Abstract
Hydrokinetic turbines extract kinetic energy from moving water to generate renewable electricity, thus contributing to sustainable energy production and reducing reliance on fossil fuels. It ...has been hypothesized that a duct can accelerate and condition the fluid flow passing the turbine blades, improving the overall energy extraction efficiency. However, no substantial evidence has been provided so far for hydrokinetic turbines. To investigate this problem, we perform a CFD-based optimization study with a blade-resolved Reynolds-averaged Navier–Stokes (RANS) solver to explore the design of a ducted hydrokinetic turbine that maximizes the efficiency of energy extraction. A gradient-based optimization approach is utilized to effectively deal with the high-dimensional design space of the blade and duct geometry, with gradients being calculated through the adjoint method. The final design is re-evaluated through higher-fidelity unsteady RANS (URANS) simulations. Our optimized ducted turbine achieves an efficiency of about 54% over a range of operating conditions, higher than the typical 46% efficiency of unducted turbines.
The HITRAN 2004 molecular spectroscopic database Rothman, L.S.; Jacquemart, D.; Barbe, A. ...
Journal of quantitative spectroscopy & radiative transfer,
12/2005, Letnik:
96, Številka:
2
Journal Article
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This paper describes the status of the 2004 edition of the
HITRAN molecular spectroscopic database. The
HITRAN compilation consists of several components that serve as input for radiative transfer ...calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e., spectra in which the individual lines are unresolvable; individual line parameters and absorption cross-sections for bands in the ultra-violet; refractive indices of aerosols; tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 39 molecules including many of their isotopologues.
The format of the section of the database on individual line parameters of
HITRAN has undergone the most extensive enhancement in almost two decades. It now lists the Einstein
A
-coefficients, statistical weights of the upper and lower levels of the transitions, a better system for the representation of quantum identifications, and enhanced referencing and uncertainty codes. In addition, there is a provision for making corrections to the broadening of line transitions due to line mixing.
Atmospheric CO2 inversions estimate surface carbon fluxes from an optimal fit to atmospheric CO2 measurements, usually including prior constraints on the flux estimates. Eleven sets of carbon flux ...estimates are compared, generated by different inversions systems that vary in their inversions methods, choice of atmospheric data, transport model and prior information. The inversions were run for at least 5 yr in the period between 1990 and 2010. Mean fluxes for 2001-2004, seasonal cycles, interannual variability and trends are compared for the tropics and northern and southern extra-tropics, and separately for land and ocean. Some continental/basin-scale subdivisions are also considered where the atmospheric network is denser. Four-year mean fluxes are reasonably consistent across inversions at global/latitudinal scale, with a large total (land plus ocean) carbon uptake in the north (-3.4 Pg C yr-1 (±0.5 Pg C yr-1 standard deviation), with slightly more uptake over land than over ocean), a significant although more variable source over the tropics (1.6 ± 0.9 Pg C yr-1 ) and a compensatory sink of similar magnitude in the south (-1.4 ± 0.5 Pg C yr-1 ) corresponding mainly to an ocean sink. Largest differences across inversions occur in the balance between tropical land sources and southern land sinks. Interannual variability (IAV) in carbon fluxes is larger for land than ocean regions (standard deviation around 1.06 versus 0.33 Pg C yr-1 for the 1996-2007 period), with much higher consistency among the inversions for the land. While the tropical land explains most of the IAV (standard deviation ~ 0.65 Pg C yr-1 ), the northern and southern land also contribute (standard deviation ~ 0.39 Pg C yr-1 ). Most inversions tend to indicate an increase of the northern land carbon uptake from late 1990s to 2008 (around 0.1 Pg C yr-1 , predominantly in North Asia. The mean seasonal cycle appears to be well constrained by the atmospheric data over the northern land (at the continental scale), but still highly dependent on the prior flux seasonality over the ocean. Finally we provide recommendations to interpret the regional fluxes, along with the uncertainty estimates.
Bone marrow stem cells give rise to a variety of hematopoietic lineages and repopulate the blood throughout adult life. We show that, in a strain of mice incapable of developing cells of the myeloid ...and lymphoid lineages, transplanted adult bone marrow cells migrated into the brain and differentiated into cells that expressed neuron-specific antigens. These findings raise the possibility that bone marrow-derived cells may provide an alternative source of neurons in patients with neurodegenerative diseases or central nervous system injury.
