Jae-Kyeong Jang

Incipient crack detection in a composite wind turbine rotor blade

This article presents a performance optimization approach to incipient crack detection in a wind turbine rotor blade that underwent fatigue loading to failure. The objective of this article is to determine an optimal demarcation date, which is required to properly normalize active-sensing data collected and processed using disparate methods for the purpose of damage detection performance comparison. We propose that maximizing average damage detection performance with respect to a demarcation date would provide both an estimate of the true incipient damage onset date and the proper normalization enabling comparison of detection performance among the otherwise disparate data sets. This work focuses on the use of ultrasonic guided waves to detect incipient damage prior to the surfacing of a visible, catastrophic crack. The blade was instrumented with piezoelectric transducers, which were used in a pitch-catch mode over a range of excitation frequencies. With respect to specific excitation frequencies and transmission paths, higher excitation frequencies provided consistent detection results for paths along the rotor blade’s carbon fiber spar cap, but performance fell off with increasing excitation frequency for paths not along the spar cap. Lower excitation frequencies provided consistent detection performance among all sensor paths.

Pyroshock Prediction of Ridge-Cut Explosive Bolts Using Hydrocodes

Pyrotechnic release devices such as explosive bolts are prevalent for many applications due to their merits: high reliability, high power-to-weight ratio, reasonable cost, and more. However, pyroshock generated by an explosive event can cause failures in electric components. Although pyroshock propagations are relatively well understood through many numerical and experimental studies, the prediction of pyroshock generation is still a very difficult problem. This study proposes a numerical method for predicting the pyroshock of a ridge-cut explosive bolt using a commercial hydrocode (ANSYS AUTODYN). A numerical model is established by integrating fluid-structure interaction and complex material models for high explosives and metals, including high explosive detonation, shock wave transmission and propagation, and stress wave propagation. To verify the proposed numerical scheme, pyroshock measurement experiments of the ridge-cut explosive bolts with two types of surrounding structures are performed using laser Doppler vibrometers (LDVs). The numerical analysis results provide accurate prediction in both the time (acceleration) and frequency domains (maximax shock response spectra). In maximax shock response spectra, the peaks due to vibration modes of the structures are observed in both the experimental and numerical results. The numerical analysis also helps to identify the pyroshock generation source and the propagation routes.

Fully Noncontact Wave Propagation Imaging in an Immersed Metallic Plate with a Crack

This study presents a noncontact sensing technique with ultrasonic wave propagation imaging algorithm, for damage visualization of liquid-immersed structures. An aluminum plate specimen (400 mm × 400 mm × 3 mm) with a 12 mm slit was immersed in water and in glycerin. A 532 nm Q-switched continuous wave laser is used at an energy level of 1.2 mJ to scan an area of 100 mm × 100 mm. A laser Doppler vibrometer is used as a noncontact ultrasonic sensor, which measures guided wave displacement at a fixed point. The tests are performed with two different cases of specimen: without water and filled with water and with glycerin. Lamb wave dispersion curves for the respective cases are calculated, to investigate the velocity-frequency relationship of each wave mode. Experimental propagation velocities of Lamb waves for different cases are compared with the theoretical dispersion curves. This study shows that the dispersion and attenuation of the Lamb wave is affected by the surrounding liquid, and the comparative experimental results are presented to verify it. In addition, it is demonstrated that the developed fully noncontact ultrasonic propagation imaging system is capable of damage sizing in submerged structures.

Development of an FPGA-based multipoint laser pyroshock measurement system for explosive bolts

Pyroshock can cause failure to the objective of an aerospace structure by damaging its sensitive electronic equipment, which is responsible for performing decisive operations. A pyroshock is the high intensity shock wave that is generated when a pyrotechnic device is explosively triggered to separate, release, or activate structural subsystems of an aerospace architecture. Pyroshock measurement plays an important role in experimental simulations to understand the characteristics of pyroshock on the host structure. This paper presents a technology to measure a pyroshock wave at multiple points using laser Doppler vibrometers (LDVs). These LDVs detect the pyroshock wave generated due to an explosive-based pyrotechnical event. Field programmable gate array (FPGA) based data acquisition is used in the study to acquire pyroshock signals simultaneously from multiple channels. This paper describes the complete system design for multipoint pyroshock measurement. The firmware architecture for the implementation of multichannel data acquisition on an FPGA-based development board is also discussed. An experiment using explosive bolts was configured to test the reliability of the system. Pyroshock was generated using explosive excitation on a 22-mm-thick steel plate. Three LDVs were deployed to capture the pyroshock wave at different points. The pyroshocks captured were displayed as acceleration plots. The results showed that our system effectively captured the pyroshock wave with a peak-to-peak magnitude of 303 741 g. The contribution of this paper is a specialized architecture of firmware design programmed in FPGA for data acquisition of large amount of multichannel pyroshock data. The advantages of the developed system are the near-field, multipoint, non-contact, and remote measurement of a pyroshock wave, which is dangerous and expensive to produce in aerospace pyrotechnic tests.

