Assessment Of Flow Characteristics Research Articles

A new DEM calibration method for wet and stick materials based on the BP neural network

The assessment of flow characteristics and the Discrete Element Method (DEM) calibrations for Wet and Sticky Materials (WSMs) are significantly demanded by the mining and transportation industries. However, the angle of repose (AoR), as a common DEM calibration method, has been facing challenges in adopting for WSMs. Due to the relatively high adhesion and cohesion of WSMs, it is difficult to form repeatable material heaps, resulting in inaccurate measurements of the AoRs. Therefore, this study aims to calibrate DEM parameters for WSMs under various conditions, utilizing a modified AoR test method and the Back Propagation-Neural Network (BP-NN). In the modified AoR test method, WSMs are discharged from a funnel using a screw feeder and fall closely against a vertical baffle to form a heap in a constrained direction. The new method combines the features of the traditional AoR test and the slump plane test to accurately measure the AoRs for different WSMs, including wet white sand, bulk coal, and corn powders. Test results are analysed to show the advantage of the modified AoR test. Furthermore, an innovative DEM calibration method based on the BP-NN is developed. By training the BP-NN with the database established according to the relationship between the measured and simulated AoRs, the DEM calibration parameters can be predicted rapidly for WSMs with different particle sizes and moisture contents. Validation is conducted for the wet white sand, from which the deviations and relative mean deviations between the experiment AoRs (Ae) and the calibration AoRs (Ac) are less than 2°and 4 % respectively, indicating the capability of the developed method for WSMs DEM calibrations.

Assessment of flow characteristics over complex terrain covered by the heterogeneous forest at slightly varying mean flow directions: (A case study of a Swedish wind farm)

The impact of heterogeneous forest canopies and complex terrain on the horizontal distortion of the inflow is studied. Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow is performed for a wind farm in Sweden for three cases associated with three different wind directions at the range of the static yaw misalignment (≃±6∘) where the yaw control system is not activated. The ground topography and forest properties for the numerical modeling are extracted from the Airborne Laser Scanning (ALS) 3D data. The wind turbines within the wind farm are introduced using the actuator disk model. To focus on the airflow deflection only by the complex terrain and vegetation, the study is limited to upstream wind turbines without any wake interaction. The predicted mean wind speed and turbulence intensity for the upstream wind turbines are compared against the nacelle-mounted anemometers taken from the wind farm’s turbine SCADA data. To quantify the additional load and moments induced at the rotor blades by the horizontal misalignment of the incoming flow, aero-structural simulation of the upstream wind turbines in the wind farm for all three cases is performed. The results show that the horizontal distortion of the inflow over the rotor swept area is usually kept below the range of static yaw misalignment (≃6∘) for the majority of the upstream wind turbines for all three cases. However, the impact of a large vertical shear exponent leading to misinterpretation of the results must be taken into consideration. Furthermore, the load imbalance of the rotor due to the vertical wind shear has the least direct contribution to the yaw moment. However, for a mean vertical shear exponent larger than α=0.25, contrary to expectation, a positive mean yaw moment under the positive-yawed inflow may be observed.

Assessment of Flow Characteristics Over Complex Terrain Covered by the Heterogeneous Forest at Slightly Varying Mean Flow Directions (a Case Study of a Swedish Wind Farm)

Assessment of Flow Characteristics Over Complex Terrain Covered by the Heterogeneous Forest at Slightly Varying Mean Flow Directions (a Case Study of a Swedish Wind Farm)

Assessment of flow characteristics through a grassed canal

Assessment of flow characteristics through a grassed canal

Extracardiac applications of MR blood pool contrast agent in children.

Magnetic resonance (MR) angiography has significantly reduced the need for diagnostic conventional angiography and is preferred over CT angiography in children because of its lack of ionizing radiation. The availability of gadofosveset trisodium (the only clinically approved blood pool MR contrast agent) has led to an increase in applications of MR for vascular imaging and an improvement in diagnostic quality of MR angiography. Gadofosveset is a gadolinium-based contrast agent that binds reversibly to albumin, resulting in increased paramagnetic effect and longer intravascular residence. This allows for high-resolution arterial and venous MR angiography, assessment of flow characteristics of vascular malformations, dynamic vascular imaging, and multi-station imaging with a single low-dose gadolinium contrast injection. The purpose of this pictorial essay is to facilitate understanding of the kinetics and safety profile of gadofosveset trisodium, discuss technical aspects of imaging, and illustrate advantages and extracardiac applications in pediatric body imaging.

