Aeroelastic testing of LCA wing models - Model fabrication - Ground testing - Wind tunnel testing and Data analysis

Aeroelastic Testing Programme of Scaled Aeroelastic model of LCA half wing with rigid fuselage

Evolution based statistical optimization technique to design the smart structural system for large aerospace structures

A numerical approach for genetics based statistical optimization technique is used to design the smart structural system for aerospace structures. An evolutionary based optimization technique like genetic algorithm (GA) has come into prominence. The reason for developing evolution based algorithm for optimization is for its robustness and randomness. Other numerical tools that are used for optimization are generally gradient based algorithm, where there is possibility of occurrence for a local optimum value. The GA developed is a niche-micro GA, where termination criteria are set in order to restart the algorithm. Stage-wise multiple objective functions and multiple termination criteria are incorporated to improve the computational effort. The current approach is very much robust to design a smart structural system through optimization for its maximum structural performance. In order to achieve maximum structural performance for the smart structural system, it is necessary to appropriately position the active elements. Here the genetic algorithm is amalgamated with finite element to perform a statistical based optimization to locate the position and size of active structural elements i.e. actuators/sensors. Majorly, nowadays the actuators and sensors that are preferred for smart structures design (i.e. Piezo patches, Piezo composite, SMA wire, SMA composite etc) develop induced strain under an external applied field. It becomes necessary to optimize the smart structures using the following parameters such as static strains, modal dynamic strains, size of the actuators/sensors, induced strain etc. A scaled T-Tail model is taken as an illustration to carry out the GA analysis for the location and sizing of PZT actuator/sensor. The structural parameters such as static strains, modal dynamic strains and geometry details are taken from NASTRAN and then interfaced with MATLAB to perform the statistical optimization analysis

Experimental Study on gsLVM3 for Transonic Buffet Estimation

In modern launch vehicles, the unsteady aerodynamic forces caused by flow separation during the transonic regime induce aeroelastic instabilities like buffeting, which may lead to structural failure. Quantifying the buffet loads in the critical transonic regime is important to ensure the safety of the vehicle structure. The complexity of the buffeting phenomena makes the computational effort ifficult to predict the aerodynamic-elastic-inertial interactions. Hence the designer has to employ experimental approach to evaluate the necessary aeroelastic characteristics of launch vehicles. This paper presents a case study of experimental aeroelastic studies on gsLVM3 launch vehicle. For this an aerodynamically shaped and dynamically scaled model is designed, fabricated and wind tunnel tested. The responses of the mounted sensors on the model have been acquired during the tunnel testing and analyzed. The transonic buffet experienced by the model has been presented in the form of dynamic bending moment for different flight conditions. Finally, the critical buffet loads for the full scale vehicle are obtained using appropriate scale factor

Strain measurements on pressure vessels

Four pressure vessels were tested for their behaviour under uniform internal pressure loadiing of 225 Kgf/cm2. The strains on the external surface were monitored, in detail in one vessel and on crucial locations for other vessels. The details of the test with the results are presented in this report

Thermo-Mechanical response of an electrically driven micro-actuator

Thermo-mechanical response of a polysilicon beam structured two hot arm horizontal actuators are investigated under electrical load. This thermo-mechanical device is operated by differential thermal expansion caused by resistive Joule heating to generate thermal expansion and movement. The present research demonstrates a good comprehension of the phenomena during Joule heating process for micro systems and the development of an analytical model and a finite element analysis. Numerically simulated results validate the analytical model at the steady state conditions. This simple device can generate a temperature of 1389K and produce a deflection of the order of 12μm at the level of low operating voltage (10 volts)

Aeroelastic testing of aerospace vehicles - Experiences gained during four decades

