Academic literature on the topic 'Tilted Additive Model'
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Journal articles on the topic "Tilted Additive Model"
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Boroumand, Farzaneh, Mohammad Taghi Shakeri, Touka Banaee, Hamidreza Pourreza, and Hassan Doosti. "An Analysis of the Areas Occupied by Vessels in the Ocular Surface of Diabetic Patients: An Application of a Nonparametric Tilted Additive Model." International Journal of Environmental Research and Public Health 18, no. 7 (April 2, 2021): 3735. http://dx.doi.org/10.3390/ijerph18073735.
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(1) Background: As diabetes melllitus (DM) can affect the microvasculature, this study evaluates different clinical parameters and the vascular density of ocular surface microvasculature in diabetic patients. (2) Methods: In this cross-sectional study, red-free conjunctival photographs of diabetic individuals aged 30–60 were taken under defined conditions and analyzed using a Radon transform-based algorithm for vascular segmentation. The Areas Occupied by Vessels (AOV) images of different diameters were calculated. To establish the sum of AOV of different sized vessels. We adopt a novel approach to investigate the association between clinical characteristics as the predictors and AOV as the outcome, that is Tilted Additive Model (TAM). We use a tilted nonparametric regression estimator to estimate the nonlinear effect of predictors on the outcome in the additive setting for the first time. (3) Results: The results show Age (p-value = 0.019) and Mean Arterial Pressure (MAP) have a significant linear effect on AOV (p-value = 0.034). We also find a nonlinear association between Body Mass Index (BMI), daily Urinary Protein Excretion (UPE), Hemoglobin A1C, and Blood Urea Nitrogen (BUN) with AOV. (4) Conclusions: As many predictors do not have a linear relationship with the outcome, we conclude that the TAM will help better elucidate the effect of the different predictors. The highest level of AOV can be seen at Hemoglobin A1C of 9% and AOV increases when the daily UPE exceeds 600 mg. These effects need to be considered in future studies of ocular surface vessels of diabetic patients.
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Chen, Huaizhen, Tiansheng Chen, and Kristopher A. Innanen. "Estimating tilted fracture weaknesses from azimuthal differences in seismic amplitude data." GEOPHYSICS 85, no. 3 (May 1, 2020): R135—R146. http://dx.doi.org/10.1190/geo2019-0344.1.
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Tilted transverse isotropy (TTI) provides a useful model for the elastic response of a medium containing aligned fractures with a symmetry axis oriented obliquely in the vertical and horizontal coordinate directions. Robust methods for determining the TTI properties of a medium from seismic observations to characterize fractures are sought. Azimuthal differencing of seismic amplitude data produces quantities that are particularly sensitive to TTI properties. Based on the linear slip fracture model, we express the TTI stiffness matrix in terms of the normal and tangential fracture weaknesses. Perturbing stiffness parameters to simulate an interface separating an isotropic medium and a TTI medium, we derive a linearized P-to-P reflection coefficient expression in which the influence of tilt angle and fracture weaknesses separately emerge. We formulate a Bayesian inversion approach in which amplitude differences between seismic data along two azimuths, interpreted in terms of the reflection coefficient approximation, are used to determine fracture weaknesses and tilt angle. Tests with simulated data confirm that the unknown parameter vector involving fracture weakness and tilted fracture weaknesses is stably estimated from seismic data containing a moderate degree of additive Gaussian noise. The inversion approach is applied to a field surface seismic data acquired over a fractured reservoir; from it, interpretable tilted fracture weaknesses, consistent with expected reservoir geology, are obtained. We determine that our inversion approach and the established inversion workflow can produce the properties of systems of tilted fractures stably using azimuthal seismic amplitude differences, which may add important information for characterization of fractured reservoirs.
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Gong, J., D. L. Wu, and V. Limpasuvan. "Meridionally-tilted ice cloud structures in the tropical Upper Troposphere as seen by CloudSat." Atmospheric Chemistry and Physics Discussions 14, no. 17 (September 26, 2014): 24915–42. http://dx.doi.org/10.5194/acpd-14-24915-2014.
