Abstract: In this paper, the stability of an equilibrium of a feedback nonlinear system with time delay and structural switching is studied. The critical case of a zero root of the characteristic equations of the linearised systems is treated by applying a Malkin-type theorem using a complete Lyapunov-Krasovskii functional.

Abstract: Turbulence is one of the most common phenomena that cause damage for aviation also characterized by a low degree of predictability. The main objective of the CONTUR campaigns ("Emerging Technologies to Counteract the Effects Induced by the Turbulent Flows of Fluid Environments") was to use a synergy of instruments to validate lidar in its mission to detect a particular type of turbulence, Clear Air Turbulence (CAT), with significant importance for aviation. To detect CAT, we used as a proxy thermal turbulences which can be detected using ground-based lidars. Turbulences formed in the planetary boundary layer can be detected by lidars because pressure gradients generate variations of the molecular depolarization values but on specific conditions. A synergy of instruments with different wavelengths of the emitted radiation can increase the accuracy of observations in the investigated areas thus validating the results. In this study, we show the results from several measurement campaigns using a Raman lidar, a Doppler wind lidar, and a Sodar. These instruments were installed at a site in the south-western part of Bucharest and the measurements collected were used in a synergetic manner to understand CAT.

Abstract: A topical issue in atmospheric science is to find ways to detect and predict clear-air turbulence (CAT). CAT is a physical phenomenon produced by the turbulent movements of air masses in cloudless areas that has potentially disastrous consequences for aircraft and/or passengers, being undetectable by the on-board equipment. In this paper, a new approach of the CAT attenuation methodology is proposed based on active control. The experimental model is represented by a realistic, elastic wing with aileron controlled by an electric linear servoactuator. Numerical simulations and experiments in the subsonic wind tunnel upgraded with a turbulence generator were performed.

Abstract: Clear air turbulence (CAT) poses a significant threat to aviation. CAT usually occurs in the lower stratosphere and the upper troposphere. It is generally associated with large scale waves, mountain waves, jet streams, upper-level fronts and tropopause folds. Aircraft can experience CAT when flying in proximity of a tropopause fold. To better understand and diagnose tropopause foldassociated CAT we selected a series of cases from among those reported by pilots between June 2017 and December 2018 in the Romanian airspace. Data on turbulence were used in conjunction with meteorological data, satellite imagery, and vertical profiles. Additionally, a set of indices as Ellrod, horizontal temperature gradient, Dutton, and Brown were computed to diagnose CAT associated with tropopause folding. These indices were also analyzed to test the physics mechanisms that may explain the occurrence of severe turbulence. Results show that out of the 420 cases announced by pilots, severe turbulence was reported in 80 cases of which 13 were associated with tropopause folding.

Abstract: In this paper, a Lyapunov-Krasovskii functional is used to obtain sufficient conditions of asymptotic stability for the equilibrium of a nonlinear feedback system with state-dependent uncontrolled switching, herein called structural switching, and with actuator delay. The solution of the problem is addressed in two steps. First, a predictive feedback method is used to compensate the actuator delay of the associated linearized system. Thus, the time-delayed control is replaced with a state delay, and the effect of the control appears in a non-homogeneous term in the linearized system. Second, a theorem of asymptotic stability of equilibrium is obtained for the nonlinear switched system, whose linearized components were considered separately in the first step. The result is also valid for certain problems of state-dependent controlled switching. The numerical application, done on a consecrated real world system, the electrohydraulic servomechanism, highlights real difficulties, which are usually avoided by academic constructs in which the results are sometimes illustrated on insignificant models, represented, for example, by 2 x 2 didactic matrices.

Abstract: In aerodynamics, the phenomenon of flutter suppression represents a great challenge. Since it is a complex and difficult process, it requires an innovative approach. In this paper, a V-shaped piezoelectric actuator whose role is to widen the aircraft flight envelope by raising the speed limit at which flutter occurs is presented. The demonstrator is in fact an intelligent model of wing, which is itself a control system, with sensors, piezo actuator and an implemented control law. The control law is obtained through the receptance method of eigenvalues assignment using the measured transfer function. The content of the paper refers to technical solutions for wing model design and to experimental results in subsonic wind tunnel. Another contribution of the paper concern the consideration of a time-delayed feedback control.

