Agency For Defense Development Research Articles

Machine learning based ship localization in shallow water using ship noise recorded by two vertical line arrays

For the application of machine learning to sound source localization, much train data distinguished from test data is needed to build the machine learning model. In Shallow-water Acoustic Variability Experiment (SAVEX-15) conducted in shallow water (water depth ∼100 m) in Northern East China Sea (ECS), ship noise of the R/V Onnuri was recorded by two vertical line arrays. Acoustic data of ∼80% was applied to the training dataset and the others having different trajectories were used for the test data. The recorded data is preprocessed by a sample covariance matrix and it is used as the input data of the machine learning model: Feedforward neural network (FNN) and support vector machine (SVM). The results by FNN and SVM will be discussed with conventional localization method using ray-based blind deconvolution (RBD) and array invariant (AI). [Work supported by the Agency for Defense Development, Korea (UD210004DD).]

Editorial Note

Editorial Note

Non-coherent turbo coded frequency shift keying for reliable covert underwater acoustic communications

This paper presented efficient receiver structure of non-coherent turbo coded FSK signals for maintaining covertness and performance in underwater communication. In aspect to covertness, direct sequence spread spectrum method, which used to hide the transmitted signal by transmitting it at low power and, thus, making it difficult for an unintended listener to detect the signal in the presence of background noise. In aspect to performance improvement in the underwater acoustic environment with multipath and Doppler spreading, non-coherent FSK which is not required phase information, weighted multiband technology, and turbo equalization model with rate of 1/3 were suggested. In order to analyze the performance by applying four bands and spreading chips with 8 and 32, the experiment was conducted on a lake by moving in the range of 300m to 500m. Through the experimental results, we confirmed the performance was improved as increasing number of bands, turbo iterations, and spreading chips. Furthermore, weighted multiband technology which allocates lower weight to inferior bands based on preamble error rates were applied for some failed packets, all packets were decoded successfully. [This research was funded by Agency for Defense Development, South Korea, Grant No. UD200010DD.]

Cancellation of multiple interferers in communication signal

The broadband impulse signal emitted by marine animals is difficult to separate from the communication signal and contaminates the phase of the symbol, causing performance reduction. In a previous study, the Green’s function of this undesired signal was estimated for each path, and the impulse signal was spatially canceled by combining it with adaptive time-reversal processing [Kim et al., J. Acoust. Soc. Am. 150, A195 (2021)]. However, when the number of impulse signals to be canceled exceeds the number of receivers, the degree of freedom in the process of designing the weight vector is limited. In this presentation, we propose an approach that provides degrees of freedom by treating the signal vectors from multiple arrivals as a single constraint. The spatially nulling impulse signal without distorting the phase of the communication signal showed a remarkable improvement in communication performance in the seagoing experimental data. [Work supported by the Agency for Defense Development, South Korea, under Grant UD200010DD.]

Long-range underwater acoustic communication of M-eyry spread spectrum with cyclic prefix

The Spread Spectrum is an effective transmission method for complex channels in underwater acoustic (UWA) communication because of the high correlation of pseudo-random noise (PN) sequence. In particular, the spread spectrum method is effective in an environment with a low signal-to-noise ratio. The bandwidth of UWA communication channel is limited due to the fact that sound wave attenuation in water is positively associated with frequency. The limited bandwidth directly leads to the low data rate of conventional direct-sequence spread spectrum UWA communication. M-ary spread spectrum (MSS) schemes using multiple orthogonal PN sequences were proposed as a solution to this problem. However, even in the MSS method, the performance may be limited by the delay spread characteristics in the multipath propagation channels. We propose a more robust communication method in the UWA channel by including Cyclic Prefix (CP) to achieve a more robust performance in the multipath channel. In the proposed method, a CP is inserted for every symbol. In the 160 km long-range UWA communication experiment conducted in the East Sea, the proposed method showed more reliable results than the conventional MSS method. [Work supported by the Agency for Defense Development, South Korea, Grant No. UD200010DD.]