Pyroshock Measurement and Characteristic Analysis of Explosive Bolt and Pyrotechnic Initiator

Pyroshock produced by the pyrotechnic devices can induce failures in nearby electronic devices. To handle and mitigate pyroshock inducing problems, appropriate measurement of pyroshock is essential. In this study, pyroshock measurement technique is established using laser Dopper vibrometers (LDVs) and shock accelerometers. Pyroshock produced by the explosive bolts and the pyrotechnic initiators under various environments is measured. The characteristics of pyroshock including the effects of supporting structures, propagation form on thin plate, sensor (contact and non-contact) types are discussed.

FPGA-based multipoint shock wave measurement system using LDVs for aerospace applications

Pyrotechnic devices are widely used in aerospace industry for variety of applications in launch vehicles, payload designs and spacecraft architectures. These devices are used to release, activate and separate structural subsystems. Ignition of these explosive carriers generates high intensity shock waves having immense drawback of cause damage to the sensitive electronic equipment due to its high frequency. Numerous experimental simulation techniques have been developed to study and characterize the behavior of pyroshock on the host structure. In this study, Field Programmable Gate Array (FPGA) based shock wave measurement system was developed using multiple Laser Doppler Vibrometers (LDVs). These LDVs simultaneously capture the shock wave at different locations generated due to explosive based pyrotechnical event. An indigenously developed Graphical User Interface (GUI) was used to visualize the voltage and acceleration plots for each channel. This paper describes the system design, integration and implementation of data acquisition system for multipoint sensing on Xilinx Virtex-6 FPGA based development hardware. Experimental setup was configured to test the reliability of the system. Mechanical shock wave was generated on the aluminum plate using a gun firing 6-mm plastic bullets. The shock wave was captured using three LDVs at various points connected to multichannel data acquisition hardware. This test was used to mimic the pyroshock wave and justify the potential of our system for real pyroshock measurement. Pyroshock generation is dangerous and expensive trial having low chances of repeating the experiment. Therefore, this technology has the advantage of measuring remotely shock response on various locations at the same time.

Nondestructive evaluation of pyroshock propagation using hydrocodes

Pyroshock or pyrotechnic shock generated by explosive events of pyrotechnic devices can induce fatal failures in electronic payloads. Therefore, understanding and estimation of pyroshock propagation through complex structures are necessary. However, an experimental approach using real pyrotechnic devices is quite burdensome because pyrotechnic devices can damage test structures and newly manufactured test structures are necessary for each experiment. Besides, pyrotechnic experiments are quite expensive, time-consuming, and dangerous. Consequently, nondestructive evaluation (NDE) of pyroshock propagation without using real pyrotechnic devices is necessary. In this study, nondestructive evaluation technique for pyroshock propagation estimation using hydrocodes is proposed. First, pyroshock propagation is numerically analyzed using AUTODYN, a commercial hydrocodes. Hydrocodes can handle stress wave propagation including elastic, plastic, and shock wave in the time domain. Test structures are modeled and pyroshock time history is applied to where the pyroshock propagation originates. Numerical NDE results of pyroshock propagation on test structures are analyzed in terms of acceleration time histories and acceleration shock response spectra (SRS) results. To verify the proposed numerical methodology, impact tests using airsoft gun are performed. The numerical analysis results for the impact tests are compared with experimental results and they show good agreements. The proposed numerical techniques enable us to nondestructively characterize pyroshock propagation.

