Influence Of Air Gap Research Articles

Study on the Influence of Air Gap on the Thermal Response Violence of Pressed Polymer Bonded Explosive Charge in Slow Cook-Off Experiment

Study on the Influence of Air Gap on the Thermal Response Violence of Pressed Polymer Bonded Explosive Charge in Slow Cook-Off Experiment

A Novel Defect Detection Method for Overhead Ground Wire.

Overhead ground wires typically have strong axial tension and are prone to structural defects caused by corrosion and lightning strikes, which could lead to serious safety hazards. Therefore, it is important to detect defects accurately and quickly to avoid those problems. Existing defect detection methods for overhead ground wires are mainly traditional metal defect detection methods, including eddy current detection, ultrasonic detection, and manual visual inspection. However, those methods have problems of low detection efficiency, high environmental requirements, and insufficient reliability. To solve the above problems, this paper studies a novel type of defect detection technology for overhead ground wire. Firstly, the magnetic leakage characteristics around the defects of overhead ground wires are analyzed, and the defect detection device is designed. Then, the influence of air gap, lift-off distance, defect width, and cross-sectional loss rate on the magnetic flux leakage signal is studied, a novel defect detection method for overhead ground wire is proposed, and experimental verification is carried out. The results show that the proposed method can accurately locate and quantify the defect, which has the advantages of good reliability and high efficiency and lays the foundation for preventing accidents caused by defective overhead ground wires.

Wave-impact forces and moments due to random waves on a jacket-type platform for different relative submergence of the deck

Force and moment measurements due to wave impacts were conducted on a jacket platform model under six distinct relative deck submergence conditions. The water depth was carefully chosen to facilitate scenarios ranging from sufficient deck air gaps to partial and complete submergence. For the purpose of our analysis, we focused on peak and average peak wave force and moment values. The study uncovers that the peak wave force towards the shore can escalate to 1.5 times the peak wave force towards the sea. Moreover, the ratio of the peak shoreward force to the average peak shoreward force fluctuates between 3 and 4, contingent upon the relative water level at the deck base and the prevailing wave condition. Remarkably, the peak upward wave force on the deck can reach 5 to 7 times the peak inline wave force. A review of existing guidelines suggests a significant need to enhance research regarding the air gap between the deck and the still water level (SWL), as well as its effect on global and local wave forces and moments on the structures. Our finding establishes that the relative water level from the base of the deck is a crucial parameter in the design process of these structures. This study presents a more in-depth understanding of the physical mechanisms at play by utilizing a realistic jacket platform model. It serves as an initial exploration into the influence of air gap and relative water depth on wave-impact forces and moments. The results obtained from this study shed light on optimal design strategies for jacket-type offshore drilling platforms, considering green water effects. This understanding will enhance the life expectancy and survivability of such platforms.

The influence of air gaps on buffer temperature within an engineered barrier system

High-level radioactive waste produced by nuclear power plants are disposed subterraneously utilizing an engineered barrier system (EBS). A gap inevitably exists between the disposal canisters and buffer materials, which may have a negative effect on the thermal transfer and water-blocking efficiency of the system. As few previous experimental works have quantified this effect, this study aimed to create an experimental model for investigating differences in the temperature changes of bentonite buffer in the presence and absence of air gaps between it and a surrounding stainless steel cell. Three test scenarios comprised an empty cell and cells partially or completely filled with bentonite. The temperature was measured inside the buffers and on the inner surface of their surrounding cells, which were artificially heated. The time required for the entire system to reach 100 °C was approximately 40% faster with no gap between the inner cell surface and the bentonite. This suggests that rock–buffer spaces should be filled in practice to ensure the rapid dissipation of heat from the buffer materials to their surroundings. However, it can be advantageous to retain buffer–canister gaps to lower the peak buffer temperature.