Abstract: Clear Air Turbulence (CAT) also known as upper air turbulence is a sudden, hazardous weather phenomenon occurring in cloudless regions and affecting especially commercial aircrafts. In case of a CAT encounter, an aircraft may suffer violent buffeting. Generally, during CAT episodes, passengers experience discomfort, but if caught unaware and not buckled up they may even sustain serious injuries. The aim of this work is to obtain a distribution of the turbulence events over the Romanian airspace, taking into account the aircraft flight levels (FLs) and the Romanian orography. Our study was carried out using 429 subjective pilot reports (AIREPs) covering a 19 months period (June 2017- December 2018). 81 of them were reported as severe turbulences, but only 51 were severe turbulence cases occurred at FL350 or higher (maybe CAT). These reports provide useful information on the occurrence of turbulences, but they are not always reliable in terms of spatial and temporal accuracy. In order to find the probability that the 51 cases were actually CAT cases, we computed the Richardson number (Ri), the Ellord (TI1) and the Dutton indices. Satellite data and meteorological parameters associated to synoptic patterns were used to diagnose the turbulence cases. The Ellrod (TI1) index proved to have the best consistency with the 51 pilot reports, but only for a few of them its values were indicative of CAT events. An important number of the 51 cases were reported over the western part of Romania as most of domestic and international flights overfly that area.

Abstract: Clear Air Turbulence (CAT) pose a threat to aviation and because are difficult to forecast represent an issue for many aviation forecasting centers. CAT usually occurs in the lower stratosphere and upper troposphere and it is associated in general with large scale waves, mountain waves, jet streams, upper-level fronts, and tropopause folds. Tropopause folds are extrusions of stratospheric air into the troposphere occurring near an upper-level frontal zone beneath the polar and subtropical jet streams. An aircraft will experience CAT when flying in the proximity of a tropopause fold. To better understand and diagnose CAT associated with tropopause folds, a series of cases were selected from all turbulence cases reported by pilots (i.e. airport report, AIREP) between 2017 - 2018 in the Romanian airspace. The data on turbulence were used in conjunction with synoptic data, EUMESAT satellite imagery, and vertical profiles (i.e. wind, potential temperature, potential vorticity) from ECMWF ERA-Interim. Using satellite imagery the tropopause folding area can be easily identified as being in the cold region of the jet-stream, close to the maximum Water Vapor gradient. In addition, a set of indices as ELLROD (TI1, TI2), Richardson number (Ri), Potential Vorticity (PV) were computed to diagnose the Clear Air Turbulence for the cases of tropopause folding. The indices values were also analyzed in order to test the physics mechanism explaining the occurrence of severe turbulence.The results showed that out of the 430 cases reported by pilots, severe turbulence was reported in 82 cases of which few where associated with tropopause folding.

Abstract: In severe cases CAT can potentially be hazardous to the health and safety of air travellers. Higher frequencies of such phenomena are expected as a result of climate change and the ever increasing number of commercial flights. The first testing campaign to detect CAT events took place between 10 and 14 September 2018. The objective of the campaign was to conduct tests to assess the performance of CAT detection using existing LIDAR systems at INOE 2000 (National Institute for Research and Development in Optoelectronics), Bucharest and UBB (Babes - Bolyai University), Cluj - Napoca, Romania.
The CONTUR1 campaign was focused on the detection of turbulent phenomena caused by the passage of large - scale airplanes - wake turbulence. This type of turbulence can be marked in space and time by continuous air trafficmonitoring over the site.

Abstract: The work starts from the linearization of a nonlinear mathematical model of the electrohydraulic servomechanism with structural switching and delayed control. The delay, as well as the switching structure, can lead to instability and to the deterioration of the dynamic system performance. Between the different approaches to the delay problem, this article considers the predictive feedback method. The question of switching structure is herein treated empirically, aiming in the numerical simulation not to impose on the system a magnitude of the disturbance of the zero equilibrium that leads to switching by changing the sign of the state variable which is the displacement of the servovalve spool. Numerical simulations allow to highlight a critical delay, which is attested by comparison to an analytical method.

Abstract: A very important component of the flight control of the airplane is the hydraulic servomechanism, which can be mechanical or electrical. In this paper a mathematical model for an electrohydraulic servomechanism (EHS) is proposed. EHS is modeled by a five-dimensional switched nonlinear system of differential equations. The novelty of the paper consists in approaching the presence of time delay in the mathematical model and in the study of the stabilization problem that arises. Since the ESH is an automatic system, there are two possible location of the delay: on state variable or on control variable. A study of the stability in the presence of delay on control will be presented.

Abstract: In the present paper a simple stability theorem is proposed for a complex nonlinear system with time-delay introduced on state and switching character. The study of the equilibrium point is made on the basis of a complete Lyapunov-Krasovskii functional. The matrix of the system has two simple zero roots which implies the framework of a Malkin type approach. The mathematical model has engineering applications such as mechanohydraulic and electrohydraulic servomechanisms that control the primary flight surfaces of the aircraft, as well as the case of an airplane wing with aileron controlled by a control law in order to attenuate vibrations and counteract turbulent perturbations.

