scholarly journals Influence of Rotating Wheels and Moving Ground Use on the Unsteady Wake of a Small-Scale Road Vehicle

2020 ◽  
Vol 106 (1) ◽  
pp. 109-137
Author(s):  
Aleksandra Anna Rejniak ◽  
Alvin Gatto
Keyword(s):  
Pressure Coefficient ◽  
Low Frequency ◽  
Scale Model ◽  
Small Scale ◽  
Simulation Methods ◽  
Oscillatory Behaviour ◽  
Road Vehicle ◽  
Unsteady Wake ◽  
Vehicle Aerodynamics ◽  
Pumping Mode

AbstractNew insights into how different ground simulation methods affect road vehicle aerodynamics are presented. Experiments are conducted on a 1/24th-scale model, representative of a Heavy Goods Vehicle, at a Reynolds number, based on width of 2.3 × 105. Particular focus lay in characterising differences in unsteady wake development, with mean drag, base pressures, and wake velocities quantified, compared, and evaluated. Distinctly, these tests include the effects of elevated blockage ratio and wheel rotation. Results show moving ground use can have a substantial influence under these conditions, with increases in wake length and average base pressure coefficient of 17% and 9%, respectively. The dominant wake dynamics, characterised by a global streamwise oscillation commonly referenced as the bubble pumping mode, was also found dependent with asymmetric shedding frequencies from both vertical and horizontal base edges higher with static ground use. For these conditions, development of a low-frequency turbulence source, near omni-directional in nature, positioned behind the model, further contaminates the flow-field. This feature disappears with moving ground use. Both the nature and characteristics of the turbulence generated behind the wheels were also found to evolve differently, with a moving ground promoting stronger and more defined oscillatory behaviour up to model mid-height, two-and-a-half widths downstream. Overall, these results highlight that while variations in time-independent quantities to differing ground simulation can often be very subtle, prompting the interpretation of negligible overall effects, in-depth consideration from a time-dependent perspective may lead to a different conclusion.

Mooring of Semi Submersibles in Extreme Sea States: Simplified Models for Wave Drift Forces and Low Frequency Damping

2018 ◽  
Author(s):  
Kjell Larsen ◽  
Tjerand Vigesdal ◽  
Rune Bjørkli ◽  
Oddgeir Dalane
Keyword(s):  
Low Frequency ◽  
Scale Model ◽  
Small Scale ◽  
Mooring System ◽  
Viscous Effects ◽  
Empirical Correction ◽  
Wave Drift ◽  
Total Wave ◽  
Wave Drift Forces ◽  
Drift Forces

This paper presents results from extensive small-scale model testing of three semi submersibles together with an overview of damping contributions of low frequency motions. The objectives of the model tests were to verify empirical correction formulas for viscous wave drift forces and to recommend and validate theoretical low frequency damping models. The main parameters of the semis such as displacement, number of columns and diameter of columns were intentionally varied in order to assess the effects on total wave drift forces and corresponding damping. The results show that viscous effects significantly increase the total wave drift forces in extreme sea states. The presence of current increases the effect. As expected, the viscous contribution to wave drift is especially important for semis with slender columns. A revised empirical correction formula for wave drift forces is proposed based on model test results. An overview of the different low frequency damping effects is given. Damping from viscous forces on the hull and damping from the mooring system are the most important sources of damping for the moored semis. A simplified model to calculate mooring system damping is proposed. For accurate prediction of low frequency motions of moored semi submersibles in extreme sea states, a damping level in the range 40–70% of critical damping should be applied for surge and sway when the empirical correction formulas for wave drift forces are applied.

