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Decision-making in major investment projects with a life cycle cost: improvement with sensitivity analysis and sustainability assessment

Wieke Stefan

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2024

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Vol. 33, No. 3

227--242

EN

This study focuses on compressor station investments in Germany’s natural gas infrastructure, offering insights applicable to machinery, energy, and maintenance cost-driven decisions. A life cycle cost (LCC) analysis can guide investment choices; however, uncertainties in input data and future developments pose risks. The LCC-based studies encounter questions impacting their results and optimal selections. These uncertainties may lead to misallocations, emphasizing the need for careful consideration of investment decisions to avoid potential consequences and efficiently allocate limited funds. Various measures are available to mitigate the uncertainties and risks in LCC analyses. Recognized measures are deterministic and probabilistic. Seven case studies on investments in the natural gas infrastructure in Germany were analyzed in this context. In addition to the executed case studies, a case study from a scientific journal (published in 2001) was included in the analysis. The case studies were conducted by transmission system operators from 2005–2015, and a retrospective view made it possible to recognize whether the best options (due to the LCC analysis) were identified. Simulations were conducted with generated models using real historical input data such as energy costs. The re-calculation of the net present value or better discounted cumulated expenditure with real input data shows that the LCC analysis results are significantly dependent on the reliability of the input data and the prediction of their development. Therefore, validating the results using appropriate measures is mandatory. This study illustrates how sensitivity analysis can be used as a deterministic method to evaluate the LCC analysis results. A company’s success is increasingly determined by its sustainability. A pure LCC analysis is insufficient, so social, ecological, and economic sustainability assessments must be conducted. This study demonstrates the effectiveness of the weighted scoring method for sustainability assessments. Although this study relates to LCC in Germany’s natural gas infrastructure, the suggested process can be adopted for other investment projects comprising capital and operational expenditures.

2

Stress assessment of a steel bullet LPG tank under differential settlement based on geodetic measurements and sensitivity analysis

Ferenc Tomasz, Gierasimczyk Rafał, Mikulski Tomasz

Polish Maritime Research

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2024

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nr 4

122--130

EN

This paper presents an analysis of a steel bullet LPG tank in operation at a base in Poland. The structure was set on a sand-gravel pillow and rigid concrete slab, and its settlement was periodically measured at five measuring points along the structure. After a few years, differential settlement was observed. Based on geodetic data, we attempt to assess the current stress level in the structure. The proposed methodology uses a sensitivity analysis apparatus. A numerical model of the structure and sand-gravel pillow is analysed using the finite element method, and the impact of variation in the stiffness of the sand-gravel pillow on the vertical displacement of the tank is determined. The algorithm involves six iterations of calculations, and after each iteration, the stiffness modified sand-gravel pillow is determined. After the sixth iteration, the vertical displacement in the FEM model is found to be similar to the measured values in the real structure. The results obtained after the last iteration are used to assess the stress state in the bullet tank’s shell structure.

3

Chattering analysis of an electro-hydraulic backstepping velocity controller

Eny Gérémino Ella, Eya Honorine Angue Mintsa, Nzue Rolland Michel Assoumou, Senouveau Nzamba

International Journal of Applied Mechanics and Engineering

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2024

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Vol. 29, no. 1

36--53

EN

This paper focuses on the chattering analysis in a backstepping controller used to drive an electro-hydraulic servo system. The chattering phenomenon, well known in sliding mode control, strongly reduces operating performance while causing premature wear of the system. Four cases are studied to highlight the factors influencing the chattering in the backstepping control. In the first case, the effect of the unmodeled fast servo valve dynamics is analysed by comparing a reduced-order backstepping controller with a full-order controller. The second case analyses the sensitivity to the tuning gains of the backstepping controller. The third case emphasises the influence of the parameter of sign function approximation. The last case analyses the sensitivity of the parameter of the time derivative of the virtual controls. The simulation results in the Matlab/Simulink show that the chattering is mitigated by an appropriate gains tuning but above all an appropriate calculation of the derivatives of the virtual controls, particularly for high-order systems.