Abstract: In aerodynamics, the phenomenon of flutter suppression represents a great challenge. Since it is a complex and difficult process, it requires an innovative approach. In this paper, a V-shaped piezoelectric actuator whose role is to widen the aircraft flight envelope by raising the speed limit at which flutter occurs is presented. The demonstrator is in fact an intelligent model of wing, which is itself a control system, with sensors, piezo actuator and an implemented control law. The control law is obtained through the receptance method of eigenvalues assignment using the measured transfer function. The content of the paper refers to technical solutions for wing model design and to experimental results in subsonic wind tunnel. Another contribution of the paper concern the consideration of a time-delayed feedback control.

Abstract: Aviation operations are often affected by some dangerous phenomena that cannot be directly observed, as volcanic ash, high concentrations of dust or Clear Air Turbulence (CAT). Therefore, a conceptual model would provide a useful tool to monitor, track and identify these elements during the forecasting processes.

Abstract: Besides the immediate effects of the biomass burning (BB) at social and economic scales, the longterm effects represent a source of pollution with consequences ranging from the effect on the Earth's radiative budget to meteorology (reduced visibility) or health issues when the pollution layers enter into the Planetary Boundary Layer. The geometry and the optical properties of the BB pollution layers can be studied by means of the lidars. In this study, the aerosol profiles stored in EARLINET database will be used to characterise the optical properties of the BB aerosol as recorded over Europe between 2000 and 2017. Several studies on BB were carried out over Europe: Southeast, West or Central and East.

Abstract: The complexity of fog formation, evolution and dissipation processes depends on physical and chemical properties of aerosols. Particulate matter concentration is much higher on hazy/foggy days, and fine-mode aerosols are predominant. Fog is influenced not only by local pollution but also by long range transport. Large scale atmospheric circulation could be a reason of aerosol concentration enhancement and also influences meteorological conditions for fog formation. Anticyclonic conditions, calm wind and pollutant settling around the droplet are the main conditions for radiation fog forming. Ground based remote sensing equipment and aerosol chemical speciation monitors [6] have been successfully used in many fog studies.

Abstract: An issue of security in aviation is the instability of the aircraft's flexible control surfaces caused by uncontrolled vibrations. Flutter is a violent vibration whose amplitude grows strongly in a short time. Once the flutter is reached, the plane is destabilized and it can no longer be controlled. In this paper it is proposed a specially designed demonstrator to extend the flight envelope by rising the speed limit at which flutter occurs. Antiflutter demonstrator is an intelligent airplane wing model made from a longeron covered by an aerodynamic layer. The wing has a primary flight control surface, an aileron, at one end, and at the other end there is a flange whose role is to fix the wing in the subsonic tunnel. The actuator consists in two V-shaped piezo stacks. The main advantage of the piezo actuator, the bandwidth (about 30 Hz), is exploited. The aero-elastic control is efficient if the deflection of the control surface is a few degrees while the frequency is at least 25-30 Hz. The control law is obtained through the receptance control method of eigenvalues assignment which is focused on measurements rather than on the conventional matrix theory.

Abstract: Two piezoelectric stacks are used as a V-shaped actuator for aerospace applications to increase the flutter speed and thus to widen the aircraft flight envelope. Flutter is a self-sustaining unstable strong oscillation of the aerospace structure whose amplitude increases in an unexpected way, leading to catastrophe. Using a piezoelectric actuator, an antiflutter demonstrator was conceived which is itself a wing model with an implemented control law. It was designed, manufactured, and tested in INCAS laboratories. The main advantage of the piezo actuator, the bandwidth (about 30 Hz, versus the measured about 5 Hz flutter frequency), is exploited. The synthesis of the control law is based on a new and powerful method named receptance method of poles assignment whose main advantage is that the control law is obtained based on online measurements rather than on the conventional matrix theory, thus avoiding the difficult operations of mathematical modeling and observer building to estimate the unmeasured state variables.

Abstract: An aviation hazard means any condition, event, or circumstance which could induce a harmful effect on an aircraft. One of the most dangerous is the clear air turbulence (CAT). This is a high altitude, sudden phenomenon encountered outside of convective clouds that causes violent buffeting of aircrafts. CAT is especially troublesome because it is often encountered unexpectedly and in commercial aviation it is a leading cause for injuries to cabin crew and passengers and the cause of million dollar and euro damages each year to airlines. However, a number of tools, including forecasts, are available to pilots for the avoidance of CAT. They are reviewed in this paper. A large consortium of institutions joined their efforts within a complex project, named CONTUR, presently ongoing in Romania, to study, detect and forecast the CAT phenomenon, as well as to develop emergent technologies that counteract its structural effects on aircrafts. Details about the under-way activities of this project are also brought forward in this paper.

