EXPERIMENTAL AND MODELING STUDIES FOR OPTIMIZING FLOCCULANT-AIDED SEDIMENT RETENTION PONDS

Attempts to control sediment-containing runoff and associated water quality problems have involved the establishment of many small to medium sediment retention ponds and the injection of nonionic and anionic polyacrylamide (PAM) flocculants to enhance colloid removal. However, to date use has been driven more by practicing engineers and trial-and-error approaches than by logical and consistent design approaches. Therefore, the purpose of this research was to optimize colloidal clay removal in PAM-aided sediment retention ponds by applying experimental and theoretical methodologies. Initially, simple measurement techniques for the molecular weight (MW) and charge density (CD) of various PAMs were tested and their characteristic behaviors in aqueous solution were investigated for use in subsequent optimization tasks. A simple intrinsic viscosity measurement technique and acid-base titration method showed their capabilities as the most plausible substitutes of state-of-the-art techniques in measuring MW and CD, respectively. Also, a cylindrical shape for PAM conformation in aqueous solution was shown to be the best assumption for predicting the characteristic behavior of PAM molecules. In adsorption and flocculation experiments with nonionic PAMs and negatively-charged kaolinite clay particles, adsorption capacities of PAMs on kaolinite were found to increase with increasing PAM MW up to a certain size (~ 18 M g/mol) but then decrease beyond this size due to entanglements between PAM molecules. Flocculation efficiency with nonionic PAM also increased with increasing MW up to a point due to its nonequilibrium kaolinite flocculation but eventually decreased by entanglements between PAM molecules. In parallel experiments with anionic PAMs and negatively-charged kaolinite particles, adsorption capacities were found to be inversely proportional to the PAM CDs, while flocculation efficiencies were directly proportional to the PAM MWs. Along with the effects of PAM MW and CD, the presence of divalent cations such as Ca2+ and Mg2+ enhanced adsorption and flocculation due to cationic bridging and/or charge screening between PAM and kaolinite (PAM-+M+-Kaolinite). However, concurring steric stabilization was also found to counteract flocculation due to the conformational compaction of adsorbed PAMs by the cationic bridging between pre-adsorbed PAM molecules (PAM-+M+-PAM). In short, PAM and solution characteristics, including change density (CD), molecular weight (MW) of PAM, and cationic species in the solution, were found to make critical effects on adsorption and flocculation and thus to be the controlling parameters in optimizing PAM applications as soil stabilizers or flocculants. In a model-based optimization of PAM-aided sediment retention ponds, the applicability of utilizing multi-dimensional Discretized Population Balance Equations combined with a Computational Fluid Dynamics (CFD-DPBE model) was demonstrated in a series of simulation tasks with a model retention pond. The CFD-DPBE model was demonstrated to be a valuable simulation tool for natural and engineering flocculation and sedimentation systems as well as flocculant-aided sediment retention ponds

Characterization of Aerodynamic Performance of Boundary-Layer-Ingesting Inlet Under Crosswind

NASA has been studying future transport concepts, envisioned to be technically realizable in the timeframe of 2020-2030, to meet environmental and performance goals. One concept receiving considerable interest involves a propulsion system embedded into a hybrid wing-body aircraft. While offering significant advantages in fuel savings and noise reduction by this concept, there are several technical challenges that are not encountered in the current fleet and must be overcome so as to deliver target performance and operability. One of these challenges is associated with an inlet system that ingests a significantly thick boundary layer, developing along the wing-body surface, into a serpentine diffuser before the flow meeting fan blades. The flow is subject to considerable total pressure loss and distorted at the fan face, much more significantly than in the inlet system of conventional aircraft. In our previous studies [1, 2], we have shown that through innovative design changes on the airframe surface, it is possible to simultaneously increase total pressure recovery and decrease distortion in the flow, without resorting to conventional penalty-ridden flow control concepts, such as vortex generator or boundary layer bleeding/suction. In the current study, we are interested in understanding the following issues: how the embedded propulsion system performs under a crosswind condition by studying in detail the flow characteristics of two inlets, the baseline and another optimized previously under the cruise condition. With the insight, it is hoped that it can help in the follow-on study by devising effective strategies to minimize flow distortion arising from the integration of an embedded-engine system into an airframe to the level acceptable to the operation and fuel consumption before 2030. To achieve these demanding goals, non-conventional concepts are called for; but technology gap is too big that it requires evolutionary approach by focusing various concepts and technologies needed in the next three generations of aircraft, respectively named as N+1, N+2, and N+3. Noticeably, considerable reduction in each category of 1 is required in N+2 (relative to Boeing 777-200 and GE90 engines) and N+3 (relative to Boeing 737-800 and CFM56-7B engines). In this study, concepts for N+2 is our interest. A concept that has potential to achieve these metrics and has been under intensive study is the hybrid wing body (HWB) airframe with a tightly integrated propulsion system, see Fig. 1. The inlet is non-circular at the entrance and the entering flow, no longer uniform or free of disturbances, and is now carrying with it a boundary layer developing along the fuselage; the inlet is thus known as boundary-layer-ingesting (BLI) inlet

Aerodynamic Design and Optimization of Fan Stage for Boundary Layer Ingestion Propulsion System