Assessment of flow characteristics around twin rudder with various gaps using PIV analysis in uniform flow

We carried out a twin-rudder performance test in a circulating water channel using particle image velocimetry (PIV). We set the distance between two single rudders to 0.5C, 0.75C, and 1.0C, where C is the chord length (C=100mm), and considered angles of attack of 10°, 20°, and 30°, respectively. A two-frame gray-level cross-correlation PIV method was used to obtain flow information. The twin-rudder model was constructed using a submerged NACA 0018 airfoil with a row arrangement. Throughout the experiments, the Reynolds number of the NACA 0018 airfoil was kept at 1.5×104. The measured results were compared with results of each case involving a single rudder. For the single rudder, flow visualization, time-mean velocity fields, and vorticity information were measured at angles of attack of 10°, 15°, 20°, and 25°. For the twin rudder, streamlines, instantaneous and time-mean velocity fields, vorticity, and turbulence intensity were measured and compared with each other to determine the critical distance between the single rudders. It was found that this critical distance should be less than 1.0C in order to decrease turbulence flow and vortices.

Transesophageal echocardiography: A screening method for pulmonary vein stenosis after catheter ablation of atrial fibrillation

Pulmonary vein (PV) stenosis has been described as a complication after catheter ablation of atrial fibrillation. The aim of the study was to investigate the diagnostic role of transesophageal echocardiography (TEE) in the assessment of PV stenosis. Ninety-one patients (71 men, mean age 57+/-16years), initially treated by catheter ablation of atrial fibrillation, underwent re-ablation because of arrhythmia recurrences. PV angiograms and TEE were performed before the first and second ablation. PVs were analysed in an intraindividual comparison by measurements of mean and peak flow velocity and of velocity time integrals and diameters. PV angiograms served as standard for assessment of PV stenosis. Sixteen of 91 patients developed PV stenoses as a consequence of the first ablation (13 mild PV stenoses, 4 moderate PV stenoses). All patients with PV stenosis were asymptomatic. In moderate PV stenosis (50-70%) a significant increase of blood flow parameters, reduction of vessel diameter, inhomogeneous blood flow and aliasing were demonstrated by TEE. Using quantitative TEE criteria moderate PV stenosis could be identified with a sensitivity of 84% and specificity of 98%. Detection of mild PV stenosis (30-50%) is challenging (sensitivity of 48% and specificity of 75%). TEE identifies significant PV stenosis by assessment of flow characteristics and vessel diameter and can thereby be used as a follow-up tool after catheter ablation of atrial fibrillation.

The assessment of flow characteristics at certain weirs in relation to the upstream movement of migratory salmonids

A major problem in relation to the rehabilitation of migratory salmonids into many industrial rivers in South Wales is the presence of large abstraction weirs which can, under certain flows, constrain the upstream migration of fish. A method is presented whereby the constraints at two weirs on the River Afan were assessed by relating the swimming capacities of different sizes of fish and the flows needed to stimulate upstream movement to the distribution of flows and current velocities. The ‘gateways’ for fish to ascend the weir are calculated, and their significance in relation to historical flow data and the requirement for remedial action are assessed.

Transcatheter hemostasis in the genitourinary tract.

Transcatheter hemostasis is applicable in a large variety of causes of genitourinary hemorrhage. The method is particularly useful in the management of trauma since temporary occlusion of the bleeding vessel usually produces cessation of hemorrhage without significant sacrifice of additional parenchyma. Control of arteriovenous fistulas requires an assessment of flow characteristics and careful tailoring of catheter and embolization technique; large emboli or glue is frequently required for occlusion of large fistulas, whereas small ones can be treated with Ivalon. Hemorrhage from renal or pelvic neoplasm is also effectively managed by transcatheter therapy.