Abstract: A very important component of the flight control of the airplane is the hydraulic servomechanism, which can be mechanical or electrical. In this paper a mathematical model for an electrohydraulic servomechanism (EHS) is proposed. EHS is modeled by a five dimensional switched nonlinear system of differential equations. The novelty of the paper consists in approaching the presence of time delay in the mathematical model and in the study of the stabilization problem that arises. Since the ESH is an automatic system, there are two possible location of the delay: on state variable or on control variable. A study of the stability in the presence of delay on control will be presented.

Abstract: Hydraulic servomechanism, as part of the flight control system, is of crucial importance for the airplane dynamics and safety. The electrohydraulic servomechanism is an automatic tracking system of the reference inputs launched by the automatic pilot. On this input channel of the control system there can be factors that lead to a delay in receiving the reference inputs by the servomechanism. In this paper the emphasis is on the synthesis of time delay control law and on the development of numerical simulations which describe the effects induced by the control delay. The mathematical model from which we start is a nonlinear system of five differential equations, and the way to solve this problem is the method of predicted feedback control.

Abstract: Electrohydraulic servomechanisms represent a field of maximum attractiveness in many industrial fields for about 70 years, but special attention is paid in particular to the performance and quality of these automatic systems in flight controls of aircraft. Electrohydraulic servomechanism considered in this paper is modeled by five dimensional switched nonlinear systems of differential equations. Intrinsically, the mathematical model of the electrohydraulic servomechanism has several shortcomings: critical case for stability and switching type nonlinearity. The shortcoming of the critical case of stability was eliminated in this paper by naturally introducing the internal leakage between the two chambers of the hydraulic cylinder in the mathematical model. Instead, the control delay was introduced, also naturally. It is worth mentioning that this mixed problem, of the electrohydraulic servomechanism switching type delayed mathematical model, is quite difficult in itself and has not been considered, as far as we know.

Abstract: Clear Air Turbulence (CAT) are hard to predict phenomena and also hard to detect ore sense in advance. Unlike other types of turbulence, for CAT there are no radar returns for the Airborne Weather Radar). This paper is an attempt to find a correlation between the CAT encounters as reported by pilots, and the relevant weather parameters obtained from the meteorological nowcast. The focus was on the gradients of the atmospheric pressure and temperature. Pilot reports (PIREPs) and weather data were retrieved from international databases (Iowa University Mesonet and National Oceanic and Atmospheric Administration).

Abstract: Wind shear and gusts are weather phenomena dangerous for aviation as well as for terrestrial systems. The objective of this work is to investigate the aerodynamic effects of these atmospheric phenomena on the elastic light structures specific for aerial vehicles. The calculations are done with a vortex-lattice method and a fluid-structure interaction solver. The results include an evaluation of the aerodynamic force changes in the case of an elastic wing and on the aeroelastic response of the wing.

Abstract: The current paper deals with calculating the accelerations on an airplane subjected to a gust. The longitudinal equations of symmetric flight of the airplane are written to include the effect of the vertical wind. Analytical solutions originating in the linearized equations of motion of the longitudinal channel (with wind effects included) are discussed.

Abstract: The main objective of the work is the validation of a control strategy for the wing model tested in the wind tunnel (WT) for several air speeds. The mathematical model of the wing, obtained by experimental identification, is a set of linear systems associated with several air speeds in WT. Introducing the actuator delay into the model is a common paradigm in the field. It is defined a problem of active control synthesis for a switching system with delay on the actuator. A predictive feedback method is used to compensate the actuator delay of the associated linearized system. Thus, the time-delayed control is replaced by a state delay, and the effect of the control appears in a non-homogeneous term in the linearized system. A theorem that gives sufficient conditions for stability, recently published by the authors of the present work, is now applied in the case of the wing model. Numerical simulations will highlight some aspects regarding the conservative character of the theorem.