•Adjoint framework to handle optimization problems with hundreds of design variables and constraints.•OpenFOAM discrete adjoint solver with competitive speed, scalability, and accuracy.•Practical ...aerodynamic design optimization for aircraft and cars.•Optimization results validated by experiments.
Advances in computing power have enabled computational fluid dynamics (CFD) to become a crucial tool in aerodynamic design. To facilitate CFD-based design, the combination of gradient-based optimization and the adjoint method for computing derivatives can be used to optimize designs with respect to a large number of design variables. Open field operation and manipulation (OpenFOAM) is an open source CFD package that is becoming increasingly popular, but it currently lacks an efficient infrastructure for constrained design optimization. To address this problem, we develop an optimization framework that consists of an efficient discrete adjoint implementation for computing derivatives and a Python interface to multiple numerical optimization packages. Our adjoint optimization framework has the following salient features: (1) The adjoint computation is efficient, with a computational cost that is similar to that of the primal flow solver and scales up to 10 million cells and 1024 CPU cores. (2) The adjoint derivatives are fully consistent with those generated by the flow solver with an average error of less than 0.1%. (3) The adjoint framework can handle optimization problems with more than 100 design variables and various geometric and physical constraints such as volume, thickness, curvature, and lift constraints. (4) The framework includes additional modules that are essential for successful design optimization: a geometry-parametrization module, a mesh-deformation algorithm, and an interface to numerical optimizations. To demonstrate our design-optimization framework, we optimize the ramp shape of a simple bluff geometry and analyze the flow in detail. We achieve 9.4% drag reduction, which is validated by wind tunnel experiments. Furthermore, we apply the framework to solve two more complex aerodynamic-shape-optimization applications: an unmanned aerial vehicle, and a car. For these two cases, the drag is reduced by 5.6% and 12.1%, respectively, which demonstrates that the proposed optimization framework functions as desired. Given these validated improvements, the developed techniques have the potential to be a useful tool in a wide range of engineering design applications, such as aircraft, cars, ships, and turbomachinery.
•Consider aerodynamics and heat transfer in turbine internal cooling optimization.•Efficient adjoint derivative computation allows large design freedom.•The gradient-based method achieves better ...performance than gradient-free methods.•Changing U-bend is more effective than changing ribs for overall performance.•Optimized ribs exhibit independent arrangement, depending on local flow conditions.
Aerothermal optimization is a powerful technique for automating the design of turbine internal cooling passages, where both pressure loss and heat transfer are considered. Existing optimization studies commonly adopt gradient-free algorithms, which can handle only a few design variables. However, to enhance heat transfer, internal cooling designs use complex geometries consisting of ribbed serpentine channels, which need to be parameterized by using a large number of design variables. To address this need, we develop herein an approach for aerothermal optimization that uses a gradient-based optimizer in conjunction with a discrete adjoint method to efficiently compute the required gradients with respect to numerous design variables. We apply this approach to the design of a ribbed U-bend channel, which is representative of a section of turbine internal cooling passages. The objective function combines heat transfer and pressure loss as a weighted sum. We find the Pareto front for these two objectives by running five optimizations with different weights. We consider both a rib-free and a ribbed U-bend configuration. For the rib-free configuration, we use 113 design variables to parameterize the U-bend shape. We compare our optimization results with those from gradient-free methods and demonstrate that the proposed method leads to lower pressure loss while enhancing heat transfer. For the ribbed configuration, we use 146 design variables and allow the ribs to change their arrangement independently (shape, height, pitch, and angle). Each rib adopts a requisite arrangement to balance heat transfer and aerodynamics, depending on the local flow conditions. Optimizing the U-bend shape is shown to be more effective for improving overall heat transfer than optimizing the rib arrangement. However, optimizing ribs is more effective for improving local heat transfer. The results demonstrate that the proposed optimization framework has the potential to handle general turbine heat transfer designs, not only for internal cooling but also for other design problems, such as film cooling and jet impingement cooling.
