发布求助
文献互助 智能选刊 最新文献

Acta Polytechnica最新文献

筛选
英文 中文
Linearisation of a second-order nonlinear ordinary differential equation 二阶非线性常微分方程的线性化
IF 0.8
Acta Polytechnica Pub Date : 2023-03-02 DOI: 10.14311/ap.2023.63.0019
A. Maharaj, P. Leach, M. Govender, David P. Day
{"title":"Linearisation of a second-order nonlinear ordinary differential equation","authors":"A. Maharaj, P. Leach, M. Govender, David P. Day","doi":"10.14311/ap.2023.63.0019","DOIUrl":"https://doi.org/10.14311/ap.2023.63.0019","url":null,"abstract":"We analyse nonlinear second-order differential equations in terms of algebraic properties by reducing a nonlinear partial differential equation to a nonlinear second-order ordinary differential equation via the point symmetry f(v)∂v. The eight Lie point symmetries obtained for the second-order ordinary differential equation is of maximal number and a representation of the sl(3,R) algebra. We extend this analysis to a more general nonlinear second-order differential equation and we obtain similar interesting algebraic properties.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43246549","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Induction motor mechanical defect diagnosis using DWT under different loading levels 不同载荷水平下感应电机机械缺陷的小波变换诊断
IF 0.8
Acta Polytechnica Pub Date : 2023-03-02 DOI: 10.14311/ap.2023.63.0001
A. Bouzida, R. Abdelli, Aimad Boudouda
{"title":"Induction motor mechanical defect diagnosis using DWT under different loading levels","authors":"A. Bouzida, R. Abdelli, Aimad Boudouda","doi":"10.14311/ap.2023.63.0001","DOIUrl":"https://doi.org/10.14311/ap.2023.63.0001","url":null,"abstract":"The information extraction capability of the widely used signal processing tool, FFT for diagnosing induction machines, is commonly used at a constant load or at different levels. The loading level is a major influencing factor in the diagnostic process when the coupled load and the machine come with natural mechanical imperfections, and at a low load, the mechanical faults harmonics are strongly influenced. In this context, the main objective of this work is the detection of the mechanical faults and the study of the effect of the loading level on the induction motor diagnostic process. We have employed a diagnosis method based on discrete wavelet transform (DWT) for the multi-level decomposition of stator current and extracting the fault’s energy stored over a wide frequency range. The proposed approach has been experimentally tested on a faulty machine with dynamic eccentricity and a shaft misalignment for three loading levels. The proposed method is experimentally tested and the results are provided to verify the effectiveness of the fault detection and to point out the importance of the coupled load.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47811461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Self-interference cancellation in underwater acoustic communications systems using orthogonal pilots in IBFD 基于IBFD正交导频的水声通信系统自干扰消除
IF 0.8
Acta Polytechnica Pub Date : 2023-03-02 DOI: 10.14311/ap.2023.63.0023
Hala A. Naman, A. E. Abdelkareem
{"title":"Self-interference cancellation in underwater acoustic communications systems using orthogonal pilots in IBFD","authors":"Hala A. Naman, A. E. Abdelkareem","doi":"10.14311/ap.2023.63.0023","DOIUrl":"https://doi.org/10.14311/ap.2023.63.0023","url":null,"abstract":"This paper proposes a Self-interference (SI) cancellation system model of Underwater acoustic (UWA) communication for in-band full-duplex (IBFD) technology. The SI channel is separated from the Far channel by exploiting a concurrently orthogonal pilot channel estimation technique using two orthogonal frequency-division multiplexing (OFDM) blocks to establish orthogonality between them based on a unitary matrix. Compared to the half-duplex channel estimator, the mean squared error (MSE) and the bit error rate (BER) provided strong evidence for the efficiency of the proposed SI cancellation. Since full-duplex systems are more efficient than half-duplex ones, the proposed approach might be seen as a viable option for them. The proposed method proved effective when used with a fixed full-duplex (FD) position and FD shifting of up to 4°. Different channel lengths and distances are adopted to evaluate the proposed method. Initial findings indicate that MSE for the SI channel minimum mean-square error (MMSE) estimator at 20 dB is 0.118 · 10−3, for fixed FD. In addition, this paper presents a geometry channel model for the Far channel in the IBFD underwater communication system that describes the propagation delay of the multipath reflection. The simulation results for the multipath propagation delay spread are similar to the traditional results, with the delay spread of the suggested model reaching (79 ms), which is close to the Bellhop simulator result (78 ms).","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41950434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Heat transfer characteristics of double pipe heat exchanger having externally enhanced inner pipe 内管外增强双管换热器的传热特性