Abstract: Atmospheric turbulence in lower troposphere or in upper troposphere and lower stratosphere (UTLS) is a current issue in modern days in the context of airline safety since no feasible technical solution is available to detect and avoid it. Project CONTUR ("Emerging Technologies to Counteract the Effects Induced by the Turbulent Flows of Fluid Environments") aims to develop emerging technologies to detect the presence of clear air turbulence (CAT) in UTLS layer, by remote sensing lidar techniques in order to solve the specific problems generated by the turbulence phenomena in airline transportation. The know-how collected during the first part of the project showed that using a singular lidar instrument is insufficient to clearly detect turbulent episodes. Therefore, the third campaign performed in the framework of CONTUR was focused on using a synergy of 3 instruments to validate lidar data in detecting CAT events. The focus of this campaign was to study thermal turbulence that occur in the lower troposphere (in atmospheric boundary layer up to 5 km altitude). A synergy of lidar and wind profilers could increase the resolution of the investigated area (Magurele, Romania) and provide information to complex factors responsible on turbulence. The results obtained in this campaign emphasized that using synergetic data obtained in boundary layer allow comparison between atmospheric different turbulence types. Thus, physical processes in UTLS can be explained by some parameters obtained in the turbulent processes in lower troposphere.

Abstract: The CONTUR project has open up new horizons for the activities aimed at counteracting the effects induced by the atmospheric turbulent flows. A tenable interinstitutional collaboration beyond the completion of the CONTUR project is to be implemented. The institutional developments with an impact on turbulent flow studies have to be considered. The most relevant topics to be included in the future joint program for research, development and innovation (CDI) will be presented and discussed.

Abstract: A main objective of the CONTUR project is the validation of a control strategy for the aileron wing model tested in the aerodynamic tunnel in the presence of a specially built turbulence generator. Two synthesis strategies of the active control performed by the actuator are considered: one non-standard, based on the so-called receptance method, and a second one, of classical type, with a control law from the family of methods with quadratic cost indices (LQR, H_infinity). Some specific aspects will be considered in the second case, such as: the influence of the actuator delay, the stability in the presence of on-line switching of the control gain etc.

Abstract: The behavior of the aircraft within turbulent atmosphere is a key aspect of design. Many books and articles deal with this topic. The current paper presents studies related to predicting the responses of aircraft flying through vertical gusts. The equations describing the dynamics of the longitudinal channel of the airplane are written to include the effect of the vertical wind. The paper includes comparisons results provided by non-linear and linearized equations of motion.

Abstract: The aim of this work is to study cases of severe turbulence associated with high vertical wind shear environments and to determine a causal distribution among CAT events. Atmospheric turbulence is a major hazard for aviation, with potential effects ranging from increased workload and stress amounts to pilots and air traffic controllers to injuries to passengers and crew, in some extreme cases. The study used a a database of 421 pilot reports (AIREP) for aircraft turbulence issued between June 2017 and Dec 2018 in the Romanian airspace. From the 421 AIREP, 78 were for severe turbulence and 49 of them were localized in the upper troposphere and lower stratosphere (UTLS) leading to their assignation to the clear air turbulence (CAT) category, after a confirmation via the analysis of corresponding satellite images. In a previous study (Livius Buzdugan et al., 2019) using the ERA-40 reanalysis data, the following turbulence indices/ predictors were computed for each severe turbulence event: Richardson number (Ri), Ellrod TI1 (Ellrod and Knapp, 1992) and TI2 (Sharman et al. 2006), Colson-Panofsky (CP) and horizontal temperature gradient magnitude. Ellrod TI1 index was confirmed as having the best performance in severe CAT diagnostics. The good performance of TI1 is analyzed in this study in terms of the vertical shear/ deformation contributors. Supplementary, the 300 hPa relative vorticity advection field is used as a proxy for imbalance linked gravity waves as possible cause for the severe CAT events (Knox et al., 2008). The results confirm the role of high vertical wind shear environments and relative vorticity advection in the generation of CAT within the studied domain and the operational benefits of using TI1 index as a diagnostic tool for CAT.

Abstract: Forecasting low level turbulence is one of the major challenges in operational aeronautical meteorology. The aim of this work is the study of some particular aspects of orographically induced wave motions, focusing on the so called "breaking waves". The impact of breaking waves on aviation operations, mainly on low-level flights might be major, conducting up to major accidents of light aircrafts due to turbulence. Therefore, the subject is important because a better understanding of the physical mechanisms on breaking waves increases the accuracy in forecasting orographic waves, mitigating the probability of aeronautical incidents occurrence, and, consequently, an increase in aviation safety. The wave motions are perhaps the best understood phenomena induced by air flowing over varying terrain. The waves induced by orography can propagate at significant distances downstream, depending on the wind and temperature profiles. There are two major disturbances associated to orographic waves: lee waves and breaking waves. If the first one is easily identified and quite frequent, the latest occurs not often enough to be studied more in depth. In this respect, even if the physical aspects of the phenomena are deeply studied, the in-situ conditions can have an unexpected impact. Taking into account the specifics of aviation operational forecasting, location identification and estimation of intensity of manifestation needs a tool to be used in real-time. Romanian topography being far from ideal, an effective forecast needs complex calculations that are difficult to be applied in quasi real-time as needed in aviation. Therefore, a conceptual approach, based on satellite imagery interpretation, is essential in short-range forecasting of phenomena as breaking waves, taking into account the complexity of terrain and dynamics of the subjacent surface. We developed, based on mountain wave conceptual models associated with shallow water wave theory, a proposal for a conceptual approach in order to identify, in real-time, the potential of atmospheric breaking waves development. The results obtained for a few breaking waves' cases confirm that our improved conceptual approach allows the forecasting in quasi real-time.

