Ground Board Research Articles

Peak patellar tendon force progressions during heavy load single-leg squats on level ground and decline board

BackgroundProgressive tendon loading programs for patellar tendinopathy typically include single-leg squats with heavy weights either on level ground or on a decline board. Changes in patellar tendon force due to variations of the heavy load single-leg squat have not yet been objectively quantified. The objective of this study was to investigate the influence of the mass of an external weight and the use of a decline board on the peak patellar tendon force during a heavy load single-leg squat. MethodsTwelve healthy participants performed single-leg back squats on a decline board and level ground at 70%, 80% and 90% of their one repetition maximum. Three-dimensional kinematics and ground reaction forces were measured and the peak patellar tendon force was calculated using musculoskeletal modelling. A two-way repeated measures ANOVA determined the main effects for the mass of the external weights and the use of a decline board as well as their interaction effect. FindingsPeak patellar tendon forces were significantly higher on the decline board compared to level ground (p < 0.05). Neither on the decline board, nor on level ground did the peak patellar tendon force increase significantly when increasing the external weights (p > 0.05). InterpretationProgression in peak patellar tendon forces during a heavy load single-leg squat can only be obtained with a decline board. Increasing the mass of the external weight from 70% to 90% of the one repetition maximum does not result in a progressively higher peak patellar tendon force.

An experimental investigation of ground board mounted microphones for outdoor noise measurement

This paper reports an experimental investigation on the use of ground board mounted microphones for making outdoor noise measurements. The experiments utilized a 400 mm diameter thin metal ground board into which a probe microphone was flush mounted at a number of different radii. The ground board was placed on the floor of an anechoic chamber and the noise level from a source at a fixed height was measured for a large number of different ground board orientations. These measurements were used to assess the variation in the sound pressure level over the ground board.

Three-Dimensional Quantitative Flow Visualization Around a Thrust Reverser

Volumetric particle tracking velocimetry measurements are performed in a low-speed wind tunnel to study the flow around a 1:12-scale aircraft model with jet engines operating with thrust reversers. The engine jet and freestream flow velocity are varied to yield a jet to freestream velocity ratio of ranging from 1.5 to 6. Measurements at such scale () require the use of strongly scattering helium-filled soap bubbles as flow tracers, which are introduced in both the jet and the freestream flow. The tracer’s three-dimensional motion is determined using an array of cameras and a Lagrangian particle tracking algorithm. The mean velocity field reveals the jet inner structure as well as its interaction with the freestream, the ground board, the nacelle, the fuselage, and the horizontal and vertical tails. The experiments allow detection of exhaust reingestion as well as the aerodynamic interference with control surfaces at the tail segments in a single measurement volume. The results are in good agreement with conventional temperature rake measurements while adding details of the flow topology and of the large-scale unsteady flow fluctuations. Finally, the jet reversal characteristics with varying freestreams and nozzle pressure ratios are assessed, demonstrating the feasibility and versatility of volumetric velocimetry measurements for industrial aerodynamics.

自動車のフロントエンド形状とエンジン冷却風による空力特性

The purpose of this research is to experimentally investigate how increase of the air inlet area of the engine cooling air affects the aerodynamic characteristics depending on the shape of the front-end of the vehicle body. A simplified 1/5 scale vehicle model was used with reproduction of the engine compartment where FF and FR type engines could be installed. In past researches, we used a rectangular front-end model, and in this research we used a round front-end model with a shape closer to the actual vehicle. In the wind-tunnel experiments, the moving-belt ground board was used to capture ground effects, measuring drag force, lift force and body surface pressure. The experiments were conducted at a wind speed and a moving belt speed of 20 m/s. As a result, the reason for the increase in drag due to the increase in air inlet area was the damming effect caused by the interference between the scavenging air flow in the engine compartment and the underfloor flow. The drag force of the round model was lower than that of the rectangular model, but the lift force was not significantly reduced.