Enhancement of low and medium frequency sound absorption using fabrics and air gaps

Porous acoustic materials are among the most frequently employed acoustic materials. This paper evaluates the acoustic performance of porous materials concerning the addition of how the fabric layout and addition of an air gap influence sound absorption coefficient at low and medium frequencies. The acoustic measurements were performed on multilayers of woven fabrics formed from different weave structures and nonwoven fabrics using an impedance tube. The result indicates that due to the different geometrical structures of woven fabric and the layout designs of multilayer fabrics, significant improvements were observed in sound absorption performance at the frequency range from 160 Hz to 3150 Hz. The air gap with a multilayer of porous material enhanced low to medium-frequency sound absorption. Furthermore, the physical fabric properties analysis of porosity using X-ray tomography indicates that the surface of a single layer of plain fabric structures is more porous than that of sateen, rib, and twill woven fabrics. The correlation between the air permeability and sound absorption coefficient (α) results indicates an inverse relationship for multilayer porous fabrics.

Dielectric Characterization of Fabric Aggregates around the 2.45 GHz ISM Band under Various Humidity, Density, and Temperature Conditions.

Fabric permittivity is critical for the manufacturing of wearable sensors and antennas as well as predicting how fabrics interact with electromagnetic fields. Engineers should also understand how permittivity changes under different temperatures, densities, and moisture content values, or when several fabrics are mixed in aggregates, when designing future applications such as microwave dryers. The permittivity of cotton, polyester, and polyamide fabric aggregates is investigated in this paper for a wide range of compositions, moisture content levels, density values, and temperature conditions around the 2.45 GHz ISM band using a bi-reentrant resonant cavity. The obtained results show extremely comparable responses for all characteristics investigated for single and binary fabric aggregates. Permittivity always increases as temperature, density, or moisture content levels rise. Moisture content is the most influential characteristic, causing enormous variations in the permittivity of aggregates. Fitting equations are supplied for all data, with exponential functions used to accurately model variation in temperature and polynomial functions employed to precisely model density and moisture content variations with low error levels. The temperature permittivity dependence of single fabrics without the influence of air gaps is also extracted from fabric and air aggregates by using complex refractive index equations for two-phase mixtures.

Acoustical behavior of camellia sinensis/ananas comosus fiber based uni-directional corrugated panel for sound damping application

To achieve a durable, rigid, and lightweight construction material, a new class of Camellia sinensis/Ananas comosus fiber-enhanced corrugated sandwich panel was designed and produced. The crushed core layer comprises sinusoidal corrugation and is manufactured by a method of mould pressing in an attempt to assess this material’s sound absorption ability. In addition, the influence of airgap and micro perforation on sound absorption properties was investigated. The samples with a greater perforation ratio and air gap are found to have a noise reduction coefficient (NRC) of 0.745, which can be used to attenuate mid- and high-range frequencies in industrial environments.

Energy storage in magnetic devices air gap and application analysis

With the rapid development of power electronic conversion technology, energy conversion has become more common than ever, and magnetic devices are more widely utilized. In power electronic conversion, magnetic devices are becoming more important and prominent, which puts forward higher requirements for the design and stability of magnetic devices. Many of domestic and foreign studies on magnetic devices pay particular attention to influence of air gap and loose magnetic field on inductance, but there is little analysis on the air gap energy storage of magnetic devices. This paper focuses on the energy storage relationship in magnetic devices under the condition of constant inductance, and finds energy storage and distribution relationship between Magnetic material and gap. The energy distribution ratio between material and gap of Magnetic Devices is verified on the dual-input power supply transformer of the energy storage converter.The innovation point of this paper is to analyze storage energy distribution ratio on the core and gap of magnetic devices from the perspective of energy that the storage energy distribution ratio of magnetic devices is changed after the addition of air gap. In the design of power supply, according to the demand of energy conversion, adjust the size of air gap appropriately, then change the energy storage position of magnetic devices, increase margin of the saturation flux density, improve the linearity of permeability, adjust the stability of switching power supply, provide theoretical reference for the design of magnetic devices of switching power supply.

