Wyniki wyszukiwania - Biblioteka Nauki

1

Poziom profesjonalizmu kadr dowódczych i jego wpływ na zdolności operacyjne Sił Zbrojnych RP

100%

Tomaszewski A.

Obronność – Zeszyty Naukowe Wydziału Zarządzania i Dowodzenia Akademii Sztuki Wojennej

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2018

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nr 2(26)

29

EN

The paper contains findings from the author’s research conducted between 2015 and 2017. The aim of the research was to determine the level of professional preparation of commanding personnel and general staff of Land Forces and to show its influence on land forces’ operational capability. The author presents the fundamental determinants of the operational capability, highlighting the significance of the competences of regular commanding officers and staff officers. The paper contains a detailed analysis of factors determining the effectiveness of professional preparation of the above-mentioned personnel during the last decade. Also, the author identifies the causes of a serious dysfunction, which in his opinion has taken place in recent years, concerning the education and professional training of commanding and general staff personnel of the Armed Forces. The hypothesis put forward in the paper is verified by the author with his own research findings as well as the research conducted in recent years by the Military Office of Social Research.

2

Risk of power cables insulation failure due to the thermal effect of solar radiation

51%

Czapp S. , Szultka S. , Ratkowski F. , Tomaszewski A.

Eksploatacja i Niezawodność

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2020

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tom Vol. 22, no. 2

232--240

EN

Low-voltage, as well as high-voltage power cable lines, are usually buried in the ground. The ampacity of the power cables in the ground mainly depends on the thermal resistivity of the soil, which may vary in a wide range. A common practice in power cable systems performance is to supply them from a pole of an overhead line. If so, a section of the line is located in free air and can be directly exposed to solar radiation. In some cases, the ampacity of power cables placed in free air is lower than in the ground. Differences in ampacities can be very high if thermal resistivity of the soil is very low, and simultaneously solar irradiation of cables in air occurs. This paper presents the risk of power cables overheating and in consequence the risk of their failure, when part of the underground power cable line is placed in free air. Temperature distribution of cables in the air (with and without solar radiation) for various load currents is presented. Thermal endurance of power cables insulation, operating with the overheating, is estimated.

PL

Linie kablowe zarówno niskiego, jak i wysokiego napięcia zwykle buduje się jako podziemne. Obciążalność kabli układanych w ziemi w znacznym stopniu zależy od rezystywności cieplej gruntu, a może się ona zmieniać w bardzo szerokim zakresie. Obecnie powszechną praktyką jest zasilanie linii kablowych z linii napowietrznych, co sprawia, że pewien odcinek linii kablowej znajduje się w powietrzu i może być poddany bezpośredniemu oddziaływaniu promieniowania słonecznego. W pewnych przypadkach obciążalność prądowa długotrwała kabli w powietrzu jest niższa niż w ziemi – różnice w tej obciążalności mogą być bardzo duże, jeżeli grunt ma niską rezystywność cieplną, a na odcinek linii w powietrzu oddziałuje promieniowanie słoneczne. W artykule przedstawiono problem przegrzania kabli elektroenergetycznych, gdy przyjęta obciążalność linii kablowej wynika z warunków dla ułożenia w ziemi, a na pewnym odcinku linia jest umieszczona w powietrzu. Przedstawiono rozkłady temperatury kabli w powietrzu (z uwzględnieniem i bez uwzględnienia promieniowania słonecznego) dla różnych prądów obciążenia kabli. Oszacowano trwałość termiczną izolacji kabli, mających przez znaczny przedział czasu temperaturę wyższą niż dopuszczalna długotrwale.

3

Impact of thermal backfill parameters on current-carrying capacity of power cables installed in the ground

51%

Szultka S. , Czapp S. , Tomaszewski A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2023

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tom Vol. 71, nr 3

art. no. e145565

EN

Proper design of power installations with the participation of power cables buried in homogeneous and thermally well-conductive ground does not constitute a major problem. The situation changes when the ground is non-homogeneous and thermally low-conductive. In such a situation, a thermal backfill near the cables is commonly used. The optimization of thermal backfill parameters to achieve the highest possible current-carrying capacity is insufficiently described in the standards. Therefore, numerical calculations based on computational fluid dynamics could prove helpful for designers of power cable lines. This paper studies the influence of dimensions and thermal resistivity of the thermal backfill and thermal resistivity of the native soil on the current-carrying capacity of power cables buried in the ground. Numerical calculations were performed with ANSYS Fluent. As a result of the research, proposals were made on how to determine the current-carrying capacity depending on the dimensions and thermal properties of the backfill. A proprietary mathematical function is presented which makes it possible to calculate the cable current-carrying capacity correction factor when the backfill is used. The research is expected to fill the gap in the current state of knowledge included in the provisions of standards.

4

Evaluation of flow resistance increase due to fouling in cooling channels: a case study for rapid injection molding

38%

Przybyliński T. , Tomaszewski A. , Krzemianowski Z. , Kwidziński R. , Rolka P. , Sapeta G. , Socha R. P.

Acta Mechanica et Automatica

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2024

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tom Vol. 18, no. 4

139--150

EN

After certain time of operation, the cross-section of cooling channels in injection molds may decrease due to fouling, i.e. the formation and growth of a layer of sediment on the walls of the channels. This phenomenon can decrease heat transfer or ultimately completely block the flow of coolant in the channel. The build-up of the sediment layer increases the temperature of the mold, which may consequently reduce the quality of the plastic products. In the paper, the pressure drop in a typical cooling channel of an injection mold is investigated, as well as the effect of the sediment layer on the coolant flow in an example channel with a diameter of 10 mm. A novelty is the developed analytical model that allows determining the pressure drop in the case when two perpendicular channels do not intersect centrally due to manufacturing inaccuracies that often happen when drilling long channels in hard materials. The proposed hydraulic model allows for calculation of the coolant pressure drop in real injection molds and can be an alternative to time-consuming CFD simulations. The presented results of measurements and the hydraulic model calculations show that the thickness of the sediment layer in the tested channel of the actual injection mold can be up to 1.7 mm. The hydraulic model proposed in this work allows for the estimation of the thickness of the sediment layer and the identification of places of local increase in the coolant velocity, where self-cleaning of the channels in injection molds may take place.