4

Weight Impact on Comparative Evaluation of Topographic Data

Borkowska Sylwia, Bielecka Elżbieta, Pokonieczny Krzysztof

Geomatics and Environmental Engineering

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2024

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Vol. 18, no. 4

97--116

EN

The paper addresses the problem of weighting in an analysis that supports the selection of a categorical data set according to user needs. Using the Relative Change (RC) of the Compound Correspondence Index (CCI), it is shown that weights have a significant impact on user choice – reaching extreme values in both urbanized and forested areas. Decreasing the weights from 0.25 to 0.17 in forested and built-up areas resulted in the maximum variations that were seen in the hot spot maps, with cold areas generally corresponding to builtup regions and hot areas to forested areas. The analysis covers seven counties that are located in different regions of Poland: Pomerania, Podlasie, Mazovia, Greater Poland and the Beskidy Mountains.

5

Analiza opłacalności wykorzystania odpadów komunalnych w procesie wytwarzania ciepła systemowego. Studium przypadku dla Pruszkowa

Mirosz Liliana, Mróz Pelagia

Gaz, Woda i Technika Sanitarna

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2024

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Nr 4

21--27

PL

Temat artykułu wynika z potrzeby zwiększania zdolności przerobowej instalacji termicznego przekształcania odpadów komunalnych (ITPOK), w związku ze wzrostem ilości tego rodzaju odpadów oraz koniecznością odchodzenia od wykorzystania w ciepłownictwie paliw kopalnych. Zaproponowano studium przypadku takiej instalacji. Wybrano miasto Pruszków, dla którego instalacja miałaby pokrywać jego podstawę ciepłowniczą. Przedstawiono analizę ekonomiczną takiej inwestycji. Wyznaczono niezbędne parametry wejściowe, tj. nominalna moc cieplna instalacji, wymagany strumień odpadów o odpowiednich właściwościach, strumień dostępny z okolic miasta (z uwzględnieniem istniejących instalacji termicznego przekształcania odpadów komunalnych), ilość substancji wprowadzanych do powietrza wraz ze spalinami. Zdefiniowane dane posłużyły do obliczenia opłacalności ITPOK na podstawie przychodów ze sprzedaży ciepła i opłaty bramowej za przyjęcie odpadów, przy uwzględnieniu nakładów inwestycyjnych i kosztów eksploatacyjnych. W obliczeniach uwzględniono przystąpienie ITPOK do unijnego systemu handlu uprawnieniami do emisji (EU ETS, z ang. EU Emissions Trading System), przy czym wykonano je dla dwóch wariantów. Jeden z nich nie powoduje zmiany cen ciepła ani opłaty bramowej w stosunku do sytuacji, gdy ITPOK nie uczestniczy w EU ETS. Drugi, koszt uczestnictwa związany z EU ETS przerzuca w 50% na odbiorców ciepła i w 50% na dostawców odpadów. Wskaźnik IRR dla pierwszego wariantu wyniósł 2%, natomiast dla drugiego 6%. Należy jednak podkreślić, że w obliczeniach zawyżono nakład inwestycyjny, ze względu na brak aktualnych zakończonych przetargów na instalacje o podobnej przepustowości do analizowanej w artykule. Są to także wartości nieuwzględniające preferencyjnego finansowania z zewnątrz w formie bezzwrotnych dotacji. Dla uzyskanego większego wyniku (6%) przygotowano analizę wrażliwości IRR. Czynnikiem najmocniej wpływającym na IRR jest nakład inwestycyjny, następnie cena ciepła i opłata bramowa. Zmiany powyższych parametrów w zakresie ± 20% powodują zmiany IRR w zakresie od ok. 4 do ok. 9%. W podsumowaniu wskazano, jak można podnieść wartość IRR, a także dlaczego inwestycja w ITPOK jest korzystna dla lokalnej społeczności i środowiska.

EN

The topic of the article results from the need to increase the capacity of municipal waste-to-energy (WTE) plants due to the growth of waste generation and the necessity to move away from the use of fossil fuels in district heating. The case study of such a plant was proposed. The city of Pruszków was selected for which the installation would cover its district heating base load. An economic analysis of such an investment was presented. The necessary input parameters were determined, i.e. the nominal thermal power of the installation, the required waste stream with appropriate properties, the stream available from the area around the city (taking into account existing thermal waste treatment installation), and the amount of substances released into the air with exhaust gases. Defined data were used to calculate the economical profitability of WTE plant taking into account revenues from heat sale and the gate fee for waste acceptance, as well as CAPEX and OPEX. The calculations took into account WTE plant's accession to the EU emissions trading system (EU ETS), and were performed for two variants. One of them does not change heat prices or gate fees compared to the situation when WTE plant does not participate in the EU ETS. The second one transfers the cost of participation related to the EU ETS in 50% to heat consumers and 50% to waste suppliers. The IRR for the first variant was 2%, while for the second one it was 6%. It should be emphasized, however, that the calculations overestimated CAPEX due to the lack of current completed tenders for installations with similar capacity to the one analyzed in the article. These values also do not take into account preferred financing in form of non-refundable grants. A sensitivity analysis for IRR was prepared for the obtained higher resułt (6%). The factor that has the greatest impact on IRR is CAPEX, followed by the heat price and the gate fee. Changes in the above parameters in the range of ± 20% cause changes IRR ranging from approx. 4 to approx. 9%. The summary indicates how the IRR value can be increased, as well as why the investment in WTE plant is beneficial for the local community and the environment

