Helicopter vibration suppression using simple pendulum absorbers on the rotor blade

A comprehensive anaytical design procedure for the installation of simple pendulums on the blades of a helicopter rotor to suppress the root reactions is presented. A frequency response anaysis is conducted of typical rotor blades excited by a harmonic variation of spanwise airload distributions as well as a concentrated load at the tip. The results presented included the effect of pendulum tuning on the minimization of the hub reactions. It is found that a properly designed flapping pendulum attenuates the root out-of-plane force and moment whereas the optimum designed lead-lag pendulum attenuates the root in-plane reactions. For optimum pendulum tuning the parameters to be determined are the pendulum uncoupled natural frequency, the pendulum spanwise location and its mass. It is found that the optimum pendulum frequency is in the vicinity of the excitation frequency. For the optimum pendulum a parametric study is conducted. The parameters varied include prepitch, pretwist, precone and pendulum hinge offset

Fish Assemblage Relationships with Physical Characteristics and Presence of Dams in Three Eastern Iowa Rivers

Fish assemblages in rivers of the Midwestern United States are an important component of the region\u27s natural resources and biodiversity. We characterized the physical environment and presence of dams in a series of reaches in three eastern Iowa rivers tributary to the Mississippi River and related these characteristics to the fish assemblages present. Some physical characteristics were similar among the 12 study reaches, whereas others differed substantially. We found a total of 68 species across the 12 study reaches; 56 in the Turkey River, 51 in the Maquoketa River and 50 in the Wapsipinicon River. Seventeen species could be described as ‘downstream-distributed’; 15 being found only in the lowest reach of one or more rivers and the other two being found only in the lowest reaches or two or more contiguous reaches including the lowest reach. Two species could be described as ‘upstream-distributed’, being found only in an uppermost reach. Non-metric multidimensional scaling ordination illustrated similarities among reaches, and five physical variables were significantly correlated with assemblage similarities. Catchment area and number of dams between reaches and the Mississippi River were strongly correlated with assemblage similarities, but the directions of their effects were opposite. Catchment area and number of dams were confounded. The collective evidence to date suggests that the pervasiveness of dams on rivers significantly alters fish assemblages, making underlying patterns of species change and relationships with naturally varying and human-influenced physical characteristics along a river\u27s course difficult to discern

D-Terms, Unification, and the Higgs Mass

We study gauge extensions of the MSSM that contain non-decoupling D-terms, which contribute to the Higgs boson mass. These models naturally maintain gauge coupling unification and raise the Higgs mass without fine-tuning. Unification constrains the structure of the gauge extensions, limiting the Higgs mass in these models to roughly less than 150 GeV. The D-terms contribute to the Higgs mass only if the extended gauge symmetry is broken at energies of a few TeV, leading to new heavy gauge bosons in this mass range.Comment: 30+1 pages, 7 figure

Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers

Using a path-integral Monte Carlo method for simulating superfluid quantum films, we investigate helium layers adsorbed on a substrate consisting of graphite plus two solid helium layers. Our results for the promotion densities and the dependence of the superfluid density on coverage are in agreement with experiment. We can also explain certain features of the measured heat capacity as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure

A new probe concept for internal pipework inspection

The interior visual inspection of nuclear pipework is a critical inspection activity required to ensure the continued safe, reliable operation of plant and thus avoid costly outages. Typically, the video output from a manually deployed probe is viewed by an operator online with the task of identifying and estimating the location of surface defects such as cracks, corrosion and pitting. However, it is very difficult to estimate the nature and spatial extent of defects from the often disorientating small field of view video of a relatively large structure. This work describes a new visual inspection system incorporating a wide field of view machine vision camera and additional sensors designed for inspecting 3 - 6 inch diameter pipes. The output of the system is a photorealistic model of the internal surface of the pipework. The generation of this model relies upon a core component of the system in the form of image feature extraction which estimates camera location. This paper considers the accuracy of this estimation as a function of the number and configuration of the extracted image features

