Pneumatic Efficiency Research Articles

Experimental investigation on the hydrodynamic performance of a pile-supported OWC-type breakwater

The present study considers the design optimisation of an Oscillating Water Column (OWC) incorporated into a pile-supported breakwater structure. This has been achieved by performing a substantial number of scaled physical model tests and a methodical variation of key device parameters within multiple configurations. The key aspects that have been investigated include: (a) the geometric characteristics of the breakwater structure, (b) the pneumatic efficiency of the OWC, (c) the geometry of the OWC chamber and (d) the relative position of the OWC chamber within the breakwater. The present work considers (monochromatic) regular waves of varying steepness and effective water depth as incident wave conditions. The efficiency of the designed structure in terms of shore protection capacity and wave energy extraction was assessed by quantifying relevant transmission coefficients and the power output metrics. This has been achieved by using a combination of collocated and complementary measuring devices, such as arrays of wave gauges, pressure transducers and a high-definition video camera. The study concluded that systematic refinement of the geometrical parameters can substantially enhance the overall hydrodynamic efficiency of a pile-supported OWC breakwater. Additionally, it was found that a configuration featuring a chamber positioned in front of the breakwater, with a relative chamber breadth of 0.67, outperforms wider breadth configurations in terms of both energy extraction efficiency and reduction of the transmission coefficient. Taken together, the present study provides an in-depth analysis of the effects of key design parameters of a breakwater-integrated OWC, its efficiency and shore protection potential.

Experimental and numerical study on noise reduction of airfoil with the bioinspired ridge-like structure

In general, the serrated blade edge can reduce the aeroacoustic noise of the thin airfoil, but the blade's integrity and pneumatic efficiency cannot be guaranteed. This research proposes a bioinspired ridge-like structure that won't affect the strength of the blade, and it has more potential to be employed as an innovative noise reduction configuration for engineering applications. The experimental data shows a significant peak noise reduction of nearly 26 dB and a magnitude decrease of more than 10 dB in the overall sound pressure level (OASPL) at a freestream velocity of 20 m/s with the attack angle 0˚. Based on the computational fluid dynamic simulation, the mechanism for the noise reduction employing the ridge-like structure is qualitatively and quantitatively examined. In summary, the ridge-like structures on the leading edge may enhance the transition to move an upstream position. Under the synergy of the ridge-like structures on the leading and trailing edges, the turbulent kinetic energy (TKE) value close to the airfoil surface is reduced, and the spanwise coherence of the surface pressure fluctuation source weakens. The phase spectra analysis indicates that the phases of the fluctuation pressure signals beside the center of the two adjacent ridge-like structures are opposite, and therefore the phase interference in the biomimetic airfoil between two adjacent ridge-like structures is significantly enhanced in the frequency range from 100 Hz to 800 Hz. For the biomimetic airfoil described in this paper, the phase interference between adjacent ridge-like structures immediately results in noise.

Experimental study of an oscillating water column converter to optimize nonlinear PTO using genetic algorithm

The characteristics of incident waves, draft depth, and orifice diameter significantly affects the performance of the OWC. This paper evaluated the hydrodynamic response of an OWC with nonlinear PTO imposed on the Caspian Sea wave conditions experimentally. Experimental tests have been done in two stages; first, considering the incident wave frequency constant in 0.4 Hz, two main variables, area ratio, and depth ratio, have considered optimizing the performance by genetic algorithm. The experiments for three area ratios of the orifice equal to 0.5%, 0.75%, and 2%, and the three depth ratio equal to 0.05, 0.14 0.33 have been done. The optimal values of the area and depth ratios are equal to 1% and 0.24, respectively. In the next step, the tests were carried out for a wide range of conditions of the Caspian Sea, and four area ratios and depth ratios, including the optimal values, repeated in the form of 800 tests. The results showed that the converter performance would be optimum for the other frequencies considering the optimal values. The optimal converter can generate 191W, while before the optimization, the highest recorded power was 132W, an increase of 45%. After optimization, the converter pneumatic efficiency has increased to 53.74%.