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Abstract. It remains challenging to quantify global cloud properties and uncertainties associated with their impacts on climate change because of our poor understanding of cloud three-dimensional (3-D) structures from observations and unrealistic/unconsidered characterization of 3-D cloud effects in Global Climate Models (GCMs). In this study we find cloud 3-D effects can cause significant error in cloud ice and radiation measurements if it is not taken into account appropriately. One of the cloud 3-D complexities, the slantwise tilt structure, has not received much attention in research and even little report is given on its global perspective. A novel approach is presented here to analyze the ice cloud water content (IWC) profiles retrieved from CloudSat and a joint radar-lidar product (DARDAR). By integrating IWC along different tilt angles, we find that Upper-Troposphere (UT) ice cloud mass between 11 and 17 km is tilted poleward from active convection centers in the tropics. This systematic tilt in cloud mass structure is expected from the mass conservation principle of the Hadley circulation with the divergent flow of each individual convection/convective system from down below, and its existence is further confirmed from cloud-resolving scale Weather Research and Forecasting (WRF) model simulations. Thus, additive effects of tilted cloud structures can induce 5–20% variability by nature or an error in satellite cloud/hydrometeor ice retrievals if simply converting it from slant to nadir column. A surprising finding is the equatorward tilt in middle tropospheric (5–11 km) ice clouds, which is also evident in high-resolution model simulations but not in coarse-resolution simulations with cumulus parameterization. The observed cloud tilt structures are intrinsic properties of tropical clouds, producing synoptic distributions around the ITCZ. These findings imply that current interpretations based on over-simplified cloud vertical structures could lead to substantial cloud measurement errors and induce subsequent impact on understanding cloud radiative, dynamical and hydrological properties.
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Gong, J., D. L. Wu, and V. Limpasuvan. "Meridionally tilted ice cloud structures in the tropical upper troposphere as seen by CloudSat." Atmospheric Chemistry and Physics 15, no. 11 (June 9, 2015): 6271–81. http://dx.doi.org/10.5194/acp-15-6271-2015.
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Abstract. It remains challenging to quantify global cloud properties and uncertainties associated with their impacts on climate change because of our poor understanding of cloud three-dimensional (3-D) structures from observations and unrealistic characterization of 3-D cloud effects in global climate models (GCMs). In this study we find cloud 3-D effects can cause significant error in cloud ice and radiation measurements if it is not taken into account appropriately. One of the cloud 3-D complexities, the slantwise tilt structure, has not received much attention in research and even less has been reported considering a global perspective. A novel approach is presented here to analyze the ice cloud water content (IWC) profiles retrieved from CloudSat and a joint radar–lidar product (DARDAR). By integrating IWC profiles along different tilt angles, we find that upper-troposphere (UT) ice cloud mass between 11 and 17 km is tilted poleward from active convection centers in the tropics [30° S, 30° N]. This systematic tilt in cloud mass structure is expected from the mass conservation principle of the Hadley circulation with the divergent flow of each individual convection/convective system from down below, and its existence is further confirmed from cloud-resolving-scale Weather Research and Forecasting (WRF) model simulations. Thus, additive effects of tilted cloud structures can introduce 5–20% variability by its nature or produce errors to satellite cloud/hydrometeor ice retrievals if simply converting it from slant to nadir column. A surprising finding is the equatorward tilt in middle tropospheric (5–11 km) ice clouds, which is also evident in high-resolution model simulations but not in coarse-resolution simulations with cumulus parameterization. The observed cloud tilt structures are intrinsic properties of tropical clouds, producing synoptic distributions around the Intertropical Convergence Zone (ITCZ). These findings imply that current interpretations based on over-simplified cloud vertical structures could lead to considerable cloud measurement errors and have a subsequent impact on understanding cloud radiative, dynamical and hydrological properties.
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WARDHANI, PRIMASARI, PEI-I. TSAI, PEI-YU CHEN, YU-YOU CHEN, and CHING-CHI HSU. "A COMPUTATIONAL STUDY OF DIFFERENT ADDITIVE MANUFACTURING-BASED TOTAL ANKLE REPLACEMENT DEVICES USING THREE-DIMENSIONAL HUMAN LOWER EXTREMITY MODELS WITH VARIOUS ANKLE POSTURES." Journal of Mechanics in Medicine and Biology 19, no. 02 (March 2019): 1940014. http://dx.doi.org/10.1142/s0219519419400141.
