Measurement Of Pressure Distribution Research Articles

2016S-GS3-3 波浪中を航走する船の非定常圧力分布計測

2016S-GS3-3 波浪中を航走する船の非定常圧力分布計測

Suppression of transonic buffet with plasma vortex generators

In the present paper, we report on the results of an experimental study of the possibility to control the transonic buffet on a rectangular wing using plasma vortex generators. The influence of the developed device on the flow consists in creating a longitudinal vortex in the boundary layer as a result of asymmetric energy supply at the surface of a small vertical wedge. The experiments were performed using a wing model with a supercritical airfoil in the range of free-stream Mach numbers 0.73 to 0.78 and Reynolds numbers Re = (2.64-2.8)·106. The experimental data obtained using the method of high-speed schlieren visualization and pressure distribution measurements in the wake of the model show that the technique allows one to control both the average flow characteristics and the characteristics of shock-wave oscillations.

Dual optical force plate for time resolved measurement of forces and pressure distributions beneath shoes and feet

Frustrated total internal reflection (FTIR) imaging was used to perform remote optical measurements of the forces/pressures exerted beneath shoes and feet during a number of different training activities including countermovement jumps, jogging and drop jumps. A single camera was used to simultaneously image two acrylic, FTIR waveguide imaging elements from below, at frame rates up to 200 frames per second. The images obtained using the camera were converted into pressure/force maps using a previously developed theory which combines the mechanics of contact of soft objects and the scattering of evanescent waves. The forces obtained from the optical measurements were shown to be in good agreement with measurements obtained from load cells placed beneath the FTIR imaging elements. The ability to produce accurate spatial maps of the force/pressure distribution beneath soft contacting objects such as feet and shoe outsoles at high frame rates has numerous potential applications in sports sciences and medicine.

Experimental study of bump effects on boundary-layer transition in compressible high Reynolds number flow

The influence of surface bumps on boundary-layer transition was experimentally investigated in the present work. The experiments were conducted in a (quasi-) two-dimensional flow at low to high subsonic Mach numbers and chord Reynolds numbers up to 10 million in the low-turbulence Cryogenic Ludwieg-Tube Göttingen. Various streamwise pressure gradients relevant for natural laminar flow surfaces were examined. Quasi-two-dimensional bumps, with a sinusoidal shape in the streamwise direction, fixed length and three different heights, were installed on a two-dimensional flat-plate model. The model was equipped with temperature-sensitive paint for non-intrusive transition detection and with pressure taps for the measurement of the surface pressure distributions. Boundary-layer transition was shown to occur at a more upstream location with increasing bump height-to-length ratio. This was mainly due to the local adverse pressure gradient on the downstream side of the bump, which was particularly pronounced in the case of the bump with the largest height-to-length ratio, thereby inducing boundary-layer separation (as verified via oil-film visualizations). In the case of the bump with the smallest height-to-length ratio, bump-induced transition was found to be dependent on global pressure gradient, Mach number and Reynolds number; however, the influence of these parameters on transition induced by bumps with larger height-to-length ratios was significantly reduced. The sensitivity of boundary-layer transition to the effect of the bumps was shown to be more pronounced with stronger global flow acceleration and at smaller Mach numbers.

Changes in foot measurements, plantar pressure and postural position during a mountain ultra-marathon race