Eight‐element self‐decoupled MIMO antenna design for 5G smartphones

A self-decoupled antenna element working at half- wavelength mode is proposed and implied into an eight-element multiple-input-multiple-output (MIMO) antenna array for the fifth-generation (5G) smartphones applications. Particularly, self- decoupled is conveyed by the feature of balanced antenna, which is composed of an open slot (0.197 λ0 × 0.035 λ0 at 3.5 GHz) excited by a two-arm feedline located on the horizontal ground board and a half-wavelength dipole-type mode is formed. A week ground current effect and high-isolation level are achieved with no additional decoupling stub. Besides, the location of the element is thoroughly considered to achieve a desirable decoupling effect. In the desired 3.5 GHz band (3.4-3.6 GHz), isolation of more than 18.5 dB and total efficiency of more than 65% are obtained. The proposed MIMO antenna was simulated and fabricated. The corresponding performances were claimed by simulated results and measured ones, a good uniformity between the two was obtained.

Reduction of Aerodynamically Undesirable Influences Due to Engine Cooling Flow in Road Vehicle

The purpose of this research is to clarify causes for the change in aerodynamic characteristics of a road vehicle model due to engine cooling flow in wind-tunnel experiments with the moving-belt ground board, in order to propose methods to reduce the drag and lift. With regard to engine cooling flow, the air-intake system was adjusted with variable opening area and position for the engine loading system of FF and FR with and without a radiator. A simplified 1/5 scale vehicle model was manufactured with transparent externals around the engine for flow visualization. The overall results show that with enlargement of the opening area, the drag and the front lift increased and the rear lift decreased. The flow visualization and the measurements of underfloor velocity and surface pressure indicated the cause of the characteristics changes. Enlargement of the opening area causes flow disturbance by merging of the scavenging flow and the underfloor flow, which has blockage effects for the upstream of each flow with keeping high pressure in the engine compartment and causes pressure loss under the floor behind the engine unit. The difference between the two engine loading systems lies indirection and location of the engine unit, which causes the differences of how the flow features affect the aerodynamic characteristics. The effect of the radiator is to reduce the range of changes in drag and lift. Finally, it is discussed that the principle of reducing drag and lift is to suppress interference of scavenging flow, and concrete methods are proposed.

Characterization of the effects of ground boards on acoustic signals

International and Federal regulations stipulate the acquisition of aircraft noise shall be conducted using inverted pressure microphones over a round ground board. These ground boards are used to provide an acoustically hard reflecting surface, limiting the effects of the potentially absorptive ground local to the test location. The microphone location is also specified to be offset from the center of the board to limit the effects of acoustic diffraction off the board edge. In order to determine the effects of the ground board on the measured acoustic signal, a comprehensive measurement campaign was undertaken at NASA Langley Research Center. The experimental setup included multiple ground board configurations placed on top of a sand pit, in an otherwise anechoic chamber. Ground board configurations included a microphone inverted and offset over the round ground board, a microphone offset and flush mounted in the ground board, and a microphone flush mounted in the sand. A detailed frequency sweep from a known source was then used to investigate the ground board effects on the recorded signal. Normal impedance measurements were also acquired to determine the reflection coefficients of the sand and ground boards. Experimental results are discussed, along with implications for future research and development.International and Federal regulations stipulate the acquisition of aircraft noise shall be conducted using inverted pressure microphones over a round ground board. These ground boards are used to provide an acoustically hard reflecting surface, limiting the effects of the potentially absorptive ground local to the test location. The microphone location is also specified to be offset from the center of the board to limit the effects of acoustic diffraction off the board edge. In order to determine the effects of the ground board on the measured acoustic signal, a comprehensive measurement campaign was undertaken at NASA Langley Research Center. The experimental setup included multiple ground board configurations placed on top of a sand pit, in an otherwise anechoic chamber. Ground board configurations included a microphone inverted and offset over the round ground board, a microphone offset and flush mounted in the ground board, and a microphone flush mounted in the sand. A detailed frequency sweep from a ...

