Air Cushion Pressure Research Articles

Simulation of body vibrations on an incompressible air cushion

Automatic assembly with a part vibrating on incompressible air cushion is considered. The equation of pressure distribution in air cushion between the part and the supporting surface of a pneumatic track is derived. To solve the equation of pressure distribution, a finite element model is constructed. The equation of part motion on air cushion and the equation of pressure distribution are solved. The zones of parameter combinations of air flow and the part motion are defined in cases of slowly damping process, slowly increasing vibrations amplitude or constant amplitude vibrations of the part on the air cushion. Dependencies of vibrations amplitude and air cushion pressure, both on air flow and the system parameters are determined.

Optimization of Groove-Hole Distribution with Equidistant and Unequal Diameter on Air-Cushion Belt Conveyor

In this paper, the research and development of the distribution of air-holes in the groove of air-cushion belt conveyor were introduced. The expressions of air-cushion pressure were given and the graph of it was shown as well. The air flow model nearby groove-holes and air outflow model on cross section were given too. In the same time, the distributing mode of equidistant air-holes with unequal diameter was studied and analyzed. In order to make up the shortage of the study on air-hole distributing mode of equidistant air-holes with unequal diameter on the air-cushion belt conveyor, an instance of the air-cushion flow field was numerically simulated based on the CFD software ,Fluent software. Several groups of data of different air-hole distributions, (for example, the center distances of air-holes in the groove of air-cushion belt conveyor are the same as each other and their diameters are different), were selected to compare with each other , and then, the results were compared with existing theory. According to the different results of the numerical simulation on the distributing mode of equidistant air-holes with unequal diameter, the optimal parameters of air-hole distributing mode were obtained, and the effect of prevent offset that comes the balance groove-hole on air-cushion belt conveyor. Moreover, the verification to prove the agreement between the results of numerically simulated and basic theory was carried out by the comparison analyses. The theoretical feasibility of air-hole distributing mode of equidistant air-holes with unequal diameter was analyzed.

MOTION CONTROL IN WAVES OF A 140M SES

This paper introduces the air cushion pressure control of the 140m Techno Super Liner (TSL), which Mitsui Engineering & Shipbuilding Co., Ltd. (MES) has constructed. TSL is an air-supported catamaran ship, which contains pressurized air between rigid side hulls. The ship dynamic performance is investigated through simulations, for the first, which is based on 3DOF motion (Heave/Pitch/Roll) and air cushion dynamics. It was performed for both model and full scale in various wave headings. The scale effect is discussed through simulation results. Then, the results of towing model tests in both regular and irregular waves are described. The model is equipped with lift fans and all the tests are carried out under the on/cushion conditions. The results of model scale simulations and model tests are compared and verified. With these results from the simulations and model tests, the design of the air cushion control system is discussed in terms of the fan stability and ship vertical accelerations. The basic concept of air-vent louver control is presented. As for the sea trial of the ship, it was successfully completed on October 12, 2005. Some of her splendid performances were demonstrated. A brief introduction of the trial is also presented in this paper.

Cobblestone Oscillations of an SES with Flexible Bag Aft Seal

The high-frequency dynamic response of surface effect ships (SES) equipped with a flexible bag aft seal is studied. The results show dominating vertical accelerations in a frequency range important for passenger comfort and crew work ability. The mathematical model for the craft dynamic response accounts for the motions and accelerations in heave and pitch induced by both the unsteady uniform pressure and the spatially varying air cushion pressure. The effect of a flexible bag aft seal and a variable leakage area under the seals is included. The bag dynamic response is treated as linear and quasistatic. It is shown how the flexible bag reduces the spatial pressure resonance frequencies of a 35 m SES. The variable leakage area under the bag is found important for the response of the craft in low sea states.

Design of ride control system for surface effect ships using dissipative control

A ride control system for active damping of heave and pitch accelerations of surface effect ships (SES) is presented. It is demonstrated that distributed effects that are a result of spatially varying pressure in the air cushion result in significant vertical vibrations in low and moderate sea states. In order to achieve high quality human comfort and crew workability it is necessary to damp these vibrations using a control system which accounts for distributed effects owing to spatial pressure variations in the air cushion. To develop such a ride control system a mathematical model describing the motion of the craft in the vertical plane is derived. This mathematical model accounts for accelerations induced by both the dynamic uniform and the spatially varying air cushion pressure. Sensor and actuator placement is discussed, and the stability of the control system is analysed using the theory of passivity. The performance of the ride control system is shown by power spectra of the vertical accelerations and the pressure variations obtained from full-scale experiments with a 35 m SES.

Urologic Prostheses

In this work, the applicability of Sequential Injection Chromatography for the determination of transition metals in water is evaluated for the separation of copper(II), zinc(II), and iron(II) cations.Separations were performed using a Dionex IonPACTM guard column (50 mm×2 mm i.d., 9 µm). Mobile phase composition and post-column reaction were optimized by modified SIMPLEX method with subsequent study of the concentration of each component. The mobile phase consisted of 2,6-pyridinedicarboxylic acid as analyte-selective compound, sodium sulfate, and formic acid/sodium formate buffer. Post-column addition of 4-(2-pyridylazo)resorcinol was carried out for spectrophotometric detection of the analytes׳ complexes at 530 nm.Approaches to achieve higher robustness, baseline stability, and detection sensitivity by on-column stacking of the analytes and initial gradient implementation as well as air-cushion pressure damping for post-column reagent addition were studied.The method allowed the rapid separation of copper(II), zinc(II), and iron(II) within 6.5 min including pump refilling and aspiration of sample and 1 mmol HNO3 for analyte stacking on the separation column. High sensitivity was achieved applying an injection volume of up to 90 µL. A signal repeatability of<2% RSD of peak height was found. Analyte recovery evaluated by spiking of different natural water samples was well suited for routine analysis with sub-micromolar limits of detection.