6

Optimized design of truck cab lightweighting based on sensitivity hierarchical comparative analysis method

Wang Yiqun, Li Di, Wu Dongze, Li Yukuan, Wang Tao, Wang Xiaokun, Liu Shaoxun

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2024

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Vol. 72, nr 5

art. no. e151043

EN

The relative sensitivity analysis method is important in the field of vehicle lightweighting. Combined with optimization algorithms, experiment of design (DOE), etc., it can efficiently explore the impact of unit mass of components on performance and search for components with lightweight space. However, this method does not take into account the size level of each component and the order of magnitude differences in sensitivity under different operating conditions. Therefore, this paper proposed a sensitivity hierarchical comparative analysis method, on the basis of which the thicknesses of 10 groups of components were screened out as design variables by considering the lightweighting effect,cab performance, and passive safety. Through the optimal Latin hypercube method, 70 groups of sample points were extracted to carry out the experimental design, the Kriging surrogate model was established and the NSGA-II genetic algorithm was used to obtain the Pareto optimal solution set, and ultimately a weight reduction of 13.13 kg was realized under the premise that the entire performance of the cab improved.

7

Experimental investigation on microstructure evolution and creep behaviour of red sandstone at elevated temperature

Yang Puchao, Wen Jun, Wenan Xie, Dai Gang, Yang Xiuting

Archives of Mining Sciences

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2024

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Vol. 69, no. 3

461--483

EN

The changes in the physical and mechanical properties of rocks under high temperatures can impact the construction safety and stability of underground geotechnical engineering. This study focuses on red sandstone treated at different temperatures, employing nuclear magnetic resonance (NMR) spectroscopy to reveal alterations in the internal pore distribution due to elevated temperatures. The results indicate that high temperatures lead to the formation of micro- to meso scale pores and macro-scale pores and cracks. Additionally, high temperatures cause a significant reduction in load-bearing capacity, accompanied by changes in creep behaviour, including a shortened steady-state creep time and an increased strain threshold for rock failure. To more accurately describe the creep behaviour of red sandstone under different temperatures and stress conditions, a novel non-constant creep model is proposed, combining a generalised Kelvin body and a fractional viscoplastic body to demonstrate its versatility in elastic, viscoelastic, and viscoplastic deformation. The model parameters are determined through numerical optimisation, and the model’s reliability is confirmed by comparing theoretical curves with experimental data. Sensitivity analysis highlights the critical roles of parameters such as shear modulus, viscosity coefficient, fractional order, and characteristic parameters in capturing various creep patterns, emphasising the model’s wide applicability. This research provides profound insights into the physical and mechanical responses of red sandstone to high temperatures and offers valuable information for engineering and geological applications in relevant fields.

8

Performance analysis on an integrated three-area thermal AGC system with various wind velocities considering HCSA-optimized PI-TIDN Controller

Babu Naladi Ram, Chiranjeevi Tirumalasetty, Devarapalli Ramesh, García Márquez Fausto Pedro

Archives of Control Sciences

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2024

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Vol. 34, No. 4

755--776

EN

This article investigates the impact of a high-voltage direct-current (HVDC) link and a wind turbine system (WTS) on the dynamics of a three-area thermal automatic generation control (AGC) system. A novel controller, the cascade of proportional-integral (PI) and tilt-integralderivative (TID) with filter coefficient (N) (PI-TIDN) controller is projected. The WTS units are subjected to various wind velocity scenarios, including fixed and random wind velocities. The controller parameters are concurrently enhanced using the hybrid crow search algorithm (HCSA). The system dynamics corresponding to the PI-TIDN controller are superior to those of PIDN and TIDN controllers. Additionally, studies with different wind velocities demonstrate that responses with fixed wind velocities are better than those with random wind velocities. Moreover, integrating WTS units with the thermal system improves dynamics compared to the thermal system alone. It is also apparent that the parallel AC-HVDC system enhances dynamics. Furthermore, sensitivity analysis exposes that the PI-TIDN controller values at nominal settings are vigorous and do not require retuning.

