Pemodelan Elemen Hingga Untuk Distribusi Temperatur Pada Proyektil Kaliber Kecil

Ammunition adalah proyektil dan pendorong atau apapun yang dapat digunakan di dalam pertempuran. Pada proyektil modern, teknologi MEMS (Microelectromechanical System) sudah banyak terintegrasi yang berguna untuk meningkatkan performa dari proyektil tersebut. Tetapi teknologi MEMS tersebut hanya ada pada proyektil berkaliber besar dikarenakan banyaknya ruang sehingga MEMS tersebut lebih terlindungi dari temperatur tinggi yang terjadi pada saat penembakan. Untuk mengukur distribusi temperatur pada proyektil pada saat penembakan merupakan suatu hal yang sulit dikarenakan tingginya temperatur pada saat internal ballistics dan tingginya kecepatan proyektil pada saat external ballistics. Salah satu metode numerik yang dapat digunakan dalam penyelesaian kasus distribusi temperatur adalah metode elemen hingga. Metode ini mampu menyelesaikan permasalahan dengan benda yang memiliki geometri kompleks, sehingga membuat metode ini lebih unggul dari metode lainnya. Dalam tugas akhir ini, metode elemen hingga diterapkan untuk kasus distribusi panas dua dimensi untuk mendapatkan distribusi dan history temperatur pada proyektil dengan 5 skenario. Dari hasil distribusi dan history temperatur akan membuktikan apakah memungkinkan untuk mengaplikasikan teknologi MEMS pada proyektil berkaliber kecil pada fase exterior ballistics. Hasil simulasi menunjukkan bahwa MEMS dapat ditempatkan dimanapun pada proyektil kecuali pada bagian permukaan proyektil. Peningkatan konduktifitas material merupakan parameter yang sangat berpengaruh pada distribusi temperatur pada proyektil dan konveksi eksternal merupakan parameter yang tidak terlalu berpengaruh pada distribusi temperatur pada proyektil. Kata Kunci: Microelectromechanical System, Metode Elemen Hingga, Exterior Ballistics, Konduksi Panas

Zones of approach for craniofacial resection: minimizing facial incisions for resection of anterior cranial base and paranasal sinus tumors

Journal ArticleAnterior cranial base tumors are surgically resected with combined craniofacial approaches that frequently involve disfiguring facial incisions and facial osteotomies. The authors outline three operative zones of the anterior cranial base and paranasal sinuses in which tumors can be resected with three standard surgical approaches that minimize transfacial incisions and extensive facial osteotomies

Small-Caliber Exterior Ballistics : Aerodynamic Coefficients Determination by CFD

The models used to calculate small-caliber projectile trajectories are often only drag-based, given the presumed short ranges and the assumed small variation of the aerodynamic parameters in flight. Depending on the type of application, "field" calibrations are then performed to compensate for the observed deviations. However, with the new small-caliber applications and the inherent increased challenges, these simplified methods do not yield satisfactory results anymore in terms of accuracy and attitude upon impact. In the first part, next to reviewing existing trajectography models, we discuss their implementation in our own trajectory program \textit{VTraj}, developed in LabVIEW. The six degrees of freedom (6 DoF) model allows to compute the flight of any symmetrical or asymmetrical projectile (spin- or fin- stabilized). Its parameters include a complete set of static and dynamic contributions, including Magnus and pitch damping forces \& moments. This model allows the analysis of all translation and angular motions of the projectile's body. The models give good agreement with published results on standard reference projectiles for the trajectory parameters. In part two, we focus on the methodology to capture the static and dynamic coefficients by steady and unsteady RANS methods for subsonic, transonic and supersonic flight conditions. Accurate resolution of the flow in the boundary layer and in the wake of the projectile proved to be of utmost importance for the correct determination of the coefficients. The coefficient extraction methods are assessed with published results for canonical shapes and good agreement is achieved. The results highlight the strong dependency of the pitch damping coefficient on the reduced pitch frequency which varies along the flight path. Rigid Body Dynamics (RBD) as well as Computational Fluid Dynamics (CFD) are finally combined in order to evaluate the behavior of specific small-caliber applications: non-lethal projectiles operating in the low subsonic domain, long-range projectiles with focus on transonic domain crossing, and asymmetric configuration are studied. The resolution of the dynamic flow around the projectile and the prediction of stability upon impact are confronted with experimental results and the match is very promising. The research also gives new insight into the diverse phenomena at hand in the transonic domain, or for projectiles with mass unbalance, and the change they impart on static and dynamic stability characteristics