Underwater acoustic communication based on chirp spread spectrum with cyclic shifted PN sequences

In this presentation, we propose a new underwater acoustic communication technique that combines a binary PN (Pseudo Noise) sequence to which cyclic shift is applied and a CSS (Chirp Spread Spectrum) method that is robust against low Doppler shift. PN sequences are known to have sharp autocorrelation function and cyclic properties. In the case of the previous CSS method, 1-bit per symbol was mapped according to the sign of the slope in the time-frequency domain of the chirp signal, but the proposed method maps 2-bit per symbol according to the cyclic shift direction of PN sequence and the slope of the chirp. As a result, the transmission data rate is doubled. For example, “00” symbol is expressed as an up-chirp and right cyclic shifted PN sequence, and “11” symbol can be expressed as a down-chirp and left cyclic shifted PN sequence. This combination can have excellent autocorrelation properties and Doppler shift immunity. The performance of the proposed method will be compared with that of the previous method by presenting the results of the sea trial. [Work supported by the Agency for Defense Development, South Korea, Grant No. UD200002DD.]

PILS 시뮬레이터를 이용한 GPS 및 통신불가 미지 실내 환경에서 자율비행 탐색임무를 위한 통합성능 분석

This study presents a PILS simulator design and its performance analysis results of autonomous exploration algorithms under infrastructure outage environments such as battle field. For this, an unstructured indoor environment is considered where drone autonomously explores and returns to the starting point without GPS and other communication linkage. At the end of the mission, the map and the location of the target are transmitted to its operator. Component algorithms necessary for this include path planning, SLAM, image processing with target recognition and its realtime integration for drone’s flight control. The simulator studied in this paper primarily constitutes the flight control system of drone that participates “Autonomous Flight Competition in Battlefield” supported by the Agency for Defense Development(ADD).

국가연구개발사업의 군사적 기원

This paper examines the continuity between the weapons development management system in the 1970s and the national research and development (R&D) programs in the 1980s in South Korea. In the 1970s, the Agency for Defense Development (ADD) carried out a series of weapons development programs, adopting standardized procedures for planning, managing, and evaluating projects from the United States Department of Defense. After the establishment of the Fifth Republic of Korea, former weapons developers launched the “Special R&D Program (Teukjeong yeon-gugaebal saeop),” modeled on the weapons development system of the ADD, and the program was followed by the national R&D programs of other ministries. By examining the process by which the Special R&D Program was established, this paper will argue that the current planning, management, and evaluation system of national R&D programs inherits the weapons development management system of the ADD.

Frequency tracking and mitigation method based on CPHD filter and adaptive multiple linear Kalman notch filter for multiple GNSS interference

NAVIGATIONVolume 67, Issue 1 p. 213-213 ERRATUMFree Access Frequency tracking and mitigation method based on CPHD filter and adaptive multiple linear Kalman notch filter for multiple GNSS interference This article corrects the following: Frequency tracking and mitigation method based on CPHD filter and adaptive multiple linear Kalman notch filter for multiple GNSS interference Sun Young Kim Chang Ho Kang Chan Gook Park Volume 66Issue 4Navigation pages: 803-830 First Published online: January 14, 2020 First published: 20 March 2020 https://doi.org/10.1002/navi.351AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat In Kim et al,1 the Acknowledgements section was published with missing content. The text “This work was done while the first author was a member of the Department of Mechanical and Aerospace Engineering, Seoul National University.” should be added. The complete Acknowledgements section is shown below: ACKNOWLEDGEMENTS A preliminary version of this paper was presented at the ION GNSS+ 2018 conference. This work has been supported by the National GNSS Research Center program of the Defense Acquisition Program Administration and Agency for Defense Development, and the Ministry of Science and ICT of the Republic of Korea through the Space Core Technology Development Program (No. NRF- 2018M1A3A3A02065722). This work was done while the first author was a member of the Department of Mechanical and Aerospace Engineering, Seoul National University. The online version was already corrected. We apologize for this error. REFERENCE 1Kim SY, Kang CH, Park CG. Frequency tracking and mitigation method based on CPHD filter and adaptive multiple linear Kalman notch filter for multiple GNSS interference. NAVIGATION. 2019; 66(4): 803- 830. https://doi.org/10.1002/navi.332Wiley Online LibraryWeb of Science®Google Scholar Volume67, Issue1Spring 2020Pages 213-213 ReferencesRelatedInformation

Thermal shock resistance of TaC/SiC coatings on carbon/ carbon composites by the CVD process

This work was supported by the Korean Government (Defense Acquisition Program Administration, DAPA) through research institute (Agency for Defense Development, ADD).