The aim of this study was to compare the plantar pressure distribution and foot measurements during standing posture before, during and after a mountain ultra-trail race. Thirty-eight runners were tested before (km-0) and after (km-171) of the Ultra-Trail Mont-Blanc 2016. Ten runners among of them were also tested at three checkpoints (km-49, km-79 and km-124). Standing erected posture was recorded on a stabilometric platform and was analyzed by the mean position of the center of pressure (CoP) on the antero-posterior (YCoP) and medio-lateral (XCoP) axis. The relative body weight under the forefoot (FPP), the foot length (LF) and the front foot width (WFF) were also measured. The rating of perceived overall fatigue (RPF) was evaluated by Borg scale. YCoP moved forward (P < 0.05) after the UTMB while FFP and WFF were increased (P < 0.05). Changes in YCoP and changes in FFP were positively correlated (r = 0.47, P < 0.05). YCoP, FFP and RPF increased significantly (P < 0.05) from the start to km-79 but were unchanged between km-79 to km-171. WFF increased at km-79 then remain unchanged until the end. XCoP and LF were unaltered throughout the UTMB. The increase of the forefoot plantar pressure is related to the forward displacement of CoP. These results explain probably why many runners have injuries in this area during a MUM. The increase of the front foot width should be taken into account for the choice of the running shoes, as much as the foot length. Le but de cette étude était de d’évaluer les modifications des pressions plantaires, des mesures du pied et de la posture, en position debout avant, pendant et après une course d’ultra-trail en montagne. Trente-huit coureurs ont été testés avant (km-0) et après (km-171) de l’ultra-trail Mont-Blanc 2016. Dix coureurs parmi eux ont également été testés à trois points de contrôle (km-49, km-79 et km-124). La posture debout a été enregistrée sur une plate-forme stabilométrique permettant d’établir la position moyenne du centre de pression (CoP) sur l’axe antéro-postérieur (YCoP) et médio-latéral (XCoP). Le poids corporel relatif sous l’avant-pied (FPP), la longueur du pied (LF) et la largeur du pied avant (WFF) ont également été mesurés. L’évaluation de la fatigue globale perçue (RPF) a été évaluée par échelle de Borg. YCoP a avancé (p < 0,05) après l’UTMB tandis que FFP et WFF ont augmenté (p < 0,05). Les changements de YCoP et les changements de FFP étaient positivement corrélés (r = 0,47, p < 0,05). YCoP, FFP et RPF ont augmenté significativement (p < 0,05) du début au km-79, mais sont demeurés inchangés entre le km-79 et le km-171. Le WFF a augmenté au km-79 puis reste inchangé jusqu’à la fin. XCoP et LF étaient inchangés tout au long de l’UTMB. L’augmentation de la pression plantaire sous l’avant-pied est liée au déplacement vers l’avant de la CoP. Ces résultats expliquent probablement pourquoi de nombreux coureurs ont des blessures dans cette zone au cours d’une MUM. L’augmentation de la largeur du pied avant doit être prise en compte pour le choix des chaussures de course, autant que la longueur du pied.

Control of Wave Energy Converters Using A Simple Dynamic Model

This paper derives a control law within the context of optimal control theory for a heaving wave energy converter (WEC) and presents its implementation procedure. The proposed control assumes the availability of measurements of pressure distribution on the buoy surface, buoy position, and buoy velocity. This control has two main characteristics. First, this control is derived based on a simple dynamic model. The forces on the WEC are modeled as one total force, and hence there is no need to compute excitation or radiation forces. Second, this control can be applied to both linear and nonlinear WEC systems. The derived control law is optimal, yet its implementation requires estimation of some force derivatives, which render the obtained control force suboptimal. Numerical testing demonstrates in this paper that the proposed simple model control can achieve levels of harvested energy close to the maximum theoretical limit predicted by singular arc control in the case of linear WEC systems.

A smart insole for monitoring plantar pressure based on the fiber Bragg grating sensing technique

