 was determined for individual penetrometers. In the next stage, the differences between the constrained modulus and undrained shear strength were determined for both penetrometers. This analysis takes into account the level of precision of the corrected cone resistance.

8

Magnetic levitation in industrial transport systems

Lis Marek, Szewczyk Krzysztof, Walasek Tomasz

Przegląd Elektrotechniczny

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2020

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R. 96, nr 12

214--217

EN

The paper presents a well known idea of using permanent magnets as a source of energy in an industrial transport system (for instance maglev). The idea of this paper is to present computation and simulation for a transport system in 2D space using the Ansys environment. An idea for a system which starts to operate only at the very moment when a worker needs help and is moving a heavy object, and is using it with a minimum amount of energy has become an idea about saving energy. When gravity is eliminated by magnetic fields forces, for moving heavy object, we only need to overcome the moment of inertia. All resistance practically disappears, because there is almost no friction in this system. In the paper the use of magnetic field concentration in Halbach array system for eliminating gravitational forces during a load movement has been presented.

PL

W pracy przedstawiono dobrze znaną ideę wykorzystania magnesów trwałych, jako źródła energii w przemysłowym systemie transportu (na przykład maglev). Ideą tego artykułu jest prezentacja obliczeń i symulacji transportu systemu w przestrzeni 2D za pomocą środowiska Ansys. Pomysł na system, który działa tylko w momencie, gdy pracownik potrzebuje pomocy i porusza ciężkim przedmiotem i używa go przy minimalnej ilości energii, staje się pomysłem oszczędzania energii. Kiedy grawitacja jest eliminowana przez siły pola magnetycznego, do przemieszczania ciężkich obiektów wystarczy jedynie pokonać moment bezwładności. Cały opór praktycznie znika, ponieważ w tym układzie prawie nie ma tarcia. W artykule przedstawiono zastosowanie koncentracji pola magnetycznego w układzie macierzy Halbacha do eliminacji sił grawitacyjnych podczas ruchu ładunku.

9

The Effect of Gradation and Grain-Size Properties of Fine Aggregate on the Building Mortars

Mehmetoğulları Ebubekir, Güneyli Hakan, Karahan Süleyman

Production Engineering Archives

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2020

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Vol. 26, Iss. 3

121--126

EN

This work is about the effect of fine aggregate properties on the physicomechanical characteristics of hardened mortars. The results indicated that the increase in grain-size of fine aggregate increases the bulk density of hardened mortars. The strength of mortars including limestone fine aggregate is higher than that of the silica-sand. Regardless of the aggregate origin, the strength of the mortars with well-graded fine aggregate for all grain-size is greater than of with uniform fine aggregate. This indicates that grading of fine aggregate increases the strength, while uniformity decreases it. The strength of mortars with well-graded fine aggregate increases as the grain-size increases. Regardless of the aggregate origin, the strength of mortars with uniform fine aggregate increases with increasing grain-size until the grain-size range of 425-1000 µm, but after this range it decreases with increasing grain-size. The thermal conductivity increases with the increase in the grain-size. Notedly, the relationship between thermal conductivity and maximum grain-size of well-graded fine aggregate has a very strong positive correlation. Further, the thermal conductivity value for mortars formed with uniform fine limestone aggregate is minimum at the grain-size range of 425-1000 µm, while it has greatest values close together from this grain-size range.

10

Udział Głównego Urzędu Miar w europejskim projekcie badawczym EMPIR w dziedzinie siły

Fidelus Janusz D.

Metrologia i Probiernictwo : biuletyn Głównego Urzędu Miar

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2020

|

nr 1 (24)

7--14

PL

W artykule przedstawiono założenia i szczegółowe cele projektu oraz aktualny stan wiedzy i możliwości uzyskania postępu w zapewnieniu spójności pomiarowej w europejskim i światowym przemyśle w zakresie siły statycznej, ciągłej i dynamicznej. Omówiono także zakres uczestnictwa GUM oraz potencjalny wpływ założonych w projekcie przedsięwzięć na środowisko, metrologię i użytkowników. Przedstawiono wzorce GUM o najmniejszej niepewności pomiarowej, na których zostaną wykonane badania siły statycznej i ciągłej.