Research air gap on electromagnetic field of high speed motor under the influence of air gap

High speed motor are mainly used in aerospace, petrochemical and NC machining fields. Complex electromagnetic field is distributed in the motor. With the continuous maturity of asynchronous motor technology, research on magnetic field has been rapidly developed. In this paper, the changes of air gap and magnetic field of high speed motor under different working conditions is introduced. The magnetic field model of high-speed motor with Maxwell electromagnetic which established theory through Ansoft finite element software. The distribution of electromagnetic field in the motor is explored. The results show that the magnetic field distribution of induction motor tends to increase with the increase of the air gap magnetic field. Therefore, this study has an important guiding significance for the motor.

Influence of air-gap and thickness on the upward flame spread over discrete wood chips

The fire hazard has frequently destroyed wooden cultural heritages. The discrete wood chips allow fire propagation quickly in practice. This study aims to clarify the effect of air–gap and thickness of wood chips in the fire propagation mechanism by experimental investigating the mass loss rate (MLR), flame spread rate (FSR), total burning duration (TBD) and the flame characteristic length (MFL). The 2 cm long and 10 cm wide wood chips were uniformly installed on a vertical sample holder. The air–gap distance and the thickness of wood chips changed from 1.0 cm to 3.0 cm and 1 mm to 4 mm, respectively. The flame spreads across with the wood grain orientation. The experimental result shows that FSR and MFL are sensitive to the air–gap distance. It is concluded that, TBD versus thickness of the sample is linear with an equation TBD (s) = 7.7 × thickness (mm) + 18.6. Concerning the fixed thickness of the sample, the TBD varies a little from the air–gap distance. The MFL increases to a peak then decreases to a low value as the thickness differing from 1 mm to 4 mm. It is observed that the air–gap makes little contribution to the TBD. The MLF history as the air–gap distance changing from 1.0 cm to 3.0 cm indicates that the distance of air–gap imposed little effect on the MFL. The a-MLR profiles mainly depend on the thickness of the sample.

Experimental study on influence of air gap on upward flame spread over discrete fuel

In a real fire scenario, the distribution of fire loads may not be continuous. In this paper, PMMA blocks (8 cm × 10 cm × 1 cm) are used as experimental materials to carry out upward flame spread experiments with different air gaps (0–18 cm) to analyze changes in burning rate, flame shape, flame height and pyrolysis front position. It is found that as the air gap increases, the burning rate and flame height both increase first and then decrease, and the turning point of this trend is predicted to be between 6 and 8 cm. In addition, it is founded that the pyrolysis reaction is accelerated due to the additional air entertainment provided by the air gap when the pyrolysis front passes through the air gap. However, this effect becomes insignificant for a larger air gap.

Study of the Influence of the Lack of Contact in Plate and Fin and Tube Heat Exchanger on Heat Transfer Efficiency under Periodic Flow Conditions

Plate fin-tube heat exchangers are widely used in air conditioning and refrigeration systems and other industry fields. Various errors made in the manufacturing process can result in the formation of an air gap between the tube and fin. Several numerical simulations were carried out for a symmetric section of plate fin-tube heat exchanger to study the influence of air gap on heat transfer under periodic flow conditions. Different locations and sizes of an air gap spanning 1/2 circumference of the tube were considered for the range of airflow velocities. Velocity and temperature fields for cases with air gap were compared with ideal thermal contact cases. Blocking of heat flow by the gap leads to the reduction of heat transfer rate. Fin discontinuity in the front of the tube causes the smallest reduction of the heat transfer rate in comparison to the ideal tube-fin contact, especially for thin slits. The rear gap position is the worst in the smallest gap range. Therefore, reversing the flow direction can lead to up to a 15% heat transfer increase, if mainly the rear gaps are present. The introduction of a thin slit in the front of the tube leads to convective heat transfer enhancement, which should be further investigated.

