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1

Effect of Acoustic Enclosure on the Sound Transmission Loss of Multi-Layered Micro-Perforated Plates

El Kharras Brahim, Garoum Mohammed, Bybi Abdelmajid

Archives of Acoustics

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2024

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Vol. 49, nr 2

241--254

EN

This study presents an examination of the transmission properties of multilayered partitions made up of multiple micro-perforated plates (MPPs) coupled to acoustic enclosures with general impedance boundaries. Multi-layered MPPs can lower the transmission while minimizing reflection in the source and receiving enclosure. Previous research has mainly focused on the double MPPs or triple MPPs partition itself. However, it is vital to analyze the in-situ sound transmission loss of the multi-layered MPP and their efficiency in a complex vibro-acoustic environment. The case when the multilayered MPPs are coupled to a receiving enclosure or coupled to both a source and receiving enclosure is investigated. The objective is to provide an analytical method to evaluate the transmission properties of multilayered MPPs coupled to acoustic enclosures while being computationally more efficient than the finite element method (FEM). Using the modified Fourier series for the acoustic pressure, a variational form for the acoustic and structure medium yields a completely coupled vibroacoustic system. A comparison between the sound transmission loss of the double MPPs, when mounted on an impedance tube and coupled to acoustics enclosures, shows the modal effect of the enclosures. The effect of enclosure shape, impedance boundary, perforation ratio, air gap thickness on the sound transmission properties of the double MPPs structure is examined for both cases. Finally, in both situations, the performance of triple MPP structure insulation is evaluated.

2

Mechanizm podzielonej płatności w branży odpadowej

Derdak Anna

Przegląd Komunalny

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2023

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nr 10

58--59

PL

Mechanizm podzielonej płatności to szczególny sposób dokonywania płatności należności podlegających podatkowi od towarów i usług. Rozwiązanie zakłada wykorzystanie rachunku VAT prowadzonego dla posiadaczy rachunków rozliczeniowych prowadzonych przez banki. Możliwe jest także stosowanie imiennych rachunków w SKOK-ach, otwartych w związku z prowadzoną działalnością gospodarczą.

3

Sensitivity analysis of a new approach to photovoltaic parameters extraction based on the total least squares method

Mesbahi Oumaima, Tlemçani Mouhaydine, Janeiro Fernando M., Hajjaji Abdeloawahed, Kandoussi Khalid

Metrology and Measurement Systems

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2021

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Vol. 28, nr 4

751--765

EN

The degradation of photovoltaic modules and their subsequent loss of performance has a serious impact on the total energy generation potential. The lack of real-time information on the output power leads to additional losses since the panels may not be operating at their optimal point. To understand the behaviour, numerically simulate the characteristics and identify the optimal operating point of a photovoltaic cell, the parameters of an equivalent electrical circuit must first be identified. The aim of this work is to develop a total least-squares based algorithm which can identify those parameters from the output voltage and current measurements, taking into consideration the uncertainties on both measured quantities. This work presents a comparative study of the Ordinary Least Squares (OLS) and Total Least Squares (TLS) approaches to the estimation of the parameters of a photovoltaic cell.

4

Optimisation of Multistep Cavity Configuration to Extend Absorption Bandwidth of Micro Perforated Panel Absorber

Falsafi I., Ohadi A.

Archives of Acoustics

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2018

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Vol. 43, No. 2

187--195

EN

Micro perforated panel (MPP) absorber is a new form of acoustic absorbing material in comparison with porous ones. These absorbers are considered as next generation ones and the best alternative for traditional porous materials like foams. MPP combined with a uniform air gap constructs an absorber which has high absorption but in a narrow bandwidth of frequency. This characteristic makes MPPAs insufficient for practical purposes in comparison with porous materials. In this study instead of using a uniform air gap behind the MPP, the cavity is divided into several partitions with different depth arrangement which have parallel faces. This method improves the absorption bandwidth to reach the looked for goal. To achieve theoretical absorption of this absorber, equivalent electro-acoustic circuit and Maa’s theory (MAA, 1998) are employed. Maa suggested formulas to calculate MPP’s impedance which show good match with experimental results carried out in previous studies. Electro-acoustic analogy is used to combine MPP’s impedance with acoustic impedances of complex partitioned cavity. To verify the theoretical analyses, constructed samples are experimentally tested via impedance tube. To establish the test, a multi-depth setup facing a MPP is inserted into impedance tube and the absorption coefficient is examined in the 63-1600 Hz frequency range. Theoretical results show good agreement compared to measured data, by which a conclusion can be made that partitioning the cavity behind MPP into different depths will improve absorption bandwidth and the electro-acoustic analogy is an appropriate theoretical method for absorption enhancement research, although an optimisation process is needed to achieve best results to prove the capability of this absorber. The optimisation process provides maximum possible absorption in a desired frequency range for a specified cavity configuration by giving the proper cavity depths. In this article numerical optimisation has been done to find cavity depths for a unique MPP.

5

Efficiency of maximum power point tracking in photovoltaic system under variable solar irradiance

Marańda W., Piotrowicz M.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2014

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Vol. 62, nr 4

713--721

EN

Field conditions decrease the energy output of photovoltaic (PV) systems, mainly due to excessive temperatures. However, in regions with moderate ambient temperatures, as in Poland, solar energy is commonly delivered with highly fluctuating irradiance. This introduces yet another source of energy losses due to the non-ideal tracking of actual position of Maximum Power Point (MPP). Majority of PV-systems are equipped with DC/AC and grid-connected inverter. Since the solar energy flux is variable, an adequate MPP-tracking algorithm is required to handle a wide range of load levels and face rapid changes of input power. Along with the essential DC/AC conversion, the quality of MPP-tracking must also be taken into account in evaluation of inverter efficiency. The tracking in dynamic conditions has been addressed only recently. Several algorithms has been studied theoretically, experimentally or in laboratory conditions by applying artificial input test-patterns. This work takes the opposite approach by applying the recorded real-life solar irradiance and simulating the tracking behavior to study the problem for true field conditions in Poland. The simulation uses the unique high-quality irradiance data collected with 200 ms time resolution. The calculation of both static and dynamic MPP-tracking efficiency has been performed for representative variable-cloudy day, applying commonly used Perturb&Observe tracking algorithm.

6

Study of Single Sensor Based Maximum Power Point Tracking Techniques for Solar Water Pumping System

Daoud A., Midoun A.

Electrical Power Quality and Utilisation. Journal

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2009

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Vol. 15, iss. 2

23--27

EN

This paper describes new techniques of maximum power point (MPP) tracking for solar water pumping system. The latter system consists of a PV array, a DC/DC buck converter and a universal motor coupled to a centrifugal pump. A conventional hill climbing method is employed to seek the MPP using the motor-pump rotation speed or the pump outlet pressure information. Experimental results are presented and a comparison with conventional algorithm which requires both voltage and current sensors is provided.