bluuebunny/crossref_metadata_2025 huggingface dataset:
Some exact explicit solutions and conservation laws of Chaffee-Infante equation by Lie symmetry analysis
Authors: Riaz Muhammad Bilal , Atangana Abdon , Jhangeer Adil , Junaid-U-Rehman M
Published: May 2021

In this work, the tanh method is employed to compute some traveling wave patterns of the nonlinear third-order (2+1) dimensional Chaffee-Infante (CI) equation. The tanh technique is successfully used to get the traveling wave solutions of a considered model in the form of some hyperbolic functions. The Lie symmetry technique is used to analyze the Chaffee-Infante (CI) equation and compute the Infinitesimal generators under the invariance criteria of Lie groups. Then we construct the commutator table, adjoint representation table, and we have represented symmetry groups for each Infinitesimal generator. The optimal system and similarity reduction method is used to obtain some analytical solutions of the considered model. With the help of the similarity reduction method, we have converted the nonlinear partial differential equation into nonlinear ordinary differential equations (ODEs). Moreover, we have shown graphically obtained wave solutions by using the different values of involving parameters. Conserved quantities of nonlinear CI equation are obtained by the multiplier approach.
Plasma-waves evolution and propagation modeled by sixth order Ramani and coupled Ramani equations using symmetry methods
Authors: Saleh R , Rashed A S , Wazwaz Abdul-Majid
Published: May 2021

Nonlinear shock waves in plasma was modeled and studied using Ramani equation of sixth order and its coupled form representing the interaction between two waves. A new combined methodology of both Lie infinitesimal transformation and singular manifold methods was exploited to create analytical solutions. The method was extended to investigate a coupled system of evolution equations as same as a single evolution equation. Soliton solutions were created for both models.
A 3D SiC MOSFET with poly-silicon/SiC heterojunction diode
Authors: Ran Sheng-Long , Huang Zhi-Yong , Hu Sheng-Dong , Yang Han , Jiang Jie , Zhou Du
Published: May 2021

A three-dimensional (3D) silicon-carbide (SiC) trench metal–oxide–semiconductor field-effect transistor (MOSFET) with a heterojunction diode (HJD-TMOS) is proposed and studied in this work. The SiC MOSFET is characterized by an HJD which is partially embedded on one side of the gate. When the device is in the turn-on state, the body parasitic diode can be effectively controlled by the embedded HJD, the switching loss thus decreases for the device. Moreover, a highly-doped P+ layer is encircled the gate oxide on the same side as the HJD and under the gate oxide, which is used to lighten the electric field concentration and improve the reliability of gate oxide layer. Physical mechanism for the HJD-TMOS is analyzed. Comparing with the conventional device with the same level of on-resistance, the breakdown voltage of the HJD-TMOS is improved by 23.4%, and the miller charge and the switching loss decrease by 43.2% and 48.6%, respectively.
Asymmetric coherent rainbows induced by liquid convection*
Authors: Shi Tingting , Qian Xuan , Sun Tianjiao , Cheng Li , Dou Runjiang , Liu Liyuan , Ji Yang
Published: May 2021

Coherent rainbows can be formed by focusing white-light laser into liquids. They are bilaterally symmetric interference rings with various shapes. Such interference rings arise from the temperature distribution of the liquid induced by laser heating, i.e., thermal lens effect, which changes the refractive index locally and thus the optical path difference. The up–down asymmetry of the interference rings is caused by convection in the liquid. With the increase of the viscosity, the interference rings change their shape from oval to circular shape. After a shutter is opened and the laser shines into the liquid, the interference rings are circular at the beginning. As time goes on, they gradually turn into anoval shape. Let the liquid go a free-fall at the beginning, the interference rings remain circular. All the three experiments have confirmed that the asymmetric interference rings are due to convection in the liquid associated with thermal lens effect. We also numerically simulate the two-dimensional heat conduction with and without convection, whose results agree well with our experimental observations.
Universal quantum circuit evaluation on encrypted data using probabilistic quantum homomorphic encryption scheme*
Authors: Zhang Jing-Wen , Chen Xiu-Bo , Xu Gang , Yang Yi-Xian
Published: May 2021

Homomorphic encryption has giant advantages in the protection of privacy information. In this paper, we present a new kind of probabilistic quantum homomorphic encryption scheme for the universal quantum circuit evaluation. Firstly, the pre-shared non-maximally entangled states are utilized as auxiliary resources, which lower the requirements of the quantum channel, to correct the errors in non-Clifford gate evaluation. By using the set synthesized by Clifford gates and T gates, it is feasible to perform the arbitrary quantum computation on the encrypted data. Secondly, our scheme is different from the previous scheme described by the quantum homomorphic encryption algorithm. From the perspective of application, a two-party probabilistic quantum homomorphic encryption scheme is proposed. It is clear what the computation and operation that the client and the server need to perform respectively, as well as the permission to access the data. Finally, the security of probabilistic quantum homomorphic encryption scheme is analyzed in detail. It demonstrates that the scheme has favorable security in three aspects, including privacy data, evaluated data and encryption and decryption keys.
Integrated superconducting circuit for qubit and resonator protection*
Authors: Yang Xiao-Pei , Han Zhi-Kun , Song Shu-Qing , Zheng Wen , Lan Dong , Tan Xin-Sheng , Yu Yang
Published: May 2021