Barut tane geometrisinin silah iç balistiğine etkisinin incelenmesi

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Bu çalışmada silahların iç balistiğinin tanımlaması yapılmıştır. İç balistik hesaplamalarına ilişkin matematik model oluşturulmuştur. Model oluşturulurken barut tane geometrisine bağlı olarak geliştirilen biçim fonksiyon kullanılmıştır. Modelin doğrulanmasında, literatürden temin edilen 40 mm silah sisteminin deneysel atış sonuçları kullanılmıştır. Deneysel çalışmada kullanılan parametreler ile kodun çözümü yapılmıştır. Matematik model ile test sonuçları kıyaslanmıştır. Sonuçlardaki sapmanın %4 seviyesinde olduğu tespit edilmiştir. Böylelikle matematik model doğrulanmıştır. Bu model kullanılarak silindirik, tek delikli silindirik, çok delikli silindirik ve küresel barut taneleri incelenmiştir. Bu tane geometrilerinin etkisi gösterilmiştir.In this study, the description of interior ballistics of guns is given. The interior ballistics mathematical model is developed for calculation. During the mathematical model development process geometrical properties of propellant are used as the form function. 40 mm gun firing experimental results which got from literature are used in the model verification process. The code solved with the parameters described in the experimental study. Results of the mathematical modal are compared with the experimental results. The comparison showed that the standard deviation between experimental and numerical results was less than 4%. Therefore the modal were verified. After verification process cylindrical, single perforated cylindrical, multi perforated cylindrical and spherical granule types are inspected with the modal. Effect of the granule geometries has shown in this study

Finite amplitude stress waves in rocks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Geology and Geophysics, 1959.Vita.Includes bibliographical references (leaves 74-78).by Donald R. Grine.Ph.D

Microelectromechanical Systems (MEMS) Interrupter for Safe and Arm Devices

This thesis addresses the development of a new micro-scale interrupter mechanism for a safe and arm device used in modern weapon systems. The interrupter mechanism often consists of a physical barrier that prevents an initial source of energy, in an explosive train, from being transferred to subsequent charges. In general, when the physical barrier is removed, the weapon is considered armed, and the charge is allowed to propagate. Several issues facing current safe and arm devices systems are the shrinking industrial base for manufacturing these devices and the desire for modern safe and arm devices to be compatible with next generation weapon systems that are generally decreasing in size and increasing in complexity. The solution proposed here is to design, fabricate, and test a conceptual interrupter mechanism using Microelectromechanical Systems (MEMS) components. These components have inherent benefits over current devices, such as smaller feature sizes and lower part counts, which have the capability to improve performance and reliability. After an extensive review of existing micro-scale safe and arm devices currently being developed, a preliminary design was fabricated in a polysilicon surface micromachining process. The operating principle of this conceptual interrupter mechanism is to have MEMS actuators slide four overlapping plates away from each other to create an aperture, thus providing an unimpeded path for an initiating energy source to propagate. Operation of the fabricated MEMS interrupter mechanism was successfully demonstrated with an approximate aperture area of 1024 μm2 being created

Aerodynamic control using distributed active bleed

A novel approach for controlling the global aerodynamic loads on lifting surfaces using regulated distributed active bleed that is driven by pressure differences across the surfaces is investigated in wind tunnel experiments. The experiments focus on the flow mechanisms that govern the interaction between the bleed and the local cross flow over a wide range of pre- and post-stall angles of attack. Particle image velocimetry (PIV) and load cell measurements indicate that low momentum quasi-steady and time-periodic bleed [momentum coefficients of O(10-4)] lead to bi-directional deflections of the time-averaged vorticity layer and effect increases or decreases in lift, drag, and pitching moment. High-speed PIV and proper orthogonal decomposition (POD) of the vorticity flux show that the bleed engenders trains of discrete vortices that advect along the surface and are associated with a local instability that is manifested by a time-averaged bifurcation of the vorticity layer near the bleed outlets. The vortices advect over several convective times and alter the vorticity flux over the airfoil and thereby the aerodynamic loads. Active bleed is also investigated on a dynamically pitching airfoil (reduced frequencies up to k = 0.42) to study the effects of modulating the evolution of vorticity concentrations during dynamic stall. Time-periodic bleed mitigates adverse pitching moment behavior (“negative damping”) that can precipitate structural instabilities while maintaining the cycle-average loads to within 5% of the base levels by segmenting the vorticity layer during upstroke and promoting early flow attachment during downstroke. The present investigations demonstrate that active bleed can be implemented for direct lift control, maneuvering, or stabilization of flexible aerostructures (airframes, flexible wings, and rotor blades).Ph.D