The present paper addresses the process of preliminary design of a low-pressure fan and outlet guide vane (OGV) of a boundary layer ingestion (BLI) propulsion system. The tail-cone thruster systems of NASA's STARC_ABL (Single-aisle Turboelectric Aircraft with an Aft Boundary-Layer propulsor) adopts an axi-symmetric BLI type inlet as opposed to other embedded engine systems. Thus, the focus of the present work is placed on maximizing the efficiency of the fan and OGV stages under a significant radial distortion. A parameterization with B-spline function for camber line angles, metal chord, thickness distribution and stacking axis of blades is presented. The flowpath lines are also parameterized by B-spline function and aggregated in the design system of blades. The design optimization with evolutionary algorithm is performed with constraints of fan pressure ratio, OGV exit swirl angle and nozzle exit properties. The inlet conditions for the turbo-machinery CFD (Computational Fluid Dynamics) domain and the design goal of the fan stage are driven by a propulsion airframe integration (PAI) model that uses a 3-D unstructured RANS (Reynolds Average Navier Stokes) solver and actuator disk model. The expected power saving of the BLI propulsor is quantified via PAI analysis and the resulting preliminary design of the fan stages is compared with a clean-inlet flow propulsor

Mitigation of Adverse Effects Caused by Shock Wave Boundary Layer Interactions Through Optimal Wall Shaping

It is known that the adverse effects of shock wave boundary layer interactions in high speed inlets include reduced total pressure recovery and highly distorted flow at the aerodynamic interface plane (AIP). This paper presents a design method for flow control which creates perturbations in geometry. These perturbations are tailored to change the flow structures in order to minimize shock wave boundary layer interactions (SWBLI) inside supersonic inlets. Optimizing the shape of two dimensional micro-size bumps is shown to be a very effective flow control method for two-dimensional SWBLI. In investigating the three dimensional SWBLI, a square duct is employed as a baseline. To investigate the mechanism whereby the geometric elements of the baseline, i.e. the bottom wall, the sidewall and the corner, exert influence on the flow's aerodynamic characteristics, each element is studied and optimized separately. It is found that arrays of micro-size bumps on the bottom wall of the duct have little effect in improving total pressure recovery though they are useful in suppressing the incipient separation in three-dimensional problems. Shaping sidewall geometry is effective in re-distributing flow on the side wall and results in a less distorted flow at the exit. Subsequently, a near 50% reduction in distortion is achieved. A simple change in corner geometry resulted in a 2.4% improvement in total pressure recovery

Xenon excimer emission from pulsed high-pressure capillary microdischarges

Intense xenon vacuum ultraviolet (VUV) emission is observed from a high-pressure capillary cathode microdischarge in direct current operation, by superimposing a high-voltage pulse of 50 ns duration. Under stagnant gas conditions, the total VUV light intensity increases linearly with pressure from 400 to 1013 mbar for a fixed voltage pulse. At fixed pressure, however, the VUV light intensity increases superlinearly with voltage pulse height ranging from 0.8 to 2.8 kV. Gains in emission intensity are obtained by inducing gas flow through the capillary cathode, presumably because of excimer dimer survival due to gas cooling

Unsteady Adjoint Approach for Design Optimization of Flapping Airfoils

This paper describes the work for optimizing the propulsive efficiency of flapping airfoils, i.e., improving the thrust under constraining aerodynamic work during the flapping flights by changing their shape and trajectory of motion with the unsteady discrete adjoint approach. For unsteady problems, it is essential to properly resolving time scales of motion under consideration and it must be compatible with the objective sought after. We include both the instantaneous and time-averaged (periodic) formulations in this study. For the design optimization with shape parameters or motion parameters, the time-averaged objective function is found to be more useful, while the instantaneous one is more suitable for flow control. The instantaneous objective function is operationally straightforward. On the other hand, the time-averaged objective function requires additional steps in the adjoint approach; the unsteady discrete adjoint equations for a periodic flow must be reformulated and the corresponding system of equations solved iteratively. We compare the design results from shape and trajectory optimizations and investigate the physical relevance of design variables to the flapping motion at on- and off-design conditions

A robust method for VR-based hand gesture recognition using density-based CNN

Many VR-based medical purposes applications have been developed to help patients with mobility decrease caused by accidents, diseases, or other injuries to do physical treatment efficiently. VR-based applications were considered more effective helper for individual physical treatment because of their lowcost equipment and flexibility in time and space, less assistance of a physical therapist. A challenge in developing a VR-based physical treatment was understanding the body part movement accurately and quickly. We proposed a robust pipeline to understanding hand motion accurately. We retrieved our data from movement sensors such as HTC vive and leap motion. Given a sequence position of palm, we represent our data as binary 2D images of gesture shape. Our dataset consisted of 14 kinds of hand gestures recommended by a physiotherapist. Given 33 3D points that were mapped into binary images as input, we trained our proposed density-based CNN. Our CNN model concerned with our input characteristics, having many blank block pixels, single-pixel thickness shape and generated as a binary image. Pyramid kernel size applied on the feature extraction part and classification layer using softmax as loss function, have given 97.7% accuracy

Investigation on estuarine turbidity maximum response to the change of boundary forcing using 3CPBE flocculation model

Hydrodynamic