Air Cushion Research Articles

Conceptual design and performance evaluation of an air-cushion floating purifier (ACFP) for improving air quality in semi-confined spaces

Exposure to particulate matter has a wide range of health effects, including respiratory and cardiovascular diseases, and an increase in mortality rates. This study presents a novel design for an air-cushion floating purifier (ACFP) that uses water to remove particulate matter (PM) from the air in building courtyards. The proposed system naturally generates a thin layer of airstream across a water surface beneath a floating board, where the friction between air and water tends to adhere PM to the water. The performance of the ACFP was evaluated in 31 laboratory experiments by monitoring PM2.5 and PM10 concentrations. The experimental results demonstrated that the ACFP reduced PM2.5 and PM10 concentrations by 92.46 and 92.96 %, respectively, after 60 min of operation. The performance of ACFP can be improved by increasing the airflow rate and surface area of the generated air cushion. The installation of multiple ACFPs in large courtyards is expected to generate a large-scale air purification effect, allowing users to inhale cleaner air. The proposed conceptual design merits further investigation and development to aid individuals afflicted by air pollution in building courtyards, especially those of public buildings such as schools, offices, and hospital buildings.

Fabrication of superhydrophobic self-cleaning Ni-Co-MoS2/Ni composite coating

This work investigated the parallel magnetically assisted jet electrodeposition of Ni-Co-MoS2/Ni superhydrophobic composite coatings. As a comparison, the effect of the magnetic field on Ni-Co alloy coatings was analyzed. Then, micro/nano MoS2/Ni particles were further added to study the performance of Ni-Co-MoS2/Ni composite coatings under different concentrations of micro/nano particles. Research indicated that the Ni-Co-MoS2/Ni composite coating surface exhibits coral like micro/nano structures, and the micro/nano structures became denser as the concentration of micro/nano particles increased. The superhydrophobic composite coatings were obtained without any chemical modification reagents. The contact angle of the superhydrophobic composite coating was as high as 153.2° and the sliding angle was 8.7° when the amount of micro/nano particles was added at 5 g/L. The coral like micro/nano structures of the composite coating provided additional air cushion to support surface water droplets and exhibited excellent self-cleaning performance. In addition, the composite coating also showed excellent corrosion resistance and wear resistance, which was still relatively intact after friction, only exhibiting few wears on coral like micro/nano structures, it still maintained a good silver mirror effect after friction. This work suggested that parallel magnetically assisted jet electrodeposition could fabricate superhydrophobic composite coatings with excellent performance.

To the question of the description of the internal combustion engine in the mathematical model of the lifting system of the hovercraft (on the example of the ZMZ-51432.10 CRS engine)

Introduction. It is known that about one third of the total capacity of the power plant of the hovercraft (SVP) is spent on the creation of an air cushion that ensures the rise of the main hull of the vessel. At the same time, in SVP, the source of mechanical energy, as a rule, is a diesel internal combustion engine (ICE). This article discusses one of the issues related to the creation of a mathematical model of the lifting system of the SVP, using: ICE, hydraulic transmission, axial fans and an air cushion nozzle scheme. Since in the vast majority of cases, the internal combustion engine performs its work in partial load modes, it becomes necessary to effectively control the power of the internal combustion engine in order to achieve its high efficiency in partial load modes.
 AIMS. The purpose of this study is to develop a mathematical description of the operation of the internal combustion engine both in external and partial modes of operation, for use in a mathematical model of the operation of the lifting system of the SVP.
 Methods. In this study, a ZMZ-51432.10 CRS diesel engine is used for the lifting system of the hovercraft.
 Results. Using the data obtained using the DIESEL-RK program for this ICE, in the Microsoft Excel environment, the corresponding trend lines were obtained for them by approximating the points that identify the partial characteristics of the engine with fourth-order polynomials, as well as the dependence of the coefficients of these polynomials on the control parameter of the ICE operation mode .
 Conclusion. The developed mathematical description of engine operation can be integrated with various load models when simulating real systems using internal combustion engines as energy sources. This means that it can also be used in mathematical modeling of the SVP lifting system in the MATLAB Simulink package.The approach proposed in this article makes it possible to build mathematical models of various systems using internal combustion engines, simplifying the study and saving computational time. Also, the results obtained can be of reference value.

