260 research outputs found

    Separation drag reduction through a spanwise oscillating pressure gradient

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    An oscillating spanwise pressure gradient is imposed numerically to control the flow separation and reduce the drag of a turbulent flow in a channel with square bars. The transverse flow produces a maximum drag reduction of 25\%, due to lower pressure and skin-friction drag forces. The pressure drag reduction reaches a maximum of 22\% and is due to a decrease of the positive high pressure in front of the bars and an increase of the low negative pressure behind the bars. The skin-friction drag reduction is caused by a lower wall-shear stress along the cavity between the bars where the flow is fully attached, while the wall-shear stress on the crest of the bars and in the separated region behind the bars is unaffected. The spanwise laminar flow obtained by neglecting the nonlinear terms involving the turbulent velocity fluctuations is used to compute the power spent for oscillating the fluid along the spanwise direction and an excellent agreement is found with the power spent obtained by the averaged turbulent flow. A marginal or negative net power saved is found by subtracting the power employed for controlling the flow from the power saved thanks to the transverse flow. The control reduces the total drag as the integral of the Reynolds stresses along the horizontal line connecting the corners of two consecutive bars is decreased, which in turn impacts on the pressure and wall-shear stress reductions

    Investigation of Ultrasonic Pulse Velocity Reduction in Reinforced Concrete Members Exposed to High Temperature

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    Nowadays, the fire resistance of reinforced concrete members is generally defined by material characteristics at elevated temperatures and temperature functions. However, the influence of steel reinforcement in concrete members exposed to high temperatures on the ultrasonic pulse velocity (UPV) measurements has still been limited. In this paper, the quality of concrete and steel reinforcement/concrete interface was assessed under high temperatures using UPV measurements. The specimens were classified into four categories: the control tested cubes without rebar; tested cubes with plain and ribbed steel rebars. Tested cubes with dimensions of 100x100x100 mm were cast and cured for 28 days at room temperature (20oC). After drying all specimens at 105oC for 48 hours, these cubes were subjected to four different temperature levels ranging from 150oC to 400oC for 4 hours before being cooled to room temperature. According to the measured values of UPV, the higher the temperature attained in specimens, the greater the following changes occurred in concrete: (i) the degradation within the concrete; (ii) the debonding of steel reinforcements in concrete

    A Conservative Front Tracking Algorithm

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    The discontinuities in the solutions of systems of conservation laws are widely considered as one of the difficulties in numerical simulation. A numerical method is proposed for solving these partial differential equations with discontinuities in the solution. The method is able to track these sharp discontinuities or interfaces while still fully maintain the conservation property. The motion of the front is obtained by solving a Riemann problem based on the state values at its both sides which are reconstructed by using weighted essentially non oscillatory (WENO) scheme. The propagation of the front is coupled with the evaluation of "dynamic" numerical fluxes. Some numerical tests in 1D and preliminary results in 2D are presented.Singapore-MIT Alliance (SMA

    THE SEATED-SINGLE-ARM-ROW AS A POST-ACTIVATION POTENTIATION EXERCISE TO ENHANCE POWER OUTPUT DURING KAYAKING ON AN ERGOMETER

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    This study investigated if the seated-single-arm-row (SSAR) could be used as a post-activation-potentiation-exercise (PAPE) during warm up to induce enhanced power output during kayaking on an ergometer. Ten well-trained kayakers (4 females, 6 males) performed three repetitions of the SSAR at 91% one-repetition maximum as the PAPE. Participants were assessed for their peak and average power output while performing 14 maximal effort strokes on a kayak ergometer; to simulate a race start; with versus without PAPE as a warm up, at three-minute intervals up to 18 minutes. Mean peak power with PAPE was found to be approximately 6% higher (1172.5 vs 1106.8 W) compared with no PAPE, t(9)=2.61, p=0.03. No differences in mean average power were found. Six out of the 10 kayakers registered higher mean peak and average power in one of their experimental trials compared with their control trial. These kayakers could be positive responders to PAPE. The SSAR performed during warm up enabled kayakers to increase their peak power output when paddling on an ergometer, but did not result in higher average power output. The utility of the SSAR as a PAPE to enhance overall power output when paddling on an ergometer, with the perspective of applying this technique to enhance performance during on-water kayaking, requires further investigation

    Shock Capturing with Discontinuous Galerkin Method

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    Shock capturing has been a challenge for computational fluid dynamicists over the years. This article deals with discontinuous Galerkin method to solve the hyperbolic equations in which solutions may develop discontinuities in finite time. The high order discontinuous Galerkin method combining the basis of finite volume and finite element methods has shown a lot of attractive features for a wide range of applications. Various techniques proposed in the literature to deal with discontinuities basically reduce the order of interpolation in the region around these discontinuities. The accuracy of the scheme therefore may be degraded in the vicinity of the shock. The proposed method resolves the discontinuities presented in the solution by applying viscosity into the shock-containing elements. The discontinuity is spread over a distance and is well approximated in the space of interpolation functions. The technique of adding viscosity to the system and the indicator based on the expansion coefficients of the solution are presented. A number of numerical examples in one and two dimensions is carried out to show the capability of the scheme for shock capturing.Singapore-MIT Alliance (SMA

    Factors influencing to use of Bluezone

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    This study aims to understand the main factors and their influence on the behavioral intention of users about using Bluezone. Surveys are sent to users through the Google Form tool. Experimental results through analysis of exploratory factors on 224 survey subjects show that there are 4 main factors affecting user behavior. Structural equation modeling indicates that trust, performance expectations, effort expectations, and social influence have a positive impact on behavioral intention of using BluezoneComment: in Vietnamese languag

    A SIMPLIFIED ASSESSMENT OF THE LOAD BEARING CAPACITY OF SUCTION CAISSON FOR OFFSHORE WIND TURBINES BASED ON FINITE ELEMENT ANALYSIS

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    Suction caisson is widely used for offshore wind turbine applications. Its loadbearing capacity depends on the bucket geometry and its embedded soil properties. This paper presents a simplified assessment of the loadbearing capacity of suction caisson based on finite element analysis using the Plaxis 2D program. The load-bearing capacity of the suction caisson is determined based on the resulting load-displacement curve via the tangent intersection method. In addition, this study developed an equivalent equation exploring the relationship between the load-bearing capacity of the suction caisson and the surface foundation. The findings in the study showed that the geometry of the suction has a significant influence on its loadbearing capacity. The suction caissons whose aspect ratios are larger resulted in higher loadbearing capacities. Besides, the equivalent equation in this study could be applied to effectively estimate the load-bearing capacity of suction caisson based on its geometry. The finite element program and the soil ground model analyzed in this study was only an assumption. In the future, experimental studies should investigate the loadbearing capacity of a suction caisson related to its geometry and the embedded soil profile using centrifuge models and large-scale models
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