Two-phase flow simulations of fixed 3D oscillating water columns using OpenFOAM: A comparison of two methods for modeling quadratic power takeoff

This study examines the performance of a numerical method that introduces an artificial sink term to the Reynolds-averaged Navier Stokes equations to simulate the flow through an orifice used as a quadratic Power Takeoff (PTO) for Oscillating Water Columns (OWCs). The method replaces the quadratic PTO by an artificial Forchheimer-flow region (referred to as the artificial Forchheimer-flow method). The performance of this method was evaluated by making comparisons with the existing experimental results for two OWCs and the numerical results obtained by using air-water two-phase flow simulations of the air flow through an orifice (referred to as the orifice-flow method). The surface elevations, velocity fields and pressure fields obtained by the orifice-flow and artificial Forchheimer-flow methods are compared. To use the artificial Forchheimer-flow method, an equation for specifying the Forchheimer coefficient is provided and the sensitivity of the pneumatic efficiency to the Forchheimer coefficient is discussed. It can be concluded that the artificial Forchheimer-flow method can satisfactorily reproduce the measured pneumatic efficiency, pressure field in the air, the velocity field in the water and the cross-sectional average velocity of the air. Compared to the orifice-flow method, the artificial Forchheimer-flow method can speed up the simulation by at least 25 times.

Precurved, Fiber-Reinforced Actuators Enable Pneumatically Efficient Replication of Complex Biological Motions.

Much of the research on bioinspired soft robotics has focused on capturing the interplay of biological form and function. However, existing soft robotic actuators are mostly made with linear or planar fabrication orientations that do not represent the resting geometry of complex biological systems, such as curved musculature. This work introduces the ability to create fiber-reinforced actuators with precurved configurations. By tuning variables such as dimensions and fiber angles, an optimization algorithm can prescribe the mechanical fabrication parameters to create a fiber-reinforced actuator that can generate controlled motion to follow a desired input trajectory. Precurved configurations introduce an additional optimization parameter, the initial bend angle, allowing for a more accurate and robust algorithm and generating a median percent error of <1%. With a customized software tool, we can take existing motion data from biological systems-such as medical imaging-and build soft robotic actuators optimized to replicate these trajectories. We can predict the motion of precurved actuators both analytically and numerically and replicate the motion experimentally, with excellent trajectory matching between the three. In constructing actuators that better match the native forms found within biological systems, we find that precurved actuators are more efficient than their initially straight counterparts. This pneumatic efficiency allows for the use of control systems with lower power and precision, lowering the economic cost of the associated control hardware, while more accurately replicating the biological motion. Taking two examples from biology, that of the human diaphragm during respiration and that of a jellyfish bell during locomotion, we design and generate fiber reinforced actuators to mimic these motions.

Wave power extraction by a nearshore oscillating water column converter with a surging lip-wall

A near-shore oscillating water column (OWC) device with a surging front-wall, which can be conveniently mounted on various cliff-like shores or coastal structures, is proposed to improve the pneumatic efficiency of wave energy extraction. Based on linear potential theory, the interaction between ocean waves and the OWC device is solved by the matched eigenfunction expansion method (MEEM). Auxiliary functions, expanded in orthogonal polynomials, are introduced to approximate the singular behaviors of fluid field in the vicinity of the salient corner. The effects of the dimensions of lip-wall and the stiffness of the spring on the hydrodynamic performances, such as the response amplitude operator (RAO), average inside free-surface elevation, phase difference between the motions of lip-wall and inside free-surface, and optimum conversion efficiency are taken into consideration. The numerical results show that the existence of a freely surging lip-wall can considerably improve the performance of the device over a wider bandwidth, especially for the intermediate and short wavelength regimes, compared with the fixed one.

Methods to Evaluate and Measure Power of Pneumatic System and Their Applications

Pneumatic system has been widely used throughout industry, and it consumes more than billions kW h of electricity one year all over the world. So as to improve the efficiency of pneumatic system, its power evaluation as well as measurement methods should be proposed, and their applicability should be validated. In this paper, firstly, power evaluation and measurement methods of pneumatic system were introduced for the first time. Secondly, based on the proposed methods, power distributions in pneumatic system was analyzed. Thirdly, through the analysis on pneumatic efficiencies of typical compressors and pneumatic components, the applicability of the proposed methods were validated. It can be concluded that, first of all, the proposed methods to evaluation and measurement the power of pneumatic system were efficient. Furthermore, the pneumatic power efficiencies of pneumatic system in the air production and cleaning procedure are respectively about 35%–75% and 85%–90%. Moreover, the pneumatic power efficiencies of pneumatic system in the transmission and consumption procedures are about 70%–85% and 10%–35%. And the total pneumatic power efficiency of pneumatic system is about 2%–20%, which varies largely with the system configuration. This paper provides a method to analyze and measure the power of pneumatic system, lay a foundation for the optimization and energy-saving design of pneumatic system.