Comparison of exhaust duct designs in launch pads for reduction of rocket jet noise

An exhaust duct is commonly installed in a launch pad to reduce the intense noise generated by the rocket exhaust jet at liftoff. In this paper, we investigate the effects of varying the length and shape of the exhaust duct by comparing the noise reduction performance of several different designs. The sub-scale exhaust ducts tested are variations of the original design by Tsutsumi et al. [AIAA Paper 2015-1007], colloquially known as “Seiji’s dog house,” and experiments are performed using cold jets of Mach 1.8 and 3.1, respectively. Linear and semi-circular microphone arrays are employed near the nozzle and at a radial distance of 100 nozzle diameters from the center of the duct outlet. A design guideline as to the length and the outlet shape of the exhaust duct, leading to the best noise reduction performance, is discussed. [This work was conducted at High-Speed Vehicle Research Center of KAIST with the support of the Defense Acquisition Program Administration and the Agency for Defense Development under Contract UD170018CD.]

Metal-Nickel Oxyhydroxide Nanostructures on Carbon Clothes As Anode Catalysts for Direct Urea Fuel Cells

Existing energy sources based on fossil fuel is an obstacle for environmental sustainability, and there is a concern regarding the depletion of fossil fuel resources [1], [2]. Therefore, it is essential to develop new alternative energy sources. As a safe and effective method of generating power, the conversion of natural biomass to electricity in the form of direct biomass fuel cell (DBFC) has attracted significant attention due to its high efficiency and low emissions [3]. Among various DBFCs, direct urea fuel cell (DUFC) using urea in wastewater and urine as fuel has recently been validated as a clean energy device [4]. The overall power response of the DUFC mainly depends on the urea oxidation reaction (UOR), so it is vital to investigate the UOR catalysts. Ni-based catalysts, which are inexpensive and commonly used as UOR catalysts, have widely utilized for replacement of noble metals. The Ni/C electrode as an anode in the reported study achieved a power density of 1.7 mW/cm2 [5], and nanostructured Ni-based catalysts or bimetallic types of catalysts also have been implemented for better performances [6], [7]. However, the above studies proceeded in an alkaline medium, which makes it difficult to use actual wastewater or urine directly as a source for fuel cells application. Since the electrochemical features of nickel-based catalysts are based on the mechanism of electrooxidation from Ni2+ to Ni3+ in alkaline medium, the catalytic activity in neutral solutions is less well distinguished [8]. Thus, nickel-based catalysts essentially comprising Ni3+ ions will more efficiently improve the UOR performances even if a neutral atmosphere of urea solution is adopted. In this study, the catalyst with a nanostructures array based on nickel oxyhydroxide with metal (metal-NiOOH) was prepared by using the electrospinning process for DUFC. The morphology and the structure of the metal-NiOOH catalysts were observed using scanning electron microscopy, Transmission electron microscopy, and X-ray diffraction methods. The metal-NiOOH catalyst used as the DUFC anode showed excellent UOR performances and power achievements in real human urine. A comprehensive investigation on the performances of metal-NiOOH and the function of internal Ni3+ ions as a catalyst in DUFC will be presented. References Suranovic, Steven. "Fossil fuel addiction and the implications for climate change policy." Global Environmental Change 23.3 (2013): 598-608. Veziroğlu, T. Nejat, and Sümer Şahi. "21st Century’s energy: Hydrogen energy system." Energy conversion and management 49.7 (2008): 1820-1831. Zhao, Xuebing, and J. Y. Zhu. "Efficient conversion of lignin to electricity using a novel direct biomass fuel cell mediated by polyoxometalates at low temperatures." ChemSusChem 9.2 (2016): 197-207. Xu, Wei, et al. "Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell." Scientific reports 4 (2014): 5863. Lan, Rong, Shanwen Tao, and John TS Irvine. "A direct urea fuel cell–power from fertiliser and waste." Energy & Environmental Science 3.4 (2010): 438-441. Ye, Ke, et al. "Facile preparation of three-dimensional Ni (OH) 2/Ni foam anode with low cost and its application in a direct urea fuel cell." New Journal of Chemistry 40.10 (2016): 8673-8680. Guo, Fen, et al. "Preparation of nickel-cobalt nanowire arrays anode electro-catalyst and its application in direct urea/hydrogen peroxide fuel cell." Electrochimica Acta 199 (2016): 290-296. Vedharathinam, Vedasri, and Gerardine G. Botte. "Direct evidence of the mechanism for the electro-oxidation of urea on Ni (OH) 2 catalyst in alkaline medium." Electrochimica Acta 108 (2013): 660-665. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.

