A. G. PAPANDREOU’S ACADEMIC ECONOMIC THOUGHT 1943–1963

Self-excited thermoacoustic instability is undesirable in propulsion and power generation systems due to its detrimental effects. In this work, we conducted experimental demonstration study of applying bias-flow perforated liners on attenuating self-excited thermoacoustic oscillations in a premixed T-shaped combustor. For this, two perforated liners with different porosities and variable bias flow rate are experimentally tested and compared. It is found that in the absence of bias flow (cooling flow), the premixed flame can produce and sustain limit cycle oscillations. The amplitude and frequency of the dominant thermoacoustic mode are approximately 215 Hz and 140 dB. However, as the cooling flow velocity is increased to 5.5 m/s, the limit cycle oscillations are completely attenuated. More than 50 dB sound pressure level reduction is achieved. High-frequency modes are dampen by more than 25 dB. Further experimental test is conducted on the perforated liner with a porosity of 2.9%. Similar attenuation effect is achieved. Finally, during the transient growth process, dominant mode switching from high (non-harmonic) to low frequency is observed. The present work shed lights on the optimum design of perforated liner on attenuating thermoacoustic instability and the dynamic behaviours of the transient growth process.

The work proposes a detailed description of the flow field throughout leaned turbine nozzles and reports a sensitivity analysis with respect to the lean angle. A phenomenological approach focuses the attention on pressure contours distribution on both inside and outside the passage. The study involves both straight and annular cascades mounting a typical intermediate reaction degree section, designed for steam turbines. Blades are built by stacking the same 2D profile along different linear axes, characterized by different angles with respect to the normal or radial direction: α=0 deg for prismatic blade and α=10 deg, 15 deg, and 20 deg for the leaned ones are considered. Experimental and numerical tests were performed at the nominal inlet flow angle in order to avoid any effect related to blade sweep. Experimental tests were carried out at the design outlet Mach number of 0.65; measurements were performed at the Laboratorio di Fluidodinamica delle Macchine of Politecnico di Milano. Only linear cascades with prismatic and 20 deg leaned blades were experimentally tested, providing data both downstream and inside the blade passage by means of pressure probe traversing, endwall pressure taps, and oil flow visualization. Experimental results were also used to validate the numerical setup, which provided a detailed computational picture of the flow field throughout the channel. The influence of the pressure contours’ shape on secondary vorticity activity downstream of the passage is highlighted and discussed, focusing the attention on secondary structures and loss distribution in this region. The resulting description of the flow field, based on the representation of pressure contours, supports the sensitivity analysis with respect to the blade lean angle, identifying the mechanism that leads the secondary vorticity to grow in regions where secondary losses and blade loading decrease.

Experimental testing and evaluation of real-scale lap-splice bolted connections used in typical lattice steel transmission towers

Behaviour of innovative stub columns utilising mild-steel plates and stainless steel tubes at ambient and elevated temperatures

Owing to their significant hardness and compressive strengths, ceramic materials are widely employed for use with protective systems subjected to high-velocity impact loadings. Therefore, their mechanical behaviour along with damage mechanisms need to be significantly investigated as a function of loading rates. However, the classical plate-impact testing procedures produce shock loadings in the brittle sample material which cause unrealistic levels of loading rates. Additionally, high-pulsed power techniques and/or functionally graded materials used as flyer plates to smooth the loading pulse remain costly, and are generally difficult to implement. In this study, a shockless plate-impact technique based on the use of either a wavy-machined flyer plate or buffer plate that can be produced by chip-forming is proposed. A series of numerical simulations using an explicit transient dynamic finite-element code have been performed to design and validate the experimental testing configuration. The calculations, conducted in two-dimensional (2D) plane-strain or in 2D axisymmetric modes, prove that the 'wavy' contact surface will produce a pulse-shaping effect, whereas the buffer plate will produce a homogenizing effect of the stress field along the transverse direction of the sample. In addition, 'wavy-shape' geometries of different sizes provide an easy way to change the level of loading rate and rise time in an experimentally tested ceramic specimen. Finally, when a shockless compression loading method is applied to the sample, a Lagrangian analysis of data is made possible by considering an assemblage of ceramic plates of different thicknesses in the target, so the axial stress-strain response of the brittle sample material can be provided.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