Balancing the ventricular outputs of pulsatile total artificial hearts.

Maintaining balanced left and right cardiac outputs in a total artificial heart (TAH) is challenging due to the need for continuous adaptation to changing hemodynamic conditions. Proper balance in ventricular outputs of the left and right ventricles requires a preload-sensitive response and mechanisms to address the higher volumetric efficiency of the right ventricle. This review provides a comprehensive overview of various methods used to balance left and right ventricular outputs in pulsatile total artificial hearts, categorized based on their actuation mechanism. Reported strategies include incorporating compliant materials and/or air cushions inside the ventricles, employing active control mechanisms to regulate ventricular filling state, and utilizing various shunts (such as hydraulic or intra-atrial shunts). Furthermore, reducing right ventricular stroke volume compared to the left often serves to balance the ventricular outputs. Individually controlled actuation of both ventricles in a pulsatile TAH seems to be the simplest and most effective way to achieve proper preload sensitivity and left-right output balance. Pneumatically actuated TAHs have the advantage to respond passively to preload changes. Therefore, a pneumatic TAH that comprises two individually actuated ventricles appears to be a more desirable option-both in terms of simplicity and efficacy-to respond to changing hemodynamic conditions.

Electrodeposition of nanotubes for corrosion inhibition: Dual role as superhydrophobic matrix and nanocontainer for storing-releasing corrosion inhibitor

The lotus leaf-inspired superhydrophobicity to prevent metal corrosion has garnered significant interest. The prevailing approach employs micro/nanoscale matrices to trap air and support water, resulting in short-term effectiveness due to air dissolution. Basic zinc carbonate nanotube (BZC NT), created via electrochemical anodization, dually achieves superhydrophobicity and contains 1-dodecanethiol as corrosion inhibitor for zinc. During the immersion under the water phase, the release of 1-dodecanethiol enables a corrosion inhibitor-air cushion, which is remarkably distinguished from the typical single air cushion formed in the superhydrophobic matrix. Using scanning Kelvin probe, the local micro-zone surface potential of Zn increases about 286 mV after being covered by superhydrophobic BZC NT (SHS BZC NT), exhibiting the high decrement of atmospheric corrosion tendency. Through typical electrochemical corrosion tests, the |Z|lf (lf = 0.036 Hz) of SHS BZC NT is about 9.78 × 106 Ω cm2, and the value is ca. 3 orders of magnitude larger than pure Zn (1.46 × 103 Ω⋅cm2). After soaking in a strong alkaline solution (pH = 11) for 24 h, the inhibitive efficiency of SHS BZC NT is 99.99%, demonstrating high corrosion inhibition effect.

Adaptive Position Control Strategy of SRM-Based EMA System for Precision Position Tracking

The electromechanical actuator (EMA) driven by switched reluctance motor (SRM) is promising to be used in the steering vane control system on the landing craft air cushion (LCAC) hovercraft due to its reduced maintenance costs and increased control flexibility. However, the system parameter uncertainty, the unknown load disturbance, and the large torque ripple of SRM make it challenging to achieve high position control precision. To improve the position control accuracy of the SRM-based EMA system, an adaptive position control strategy is proposed in this paper. Firstly, an adaptive fast terminal sliding mode controller (AFTSMC) is designed to address the issues of model parameter estimation and load disturbance rejection, which improves the dynamic response performance of the SRM-based EMA system. Secondly, a current-limited direct torque controller (CL-DTC) is proposed to track the reference torque calculated by AFTSMC with lower torque ripple and to limit the excessive currents of SRM at the same time, which helps further enhance the position control precision and prevent the SRM-based EMA from overheating. Finally, the proposed position control strategy is tested and compared with other three position controllers based on simulations and experiments. The results demonstrate the effectiveness and superiority of the proposed position control strategy.