A semi-infinite waveguide acts as a mirror and helps protect the qubit in front of it from decoherence. Here, we investigate the interference effect in an open waveguide consisting of resonators with different decay rates. We find that a lossy resonator works as a mirror and changes the effective decay rate of the other. The spontaneous radiation of qubit is related to its environment, and we can control it by arranging the lossy resonator’s position or frequency. Our approach helps improving the qubit performance, as well as the quantum gate fidelities.
Magnetic anisotropy manipulation and interfacial coupling in Sm3Fe5O12 films and CoFe/Sm3Fe5O12 heterostructures*
Authors: Shen Lei , Wu Guanjie , Sun Tao , Meng Zhi , Zhou Chun , Liu Wenyi , Qiu Kang , Ma Zongwei , Huang Haoliang , Lu Yalin , Zhang Zongzhi , Sheng Zhigao
Published: May 2021

The magnetic anisotropy manipulation in the Sm3Fe5O12 (SmIG) films and its effect on the interfacial spin coupling in the CoFe/SmIG heterostructures were studied carefully. By switching the orientation of the Gd3Ga5O12 substrates from (111) to (001), the magnetic anisotropy of obtained SmIG films shifts from in-plane to out-of-plane. Similar results can also be obtained in the films on Gd3Sc2Ga3O12 substrates, which identifies the universality of such orientation-induced magnetic anisotropy switching. Additionally, the interfacial spin coupling and magnetic anisotropy switching effect on the spin wave in CoFe/SmIG magnetic heterojunctions have also been explored by utilizing the time-resolved magneto–optical Kerr effect technique. It is intriguing to find that both the frequency and effective damping factor of spin precession in CoFe/SmIG heterojunctions can be manipulated by the magnetic anisotropy switching of SmIG films. These findings not only provide a route for the perpendicular magnetic anisotropy acquisition but also give a further path for spin manipulation in magnetic films and heterojunctions.
Features of commissioning a gas turbine unit with a low-emission combustion chamber
Authors: Vorotyntsev I E , Tyulkin D D , Fedorchenko D G , Tsybizov Yu I
Published: May 2021

Environmental safety issues are a priority in the modernization development of aviation or ground-based combustion chambers of gas turbine engines. In order to reduce the emission of harmful substances from combustion products, a low-emission combustion system, which is based on the concept of LPP (Lean-premixed and prevaporised), is being used today. This concept implements the principle of burning “ultra-poor” premixed air-fuel mixtures. The operational experience of combustion chambers developed in accordance with the indicated concept shows that one of the implementation problems is the difficulty in ensuring a good start. This paper presents the results of adjusting the operating process of a modern combustion chamber, launching a gas turbine unit, including drawing up a fuel supply control algorithm, experiments with igniting ignition devices and setting the gas turbine on idle mode. A feature of the commissioning work is the debugging of the operating process of the combustion chamber directly as part of the gas turbine unit, bypassing the traditional pilot-testing on the rig.
Comparative assessment of different hybrid propulsion system types’ efficiency for commuter aircrafts
Authors: Zakharchenko V S , Varyukhin A N , Rakhmankulov D Ya , Suntsov P S
Published: May 2021

This paper contains a comparative efficiency assessment of various concepts of hybrid propulsion systems (traditional, parallel turboelectric based on hybrid turboprop engines and serial hybrid) in accordance with the level of parameters of 2020 and 2030 for commuter aircrafts with capacity up to 19 passengers.
A method for checking the possibility of joint work of the auxiliary power unit and the starter
Authors: Popov G M , Zubanov V M , Novikova Yu D , Matveev V N , Baturin O V
Published: May 2021

This paper describes the algorithm developed by the authors for matching the workflow of the auxiliary power unit to the air turbine used when starting the engine. This technique is applied to determine the possibility of starting a gas turbine engine, calculate its time and basic parameters under all operating conditions (including in flight), as well as to select a new auxiliary power unit (APU) or an air turbine for an existing system. The developed technique considers structural, strength, operational and other limitations. The results were implemented as a computer program.
Development of an electric propulsion system demonstrator for an ultralight manned aircraft
Authors: Varyukhin A.N. , Zakharchenko V.S. , Geliev A.V. , Zhuravlev D.I. , Kiselev I.O. , Zagumennov F.A. , Kazakov A.V.
Published: May 2021

A description of a full electric propulsion system demonstrator with an energy source based on a battery pack for an ultralight manned Sigma-4 aircraft is presented. The main characteristics and functionality of the main units and devices of the electric propulsion system and its control system are presented.
3D optimization of the hollow fan blade internal structure
Authors: Salnikov Anton
Published: May 2021