Noninvasive Urea Monitoring Using a Flexible Electrochemical Sweat Based Sensor

With the development of technology in healthcare systems, interest in a wearable, portable, and even implantable device is growing, allowing health indicators to be read by direct skin contact [1], [2]. The non-invasive sensing platform overcomes the inconvenience of the conventional monitoring system and enabling easy and quick medical diagnosis in real time [3]. Urea is a major metabolite of the human body in a form of nitrogen, a key biomarker above the renal failure, dehydration, and hepatic issues [4], [5]. Urea detection is conceivable from serum, urine, and sweat in the body. The concentration of urea in the sweat is higher than that of serum so sweat based urea sensor can substitute the current pricking test method [6]. Higher levels of urea in sweat are also essential notices because they are correlated with uremia [7]. To sense the non-electric active of urea, the present method uses an enzyme in electrochemical sensors. The enzyme-based sensor consists of an enzyme (urease) and a mediator, which distinguishes the urease-catalyzed hydrolysis products [8]. However, the enzymatic sensor is complex, unstable, and costly, so non-enzyme sensors are better suited for wearable sensor devices. Nickel-based catalysts with nanostructures, large surface area, good electrical conductivity, and low cost are the best nominees for urea detection as they oxidize urea without enzymes [9]. Recently, a polymer-type substrate has been utilized for the flexible and wearable sensor device which requires porous and conductive polymers. Herein, we investigated a facile approach to form nickel oxyhydroxide with metal (metal-NiOOH) based flexible electrochemical sensor by electrospinning method. The morphology and the structure of the metal-NiOOH catalysts were observed using transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The metal-NiOOH catalysts with polymer showed excellent flexibility and competent linear sensitivity to urea electrooxidation in the physiological concentration area. A comprehensive investigation of the performances regarding metal-NiOOH as a catalyst in a sweat-based sensor will be presented. References Feiner, Ron, et al. "Engineered hybrid cardiac patches with multifunctional electronics for online monitoring and regulation of tissue function." Nature materials 15.6 (2016): 679. Liu, Yuhao, Matt Pharr, and Giovanni Antonio Salvatore. "Lab-on-skin: a review of flexible and stretchable electronics for wearable health monitoring." ACS nano 11.10 (2017): 9614-9635. Pickup, John C., et al. "In vivo glucose monitoring: the clinical reality and the promise." Biosensors and Bioelectronics 20.10 (2005): 1897-1902. D'Apolito, Maria, et al. "Urea-induced ROS cause endothelial dysfunction in chronic renal failure." Atherosclerosis 239.2 (2015): 393-400. Thudichum, J. L. W. "On the analysis of urea in urine for clinical purposes." British medical journal 1.38 (1857): 788 Stefaniak, Aleksandr B., and Christopher J. Harvey. "Dissolution of materials in artificial skin surface film liquids." Toxicology in Vitro 20.8 (2006): 1265-1283. Kazory, Amir. "Emergence of blood urea nitrogen as a biomarker of neurohormonal activation in heart failure." The American journal of cardiology 106.5 (2010): 694-700. Liu, Yan-Ling, et al. "Flexible electrochemical urea sensor based on surface molecularly imprinted nanotubes for detection of human sweat." Analytical chemistry 90.21 (2018): 13081-13087. Mahshid, Sahar Sadat, et al. "Template-based electrodeposition of Pt/Ni nanowires and its catalytic activity towards glucose oxidation." Electrochimica Acta 58 (2011): 551-555. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.

