Temasek Laboratories

Engineering, Singapore

Temasek Laboratories

Engineering, Singapore
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Chang P.-H.,National University of Singapore | Chang P.-H.,Temasek Laboratories | Li J.-M.,National University of Singapore | Li J.-M.,Temasek Laboratories | And 3 more authors.
AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting | Year: 2017

To use tunable diode laser absorption spectrometer (TDLAS) technique in liquid-fuel pulse detonation engines (PDEs), this study attempted to obtain the temperature-dependent absorption spectra of fully and partially vaporized Jet A-1/nitrogen mixtures using the Fourier transform infrared (FTIR) spectrometer. The testing were conducted at the temperatures up to 180 °C with the mixture compositions set to two overall equivalence ratios of 1.0 and 2. 0. The results showed that the relatively larger absorbance occurred in the range of 2850-3000 cm-1. The amplitude of absorption spectra increased with increasing equivalence ratio. The discrepancy of the absorption cross sections in Beer’s Law between these two equivalence ratios was found, which can be attributed to the difference in Jet A-1 vapor species. Therefor it suggests that the variation of species in vapor-phase Jet A-1 should be considered when investigating absorption spectra of saturated Jet A-1 vapor. Because simultaneous measurements of variation of species in vapor-phase Jet A-1 and TDLAS are not easy to achieve. The method in a basis of two different wavelengths was proposed. After taking ratio of the transmissions of the selected two wavelength, the vapor concertation can be derived from the function of the ratio of absorption cross section with temperature, even if the detailed compositions of vapor-phase Jet A-1 are unknown. This method has the potential to determine time-resolved Jet A-1/air mixture compositions in PDEs or other combustion based applications. © 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Tong C.T.,Temasek Laboratories | Tong C.T.,DSO National Laboratories | Huat C.T.,Temasek Laboratories | Huat C.T.,DSO National Laboratories
APCAP 2016 - 2016 IEEE 5th Asia-Pacific Conference on Antennas and Propagation, Conference Proceedings | Year: 2016

This paper presents an approach for a fast evaluation of the bandwidth performance of reflectarray by incorporating the simulated reflectarray element phase response into the theoretical formulation of [1]. © 2016 IEEE.

Cui Y.D.,National University of Singapore | Zhao Z.,National University of Singapore | Zheng J.,National University of Singapore | Li J.-M.,National University of Singapore | And 2 more authors.
AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting | Year: 2017

The present study is to investigate the flow separation control process over a NACA0015 airfoil model in wind tunnel under the actuation of the nanosecond dielectric barrier discharge (NS-DBD) pulsed plasma actuators, by detail force measurements and flow field survey with dynamic PIV techniques. The Reynolds numbers tested were from 268k up to 463k. The results have shown that the NS-DBD pulsed plasma has strong effects on the separated shear layer when the actuation location is close to the separation point, dependent on the angle of attack, Reynolds number, and the plasma actuation frequency. The first few plasma pulses have much stronger effects on the separated flow: each pulse generates a spanwise vortex, the separated shear layer is manipulated, and the separation flow is shifted from the leading-edge to downstream. It seems that the following plasma pulses have less effects on the delayed separated flow, but provide necessary sustainable actuation to maintain the controlled quasiperiodic flow state, characterized by a partially reattached flow with a train of moving vortices over suction surface. The separated flow is suppressed more with increasing the actuating frequency. The study also reveals that the NS-DBD acts as a trip device at the very narrow angles of attack just around the stall angle, where a bi-stable mode exists for the airfoil studied here which exhibits a leading-edge stall behavior. The lift increment is slightly higher at the actuating frequency around of F+ = 0.5, due to a large and unsteady recirculating flow structure formed over the airfoil. While the drag is more dependent on the actuating frequency and angles of attack and no drag reduction is observed at high post-stall angles of attack. © 2017 by Temasek Laboratories, National Univesity of Singapore.