Design optimization to reduce fan impeller mass is an important and urgent task. One way to solve the problem is to design a hollow blade. In addition to lightening the blade this also reduces the fan disk load, that in turn makes it possible to minimize the weight of the disk and the weight of the impeller as a whole. The hollow blade has a complex shape, and this significantly increases development time because modification of the structure in order to define its optimal shape is a very time-consuming and costly task. Therefore, automating this process and transforming it into an optimization task is very important and relevant. In this paper, an approach to optimal hollow fan blade design in the form of an optimization problem in 3D formulation is developed. To do this, a parameterized 3D model of the hollow blade was created in the ANSYS APDL environment. Using the developed model, a comparative optimization of a typical hollow blade was carried out.
A preliminary design of a schematic evaluation of low emission turbofan combustors
Authors: Krishna Vamsi U , Mitrokhov N V
Published: May 2021

This paper examines low emission combustion technologies (LECT) schemes suitable to the sixth generation high-bypass Turbofan engines designed to operate on narrow-body aircraft with a rated thrust (F∞ in kN) of 90-250 kilo-Newton(kN) and an overall pressure ratio of (Π∞) ≥ 30. The examined schemes are based on 11th regulatory standards of the Committee on Aviation Environmental Protection (CAEP). A brief overview on emissions is provided.
A new look at the application of metal matrix composites in a future aviation engine
Authors: Mileiko S T
Published: May 2021

Three types of composites, namely (1) carbon-fibre/metal-matrix, (2) oxide-fibre/molybdenum-matrix, and (3) oxide-fibre/high-entropy-matrix are considered as potential materials for future aviation engines. Technological schemes for producing the composites and their mechanical properties, as well as the potential of future development to maturing them are presented.
Tungsten Carbide Nanopowder Influence Study on Tensile Strength of GRP Specimens Made of Lavesan Glass Fabric and EPR 320 Momentive Epoxy
Authors: Gavrish V , Chayka T , Oleynik A. , Gavrish O.
Published: May 2021

This paper presents the test results of fiberglass samples consisting of glass fiber Lavesan (Italy) and a binder - EPR 320 epoxy resin modified with tungsten carbide (WC) nanopowder. The positive effect of nanopowder on the tensile strength and the increase in tensile strength of more than 1.5 … 2.5 times with the addition of additives in the mass concentration of 1 … 4% to the mass of the resin are shown.
Degradation of elastic characteristics of the CFRP used in the design of a gas turbine engine as a result of high-cycle fatigue damage
Authors: Nikhamkin M.Sh. , Solomonov D.G.
Published: May 2021

Carbon fiber reinforced polymers (CFRP) are increasingly being used in heavily loaded parts of aircraft engines. CFRP fan blades, vanes must successfully resist fracture due to high-cycle fatigue. One of the consequences of fatigue damage is a decrease in the rigidity of the material and a drop in the natural vibration frequencies of parts. These effects are of interest when developing fatigue fracture models and predicting durability. The purpose of this article is to develop a method and obtain experimental data on the decrease of elastic characteristics of CFRP as a result of progressive fatigue damage. The developed technique consists of two stages. During the first one, the natural frequencies and eigenmodes of the samples during their fatigue testing are experimentally obtained. During the second stage, the four elasticity parameters of the CFRP laminate monolayer are identified via the natural frequencies. The inverse numerical/experimental technique for material properties identification is applied. The dependences of elastic characteristics on the relative fatigue life are obtained as experimental results of both modal and fatigue tests. The results can be useful in studying the fatigue behavior of the examined materials and in creating methods for calculating fatigue life.
Studying the layer structure formation in laser additive manufacturing with AlMg6 alloy wire
Authors: Eremeev A.D. , Tsibulskiy I.A. , Akhmetov A.D. , Mukin D.V. , Davletshin A.O.
Published: May 2021

When processing aluminum alloys with repeated laser radiation, which is typical for both multi-pass welding and additive manufacturing, volatile chemical components are being burnt. Due to the processing zone overheating if there are residual stresses, the probability of there being structural defects and deformations and, consequently, distortion of the final shape of the sample increases. Studies of the wall’s structure forming process during laser additive manufacturing with AlMg6 alloy wire, fulfilled based on experiments and computational methods, allowed us to obtain the necessary data for optimizing the process and determining the laser treatment modes. The simulation of the thermocyclic effect of laser radiation on the wall and the selection of mode parameters for the optimal structure of the material and the shape of the bead were performed. The results for the chemical composition of the final material, the number of defects and mechanical properties were quite satisfactory.
An Assessment of the Controllability of the Main Parts of Aircraft Engines During Capillary Non-destructive Testing
Authors: Ospennikova O G , Kudinov I I , Golovkov A N , Generalov A S , Skorobogatko D S
Published: May 2021