EN

The article presents the assumptions and detailed objectives of the project as well as the current state of the art and the possibilities of achieving progress in ensuring traceability in European and global industry in the field of static, continuous and dynamic force. The scope of GUM participation and the potential impact of the design assumptions on the environment, metrology and users were also discussed. GUM standards with the lowest measurement uncertainty, on which static and continuous force tests will be performed, are presented.

11

Wpływ kształtu imperfekcji geometrycznych dźwigarów dachowych na siły w tężniku połaciowym poprzecznym

Czepiżak Dariusz

Builder

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2020

|

R.24, nr 4

88--91

PL

Projektując stężenia połaciowe poprzeczne [1], zaleca się przyjmować zastępcze obciążenie od imperfekcji geometrycznych dźwigarów dachowych. Obciążenie to można bezpiecznie oszacować [1] przy założeniu stałej na długości elementu stabilizowanego siły ściskającej i imperfekcji w kształcie paraboli o strzałce e0. W pracy, dla różnych kształtów imperfekcji geometrycznych elementów stabilizowanych, wyznaczono obciążenia imperfekcyjne oraz siły w prętach tężnika połaciowego i porównano je z siłami wyznaczonymi wg [1]. Wyniki analiz przedstawiono w tabeli i sformułowano syntetyczne wnioski.

EN

During designing transverse roof bracing, [1] recommends taking into account equivalent stabilizing load from geometrical imperfections of roof girders. This load can be safely estimated [1] assuming a constant compression force along the length of the stabilized element and initial parabolic imperfection with maximum amplitude e0. In the paper, for different shapes of geometrical imperfections of stabilized elements, imperfect loads and forces in the roof bracing were determined and compared with the forces determined according to [1]. The results of the analyzes are presented in the table and synthetic conclusions were formulated.

12

Concrete Capillarity under Different Curing Conditions Produced in Kurdistan-Iraq

Herki Bengin A.

Advances in Science and Technology. Research Journal

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2020

|

Vol. 14, no 2

131--139

EN

This study discussed the effect of the curing condition on the capillary water absorption of concrete incorporating the locally available materials. The compressive strength and ultrasonic pulse velocity (UPV) as part of mechanical and durability properties of concrete were also investigated. The engineering properties were conducted on concrete under three different curing conditions at different curing ages of 2 days, 7 days and 28 days. The three different curing conditions were water curing, dry curing and gunny-covered curing. According to the results obtained, the concrete under water curing condition demonstrated a lower capillary water absorption (CWA) at 2 and 7 days ages and the concrete under gunny-covered condition demonstrated lower CWA at 28 days of age, compared with the other curing conditions. It is interesting to see that the compressive strength (38 MPa) of concrete was almost the same at 28 days age under the gunny-covered and water curing conditions.

13

Istota bezpieczeństwa dyplomacji

Domeracki Krzysztof

Zeszyty Naukowe Wyższej Szkoły Zarządzania Ochroną Pracy w Katowicach

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2019

|

Nr 1(15)

89--102

PL

Artykuł stanowi próbę zdeﬁniowania pojęcia bezpieczeństwa dyplomacji i jest przyczynkiem do dalszej dyskusji nad zagadnieniem, w szczególności w kontekście zwiększającej się dynamiki w relacjach międzynarodowych oraz rozszerzającej się przestrzeni konfrontacji między podmiotami bezpieczeństwa. Praca prezentuje zagadnienie w odniesieniu do roli dyplomacji i siły w stosunkach międzynarodowych w kontekście realizacji interesów narodowych. Poruszana jest również kwestia bezpośrednich ataków na personel dyplomatyczny oraz na przedstawicielstwa dyplomatyczno-konsularne jako jeden z efektów rywalizacji pomiędzy państwowymi podmiotami bezpieczeństwa.

EN

The paper examines the diplomatic security phenomena throughout an epistemological and ontological view. In the article the Author tries to put a diplomatic security in broader terms related to diplomacy and security, as well as depicts and defines its role, scope and assumptions. The issue is much more important due to rising dynamics of international relations well as still expanding “space confrontation” between states. It is also crucial because sometimes the effects of this confrontation are direct attacks on diplomats or diplomatic and consular missions. The paper depicts an introduction to diplomatic security issues. The sketch of the theory of diplomacy and security is also given.