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Total ankle replacement (TAR) surgery is one of the useful methods to treat ankle arthritis. Selective laser melting that is an additive manufacturing (AM) technique has made it possible to fabricate orthopedic implants. However, there are rare studies to analyze AM implants using finite element method. Thus, the purpose of this study was to investigate the effect of the various porous designs with three types of tibial shapes for five ankle postures using three-dimensional (3D) human lower extremity models. The variable-axis-mobile-bearing (VAMB) TAR models were developed in one solid TAR design and three porous TAR designs on the tibial and talar components. Additionally, three shape designs (curved, flat, and tilted) of the tibial component were also evaluated. Each TAR design was assembled on the human lower extremity model with standing, inversion, eversion, plantar flexion, and dorsiflexion ankle postures. The results showed that there was a minor effect among the solid and porous TAR designs on the implant stability, the bone stress, and the implant stress. However, those performances in the plantar flexion were significantly reduced compared to that in the other ankle postures. Although the porous TAR designs have a higher risk of implant failure and bone breakage, it may have better bone-implant bonding ability. This study could help engineers and surgeons to understand the design rationale and biomechanics of AM-based TAR devices.
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Li, Rong, and Jun Xiong. "A numerical prediction of residual stress for a thin-walled part with geometrical features fabricated by GMA-based additive manufacturing." Rapid Prototyping Journal 26, no. 2 (September 19, 2019): 299–308. http://dx.doi.org/10.1108/rpj-08-2018-0193.
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Purpose An accurate prediction of process-induced residual stress is necessary to prevent large distortion and cracks in gas metal arc (GMA)-based additive manufactured parts, especially thin-walled parts. The purpose of this study is to present an investigation into predicting the residual stress distributions of a thin-walled component with geometrical features. Design/methodology/approach A coupled thermo-mechanical finite element model considering a general Goldak double ellipsoidal heat source is built for a thin-walled component with geometrical features. To confirm the accuracy of the model, corresponding experiments are performed using a positional deposition method in which the torch is tilted from the normal direction of the substrate. During the experiment, the thermal cycle curves of locations on the substrate are obtained by thermocouples. The residual stresses on the substrate and part are measured using X-ray diffraction. The validated model is used to investigate the thermal stress evolution and residual stress distributions of the substrate and part. Findings Decent agreements are achieved after comparing the experimental and simulated results. It is shown that the geometrical feature of the part gives rise to an asymmetrical transversal residual stress distribution on the substrate surface, while it has a minimal influence on the longitudinal residual stress distribution. The residual stress distributions of the part are spatially uneven. The longitudinal tensile residual stress is the prominent residual stress in the central area of the component. Large wall-growth tensile residual stresses, which may cause delamination, appear at both ends of the component and the substrate–component interfaces. Originality/value The predicted residual stress distributions of the thin-walled part with geometrical features are helpful to understand the influence of geometry on the thermo-mechanical behavior in GMA-based additive manufacturing.
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Wang, Yuan, Jianrun Zhang, Lan Chen, Naifei Ren, Lei Li, Bo Wu, and Xinzhou Zhang. "The effect of structural-acoustic coupling on the sound field in a trapezoidal enclosure." Noise Control Engineering Journal 67, no. 3 (May 1, 2019): 180–89. http://dx.doi.org/10.3397/1/376716.
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The sound field characteristics in a trapezoidal enclosure surrounded by a flexible wall, which is adjacent to the tilted one, are investigated and compared with the case of a rectangular enclosure. The acoustic modes of trapezoidal enclosure are obtained by the coupling of the modes of rectangular enclosure that bounds it. The coupling system model is then built between trapezoidal enclosure modes and flexible wall modes using modal coupling theory. Based on the coupled system model, the effect of flexible wall modal density on the resonance frequencies and the decay times of coupled system are analyzed. Compared with the case of rectangular enclosure, the variation of the resonance frequency and the decay time of enclosure-controlled system mode is determined by its mode indices and tilted wall location when the panel modal density is changed. When the modal indices of trapezoidal sound field in the two directions unparallel to the tilted wall are equal to zero simultaneously, the effect of inclination angle on the resonance frequencies and decay times of these coupled system modes can be neglected. Otherwise, the coupling system modes behaviors are changed with the elevation angle. In addition, the coupling selection between the modes of trapezoidal enclosure and flexible wall is discussed in detail.