The aim of this paper is to determine uncontrolled zones in the main parts of aircraft engines during capillary control using a luminescent set of flaw detection materials LYuM1-OV. The main factors affecting the defect detection process have been described. The approach not previously used in the practice of aviation enterprises has been experimentally tested. This approach takes into account the quality of applying a film-forming developer to various surfaces of structural elements of aircraft parts, using luminescence brightness samples. The research has clearly shown the control zones of holes of different diameters and herringbone type locks of different widths. It is established that the data presented in literature sources of technical and technological documentation on the controllability of holes and herringbone type locks differs from the experimental data.
Verification of a Mathematical Model of a Dry Friction Damper for a GTE Blade
Authors: Yakovkin V N , Besschetnov V A
Published: May 2021

This paper presents the verification of the mathematical model utilized to calculate the damping capacity of a dry friction damper. The mathematical model is based on determining natural frequencies and mode shapes, as well as relative characteristics of the friction energy losses. To estimate the applicability of the mathematical model to full-scale assemblies of a gas-turbine engine, the model was verified by the results of the experiment. The experiment was carried out in a laboratory where the damping capacity of the gas-turbine engine blade with a model under-platform damper was examined at constrained and damped oscillations. During the experiment multiple materials of contact pair were examined to determine how microslip affects the damping capacity. Based on the results of comparing calculations with the experiment, by selecting the dry friction coefficient, a good convergence on the oscillation decrement and natural frequency was achieved. The conducted research has shown that the mathematical model provides reliable results with Coulomb friction and can consider microslip effects on the damper capacity.
Modeling Rig Dynamics to Determine Dynamics of GTE Elements’ Performance under Shaker Conditions
Authors: Utkin A.O. , Yakovkin V.N.
Published: May 2021

During shaker tests to determine the strength properties of the test article, it can be difficult to shake the article to the required in the concentrator stresses. This may be due to the losses of the force transmitted from the shaker to the test article, which occur due to an improperly designed rig. Using some methods for rig designing, along with numerical modeling, provides the possibility to make an easy-to-excite rig with minimum loss of transmitted forces. This paper deals with the modeling of the “article – rig – shaker” system executing constrained oscillations under the influence of harmonic excitation. The model’s response dependencies on dynamic excitation caused by the oscillation frequency have been outlined. The excitation level’s influence on the dynamic parameters of the model have been analyzed.
The influence of nonuniform heat transfer coefficient distribution on the value of thermal deformations in mechanical gas dynamic seal rings
Authors: Vinogradov A , Novikova J , Shipunov V
Published: May 2021

Currently, many different aircraft engine types exist. They have a wide range of operating conditions: the flight speed can vary from zero to hypersonic values, the flight altitude from near-earth conditions to space flights. During the flight, loads are not kept constant. Engines have significant dynamic overloads, temperature and pressure differences, can operate in conditions of high humidity or dust, as well as in various aggressive environments. The development of aviation and rocket engine building is associated with a continuous increase in the working thermodynamical cycle parameters.

Further improvement of gas turbine engines (GTE) can be carried out in two directions. The first is using new advanced engine designs based on a modernized cycle, with a different fuel, original design, and power scheme. This direction also includes the application of new high-performance elements in the engine: bearings, seals, coatings, etc. The second direction is related to the improvement of existing structures, increasing their efficiency by more detailed working conditions forecasting based on the use of modern computing software systems. This article presents a study of the potential mechanical face gas dynamic seal (FGDS) in the support in an aircraft engine compressor. Aircraft engines are characterized by multi-mode operation and high temperature levels in the internal cavities. For a FGDS operating with a working gap of several microns the exact determination of the deformation value is a very important result of the design process. This article considers the influence of the convective heat transfer coefficients distribution on the value of sealing rings thermal deformations. To achieve this goal, two compaction models were created: the gas-dynamic model for determining the convective heat transfer coefficients in the ANSYS CFX software program; and the structural model for calculating the resulting deformations. Interaction between the models was performed based on a specially created methodology. The obtained results can be used in the design of a FGDS for the supports in the compressors of aircraft engines and power plants.
Rapid gas temperature measurement device for gas turbine engines with detection of pre-surge phenomena
Authors: Artyukhov A V , Babkin V I , Sukhinets Z A , Gulin A I
Published: May 2021

A differential system for measurement of gas temperature in gas turbine engines (GTE) using acoustic multi-vibrators was presented. Application of acoustic multi-vibrators improves the response time by three orders of magnitude compared to thermocouples. Combined use with a gas flow meter and a vibration sensor makes it possible to measure the low-frequency component of acoustic vibrations of flowing gases in a GTE’s combustion chamber. As an example, a calculation to determine the resonance frequency of a combustion chamber of a GTE was given.
Computational and experimental study of bird failure at different speeds of collision with a flexible plate
Authors: Shorr B F , Serebriakov N N , Mel’nikova G V , Siversky A S , Nikiforov V S
Published: May 2021