Polarization reconfigurable slot antenna for 5.8 GHz wireless applications

A CPW-fed circular polarization reconfigurable antenna is proposed in this paper. The antenna consists of two symmetrically placed inverted L-shaped slots. By using a T-type bias device to change the bias states of two PIN diodes which connect the two slots with the feed port respectively, right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) can be realized accordingly. For both states, the measured −10 dB impedance bandwidth is 5.78–5.96 GHz, while the measured 3 dB axial ratio bandwidth is 5.64–5.91 GHz (4.7%), both the bandwidths can cover the 5.8 GHz ISM band. By using floating ground and reflector board to enhance the front to back ratio of the antenna, 6.84 dBi measured gain can be realized at 5.8 GHz.

Design of a compact low‐cost GPS antenna for high‐overload applications

AbstractA novel compact global positioning system antenna design of helical antenna operated at its normal mode is presented for high‐overload applications. A grounded matching stub is introduced for good impedance matching and a LNA module is implemented on ground board. The prototype of extremely compact size (22 × 19 mm2) is fabricated and experimentally investigated. The measured 10‐dB impedance bandwidth is almost 14 MHz around the center frequency 1575 MHz. An omnidirectional pattern in broadside of the antenna is achieved and the capability of stable signal reception under various motion attitude is verified by experiments. The proposed antenna is suitable for applications in systems where compact operation and high overload are the major concerns, especially for installation in an artillery fuze.

Aerodynamic effects by cooling flows within engine room of a car model

The purpose of this research is to clarify the change of characteristics of aerodynamic drag and lift of a car by the engine loading system (engine arrangement) and the air inlet system (opening area and position) with and without a radiator in wind-tunnel experiments. A simplified car model with 1/5 scale is generated with reproduction of the engine room covered with the transparent acryl externals for visualization. In the wind-tunnel experiments, the moving-belt ground board is adopted to include ground effects with force measurements by use of load cells. The flows are visualized by the smoke method. As results, with enlargement of the opening area, the drag increased overall although depending largely on the engine loading system and the inlet opening position, the front lift increased and the rear left decreased; the effect of the radiator was to relieve the change of the drag and lift.

Experimental Study of CLARK-Y Smoothed Inverted Wing with Ground Effect

Aerodynamic characteristics of inverted single element airfoil with and without ground effect had been investigated experimentally in Low-Speed Wind Tunnel of test cross section area (0.7x0.7 m) and maximum velocity 55 m/s to quantify the aerodynamic characteristics of inverted CLARK-Y smoothed airfoil. The ground effect was introduced by using a fixed flat board moves vertically to produce the required distance between the airfoil and ground board. The model was tested with and without ground effect and at various wind tunnel velocities (Reynolds numbers), ride heights (ground clearances) and angles of attack. Data obtained in airfoil experiments include sectional forces and surface pressure data. Results are compared with the free-drive case and with published works. Data indicated that the pressure distribution increased at the upper and lower surfaces in ground proximity, at low angles of attack, and increased also with incidence. The negative lift coefficient increased with angle of attack except the angles of attack larger than 10 and with ground effects except at ride heights of less than 0.1c due to the force reduction phenomena. The drag coefficient increased with the ground effect which caused a decrease in the airfoil efficiency. The aerodynamic characteristics remain relatively an affected by the velocity change. The experimental data were compared with published works and showed good results.

Differential- and common-mode radiofrequency interference filters based on complementary split ring resonators: a conduction and radiation impact analysis

This paper aims to analyse the design techniques of differential transmission lines loaded with metamaterials. Specifically, complementary split-ring resonators were etched on the ground plane of a microstrip transmission line in order to mitigate both differential- and common-mode propagation in differential signalling. Several prototypes were manufactured and characterised in printed circuit boards. The topologies under test were measured and compared as radiofrequency interference filters, taking into account frequency response, signal integrity, and near- and far-field radiation impact with regard to a reference (solid ground) board.