IF 0.8
Acta Polytechnica Pub Date : 2023-03-02 DOI: 10.14311/ap.2023.63.0065
Balasubramanian Vijayaragavan, S. P. Asok, Chandrasekar Ramalekshmi Shakthi Ganesh
{"title":"Heat transfer characteristics of double pipe heat exchanger having externally enhanced inner pipe","authors":"Balasubramanian Vijayaragavan, S. P. Asok, Chandrasekar Ramalekshmi Shakthi Ganesh","doi":"10.14311/ap.2023.63.0065","DOIUrl":"https://doi.org/10.14311/ap.2023.63.0065","url":null,"abstract":"An investigation on enhancement of heat transfer is carried out for a double pipe heat exchanger in which the outer wall of the inner pipe is provided with circumferential labyrinth passages. Rectangular and triangular cavities with fixed labyrinth tooth thickness, height, and pitch are considered and the effect of added labyrinth structures on the heat transfer characteristics is discussed. A two-dimensional steady numerical simulation is carried out using ANSYS-FLUENT software. The flow Reynolds number equals to 20 000 and 43 000 for the hot and cold fluids, respectively, while other fluid properties are constant. From the numerical analysis carried out in this work, it is identified that the added labyrinth passages in the heat exchange surface improve the heat transfer rate and can reduce the length of the heat exchanger. Numerical predictions agree well with the results obtained from the experiment conducted.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48794071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Femtosecond laser processing of advanced technical materials 飞秒激光加工先进技术材料
IF 0.8
Acta Polytechnica Pub Date : 2023-03-02 DOI: 10.14311/ap.2023.63.0036
T. Primus, M. Novák, P. Zeman, F. Holešovský
{"title":"Femtosecond laser processing of advanced technical materials","authors":"T. Primus, M. Novák, P. Zeman, F. Holešovský","doi":"10.14311/ap.2023.63.0036","DOIUrl":"https://doi.org/10.14311/ap.2023.63.0036","url":null,"abstract":"Ultra-short pulsed laser ablation may be used for high-precision machining with very low thermal influence on the processed materials. Due to this reason, lasers are increasingly used for processing of advanced materials, such as titanium alloys, nickel-based alloys or steel, every year. In this study, four advanced technical materials were analysed and compared under femtosecond laser irradiation with three different wavelengths. The main laser-material interaction parameters were identified, namely the ablation threshold and removal efficiency parameters. Higher removal rates were found for Ti6Al4V alloy with all three harmonic wavelengths. To increase process productivity, a method of increasing the repetition rate and scanning speed was presented. With the maximum repetition rate, the productivity increased five-fold with a similar removed depth and surface quality. Finally, the suitability of the identified parameters with regard to quality and productivity was demonstrated for fabrication of two complex structures – honeycomb and dot – which has the potential to improve friction properties of advanced materials.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46726294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Comparative study of state space averaging and PWM with extra element theorem techniques for complex cascaded DC-DC Buck converter 复杂级联DC-DC降压变换器状态空间平均与带额外元素定理的PWM技术的比较研究
IF 0.8
Acta Polytechnica Pub Date : 2023-03-02 DOI: 10.14311/ap.2023.63.0050
Sangeeta H. Shete, P. Joshi