This article presents an experimental and computational study of bird collision with a flexible plate at different impact speeds. Tests were carried out with the aid of a pneumatic gun. The bird mass in the study was about 300 g, and the speed range was 49-75 m/s. The actual mechanical properties of the plate were determined with tensile tests of flat specimen-witness. A video recording and strain gauging were performed during the strike. Some frames of high speed video recording for the highest bird’s velocity c = 75 m/s are presented in the article to demonstrate the process of bird rupturing. Different models of the bird material were examined to compare computational and measured strains.
Improving methods for predicting defects based on vibrography
Authors: Panov V.A. , Zasenko T.V , Zyuzin D.A. , Makovetskii-Serebryakov D.B.
Published: May 2021

The article is devoted to the broadband vibrodiagnostics of jet engines. The material discusses the main causes that affect the level of vibration of the engine. Using the methods for controlling vibrations in a wide frequency band, an analysis was made of the criteria that cause defects and their manifestations in a wide frequency band of vibrations. The author has studied the effect of defects in parts and assembly units on vibration levels in a wide range. Based on the data obtained, it was found that the results allow to determine the bottlenecks of the gas turbine engine with accuracy to the details of the assembly units.
A novel detergent-based decellularization combined with carbodiimide crosslinking for improving anti-calcification of bioprosthetic heart valve
Authors: Luo Yu , Huang Shenyu , Ma Lie
Published: May 2021

Currently, valve replacement surgery is the only therapy for the end-stage valvular diseases because of the inability of regeneration for diseased heart valves. Bioprosthetic heart valves (BHVs), which are mainly derived from glutaraldehyde (GA) crosslinked porcine aortic heart valves or bovine pericardium, have been widely used in the last decades. However, it is inevitable that calcification and deterioration may occur within 10–15 years, which are still the main challenges for the BHVs in clinic. In this study, N-Lauroylsarcosine sodium salt (SLS) combined with N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) were utilized to decellularize and crosslink the heart valves instead of GA treatment. The obtained BHVs exhibited excellent extracellular matrix stability and mechanical properties, which were similar with GA treatment. Moreover, the obtained BHVs exhibited better in vitro biocompatibilities than GA treatment. After subcutaneous implantation for 30 d, the obtained BHVs showed mitigated immune response and reduced calcification compare with GA treatment. Therefore, all the above results indicated that the treatment of SLS-based decellularization combined with EDC/NHS crosslink should be a promising method to fabricate BHVs which can be used in clinic in future.
Evaluations of certain Catalan-Hankel Pfaffians via classical skew orthogonal polynomials
Authors: Shen Bo-Jian , Li Shi-Hao , Yu Guo-Fu
Published: May 2021

This paper is to evaluate certain Catalan-Hankel Pfaffians by the theory of skew orthogonal polynomials. Due to different kinds of hypergeometric orthogonal polynomials underlying the Askey scheme, we explicitly construct the classical skew orthogonal polynomials and then give different examples of Catalan-Hankel Pfaffians with continuous and q-moment sequences.
Liquid-liquid capillary rise
Authors: Rasuceanu I , Patrascu C , Magos I , Trandas N , Balan C
Published: May 2021

We study the dynamics of capillary rise of a liquid-liquid interface using two immiscible liquids. By adjusting the height of the less dense fluid column, we measure the rise of the ensemble in the tube. A theoretical model is proposed that captures the time dependence of the position of the interface. Particular attention is given to the dynamics of the oil-water interface. Different types of flow regimes are identified and compared with previous theoretical and experimental findings. The theoretical model was found to be in good qualitative agreement, even though the contact angles of the two interfaces do not remain constant during the elevation of the fluid.
The fracture of yield stress fluid jet in air and in viscous fluids
Authors: Broboana D , Ionescu C S , Balan C
Published: May 2021

One of the largest family of complex materials are represented by fluids with yield stress. In this category are included creams, pastes, greases, gels, in general materials which start to flow at a certain value of the imposed shear stress. A common characteristic of yield stress materials is the association of material instability with the onset of the fluid behavior. The present paper is concerned with the experimental investigations and numerical modeling of the dynamics of a yield stress fluid jet in air or immersed in viscous/viscoelastic liquids. A cream jet at constant flow rate is generated through a capillary with a syringe pump and the visualizations of its motion in a vessel filled with an immiscible fluid is performed with normal and high-speed cameras. One goal of the study is to test the capability of the VoF code to simulate the jetting phenomena, the rheology of the sample being modeled with the Carreau equation and the Herschel-Bulkley relation, respectively. The visualizations show the specific yield stress instabilities from jetting to coiling, buckling and fracture.
Human CO2 generation rates in small enclosures for different test cases
Authors: Georgescu Matei-Razvan , Nastase Illinca , Meslem Amina , Sandu Mihnea , Bode Florin
Published: May 2021

The present study deals with experimental measurements of CO2 generation rates, due to the human occupation of a full-scale experimental mock-up simulating the astronaut crew quarters aboard the International Space Station. The estimation of CO2 generation rates follows different methods as described in the literature. A single test subject in four different testing cases is considered, one at rest representing the baseline case and the other three cases at varying levels of physical activity or at rest but with a fixed breathing frequency requested from the human subject. The study results indicate that imposing a fixed breathing rate even while at rest increases the generation rate unpredictably. Following literature metabolic rate estimations, the latter two cases are equivalent to the subject being engaged in light or medium physical activities. The results are used to form recommendations for studies measuring human CO2 generation rates.
Environmental impact of bituminous mixtures produced with reclaimed asphalt pavement and rejuvenator
Authors: Forton A , Ciutina A , Marc P
Published: May 2021