Low Frequency Vibration Control of the Offshore Fixed Platforms by Using Tuned Liquid Column Damper

2014 ◽  
Author(s):  
Chan Hui Lee ◽  
Heui Won Kim ◽  
Won Ho Joo
Keyword(s):  
Vibration Control ◽  
Low Frequency ◽  
Tall Buildings ◽  
Liquid Column ◽  
Scale Model ◽  
Small Scale ◽  
Tuned Liquid Column Damper ◽  
Low Frequency Vibration ◽  
Design Variables ◽  
Liquid Column Damper

The offshore fixed platforms are confronted with greater wind and wave forces as their installation site moves toward the deep sea, so it is definitely necessary to reduce the low frequency vibration of structures for the safety and comfort of crews. The dynamic dampers are generally used to reduce vibration of structures. Especially, the tuned liquid column damper (TLCD) has been applied to reduce the low frequency vibration of onshore tall buildings. In this paper, the design procedure of TLCD is proposed to control the low frequency vibration of fixed platforms through the simulation and experiment with a small-scale model. The vibration control target is the surge motion of fixed platforms and the major design variables of TLCD are mass and damping ratios. The optimized design variables of TLCD are determined from the calculation of the amplification factor. In the experiment, the effects of mass and damping ratios are considered by changing the breadth of column, the opening ratio and number of the orifices. The results of experiment are found to well agree with the simulation. The 83% of structure vibration level can be reduced by applying the optimized TLCD.

RANCANG BANGUN PERANGKAT EKSPERIMENTASI PROSES PIROLISIS BIOMASA GELOMBANG MIKRO

2013 ◽  
Vol 14 (2) ◽  
Author(s):  
Noor Fachrizal
Keyword(s):  
Large Scale ◽  
Continuous Model ◽  
Biomass Energy ◽  
Scale Model ◽  
Small Scale ◽  
Laboratory Apparatus ◽  
Liquid Form ◽  
Large Scale Model ◽  
Bio Oil ◽  
Pyrolysis Of Biomass

Biomass such as agriculture waste and urban waste are enormous potency as energy resources instead of enviromental problem. organic waste can be converted into energy in the form of liquid fuel, solid, and syngas by using of pyrolysis technique. Pyrolysis process can yield higher liquid form when the process can be drifted into fast and flash response. It can be solved by using microwave heating method. This research is started from developing an experimentation laboratory apparatus of microwave-assisted pyrolysis of biomass energy conversion system, and conducting preliminary experiments for gaining the proof that this method can be established for driving the process properly and safely. Modifying commercial oven into laboratory apparatus has been done, it works safely, and initial experiments have been carried out, process yields bio-oil and charcoal shortly, several parameters are achieved. Some further experiments are still needed for more detail parameters. Theresults may be used to design small-scale continuous model of productionsystem, which then can be developed into large-scale model that applicable for comercial use.

scholarly journals Experimental Study on the Behavior of Existing Reinforced Concrete Multi-Column Piers under Earthquake Loading

2021 ◽  
Vol 11 (6) ◽  
pp. 2652
Author(s):  
Jung Han Kim ◽  
Ick-Hyun Kim ◽  
Jin Ho Lee
Keyword(s):  
Seismic Performance ◽  
Seismic Design ◽  
Bridge Piers ◽  
Scale Model ◽  
Inertia Force ◽  
Small Scale ◽  
Lap Splice ◽  
Existing Structures ◽  
Seismic Design Code ◽  
Seismic Force

When a seismic force acts on bridges, the pier can be damaged by the horizontal inertia force of the superstructure. To prevent this failure, criteria for seismic reinforcement details have been developed in many design codes. However, in moderate seismicity regions, many existing bridges were constructed without considering seismic detail because the detailed seismic design code was only applied recently. These existing structures should be retrofitted by evaluating their seismic performance. Even if the seismic design criteria are not applied, it cannot be concluded that the structure does not have adequate seismic performance. In particular, the performance of a lap-spliced reinforcement bar at a construction joint applied by past practices cannot be easily evaluated analytically. Therefore, experimental tests on the bridge piers considering a non-seismic detail of existing structures need to be performed to evaluate the seismic performance. For this reason, six small scale specimens according to existing bridge piers were constructed and seismic performances were evaluated experimentally. The three types of reinforcement detail were adjusted, including a lap-splice for construction joints. Quasi-static loading tests were performed for three types of scale model with two-column piers in both the longitudinal and transverse directions. From the test results, the effect on the failure mechanism of the lap-splice and transverse reinforcement ratio were investigated. The difference in failure characteristics according to the loading direction was investigated by the location of plastic hinges. Finally, the seismic capacity related to the displacement ductility factor and the absorbed energy by hysteresis behavior for each test were obtained and discussed.

