Observations of Severe In-Flight Environments on Airplane Composite Structural Components

Direct or indirect lightning strikes have caused reactor trips in nuclear power generating stations. If nuclear power generating stations do not have adequate lightning protection and grounding, such stations may be exposed to greater risk of loss of offsite power, fire, and damage to redundant trains of engineered safeguard equipment. The loss of offsite power is an important initiating event for design basis accidents. I studied the effects of lightning strikes on reactor trips or misoperation of the equipment from January 1984 through September 2000. From this study, I found that most of the lightning strikes operated the overvoltage protection devices for the control rod drive system. In others, the lightning strikes had partially damaged the main/startup transformers, tripped the switchyard breakers or tripped the transmission lines and, by that, affected the availability of the required stable offsite power sources to the nuclear power generating stations. Direct lightning strikes, electrostatic discharges, lightning electromagnetic impulse can disrupt the electrical and electronic equipment used in the reactor protection system and the other safety systems. The use of the integrated protection and microprocessor-based systems in simplified passive advanced light water reactors and the digital systems replacing the existing analog systems may be more vulnerable to a lightning strike. The protection from lightning could include the installation of lightning dissipation arrays, installation of ferrite shields, installation of a secondary shield or the addition of a short time delay on the power supply monitoring card to allow the transients to dissipate. The instruments and computer grounding system may be grounded through a separate radial grounding system that may be connected to the station grounding grid at only one point to avoid circulating currents. Advanced surge protection devices that include gas discharge tubes, Zener diodes for accurate and fast( picoseconds) voltage control, and metal oxide varistors can be used to protect the electrical and electronic safeguard equipment from high voltage transients associated with lightning.

This paper presents an evaluation of transient electromagnetic phenomena inside lightning protection systems (LPS) model of truss bridge resulting from direct lightning strikes. The simulation model is base on the coupled transmission line network in the frequency domain combined with the Fourier transform technique, which is employed to evaluate the electromagnetic transient surge current distribution in LPS. The transient magnetic fields are calculated based on difference method. After comparing with the standard “IEC62305-4”, it can be seen that the calculation is accurate and the method is simple The paper provides a new idea for the optimization design of truss bridge LPS, and it puts forward some suggestions on the design and construction of truss bridge LPS.

Influence of photovoltaic support on lightning transient under direct lightning strike

The protection of tall structures against direct lightning strikes is usually provided by the installation of a lightning rod of the determined height on the top of the structure. The tip of the rod instead of the top of the structure becomes the point of the initiation of the upward lightning or intercepts the downward lightning. The installed lightning rod does not decrease, even slightly increases the number of lightning incidents to the protected structure. However, there is another alternative lightning protected system, which is being installed instead of the lightning rod, reduces significantly the number of lightning strikes to the structure. This system consists typically of a hemisphere of a large radius with an array of many thin metal splines with sharpened tips distributed evenly over the hemisphere's surface (LPAS). Such LPAS is usually installed on the top of the structure to be protected.

The wind power system has always focus on the problem of lightning protection of wind turbine blades. Because of the increase of the capacity of wind turbines, the effective height of the wind turbines and the length of the blades also increase a lot, and the problem of the lightning protection failure of the existing blade lightning protection system (LPS) against direct lightning strikes has become prominent as well. There is still short of an optimization design of the LPS which can not only meet engineering requirements but receive all the downward lightning leaders. In this paper, a design scheme of overlying conductors on both of the leading edge and the tailing edge outside the tip of the blade was proposed to solute the delamination damage of the blades. This design of LPS could reduce the vicinal electric field of the down conductors, and reduce the probability of the streamer discharge incept from the down conductor as well as the discharge incept outside the laminate. The experimental study on the lightning protection performance was carried out under lightning and switching impulse voltage. The experimental results showed that the overlying conductors can effectively receive the downward leader to protect the blade from being penetrated in its laying range, but the protection efficiency would decline sharply when the downward leader developed outside the laying range. The covering length of the conductors should be 12% of the total length of the wind turbine blade, which can reduce the lightning damage by 90% or above.