Design of an 868 MHz Printed S-Shape Monopole Antenna

The purpose of this work is to design and analyze an s-shaped printed circuit board (PCB) monopole antenna. The antenna was analyzed to operate at a resonance frequency band of 868 MHz; acceptable in 915 MHz as well. The s-shape is selected due to the need of reducing the overall size of the normal monopole antenna. The printed antenna was designed with an approximate overall size of 39 × 56 mm2 of which the antenna’s upper side is 26 × 39 mm2 while its reference ground board was sized at 39 × 30 mm2. The antenna is fed by a strip line of 3 × 1.5 mm2, in series with a 4.4 pF capacitance and shunt with an 8.7 nH inductance for purpose of antenna’s impedance matching with the input. A couple of existing publications showed that PCB antenna is not a new technology; however not an old technology for telecommunication industry. The raised problem by this work was duly solved with HFSS as a tool; excellent results are presented. After duly matching the antenna’s impedance with 50 Ω microstrip feed-line, solutions for overall performance were analyzed and demonstrated optimal: radiation patterns were proven omnidirectional, antenna gain optimized. The present antenna prototype’s overall dimensions can be readjusted according to any industrial and manufacturing requests.

Electromagnetic interference reduction in printed circuit boards by using metamaterials: a conduction and radiation impact analysis

This work aims to compare the implementation of two metamaterials for reducing electromagnetic interference (EMI) in printed circuit boards. Specifically, complementary split-ring resonators (CSRRs) and electromagnetic bandgaps (EBGs) were etched on the ground plane of a microstrip transmission line. Both techniques were compared as EMI filters, taking into account frequency response, signal integrity, and near- and far-field radiation with regard to a reference (solid ground) board. The results of electromagnetic simulations and experimental tests show similar EMI rejection levels in both cases, but CSRRs have a significantly better signal integrity response whereas EBGs behave as lower electromagnetic radiation elements in the operation frequency band.

Area-wide infrasound measurements for two wind turbine facilities

Area-wide measurements of low frequency wind turbine noise were conducted in residential areas adjacent to two different wind turbine facilities in Southern California. The residential measurement location distances ranged from 615 m to 9 km from wind turbines. Additional measurements were also conducted at distances as close as 125 m from the wind turbines. To obtain the residential measurement data, simultaneous digital recordings were made inside and outside residences using microphones designed to achieve a linear response down to 0.07 Hz. The outdoor measurements were conducted with a ground board and two windscreens. The recorded data at residences were analyzed using a cross-spectral technique to minimize the effects of wind acting on the microphone. The data clearly show the presence of infrasound at the blade passage frequency of the wind turbines as well as at the associated harmonics. The primary range of interest is frequencies between 0 and 10 Hz. The residential data in some instances indicate higher levels of infrasound indoors compared to outdoors, indicating a potential amplification of very low frequency sound energy by the residential structure. Representative infrasound data for both facilities are presented and discussed.

SCS-CN Based Quantification of Potential of Rooftop Catchments and Computation of ASRC for Rainwater Harvesting

