Spectral processing of point-sampled geometry

We present a new framework for processing point-sampled objects using spectral methods. By establishing a concept of local frequencies on geometry, we introduce a versatile spectral representation that provides a rich repository of signal processing algorithms. Based on an adaptive tesselation of the model surface into regularly resampled displacement fields, our method computes a set of windowed Fourier transforms creating a spectral decomposition of the model. Direct analysis and manipulation of the spectral coefficients supports effective filtering, resampling, power spectrum analysis and local error control. Our algorithms operate directly on points and normals, requiring no vertex connectivity information. They are computationally efficient, robust and amenable to hardware acceleration. We demonstrate the performance of our framework on a selection of example applications including noise removal, enhancement, restoration and subsampling

Dynamic Pressure Sensing for the Flight Test Data System

This thesis describes the design, assembly, and test of the FTDS-K, a new device in the Boundary Layer Data System (BLDS) family of flight data acquisition systems. The FTDS-K provides high-frequency, high-gain data acquisition capability for up to two pressure sensors and an additional three low-frequency pressure sensors. Development of the FTDS-K was separated into a core module, specialized analog subsystem, and practical testing of the FTDS-K in a flow measurement mission. The core module combines an nRF52840-based microcontroller module, switching regulator, microSD card, real-time clock, temperature sensor, and trio of pressure sensors to provide the same capabilities as previous-generation BLDS-P devices. An expansion header is included in the core module to allow additional functionality to be added via daughter boards. An analog signal chain comprised of two-stage amplification and fourth-order active antialiasing filters was implemented as a daughter board to provide an AC-coupled end-to-end gain of 7,500 and a DC-coupled end-to-end gain of 50. This arrangement was tested in a wind tunnel to demonstrate that sensors with a full-scale range of 103 kPa can be used to reliably discriminate between laminar and turbulent flows based on pressure fluctuation differences on the order of tens of Pa. A combination of wind-off correction and band-filtering was used to reduce the effect of inherent and induced electrical noise, while two-sensor correlation was tested and shown to be effective at removing certain types of noise. Total power consumption for the FTDS-K in a representative mission is 208 mW, which translates to an operational endurance of 9 hours with 2 AAA LiFeS2 cells at -40°C

Wavelet Analyses of F/A-18 Aeroelastic and Aeroservoelastic Flight Test Data

Time-frequency signal representations combined with subspace identification methods were used to analyze aeroelastic flight data from the F/A-18 Systems Research Aircraft (SRA) and aeroservoelastic data from the F/A-18 High Alpha Research Vehicle (HARV). The F/A-18 SRA data were produced from a wingtip excitation system that generated linear frequency chirps and logarithmic sweeps. HARV data were acquired from digital Schroeder-phased and sinc pulse excitation signals to actuator commands. Nondilated continuous Morlet wavelets implemented as a filter bank were chosen for the time-frequency analysis to eliminate phase distortion as it occurs with sliding window discrete Fourier transform techniques. Wavelet coefficients were filtered to reduce effects of noise and nonlinear distortions identically in all inputs and outputs. Cleaned reconstructed time domain signals were used to compute improved transfer functions. Time and frequency domain subspace identification methods were applied to enhanced reconstructed time domain data and improved transfer functions, respectively. Time domain subspace performed poorly, even with the enhanced data, compared with frequency domain techniques. A frequency domain subspace method is shown to produce better results with the data processed using the Morlet time-frequency technique