낮은 임계 가속도를 가지는 실리콘 기반 MEMS 가속도 스위치에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 김용권.Abstract In this paper, MEMS acceleration switch with low threshold acceleration below 10 g and fine environmental characteristics are developed. Limits of the previously reported low-g MEMS switches were addressed in terms of environmental test issues and the solutions for them were suggested and integrated in the proposed low-g MEMS acceleration switch. Fabrication process consists of one silicon-on-insulator substrate and two glass substrates for base and package, respectively. Single-crystalline silicon was chosen as the structural material for high thermal stability and stress-free structure. After the fabrication, height profiles of the free-hanging proof masses were measured to show that the fabricated switches does not suffer from stress problems. The size of single switch was measured as 2150 x 4240 x 1180 µm3 and the average proof mass, initial gap, and the spring constant was 307.38 µg, 6.39 µm, and 3.29 N/m, respectively. The calculated threshold acceleration thus was 6.98 g. In the electrostatic operation test, the response time of the switch was measured to be shorter than 1.2 ms and the minimum contact resistance was 8.5 Ω at the contact force of 284 µN. Life cycle test was carried out to show that the developed switch could operate more than 10,000 cycles without failure. Rotation-table experiment was carried out in sequence to reveal that the switch operates at 6.61 g. The error analysis was carried out in the consideration of the off-axis force generated during the rotation-table experiment. From the experimental values, the off-axis force was calculated as 2.091 μN and the resulting reduction in the initial switching gap was simulated as 0.236 μm. The reduced threshold acceleration thus was estimated to be 6.512 g, which agrees well with the measured threshold acceleration value of 6.61 g. Rotation-table test using another switch was conducted to model the relation between the off-axis force and the operating acceleration of the developed switch. Least squares method was used in the analysis and the original threshold acceleration (a_th) of the switch was calculated as 6.16325 g. The error rate (ε) due to the off-axis force was calculated as -0.22693 g/µN. The modeled operating acceleration of the switch in terms of the off-axis force matched well with the measurements, showing the maximum error less than 1.6%. Heating, sealing, high-g, and impact tests were conducted in sequence to validate the environmental characteristics of the switch. Test condition of 80 °C for 6 hours were adopted for heating test and the tested switch operated more than 200 cycles normally after the test. For sealing test, gross leak test using penetrant dye (Rhodamine B) and fine leak test using tracer gas (helium) were conducted sequentially. 10 samples were put into both of the tests. In the gross leak test, no signs of dye penetration were observed after pressurizing the samples in the dye solution. The tested switches were then put into the fine leak test. In the fine leak test, helium leak rates were measured and all of the tested samples showed leak rate lower than 5.8x10-8 atm cc/s He, which is the reject limit provided by MIL-STD-883E. High-g test and drop impact test were also performed to validate the effectiveness of the displacement-restricting structure. As a result of the high-g test, the developed switch was able to operate without breaking after experiencing the acceleration of 300 g in the ±x ̂, ±y ̂, and ±z ̂ axes. In addition, the drop impact test has proved that the developed switch can withstand an impact as high as 1000 g. The MEMS acceleration switch developed throughout this study is the first to attain low threshold and good environmental characteristics at the same time. Therefore, the author believes that the switch developed in this study is the most suitable one for safety arm unit application among the low-g switches developed so far.1. Introduction 1 1.1. Sensing of acceleration 1 1.2. Safety arm unit and MEMS acceleration switches 8 1.3. Literature review 14 1.4. Motivation and purpose 19 1.5. Contribution 20 1.6. Composition of thesis 22 2. Theory and design of low-g MEMS acceleration switch 23 2.1. Basic theories on acceleration switch 23 2.1.1 Static threshold acceleration 23 2.1.2 Determining the initial gap 25 2.1.3 Serpentine spring 27 2.1.4 Parallel plate damper 31 2.2. Model description 34 2.2.1 Base glass substrate 36 2.2.2 SOI substrate 36 2.2.3 Packaging glass substrate 37 2.3. FEM simulation 38 2.3.1 Force, displacement, stress simulation 38 2.3.2 Modal analysis Resonant frequency 40 2.4. MATLAB code for MEMS switch 45 3. Fabrication of low-g MEMS acceleration switch 63 3.1. Overall fabrication process 63 3.2. Base glass substrate 65 3.3. SOI substrate 69 3.4. Bonded susbtrate & packaging 72 3.5. Fabrication results 79 4. Characterization of low-g MEMS acceleration switch 84 4.1. DC operation test & lifecycle test 84 4.2. Rotation-table experiments 93 4.3. Effect of the off-axis force on the operating acceleration 101 4.4. Heating test 111 4.5. Sealing test 112 4.6. High-g test & drop impact test 118 5. Conclusion 125 References 128 Abstract (Korean) 136Docto