Development in Two-Dimensional Nanomaterials for Wearable Health Monitoring Systems

By virtue of the technology in ubiquitous computing and smart textile, gas sensor with wearability has been developed to play an imperative role in improving future healthcare. [1] The sensor revolution can significantly impact on outpatient care and management of chronical diseases by offering real-time condition monitoring. The combination of many technology is on the verge of producing this dramatic advance, and the significance placed on the development of sensor performance. [2] Recently, two-dimensional (2D) nanostructured materials have been regarded as instrumental sensing materials due to their working ability at low temperature. One attractive approach to enhance performance of 2D materials-based sensor is to hybridize with metal oxide. By grafting two nanostructured materials, sensing performance can be highly advanced by hybridization effects. [3] Another innovative strategy is to adapt newly discovered 2D materials. 2D transition metal carbides and/or carbonitrides (called MXenes) have recently shown excellent properties particularly in energy storage, and water purification applications. [4] Boundless combination of constituent elements and ordered structure in MXenes provides many opportunities to tailor its properties for different applications. In this study, 2D nanostructured nanomaterials and their hybrids were explored to develop wearable chemical sensor for precise health monitoring systems. Graphene oxide (GO) and molybdenum disulfide (MoS2) were studied to understand the effect of surface dangling bonds on gas sensing properties. To enhance sensing performance, 2D nanomaterials was combined with metal oxides. The gas sensing performance of the GO/TiO2 hybrid was improved by decorating titanium dioxide (TiO2). [5] After photo-reduction, the gas sensing behavior was converted from n-type to p-type with extended long-term stability. Moreover, 2D MXene was introduced as a promising room-temperature sensing material with their intriguing surface chemistry. The capability of titanium carbide (Ti3C2Tx) to sense an array of VOC gases was demonstrated, and its possible sensing mechanism was proposed in terms of the interaction between sensing species and the oxygen terminated surface of MXene. Another MXene material, vanadium carbide (V2CTx), was also investigated. 2D V2CTx gas sensors showed outstanding gas sensing performance including high sensitivity toward non-polar gases such as hydrogen and methane. Transformation of ordered structure and constituent elements of MXenes largely influenced on interaction between analyte and MXenes showing outstanding selectivity and limit of detection to non-polar gases. References Gravina, Raffaele, et al. "Multi-sensor fusion in body sensor networks: State-of-the-art and research challenges." Information Fusion 35 (2017): 68-80.Yao, Shanshan, Puchakayala Swetha, and Yong Zhu. "Nanomaterial‐Enabled Wearable Sensors for Healthcare." Advanced healthcare materials 7.1 (2018): 1700889.Chatterjee, Shyamasree Gupta, et al. "Graphene–metal oxide nanohybrids for toxic gas sensor: a review." Sensors and Actuators B: Chemical 221 (2015): 1170-1181.Anasori, Babak, Maria R. Lukatskaya, and Yury Gogotsi. "2D metal carbides and nitrides (MXenes) for energy storage." Nature Reviews Materials 2 (2017): 16098.Lee, Eunji, et al. "Enhanced Gas-Sensing Performance of GO/TiO2 Composite by Photocatalysis." Sensors 18.10 (2018): 3334. Acknowledgement This research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), grant funded by the Korea Government Ministry of Trade, Industry and Energy (20158520000210), and Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD).

Non-Enzymatic Urea Biosensor Based on Silver-Nickel Oxyhydroxide Nanorods Composite Electrode