Analysis of Turbulent Flow Behavior in Helicopter Rotor Hub Wakes

The rotor hub is one of the most important features of all helicopters, as it provides the pilot a means for controlling the vehicle by changing the characteristics of the main and tail rotors. The hub also provides a structural foundation for the rotors and allows for the rotor blades to respond to aerodynamic forces while maintaining controllability and stability. Due to the inherent geometry and high rate of rotation, the rotor hub in its current form acts a large bluff body and is the primary source of parasite drag on the helicopter, despite its relatively small size. The rotor hub also produces a highly turbulent wake which can affect the performance of the vehicle\u27s empennage and tail rotor. Much of the characteristics and behaviors of this wake are still difficult to predict and analyze, but the application of numerical simulations makes this task easier and more efficient. The turbulent and frequency content characteristics were examined in the wakes of four helicopter rotor hub geometries in forward flight. Computational fluid dynamics (CFD) simulations were performed using NASA\u27s OVERFLOW 2.2n Reynolds-averaged Navier Stokes solver, and the simulations imposed flow conditions based on previous and current experimental and numerical studies. Surface force and velocity harmonics for several frequencies were computed and qualitatively compared against available experimental results. Components of the Reynolds stress tensor were computed and examined. Production and transport of the turbulent kinetic energy are examined through the rotor hub wakes at six stream-wise coordinates. Frequency content was found to be concentrated towards the retreating side of all hubs in most of the frequencies examined, and certain geometrical features of the hubs were found to contribute significantly greater portions of this frequency content than others. Reynolds stresses showed similar concentrations as the mean velocity contours, which displayed a general bias towards the advancing side due to the increased relative velocity. Modal analysis of the instantaneous Reynolds stresses showed that perturbations directly behind the advancing side could only be captured with a large set of modes. Integrations of a turbulent kinetic energy flux and the stream-wise third-order moment showed a nearly-linear relation between the frontal area of the hubs and the magnitudes of these quantities

Graph Spectral Image Processing

Recent advent of graph signal processing (GSP) has spurred intensive studies of signals that live naturally on irregular data kernels described by graphs (e.g., social networks, wireless sensor networks). Though a digital image contains pixels that reside on a regularly sampled 2D grid, if one can design an appropriate underlying graph connecting pixels with weights that reflect the image structure, then one can interpret the image (or image patch) as a signal on a graph, and apply GSP tools for processing and analysis of the signal in graph spectral domain. In this article, we overview recent graph spectral techniques in GSP specifically for image / video processing. The topics covered include image compression, image restoration, image filtering and image segmentation

Design, fabrication and acoustic tests of a 36 inch (0.914 meter) statorless turbotip fan

The LF336/E is a 36 inch (0.914 meter) diameter fan designed to operate in a rotor-alone configuration. Design features required for modification of the existing LF336/A rotor-stator fan into the LF336/E statorless fan configuration are discussed. Tests of the statorless fan identified an aerodynamic performance deficiency due to inaccurate accounting of the fan exit swirl during the aerodynamic design. This performance deficiency, related to fan exit static pressure levels, produced about a 20 percent thrust loss. A study was then conducted for further evaluation of the fan exit flow fields typical of statorless fan systems. This study showed that through proper selection of fan design variables such as pressure ratio, radius ratio, and swirl distributions, performance of a statorless fan configuration could be improved with levels of thrust approaching the conventional rotor-stator fan system. Acoustic measurements were taken for the statorless fan system at both GE and NASA, and when compared to other lift fan systems, showed noise levels comparable to the quietest lift fan configuration which included rotor-stator spacing and acoustic treatment. The statorless fan system was also used to determine effects of rotor leading edge serrations on noise generations. A cascade test program identified the serration geometry based on minimum pressure losses, wake turbulence levels and noise generations

SAMPLE III SC.02 - Studying, sAmpling and Measuring of aircraft ParticuLate Emissions III: Specific Contract 02

The objectives of this specific contract were: - to provide support to the SAE E-31 in drafting the Aerospace Recommended Practice (ARP) on the measurement of aircraft engine non-volatile particulate matter (nvPM) mass and number emissions; and - to improve the sampling system that was manufactured during SAMPLE III SC.01 according to the preliminary specifications of the draft ARP, to assess its operating parameters at the SR Technics engine testing facility in Zürich and to perform a comparison with the sampling line installed at this facility. In order to deliver the aforementioned objectives numerous design, experimental and desk based studies were performed: - coordination of and contribution to SAE E-31 meetings and teleconferences; - manufacture of a sampling system to allow remote operation and monitoring and simultaneous sampling within SR Technics test cell; and - conduct numerous piggy back and dedicated engine test campaigns at SR Technics