The analysis of plantar pressure distribution is essential in the field of biomedical and sports-related applications. In this study, a smart insole was developed for the measurement of plantar pressure distribution and the evaluation of body postures using optical fiber Bragg grating (FBG) sensing technology. Four FBG sensors characterized by four different center Bragg wavelengths, 1528 ± 0.3, 1532 ± 0.3, 1535 ± 0.3 and 1539 ± 0.3 nm, were located at the first metatarsus, third metatarsus, fifth metatarsus and heel position, respectively. The measurement sensitivity of all the FBG sensors was 0.000412 nm/kPa, approximately. Silica gel material of modulus = 10 MPa was selected to incorporate the FBG sensors. All FBG sensors were multiplexed together with one optical fiber cable. The performance and functional properties of all FBG-based pressure sensors were calibrated in the laboratory to evaluate plantar pressure distribution. A male subject was selected for performing four tasks, namely standing in an upright position, leaning forward, squat position and forward fold. During standing tests, plantar pressure observed at the heel position was around 57% higher than that at the first and third metatarsus, while the pressure of the fifth metatarsus position presents minimal pressure, which is only 37% that of the pressure of the heel position. When the subject performs leaning forward, the squat position and forward fold posture, the first and third metatarsi show maximum pressure, while the pressure decreases at the fifth metatarsus position. However, almost zero pressure is observed at the heel position when the subject changes the body postures of leaning forward, squat and forward fold posture. The extreme pressure of the forward fold posture was 1750 kPa acquired at the first metatarsus, which is 52% and 62% higher than those at the fifth and third metatarsi, respectively. Therefore, the smart insole successfully recorded both plantar pressure distribution and body posture changes regarding the wavelength values collected by the FBG sensors.

The Influence of Long-Term Use Of High-Heeled Shoes for Women`s Posture and Lower Extremity Muscle Strength

Background. Wearing high-heeled shoes can cause posture distortions: the head position is tilted forward, increased lordosis of the lumbar spine anterior pelvic tilt, knees flexed with some knee ‘varus’, hyper-supination of the foot (Pannell, 2012). These changes cause muscle imbalance: abdominal core muscles, upper back erectors spinae get elongated and weakened, gluteal muscles are weakened. Hamstrings get slightly elongated but are not necessarily weakened. Hip flexors and lower back muscles get shortened and strengthened. Soleus and gastrocnemius muscles get shortened and strengthened. Aim of the study was to determine the long-term effect of wearing high-heeled shoes on women’s leg muscles and posture. Methods. Twenty nine women took part in the study. They were divided into two groups: those who met the research criteria and wore high heeled shoes and those, who did not. We used a questionnaire to assign participants to one of the research groups, and measured muscle strength using a hand-held dynamometer, we measured pressure distribution in a specifc foot area using a “Matscan” mat and evaluated posture according W. K. Hoeger’s method. Results. Strength of only three muscle groups differed between women wearing and not wearing high heels, muscle strength of thigh flexors, shin erector and feet plantar flexors in women regularly wearing high heels were greater compared to women that did not wear high heels. Measurements of static feet load distribution showed that in women wearing high-heeled shoes, 71.01% of weight went on heels and only 28.98% ‒ on toes and forefoot, while in women not wearing high heels weight was distributed equally ‒ 49.28% goes on heels and 50.72% on toes and forefeet. Study results showed that 41.3% of women regularly wearing high-heeled shoes had excellent posture, while 45.7% of women not wearing high-heeled shoes had excellent posture. Conclusions. Muscle strength of thigh flexors, shin erector and feet plantar flexors in women regularly wearing high heels was greater compared to women that did not wear high heels. Feet static support centre in women, who regularly wore high heeled shoes was distributed towards the heel while feet static support centre in women not wearing high heels was distributed equally along the foot. There were no signifcant differences evaluating posture in women wearing and not wearing high heels. The most common posture problems in women regularly wearing high-heeled shoes were: knees in varus position, head and abdomen in protraction, and increased lumbar lordosis.Keywords: high-heeled shoes, posture, muscle strength.

Study on Virtual Simulation Method of Driver Seat Comfort

Pressure distribution of the human-machine interface is a key factor which affects the comfort. Because every part of the human body has different tolerance to pressure, high or low pressure will make the driver feel uncomfortable. Through the virtual simulation method combining 3D modeling and finite element analysis, the human body and seat finite element model is established to simulate the interaction of the contact interface, the human-seat coupling model was constructed and finally imported into ANSYS for finite element analysis and compared with the actual measured pressure distribution. The pressure distribution obtained by this method was proved to be feasible for evaluating driver comfort. When apply on seat back comfort study, the changes in the pressure distribution under various conditions can be observed by changing parameters such as seat inclination. The model can be used as a scientific basis for seat comfort assessment and optimization, and the researchers can understand the pressure on the driver’s various parts to guide the seat comfort design.