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Wu, Fei, Junchan Wang, Yuzhuang Zhou, Xiaoxin Song, Chengxin Ju, Chengming Sun, and Tao Liu. "Estimation of Winter Wheat Tiller Number Based on Optimization of Gradient Vegetation Characteristics." Remote Sensing 14, no. 6 (March 10, 2022): 1338. http://dx.doi.org/10.3390/rs14061338.
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Tiller are an important biological characteristic of wheat, a primary food crop. Accurate estimation of tiller number can help monitor wheat growth and is important in forecasting wheat yield. However, because of leaf cover and other factors, it is difficult to estimate tiller number and the accuracy of estimates based on vegetation indices is low. In this study, a gradual change feature was introduced to optimize traditional prediction models of wheat tiller number. Accuracy improved in optimized models, and model R2 values for three varieties of winter wheat were 0.7044, 0.7060, and 0.7357. The optimized models improved predictions of tiller number in whole wheat fields. Thus, compared with the traditional linear model, the addition of a gradual change feature greatly improved the accuracy of model predictions of wheat tiller number.
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Nozari, K., and S. Shafizadeh. "Realization of blue spectrum in generalized Galileon super-inflation models." International Journal of Modern Physics D 26, no. 03 (February 3, 2017): 1750016. http://dx.doi.org/10.1142/s021827181750016x.
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In the spirit of Galileon inflation and by considering some sorts of noncanonical kinetic terms in the action, we realize a stage of super-inflation leading to a blue-tilted tensor perturbation. We show also that addition of Galileon-like term to the action leads to avoidance of ghost instabilities in this setup.
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Ivanov, Yuriy, and Alexey Stovas. "S-wave singularities in tilted orthorhombic media." GEOPHYSICS 82, no. 4 (July 1, 2017): WA11—WA21. http://dx.doi.org/10.1190/geo2016-0642.1.
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Quasi S-wave propagation in low-symmetry anisotropic media is complicated due to the existence of point singularities (conical points) — points in the phase space at which slowness sheets of the split S-waves touch each other. At these points, two eigenvalues of the Christoffel tensor (associated with the quasi S-waves) degenerate into one and polarization directions of the S-waves, which lay in the plane orthogonal to the polarization of the quasi longitudinal wave, are not uniquely defined. In the vicinity of these points, slowness sheets of the S-waves have complicated shapes, leading to rapid variations in polarization directions, multipathing, and cusps and discontinuities of the shear wavefronts. In a tilted orthorhombic medium, the point singularities can occur close to the vertical, distorting the traveltime parameters that are defined at the zero offset. We have analyzed the influence of the singularities on these parameters by examining the derivatives of the slowness surface up to the fourth order. Using two orthorhombic numerical models of different shear anisotropy strength and with different number of singularity points, we evaluate the complexity of the slowness sheets in the vicinity of the conical points and analyze how the traveltime parameters are affected by the singularities. In particular, we observe that the hyperbolic region associated with the singularity points in a model with moderate to strong shear anisotropy spans over a big portion of the slowness surfaces and the traveltime parameters are strongly affected outside the hyperbolic region. In general, the fast shear mode is less affected by the singularities; however, the effect is still very pronounced. Moreover, the hyperbolic region associated with the singularity points on the slow S-wave affects the slowness surface of the fast mode extensively. In addition, we evaluate a relation between the slowness surface Gaussian curvature and the relative geometric spreading, which has anomalous behavior due to the singularities.
Book chapters on the topic "Tilted Additive Model"
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Bui, Van-Hung, Patrick Gilles, Guillaume Cohen, and Walter Rubio. "Develop Model for Controlled Depth Milling by Abrasive Water Jet of Ti6Al4V at Jet Inclination Angle." In Lecture Notes in Mechanical Engineering, 21–27. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-70566-4_5.
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AbstractAbrasive water jet machining (AWJM) is an interesting solution for the production of shallow pockets in metal sheets made of titanium alloys. Indeed, it produces low cutting forces and heat generation and prevents deformation of these parts after machining. In addition, it has the advantage of only using two raw materials: sand and water. It is possible to generate pocket edges with an imposed geometry using AWJM, but it is necessary to tilt the axis of the jet. The material removal mechanism is then a function of the inclination angle. The presented study propose an improved model for modelling the pocket profile in TiAl6V parts. The experimental results shows that the model is efficient as the precision is around 5%.