{"title":"Comparative study of state space averaging and PWM with extra element theorem techniques for complex cascaded DC-DC Buck converter","authors":"Sangeeta H. Shete, P. Joshi","doi":"10.14311/ap.2023.63.0050","DOIUrl":"https://doi.org/10.14311/ap.2023.63.0050","url":null,"abstract":"Until now, most commonly used state space averaging and PWM techniques have been applied to different converter topologies and their advantages and disadvantages were stated. However, the superiority of an analytical technique was not justified based on a parametric comparison of these techniques for the same converter topology. Hence, in this paper, first time a comparative evaluation of two commonly used modelling techniques for fourth order converter is presented. The first approach makes use of a state-space averaging of the converter and is based on analytical manipulations using different state representations of the converter. The second approach is based on PWM switch modelling with an extra element theorem and consists of topological manipulations. The two modelling techniques are applied to the same complex cascaded DC-DC Buck converter and a transfer function is obtained. These techniques are compared for different features and the study concludes that state space modelling technique is systematic and less complicated than PWM switch modelling with an extra element theorem for a higher order converter.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45252224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Theoretical analysis of the influence of the chevron inclination angle on the thermal performance of a gasket plate heat exchanger 人字形倾角对垫板式换热器热性能影响的理论分析
IF 0.8
Acta Polytechnica Pub Date : 2022-12-31 DOI: 10.14311/ap.2022.62.0627
E. Nogueira
{"title":"Theoretical analysis of the influence of the chevron inclination angle on the thermal performance of a gasket plate heat exchanger","authors":"E. Nogueira","doi":"10.14311/ap.2022.62.0627","DOIUrl":"https://doi.org/10.14311/ap.2022.62.0627","url":null,"abstract":"Different models are applied for an experimental and theoretical determination of the thermal and hydraulic performance of gasket plate heat exchanger. One of the relevant aspects of recent works is the influence of the chevron inclination angle between the heat exchanger plates. This work aims to analyse the impact of the chevron inclination angle by applying an effective concept in a sunflower vegetable oil cooler. Comparisons are made with theoretical and experimental results from the literature for works that consider angles of inclination equal to 30◦, 45◦, and 60◦. An analysis model that does not consider the inclination angle as an explicit parameter is included for comparison purposes. In addition to the angle of inclination, two other parameters, the mass flow rate of the cold fluid (water) and the number of plates, are considered crucial for determining and analysing the results. Nusselt number, global heat transfer coefficient, effectiveness, heat transfer rate, and outlet temperatures for hot and cold fluids are presented in a graphical format. The results point to the need to improve models applied to gasket plate heat exchangers concerning the influence of the inclination angle since there are significant differences between those obtained and analysed in this work.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2022-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48667803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Stone Topography – Useful Tool in Monuments Restoration Process 石头地形——古迹修复过程中的有用工具
IF 0.8
Acta Polytechnica Pub Date : 2022-12-31 DOI: 10.14311/ap.2022.62.0589
Michal Cihla, K. Kovářová, Richard Malát, J. Valach
{"title":"Stone Topography – Useful Tool in Monuments Restoration Process","authors":"Michal Cihla, K. Kovářová, Richard Malát, J. Valach","doi":"10.14311/ap.2022.62.0589","DOIUrl":"https://doi.org/10.14311/ap.2022.62.0589","url":null,"abstract":"The surface of building stone on historic buildings often bears the original traces of craftsmanship processing. These are an integral part of the visual appearance of the monument and thus its value, which needs to be protected. For studying and identifying traces and subsequent reconstruction of stonemason's tools, we use the methods of traceology and mechanoscopy. Using modern imaging techniques, we can identify the stonemason's tool used, reconstruct the shape of its blade, and determine how it was used. The obtained results can be used in the process of monument care, especially in the process of preparation and implementation of restoration interventions on the objects, but they are also useful for completing the historical context of the monument. Our research is focused on the systematic study of the surface topography of the stone monuments in Prague. The obtained results were systematically divided according to individual historical period. As a model example of the use of the above-mentioned methods and approaches, we present the topography of stone elements and the development of stonemason's craft in Gothic Prague. The development of the stonemason's craft within one city in a given period can be documented on selected examples arranged chronologically in succession.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2022-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46172735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Study of surface roughness with MHD and couple stress fluid on porous curved annular plates 多孔弯曲环形板表面粗糙度的MHD和耦合应力流体研究