Experimental research on the lowering process of the three and four-bucket jacket foundation of offshore wind turbine

Whether or not the top of the multi-bucket jacket foundation is open during the lowering process affects the air-water replacement process in the bucket. The bucket's layout impacts the skirt effect, the shielding effect under the wave load, and the force during the lowering process. For four types of multi-bucket jacket foundations, the method of the experiment is adopted to study the influence of the foundation structure type, the lowering velocity, the perforation ratio of the top, and the initial air storage in the bucket on the foundation dynamic characteristics and response mechanism during the lowering process under the two construction methods of ventilation and active air storage. During the lowering operation of the top ventilation, the air pressure response trend of the three-bucket and four-bucket jacket foundation with the same size are consistent. The effect of the lowering velocity on the air cushion height in the bucket is greater than that of the perforation ratio. During the lowering process of active air storage, before the top cover is completely submerged, the air cushion height in the bucket basically increases linearly, and is stable when it continues to be lowered, and increases slightly at the landing on the seabed stage. The dynamic amplification factor (DAF) value and failure factor of the sling during the lowering process of the four kinds of multi-bucket jacket foundations all meet the design requirement. The initial air storage in the bucket can be between 5% and 15%.

Temperature Dependent Anti-Icing Performance of the Microstructure Surface: Wettability Change and Ice Nucleation

Icing has caused much inconvenience to daily production and life. A microstructure surface possessing a hydrophobic property is an effective countermeasure to impede or delay ice formation for anti-icing purposes. However, surface wettability is sensitive to environmental conditions such as temperature and humidity. In the worst-case scenario, a Wenzel state drop forms and causes degradation of surface anti-icing performance. In this study, a copper alloy was used as the testing sample, and the surface was fabricated using mechanical polishing, micro-milling machining and ultrafast laser etching to form the desired topology and microstructures. The hydrophobicity and icephobicity of four types of surfaces including smooth flat, rough flat, rough microstructure and smooth microstructure were tested by depositing droplets from room temperature to an ultralow subzero temperature condition (below −30 °C). At −10 °C, the icephobicity of the surface was consistent with the surface wettability at room temperature. However, the hydrophobicity of the surface slightly decreased, and a Wenzel state drop formed on the microstructure surface. At −30 °C, the apparent contact angle and the ice–substrate contact area were mainly affected by ice nucleation rather than surface wettability. The bottom layer of the droplet froze after immediate contact with the substrate due to a higher degree of supercooling. The formation of a Cassie state drop reduced the ice–substrate contact area and created more air cushions, which facilitated the extension of the icing process of the drop. The enhancement in the anti-icing performance of the microstructure surface was analyzed from a theoretical basis.

Numerical simulations of towing a jacket foundation with triple buckets

Offshore wind energy is developing fast as a promising renewable energy resource that can be helpful in achieving the global net-zero emissions goal. In recent years, offshore wind turbine projects have gradually moved towards far-offshore sea areas, where massive jacket foundations with suction buckets are suitable options. To reduce transportation costs, the wet-towing method is usually favourable since the required buoyancy of the foundation can be provided by the air cushions in the suction buckets. This engineering background brings us a research topic that involves towing and air cushions in waves. This study considers the towing problem of a jacket foundation with triple suction buckets. First, numerical analysis in the frequency domain is conducted using WAMIT®. In particular, the NEWMODES subroutine is extended to consider three separate motion modes in the buckets. Numerical predictions of the natural period show satisfactory agreement with the available experimental data in the literature. Moreover, a time-domain numerical model is developed to simulate towing of the jacket foundation in regular waves based on the potential flow theory. The time-domain model numerically solves the towing force in regular waves, the body motions and the air pressures in the buckets. The simulation results generally agree well with the published experimental data. Besides, the present simulation results suggest that the transit towing force and the forward speed of towed triple-bucket jacket may be considerable in the initial towing stage.

Experimental study on the air cushion effect during the flooding process of a damaged ship cabin

In the rapid flooding process of a damaged ship, the air trapped in a damaged cabin will be compressed into an air cushion, which causes the air cushion effect (ACE). The ACE has a significant influence on the flooding process of an airtight cabin. In this paper, a three-cabin model is designed according to a parent ship, and a series of model experiments are carried out. First, the air-tightness ratio is defined by combining various air vents with different opening areas, and the flooding model experiments of different air-tightness ratios are carried out. The heeling and trimming angles of the model, the overpressure of the air cushion, and the water height inside the flooding cabin are recorded and analyzed, and the characteristics of ACE are summarized. Second, different forms of air vents with a same air-tightness ratio are designed, and the influence of the air vent distribution on the flooding process is analyzed. With the quasi-static method used for comparisons, the numerical results are compared with the experimental ones to check the effectiveness of the quasi-static method on the rapid flooding problems. The research on ACE can guide the design of ship subdivisions and provide a reference for the rescue of shipwreck accidents.