Comparison of Plantar Pressure Distribution During Walking After Two Different Surgical Treatments for Calcaneal Fracture

The aim of our study was to compare gait in terms of foot loading and temporal variables after 2 different operative approaches (the extended lateral approach [ELA] and sinus tarsi approach). Twenty-two patients who sustained an intra-articular calcaneal fracture underwent plantar pressure distribution measurements 6 months after surgery. Measurements were performed while patients walked on the pedobarography platform. The values of dynamic variables were significantly lower on the operated limb in the ELA. In the sinus tarsi approach, no differences were observed between the operated and uninjured limbs (UIN) at peak pressure and at maximal vertical force. The values of temporal variables (contact time of the foot and of the heel) between the operated and UIN differed in the ELA. The hypothesis that differences in foot load between operated and UIN will be more significant in the ELA was confirmed. Our results showed that the differences in loading and temporal variables between the operated and the UIN persisted 6 months after surgery in both methods. The operated limb was less loaded, with the tendency to shift the load toward the midfoot and forefoot. After the less invasive sinus tarsi approach, the dynamic and temporal variables on the operated limb were nearly the same as those on the healthy one. The sinus tarsi surgical approach can be recommended for treatment of displaced calcaneal fractures.

Flexible piezoresistive sensor matrix based on a carbon nanotube PDMS composite for dynamic pressure distribution measurement

Abstract. A highly flexible, piezoresistive sensor matrix based on a carbon nanotube (CNT) polymer composite is developed for pressure distribution measurement applications. With an overall height of about 400 µm, the sensors can measure pressure directly, without any deformation elements, such as a cantilever or a deformation membrane. The measurement range is from 2.5 to 640 kPa. Both the position and the pressure of the applied load can be measured and visualized as a resistance change. The relative resistance measurement deviation of the data acquisition system is lower than 3 % for the resistance range of 610Ω to 380 kΩ. This corresponds to a systematic deviation of pressure measurement of less than 3 % in the measurement range. Besides the measurement of pressure, different sizes of loads can be detected as well. The developed fast and compact measurement system allows dynamic pressure measurement, such as gait analysis when used in an insole application.

Motor strategy for rapid gait initiation under conditions of limited center of pressure control.

[Purpose] The general motor strategy for gait initiation is achieved by the difference between the center of gravity and center of pressure; it be as bigger under speed optimization. This study aimed to investigate the motor pattern in rapid gait initiation under conditions of limited backward displacement of center of pressure. [Participants and Methods] The participants were 30 healthy young males (mean age, 19.7 ± 1.0 years). They performed a gait initiation task at three center of pressure start positions (anterior, middle, and posterior) and two speed conditions (normal and rapid). The gait initiation motion was measured using a video camera and motor pattern in the images was classified. The center of pressure position was continuously monitored using a pressure distribution measurement system. [Results] Forward tilt pattern was the most common under no limited center of pressure control and normal speed. The backward tilt pattern was the most preferred in the posterior position under limited center of pressure control and rapid speed. Displacement of the center of pressure showed a significant decline when the center of pressure start position was displaced backward. [Conclusion] The backward tilt pattern is the most effective motor strategy to increase the forward speed of the center of gravity.