9

The system reliability of steel trusses with correlated variables

Kubicka Katarzyna, Radoń Urszula

Archives of Civil Engineering

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2024

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Vol. 70, nr 2

163--178

EN

The paper focuses on the system reliability of steel trusses with correlated variables. The correlation between bearing capacities of bars was considered. Two static truss schemes were considered. Nodal forces were the only load. The Finite Element Method analysis was conducted in Robot Structural Analysis program. To conduct system reliability analysis it is essential to find cut-sets, it was realized by stiffness matrix spectral analysis. Then reliability analysis was performed in Sysrel module of Strurel computing environment. First Order Reliability Method was used as the base, Subset Simulation method was used to check the correctness of the results. The sensitivity analysis of reliability index enabled the authors to draw conclusions, which variables have the greatest influence on the reliability of the structure. The effects of actions and bearing capacities were assumed to be the only random variables and that the excessing the bearing capacities of bars is the only way the structure can get into failure area.

PL

W artykule przedstawiono analizę wpływu korelacji między zmiennymi losowymi na uzyskiwany wskaźnik niezawodności, z wykorzystaniem analizy systemowej. W pracy uwzględniono kratownice stalowe o dwóch różnych geometriach, w obu przypadkach były to konstrukcje statycznie niewyznaczalne. Założono, że jedynym obciążeniem działającym na kratownice są siły skupione, zaczepione w węzłach pasa dolnego. W pierwszym kroku przeprowadzono obliczenia statyczno-wytrzymałościowe w programie Robot Structural Analysis, uzyskując wartości nośności oraz efektu oddziaływań dla poszczególnych prętów kratownic. Jako zmienne losowe przyjęto efekt oddziaływań (E) oraz nośności poszczególnych elementów (N), o współczynnikach zmienności odpowiednio 6% i 10%. Założono, że wszystkie zmienne mają rozkład normalny. Jako kryterium zniszczenia elementu przyjęto przekroczenie nośności w prętach. Po oszacowaniu niezawodności poszczególnych elementów określono wszystkie możliwe schematy zniszczenia (cut-sets). W tym celu wykorzystano analizę spektralną macierzy sztywności konstrukcji, z wykorzystaniem informacji o niezawodnościach elementów.

10

Extended Evaluation of the Impact of Rainfall, Sewer Network and Land Use Retention on Drainage System Performance in a Multi-Criteria Approach – Modeling, Sensitivity Analysis

Szeląg Bartosz, Fatone Francesco, Kiczko Adam, Majerek Dariusz, Białek Anita, Łagód Grzegorz, Piotrowicz Adam, Dąbek Lidia

Advances in Science and Technology. Research Journal

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2024

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Vol. 18, no 6

291--303

EN

An extensive methodology for analyzing the impact of catchment and sewer network retention on drainage system operating conditions during hydraulic overloading is presented. To evaluate the performance of the sewer system and identify the need for repair actions, logistic regression models were developed to predict the unit flooding volume and manhole overflowing. An advanced sensitivity analysis was performed to determine the key parameters (retention and roughness of impervious and pervious areas as well as sewer channel retention) conditioning the reduction of uncertainty in the simulation results and ensuring the assumed hydraulic effect. A coefficient expressing the quotient of the duration of rainfall conditioning the exceedance of the limits of the unit flooding volume (13 m3·ha−1) as well as the degree of overflowed manholes (0.32) was determined, allowing the determination of the key performance criterion of the sewer network to take corrective action depending on field and channel retention. It was shown that the catchment area retention had the key influence on the conditions of sewer operation and the probability of remedial work. Increasing the rainfall duration led to a decrease in sensitivity coefficients with respect to the identified parameters of the SWMM model, which is important when selecting rainfall events for the calibration and validation sets. The usefulness of the developed methodology was demonstrated at the stage of building mechanistic models, which is of significance when planning field studies.