Finite Volume Method for Transient Pipe Flow with an Air Cushion Surge Chamber Considering Unsteady Friction and Experimental Validation

In various water transmission systems such as long-distance water transfer projects and hydropower stations, accurate simulation of water hammer is extremely important for safe and stable operation and the realization of intelligent operations. Previous water hammer calculations usually consider only steady-state friction, underestimating the decay of transient pressure. A second-order Finite Volume Method (FVM) considering the effect of unsteady friction factor is developed to simulate the water hammer and the dynamic behavior of air cushion surge chamber in a water pipeline system, while an experimental pipe system is conducted to validate the proposed numerical model. Two unsteady friction models, Brunone and TVB models, were incorporated into the water hammer equations, which are solved by the MUSCL–Hancock method. One virtual boundary method was proposed to realize the FVM simulation of Air Cushion Surge Chamber. Comparisons with water hammer experimental results show that, while the steady friction model only accurately predicts the first pressure peak, it seriously underestimates pressure attenuation in later stages. Incorporating an unsteady friction factor can better predict the entire pressure attenuation process; in particular, the TVB unsteady friction model more accurately reproduces the pressure peaks and the whole pressure oscillation periods. For water pipeline systems with an air cushion surge chamber, energy attenuation of the elastic pipe water hammer is primarily due to pipe friction and the air cushion. The experimental results with the air cushion surge chamber demonstrate that the proposed FVM model with the TVB unsteady friction model and the air chamber polytropic exponent near 1.0 can well reproduce the experimental pressure oscillations.

Experimental study on the drop test on wet deck slamming for a SWATH segment model

Wet deck slamming is a serious issue for high-speed catamarans if the relative vertical motions are higher. In this study, a drop test on wet deck slamming is conducted for a small waterplane area twin hull segment model, and the vertical water-entry model test is performed under different drop heights and speeds. The slamming pressure under the wet deck and the acceleration are measured. The flow field is obtained through particle image velocimetry measurement. A high-speed camera observation during wet deck slamming shows that air is pressed into water, and a water–gas mixture is formed due to the air compressibility effect. The slamming pressure shows an oscillating property with multiple frequency components, which is due to the air cushion effect caused by the volume variation of the water–gas mixture and the acoustic wave oscillation with the air pocket. The effects of the drop height variation and the constant-drop speed on the slamming load are analyzed. The results show that the pressure peak appears during the demihull's bottom slamming and wet deck slamming. The acceleration time record produces two peaks, one for the demihull's bottom slamming and another for the wet deck slamming. In conclusion, the air cushion effect can reduce the wet deck slamming pressure.

Preparation and characterization of carnauba wax-based particle with hierarchical structure and its use as hydrophobic coating for chitosan films

To improve the hydrophobicity of polysaccharide-based films, hydrophobic carnauba wax-based particles were prepared by Pickering emulsion. The influence of the different size of the particles on the structure and hydrophobicity of the chitosan coating films were investigated. The results showed that micro-scale particles (average particle size 25.04 μm) with nano-scale (5–10 nm) TiO2 uniformly distributed on the surface of the particles were formed by Pickering emulsion. The chitosan coating films showed higher contact angle and lower sliding angle compared to the control due to the hierarchical structure, hydrophobicity and arrangement of the particles. In addition, the small particle (23–48 μm) coating film showed higher hydrophobicity than the large particle coating film (48–70 μm) due to the small particle size and the formation of more small gaps. The gaps were conducive to form “air cushion” which reduced the contact area between water and the coating films and thus increased contact angle and decreased sliding angle. The coating films showed high chemical stability and low residual rates of liquid food. The results suggest that Pickering emulsion is an effective method to create wax-based particles with hierarchical structure and the particles have potential to be used as hydrophobic coating materials.

