Kumar Vikram Singh

Modern Applications of Nanotechnology in Textiles

Nanotechnology (NT) deals with materials 1 to 100 nm in length. At the National Nanotechnology Initiative (NNI), NT is defined as the understanding, manipulation, and control of matter at the above-stated length, such that the physical, chemical, and biological properties of the materials (individual atoms, molecules, and bulk matter) can be engineered, synthesized, and altered to develop the next generation of improved materials, devices, structures, and systems. NT at the molecular level can be used to develop desired textile characteristics, such as high tensile strength, unique surface structure, soft hand, durability, water repellency, fire retardancy, antimicrobial properties, and the like. Indeed, advances in NT have created enormous opportunities and challenges for the textile industry, including the cotton industry. The focus of this paper is to summarize recent applications of NT as they relate to textile fibers, yarns, and fabrics.

Transcendental Eigenvalue Problem and Its Applications

The algebraic eigenvalue problem is frequently encountered when analyzing the behavior of a multi-degree-of-freedom dynamic system. The characteristic equation associated with the algebraic eigenvalue problem is a polynomial that defines the eigenvalues by its roots. Dynamics and stability of distributed parameter systems are characterized by transcendental eigenvalue problems, with transcendental characteristic equations. By the use of finite element or finite difference methods, the transcendental eigenvalue problem is transformed to an algebraic problem. Because the behavior of a finite dimensional polynomial is fundamentally different from a transcendental function, such an approach may involve an inaccurate solution, which is attributed to a discretization error. The main idea is to replace the continuous system with variable physical parameters by a continuous system with piecewise uniform properties. The matching conditions between the various parts of the continuous model are expressed as a transcendental eigenvalue problem, which is then solved by the Newtons eigenvalue iteration method. Some classical problems in structural dynamics and stability are solved to demonstrate the method and its application.

Receptance-Based Active Aeroelastic Control Using Multiple Control Surfaces

Design of next generation aircraft/sensorcraft for improved performance, such as gust load alleviation towards aircraft stability and flutter suppression during its flight operation, may necessitate wing technology that can be controlled and manipulated by active means. Moreover, in recent years the efforts are underway to realize “Fly by Feel” concepts, which are aimed in utilizing on-board sensors (embedded) and actuators (control surfaces) of the aircraft towards the design of active control system for desired performance. This paper presents active control strategies for wings having multiple control surfaces, which are purely based upon in-flight receptance (measured) data. The proposed receptance based control approach has several advantages over the traditional state-space based control because it circumvents approximation errors in reduced order modeling; it captures the true interaction between structure and aerodynamic loads; and it requires modest size of matrices (depending upon the available number of sensors and actuators) for control gain computations. In this study, multi-input state and output feedback control strategies for active aeroelastic control using the method of receptances is developed. The control gains are computed for the extension of flutter boundaries via pole placement. At first, by using numerical receptances obtained from the aeroelastic model of a flexible wing having multiple control surfaces, the proposed methodology is demonstrated. In order to test and demonstrate the receptance method for more complex aircraft geometries, configurations and aerodynamic loading conditions, numerical receptances from Finite Element models of aircraft wings with multiple control surfaces were extracted for the proposed control design. Presented studies and control approach may become the basis for optimal placement and sizing of control surfaces in a given wing section for active aeroelactic control and enhanced flight performance.

Dynamic Absorption by Passive and Active Control

The motion of a particular degree-of-freedom in a harmonically excited conservative system can be vanished by attaching an appropriate dynamic absorber to it. It is shown here that under certain conditions, which are characterized in the paper, the steady state motion of a damped system may be completely absorbed, without loss of stability, by active control implementing a single sensor and an actuator. The results are established theoretically and they are demonstrated by means of analytical examples.

Active Aeroelastic Control Using the Receptance Method

The control and manipulation of dynamic instabilities, such as flutter, is termed as aeroelastic control and is extremely important in designing next generation flexible and maneuverable aircrafts. One of the goals of an aeroelastic control is to extend stable fight conditions for a large range of aerodynamic flow conditions. The associated control problem deals in adjusting and assigning the eigenvalues (which determine the natural frequencies and damping ratios) of the aeroelastic system for achieving the desired closed-loop behavior by active or passive means. In this paper, an active aeroelastic control problem, associated with the wing model, is formulated and eigenvalue assignment to achieve flutter free flight envelope is developed by using a new control methodology known as the Receptance Method. This method is entirely based upon transfer functions, typically obtained from a standard modal test by using actuators and sensors. This method has several advantages over traditional aeroelastic control approach which leads to state-space formulations. For example, it does not require the estimation of structural matrices (i.e. mass, stiffness and damping) as well as rational function approximations of aeroelastic influence coefficient matrices. The control gains are obtained without the knowledge of system matrices and purely from the receptance matrices. The feasibility study of this approach for aeroelastic control is considered here using several simple numerical aeroelastic systems. The control gains for eigenvalue assignments are obtained from receptance matrices and the performance of the controller is compared with those obtained by the state-space approach. Numerical examples associated with the eigenvalue assignment problems to adjust the natural frequency as well as damping ratio and to extend the flutter envelope by active means are presented. The actuator dynamics of the control surface and its effect on receptance based control is also studied. We envision that this new approach will facilitate an alternative method to address aeroelastic control problems and eventually will provide a practical solution for implementing active aeroelastic control.Copyright