Zhao Z.,National University of Singapore | Cui Y.D.,National University of Singapore | Li J.-M.,National University of Singapore | Zheng J.,National University of Singapore | And 2 more authors.
AIAA SciTech Forum - 55th AIAA Aerospace Sciences Meeting | Year: 2017

In this paper, we investigated how the NS-DBD plasma actuator interacts with the separated flow over an NACA0015 airfoil by force and particle imaging velocimetry (PIV) measurements in a low speed wind-tunnel. The freestream velocity tested was 30m/s, corresponding to Reynolds numbers of 160k. The PIV measurements were conducted at two excitation frequencies and two angles of attack. The force measurements show that the excitation frequency of NS-DBD has strong effects on the aerodynamic performance of the airfoil. At AOA= 16° and the excitation frequency of F+ = 0.53, periodic vortices close to the airfoil surface are observed by PIV measurements. These vortices’ evolution above the airfoil plays very important role on the aerodynamic performances. These vortices provide an extra lift, leading to maximum lift increment; on the contrary, a quasisteady flow state with smaller separation region is formed at higher excitation frequency of F+ = 1.06, resulting in decreases of drag. For AOA = 24°, the NS-DBD still has strong effect on the separated flow by the force measurements and averaged PIV measurements, but the frequency influence cannot be observed clearly by instantaneous PIV measurements. © 2017 by Temasek Lab National University of Singapore.

Wang B.,National University of Singapore | Khoo B.C.,National University of Singapore | Khoo B.C.,Temasek Laboratories
Journal of Computational Physics | Year: 2013

In this paper, we present a hybridizable discontinuous Galerkin (HDG) method for solving the Stokes interface problems with discontinuous viscosity and variable surface tension. The jump condition of the stress tensor across the interface is naturally incorporated into the HDG formulation through a constraint on the numerical flux. The most important feature of HDG method compared to other DG methods is that it reduces the number of globally coupled unknowns significantly when high order approximate polynomials are used. For problems with polygonal interfaces, it provides optimal convergence rates of order k + 1 in L2-norm for the velocity, pressure and as well as the gradient of velocity. Furthermore, a new approximate velocity can be obtained by an element-by-element postprocessing which converges with order k + 2 in the L2-norm. For Stokes interface problems with curved interfaces, we use general curvilinear element to ensure the optimal convergence rates. An error estimate is given for the approximation of the interface. It indicates that curvilinear elements of degree 2k + 1 should be used for optimal convergence rate of order k + 1. © 2013 Elsevier Inc.

Liao F.,National University of Singapore | Liao F.,Temasek Laboratories | Wang J.L.,Nanyang Technological University
AIAA Guidance, Navigation, and Control Conference 2012 | Year: 2012

In this paper, an unified consensus-based feedback control strategy is proposed for formation and reconfiguration control of nonholonomic UAVs with velocity constraints. A state-dependent network topology is used to model the communication links among UAVs. Based on the conception of consensus, proportional and integral (PI) control of the relative position between vehicles is introduced to achieve and maintain a desired formation configuration. A bounded time-varying control parameter is designed for each UAV to ensure that its velocity always satisfy the given velocity constraints. The proposed control strategy is shown to guarantee that the multi-UAV system converge to a desired formation configuration subject to the given velocity constraints. An example is used to demonstrate the proposed approach. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Yu K.,National University of Singapore | Shen K.,National University of Singapore | Shao S.,National University of Singapore | Ng W.C.,National University of Singapore | And 2 more authors.
IEEE Transactions on Biomedical Engineering | Year: 2011