14

Mechanical and mathematical research of local deformations of a steel roller shell with a variable geometry of contact surface

Doudkin Mikhail, Kim Alina, Sakimov Murat

Production Engineering Archives

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2019

|

Vol. 23

27--35

EN

The article is devoted to solving the fundamental and applied problem of nonlinear structural me-chanics of machines by introducing into the drum two additional stop cylinders with supporting rollers at the end and adjustable length, providing a given elliptical or circular shape of a flexible shell with a smoothly variable geometry in the area of its contact with compacted pavement material. Compaction of soil, gravel and asphalt concrete in the sphere of road is not only an integral part of the technological process of the roadbed, road foundation and surface construction, but it is actually the main operation to ensure their strength, stability and durability. The quality, cost and speed of road construction, the possibility of using fundamentally new technologies, structures and materials is largely determined by the availability of modern road machinery.

15

An experimental study of cutting fluid on drilling AISI 1040 steel

Alim Md. Abdul, Uddin Md. Julhash, Islam Md. Ariful

Journal of Mechanical and Energy Engineering

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2019

|

Vol. 3, No 1

7--12

EN

This experimental study investigated the effects of a conventional cutting fluid during drilling cylindrical holes on workpiece materials made of the AISI 1040 steel. Drilling responses were compared between dry and wet (in presence of the cutting fluid) cutting conditions with respect to drilling force, roundness deviation and taper of the hole, and chip morphology. High production machining and drilling with high cutting speed, feed, and depth of cut were found to be inherently associated with the generation of a large amount of heat and high cutting temperature. In a dry condition such high cutting temperature not only reduces dimensional accuracy and tool life but also impairs the roundness deviation and taper of the hole. The use of a conventional cutting fluid, in such a situation, was very effective to reduce the cutting temperature. In a dry cutting condition, numerous tool-wears were found on the drill bits. Drilling in such a dry condition seriously affects roundness of the hole, and chip shape and color. Contrastingly, use of a traditional cutting fluid reduced temperature as well as improved roundness and taper of the hole. It also acted as a lubricate at the tool tip–work surface interface. Overall, the conventional cutting fluid enhanced the quality of the machine work and potentially can increase machine life of drill bits.

16

Power–velocity relationship and muscular strength in female volleyball players during preparatory period and competition season

Buśko Krzysztof

Acta of Bioengineering and Biomechanics

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2019

|

Vol. 21, no. 2

31--36

EN

The aim of the study was to investigate changes of power–velocity relationship and muscular strength of female volleyball players during preparatory period and competition season. Methods: The study was conducted on eleven female volleyball players: age 21.6 ± 1.7 years, body height 177.9 ± 4.7 cm, body mass 71.3 ± 6.6 kg. Power–velocity relationship was determined by means of five maximal 10-second cycloergometer efforts with external loads equal to: 2.5, 5, 7.5, 10 and 12.5% of body weight (BW). The joint torque of flexors and extensors of an elbow, shoulder, hip, knee and trunk was measured using a torque meter. The measurement were taken before (I) and after (II) the preparatory period, after the first (III) and second (IV) competitive season. Results: The power with a load equal to 2.5, 5.0, 7.5, 10.0% BW increased significantly after first and second competitive season. The sums of joint torque for the lower and upper limb changed insignificantly. In the case of the right upper limb, sum of the joint torques was significantly reduced by 9.5% between measurement I and IV. Sum of the left upper limb was significantly decreased by 9.8% between measurement I and II. Sum of the joint torque of the trunk was significantly increased between measurements I and II, III and IV by 12.9%, 12.3% and 11.2%, respectively. Conclusion: Obtained results may suggest that selection of the training loads was adequate for training power output and muscle strength of lower limbs but too little emphasis was placed on development of strength in the muscles of the upper limbs.

17

Jumping performance and take-off efficiency in two different age categories of female volleyball players

Jandova Sona, Janura Miroslav

Acta of Bioengineering and Biomechanics

|

2019

|

Vol. 21, no. 2

55--61

EN

Vertical jump height is recognised as a determinant factor in elite volleyball performance. In previous studies there are different opinions on whether vertical jump height performance improves during maturation or not. The aim of this study was to assess the differences in jumping abilities in two different age groups of female volleyball players and to determine the take-off efficiency during repeated jumps. Methods: Seventeen female volleyball players from two different age categories – adults and under 16 years – participated in this study. Quattro Jump 9290BA force platform (Kistler, Winterthur, Switzerland) was used to assess the jumping performance during squat jumps, counter movement jumps, and 45-second continuous jumps. Results: Jumping performance did not differ significantly between the two groups. The main efficiency of the conversion of mechanical work into mechanical energy was only 24% and it decreased during the test. Conclusions: The influence of age on the jumping performance in a group of female volleyball players was not confirmed. Take-off efficiency was in both groups quite low and it did not improve during the test.