Aerospace vehicles are constructed as light weight, thin walled structures, in order to facilitate more pay loads with improved flight performance. Further, the complex aerodynamic shape requirements bring additional problems to structural designers and analysts to qualiy the thin-walled structures; for example wings, fails and slender bodies like fuselage, launch vehicles must be examined such that they will not develop any aeroelastic instabilities within the specified flight regime. Aeroelasticiy is a science that deals wih an interaction between elastic, inertial and aerodynamic forces. Simulation of aeroelastic system involves coupled structural dynamics and aerodynamics, where analytical models are normally employed. Aerodynamic theories to build such analytical models of lifting surfaces and bodies are well established both in subsonic and supersonic regimes; however there is still not much confidence level achieved in the transonic regime to qualify any aerospace vehicle only through theoretical analysis procedures. Therefore, it becomes appropriate to use the experimental approach to evaluate the transonic aeroelastic characteristics of aerospace vehicles. In the last four decades, Aeroelasticity Group of Structural Technologies Division, NAL has carried out a number of aeroelastic testing projects and contributed immensely to the national aerospace programmes; to name a few LCA, SARAS, SLV, ASLV, PSLVand GSLV. Different kinds of aeroelastic problems have been addressed; both stabilty (flutter, divergence) and response (buffet) solutions are obtained experimentally. Indeed, during the last four decades, the model design and aeroelastic testing methodologies have been evolved to a matured state. Aeroelastic Testing (AET) has the following modules: 13; x2022; Deriving appropriate aeroelastic scale factors13; x2022; Design methodology (Equivalent or Replica)13; x2022; Simulation of boundary effect through model support system13; x2022; Fabrication of components and assembly procedures13; x2022; Non-structural mass simulation13; x2022; Instrumentation on the model and calibration of the sensors13; x2022; Qualification studies for both strength and stiffness13; x2022; Qualification studies for checking the dynamic simulation13; x2022; Wind tunnel testing13; x2022; Data analysis and results interpretation for the full scale vehicle13; AET plays an important role in understanding the aeroelastic behavior of any aerospace vehicle, which either operates at transonic regime or cross over it. This paper brings out our experiences that have been gained in the last four decades of testing the flight vehicles in 1.2m NAL trisonic wind tunne

Modelling and Analysis of MEMS Thermal Actuator

This report presents the design and comparative performance evaluation of two hot arm asymmetrical electrothermal micro actuators. Also this report confers detail on a polysilicon thermal actuator designed with two hot arm and one cold arm of different length and width based on asymmetrical thermal expansion of two beams caused by ohmic heating. Because of the interference of the different heat transfer modes (such as conduction, convection, and radiation), the motion simulation becomes complex. This work reveal a good understanding of the phenomena during a Joule heating process for micro-systems and the development of an analytical model and a finite element analysis. Comparisons between analytical and numerical simulation results validate the steady-state conditions

Characterization of piezoelectric stack actuators for structural control applications

In this paper we experimentally evaluate the response of several piezoelectric stack actuators under different loading conditions (mechanical, electrical and electromechanical). An improved smart material actuators measurement method suited for static and dynamic actuation is devised (Fig. 1). The output displacement of the active material is recorded under various prestress level and voltage values. The measurements indicate a strong dependence of piezoelectric properties under electromechanical loading conditions for the actuators. Results indicate that certain operating conditions (i.e., mechanical prestress) can improve actuation capabilities

Development of Active Engine Mount System using PZT Actuators for Low Speed Transport Aircraft

The progress of the first phase of project has been reviewed on October 2009. In this technical review, the design aspects of active struts and analysis result have been presented. The expert members have examined the feasibility of the active strut based AVC solution for the engine mount system. This report has narrated the technical details of the works so far carried out

Active Vibration Control of L40 deck plate using smart materials

Application of smart materials such as piezoelectric actuators/sensors for space structural control has been explored. The L40 deck sandwich deck plate is taken as an illustration. Both analytical and experimental AVC studies are performed on the deck plate. The results that are presented in this report have been reviewed by a duly constituted committee, consists of LPSC scientists and expert members from IISC and ADA