Urea is an end-product of the metabolism of nitrogenous compounds, which can be detected in the blood as well as urine [1]. Ammonia catabolized by protein metabolism is converted into urea by liver and kidneys [2]. Consequently, the concentration of urea in the urine or blood is a suitable biomarker that monitors liver and kidney function. If a sensor platform can immediately determine the level of urea in the biological fluid, it will be valuable for many patients when estimating the concentration of urea in the blood. Investigation on urea biosensors has been mainly guided out the advancement of enzyme-based catalysts [3]. However, the limitations such as denaturation of enzyme and mobilization to the catalysts lead to the lack of stability. Consequently, the improvement of non-enzyme-based catalysts can work the constraints mentioned above, thereby allowing the progression of urea biosensors. Many non-enzymatic catalysts have been investigated to catch urea molecules, including noble metals, transition metals, and metal hydroxide [4]-[6]. With them, the Ni-based catalysts are the most encouraging suggestion, because it gives excellent electrocatalytic efficiency, biocompatibility, nontoxicity, and high electron transfer. [7]. Although nickel-based catalysts are admitted being an excellent facilitator for the urea electrooxidation, published investigations are few in the nickel-based catalysts for biosensor applications. The inadequacy of research in the biosensor area is related to the mechanism of nickel-based catalysts in alkaline medium. Ni(OH)2 (Ni2+) is electrochemically oxidized to NiOOH (Ni3+) before electrocatalytic urea oxidation. However, since the pH of human blood is neutral (7.35-7.45), it is necessary to develop catalysts as a biomarker for urea electrooxidation which does not depend on pH. Therefore, the nickel-based catalysts intrinsically involving Ni3+ ion will more efficiently improve the electrooxidation performance of the urea. In this study, A composite catalyst based on silver-nickel oxide hydroxide nanorods (Ag-NiOOH) was synthesized for non-enzymatic urea detection. The Ag-NiOOH was characterized by energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction techniques. The morphology and the structure of the Ag-NiOOH were investigated using scanning electron microscopy. The Ag-NiOOH coated carbon paper was employed to fabricate a new electrochemical sensor for urea detection. The Ag-NiOOH/carbon paper electrode showed a very high sensitivity of 177 μAmM−1cm−2, a low detection limit of 5 μM and a response time of 1.5 s. Detailed discussion on the performance of Ag-NiOOH and the role of inherent Ni3+ ions as a catalyst in urea biosensor will be given. References Coll, Elisabeth, et al. "Serum cystatin C as a new marker for noninvasive estimation of glomerular filtration rate and as a marker for early renal impairment." American journal of kidney diseases 36.1 (2000): 29-34.Jakhar, Seema, et al. "Preparation, characterization and application of urease nanoparticles for construction of an improved potentiometric urea biosensor." Biosensors and Bioelectronics 100 (2018): 242-250.Liu, Baohong, et al. "Studies on a potentiometric urea biosensor based on an ammonia electrode and urease, immobilized on a γ-aluminum oxide matrix." Analytica chimica acta 341.2-3 (1997): 161-169.Boggs, Bryan et al. "Urea electrolysis: direct hydrogen production from urine." Chemical Communications 32 (2009): 4859-4861.Chen, Sheng, et al. "Size Fractionation of Two‐Dimensional Sub‐Nanometer Thin Manganese Dioxide Crystals towards Superior Urea Electrocatalytic Conversion." Angewandte Chemie International Edition 55.11 (2016): 3804-3808.Wu, Mao-Sung, et al. "Hydrothermal growth of vertically-aligned ordered mesoporous nickel oxide nanosheets on three-dimensional nickel framework for electrocatalytic oxidation of urea in alkaline medium." Journal of power sources 272 (2014): 711-718.Li, Chengchao, et al. "A novel amperometric biosensor based on NiO hollow nanospheres for biosensing glucose." Talanta 77.1 (2008): 455-459. Acknowledgement This work was supported by Agency for Defense Development (ADD) as global cooperative research for high performance and light weight bio-urine based fuel cell (UD160050BD) and the Ocean University of China-Auburn University (OUC-AU) Grants program.

Experimental validation of a velocity obstacle based collision avoidance algorithm for unmanned surface vehicles

This paper presents experimental validation results of autonomous collision avoidance algorithms using an unmanned surface vehicle (USV). For autonomous collision avoidance while following given waypoints, the existing line-of-sight (LOS) guidance and velocity obstacle (VO) algorithms are modifed and applied to this USV. The proposed collision avoidance algorithm considers the rule 13 to 17 in the international collision regulations (COLREGs) and provides a rule-compliant evasive path. The performance and practical validity of the developed autonomous navigation and collision avoidance capabilities are demonstrated and discussed using the results of real-sea experiments conducted with the USV M-Searcher, developed by the Agency for Defense Development, Republic of Korea.