The paper focuses on the investigation of the potential environmental impact related to the production of several types of bituminous mixtures containing different dosages of Reclaimed Asphalt Pavement (RAP) and Rejuvenator (Rej). All materials used in the presented study are specific and generally used for pavements in Romania. The RAP material was considered as an inert material and it was used in three dosages (25%, 50% and 75%). For the bituminous mixture produced with 50% RAP material, a rejuvenator consisting in a mixture of vegetal oils was used in three dosages of 0.2%, 0.4% and 0.6% by mass of RAP material. A total of seven types of bituminous mixtures were considered including one ‘conventional’ mixture produced with virgin materials and used as reference. The Environmental Impact Assessment was estimated for the production process of the analysed bituminous mixtures, by using Eco-indicator 99 method within SimaPro software. The results prove that the addition of RAP material leads to a net decrease of the energy use and environmental impact. Besides, when rejuvenators are used in this process, they can affect the energy balance and reduce the difference in environmental impact.
Flow investigation around cylinders assembled in a confined straight channel geometry
Authors: Tanase Nicoleta-Octavia , Broboana Diana , Balan Corneliu
Published: May 2021

The paper is dedicated to experimental and numerical investigations of the dynamics of 3D-flow around a cylinder with 10 mm diameter. The cylinder is positioned in a confined geometry represented by a long straight channel with 50 mm width and 10 mm height. The study analyses the dependence on the Re-number of the path lines distributions in the vicinity of the immersed cylinder. The visualized flow patterns are fairly reproduced by the numerical solutions of the Navier-Stokes equations up to Re = 1000. The velocity and wall stresses are computed in the vicinity of the cylinder. One main goal of the present work is established by the correlation between the flow pattern, wake boundary and wall shear stress distributions down-stream the cylinder.
Determination of the separation points for the flow around blunt bodies: experimental and numerical studies
Authors: Tănase N O , Simionescu Ş M , Păduroiu M M , Bălan C
Published: May 2021

The paper is concerned with experimental studies and numerical modelling of the air flow around blunt bodies (cylinder, aerodynamic profile) inside a wind tunnel. The range of the investigated Reynolds numbers is 12000<Re<35000. The main goal of the work is to establish a CFD procedure to analyse the flow pattern in the vicinity of the bodies and to predict the position of the boundary layer detachment. The computations are performed with several turbulence models implemented in the ANSYS Fluent code. The direct visualizations and the numerical results are corroborated, with the aim to investigate the positions of the separation points and the flow spectrum developed downstream the bodies.
Evolution of renewable energy consumption in the European countries
Authors: Stoenoiu C E , Balan M C , Serban F M , Cristea C
Published: May 2021

This study performs an exploratory analysis of the evolution of consumption of RES for EU28 countries over the ten years studied. Through the analysis, the document presents: the consumption by sectors of production and by renewable energy sources, analyses the evolution of consumption from RES: between countries and regions. Regarding the consumption of RES, it is increasing, reaching in 2017 compared to 2008 to increase by 147.8%.
Numerical investigation of a reduced scale Lenz wind turbine model for aerodynamic tunnel applications
Authors: Bucur I O , Malael I , Preda D
Published: May 2021

Renewable energy sources represent efficient and reliable energy solutions for the modern world, as they are eco-friendly alternatives to fossil fuels or nuclear power plants. The technologies available nowadays allow researchers to perform in-depth computational fluid dynamics analysis for systems that can generate green energy. The wind energy industry developed considerably as classic wind turbine models (horizontal axis wind turbines and vertical axis wind turbines) are constantly optimized and new configurations are studied in order to asses better performances. This paper presents the numerical investigation campaign of a reduced scale Lenz wind turbine model. The Lenz model has three blades that are attached directly on a vertical shaft. For the numerical simulations of the model, the ANSYS Fluent software is employed. For the evaluation of its self-starting behaviour the six degree of freedom method was employed and the configuration was studied for different moments of inertia. Furthermore, the chosen range of inlet velocities allowed the investigation of the influence of high Reynolds numbers on the proposed Lenz model and the vorticity magnitude contours were computed for different azimuth angles. Future work includes the validation of the numerical results with experimental data obtained during a wind tunnel testing campaign.
Performance of autoclaved aerated concrete (AAC) exposed to standard fire
Authors: Stanescu Adrian Andrei , Lalu Octavian , Luca Oana , Gaman Florian
Published: May 2021