11

A new geometric approach to multiobjective linear programming problems

Kaci Mustapha, Radjef Sonia

Mathematica Applicanda

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2023

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Vol. 51, no. 1

3--12

EN

This paper is a follow-up to a previous work where we developed a new geometric approach to sensitivity analysis. In this paper, we present a simple method to determine whether a given multiobjective linear programming problem (MOLPP) has an ideal solution (i.e. all of the objective functions are optimized simultaneously) without having to calculate the optimal value of each objective function. First, we divide the space of linear forms into a finite number of sets based on a fixed convex polygonal subset of R2 using an equivalency relationship. All the elements from a given equivalency class have the same optimal solution. Next, we characterize the equivalence classes of the quotient set using a geometric approach to sensitivity analysis. Finally, a numerical example is given to illustrate the method.

PL

W tym artykule przedstawiamy nową metodę rozwiązywania problemów programowania liniowego z wieloma celami (MOLPP), która eliminuje potrzebę obliczania optymalnej wartości każdej funkcji celu. Metoda ta jest kontynuacją naszych wcześniejszych prac dotyczących analizy wrażliwości, gdzie opracowaliśmy nowe podejście geometryczne. Pierwszym krokiem naszego podejścia jest podział przestrzeni form liniowych na skończoną liczbę zbiorów opartych na stałym wypukłym podzbiorze wielokąta R2. Dokonujemy tego za pomocą relacji równoważności, która zapewnia, że wszystkie elementy z danej klasy równoważności mają takie same rozwiązanie optymalne. Następnie charakteryzujemy klasy równoważności zbioru ilorazowego za pomocą podejścia geometrycznego do analizy wrażliwości. Ten krok jest kluczowy w identyfikacji rozwiązania idealnego dla MOLPP. Korzystając z tego podejścia, możemy określić, czy dana MOLPP ma rozwiązanie idealne, bez konieczności obliczania optymalnej wartości każdej funkcji celu. Jest to znacząca poprawa w stosunku do istniejących metod, ponieważ znacznie zmniejsza złożoność obliczeniową i czas wymagany do rozwiązania MOLPP. Aby zilustrować naszą metodę, przedstawiamy numeryczny przykład, który dowodzi jej skuteczności. Nasza metoda jest prosta, ale potężna i może być łatwo zastosowana do szerokiego zakresu MOLPP. Niniejsza praca przyczynia się do dziedziny optymalizacji poprzez przedstawienie nowego podejścia do rozwiązywania MOLPP, które jest wydajne, skuteczne i łatwe do zaimplementowania.

12

The Method for Assessing the Impact of Variable Coal Demand on the Efficiency of Mine Operations

Fuksa Dariusz

Inżynieria Mineralna

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2023

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no. 1

267--273

EN

The method presented in the article is based on Monte Carlo simulation and involves studying the impact of random demand fluctuations on the efficiency of mines and mine groups (companies). For random demand fluctuations, a normal distribution is assumed, and the analysis variants present-ed include: • Adopting the mean and variance values based on retrospective data, • Considering the most probable forecast error resulting from predictive formulas, • Taking into account correlated changes in demand. The results obtained are presented in the form of histograms of the degree of operational lever-age. These histograms allow for predicting how the degree of operational leverage of mines will develop, as well as estimating the direction and probability of these changes. The developed and veri-fied sensitivity analysis using real examples constitutes a useful element in rationalizing decision-making processes.

PL

Zaprezentowana w artykule metoda oparta jest na symulacji Monte Carlo i obejmuje badanie wpływu wahań losowych zapotrzebowania na efektywność kopalń oraz ich grup (spółek). Dla losowych wahań zapotrzebowania przyjęto rozkład normalny, a przedstawione warianty analizy uwzględniają: • przyjęcie wartości oczekiwanej i dyspersji według danych retrospektywnych; • przyjęcie najbardziej prawdopodobnego błędu prognozy wynikającego z formuł predykcyjnych; • uwzględnienie skorelowanych zmian zapotrzebowania. Uzyskane wyniki przedstawiono w postaci histogramów stopnia dźwigni operacyjnej. Pozwalają one przewidywać, jak będzie kształtował się stopień dźwigni operacyjnej kopalń, jak również umożliwia oszacować, w którym kierunku zmiany te będą postępować i z jakim prawdopodobieństwem. Opracowana i zweryfikowana na realnych przykładach analiza wrażliwości stanowi przydatny element racjonalizacji procesów decyzyjnych.