Wave power extraction from a bottom-mounted oscillating water column converter with a V-shaped channel

An analytical theory is developed for an oscillating water column (OWC) with a V-shaped channel to improve the pneumatic efficiency of wave energy extraction. An eigenfunction expansion method is used in a cylindrical coordinate system to investigate wave interaction with the OWC converter system. Auxiliary functions are introduced to capture the singular behaviours in the velocity field near the salient corners and cusped edges. Effects of the OWC dimensions, the opening angle and length of the V-shaped channel, as well as the incident wave direction, on the pneumatic efficiency of wave energy extraction are examined. Compared with a system without the V-shaped channel, our results show that the V-shaped channel can significantly increase the conversion efficiency and widen the range of wave frequency over which the OWC system can operate at a high efficiency. For typical coastal water depths, the OWC converter system can perform efficiently when the diameter of the OWC chamber is in the range of 1 5 – 1 2 times the water depth, the opening angle of the V-shaped channel is in the range of [ π /2, 3 π /4] and the length of the V-shaped channel is in the range of 1–1.5 times the water depth.

Effect of duct extension on pneumatic efficiency of Backward Bent Duct Buoy (BBDB)

The Backward Bent Duct Buoy (BBDB) is a wave energy converter which works on the principle of the Oscillating Water Column theory. The air displaced due to the rising and falling water surface in the oscillating water column is used to drive an electric machine to generate power. A physical model of the prototype BBDB with a geometric scale of 1:8 made of acrylic glass of size 412 × 280 × 255 mm was tested in the wave flume at the Centre for Water Resources laboratory, Anna University to determine the pneumatic efficiency of BBDB. The pneumatic efficiency, which is the ratio of output power of the displaced air to the input power due to waves, is primarily dependent on the amplitude of oscillation of the water column in the vertical air chamber. The effect of increasing the length of the horizontal duct on pneumatic efficiency has been studied. It was found that the duct length affects the primary conversion efficiency considerably and longer ducts may not necessarily improve the efficiency. It was observed that the BBDB model with the duct length of 412 mm shows better primary conversion efficiency of 5.3% and the area of the orifice opening also has an effect on the pneumatic efficiency.

Efficiency of OWC wave energy converters: A virtual laboratory

The performance of an oscillating water column (OWC) wave energy converter depends on many factors, such as the wave conditions, the tidal level and the coupling between the chamber and the air turbine. So far most studies have focused on either the chamber or the turbine, and in some cases the influence of the tidal level has not been dealt with properly. In this work a novel approach is presented that takes into account all these factors. Its objective is to develop a virtual laboratory which enables to determine the pneumatic efficiency of a given OWC working under specific conditions of incident waves (wave height and period), tidal level and turbine damping. The pneumatic efficiency, or efficiency of the OWC chamber, is quantified by means of the capture factor, i.e. the ratio between the absorbed pneumatic power and the available wave energy. The approach is based on artificial intelligence—in particular, artificial neural networks (ANNs). The neural network architecture is chosen through a comparative study involving 18 options. The ANN model is trained and, eventually, validated based on an extensive campaign of physical model tests carried out under different wave conditions, tidal levels and values of the damping coefficient, representing turbines of different specifications. The results show excellent agreement between the ANN model and the experimental campaign. In conclusion, the new model constitutes a virtual laboratory that enables to determine the capture factor of an OWC under given wave conditions, tidal levels and values of turbine damping, at a lower cost and in less time than would be required for conventional laboratory tests.