宇宙機器の認定試験における衝撃応答スペクトラムの相似性と再現性の評価

The shock loading on satellite components during any of the separation events (of rocket boosters, rocket stages, and the payload fairing) leading to the eventual separation of a satellite at its destination orbit may be detrimental to satellite components. Generally, the shock response spectrum (SRS) describes the shock severity level in a Qualification Testing (QT). In QT, a component is subjected to an extreme (simulated) environmental condition, such as shock, as a means of guaranteeing its performance when used in an environment of similar severity. Shock simulation by a mechanical impact is one of several shock qualification test methods. The problem in QT, especially when using a mechanical impact simulator, is that the shock tests show a huge variability from test to test and generating repeatable SRS profiles that satisfy the target shock level involves a lot of trial-and-error (up to 85 have been reported in the literature). Moreover, fully characterizing a mechanical impact involves understanding the interaction of several parameters, such as the impact velocity, impact angle, and absorber materials between impacting bodies. To reduce the number of trial- and-error and facilitate rapid testing, testing facilities match a target SRS to a database shock and retrieve its associated testing conditions. This process relies on the similarity between the target SRS and the database SRS. The purpose of this research is to investigate the SRS variation in tests simulated using an air gun shock testing machine and reduce the trial and error before satisfying a QT requirement. In particular, this research contributes a new similarity metric, the weighted RMSE, that can be used by commercial testing facilities to retrieve an SRS similar to a target SRS from a database of previous shock tests. In an SRS database retrieval task, the weighted RMSE outperformed other known SRS similarity measures in that it not only retrieves the SRS most similar to the target SRS, but also an SRS that satisfies the requirement that at least 50% of the measured SRS shall exceed the target SRS. Moreover, the SRS response of impact shocks using the air gun shock machine were characterized experimentally. This research shows that with careful data acquisition, at a given driving pressure, the knee frequency of the measured SRS is influenced by the mass and material of the projectile. The heavier, metallic projectile tends to excite a higher knee frequency, than the lighter, non-metallic projectile.九州工業大学博士学位論文 学位記番号：工博甲第524号 学位授与年月日：令和3年6月28日1. Introduction|2. Literature Review|3. Retrieving an SRS from a database of shocks: Case-based Rapid Shock Qualification Testing of Spacecraft Components|4. Characterization of the Shock simulation on an air gun shock machine|5. Retrieving an SRS from a database for Rapid Qualification Testing|6. Conclusion and Future Work九州工業大学令和3年

Experimental studies on shock wave interactions with flexible surfaces and development of flow diagnostic tools