IF 0.8
Acta Polytechnica Pub Date : 2022-12-31 DOI: 10.14311/ap.2022.62.0574
Salma Alla Baksh, Hanumagowda Bannihalli Naganagowda
{"title":"Study of surface roughness with MHD and couple stress fluid on porous curved annular plates","authors":"Salma Alla Baksh, Hanumagowda Bannihalli Naganagowda","doi":"10.14311/ap.2022.62.0574","DOIUrl":"https://doi.org/10.14311/ap.2022.62.0574","url":null,"abstract":"The purpose of this article is to examine the effect of surface roughness on porous curved annular plates lubricated with couple stress fluid in the presence of magnetic field. The MHD-Stochastic Reynolds equation is derived using Christensen’s stochastic model and applied to predict the squeeze film characteristics of porous curved annular plates. The expressions for squeeze film pressure, load-carrying capacity, and squeeze film time are obtained analytically, the results are discussed for various values of operating parameters, and are plotted graphically. It is found that the squeeze film characteristics of porous curved annular plates are improved using a non-Newtonian fluid in the presence of an external magnetic field. The effect of roughness parameter is to increase (decrease) the squeeze film attributes for azimuthal (radial) roughness configuration as compared to the smooth case. Furthermore, the effect of permeability parameter is to decrease the pressure, load-carrying capacity, and squeeze-film time as compared to the non-porous case.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2022-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48846018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 1
Application of strut-and-tie models for assessing RC half-joints not complying with current code specifications 杆系模型在评估不符合现行规范的钢筋混凝土半节点中的应用
IF 0.8
Acta Polytechnica Pub Date : 2022-12-31 DOI: 10.14311/ap.2022.62.0607
G. Kotsovou, E. Vougioukas, D. Cotsovos
{"title":"Application of strut-and-tie models for assessing RC half-joints not complying with current code specifications","authors":"G. Kotsovou, E. Vougioukas, D. Cotsovos","doi":"10.14311/ap.2022.62.0607","DOIUrl":"https://doi.org/10.14311/ap.2022.62.0607","url":null,"abstract":"The work described is concerned with an investigation of the effectiveness of the use of strut-and-tie models for the structural assessment of half joints. Such elements form a part of many existing bridges which, although not complying with current code specifications, have not as yet displayed any significant signs of distress in spite of the increase in traffic volume and loads over the years. The work is based on a comparative study of the predicted and experimentally established values of load-carrying capacity and location and causes of failure of half-jointed beams with reinforcement layouts that replicate those found in structures designed in accordance with previous code specifications. The results obtained show significant shortcomings of the assessment method as this is found not only to underestimate load-carrying capacity by a margin ranging between 40 % and 65 %, but also to often fail to identify the location and causes of failure. Therefore, there is a need for an alternative assessment method that will be based on concepts capable of both providing a realistic description of structural-concrete behaviour and identifying the causes of failure leading to the loss of load-carrying capacity.","PeriodicalId":45804,"journal":{"name":"Acta Polytechnica","volume":" ","pages":""},"PeriodicalIF":0.8,"publicationDate":"2022-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49042845","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
首页 上一页 下一页 尾页
0
×
引用
GB/T 7714-2015
复制
MLA
复制
APA
复制
导出至
BibTeX EndNote RefMan NoteFirst NoteExpress
×
提示
您的信息不完整，为了账户安全，请先补充。
现在去补充
×
提示
您因"违规操作"
具体请查看互助需知
我知道了
×
提示
现在去查看 取消
×
提示
确定
请完成安全验证×
相关产品
×
本文献相关产品
联系我们：info@booksci.cn Book学术提供免费学术资源搜索服务，方便国内外学者检索中英文文献。致力于提供最便捷和优质的服务体验。 Copyright © 2023 布克学术 All rights reserved.
京ICP备2023020795号-1
ghs 京公网安备 11010802042870号
Book学术文献互助
Book学术文献互助群
群 号：604180095
Book学术官方微信