Magnetic measurement and analysis of c-type amorphous by an improved adjustable air gap tester

A novel magnetic properties tester is designed to accurately and conveniently change the air gap of the core, which can fix cores of various types. The dynamic magnetic characteristics of the amorphous core under sinusoidal excitation within 20 kHz is measured with different air gap lengths and magnetic flux density. It is found that in the case of the small air gap, the total loss decreases as the air gap increases. When the frequency is 20 kHz and the flux density is 0.1 T, the loss can even be reduced by 7%. This paper analyzes the experimental data and summarizes the influence of the air gap and magnetic flux density about the core loss. Besides, the influence of air gap on magnetic flux density distribution is illustrated and analyzed by the means of FEM (Finite Element Method). It is valuable for the design of high frequency transformer and inductor.

Study on vibration characteristics of motorized spindle based on multi-physics fields

Ceramic motorized spindle plays an important role on CNC machine tool. Its dynamic characteristic determines the machining quality of spindle. This paper established a dynamics model of ceramic bearing, and explored the relationship of bearing stiffness and vibration response. The temperature field model of ceramic motorized spindle was established to analyze the temperature field. The motorized spindle air gap influence on unbalanced magnetic pull was studied. The dynamic model of ceramic motorized spindle was established through considering the multiple physical fields influence factors, the changing law of dynamic characteristics was studied. It has been verified by experiments. The average error of ceramic spindle decreased from 5.1% to 2.1%. The establishment of multi-fields dynamic model provided an important guidance for spindle design.

Metasurface Concept for mm-Wave Wideband Circularly Polarized Horns Design

A novel millimeter-wave (mm-wave) wideband circularly polarized (CP) horn antenna using iris polarizer is reported. By introducing the metasurface concept, the electrical contact problem at the mm-wave band for waveguide-separated components of high-performance CP horn antenna is eliminated. The influence of air gaps on polarizer and whole horn antenna loaded and unloaded metasurface is analyzed and explained. According to simulation, small air gaps of the metal-to-metal contacting plane would not harm the horn performance after loading the metasurface, which means the proposed method can achieve a better tolerance of manufacturing and assembly errors and is more suitable for high-frequency CP horn design. For validation, the proposed horn antenna has been fabricated and its performance is evaluated. The measurement results are in good agreement with the simulation results. The experimental results of 37.8% bandwidth from 75 to 110 GHz for both the axial ratio (AR) <; 3 dB and |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -13 dB are achieved.

Experimental Study of the Shock Wave Attenuation in the Water Mist with Air Gaps

The paper aims to propose ways for enhancing the effect of attenuating shock waves in the water mist. The fulfillment of this task can significantly contribute to the perfection of technologies for protecting from accidental explosions and the design of protective facilities. A series of experiments were carried out to investigate the influence of air gaps on shock wave attenuation in the water mist. A shock tube with hydraulic equipment capable of producing a 3-meter long dispersed water barrier with droplets ranging from 25 to 400 microns and total flow rate 14.5 l/s within a tube was used during testing. The paper analyzes shock wave attenuation within a tube in the water mist with and without air gaps. It has been established that in conditions when a 3-meter long water mist contains four air gaps, every 20 centimeters in width, overpressure reduction coefficient is 1.10-1.15 times higher than the one in the water mist without air gaps.

Theoretical model and analysis of an electromagnetic vibration energy harvester with nonlinear damping and stiffness based on 3D MEMS coils

This paper presents a micro electromagnetic vibration energy harvester (VEH) that uses complementary metal-oxide-semiconductorcompatible 3D micro-electromechanical system coils and a ferromagnetic core to improve efficiency and output power. A systematic model is proposed to describe the nonlinear electromagnetic damping coefficient and nonlinear attraction between the magnet and the ferromagnetic core. The nonlinear model agrees well with the finite element calculation results. Then, a vibration model is established by considering nonlinear stiffness and damping coefficient to obtain the dynamic characteristics and output performance of the system. Furthermore, a numerical method is conducted to systematically investigate the influence of air gap and initial magnet offset under different excitation amplitudes. The simulation results indicate that with a smaller air gap, the output power is higher. Moreover, there is an optimal initial magnet offset in relation to the air gap to maximise the output power of the system. These conclusions and analysis models can be generalised and can be used as a guidance for the designs of similar structural devices. The results also show that the structure proposed in this study can significantly enhance the energy harvesting performance compared with published data of conventional VEHs.