Abstract: Atmospheric turbulence has always been a challenging issue for the aviation industry due to the various complications it causes during flights. It is more detrimental for commercial airlines, since the flight routes are planned in such a way as to save as much money on fuel as possible and to respect a certain time schedule. Today's airlines use a complex algorithm called GTG (Graphical Turbulence Guidance) that analyses data from various sources in order to forecast turbulence regions at altitudes from 6 to 12 km (around the tropopause). An important parameter used by the newest version of the algorithm is EDR (eddy dissipation rate), which measures the intensity of the turbulence region. Not only are in situ EDR measurements consistent with the theoretical analysis, but are also a useful addition to PIREPs data (pilot reports). One of the most useful properties of EDR is that it is independent of aircraft type and it can be measured on the ground as well as in the air. In the last two decades there have been numerous data analyses and experimental verifications that validate the use of EDR in modern forecasting algorithms and also encourage any future improvements. The goal of this presentation is to validate the use of EDR in aviation and put forward all of its advantages in order to emphasize the importance of the current and future studies made on the subject of Eddy Dissipation Rate.

Abstract: Convective turbulences, usually associated with thunderstorms, are one of the main factors that generates convective clouds (i.e. cumulonimbus). They are formed in the Planetary Boundary Layer (PBL) when warm air masses rise, especially in warm summer days. The main objective of the second CONTUR (Emerging Technologies to Counteract the Effects Induced by the Turbulent Flows of Fluid Environments) campaign was to investigate the capability of ground-based lidar instruments to detect this type of turbulence. It is assumed that thermal turbulences can be detected by lidar since pressure gradients generate variations of the molecular depolarization values. If the collected data indicate that Lidar instruments are able to detect thermal turbulence at low altitudes, a similar optimized instrument can be developed to be used on different research aircrafts for the detection of high-altitude turbulences - CAT.

Abstract: The paper deals with a study regarding the influence of the atmospheric turbulences on airplanes and passengers. A significant number of people are injured yearly by turbulences, while not wearing seatbelts. Sometimes, the atmospheric turbulences require an aircraft to divert, with all the inconvenience and associated costs that entails. Lacking accurate information to guide them, pilots may opt to minimize risk, but this can adversely impact fuel costs. With industry-wide sharing of actual occurrences, in real time, pilots could take appropriate action with confidence. Aviation experts describe turbulence as random, unpredictable motion occurring between layers of air moving at different speeds. A number of agencies, including the Federal Aviation Administration (FAA) along with the airlines, developed different technologies that could help the pilots avoiding the encountered turbulences. There are five type of atmospheric turbulences: convective turbulences, mechanical turbulences, mountain-wave turbulences, wake turbulences, and clean-air turbulences. The aviation community, in order to provide a standard for reporting and describing turbulence, has classified turbulence into intensities according to its effect on aircraft and occupants as follows: 1) light (no difficulty for the cabin); 2) moderate (the passengers have to strain their seat belts); 3) severe (Passengers are pushed violently against their seat belts); 4) extreme (the plane is very difficult if not impossible to control). From the mathematical description point of view, the atmospheric turbulence is a stochastic process defined by velocity spectra; there are two spectral forms for the atmospheric turbulences, provided by Dryden & von Karman and adopted by the International Civil Aviation Organization Standard Atmosphere. In the Dryden spectral model, the forming filters are derived from the spectral square roots of the spectrum equations, the definitions of the longitudinal, lateral, and vertical component spectra functions being provided by MIL-HDBK-1797/1797B. NASA, FAA, and other research groups work to develop onboard turbulence detection and display systems that have to provide to the pilot a direct indication of the severity of turbulences ahead of the aircraft. Therefore, this kind of system is still an open research chapter.