Combining timber and glass in the wall elements of the building envelope with the proper orientation of such transparent façade elements enables the utilization of solar energy for heating and internal illumination of the building. However, the asymmetrical layout of timber-glass wall elements in such buildings can result in problems with the horizontal stability of the structure, so their participation to load-bearing capacity of the structure is usually neglected. The study deals with solutions for such elements as horizontal load-bearing members with proper connection details. First, specifically developed timber-glass wall elements were experimentally tested under monotonic and cyclic horizontal point load, and further in combination with classical timber-framed wall elements implemented into special single and two-storey box-house models, which were further experimentally tested on the shaking table. In the second part as the main goal of the study, a quite simple mathematical model of the box-house prototypes is developed using a fictive diagonal element for simulating the racking stiffness of the bracing timber-glass wall element. The calculated results for the 1st vibration period are compared with the previously measured experimental results to prove an accuracy of the developed model. Finally, a linear time-history calculation is done as a sample presentation of the developed mathematical model using Landers acceleration spectrum. The developed mathematical model enables a simple and effective seismic response calculation of timber buildings considering the developed timber-glass wall elements as load-bearing bracing elements against horizontal load actions. The model can also be recommended for using in further parametric numerical academic studies analysing the influence of various parameters.

Introduction. In the current climate, a central focus in supporting the development of Russia’s construction industry is on what measures are included in the government’s crisis package. In the first quarter of 2022, it included 17 measures directly and 40 measures indirectly impacting the nation’s construction and housing-and-utilities sectors. The prompt passage of such measures, which are to be implemented based on relevant resolutions, enactments, and laws, is aimed at creating a barrier-less environment with a focus on accelerating construction, keeping down building materials prices, and adjusting the prices of existing contracts for supply of building materials in a timely manner. The ever-mounting sanctions pressure is only raising the bar on objectives to be achieved in the area of residential construction, infrastructural transformations, and improvements in construction process innovation, including the implementation of digitalization and use of platform-based solutions to communications issues. Given the scale of the work that lies ahead, there is a need to search for new forms of managing the sector, with a focus on experimental testing of potential methods for resolving the issues in the construction sector that have exacerbated in the conditions of external sanctions pressure.
 
 Materials and methods. The authors’ view of transformations in Russia’s construction sector is focused on the following: 1) the need to restructure the nation’s construction authorities and establish three separate ministries — one for construction, one for municipal services, and one for utility infrastructure; 2) the need to employ alternative models for tackling the housing problem and the need to experimentally test the savings-and-loan and rent models; 3) the need for sound import substitution measures and price-setting procedures; 4) the need to create a comfortable business environment with relevant out-of-court settlement mechanisms in place; 5) the need to establish new requirements for applied research. The last item is of particular significance, for any support and development measures need to be scientifically substantiated through the utilization of a variety of problem solving methods and experimental testing and scaling up of newly developed mechanisms and methods. 
 
 Results. Best practices related to seeking effective solutions indicate that in a mobilization economy testing a particular organizational, investment, or digitalization model in real time will help to not only obtain an objective picture of its effectiveness but also identify the bottlenecks to its application in practice. Moreover, the authors’ analysis suggests that, if the nation’s expertise centers are to resolve most of the development objectives for the construction sector in the current climate of external sanctions pressure, they must not overlook the benefits of creating ecosystems and employing platform-based solutions.
 
 Conclusions. Given regional best practices in residential construction, the use of long established EU requirements for price-setting in construction, the inevitable shift to Building Information Modeling, and the current level of applied research in Russia, it appears to be worth focusing on maximizing the industry’s research potential. The shortest route is by way of concerted efforts in the development, experimental testing, and implementation of new models for the development of the construction, municipal services, and utility infrastructure sectors.

The article introduces a potentia l use of a combination of the method of numerical modelling and experimental tests for the treatment of the structure of a wooden prefabricated staircase with one-sided suspended stairs. Numerical modelling was used to fi nd critical details, which were experimentally tested on partial models in the scale 1:1. The results of the numerical modelling in combination with experimental testing were used for designing a prototype of a wooden prefabricated staircase with one-sided suspended stairs. The designed prototype of a staircase in two versions was experimentally tested in the scale 1:1 in compliance with Czech design standards CSN 73 0035, CSN 73 2030 and ETAG008 – Guideline for European technical approval of prefabricated stair kits in edition January 2002 in terms of ultimate and serviceability state design.