The effect of gap on the quality of glass-to-glass welding using a picosecond laser

In order to study the influence of air gap and focus position on the quality of ps-laser glass-to-glass welding we implemented a method of detecting the air gap between glass surfaces based on optical thin film interference. The method allows real-time optimization of the welding process. We measure the air gap between glass surfaces to be bonded and the laser focal position, which are set as the constraint conditions affecting the nonlinear self-focusing of the laser beam. The processing parameters of picosecond laser welding are determined and the welding strength and the morphology of bonded zone are detected and observed. Laser welding with good performance can be achieved with an air gap of 2 μm. SEM microscopy shows that the bonding region between two glass surfaces is very smooth in the vicinity of the tear-drop shaped cross-sectional structure of the welded glass. A tensile strength inspection fixture is designed, and we measured a tensile fracture strength of over 30 MPa for the welded glass. Through confocal microscope analysis, the width and depth of fracture morphology of welded samples are shown to change with air gap, which is consistent with the theoretical analysis.

Modeling of airgap influence on DC voltage generation in a dynamo-type flux pump

High-temperature superconducting (HTS) flux pumps are promising devices to maintain steady current mode in HTS magnets or to energize rotor windings in motors and generators in a contactless way. Among different types of flux pumps, the dynamo-type flux pump has been very common due to its simple structure and ease of maintenance. However, understanding the principle of dynamo-type flux pump has been challenging despite the recent progress. This article employs an efficient numerical model based on minimum electromagnetic entropy production method to analyze the performance of the flux pump in open-circuit mode. This model is much faster and efficient than previous works on flux pumps. In addition to the main behavior of the flux pump, this work investigates the influence of airgap and critical current density on open-circuit DC voltage of the flux pump. We compare the modeling results of open-circuit DC voltage for different airgaps to experimental ones obtained in (Bumby et al 2016 Appl. Phys. Lett. 108 122601), showing good agreement. Modelling results show that with increasing airgap, pumping voltage in the superconducting tape does not cease, but only reaches to insignificantly low values, which is not measurable via experiments. In addition, the voltage in open-circuit does not depend on the critical current density, as long as the superconducting tape is fully saturated with screening currents.

Impact of transverse magnetic fields on dose response of a nanoDot OSLD in megavoltage photon beams

PurposeWe investigated the impact of transverse magnetic fields on the dose response of a nanoDot optically stimulated luminescence dosimetry (OSLD) in megavoltage photon beams. MethodsThe nanoDot OSLD response was calculated via Monte Carlo (MC) simulations. The responses RQ and RQ,B without and with the transverse magnetic fields of 0.35–3 T were analyzed as a function of depth at a 10 cm × 10 cm field for 4–18 MV photons in a solid water phantom. All responses were determined based on comparisons with the response under the reference conditions (depth of 10 cm and a 10 cm × 10 cm field) for 6 MV without the magnetic field. In addition, the influence of air-gaps on the nanoDot response in the magnetic field was estimated according to Burlin’s general cavity theory. ResultsThe RQ as a function of depth for 4–18 MV ranged from 1.013 to 0.993, excepting the buildup region. The RQ,B increased from 2.8% to 1.5% at 1.5 T and decreased from 3.0% to 1.1% at 3 T in comparison with RQ as the photon energy increased. The depth dependence of RQ,B was less than 1%, excepting the buildup region. The top air-gap and the bottom air- gap were responsible for the response reduction and the response increase, respectively. ConclusionsThe response RQ,B varied depending on the magnetic field intensity, and the variation of RQ,B reduced as the photon beam energy increased. The air-gaps affected the dose deposition in the magnetic fields.