Sensitivity of acoustic predictions on the mesh size of large-eddy simulation of supersonic jet

Intense noise produced by the supersonic jet plume from a rocket can cause damage to its structural system and even a failure during launch. In order to predict the acoustic loading by rocket jet noise, large-eddy simulation (LES) is commonly employed for analysis of the jet flow field that is subsequently used as a source condition for predicting the acoustic field. Although desirable from the accuracy standpoint, LES of a supersonic jet is often burdened by an overwhelming computational cost in both runtime and memory. In this talk, we discuss the sensitivity of acoustic predictions on the spatial resolution of LES, and propose a guideline for reducing the mesh requirement. . Here, the flow field of a supersonic jet is calculated using a hybrid RANS/LES scheme on meshes of different sizes, and is fed into the Helmholtz-Kirchhoff integral for prediction of the acoustic farfield. Changes in overall sound pressure level (OASPL) and directivity of the Mach radiation are monitored as the LES mesh varies in size. The study suggests that (a) the accuracy of the acoustic prediction is not much affected by the use of a coarser mesh to a certain extent and (b) the resulting improvement in computation speed and economy thus outweighs the loss of details in LES, given the prediction of acoustic loading as the ultimate goal. (This work was conducted at High-Speed Vehicle Research Center of KAIST with the support of the Defense Acquisition Program Administration and the Agency for Defense Development under Contract UD170018CD.)Intense noise produced by the supersonic jet plume from a rocket can cause damage to its structural system and even a failure during launch. In order to predict the acoustic loading by rocket jet noise, large-eddy simulation (LES) is commonly employed for analysis of the jet flow field that is subsequently used as a source condition for predicting the acoustic field. Although desirable from the accuracy standpoint, LES of a supersonic jet is often burdened by an overwhelming computational cost in both runtime and memory. In this talk, we discuss the sensitivity of acoustic predictions on the spatial resolution of LES, and propose a guideline for reducing the mesh requirement. . Here, the flow field of a supersonic jet is calculated using a hybrid RANS/LES scheme on meshes of different sizes, and is fed into the Helmholtz-Kirchhoff integral for prediction of the acoustic farfield. Changes in overall sound pressure level (OASPL) and directivity of the Mach radiation are monitored as the LES mesh varies in s...

Measurements of mid-frequency bottom backscattering during KOREX-17

Measurements of mid-frequency bottom backscattering strength were made on May 30, 2017, as part of the Korea Reverberation Experiment (KOREX-17) in a shallow water region located at the south coast of Korea. The acoustic data were transmitted and received as functions of frequency (4, 6, and 8 kHz) and pulse length (2 and 4 ms) using semi-monostatic sonar system composed of omni-directional acoustic source and receiver, which was deployed from the R/V Mirae. The bottom backscattering strength were extracted from intensity-averaged reverberation level for 30 individual pings. The water depth measured by an echo sounder was about 35 m and bottom was approximately flat, having a slope less than 1° over the experimental area. The surficial sediment was estimated to be silty sediment, having a mean grain size of 6 phi from grain size analysis. In this talk, the measurement results of bottom backscattering strengths will be presented as a function of grazing angle and compared to the predictions obtained by Lambert’s law and APL-UW scattering model. [Work supported by Agency for Defense Development, Korea(UD160006DD).]

Geoacoustic inversion of 3.5-kHz towed receiver data from the KOREX-17

The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters obtained by the empirical relationship to mean grain size and a sediment layering information obtained by a chirp sonar survey. [Work supported by Agency for Defense Development, Korea (UD170014DD).]The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters ob...

Oceanographic effects on mid-frequency acoustics during KOREX-17

A 9-day mid-frequency, shallow water experiment was conducted off Geoje Island, Republic of Korea, in May 2017. The experiment consisted of transmission, reverberation, and backscatter measurements. The experiment site includes a shallow bay, with water depth less than 30 m, which opens to the Korea Strait where the depth reaches 60 m at a range of a few kilometers from the bay entrance. While the bathymetry of the site is well documented, the geo-acoustic properties of the area is complex, comprised of mud with rock outcrops and regions of sand. The oceanography during the experiment was dominated by tidal forcing and this is expected to be the main source of temporal variability in propagation and reverberation at the site. This paper focus on understanding the variability of the water column in space and time by analyzing data from CTD casts and from a CTD chain, supplemented by data from a nearby oceanographic buoy. A preliminary assessment of the impact of this variability on transmission loss is also examine. [Work supported by the Office of Naval Research and the Agency for Defense Development.]