Practical Approach for Absolute Density Field Measurement Using Background-Oriented Schlieren

A practical approach for deriving the absolute density field based on the background-oriented schlieren method in a high-speed flowfield was implemented. The flowfield of interest was a two-dimensional compressible flowfield created by two supersonic streams to simulate a linear aerospike nozzle operated under a supersonic in-flight condition. The linear aerospike nozzle had a two-dimensional cell nozzle with a design Mach number of 3.5, followed by a spike nozzle. The external flow simulating the in-flight condition was 2.0. The wall density distribution used as the wall boundary condition for Poisson’s equation to solve the density field was derived by a simplified isentropic assumption based on the measured wall pressure distribution, and its validity was evaluated by comparing with that predicted by numerical simulation. Unknown coefficients in Poisson’s equation were determined by comparing the wall density distribution with that predicted by the model. By comparing the derived density field based on the background-oriented schlieren method to that predicted by the model and numerical simulation, the absolute density field was derived within an error of 10% on the wall distribution. This practical approach using a simplified isentropic assumption based on measured pressure distribution thus provided density distribution with sufficient accuracy.

Asymmetry and global instability of real minivans' wake

Three minivan cars tested in real flow conditions are investigated through base pressure distribution, force balance and velocity measurements. Discontinuous transitions of permanent wake reversals and bistable dynamics between two well-defined states are observed varying ground clearance, pitch and yaw, with open and closed air-intake. These transitions prove that the cars undergo the same global z-instability as the square-back Ahmed body (M. Grandemange, M. Gohlke and O. Cadot, Physics of Fluids, 25, 2013). The contribution of the global instability to the lift coefficient is estimated to 0.012 and 0.024 depending on the wake state. Eventually, the potential of direct passive control of the z-instability is demonstrated by improving from 4.6% to 8.3% the drag reduction obtained by closing the front air-intake of the car.

Mode of median nerve irritation under different wrist forcing postures observed by ultrasonography and foot pressure measurement system

Objective: To analyze the influence of simulation mouse use motion under different wrist forcing postures on median nerve, tendons and ligaments in the carpal tunnel. Methods: From June to November in 2017, a total of 49 healthy volunteers [aged from 18 to 27 years, 24 males (48 cases of hands) and 25 females (50 cases of hands)] were selected in the Institute of Digitized Medicine and First Affiliated Hospital of Wenzhou Medical University.Three hand postures of the volunteers were simultaneously and continuously measured by using LOGIQ E9 ultrasonic diagnostic apparatus and Zebris foot pressure distribution measurement system.Seventeen parameters of nerves, tendons and ligaments in carpal tunnel were observed under natural (0 N), and two forced (25 and 50 N) states.Double factor variance analysis was performed with generalized estimating equation (GEE). Results: With increasing pressure (0, 25 and 50 N) of hand postures, the distance between median nerve and transverse carpal ligament were all less than 0.2 cm.The differences in both the distance between median nerve and flexor pollicis longus under the hand pressure changes or under the hand posture changes and the top angle of a triangle composed of median nerve, flexor pollicis longus and flexor digitorum superficialis group under the hand pressure changes or under the hand posture changes were all significant under the GEE analysis (all P<0.01). There were no significant changes in all other structural parameters in the carpal tunnel with the increasing of hand pressure (all P>0.05). Conclusions: The influence of the transverse carpal ligament to the median nerve belongs to the mechanism of pressure-induced irritation damage.The influence of flexor pollicis longus to median nerve belongs to the mechanism of tension-induced irritation damage.The influence of flexor digitorum superficialis to median nerve belongs to the mechanism of mixed shear irritation damage.

Inflow angular dependence of the capture coefficient in cryopumps

This study investigated the inflow angle and capture coefficient є using numerical simulation, and then validated the inferred relation by experimentation. The inflow angular dependent capture coefficient є(θ) of a cylindrical cryopump used to create a high-vacuum environment for electric propulsion tests was calculated from a three-dimensional particle trajectory simulation. Results show that є(θ) is 0.25–0.83 as a function of the inflow angle of particles to the pump surface. A total capture coefficient єtotal is obtained by integration of the є(θ) multiplied by the flux distribution of particle to the pump surface. For the thermal inflow flux, єtotal is calculated as 0.55 for the cylindrical cryopump alone and 0.70 for a cylindrical cryopump with a duct for a gate valve. The analytically estimated єtotal was evaluated by pressure distribution measurements taken in a φ2.0 × 3.0 m vacuum chamber evacuated by two cylindrical cryopumps. The numerically simulated pressure shows good agreement with the measured pressure within ±6%. Further investigation of the improvement of the єtotal when the particles flow directly to a pump demonstrates that єtotal increases 16% when particles flow directly to a pump.