Conference papers on the topic "Tilted Additive Model"
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Johlen, Dietmar, Peter Klose, Hagen Renner, and Ernst Brinkmeyer. "Strong LP11-Mode Splitting in UV Side-Written Tilted Fiber Gratings." In Bragg Gratings, Photosensitivity, and Poling in Glass Fibers and Waveguides. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/bgppf.1997.bmg.12.
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Dual-mode fiber gratings are promising components for mode converters and reflectionless band filters. In order to be able to use standard telecommunication fibers, which are single-moded at the wavelengths of interest, one can increase the refractive index by UV laser-beam side-writing such that higher modes propagate through the grating region. We show here that UV side-writing is an efficient method to increase the refractive index to allow higher modes to propagate. In addition, the problems of multiple resonant peaks due to weakly broken higher-mode degeneracy [1] is circumvented by breaking the degeneracy such strongly that the resonant peaks are spectrally widely separated.
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Denman, Paul A., Ashley G. Barker, Charith W. Jayatunga, and James J. McGuirk. "Modelling and Measurements of Combustor Cooling Tile Flows." In ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38793.
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Pressure to reduce available cooling air in modern combustors has driven recent interest in cooling technology based on double-skinned combustor liners, i.e. tiles containing multiple pin-type pedestals to enhance heat transfer. The design of such systems is, however, hampered by the multiplicity of parameters needing optimisation: feedhole configuration, pedestal configuration, tile configuration (e.g. tile overlap). Much experimental testing is currently needed. In addition, the simulation of flow and heat transfer in cooling tile geometries using RANS-based CFD is made particularly difficult by the impossibility of resolving every individual pin in the pedestal matrix whilst retaining an overall CFD problem of reasonable size. The present paper describes a mixture of experimental and computational work undertaken to explore cooling tile flows. On the experimental side, a large-scale Perspex aerodynamic rig of a cooling tile was constructed. Measurements at representative Reynolds numbers were possible and delivered information on discharge coefficients, pressure drops and flow splits for various tile configurations. The same tile geometries were subsequently modeled using a RANS-based CFD approach. The novelty in these simulations was the use of a ‘sub-grid-scale’ model for the pedestal flow and heat transfer. This approach has previously been used in combustor heatshield predictions; it is demonstrated in the present work how it may also be applied to cooling tiles.
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Khalili, Sadegh, Mohammad I. Tradat, Kourosh Nemati, Mark Seymour, and Bahgat Sammakia. "Impact of Tile Design on Thermal Performance of Open and Enclosed Aisles." In ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2017 Conference on Information Storage and Processing Systems. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/ipack2017-74339.
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In raised floor data centers, tiles with high open area ratio or complex understructure are used to fulfill the demand of today’s high-density computing. Using more open tiles reduces pressure drop across the raised floor with the potential advantages of increased airflow and lower noise. However, it introduces the disadvantage of increased non-uniformity of airflow distribution. In addition, there are various tile designs available on the market with different opening shapes or understructures. Furthermore, a physical separation of cold and hot aisles (containment) has been introduced to minimize the mixing of cold and hot air. In this study, three types of floor tiles with different open area, opening geometry, and understructure are considered. Experimentally validated detail models of tiles were implemented in CFD simulations to address the impact of tile design on the cooling of IT equipment in both open and enclosed aisle configurations. Also, impacts of under-cabinet leakage on the IT equipment inlet temperature in the provisioned and under-provisioned scenarios are studied. Finally, a predictive equation for the critical under-provisioning point that can lead to a no-flow condition in IT equipment with weaker airflow systems is presented.
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Cheng, Bo, and Kevin Chou. "Deformation Evaluation of Part Overhang Configurations in Electron Beam Additive Manufacturing." In ASME 2015 International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/msec2015-9477.
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Powder-bed electron beam additive manufacturing (EBAM) has emerged as a cost-effective process for many industrial applications. Intuitively, EBAM would not require support structures for overhang geometry because the powder bed would self-support the overhang weight. However, without a proper support structure, overhang warping actually occurs in practices. In this study, a two dimensional (2D) finite element (FE) model was developed to study the thermomechanical process of EBAM. The model was applied to evaluate (1) the process parameter effect, (2) the overhang and support configuration effect, and (3) the powder porosity effect on overhang deformations. The major results are summarized as follows. (1) Increasing the beam speed and diameter will result in less deformation in an overhang area, while increasing the beam current will worsen the deformation condition. (2) A smaller tilt angle will cause a larger overhang deformation. (3) A support column, even placed away from the solid substrate side, will minimize overhang deformations. (4) An anchor-free solid piece beneath the overhang can reduce the deformation with an appropriate gap. (5) A lower powder porosity level may alleviate overhang deformations.