This paper presents the results of an experimental study carried out within the National Institute for Research, Development in Constructions, Urbanism and Sustainable Territorial Development URBAN INCERC, on a system of walls made of ACC blocks, according to the standard SR EN 771-4 [8], having a density of 480 kg/m3 and standardized compressive strength of 3.5 N/mm2, using mortar type binder class M2.5 with compressive strength of 2.5 N/mm2. It was exposed to the action of standardized fire for a period of 220 minutes, after 10 days from the execution of the masonry. The results showed that, following the tests on the burned samples, extracted from the wall subject to the test, the standardized unit compressive strength decreased by 54%.
Parameter tuning process for a closed-loop pneumatic actuator
Authors: Cococi V N , Safta C A , Călinoiu C
Published: May 2021

Pneumatic drives are light weight, small-sizes, simple to install and to maintain. Pneumatic drives have a robust design and operation. They are clean and cheap, have no temperature limitation, and so, they are preferred in many branches of manufacturing and process industry. The well-known pneumatic actuators are widely used in closed-loop positioning systems because of their dynamic performance and mechanical flexibility in different electro-mechanical systems arrangements. The goal of the paper is to find the parameters of a closed-loop pneumatic actuator so that a good dynamic behaviour of the system is obtained. The parametric tuning process is developed by using numerical simulation technique. So, it was seen that using a proportional controller, the pneumatic actuator has an asymptotic stability for different values of the proportional gain K

p
. Starting with K

p
= 8 the system remains stable, but oscillations of low amplitude appears.
Review on Modern Photovoltaic Panels – Technologies and Performances
Authors: Budea S , Safta C A
Published: May 2021

In this article, the authors reviewed the modern technologies for manufacturing transparent, bifacial, flexible panels and other similar solutions. Passive or active cooling solutions, with air or water vapor, or energy storage solutions are analysed. If the passive air cooling of the photovoltaic panel can achieve a reduction of its temperature by only 10 °C, by active cooling, a cooling with over 30 °C can be obtained. These technologies are aimed to improve the energy efficiency of photovoltaic panels. The article presents examples of photovoltaic panels’ own applications, as well as hybrid PV, realizing the cooling of the PV panel and the recovery of the thermal energy in the form of hot air or hot water, with good efficiency.
Forecasting solar radiation using a deep long short-term memory artificial neural network
Authors: Carutasiu Mihail-Bogdan , Ionescu Alin , Ionescu Constantin , Necula Horia
Published: May 2021

Solar systems are widely used to mitigate the environmental impact of the energy sector and their importance has constantly increased due to the recent EU’s strategy to lower the CO2 emissions. Moreover, the newest Energy of Buildings Directive empathises the importance of producing energy from renewable sources to decrease the overall impact of buildings over the total end-use energy consumption. Generally, the systems’ performances are highly correlated with the incident solar radiation and outdoor air temperature. Thus, being able to accurately forecast these two parameters represents a vital step in dimensioning and maximizing the overall energy production. This Paper presents the results obtained by implementing a deep recurrent artificial neural network (ANN) trained with on year solar radiation data harvested from the UPB campus. The time series data was modelled using a special ANN architecture – the LSTM (Long Short-Term Memory) – due to its special designed internal ‘memory’ which increases its capabilities of predicting temporal sequence data. The model uses sequences of 24 hours and the resulted mean squared error (mse) for both training and validation data is under 30%.
Modelling the active sludge treatment process in recirculation basins using the simulink environment
Authors: Dordescu M , Nicolescu F
Published: May 2021

In the global context of environmental protection and the reduction of its pollution, wastewater treatment has a special role. Starting from this general framework and considering the need for an integrated approach to water as a natural resource, the aim is to introduce new treatment technologies in which human intervention tends to zero. That is why modelling, and simulation techniques highlight automation solutions and their implementation. In our paper we tried to model a biological purification process using Simulink techniques.
Hydraulic Modelling of the Water Supply System of Năsăud City, Bistriţa Năsăud County
Authors: Agafiţei Alina , Pavel Vasile Lucian , Rlan Toma Cristina Mihaela V. , Toma Daniel
Published: May 2021

The paper presents a study of hydraulic modelling of the drinking water and sewage distribution network in Nasaud City, Bistrija Nasaud County from Romania, which includes a calibrated simulation of the flow through networks, and allows the elaboration of a future strategy of developing the networks of water and sewage. The need to develop hydraulic models as accurately as possible results from the fact that, by creating and calibrating the hydraulic model of a system, a variety of system problems can be identified, solutions can be mitigated to them by addressing the problem of rehabilitation, expansion or design of new systems. The results can be tracked both at the scale of time, and in real time by simulating the functioning of the system at these time scales. We decided to approach the problems of sizing and verifying the network using software solutions packages, in this case the MIKE URBAN calculation program, which can import and export network data as ESRI ArcView shape files, allowing the network data to be directly imported and exported into and from ArcView. Thus, the network is completely resolved, the calculation of hydraulic sizing and verification of the network being performed in all nodes.
Total equivalent warming impact calculation for air conditioning technological application
Authors: Vinceriuc M , Tarlea G M
Published: May 2021