The Research on the Fuel Performance of Fsae EFI Engine

For the modeled engine, the soft AVL-BOOST is applied to do the single-dimensional cycling simulation and calculation. And then the engine performance after assembling the improving limiter（its diameter is 20mm） is analyzed. According to the calculation and analysis, the torque and pneumatic efficiency are largely affected by limiter, the maximum torque and pneumatic efficiency decreases 20 percents and 30 percents respectively. The limiter not only improves the engine’s fuel performance, but also reduces its power performance.

A Decade of Wave Power Development in India—The Challenges

Wave energy research in India started in 1984. Six years of research by the Indian wave energy group culminated in the installation of a 150 kW capacity pilot wave power plant in Vizhinjam, off Trivandrum in the Kerala state, in the Arabian Sea during 1990 (Figure 1). The problems encountered during the research, construction and installation directed the group to continue the research effort. The structural configuration of the caisson has changed considerably so that it has sufficient floating stability during towing, enough space for sand ballasting to increase the stability of the caisson against horizontal sliding and overturning and sufficient space at the rear of the caisson for berthing vessels (Figures 2 and 3). After the installation of a wave power caisson of 150 kW off Trivandrum, further attention was focused on a 1 to 2 MW wave power plant for sites, where new breakwaters for harbors is envisaged (Thangassery Harbour in the West Coast of India (Figure 4) and Mus Bay in Car Nicobar Islands (Figure 5) in Bay of Bengal). Optimum center to center spacing between the caissons was determined based on physical model studies. Further research was carried out to improve the wave to pneumatic efficiency by changing the harbor configuration. Techniques to reduce the wave force on the caisson were also simultaneously studied. The wave power economics is site specific. Two sites (Thangassery in Kerala and Mus bay in Car Nicobar Island) were selected to analyze the wave power economics. Wave power is not likely to become economical in the near future. A continued research effort in the research is very important in order to improve the efficiency of wave power conversion and reduce the cost of construction. A decade of experience (1986 to 1996) in wave power research is presented in this paper.

ELECTROPNEUMATIC TRANSDUCERS AS SECONDARY ACTUATORS FOR ACTIVE NOISE CONTROL, PART I: THEORETICAL ANALYSIS

A theoretical analysis is presented of an acoustic source which operates by the release of compressed air through an aperture, the area of which is made to vary with time. A distinction is made between sonic and subsonic compressed air sources (depending on the Mach number at the throat), and in both cases simple equations are derived that describe the acoustical characteristics of the device. The theory is also developed with a view to using the source as a secondary actuator in an active noise control system, and the pneumatic efficiency and linearity of compressed air sources are discussed. Although the sonic source has a high internal acoustic impedance and its output is almost linearly dependent on the aperture opening, it is shown to be very inefficient. The subsonic source can be much more efficient than the sonic one but the output is generally no longer a linear function of aperture opening. A simple method of linearizing such a source is discussed. A numerical comparison between compressed air sources and electrodynamic loudspeakers shows that the former offer a useful alternative for active noise control, especially when the secondary source has to act in an extreme environment. The subsonic compressed air source is particularly useful when efficiency is a major issue. Details and results of the experimental evaluation of a subsonic compressed air source built at the Laboratory of Acoustics of the Faculté Polytechnique de Mons (Belgium) are presented in companion paper (Part II).

ELECTROPNEUMATIC TRANSDUCERS AS SECONDARY ACTUATORS FOR ACTIVE NOISE CONTROL, PART II: EXPERIMENTAL ANALYSIS OF THE SUBSONIC SOURCE

An experimental analysis of a subsonic compressed-air sound source has been carried out. The design of the source is described, in which a sliding plate which modulates the air flow is driven by an electrodynamic shaker. Friction between the sliding plate and its housing are reduced by coating their faces with glass-filled PTFE. The alternating acoustic pressure at the source output has been measured for various conditions. On the basis of these experimental results, the validity of the theoretical model derived in a companion paper is assessed. Predistortion of the subsonic source to produce a sinusoidal output is considered. A predistortion processor is placed in series with the electrodynamic shaker, the output of which is being computed on the basis of the fundamental equation of the subsonic compressed-air source. The measurement of the pneumatic efficiency of the source is also considered, by using a hot-wire anemometer for the measurement of the air flow across the source. The experimental results are found to be in good agreement with the theoretical predictions developed in the companion paper, Part I.