Wave Energy Hyperbaric Device for Electricity Production

2007 ◽  
Author(s):  
Segen F. Estefen ◽  
Paulo Roberto da Costa ◽  
Eliab Ricarte ◽  
Marcelo M. Pinheiro
Keyword(s):  
Power Generation ◽  
Wave Energy ◽  
Experimental Results ◽  
Electricity Production ◽  
Scale Model ◽  
Small Scale ◽  
Regular Waves ◽  
Hyperbaric Chamber ◽  
Small Scale Model

Wave energy is a renewable and non-polluting source and its use is being studied in different countries. The paper presents an overview on the harnessing of energy from waves and the activities associated with setting up a plant for extracting energy from waves in Port of Pecem, on the coast of Ceara State, Brazil. The technology employed is based on storing water under pressure in a hyperbaric chamber, from which a controlled jet of water drives a standard turbine. The wave resource at the proposed location is presented in terms of statistics data obtained from previous monitoring. The device components are described and small scale model tested under regular waves representatives of the installation region. Based on the experimental results values of prescribed pressures are identified in order to optimize the power generation.

scholarly journals Roughness Lengths for Momentum and Heat Derived from Outdoor Urban Scale Models

2007 ◽  
Vol 46 (7) ◽  
pp. 1067-1079 ◽  
Author(s):  
M. Kanda ◽  
M. Kanega ◽  
T. Kawai ◽  
R. Moriwaki ◽  
H. Sugawara
Keyword(s):  
Wind Direction ◽  
Roughness Length ◽  
Scale Dependence ◽  
Scale Model ◽  
Small Scale ◽  
Physical Scale ◽  
Scale Models ◽  
Roughness Lengths ◽  
Urban Sites ◽  
Obstacle Height

Abstract Urban climate experimental results from the Comprehensive Outdoor Scale Model (COSMO) were used to estimate roughness lengths for momentum and heat. Two different physical scale models were used to investigate the scale dependence of the roughness lengths; the large scale model included an aligned array of 1.5-m concrete cubes, and the small scale model had a geometrically similar array of 0.15-m concrete cubes. Only turbulent data from the unstable boundary layers were considered. The roughness length for momentum relative to the obstacle height was dependent on wind direction, but the scale dependence was not evident. Estimated values agreed well with a conventional morphometric relationship. The logarithm of the roughness length for heat relative to the obstacle height depended on the scale but was insensitive to wind direction. COSMO data were used successfully to regress a theoretical relationship between κB−1, the logarithmic ratio of roughness length for momentum to heat, and Re*, the roughness Reynolds number. Values of κB−1 associated with Re* for three different urban sites from previous field experiments were intercompared. A surprising finding was that, even though surface geometry differed from site to site, the regressed function agreed with data from the three urban sites as well as with the COSMO data. Field data showed that κB−1 values decreased as the areal fraction of vegetation increased. The observed dependency of the bulk transfer coefficient on atmospheric stability in the COSMO data could be reproduced using the regressed function of Re* and κB−1, together with a Monin–Obukhov similarity framework.

Staged-Air Ratio Optimization for a New Down-Fired Technology within a Cold Small-Scale Model of a 350 MWeUtility Boiler

2011 ◽  
Vol 25 (4) ◽  
pp. 1485-1496 ◽  
Author(s):  
Min Kuang ◽  
Zhengqi Li ◽  
Pengfei Yang ◽  
Jinzhao Jia ◽  
Qunyi Zhu
Keyword(s):  
Scale Model ◽  
Small Scale ◽  
Ratio Optimization ◽  
Small Scale Model

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

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