This paper shows an aggregated compact cooling liquids (refrigeration system) used in air conditioning technological process who works in present with R407C refrigerant. The paper has focused on theoretical study case. Regarding F-Gas Regulation the optimum alternative for this application is R134a refrigerant with Total Equivalent Warming Impact (TEWI) calculation.
Effect of DO, Alkalinity and pH on Nitrification Using Three Different Sunken Materials Types in Biological Aerated Filter BAFs
Authors: Faskol A S , Racoviţeanu G
Published: May 2021

The overall aim of this search investigated the effect of DO, alkalinity, and pH on nitrification in biological aerated filter system BAFs. The laboratory experiments by three identical pilot-scales downflow of BAFs using three different sunken materials types, 0.78±0.60 mm activated carbon-based material bed, 0.95±0.58 mm sand-based material bed, and 3.28±2.14 mm ceramic particle-based material bed, as attached growth zone in the treatment of municipal wastewater. As results of the experiments showed that activated carbon-based material bed when the mean concentration of dissolved oxygen was 6.76±2.25 mg/L and the mean alkalinity concentration was 77.25±2.60 mg CaCO3/L and the mean pH value was 7.21±0.20 the mean nitrification efficiency has reached of 90.11%. In the sand-based material bed when the mean concentration of dissolved oxygen was 7.33±1.82 mg/L and the mean alkalinity concentration was 77.56±2.77 mg CaCO3/L and the mean pH value was 7.22±0.20 the mean nitrification efficiency has reached of 87.74%. In the ceramic particle-based material bed when the mean concentration of dissolved oxygen was 6.37±1.84 mg/L and the mean alkalinity concentration was 77.31±2.71 mg CaCO3/L and the mean pH value was 7.22±0.20 the mean nitrification efficiency has reached of 85.17%.
Analysis of numerical and experimental results of a solar glazed air collector configuration in Romania climate
Authors: Sima C , Teodosiu C , Croitoru C , Bode F
Published: May 2021

This paper proposes an experimental and numerical study (based on CFD – Computational Fluid Dynamics technique) dealing with a glazed transpired solar collector (GTC), having the distance between the glass and absorber plate of 50 mm. The behaviour of the GTC has been studied for different air flow rates. Based on the results obtained, it can be concluded that this GTC configuration behaves best for air flow rates of about 300 m3/h. On the other hand, further studies are needed to improve the numerical model (especially regarding the introduction of boundary conditions based on measured data).
Seismic performance assessment based on displacement capacity of unreinforced masonry structures
Authors: Scupin A , Văcăreanu R , Pavel F
Published: May 2021

The National Geological Museum is a representative building for the typology of historic unreinforced masonry structures built in Romania at the beginning of the XX century. The seismic behaviour was studied with respect to the displacement capacity, by comparing the initial structural configuration of the building with the retrofitted one. Taking into account the irregularities of the structure and the localized reinforced concrete jacketing works done in the 80s’, global results were proven to be misleading. Thus, relative floor displacements were used to study the behaviour of individual walls involved in local failures. Limit state thresholds based on relative displacements were used in order to calibrate the initial model with the post-earthquake damage assessment and then they were compared to the results obtained for the retrofitted model to establish the effectiveness of the strengthening works.
General design considerations for applying thermal insulation layers underneath foundations of buildings placed within the main seismic regions of Romania
Authors: Popescu Andrei-Laurenţiu
Published: May 2021

Worldwide common efforts towards developing a sustainable, competitive, eco-friendly and efficient built environment have led to a new legal and technical spectrum of rules and requirements for high energy performance buildings. Provision of solutions for a continuous thermal envelope is sometimes essential in designing such buildings. Mitigating, as much as possible, the thermal bridging phenomenon is highly important and should be accounted from the very beginning in the design process. This issue can be addressed through various solutions when it comes to thermally insulating the superstructure but can be quite challenging and limited at infrastructure level, particularly for buildings set in areas exposed to earthquakes. This paper explores existing technical literature, local codes, norms and standards, with the twofold purpose of: (1) providing a view on the relevant available research and design prescriptions; and (2) outlining incipient general design considerations related to the feasibility of applying specific thermal insulation materials beneath buildings located within the main seismic regions of Romania.
Experimental study of the chemo-mechanical properties of the interfacial transition zone of concrete
Authors: Girboveanu A , Jebli M , Jamin F , Huon V , El Youssoufi M S , Georgescu D P
Published: May 2021

This article presents an experimental study of the chemical and mechanical properties of the cement paste / aggregate interphase. Interfacial Transition Zone (ITZ) represent the contact zone of the cement paste with the aggregate with a thickness of about 20 - 50 μm. This zone has different mechanical and chemical properties compared to the bulk paste. Cement paste / limestone aggregate composite samples were performed to allow the study of the chemical and mechanical properties of ITZ. The cement paste is made with Portland cement with a water/cement mass ratio of 0.4. Calcium concentration profiles in the ITZ show a high concentration of calcium due to the presence of portlandite and ettringite. The nano-indentation tests indicate weakness of ITZ compared to bulk cement paste.