Analytical model for dust generated by air-cushion vehicles

The air-cushion vehicle (ACV) is widely used over unconsolidated soils and rugged terrain. This off-the-road vehicle can have mobility problems as well as cause environmental problems. Most of these problems cannot be fully controlled but measures can be taken to minimize their effect. Two of the mobility problems are dust generation and ground surface erosion. This research is a continuation of previous attempts at understanding the mechanics of dust generation and the evaluation of parameters representing soil resistance to disturbance under the air cushion pressure. Specifically this research provides a comprehensive analytical approach by which the characteristics of ACV dust raising, residence time and sedimentation rates are evaluated. Stoke's Law is used in this analysis with concomitant practical assumptions. Field utilization of these models is developed, and predetermination of dust size distribution above ground level, as well as possible particulate dispersions during the dust raising stage are reported. With this information the dust distribution and amount of dust in the atmosphere can be predicted at any time and at any elevation above the ground. Relationships between the quasi-theoretical analyses and the experimental results were considered and found to be in good agreement.

Nonlinear water wave generation using the method of lines

The method of lines is applied to the two-dimensional nonlinear water wave generation resulting from the abrupt acceleration from rest to constant speed of a pressure distribution on the surface of initially calm water. The surface pressure distribution can be viewed as modeling the air cushion pressure of a surface effect ship. Steady state at the craft is achieved for all cases computed, most of which are highly nonlinear and which exhibit sharp downstream wave crests that approach the limiting sharpness of the Stokes wave for steady irrotational gravity waves. Computations show pronounced sharpening of wave crests, broadening of wave troughs, and shortening of wavelengths compared to linear theory. Wave resistance, rates of work, and energy are computed. Computer time is saved by applying the method of lines in a local neighborhood of the free surface in combination with a standard Laplace solver below. Results are presented.

AIR-CUSHION SOCKET FOR K. B. M. PROSTHESIS AND SOME BIOMECHANICAL CONSIDERATION

The air-cushion socket of below knee prosthesis was designed by Wilson in 1968. This socket is a modification of P. T. B. socket having three parts which are hard outer shell with no bottom, silicon rubber made inner elastic socket and a cap covering distal end of socket. In between the inner elastic socket and a cap, air-tight space is formed. This air-tight space acts like an air mat, supports a part of body weight at the stump end and aids suspension of prosthesis during swing phase. The fabrication of this socket, however, is too complicated.The purpose of this study was to investigate the real function of air-cushion as well as to simplify fabricating method.Methods:1) The fabrication of socket was simplified making an inner socket with elastic silicon rubber made lower part and flexible resin made upper part, and rigid outer socket. Socket was designed for K. B. M. socket.2) Pressure of air-cushion and strain of socket were recorded during walking with foot switches to show walking phase.3) Two sockets were made. One was fabricated from the positive model from original K. B. M. socket, another was fabricated from the positive model according to Wilson's method. Former was called A-socket, latter was called B-socket. A piece of 2mm thickness of leather was attached to the patella tendon seat of B-socket later.Results:1) Dynamic change of pressure of A-socket was total 17.54mmHg±0.98, that of B-socket was 21.47mmHg±0.93, and that of B-socket with 2mm thickness leather attached to patella tendon seat was 20.37mmHg±0.96.2) Pressure of air-cushion suddenly began to increase from heel contact and got into a peak at foot flat. From heel off, pressure began to decrease suddenly and got into a peak at just after toe off.3) The strain of socket was maximum at later half of midstance.Conclusion:1) The air-cushion plays an important role for the weight bearing at the begining of stance phase.2) Patella tendon seat supports weight mainly at the later half of stance phase.3) Suspension at push off and early part of swing phase is important.

Dynamic Interactions of High Speed Tracked Air Cushion Vehicles With Their Guideways: Part I of a Parametric Study

The vehicle-guideway system is modeled as an arbitrary number of lumped, doubly-sprung vehicle mass systems traveling in tandem along simple supported beams. The vehicle load is transmitted to the guideway as a time-varying uniform pressure compatible with vehicle motion. Effects of the dimensionless system parameters on vehicle heave acceleration, and guideway deflections and bending moments at high vehicle speeds are evaluated. Results for a vehicle which includes pitching motion compare favorably with those for a vehicle without pitch where the front and rear masses are uncoupled. By proper choice of parameters, passenger compartment heave accelerations can be minimized, although to keep this acceleration below 0.05g for vehicles traveling 100–300 mph requires systems with low vehicle to beam mass and frequency ratios as well as low vehicle lower to upper mass ratios. The benefits of distributed air cushion pressure to vehicle and guideway design are shown. Also, if the ratio of lower to upper vehicle mass is low, a constant moving pressure conservatively predicts the guideway response.

An Investigation of Hovercraft Wavemaking

The main purpose of the investigation has been to clarify the definition of hovercraft wavemaking resistance and to improve understanding of the physical mechanism. The most literal definition of wave resistance as the force which makes the waves is proposed and its practical and theoretical implications are considered. Various interim accounts of this work have already been written, but the time now seems appropriate to assemble and review the overall picture which is emerging.The pattern of forces on a hovercraft over water is often difficult to analyse because of the complicated interaction between wavemaking, jet air momentum, cushion pressure, wetting and other effects. It is important, however, in making power predictions that the physical interpretation and corresponding scaling laws of the various forces should be understood. A significant feature of the present approach is that a positive and unambiguous basis for identifying the wavemaking force is offered and compared with theoretical predictions. This force, according to the definition proposed, is assured a proper compliance with the physical laws which govern the waves generated and the corresponding scaling and interference effects, which are predicted by theory.