Receptance-Based Active Aeroelastic Control with Embedded Control Surfaces Having Actuator Dynamics

To implement active aeroelastic control, control surfaces on a given wing configuration are moved using actuators having their own dynamic characteristics. The inclusion of actuator dynamics leads to the coupling of aeroelastic and actuator modes, and may result in instability in the closed-loop coupled aeroservoelastic system. During the design phase, various types of actuators may be considered, and hence, the stability and performance of the coupled system needs to be evaluated. In this research, a simultaneous control for aeroelastic and actuator poles is developed, which allows for the desired pole placement in a coupled aeroservoelastic system. This enables flutter boundary extension and suppression of flutter instabilities. The design of the controller is based on the method of receptances and requires the transfer functions associated with the aeroelastic structure and the actuators. This approach also allows the partial control of some selected aeroelastic modes without influencing the actuator m...

Quadratic Partial Eigenvalue Assignment Problem with Time Delay for Active Vibration Control

Partial pole assignment in active vibration control refers to reassigning a small set of unwanted eigenvalues of the quadratic eigenvalue problem (QEP) associated with the second order system of a vibrating structure, by using feedback control force, to suitably chosen location without altering the remaining large number of eigenvalues and eigenvectors. There are several challenges of solving this quadratic partial eigenvalue assignment problem (QPEVAP) in a computational setting which the traditional pole-placement problems for first-order control systems do not have to deal with. In order to these challenges, there has been some work in recent years to solve QPEVAP in a computationally viable way. However, these works do not take into account of the practical phenomenon of the time-delay effect in the system. In this paper, a new direct and partial modal approach of the quadratic partial eigenvalue assignment problem with time-delay is proposed. The approach works directly in the quadratic system without requiring transformation to a standard state-space system and requires the knowledge of only a small number of eigenvalues and eigenvectors that can be computed or measured in practice. Two illustrative examples are presented in the context of active vibration control with constant time-delay to illustrate the success of our proposed approach. Future work includes generalization of this approach to a more practical complex time-delay system and extension of this work to the multi-input problem.

Developing predictive tools for friction stir weld quality assessment

Abstract This research programme explores predictive tools that assess friction stir weld quality in aluminium alloys through dynamic characterisation. The study focuses on the correlations between dynamic interrogations measures of friction stir welded panels with the weld energy, as welded mechanical properties and the microstructure. 7136-T76 aluminium extrusions were joined at unique weld energies, and to characterise and identify the friction stir welds through non-destructive techniques, theoretical modelling and lab scale dynamic testing were conducted to establish the correlation between the weld energy and the associated spectral characteristics of the beam (natural frequencies/mode shapes). In this non-destructive evaluation study, the modal parameters were measured and were correlated with the friction stir weld microstructure and the physical parameters of the welded components, such as axial and flexural rigidities. The viability of weld parameter identification and weld quality assessment of friction stir welding beams using dynamic interrogation techniques is demonstrated.

Revitalizing the Engineering Curriculum Through Studio Based Instruction

Engineering curricula, regardless of the specific discipline, need to evolve. Realizing also that the pedagogical value of any educational artifact is closely linked to the methods of instruction used to interact with students, it is imperative that the development of new learning materials be accompanied by the implementation of innovative techniques with demonstrated success in knowledge transfer. This paper presents details of the development of studio styled modules associated with groups of courses within the mechanical and manufacturing engineering curriculum. Within each studio, newly developed activities engage students through experiential learning techniques. These activities, or learning exercises, represent a fusion of hands-on experimentation and computational simulation/analysis in key areas of engineering, such as dynamical systems, thermal sciences and materials. This endeavor is also intended to promote STEM education through enhancements in the quality of technical content, methods of instruction, training of student as effective educators, and the establishment of outreach activities expected to have an enduring effect on the preparation and recruitment of young talent into the sciences.Copyright

Optimization of Control Surface Parameters with Augmented Flutter Boundary Constraints

This paper presents the formulation and solution strategy for estimating the optimal parameters associated with the control surfaces on aircraft wings towards active aeroelastic control. In this study the optimal sizing of control surfaces is investigated in order to achieve the flutter suppression and flutter boundary extension for a given flight envelop. The objective of the optimization process is to minimize the control gain norms (control force requirement) while satisfying the constraints on closed loop eigenvalues, which defines the extension of the open loop flutter boundary. The proposed optimization approach relies on modest size of matrices which consists of frequency response transfer functions that may be available from embedded sensors and actuators on the aircraft wings. This optimization process is demonstrated by using numerical receptances obtained from the aeroelastic models of wings having single and multiple control surfaces and by solving optimization problems associated with single input, multi-input state feedback and output feedback problems with augmented flutter boundary constraints. It is anticipated that such an approach may be useful in design phase of aircraft wings and may facilitate optimal placement and sizing of control surfaces, for a given wing configuration, towards enhanced flight performance.