18

Assessment of distribution of plantar pressures and foot characteristics during walking in pregnant women

Mikeska Ondřej, Gimunová Marta, Zvonař Martin

Acta of Bioengineering and Biomechanics

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2019

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Vol. 21, no. 3

49--56

EN

The main purpose of this research was to analyse the distribution of plantar pressures and foot characteristics during walking between weeks 27 and 36 of pregnancy. The secondary purpose was to test the effect of the customized orthopaedic shoes that were worn by the experimental group. Methods: Pregnant women (n = 73) were divided into 2 groups, control group (n = 38) and experimental group (n = 35) which completed 5 gait trials on a walkway (1.55m) at a self-selected velocity of gait, where force, pressure and remaining foot characteristics were sampled and displayed by Novel database pro m (version 25.3.24). Results: Analysis of foot characteristics did not reveal important changes. Analysis of the distribution of plantar pressures revealed few changes in the pre- and post-measurement of the experimental and control groups between weeks 27 and 36 of pregnancy. In the last measurement, there is a significant increase of peak pressure only in the midfoot area of the left foot (151.1 ± 41.2 kPa) and in the hindfoot area of the right foot (346.3 ± 104.1) of the experimental group. The control group exhibits similar pressure development for both of foot. Conclusions: Monitored parameters demonstrated in certain areas notably development of force and contact area. Results of foot characteristics did not reveal a significant changes. As both groups registered similar values in certain areas in a comparison of pre/post measurement characteristics, the influence of specific orthopaedic shoes cannot be conclusively demonstrated in the experimental group.

19

Anthropometric and strength profiles of professional handball players in relation to their playing position – multivariate analysis

Lijewski Marcin, Burdukiewicz Anna, Pietraszewska Jadwiga, Stachoń Aleksandra, Andrzejewska Justyna, Chromik Krystyna

Acta of Bioengineering and Biomechanics

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2019

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Vol. 21, no. 4

147--155

EN

In team sports, the varied levels of physical demand associated with different field positions are reflected in the morphofunctional features of the players. The aim of this work was to recognize how the playing position in the team depends on the anthropometric profiles and the strength level of professional handball players. Methods: A body mass, stature, lower and upper extremity length, circumferences and skinfolds were measured in the male professional athletes. The body composition was analysed using a bioelectrical impedance method. Additionally, hand grip and back strength were measured. A statistical analysis was carried out using routinely statistic methods and principal component analysis. Results: Pivot players usually have the most athletic figure in terms of size and weight and relatively short legs. The backs are characterized by the android body type and low subcutaneous fat content, and a large mass of body cells. The backs and pivots have the same strength of back and hand grip. Goalkeepers have relatively long upper and lower limbs and high back and hand grip strength. The wingers are usually slender, have medium length limbs, low body fat percentage, significant extracellular mass and the lowest muscle strength. Conclusions: The results of the multivariate analysis were a notable and valuable addition to the study of morphological and strength differences in a group quite homogeneous like a handball team. The principal component analysis allowed for a reduction of the multidimensional structure to three variables describing body massiveness, strength, and the length and height aspect of the body.

20

Structure and properties of the steel railway wheel disc after forced cooling

Vakulenko I., Grischenko N., Vakulenko L., Efremenko V., Proiydak S., Perkov O.

Zeszyty Naukowe. Transport / Politechnika Śląska

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2018

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z. 98

173--180

EN

The technological use of accelerated cooling makes it possible to improve the carbon steel properties of the all-rolled railway wheel disc. The properties’ complex depends on the temperature of the accelerated cooling termination. This is determined by the ratio of the carbon atoms emitted from the supersaturated solid solution to the crystal structure defects and dispersion strengthening from carbide phase particles. If the cooling stops at a temperature above 350°C, the decline rate of the strength properties increases. This is caused by the excessive softening effect of the solid solution breakdown and cementite spheroidization during the processes of dispersion hardening.