Hillslope Asymmetry Maps Reveal Widespread, Multi-Scale Organization

Hillslope asymmetry is the condition in which oppositely-facing hillslopes within an area have differing average slope angles, and indicates aspect-related variability in hillslope evolution. As such, the presence, orientation and magnitude of asymmetry may be a useful diagnostic for understanding process dominance. We present a new method for quantifying and mapping the spatial distribution of hillslope asymmetry across large areas. Resulting maps for the American Cordillera of the Western Hemisphere and the western United States reveal that hillslope asymmetry is widespread, with distinct trends at continental to drainage scales. Spatial patterns of asymmetry correlate with latitude along the American Cordillera, mountain-range orientation for many ranges in the western United States, and elevation in the Idaho Batholith of the Northern Rocky Mountains. Spatial organization suggests that non-stochastic, process-driven controls cause these patterns. The hillslope asymmetry metric objectively captures previously-documented extents and frequencies of valley asymmetry for the Gabilan Mesa of the central California Coast Range. Broad-scale maps of hillslope asymmetry are of interest to a wide range of disciplines, as spatial patterns may reflect the influence of tectonics, atmospheric circulation, topoclimate, geomorphology, hydrology, soils and ecology on landscape evolution. These maps identify trends and regions of hillslope asymmetry, allow possible drivers to be spatially constrained, and facilitate the extrapolation of site-specific results to broader regions

Processing and analysis methods for transonic cavity flow

This paper focuses on the localisation of noise sources in transonic cavity flows. Beamforming is used to estimate the pressure fluctuations inside a resonant transonic cavity, showing the localisation of the main sources of noise using an acoustic array and also combining it with a mean flow-field. The influence of the microphone array position, density, and shape is investigated. The presented method models the noise propagation with simple assumptions that are easily applicable to wind tunnel testing and may help localise the noise sources from complex geometries without intrusive methods

Introducing a new method for efficient visualization of complex shape 3D ultrasonic phased-array C-scans

Automated robotic inspection systems allow the collection of large data volumes, compared to existing inspection systems. To maximize the throughput associated with the nondestructive evaluation phase, it is crucial that the reconstructed inspection data sets are generated and examined rapidly without a loss of detail. Data analysis often becomes the bottleneck of automated inspections. Therefore, new data visualization tools, suitable to screen the NDT information obtained through robotic systems, are urgently required. This paper presents a new approach, for the generation of three-dimensional ultrasonic C-scans of large and complex parts, suitable for application to high data throughput ultrasonic phased array inspection. This approach produces 3D C-scan presented as colored tessellated surfaces and the approach works efficiently on challenging geometry, with concave and convex regions. Qualitative and quantitative results show that the approach runs up to 500 times faster than other C-scan visualization techniques

Implications of Halo Inside-out Growth on the X-Ray Properties of Nearby Galaxy Systems within the Preheating Scenario

We present an entirely analytic model for a preheated, polytropic intergalactic medium in hydrostatic equilibrium within a NFW dark halo potential in which the evolution of the halo structure between major merger events proceeds inside-out by accretion. This model is used to explain, within a standard $\Lambda$CDM cosmogony, the observed X-ray properties of nearby relaxed, non-cooling flow groups and clusters of galaxies. We find that our preferred solution to the equilibrium equations produces scaling relations in excellent agreement with observations, while simultaneously accounting for the typical structural characteristics of the distribution of the diffuse baryons. In the class of preheating models, ours stands out because it offers a unified description of the intrahalo medium for galaxy systems with total masses above \sm 2\times 10^{13}\msun, does not produce baryonic configurations with large isentropic cores, and reproduces faithfully the observed behavior of the gas entropy at large radii. All this is achieved with a moderate level of energy injection of about half a keV, which can be easily accommodated within the limits of the total energy released by the most commonly invoked feedback mechanisms, as well as with a polytropic index of 1.2, consistent with both many observational determinations and predictions from high-resolution gas-dynamical simulations of non-cooling flow clusters. More interestingly, our scheme offers a physical motivation for the adoption of this specific value of the polytropic index, as it is the one that best ensures the conservation after halo virialization of the balance between the total specific energies of the gas and dark matter components for the full range of masses investigated.Comment: 18 pages, 11 figures, accepted for publication in the Astrophysical Journa

Solving Tree Problems with Category Theory

Artificial Intelligence (AI) has long pursued models, theories, and techniques to imbue machines with human-like general intelligence. Yet even the currently predominant data-driven approaches in AI seem to be lacking humans' unique ability to solve wide ranges of problems. This situation begs the question of the existence of principles that underlie general problem-solving capabilities. We approach this question through the mathematical formulation of analogies across different problems and solutions. We focus in particular on problems that could be represented as tree-like structures. Most importantly, we adopt a category-theoretic approach in formalising tree problems as categories, and in proving the existence of equivalences across apparently unrelated problem domains. We prove the existence of a functor between the category of tree problems and the category of solutions. We also provide a weaker version of the functor by quantifying equivalences of problem categories using a metric on tree problems.Comment: 10 pages, 4 figures, International Conference on Artificial General Intelligence (AGI) 201