<div class="htmlview paragraph">The effects of engine operating conditions on the octane requirement and the resulting knock-limited output were studied on a single cylinder engine using production cylinder heads. A 4-valve cylinder head with port deactivation was used to study the effect of fuel octane, inlet air temperature, coolant temperature, air/fuel ratio, compression ratio and exhaust back pressure. The effect of the thermal environment was studied in more detail using separate cooling systems for the cylinder head and engine block on a 2-valve cylinder head.</div> <div class="htmlview paragraph">The results of this study compared closely with results found in the literature even though the engine and/or operating conditions were quite different in many cases. Guidelines on the effect of various parameters on the octane requirement of an engine can be summarized as follows:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"><div class="htmlview paragraph">Spark Advance: 1 ON/1° SA</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Air Temperature: 1 ON/7 K</div></li> <li class="list-item"><div class="htmlview paragraph">Air/Fuel Ratio: peaks at 5% rich of stoichiometric, decreases by around 2 ON / air/fule ratio around peak</div></li> <li class="list-item"><div class="htmlview paragraph">Intake Pressure: 3-4 ON/10 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Compression Ratio: 5 ON/CR</div></li> <li class="list-item"><div class="htmlview paragraph">Exhaust Back Pressure: 1 ON/30 kPa</div></li> <li class="list-item"><div class="htmlview paragraph">Coolant Temperature: 1 ON/10 K (Similar effect of head and block temperature., Larger effect at low speed.)</div></li> </ul> </div>

Lightning overvoltages in low-voltage circuits in houses originating from a distribution line or an antenna have been actively studied. However, the mechanism by which damage is caused to home appliances due to a lightning strike to the ground near the house is still unclear. This paper discusses lightning overvoltages and currents in low-voltage circuits for various scenarios, such as a lightning strike to the ground, a direct strike to a distribution line, and a direct strike to an antenna. Simulations are carried out using the Electromagnetic Transients Program. From the simulation results, direct lightning strikes cause the most serious damage to home appliances, but nearby lightning strikes should also be considered when designing lightning protection schemes.

It is well known that the amount of damage caused by lightning strikes to protected composite airframe structures depends on the paint characteristics, often applied on the surface of composite structures to protect from environmental effects and to personalise a product. In this work, physically based models of the mechanical loads induced by lightning strikes are employed in the generation of the mechanical overpressure fields due to a simulated lightning strike, while accounting for the paint thickness. These fields are then implemented into a three-dimensional finite element framework and combined with a damage model to predict the effect of paint thickness on the mechanical damage in composite structures subjected to this type of events. These models accurately predict the increase of damage extent with the increase of paint thickness, which is corroborated by experimental observations from industry and by the experimentally observed trends reported in literature.

Lightning is a natural phenomenon that can cause serious damages in power systems including wind farms. Wind Turbines (WTs) are tall structures and are often installed in areas with high lightning activity levels which makes them exposed to direct strike. One of the parameters affecting the lightning performance is the impedance of lightning channel. In this paper the effects of this impedance on the induced overvoltage in wind turbines is investigated. The case study is carried out on a WT with 2 MVA of rated power where direct lightning strike with maximum current magnitude of 50kA is struck to the WT. The results of different scenarios are compared, and it is shown that as the value of lightning channel impedance gets higher, the overvoltage caused by the corresponding lightning strike, with the same current magnitude, increases too. This shows the importance of the lightning channel impedance's effect on high-voltage studies of WTs, as it can help in selecting proper lightning protection devices.

The electromagnetic transients of lightning protection system(LPS) under direct lightning strike is studied using NEC2. By employing antenna return-stroke model, lightning channel’s inducing effect and finite conductivity of ground are all taken into account. Results show that the lightning channel’s inducing effect tends to decrease the current flowing through horizontal conductors, and increases the current flowing through vertical conductors near the striking point. The results obtained under perfect ground assumption have a good agreement with the published experimental results. The simulation also predicts that the finite conductivity of the ground affects the branch current significantly, it increase the LPS’s current dissipating efficiency, the higher the soil resistivity, the more uniform the current flowing in vertical conductors.

