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CONTENTS
Volume 7, Number 1, January 2011
 

Abstract
It has been shown in the literature that active adjustment of the intake area of a jet engine has potential to improve its fuel efficiency. This paper presents the design and control of a novel proof-of-concept active jet engine intake using Nickel-Titanium (Ni-Ti or Nitinol) shape memory alloy (SMA) wire actuators.The Nitinol SMA material is used in this research due to its advantages of high power-to-weight ratio and electrical resistive actuation. The Nitinol SMA material can be fabricated into a variety of shapes, such as strips, foils, rods and wires. In this paper, SMA wires are used due to its ability to generate a large strain: up to 6% for repeated operations. The proposed proof-of-concept engine intake employs overlapping leaves in a concentric configuration. Each leaf is mounted on a supporting bar than can rotate. The supporting bars are actuated by an SMA wire actuator in a ring configuration. Electrical resistive heating is used to actuate the SMA wire actuator and rotate the supporting bars. To enable feedback control, a laser range sensor is used to detect the movement of a leaf and therefore the radius of the intake area. Due to the hysteresis, an inherent nonlinear phenomenon associated with SMAs, a nonlinear robust controller is used to control the SMA actuators. The control design uses the sliding-mode approach and can compensate the nonlinearities associated with the SMA actuator. A proof-of-concept model is fabricated and its feedback control experiments show that the intake area can be precisely controlled using the SMA wire actuator and has the ability to reduce the area up to 25%. The experiments demonstrate the feasibility of engine intake area control using an SMA wire actuator under the proposed design.

Key Words
shape memory alloy wire; Nitinol; jet engine intake; sliding mode control.

Address
Gangbing Song: Department of Mechanical Engineering, University of Houston, N207 Engineering Building 1,Houston, TX 77204-4006, USA
Ning Ma: Department of Mechanical Engineering, University of Houston, N207 Engineering Building 1,Houston, TX 77204-4006, USA
Luyu Li: Department of Mechanical Engineering, University of Houston, N207 Engineering Building 1,Houston, TX 77204-4006, USA
Nick Penney: Ohio Aerospace Institute (OAI), 22800 Cedar Point Road, Cleveland, OH 44142, USA
Todd Barr: Jackson & Tull Aerospace Division, Cleveland, OH 44135, USA
Ho-Jun Lee: NASA Johnson Space Center, Houston, TX, USA
Steve Arnold: NASA Glenn Research Center, 21000 Brookpark Road, Cleveland, OH 44135, USA

Abstract
The mechanical properties obtained from mechanical tests, such as tensile, buckling, impact and fatigue tests, are largely applied to several materials and are used today for preliminary studies for the investigation of a desired element in a structure and prediction of its behavior in use. This contribution focus on two widely used different tests: tensile and fatigue tests. Small PZT (Lead Titanate Zirconate) patches are bonded on the surface of test samples for impedance-based health monitoring purposes. Together with these two tests, the electromechanical impedance technique was performed by using aluminum test samples similar to those used in the aeronautical industry. The results obtained both from tensile and fatigue tests were compared with the impedance signatures. Finally, statistical meta-models were built to investigate the possibility of determining the state of the structure from the impedance signatures.

Key Words
structure health monitoring; electromechanical impedance; tensile tests; fatigue tests; statistical meta-modeling.

Address
Lizeth Vargas Palomino: School of Mechanical Engineering, Federal University of Uberlandia, Campus Santa Monica, Avenida Joao Naves de Avila 2121, Bloco 1M, 38400-902 Uberlandia, Brazil
Jose dos Reis Vieira de Moura Jr.: School of Mechanical Engineering, Federal University of Uberlandia, Campus Santa Monica, Avenida Joao Naves de Avila 2121, Bloco 1M, 38400-902 Uberlandia, Brazil
Karina Mayumi Tsuruta: School of Mechanical Engineering, Federal University of Uberlandia, Campus Santa Monica, Avenida Joao Naves de Avila 2121, Bloco 1M, 38400-902 Uberlandia, Brazil
Domingos Alves Rade: School of Mechanical Engineering, Federal University of Uberlandia, Campus Santa Monica, Avenida Joao Naves de Avila 2121, Bloco 1M, 38400-902 Uberlandia, Brazil
Valder Steffen Jr.: School of Mechanical Engineering, Federal University of Uberlandia, Campus Santa Monica, Avenida Joao Naves de Avila 2121, Bloco 1M, 38400-902 Uberlandia, Brazil