High-speed tracked vehicles have complex powertrains that, in addition to power transfer and transformation, also perform the functions of vehicle steering and braking systems, as well as power supply system for various subsystems on the vehicle. Analyzing the power balance of a tracked vehicle, especially in specific moving scenarios such as the turning process, is of great importance for understanding the power requirements and workload of the powertrain components and their optimization. A simulation model was developed, based on the construction parameters of an experimentally tested high-speed tracked vehicle to reduce the time and material resources required for experimental testing. Both the simulation and experimental tests were conducted using the same input parameters and driving conditions for different vehicle turning scenarios. Simulation and experimental test results are compared to verify the accuracy of the simulation model. The analysis of the obtained results shows that the average value of the relative rpm error is about 5%, the average value of the relative torque error is about 7%, while the average value of the relative power error is about 6.5%.

Experimental investigation of a new smart energy management algorithm for a hybrid energy storage system in smart grid applications

Unmanned Aerial Vehicles (UAVs) have become more and more popular, and how to control them through advanced control techniques becomes crucial. Although there are many different control methods that can be applied to the control of UAVs, nonlinear control techniques are more practical since the inherent nonlinear features of most UAVs. In this paper, three widely used nonlinear control techniques including Feedback Linearization Control (FLC), Sliding Mode Control (SMC), and Backstepping Control (BSC) are investigated, implemented and experimentally tested on a unique quadrotor UAV (known as Qball-X4) test-bed available at the Networked Autonomous Vehicles (NAV) Lab in Concordia University. The advantages and disadvantages of these three control techniques with application to the Qball-X4 UAV are revealed through both simulation and experimental tests. Sliding mode control is well known for its capability of handling uncertainties, and is demonstrated to be the most robust and best performance controller for Qball-X4. Feedback linearization control and backstepping control are demonstrated a bit weaker than sliding mode control. Comparison of these three controllers is also carried out in both theoretical analysis and experimental testing under same flight conditions. Testing results and comparison show the different features of different control methods and provide a view on how to choose an appropriate controller for controlling the Qball-X4 and other UAVs under a specific condition.

The performance of pumps when working with non-Newtonian fluids significantly change with respect to water. In several experimental tests with non-Newtonian fluids, significant deration of head and the presence of head instability were observed. The present work aims to better understand this phenomenon since the reasons that originate it are not clear. Two small size centrifugal pumps were experimentally tested with different mixtures of kaolin-in-water, which showed a verified non-Newtonian behavior. The rheology of the mixtures and the particle size distribution of kaolin powder were measured to characterize the fluids. Similar to previous tests, a strong reduction of head and the appearance of instability were observed at low flow rates and, in some cases, also at higher flow rates. This behavior was related to the presence of air trapped into the fluid that, within the pump, generated a phenomenon known as gas-locking, which in literature it has been studied in detail with water but not with non-Newtonian fluids. Moreover, in some working conditions, non-stable time-varying phenomena are observed and their consequence on performance commented. Comparing the two pumps, characterized by a similar specific speed but by a different geometry, the head drop manifested itself with different intensity.

Windows are major contributors to energy demand in residential homes because of their inferior thermal resistance compared with the opaque envelope and sometimes from unwanted solar heat gain. Window attachments can help to mitigate this demand by controlling the solar heat gains and enhancing the thermal resistance of the windows. In this study, the energy savings potential of cellular shades in residential homes is studied using experimental testing and energy simulations. The energy performance of the shading devices was experimentally tested during the heating season from December 2019 to May 2020 with a focus on cellular shades. Five shading devices—three single and two double cellular/cell-in-cell shades—were used to compare the performance with generic horizontal (venetian) blinds using two nearly identical sideby-side rooms in a residential building with their exterior window facing east. Another objective of the experimental testing was to evaluate any impact of the side-channel of the shading device on energy savings. To observe the impact of the side-channels on energy savings, from shades in two of the test cases, cellular shades with side-channels were used. From the experimental testing, daily energy savings in the range of 9% to 23% were observed by considering data from 6 p.m. until 6 a.m. of the next day.

We present the experimental-numerical analysis of the influence of temperature on mechanical properties of structural high-strength steel class S690QL. Since the steel S690QL belongs to a group of steels with good mechanical properties, the aim of this paper is to determine the highest temperatures at which these good characteristics are kept. Experimental tensile testings of the specimens were performed at five different temperatures in the range from 20 to 550°C. Beside experimental testing, strengthening curves were calculated and numerical analysis using finite element method was performed. Both the experimental and numerical results have shown that decrease of mecahanical properties occurs at approximately 450°C.

Buckling and fracture analysis of thick and long composite cylinders with cutouts under axial Compression: An experimental and numerical campaign