Rooftop rainwater harvesting, among other options, play a central role in addressing water security and reducing impacts on the environment. The storm or annual storm runoff coefficient (RC/ASRC) play a significant role in quantification of potential of rooftop catchments for rainwater harvesting, however, these are usually selected from generic lists available in literature. This study explores methodology/procedures based on one of the most popular and versatile hydrological model, Soil Conservation Service Curve Number (SCS-CN) (SCS 1986) and its variants, i.e., Hawkins SCS-CN (HSCS-CN) model (Hawkins et al. 2001), Michel SCS-CN (MSCS-CN) model (Michel et al. Water Resour Res 41:W02011, 2005), and Storm Water Management Model-Annual Storm Runoff Coefficient (SWMM-ASRC) (Heaney et al. 1976) and compares their performance with Central Ground Board (CGWB) (CGWB 2000) approach. It has been found that for the same amount of rainfall and same rooftop catchment area, the MSCS-CN model yields highest rooftop runoff followed by SWMM-ASRC > HSCS-CN > SCS-CN > CGWB. However, the SCS-CN model has close resemblance with CGWB approach followed by HSCS-CN model, SWMM-ASRC, and MSCS-CN model. ASRCs were developed using these models and it was found that MSCS-CN model has the highest value of ASRC (= 0.944) followed by SWMM-ASRC approach (=0.900), HSCS-CN model (=0.830), SCS-CN model (=0.801), and CGWB approach (=0.800). The versatility of these models lies to the fact that CN values (according to rooftop catchment characteristics) would yield rooftop runoff and therefore ASRC values based on sound hydrological perception and not just on the empiricism. The models have inherent capability to incorporate the major factors responsible for runoff production from rooftop/urban, i.e., surface characteristics, initial abstraction, and antecedent dry weather period (ADWP) for the catchments and would be better a tool for quantification rather than just using empirical runoff coefficients for the purpose.

Particle image velocimetry studies around a rectangular body close to a plane wall

Flow structures around a rectangular body located close to a ground board in a free-surface water channel were investigated using the particle image velocimetry (PIV) technique. The rectangular body is set with α = 0 ° and α = 10 ° yaw angles referenced to the flow direction, and measurements were performed on the vertical and horizontal planes. The PIV technique provided instantaneous and time-averaged flow fields for Reynolds number Re H =1.2×10 4 based on the model height. For α = 0 ° , the results indicate that the flow structure in the wake region vary significantly with the elevation level from the ground surface. An asymmetric large circulating flow region is identified in the wake region for α = 10 ° . The instantaneous flow fields reveal the presence of small-scale vortices in the main flow over the separation line. These small-scale vortices coalesce to form larger-scale vortices.

Monopole Crescent Elliptical Antenna with Band-Notched Characteristics for UWB Applications

A compact antenna with extended band-notched characteristics was designed for ultra wideband (UWB) communications. The antenna consists of a crescent-shaped elliptical patch with a T-shaped stub and a square ground board plane. The antenna is easily integrated with radio-frequency/microwave circuits to reduce the manufacturing cost. The central frequency and the notch bandwidth can be adjusted by changing the size of the T-shaped stub. Simulations verify the design characteristics. Measurements show that the antenna produces the UWB working bandwidth.

Flow structures around a three-dimensional rectangular body with ground effect

An experimental investigation of the flow over the rectangular body located in close proximity to a ground board was reported using the particle image velocimetry (PIV) technique. The present experiments were conducted in a closed-loop open surface water channel with the Reynolds number, <TEX>$Re_H=1.2{\times}10^4$</TEX> based on the model height. In addition to the PIV measurements, flow visualization studies were also carried out. The PIV technique provided instantaneous and time-averaged velocity vectors map, vorticity contours, streamline topology and turbulent quantities at various locations in the near wake. In the vertical symmetry plane, the upperbody flow is separated from the sharp top leading edge of the model and formed a large reverse flow region on the upper surface of the model. The flow structure downstream of the model has asymmetric double vortices. In the horizontal symmetry plane, identical separated flow regions occur on both vertical side walls and a pair of primary recirculatory bubbles dominates the wake region.

2차원 지면효과에 대한 난류 유동장 해석 Part II. 지면경계 조건의 영향에 대한 연구

A comparative study on ground boundary conditions for the airfoil in ground effect has been carried out. The objective of the present study is to clarify effects of the ground boundary conditions so that it will be helpful to analyse results of wind tunnel tests using the fixed ground board or the image method. A low Mach number preconditioned Navier-Stokes solver using the overlap grid method has been applied. It has been turned out that results with the symmetric boundary condition are almost the same to those with the moving boundary condition. Results with the fixed ground boundary show discrepancy to those with the moving boundary condition when flow separation on the ground board takes place.