13

Choice of the p-norm for high level classification features pruning in modern convolutional neural networks with local sensitivity analysis

Jeczmionek Ernest, Kowalski Piotr A.

International Journal of Applied Mathematics and Computer Science

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2023

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Vol. 33, no. 4

663--672

EN

Transfer learning has surfaced as a compelling technique in machine learning, enabling the transfer of knowledge across networks. This study evaluates the efficacy of ImageNet pretrained state-of-the-art networks, including DenseNet, ResNet, and VGG, in implementing transfer learning for prepruned models on compact datasets, such as FashionMNIST, CIFAR10, and CIFAR100. The primary objective is to reduce the number of neurons while preserving high-level features. To this end, local sensitivity analysis is employed alongside p-norms and various reduction levels. This investigation discovers that VGG16, a network rich in parameters, displays resilience to high-level feature pruning. Conversely, the ResNet architectures reveal an interesting pattern of increased volatility. These observations assist in identifying an optimal combination of the norm and the reduction level for each network architecture, thus offering valuable directions for model-specific optimization. This study marks a significant advance in understanding and implementing effective pruning strategies across diverse network architectures, paving the way for future research and applications.

14

Modeling of the influence of elevated temperature on oxygen distribution in soft tissue

Jasiński Marek, Zadoń Maria

Engineering Transactions

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2023

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Vol. 71, iss. 3

287--306

EN

The purpose of the study was to analyze the combined model of bioheat transfer and oxygen distribution in tissue during exposition to the external heat impulse. The effect of temperature and thermal damage to the tissue on the values of its thermophysical parameters was taken into account. The variable value of the perfusion coefficient affects the blood velocity in the capillary and thus the distribution of the partial oxygen pressure in the tissue. Various models of the oxygen dissociation curves were also considered and a sensitivity analysis was performed for the parameters of the oxygen distribution model. In the numerical realization stage, the finite difference method and the shooting method were used.

15

Maintenance policy of degradation components based on the two-phase Wiener process

Song Minqiao, Zhang Yingzhi, Yang Fang, Wang Xiaofeng, Guo Guiming

Eksploatacja i Niezawodność

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2023

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Vol. 25, no. 4

art. no. 172537

EN

This paper proposes a condition-based maintenance policy for the two-phase Wiener degradation process components. The main contribution of this article is to provide the time distribution of degradation failures for the two-phase Wiener process degradationcomponent, as well as the modeling and solving methods for two-phase maintenance. The two-phase maintenance policy includes two-phase inspection and preventive replacement maintenance operations. The established optimization maintenance policy model aims to minimize long-term operation costs. The specific cost calculation equation and the solution method of the maintenance model are given. The feasibility of the maintenance policy model is verified using the two-phase degradation data of the Liquid Coupling Devices. The Particle swarm optimization algorithm can stably solve the described problem, and the results show that the two-phase maintenance policy can be more economical and improve components availability. After that, we also analyzed the impact of the cost parameters on the maintenance policy through sensitivity analysis.

16

On second-order derivatives of the efficient point multifunction in parametric vector optimization problems

Pham Thanh-Hung, Nguyen Thanh-Sang

Control and Cybernetics

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2023

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Vol. 52, No. 4

381--403

EN

In this paper, we establish formulae for inner and outer evaluation of the second-order contingent derivative of index nu of the efficient point multifunction in parametric vector optimization problems. The results contained in this paper extend the results of Chuong (2013a) to the second-order sensitivity analysis case. On the other hand, examples are provided for purposes of analyzing and illustrating the obtained results. Concerning the potential domain of application, the functioning of the majority of economic systems depends on a set of indicators (criteria), i.e., the substance of economic systems includes multiple criteria and only the lack of mathematical methods in solving the problems of vector optimization is an obstacle to the effective use of the respective models. Therefore, the study of vector optimization problems is necessary and has practical significance.