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Huang, Pu, Yongqiang Li, Yong Chen, and Jun Zeng. "A Digital Material Design Framework for 3D-Printed Heterogeneous Objects." In ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-60181.
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In the paper a digital material design framework is presented to compute multi-material distributions in three-dimensional (3D) model based on given user requirements for additive manufacturing (AM) processes. It is challenging to directly optimize digital material composition due to extremely large design space. The presented material design framework consists of three stages. In the first stage, continuous material property distribution in the geometric model is computed to achieve the desired user requirements. In the second stage, a material dithering method is developed to convert the continuous material property distribution into 3D printable digital material distribution. A tile-based material patterning method and accordingly constructed material library are presented to efficiently perform material dithering in the given 3D model. Finite element analysis (FEA) is used to evaluate the performance of the computed digital material distributions. To mimic the layer-based AM process, cubic meshes are chosen to define the geometric shape in the digital material design stage, and its resolution is set based on the capability of the selected AM process. In the third stage, slicing data is generated from the cubic mesh model and can be used in 3D printing processes. Three test cases are presented to demonstrate the capability of the digital material design framework. Both FEA-based simulation and physical experiments are performed; in addition, their results are compared to verify the tile-based material pattern library and the related material dithering method.
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Marzban, Mostapha, and Aria Alasty. "Stability Control of an Amphibious Single Wheel Robot." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-44020.
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Single wheel robots are typically those kinds of robots which contain all the necessary mechanizations, namely the stabilization and driving mechanizations, within a shell-liked housing appearing analogous to a wheel. These robots have proved to be useful in various fields of industry due to their advantages of giving high instant acceleration and maintaining high cruise speeds for considerable amount of time in addition to being compact and small. It is a sharp-edged wheel actuated by a spinning flywheel for steering and a drive motor for propulsion. The spinning flywheel acts as a gyroscope to stabilize the robot and it can be tilted to achieve steering. In this paper first the kinematics of a single wheel robot, like Gyrover, in water is considered and then a simple mechanism for its movement in water is proposed. After hydrodynamic analysis of the robot a complete dynamics model is designed with Lagrange energy method. Then a stabilizer controller is designed to balance the robot with nonlinear control approach. For simplicity the added mass effect in hydrodynamic analysis, has been neglected. This complete model can be used for examining the behavior of the robot in designing a controller.
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Bhopte, Siddharth, Madhusudan K. Iyengar, Bahgat Sammakia, Roger Schmidt, and Dereje Agonafer. "Numerical Modeling of Data Center Clusters: Impact of Model Complexity." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-13494.
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Data centers are facilities that house large numbers of computer servers that dissipate high power. With the rapid increase in the heat flux of such systems, their thermal management has become a challenge that needs to be addressed. Computational analyses using a CFD code is a very useful technique that helps the engineer to understand and solve the data center cooling problem. In this paper the state of the art of numerical modeling of data center is discussed. Representative systems are modeled using the two most prominent approaches. Variation in results with the addition of modeling details is presented. The effect of under floor parameters such as the conditioned chilled air supply flow rate, the under floor plenum depth, and the tile opening flow resistance, is discussed. Total flow rate delivered by the Computer Room Air Conditioning (CRAC) unit depends on blower and system characteristic curves, as specified by the vendor. Impact of plenum depth and tile resistance on total CRAC flow rate is discussed. Under floor blockages such as cables, pipes, and random materials, impede the flow of the cold air stream and yield unpredictable air flow patterns. Currently, models with idealized plenums are used for simulation of data centers. The effect of including blockages in CFD analyses is discussed. A novel approach that defines safe and critical paths under plenum for routing the blockages is presented.
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Tafti, D. K., and R. G. Menon. "Large-Eddy Simulations of Flow Induced Vibrations in a Vacuum Flasher Unit." In ASME 2002 Pressure Vessels and Piping Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/pvp2002-1576.