Abstract: Aeolus is the first space mission designed to retrieve wind profiles at a global scale. The Aeolus mission is part of the "Earth Explorers" program developed by ESA, and is equipped with a single instrument, a wind lidar generically named ALADIN. These lidar observations will significantly improve weather and climatic forecasts.
As for any new earth observation mission, calibration and validation (CAL/VAL) activities are organized using, among others, ground based remote sensing instruments. In Romania two ground based multi-wavelength Raman and depolarization lidar stations from the EARLINET (www.earlinet.org) and ACTRIS (www.actris.eu) European networks are involved in the CAL/VAL of the Aeolus L2A aerosol product: INOE2000, Magurele, and UBB in Cluj-Napoca. The L2A product gives information about aerosol and cloud profiles along the satellite's orbit.
For the CAL/Val activities, a measurement plan was set at the two stations up considering the orbits of Aeolus (overpass within a 100 km radius from each station). The measurement plan generally consists of two 3h nighttime measurement sets / week and one 2h daytime measurement. For Aeolus two more weekly measurement 4h sets were added taking into account the overpass schedule.
The work presented, shows preliminary measurements from the two lidar stations obtained during Aeolus overpasses. An in-depth comparative analysis will be carried out once Aeolus products become available.

Abstract: The goal of this work is the development of a reduced order computational model for the prediction of the dynamic aeroelastic behavior of a wind tunnel wing model. The velocities of interest belong to incompressible flows type regime. The wing may have trailing and/or leading-edge control surfaces drove by electric or piezoelectric actuators. The aeroelastic model is linear, based on the Lagrange equations and on different aerodynamic models in time and frequency domains. A potential source of nonlinearities due to the actuating system is investigated, too. The number of degrees of freedom is between two and six for the wing. For each of the control surfaces we assume a single and rigid type displacement. The numerical results include the flutter prediction and gust and atmospheric turbulence effects. The aim is first to accurately predict the dynamics of an experimental wing model tested in the wind tunnel and after then to add to the computational model the active control features needed for the mitigation of gust and atmospheric turbulence effects. The context of the paper is represented by the activities taking place within an ongoing UEFISCDI project, PCCDI 87/2018.

Abstract: The goal of this work is the comparison of different gust and atmospheric turbulence model used for the numerical prediction of rigid and flexible wings in incompressible flows. The aerodynamic mathematical model used is unsteady and dedicated for medium and high aspect ratio wings. The wing may have trailing and/or leading-edge control surfaces. For aeroelastic calculations we are using a reduced order model presented in a companion paper. The numerical results are for different gust and atmospheric turbulence models. The aim of the numerical calculations is to compare the results and after then and based on the conclusions to build a rational strategy for the development of a computational model for testing active control solutions for the mitigation of gust and atmospheric turbulence effects. The context of the paper is represented by the activities taking place within an ongoing UEFISCDI project, PCCDI 87/2018.

Abstract: The Atmospheric Dynamics Mission (ADM) AEOLUS is the first satellite to comprehensively monitor wind speed and direction in the lowermost 30 kilometers of the atmosphere, around the globe. Up till now, meteorologists have collected information on winds from a number of sources, including weather balloons and airplane flights. No satellite has ever measured winds directly, from space, before AEOLUS, even though wind speed and direction can be inferred, for example, from satellite measurements of the movement of clouds. The mission was launched by ESA on August 22nd, 2018 and it has a lifetime of three years. However, AEOLUS is a demonstration project and if its technology proves solid, it could pave the way for other future wind-mapping satellites.
Generally, AEOLUS's data feed into numerical weather predictions, in which weather services incorporate atmospheric parameters such as temperature, pressure and humidity to generate forecasts. AEOLUS's laser cannot see through thick clouds, so it will not be able to penetrate storm systems such as cyclones, but this makes it even more suitable for studies dedicated to clear air phenomena.
In an attempt to go beyond the common use of AEOLUS data, an ongoing activity part of the current stage - 2 of CONTUR implementation plan, is aimed at finding out if the AEOLUS satellite data analysis would allow the identification of clear air turbulence (CAT) high risk zones. A particular emphasis will be put on the Romanian airspace.

Abstract: Turbulence phenomena have an important impact on the human activities performed in the terrestrial environment. The CONTUR complex project is aimed at the development of emerging technologies to counteract the effects induced by the turbulent flows. CONTUR is divided into two complementary component projects, one dedicated to the study of clear air turbulence and the second focused on the design of new active control technologies to reduce vibrations. An overview of the activities performed during the first months of the project as well as the future plans are presented.