Fabrication of self-healable superhydrophobic polyurethane coating based on functional CeO2 nanoparticles for long-term anti-corrosion application

Corrosion of mild steel is everywhere and eco-friendly and efficient corrosion protection strategies deserve to be popularized. Superhydrophobic coatings are available for metal corrosion protection, but the limited-service life restricts their development. Here, we prepared environmentally friendly coatings with long-term corrosion resistant using a simple spray strategy. A two-layer superhydrophobic self-healable composite coating was prepared by spraying WFPU and fluoroCeNPs onto mild steel. The bottom WFPU prevents corrosion by corrosion inhibitor CeO2 and repairs physical scratches by heating. The upper layer of fluoroCeNPs prevents the penetration of corrosive media by forming an air cushion at the solid-liquid interface. The combination of low surface energy and micro/nano hierarchical structure allows WFPU/fluoroCeNPs coating to exhibit superhydrophobicity and low adhesion, with a water contact angle of 157° and adhesion force 12.8 μN. In addition, WFPU/fluoroCeNPs coating exhibit excellent corrosion resistance, with an impedance modulus of 7.2 × 109 Ω cm2 at low frequency (f = 0.01 Hz), which remains at 108 Ω cm2 after 60 days in 3.5 wt% NaCl solution. After self-healing, the material can recover to its original state, both in terms of mechanical and corrosion protection properties. This new composite coating, which combines environmental protection, energy saving and remarkable effects, has a wide application value for the protection of metal against corrosion.

Modeling and experimental study of the cushion lift dynamics system of a polar hovercraft

This paper investigates the cushion lift dynamics of a polar hovercraft. The motion of the flexible skirt on the ice surface is simplified and a mathematical model is established to study the dynamic response characteristics of the hovercraft in the process of lifting and moving over ice. This model considers the pressure/flow characteristics, skirt pressure, air cushion pressure, and flow rate of the fan of the hovercraft, and establishes a simulation using a C++program. When the hovercraft is pushed by the propeller, a thrust of 10 kN will cause a pressure difference of about 450 Pa between the front and rear chambers, 0.06 m in the height of the upstream and downstream discharge flows, and a decrease of about 0.4° in the longitudinal inclination angle. Changing the pitch angle to 0.5° creates a pressure difference of about 500 Pa between the chambers and a height difference of 0.07 m between the discharge. When the hovercraft speed is low, the wind speed has a small impact on the air cushion pressure of the lift system. The results of this research provide important technical and experimental foundations for further studies on the ice surface kinematics and safety control strategy of polar hovercraft.

Vertical dynamics of high-pressure air cushion bearing module: Stability and auto-oscillation

Unstable static equilibrium and vertical auto-oscillations are problems encountered in the application of a high-pressure air cushion module (ACM) for the indoor transportation of heavy loads. The results of two base methods are compared: linear stability analysis based on the linearized equations of the perturbed motion coupled to airflow fluctuations and numerical evaluation of the nonlinear dynamic response of the system. The main distinguishing feature of the analysis is that it comprehensively examines air compressibility in the cushion plenum and in the inlet and outlet flow zones. Accordingly, the study and its findings are valid for high-pressure and low-flow applications of air cushion transportation. A narrow stability region in the parameter domain is identified when the cushion pressure approximates the supply pressure. The peculiarities of the vertical dynamics of the system near stable and unstable static equilibrium positions are described, and influence of viscous damping is considered. The study results contribute to the generalized representation of the stability and vertical dynamics of ACMs and to the theoretical database for ACM design.

Air entrapment at impact of a conus onto a liquid

In this experimental work, a conus impacts a deep liquid pool at a speed varying from 1.3 to $19.0\ {\rm cm}\ {\rm s}^{-1}$ . Two liquids (2.5 % butanol–water solution or distilled water) and four coni made from duralumin with a diameter of 180 mm and different deadrise angles $\beta$ ( $2^{\circ }$ , $3^{\circ }$ , $4^{\circ }$ and 5 $^{\circ }$ ) are tested. An air cushion is trapped between the conus solid surface and the liquid. Several types of bubble patterns after the collapse of the air cushion are observed: one or multiple bubbles near the conus centre (vertex), irregular trails of bubbles on the conus surface and a ring of bubbles in a ‘necklace’-shaped arrangement. With a total internal reflection set-up and appropriate image post-processing, the external and internal radii of the ring-shaped wetted area are estimated for each frame. The external (internal) radius increases (decreases) in time following a linear (exponential) law. The speed of the outer border of the wetted area is in agreement with the Wagner theory for a body impacting onto a liquid. The initial radius of the annular touchdown region is estimated as the intersection of the relevant fitting curves. In the studied range of parameters, the initial radius obeys a universal scaling law, which follows from the air–water lubrication–inertia balance.