Searching for target images in large volume imagery is a challenging problem and the rapid serial visual presentation (RSVP) triage is potentially a promising solution to the problem. RSVP triage is essentially a cortically-coupled computer vision technique that relies on single-trial detection of event-related potentials (ERP). In RSVP triage, images are shown to a subject in a rapid serial sequence. When a target image is seen by the subject, unique ERP characterized by P300 are elicited. Thus, in RSVP triage, accurate detection of such distinct ERP allows for fast searching of target images in large volume imagery. The accuracy of the distinct ERP detection in RSVP triage depends on the feature extraction method, for which the common spatial pattern analysis (CSP) was used with limited success. This paper presents a novel feature extraction method, termed common spatio-temporal pattern (CSTP), which is critical for robust single-trial detection of ERP. Unlike the conventional CSP, whereby only spatial patterns of ERP are considered, the present proposed method exploits spatial and temporal patterns of ERP separately, providing complementary spatial and temporal features for high accurate single-trial ERP detection. Numerical study using data collected from 20 subjects in RSVP triage experiments demonstrates that the proposed method offers significant performance improvement over the conventional CSP method (corrected p-value < 0.05, Pearson r=0.64) and other competing methods in the literature. This paper further shows that the main idea of CSTP can be easily applied to other methods. © 2011 IEEE.

Lei L.,Temasek Laboratories | Lie J.P.,Temasek Laboratories | Gershman A.B.,TU Darmstadt | See C.M.S.,Temasek Laboratories
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2010

Two new approaches to adaptive beamforming in sparse subarray-based sensor arrays are proposed. Each subarray is assumed to be well calibrated but the intersubarray gain and/or phase mismatches are assumed to remain unknown or imperfectly known. Our first approach is based on a worst-case beamformer design that, unlike the existing worst-case designs, exploits a structured ellipsoidal uncertainty model for the signal steering vector. Our second approach exploits the idea of estimating the signal steering vector by maximizing the output power of the minimum variance beamformer. Several modifications of our second approach are developed for the cases of gain-and-phase and phase-only intersubarray distortions. ©2010 IEEE.

Liu A.Q.,Xi'an Jiaotong University | Liu A.Q.,Nanyang Technological University | Zhu W.M.,Nanyang Technological University | Song Q.H.,Xi'an Jiaotong University | And 4 more authors.
2013 Transducers and Eurosensors XXVII: The 17th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS and EUROSENSORS 2013 | Year: 2013

In this paper, we demonstrate a metamaterial tunable filter with liquid metal, which can be tuned by changing the air pressure within the channels. In experiment, it measures a 3.3-GHz tuning range for the tunable metmaterial unit with the working wavelength of 11.27 GHz. The tuning of 9 × 9 unit array is demonstrated. Different from traditional metamaterials, the metal patterns of the tunable metamaterial filter are liquid state which can be reshaped once fabricated. The liquid state metal pattern not only advances in flexible tuning method, but also results in large tuning range for vast applications, such as tunable filter, accelerometer and optical switch. © 2013 IEEE.

Li H.,Nanyang Technological University | Tay R.Y.,Nanyang Technological University | Tay R.Y.,Temasek Laboratories | Tsang S.H.,Temasek Laboratories | And 2 more authors.
Electrochimica Acta | Year: 2015

Reduced graphene oxide (rGO)/boron nitride (BN) composite films were successfully fabricated by facile vacuum filtration and subsequent thermal treatment. Their morphology, structure and electrochemical performance were systematically characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. Importantly, the as-prepared rGO/BN composite film with a 2 wt.% BN content as binder-free anode material for lithium ion batteries (LIBs) exhibited a high reversible capacity of 278 mAh·g-1 at a high current density of 100 mA·g-1, high rate capability, and high capacity retention over the first 200 cycles. The enhanced electrochemical performances of rGO/BN composite film are attributed to the unique structure and the synergistic effects between layered BN and graphene, which favored electrolyte penetration and buffered the volume expansion during the lithiation and delithiation process. In addition, this work not only provides a versatile strategy for fabrication of other graphene-based films, but also shows the potential promise of rGO/BN composite film for other energy storage devices. © 2015 Elsevier Ltd. All rights reserved.

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