Nowadays, light-weight composite materials have increasingly used for high-speed flight vehicles to improve their performance and efficiency. At supersonic speed, sonic fatigue, panel flutter, severe instabilities, and even catastrophic structural failure would occur due to the shock wave impingement on several flexible components of a given structural system either internally or externally. Therefore, investigation on shock wave interaction with flexible surfaces is crucial for the safety and performance of high-speed flight vehicles. This work aims to investigate the mechanism of shock wave interaction with flexible surfaces with and without the presence of the boundary layer. The first part involves the shock wave generated by supersonic starting jets interaction with flexible surfaces and the other one focuses on shock wave and boundary layer interaction (SBLI) over flexible surfaces. A novel miniature and cost-effective shock tube driven by detonation transmission tubing was designed and manufactured to simulate the supersonic starting jet and investigate the interaction of a supersonic starting jet with flexible surfaces. To investigate the characterization of this novel type shock tube, the pressure-time measurement in the driven section and the time-resolved shadowgraph were performed. The result shows that the flow structure from the open end of the shock tube driven by detonation transmission tubing agrees with that of conventional compressed-gas driven shock tubes. Moreover, this novel type of shock tube has good repeatability of less than 3% with a Mach number range of 1.29-1.58 when the weight of the NONEL explosive mixture varies from 3.6mg to 12.6mg. An unsteady background oriented schlieren (BOS) measurement system and a sprayable Polymer-Ceramic unsteady pressure sensitive paint (PC-PSP) system were developed. The preliminary BOS result in a supersonic wind tunnel shows that the sensitivity of the BOS system is good enough to visualize weak density variations caused by expansion waves, boundary layer, and weak oblique shocks. Additionally, compared with the commercial PC-PSP from Innovative Scientific Solutions Incorporated (ISSI), the in-house developed unsteady PSP system has higher pressure sensitivity, lower temperature sensitivity, and photo-degradation rate. To identify the shock movement, distortion and unsteadiness during the processes of the supersonic starting jet impingement and shock wave boundary layer interaction (SBLI) over flexible surfaces, an image processing scheme involving background subtraction in the frequency domain, filtering, resampling, edge detection, adaptive threshold, contour detection, feature extraction, and fitting was proposed and applied to process shadowgraph and schlieren sequences automatically. A large shadowgraph data set characterized by low signal to noise ratio (SNR) and small spatial resolution (312×260-pixel), was used to validate the proposed scheme. The result proves that the aforementioned image processing scheme can detect, track, localize, and fit shock waves in a subpixel accuracy. The mechanism of the interaction between the initial shock wave from a supersonic starting jet and flexible surfaces was investigated based on a square shock tube driven by detonation transmitting tube. Compared with that of the solid plate case, flexible surfaces can delay the shock reflection process because of the flexible panel deformation generated by the pressure difference between the top and the bottom. The delay time is around 8µs in the case of 0.1mm thick flexible surface, whereas it declines to around 4µs in the case of 0.3mm thick flexible surface because of the lower flexibility and deformation magnitude. However, interestingly, the propagation velocity of the reflected shock wave is basically the same for the solid plate and flexible panels, which means the flexible surface doesn’t reduce the strength of the reflection wave, although it delays its propagation. Also, there is not an apparent difference in the velocity of the reflected shock wave in the case of different incident shock Mach numbers when Ms varying from 1.22 to 1.54. These experimental results from this study are useful for validating numerical codes that are used for understanding fluid-structure interaction processes

Investigation Of Predicted Helicopter Rotorhub Drag and Wake Flow with Reduced Order Modeling

The rotor hub is one of the most important components of the modern helicopter. This complex collection of linkages and plates has numerous responsibilities, including the translation of pilot input to system response, anchoring the blades to the rotor mast, and sustaining the various forces transmitted by the blades. Due its intricate design and relatively small sized components the rotor hub interacts with the incoming flow to create a highly chaotic, turbulent wake which impinges on the fuselage and empennage. This assembly has also been found to be one of the primary contributors to the total vehicle parasite drag. Unfortunately studying the rotor hub and its wake more closely is made difficult by the limitation of both modern experimental and computational methods. From an experimental standpoint tests are expensive to run, difficult to gather large amounts of data from, and can require full or high scale Reynolds numbers. Computational Fluid Dynamics (CFD) predictions of hub flows are limited by high grid resolution requirements, and lengthy grid generation and simulation times. Modal decompositions provide robust options for reduced order modeling of fluid flows. Several modal decomposition methods are tested for the validity of their application to the complex flow fields that form around rotor hubs. Four variations of two rotor hub designs, a baseline and low drag, are simulated in forward flight. This selection of hubs was chose to examine the effects of both hub geometry and aerodynamic optimization on the rotor hub surface forces and wake. Flow solutions were found using the OVERFLOW2.2n overset, structured, RANS solver created and maintained by NASA. Simulations were conducted using a fully turbulent model and the grid generation and computational equations specifics are discussed in further detail. Each of the four hub variants was subjected to the same flow conditions. Several variants of modal decomposition and other post processing techniques were used on the resultant surface force and wake data in order to Characterize the hub flow field