17

Sensitivity analysis of the dem model numerical parameters on the value of the angle of repose of lunar regolith analogs

Młynarczyk Przemysław, Kolusz Adam, Gallina Alberto

Artificial Satellites : Journal of Planetary Geodesy

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2023

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Vol. 58, Special Issue 1

188--202

EN

The discrete element method (DEM) is a numerical technique used in many areas of modern science to describe the behavior of bulk materials. Terramechanics of planetary soil analogs for in situ resource utilization activities is a research field where the use of DEM appears to be beneficial. Indeed, the close-to-physics modeling approach of DEM allows the researcher to gain much insight into the mechanical behavior of the regolith when it interacts with external devices in conditions that are hard to test experimentally. Nevertheless, DEM models are very difficult to calibrate due to their high complexity. In this paper, we study the influence of fundamental model parameters on specific simulation outcomes. We provide qualitative and quantitative assessments of the influence of DEM model parameters on the simulated repose angle and computational time. These results help to understand the behavior of the numerical model and are useful in the model calibration process.

18

Modeling and experimental investigation of a controllable rotary fluid damper

Cao X., Zhou J., Yu M., Wang Y.

Archives of Mechanics

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2023

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Vol. 75, nr 4

493--516

EN

Controllable rotary fluid damper (CRFD) is an efficient and cheap energy dissipation device, which is used to reduce the impact of vibration in mechanical systems. In this paper, the CRFD controlled by a servo motor is developed to reduce the effects of vibrations in the helicopter flight control system. The dynamic mechanical characteristic of the CRFD is experimentally investigated by the MTS machine. Due to the complex factors such as high shear thinning rate and compressibility of the damping medium, inertia of moving parts and internal friction, the CRFD studied has highly nonlinear hysteresis characteristics. The accuracy of the damper modeling is of great significance for designing effective vibration reduction methods. Therefore, a new generalized viscous–nonlinear elastic model is proposed to track the mechanical characteristics of CRFD. On the basis of parameter sensitivity analysis, the proposed generalized viscous–nonlinear elastic model is modified. According to the identification results of the modified model, the main parameters are fitted as polynomial functions of motor rotation angle. Through error analysis between analytical torques and experimental torques, it is concluded that the modified generalized viscous–nonlinear elastic model has the smallest error compared with Kwok and Maxwell models, which indicates that the proposed modified model can accurately describe the mechanical characteristics of the CRFD under different working conditions.

19

Damage behaviour and GTN parameter analysis of TC4 powder metallurgy titanium alloy during hot deformation

Liu Ronge, Wang Baoyu, Hu Shushan

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e165, 2023

EN

The damage and fracture behaviour of TC4 powder metallurgy titanium alloy were studied by isothermal uniaxial tensile tests. The results show that microcracks formed at grain boundaries, inclusions, initial pores, and adjacent pores and cracks were gathered and perpendicularly linked to the tensile direction, eventually leading to the macroscopic fracture of the material. Increasing the temperature and strain rate promotes the occurrence of dynamic recovery and subgrain merging nucleation, which leads to an increase in the fracture strain and plasticity of the material. Combined with the response surface methodology and genetic optimization algorithm, the GTN damage parameters were obtained by the reverse calibration method. The calculated flow stresses, based on the GTN damage model, are in good agreement with the experimental ones, indicating that the damage parameters can reflect the damage process of the material. In this study, the sensitivity of the damage parameters along with the influence of temperature and strain rate on them was analysed.

20

Analysis of seismic damage features of HSR CRTS III SBT simply supported bridge system

Liu Lili, Jiang Lizhong, Zhou Wangbao, Liu Xiang, Feng Yulin

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e76, 2023

EN

In order to investigate the seismic damage features of high-speed railway (HSR) China Railway Track Slab III (CRTSIII) slab ballastless track (SBT) simply supported bridge systems, a nonlinear finite element model of HSR CRTS III SBT simply supported bridge system was established. The damage mechanisms and peak and residual displacement distribution patterns of their critical components under seismic action were investigated. In addition, the sensitivity of rail irregularity to the seismic residual deformation in such critical components was analyzed. The results indicated that midspan piers and bearings are more susceptible to failure than side span piers and bearings, and fixed bearings are more prone to failure than sliding bearings. Fastener and isolation layer deformation increases sharply on both sides of the beam joint. Rail deformation exhibits a parabolic shape that is large in the middle and small at both ends. The critical components of even-span and odd-span systems have significantly different patterns of seismic deformation distribution. Rail irregularity is mainly attributable to bearing residual deformation, pier residual deformation, and fastener residual deformation successively, and the superposition of bearing residual deformation and pier residual deformation is approximately equivalent to rail deformation. Rail irregularity is most sensitive to pier deformation, followed successively by bearing and fastener deformation.