Some Specific Features in the Formation of Pressure in Sliding Bearing Clearance

Results of theoretical and experimental studies of the pressure distribution in the sliding bearing clearance are presented considering the influence of dissipative processes. The results obtained allow a more accurate description of special features in the formation of pressure in sliding bearing clearance that cannot be taken into account within the framework of the traditional approach based on the Navier–Stokes equation. The theoretical data are supported by the results of pressure distribution measurement in the clearance between the cylindrical racer of the bearing and the shaft fixed in it.

A Study of the Mechanical Properties and Gait Cycle Parameter for a Below-Knee Prosthetic Socket

This work involved an experimental study into the tensile and fatigue properties of selected below-knee prosthetic socket materials fabricated using a vacuum moulding technique. The composite materials were composed of number of carbon-fibre layers (8 layers) and carbon fibre with perlon layers (11 layers).The Ground Reaction Force (GRF), Center of Pressure (COP) and pressure distribution) for a patient of around 27years old of height 170cm and weight75kg were measured, and the results showed that the ultimate stress (Ϭutt)for carbon fibrewas135 MPa, while for carbon fibre with perlon in an 80:20 matrix, it was 98 MPa.The fatigue limit for carbon fibre was 30 MPa and for carbon fibre with perlon it was 45 MPa. The data on gait cycle GRF was gained by using a force plate to measure pressure distribution using an F-socket, and these were collected using a patient with a below-knee amputation wearing a prosthetic of type BK. The internal pressure between the patient’s stump and the prosthetic socket was measured by using the F-socket Mat scan sensor; this reached its maximum value (52KPa) at both heel strike and toe off.

Pressure distributions generated by vaporizing metal foils

Abstract The pressure distributions generated by vaporizing metal foils were studied. An analytical model which described the dynamic mechanical behavior of a rectangular plate under an impulsive loading was introduced. The formed parts of free bulging tests were analyzed using the optical measurement system. Two measurement methods for pressure distributions were introduced and compared. Both the perforated sheet forming test and the pressure film were found to be effective method to measure pressure distributions. The cost of perforated sheet forming test was cheap and the pressure film was easy to operate. Three different pressure distributions were measured and discussed, namely single pressure distribution, tailored pressure distribution and double-direction pressure distribution. These three pressure distributions could be applied in different metal forming processes.

Numerical and experimental investigations on the hydrodynamic radial force of single-channel pumps

In order to clarify the generation mechanism and characteristics of hydrodynamic radial force in single-channel pumps, the transient flow in three single-channel pumps was analyzed by computational fluid dynamics (CFD). The three pumps had the identical impeller but with a spiral volute (model 1), a circular volute (model 2), and a torus (model 3). Experiments on pump performance were performed and high frequency pressure sensors were mounted in the spiral volute to measure pressure distribution in the volute of model 1. It indicates that the numerical results are approximately consistent with the experimental results. The radial force is mainly caused by the pressure acting on the blade. The impeller radial force in model 1 was the largest while the model 3 was the smallest, as it is not affected by rotor stator interaction, and rotor stator interaction plays a vital role in the shock load of pumps. The radial forces of different rotational speed were analyzed and indicated that Reynolds number has little influence on the radial force coefficient CF. The dominant frequency of the radial force on the impeller is the rotational frequency of impeller for all rotational speeds. Moreover, the amplitude of the radial force fluctuations increased with increasing flow rate in model 2, but the change was not obvious with the increasing of flow rate in model 3, while at lower flow rate the largest amplitude of the radial force fluctuations was presented in models 1.