Analysis of fixation materials in micro-CT: It doesn't always have to be styrofoam.

Good fixation of filigree specimens for micro-CT examinations is often a challenge. Movement artefacts, over-radiation or even crushing of the specimen can easily occur. Since different specimens have different requirements, we scanned, analysed and compared 19 possible fixation materials under the same conditions in the micro-CT. We focused on radiodensity, porosity and reversibility of these fixation materials. Furthermore, we have made sure that all materials are cheap and easily available. The scans were performed with a SkyScan 1173 micro-CT. All dry fixation materials tested were punched into 5 mm diameter cylinders and clamped into 0.2 ml reaction vessels. A voxel size of 5.33 μm was achieved in a 180° scan in 0.3° steps. Ideally, fixation materials should not be visible in the reconstructed image, i.e., barely binarised. Besides common micro-CT fixation materials such as styrofoam (-935 Hounsfield Units) or Basotect foam (-943 Hounsfield Units), polyethylene air cushions (-944 Hounsfield Units), Micropor foam (-926 Hounsfield Units) and polyurethane foam, (-960 Hounsfield Units to -470 Hounsfield Units) have proved to be attractive alternatives. Furthermore, more radiopaque materials such as paraffin wax granulate (-640 Hounsfield Units) and epoxy resin (-190 Hounsfield Units) are also suitable as fixation materials. These materials often can be removed in the reconstructed image by segmentation. Sample fixations in the studies of recent years are almost all limited to fixation in Parafilm, Styrofoam, or Basotect foam if the fixation type is mentioned at all. However, these are not always useful, as styrofoam, for example, dissolves in some common media such as methylsalicylate. We show that micro-CT laboratories should be equipped with various fixation materials to achieve high-level image quality.

Vibration analysis of a hyperloop pod with a novel hybrid levitation in accelerating and braking maneuvers

Hyperloop, a very high-speed transportation system including a pod transporting the passengers in a tube, forms the core debate in numerous recent investigations. The present paper, furthering the current advanced findings, proposes a novel hybrid levitation including Electro-Dynamic Suspension (EDS) and air cushions for the pod in the hyperloop system. It also presents a vibrational model for the hybrid levitation pod to predict the vibration behavior of the pod in accelerating and braking maneuvers. In this regard, an industrial pod is designed conceptually by performing preliminary calculations. Via CFD simulations in Ansys Fluent software, we hold forth a nonlinear dynamic model for the air cushions. Then, the paper analyzes a 3-DOF vibration model of the pod and verifies it by comparing the related results with obtained ones from the MSc ADAMS software. Afterward, the mentioned vibration model is developed into a 7-DOF model to predict the vibration behavior of the pod in accelerating and braking maneuvers. Also, the governing dynamic equations of the system are derived and numerically solved. Finally, the vibration behavior of the pod in different accelerating and braking conditions is investigated.

Regulating air cushioning and bubble entrapment in charged droplet impact via external electric fields

Air cushioning and bubble entrapment are common phenomena observed during low-velocity droplet impact on solid or fluid surfaces, whereby a thin layer of air mediates the lubrication pressure. Previously, it is found that both charging droplets and the application of external electric fields can eliminate air cushioning and bubble entrapment. In this study, we numerically investigate the air cushioning and bubble entrapment in the charged droplet impacting onto a solid surface under external electric fields. It is found that the presence of net charge has a field enhancement effect on polarized charges on the same side while weakening the electric field of polarized charges on the opposite side, which can be linearly superimposed in the atmospheric environment. Based on the mirror charge model, the scaling law of the electric field threshold required for the impact of charged droplets without air cushioning or bubble entrapment is given. A fitting function based on the scaling law shows a good agreement with the phase diagram of a charged droplet impact modes under electric fields. These findings offer valuable insight for applications that rely on charged droplets' impact under electric fields, such as electrohydrodynamic printing and spray coating, to mitigate the negative impact of air cushioning or bubble entrapment.