To investigate the presence of autoantibody deposition against type 2 tissue transglutaminase (TG2; a reliable marker of the whole spectrum of gluten sensitivity) in the jejunal tissue and brain of ...patients with gluten ataxia and in control subjects.
The authors evaluated jejunal biopsy samples from nine patients with gluten ataxia and seven patients with other causes of ataxia for the presence of TG2-related immunoglobulin deposits using double-color immunofluorescence. Autopsy brain tissue from one patient with gluten ataxia and one neurologically intact brain were also studied.
IgA deposition on jejunal TG2 was found in the jejunal tissue of all patients with gluten ataxia and in none of the controls. The intestinal IgA deposition pattern was similar to that seen in patients with overt and latent celiac disease and in those with dermatitis herpetiformis. Widespread IgA deposition around vessels was found in the brain of the patient with gluten ataxia but not the control brain. The deposition was most pronounced in the cerebellum, pons, and medulla.
Anti-tissue transglutaminase IgA antibodies are present in the gut and brain of patients with gluten ataxia with or without an enteropathy in a similar fashion to patients with celiac disease, latent celiac disease, and dermatitis herpetiformis but not in ataxia control subjects. This finding strengthens the contention that gluten ataxia is immune mediated and belongs to the same spectrum of gluten sensitivity as celiac disease and dermatitis herpetiformis.
PU.1 is a member of the ets family of transcription factors and is expressed exclusively in cells of the hematopoietic lineage. Mice homozygous for a disruption in the PU.1 DNA binding domain are ...born alive but die of severe septicemia within 48 h. The analysis of these neonates revealed a lack of mature macrophages, neutrophils, B cells and T cells, although erythrocytes and megakaryocytes were present. The absence of lymphoid commitment and development in null mice was not absolute, since mice maintained on antibiotics began to develop normal appearing T cells 3–5 days after birth. In contrast, mature B cells remained undetectable in these older mice. Within the myeloid lineage, despite a lack of macrophages in the older antibiotic‐treated animals, a few cells with the characteristics of neutrophils began to appear by day 3. While the PU.1 protein appears not to be essential for myeloid and lymphoid lineage commitment, it is absolutely required for the normal differentiation of B cells and macrophages.
•Simultaneously considering hydrodynamic resistance and wake distortion is necessary.•Gradient-based optimization method allows large design freedom for hull shape.•The suction effect of propellers ...impacts the optimized shapes.•Imposing proper geometric constraints ensures practical hull shapes.
Computational fluid dynamics (CFD) based optimization is becoming increasingly popular in hydrodynamic design of ship hulls because it provides a fully automatic framework with a shorter design cycle than a human-supervised design tool. Despite the above advantage, CFD-based optimization requires careful attention to relevant design considerations, such that the final design is useful in practice. These considerations include all relevant objectives (such as drag and wake distortion) and constraints (such as volume, thickness, and curvature). Although constraints have been included in previous hull shape optimization studies, these studies have typically considered only one objective. To address this shortcoming, we conduct design optimization for self-propulsion by simultaneously considering drag and propeller-wake distortion. We use a gradient-based optimization framework that includes a discrete adjoint method for efficient derivative computation, which allows us to use a large number of design variables to parameterize the complex hull shape and thus gain a large amount of freedom for geometric modification. We impose appropriate geometric constraints (volume, thickness, and curvature) on the hull surface to ensure a practical design. In addition, we use a weighted objective function that includes drag and wake distortion to construct a Pareto front with five optimizations. We also consider hull-propeller interaction by comparing optimization results with and without a propeller. We use the Japan bulk carrier (JBC) as the baseline model and focus on optimizing the stern region. We find that optimizing for only one objective results in a large penalty on the other objective, whereas a weighted objective balances the penalty and achieves simultaneous improvement in drag and wake distortion. Moreover, we observe that the suction effect of the propeller suppresses the flow separation near the bilge tube and smooths out the velocity distortion at the propeller plane; these are effects that would end up affecting the optimized shapes. Our results demonstrate that it is necessary to simultaneously consider drag and wake distortion in hull-shape-optimization studies, and that constrained shape optimization with a large number of design variables is possible with the discrete-adjoint method.
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