<div class="htmlview paragraph">A detailed description is presented of the design and fabrication of the Marvel II composite wing. The wing was constructed in a short time using a combination of sailplane and modern prepreg composite structures technologies. The wing design requirements were to minimize the use of metal in the structure, to develop a high performance flap system which would be insensitive to a sand environment, and to explore composite production structural concepts.</div> <div class="htmlview paragraph">The desired high lift capability was achieved through the use of a double slotted flap with a fixed slat. A unique flap support mechanism was developed to give excellent flap positioning over the flap angle range.</div> <div class="htmlview paragraph">The wing was constructed in three major assemblies, the spars, the wing skins, and the flap and ailerons. The wing spar was constructed applying conventional sailplane techniques which uses a wet layup of S-glass rovings.</div> <div class="htmlview paragraph">The fabrication of the wing skins was made in three steps. The original XV-11A wing was extended and used as the male mold. A heat resistant female mold was fabricated using an epoxy-graphite paste with a honeycomb backing. The mold had excellent dimensional stability and was light (300 lbs.). The wing skins were fabricated using Kevlar 250 deg. prepreg, Nomex honeycomb, and some high density foam. The wing skins were cured using a vacuum bag process.</div> <div class="htmlview paragraph">The Marvel II wings were designed and fabricated along with major modifications to the fuselage in an eight month period. The aerodynamic performance was outstanding with an airplane lift coefficient in excess of 3.0. There were no structural problems encountered in the flight test program. The structural weight was much higher than expected. It was found that the weight of secondary structure was difficult to control.</div> <div class="htmlview paragraph">From this development program, a methodology to produce excellent dimensional fidelity, and high structural efficiency wings has evolved. From the lessons learned on this prototype development program it is now possible to produce composite wing and fuselage structures for limited production aircraft at a modest cost and in a relatively short time frame.</div>

Lightning protection and surge protection measures are essential for the availability of wind turbines and for their profitability. Whereas the electric and electronic equipment can be protected by a comprehensive surge protection concept, outer structures particularly the rotor blades are hit by direct lightning strikes. In defined maintenance cycles these damages are inspected and repaired in costly operations. In this paper a method for lightning current measurement is presented. It enables the operator to measure lightning currents directly and to determine their parameters like amplitude, current rise time and charge. The presented system with three sensor units is originally developed for wind turbines, to adapt maintenance cycle times to the real number of lightning strikes. Further applications in other industries are possible.

Indonesia is located in a tropical region and has a high number of lightning flash density. In 2021, the latest oil tank fire incident in Balongan and Cilacap, Indonesia, caught the attention of lightning engineers. The oil and gas industry in Indonesia, in general, implements international standards related to lightning protection, such as the NFPA and API standards. However, due to the difference between lightning characteristic in tropical and sub-tropical area, the oil tank and refineries in the tropical area are not inherently self-protected againts lightning direct strikes. Oil and gas industries in tropical area requires additional lightning protection to prevent direct lightning strikes on tank wall, breather valve, and automatic tank gauging (ATG). Based on lightning characteristic in general, lightning can melt oil tank, causing the tank to leak. The voltage difference between the tank wall and the floating roof can cause sparks, then leads to the occurrence of fire. This paper discusses the potential of lightning strike that causes fire tank, including the existance of international standard in tropical area, and the solution of lightning threat, based on captured lightning data.

<div class="section abstract"><div class="htmlview paragraph">Friction heating in solid cylindrical body contact has been an interesting subject for a long time for physicists (i.e. tribologists) and application engineers. In the current environment where the industry product, such as Diesel Rotary Pump (DRP) which operates at higher speed, the temperature rise from the friction contact is of great importance to the manufacturer for thermal safety and its environment effect.</div><div class="htmlview paragraph">In this paper, a steady-state temperature rise under friction heating is studied on a pump roller to cam ring contact within a cyclic segment of a DRP using quasi steady thermal modeling by both the analytical solution developed to the equations from friction heating and thermal conduction and colling, and the finite element analysis (FEA) method constructed with heat flux data from actual hardware test.</div><div class="htmlview paragraph">In addition to the analytical solution and FEA results, an experimental test was conducted to measure and collect the thermal temperature data adjacent to the contact region to correlate the results from analytical solution and FEA simulation, they are found in good agreement.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In this paper, it is explained how composite structures, made of continuous fibers embedded in a polymer matrix, are designed and analyzed in the aerospace industry. The strategy is based on the building block approach, in which the knowledge on the composite material and structure is built step by step from the coupon level up to the final full scale structure. Damage is then discussed, as it can't be ignored when composites are concerned. The approach available in the SAMCEF finite element code is then described. It is based on the continuum mechanics approach, and allows studying the progressive failure of composites in the plies and at their interface (so considering delamination). The material models are described, and their use is illustrated at the coupon level. The identification procedure for this damage models is also discussed. It is therefore shown how this information of the material behavior can be used at the upper stages of the building block approach and so applied to larger scale structures. It is advocated here that this approach can be used for the automotive applications, leading to a transfer of technology from aerospace to automotive.</div></div>