Abstract
Geopolymer concrete is finding a growing number of niche applications in the field of civil engineering due to its high compressive strength and strength gain rate, retainage of structural properties in elevated temperature environments, chemical stability in highly acidic conditions and environmental benefits. Combining the above mentioned characteristics with induced electrical conductivity, could enable geopolymer cement to serve as a smart and sustainable cementitious material suitable for health monitoring of civil structures. Carbon fibers were added to fresh geopolymer and OPC (ordinary Portland cement) mixes to enhance their electrical conductivities. AC-impedance spectroscopy analysis was performed on the specimens with fiber fraction ranging from 0.008 to 0.8 with respect to the weight of cementitious binder, to measure their electrical resistivity values and to determine the maximum beneficial fiber content required to attain electrical percolation. Experimental observations suggest that CFR-geopolymer cement exhibits superior performance to CFR-OPC in terms of conducting electrical current.

Key Words
geopolymer concrete; electrical conductivity; carbon fibers; health monitoring; ac-impedance spectroscopy; CFR (carbon fiber reinforced).

Address
Saiprasad Vaidya: Trenchless Technology center, Louisiana Tech University, Ruston, USA
Erez N. Allouche: Faculty of Civil Engineering, Louisiana Tech University, Ruston, USA

Abstract
A deeper understanding of the effectiveness of adopting devices mounting shape memory alloy(SMA) elements in applications targeted to the mitigation of vibrations is pursued via an experimental approach. During a seismic event, less than 1000 loading-unloading cycles of the alloy are required to mitigate the earthquake effects. However, the aging effects during the time of inactivity prior to the oscillations (several decades characterized by the yearly summer-winter temperature wave) should be considered in order to avoid and/or minimize them. In this paper, the results obtained by carrying out, in different laboratories, fatigue tests on SMA specimens are compared and discussed. Furthermore, the effects of seismic events on a steel structure, with and without SMA dampers, are numerically simulated using ANSYS. Under an earthquake excitation, the SMA devices halve the oscillation amplitudes and show re-centering properties. To confirm this result, an experimental campaign is conducted by actually installing the proposed devices on a physical model of the structure and by evaluating their performance under different excitations induced by an actuator.

Key Words
damping; fatigue life; passive control systems; shape memory alloys; vibration mitigation.

Address
G. Carreras: Department of Applied Physics, ETSECCPB, UPC, E-08034 Barcelona, Catalonia, Spain
F. Casciati: Department of Structural Mechanics, University of Pavia, Pavia, Italy
S. Casciati: Department ASTRA, University of Catania, Syracuse, Italy
A. Isalgue: Department of Applied Physics, ETSECCPB, UPC, E-08034 Barcelona, Catalonia, Spain
A. Marzi: Department of Structural Mechanics, University of Pavia, Pavia, Italy
V. Torra :Department of Applied Physics, ETSECCPB, UPC, E-08034 Barcelona, Catalonia, Spain

Abstract
In this study, an output-only modal identification approach is proposed for decentralized wireless sensor nodes used for linear structural systems. The following approaches are implemented to achieve the objective. Firstly, an output-only modal identification method is selected for decentralized wireless sensor networks. Secondly, the effect of time-unsynchronization is assessed with respect to the accuracy of modal identification analysis. Time-unsynchronized signals are analytically examined to quantify uncertainties and their corresponding errors in modal identification results. Thirdly, a modified approach using complex mode shapes is proposed to reduce the unsynchronization-induced errors in modal identification. In the new way, complex mode shapes are extracted from unsynchronized signals to deal both with modal amplitudes and with phase angles. Finally, the feasibility of the proposed approach is evaluated from numerical and experimental tests by comparing with the performance of existing approach using real mode shapes.

Key Words
output-only modal identification; wireless sensor network; time-delayed signals; time-unsynchronization effect; complex mode shapes.

Address
Jae-Hyung Park: Department of Ocean Engineering, Pukyong National University, Busan, Korea
Jeong-Tae Kim :Department of Ocean Engineering, Pukyong National University, Busan 608-737, Korea
Jin-Hak Yi: Korea Ocean Research & Development Institute, Ansan, Korea


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