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Large-eddy simulations of flow through a vacuum flasher are conducted to study unsteady flow dynamics and resulting flow-induced vibrations. The objective of this study is to isolate energetic vibrational modes encountered in the vessel, and also study the effect of a “Vibration Reducer” (VR), which is found to be highly effective in practice. An energetic mode at 3 Hz is found to exist in tile overhead lines coming out of the dome of the flasher vessel. These simulations show that by placing the VR, a perforated pipe, in tile dome region, the amplitude of the 3 Hz mode can be reduced by a factor of 5, provided that the effective open area of the VR is optimized. In addition, by stabilizing the flow, these simulations predict that the VR also decreases the overall pressure drop by 35%.
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Geffroy, Stefan, Stephan Wegner, Stefan Gels, Hubertus Murrenhoff, and Katharina Schmitz. "New Design Concepts for the Tribological Contact of Cylinder Block and Valve Plate." In BATH/ASME 2020 Symposium on Fluid Power and Motion Control. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fpmc2020-2725.
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Abstract Axial piston machines are the most widely used type of hydraulic displacement machines and are characterized by their high reliability and efficiency. However, in order to ensure the high efficiency, the tribological contacts have to be precisely optimized. One of the three essential contacts in axial piston machines is the contact of valve plate and cylinder block, which is the subject of this paper. In a previous research project, a simulation model was built up specifically for the tribological contact of valve plate and cylinder block. A test rig was developed and installed for the validation of the simulation results. Both, the experimental and the simulation results show that the cylinder block tilts to the high-pressure side. It holds this preferred position nearly constantly for the different load situations over one revolution with four or five pistons pressurized with high pressure at the same time. The tilting increases the danger of solid body contact in the area of minimum gap height. In addition, it leads to temperature hot spots. Both effects necessitate the use of coatings as alternatives to the commonly used leaded alloys. This paper presents new design concepts for the optimization of the tribological contact of valve plate and cylinder block. Additional pressure pockets in the valve plate’s high-pressure kidney generate a torque and thus reduce the tilt angle of the cylinder block. By implementing additional pressure pockets at the cylinder block an imbalance results, which prevents a constant preferred position. Both concepts have the aim to reduce the heat concentration and improving the overall behavior of the tribological contact. The development and comparison of these concepts are based on a numerical analysis.
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Toulouse, Michael M., David Lettieri, Van P. Carey, and Cullen E. Bash. "Experimental Validation of the COMPACT Code in Data Centers." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40210.
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This paper summarizes the comparison of predictions by a compact model of air flow and transport in data centers to temperature measurements of an operational data center. The simplified model and code package, referred to as COMPACT (Compact Model of Potential Flow and Convective Transport), is intended as an alternative to the use of time-intensive full CFD thermofluidic models as a first-order design tool, as well as a potential improvement to plant-based controllers. COMPACT is based on potential flow and combined with an application of convective energy equations, using sparse matrix solvers to seek flow and temperature solutions. Full-room solutions can be generated in 15 seconds on a commercially available laptop, and an accompanying graphical user interface has also been developed to allow quick configuration of data center designs and analysis of flow and temperature results. Experiments for validation of the model were conducted at the HP Labs data center in Palo Alto, CA, which is in a traditional configuration consisting of inlet floor tiles feeding cold air between two rows of multiple server racks. Subsequently, air exits either through ceiling tiles or direct room-return to CRAC units located on the side of the room. Temperatures were recorded at multiple points along entering and exiting flow faces within the room, as well as at various points in cold and hot aisles, and are presented and compared to model predictions to assess their accuracy. Areas of greater and lesser accuracy are analyzed and presented, in addition to conclusions as to the strengths and weaknesses of the model. For some cases, the average predicted temperature along in-flowing rack faces was within one degree of the average measured temperature. However, the differences in temperature are not evenly distributed. The most pronounced variations between the model and room measurements were located in areas above server racks where recirculation was shown to most likely occur. In these areas, the predicted temperature was higher than experimental values; this can likely be attributed to the absence of buoyancy effects in the simplified potential flow model. Adaptations of the model and its configuration standards for more accurate temperature distributions are proposed, as well as investigations into the effect on temperature comparisons to idealized model output by unaccounted heat sources or flow phenomena.