Abstract: The aeronautical wind tunnels have a low degree of turbulence because the aircraft usually fly at altitudes of order of kilometers, in low level of turbulence. Unfortunately, such wind tunnels are not adequate for ground applications such as wind turbines, cars and buildings where the level of turbulence is relatively high. The simplest way to increase the degree of turbulence of aeronautical wind tunnels is to introduce a screen upwind to experimental chamber. Unfortunately, few papers deal with the numerical simulation of the screen with an emphasize on the wake. For this reason, the present papers highlights some particularities on numerical simulation of the screen and consider several solutions for the turbulence generator to be used in wind tunnel experiments.

Abstract: The present paper addresses the problem of active vibration control for a weakly damped 2-D rigid wing, with two degrees of freedom - plunge and pitch motions -, in the presence of unsteady aerodynamics, by means of an dedicated servoactuator. The mathematical model is a nonlinear one. A third degree of freedom is represented by the angle of deflection of an aileron by means of which the control variable is inserted in system. A challenging aspect of this study is the introduction of the time delay on control variable, which is of practical interest. The active control synthesis requires a prior analysis of the system, followed by the application of a predictor feedback. The background of the synthesis is the linear-quadratic synthesis (LQR). The context of the paper is represented by the activities taking place within an ongoing UEFISCDI project.

Abstract: The goal of this work is the development of a useful reduced order computational model for the prediction of the dynamic aeroelastic behavior of a wind tunnel wing model. The aeroelastic computational is linear, based on the Lagrange equations and on different aerodynamic models in time and frequency domains. The number of degrees of freedom is between two and six and a control surface of aileron type is included in the model. The numerical results include the flutter prediction and gust and atmospheric turbulence effects. The aim is first to accurately predict the dynamics of an experimental wing model tested in the wind tunnel and after then to add to the computational model the active control features needed for the mitigation of gust and atmospheric turbulence effects. The context of the paper is represented by the activities taking place within an ongoing UEFISCDI project.

Abstract: Clear Air Turbulence (CAT) is a dangerous weather phenomena affecting especially commercial aircraft. The study started using subjective pilot reports (AIREP), to obtain a distribution of CAT events in Romanian aerial space for an year. These reports provide useful information on occurrences of turbulences, however they are not always reliable in terms of spatial and temporal accuracy. The study assumes a data base with meteorological parameters associated to synoptic patterns and dynamic processes. The satellite data will be also used. In addition, theoretical considerations regarding the indices related to the responsible processes will be analyzed. All of these will allow to obtain some criteria for appearance of clear air turbulence.

Abstract: The first CONTUR ("New technologies to COMbat the effects to clear air TURbulences") campaign will focus on the investigation of air turbulence events. Lidar depolarization profiles will be used together with CCD imaging to monitor the airplane overpass occurrences over Magurele. It is assumed that airplane's wings and engines can cause air turbulence that can be detected by lidar since pressure gradients could cause slight variations of the molecular depolarization values. The study will test these assumptions and will assess the capability of the lidar instrument to highlight air turbulence from depolarization profiles.

Abstract: Occurrence of clear air turbulence (CAT) events has a high impact on commercial aviation, one of the most notable consequences of these events being seen in reduced structural resistance of airborne platforms. Currently, CAT detection's is performed with a limited success rate by ultra-sensitive radar systems or active remote sensing systems. In this context, new detection methodologies of high precision and cost-efficient are desired. Thru this paper, it is aimed to present a new approach for CAT events detection based on high spectral resolution lidars (HSRL), systems capable of retrieving the finest variations of atmospheric densities caused by turbulences. For this, series of validation tests will be performed with INCAS's airborne platform: Hawker Beechcraft King Air C90 GTx equipped with the Multiply system, a newly developed HRSL system characterized by laser with a pulse repetition rate of 4 kHz, a pulse energy of 2mJ@1064nm, 1.5mJ@532nm (to be attenuated at the output), 1.5mJ@355nm, a pulse duration of 5-6 ns, a beam diameter smaller than 9 mm, a beam divergence smaller than 0.5 mrad, a polarization purity better than 0.3% and maximum power consumption smaller than 2 kW.

Abstract: The upgraded boundary layer wind tunnel at the Aerodynamics and Wind Engineering Laboratory "Constantin Iamandi" is able to generate a velocity field and turbulent structure adapted to new climate change conditions. The tunnel can model more complex wind engineering phenomena and acquire data using modern precision measurement techniques. Static and dynamic wind effects on structures, building aerodynamics, snow drifting, combined wind and rain action, pollution, wind energy are all included in a list of possible applications of the largest research infrastructure for wind engineering in Romania.