Laser ultrasonic propagation visualization in plates with liquid boundaries

O arrays of metallic nanoholes have demonstrated great potential as sensors for the detection of analytes, including biomarkers for early diagnosis of diseases and viruses. These nanoplasmonic structures have been integrated into microfluidic environments in lab-on-chip formats towards the development of commercial-competitive biochemical diagnostics. The use of nanohole arrays in flow-through fashion has demonstrated additional benefits in terms of transport, such as targeted analyte delivery to the active sensing surface, effective analyte utilization and faster response times. In many applications, however, sensing must be achieved using samples with very low concentration of the target analyte. In order to overcome this challenge, concentration and purification stages are commonly employed before sensing. Among different approaches for achieving analyte preconcentration, electrokinetic techniques have demonstrated suitable for on-chip integration. The metallic nature of nanohole arrays offers the possibility to extend their use as active concentrators through electric field gradient focusing (EFGF) and the utilization of a pressure bias. Here we present the additional capabilities of the optofluidic structures to tailor the final concentration and spatial location of the analyte within the microfluidic chip, and the possibility to achieve transport control of the concentrated analyte using the nanoplasmonic structure as active switch. These demonstrated abilities extend the potentials of metallic nanohole arrays to achieve transport, concentration, active control and sensing using the same nanoplasmonic structure. Carlos Escobedo, J Phys Chem Biophys 2013, 3:5 http://dx.doi.org/10.4172/2161-0398.S1.004N effects in optical fibers impose different limitations on the communications link, and an understanding of such effects is almost a prerequisite for actual lightwave-system designers. On the other hand, they offer a variety of possibilities for all-optical signal processing, amplification and regeneration. Using conventional optical fibers for these applications, a length of several kilometres is usually required due to their relatively small nonlinear parameter ( γ ∼ 1.3W-1 /Km ). Such long fibers pose some practical limitations, concerned namely with the size and stability of the system. The required fiber length is reduced to about 1 km using highly nonlinear silica fibers with a smaller effective mode area, and hence, a larger nonlinear parameter ( γ ∼ 11 W-1 /Km ). A further reduction in fiber length by one order of magnitude has been achieved in recent years using nanowires and microstructured optical fibers with an extremely small effective mode area and significantly enhanced nonlinear characteristics. Another main advance was the production of highly nonlinear fibers using materials with a nonlinear refractive index higher than that of the silica glass, namely lead silicate, tellurite, bismuth glasses and chalcogenide glasses. Using such fibers, the required fiber length for nonlinear processing can be dramatically reduced to the order of centimetres. In this lecture, we review the effects, both detrimental and potentially beneficial, of optical nonlinearities both in conventional and in highly nonlinear fiber systems. Such lecture will be based on my book “Nonlinear Effects in Optical Fibers”, recently published by John Wiley & Sons, with the sponsorship of the Optical Society of America. Mario F. S. Ferreira, J Phys Chem Biophys 2013, 3:5 http://dx.doi.org/10.4172/2161-0398.S1.004M surface-directed vapor-liquid-solid (SVLS) growth of nanostructures has been shown to be a promising platform for horizontal formation of nanowires (NWs) and their scalable interfacing. One of the benefits of this method is elimination of post-growth assembly processes and offering a direct route for in-situ device integration. We have been exploring thisapproach for growth of a variety of semiconductor heterojunctions and in this talk we present some of our latest data on growth and characterization of TiO2and CdSe on GaN and Sapphire. While lattices of the selected crystals theoreticallydo not show any matches, directed and horizontal growth indicates existence of a pseudo-lattice match in a preferred growth direction. Results show that this preferred direction is required to be along the width of a NW. However, in better lattice-matched heteroepitaxies, this match could be overshadowed by the lattice match along the NW length. We also present examples on influence of the substrate on defining thenanocrystal orientation and contrast them with other classes of crystals such as wurtzite or cubic that tends to growin specific crystal orientations regardless of the structure of the substrate.I this article, a buried ridge waveguide InGaAsP laser array bonded onto Si waveguide by selective area metal bonding (SAMB) is presented. The SAMB method is an improved metal bonding method which separates optical coupling area from bonding area laterally so as to effectively avoid light absorption of bonding metal. Compared with AlGaInAs lasers, the InGaAsP lasers are without Al oxidation and non radiative surface recombination issues. The fabrication process mainly includes making holographic gratings on the surface of III-V active region, etching active region to attain different widths, epitaxial growth of upper waveguide layer, Helium ion implantation and evaporating electrode metal on both sides of the active region, substrate thinning and evaporating electrode metal, etching Si waveguide and evaporating bonding metal on both sides of Si waveguide, bonding III-V material and Si waveguide. By varying the width of active region, different wavelengths can be easily obtained. The significant advantage of this method lies in simple fabrication process and low-cost to achieve multi-wavelength laser array with low threshold current, high output power, good thermal stability, and desirable optical spot. The typical hybrid laser has a threshold of 14mA with a cavity length of 300μm. The output power is 5mW when the current is 100mA. The maximum operating temperature can be much higher than 50°C. A near-field image proves most of the optical field distributed in the Si waveguide. The simplicity and flexibility of the fabrication process and high yield make this approach a practical way to achieve Si based laser. Jiaoqing Pan et al., J Phys Chem Biophys 2013, 3:5 http://dx.doi.org/10.4172/2161-0398.S1.004A hybrid optical amplifiers (HOAs) are designed in order to maximize the span length, to minimize the impairments of fiber nonlinearities, and to enhance the bandwidth of optical communication system. In this investigation, the three types of HOAs are compared with Conventional Optical Amplifiers (COAs), such as Raman-EDFA-Raman (R-E-R), Raman-EDFA (R-E) and R-S. In the proposed system, 98 continuous wave lasers with carefully selected central frequency are utilized as the transmitter’s source. The data stream from 2.488 Gbps pattern generator with NRZ binary sequence is pre-coded and drives a sine square amplitude modulator. At the receiver side, PIN photo detector is used. Both the transmitter and receiver arms are made up of stretch 26 km of single mode fiber with 16 ps/nm/km dispersion and 4 km of dispersion compensated fiber with -96 ps/nm/ km dispersion. In this paper, we show that Raman-EDFA hybrid optical amplifier (HOA) gives the better performance at reduced channel spacing ( 30 dB), gain (>23.3) and least BER (< 4.6 × 10-16) with minimum utilization of bandwidth. Further, the EDFA and Raman-EDFA (R-E) is investigated for long haul communication at different number of spans. It is reported that, 70 km (10 km DCF + 60 km SMF) is the optimal span distance at which Raman-EDFA HOA achieve 2450 km of transmission distance with acceptable BER (1.09×10-9) and quality factor (15.63 dB). R. S. Kaler, J Phys Chem Biophys 2013, 3:5 http://dx.doi.org/10.4172/2161-0398.S1.004