Water Mist System for Shipboard Machinery Space Fires

Water mist has been determined to be a preferred alternative to Halon 1301 total flooding to extinguish fires occurring in ship machinery spaces and pump rooms, because it is toxicologically and physiologically inert. Water mist systems produce a drop size distribution with a range of drop sizes under 1000 μm, while the more conventional sprinkler systems produce much coarser particles. The smaller particle sizes have greater cooling efficiencies because evaporation and cooling are controlled by surface area, and the surface area of a large number of small droplets is greater than that of a small number of large droplets of the same total volume.

Posted in: Briefs, Mechanical Components

Axial Field Electric Motor

An axial field electric motor comprises one or more elements such as a rotor mounted for rotation and multiple axial flux permanent magnets carried by the rotor. The axial flux permanent magnets are oriented such that an associated magnetic flux produced thereby is at least substantially axially oriented. The axial flux permanent magnets are positioned around the rotor with alternating orientations of flux direction so that a flux direction of adjacent magnets is at least substantially axially oriented but opposite in direction. The radial flux permanent magnets are also carried by the rotor and oriented so that an associated magnetic flux produced is at least substantially radially oriented.

Posted in: Briefs, Mechanical Components

Miniature Rotorcraft Flight Control Stabilization System

Autonomous rotorcraft provide improved capability in performing military missions such as reconnaissance, targeting, border patrol, and environmental sensing. A common difficulty in applying miniature rotorcraft to these areas is the complexity and specialization of the control. In general, rotorcraft have extreme vibration that make miniature inertial measurement difficult. Sources of vibration include the main rotor, tail rotor, and blade flapping dynamics. Typical sensors include MEMS accelerometers, which are sensitive to vibration. Inclusion of alternative and or redundant sensors may be used to reduce vibration sensitivity and add useful additional feedback.

Posted in: Briefs, Physical Sciences

Studies of Dynamic Fracture in Brittle Materials

A program of research spanning several years ending in November 2005 was dedicated primarily to formulation and analysis of canonical boundary- value problems in mathematical modeling of dynamic fracture in brittle materials. The sub-topics within the broad topic of dynamic fracture in brittle materials that were studied, and the accomplishments in each sub-topic, are summarized as follows:

Posted in: Briefs, Physical Sciences

Acceleration Strain Transducer Containing Cantilever Flaps

A recently invented acceleration strain transducer is based on the principle of a conventional spring-and-mass acceleration transducer combined with a linear strain sensor that measures the acceleration-induced deflection of the spring. The invention is compatible with any of a variety of linear strain sensors, including conventional foil resistance strain gauges, fiber-optic and fiber-laser strain sensors, and electrically-conductive-liquid strain sensors.

Posted in: Briefs, Physical Sciences

Simulation of Airflow Through a Test Chamber

A computational-simulation study of the flow of air through a thermo-anemometer chamber was performed to resolve what originally seemed to be an anomaly in the measurement data obtained by use of the chamber. The thermo-anemometer chamber is a test chamber used to measure the rate of generation of heat by a device placed within it. In the original application that produced the apparent anomaly that prompted this study, the chamber was used to measure the power dissipation (as manifested by heating) in an operating power-supply inductor. The apparent anomaly was that the heating of the inductor as calculated from the measurements made by use of the chamber seemed unrealistically high.

Posted in: Briefs, Physical Sciences

Study of Submodeling of a Small Component in a Structure

A study was performed to evaluate the accuracy achievable in the use of submodeling in finite-element modeling of the mechanical response of a structural system that includes components embedded in a larger structure that is subjected to a large transient load. The specific system studied was a simplified model of a “smart” projectile containing a substructure that supported an electronic-circuit board on which were mounted two capacitors and an eight-lead integrated circuit (see figure). The main body or shell of the projectile was represented as a cylindrical ring supporting the substructure. The dimensions of the various components were chosen to be typical of “smart” munitions. The transient load condition was represented by a velocity-versus-time boundary condition, typical of the velocity versus time of a projectile at launch, imposed at the lower surface of the cylindrical ring.

Posted in: Briefs, Information Technology

Next-Generation Information Systems Architectures

A document describes a paradigm in which low-altitude unmanned aerial vehicles (UAVs) with wireless communication capability are used to assist networking among a set of ground stations. This new paradigm is attractive because UAVs can be dynamically deployed in a wide variety of geographical territories. Furthermore, UAVs often have high-quality line-of-sight communication links with other UAVs, and ground stations as aerial links usually suffer relatively little shadowing compared with their terrestrial counterparts.

Posted in: Briefs, Information Technology

Weapon and Armor System Power in Future Combat Vehicles

Future combat vehicles will require unconventional weapons and armor systems such as electromagnetic (EM) or electrothermal chemical (ETC) guns, electromagnetic (EM) armor, and directed- energy weapons (DEWs). To meet these requirements, a hybrid electric power system has been identified as the best alternative to support the demand for propulsion, continuous auxiliary power demand, and pulsed power demand for weapons and armor.

Although the development of these weapons and armor technologies is progressing at a fast rate and can be demonstrated at a smaller scale today, the power supply needed in the vehicles to support these systems presents a great challenge to technology developers and vehicle integrators.

In a 20-ton combat hybrid vehicle platform, power supply will mainly consist of two sources of energy: a prime power source driving an AC generator such as a heat engine, and an energy storage system consisting of advanced batteries, ultra capacitors, and flywheels, or a combination of these three devices. Currently and in the near term, the prime power will be either a diesel engine or a turbine, and in the far term, fuel cells may become viable options.

The power supply has to meet the demands of mobility, lethality, and survivability. The demand for electric power becomes even more challenging during silent watch, when the power draw must be provided solely from energy storage for extended periods of times (4 to 8 hours). Power supply must be delivered in two forms: continuous and pulsed. For a vehicle weighing about 20 tons, the continuous power ranges from 400 to 500 kW, which is supplied from the main prime mover, supplemented by 25-30 kW-hr of energy from a storage system. Pulsed power, however, depends on the loads and repetition rate.

Since electric power is used for continuous loads such as mobility, and also for pulsed loads such as electric weapons, it would make sense to have one common power and energy management system onboard the vehicle to distribute electric power to various users according to a defined precedence. Thus, a Combat Hybrid Power System (CHPS) program was introduced to evaluate such a power management and distribution system.

Enabling Technologies

The CHPS program was initiated by the Defense Advanced Research Projects Agency (DARPA) and continued by the U.S. Army RDECOM – TARDEC (Tank Automotive Research, Development and Engineering Center). The major goal was to design, develop, and test a 15-ton notional hybrid electric combat vehicle, incorporating all the power demand onboard a vehicle system, and assess the feasibility of simultaneous power distribution to propulsion.

In the course of designing the components for the 15-ton combat vehicle, some critical and enabling technologies were identified. They included high-temperature power electronics, high-energy-density and high-power-density batteries (namely Li-Ion batteries), and high-torque-density traction motors. To the extent possible, all the components and auxiliary systems had to be integrated within the space available in a 15-ton combat vehicle. Two technical challenges appeared: the amount of power needed for all the loads, and the size and weight of the components. A first estimation revealed that using state-of-the-art technologies would require at least twice the space available within a combat vehicle.

The most aggressive goals were set for the power electronics, the motor and generator inverters and rectifier, and the DC-DC converters, and also for the thermal management. Another aggressive metric was set for the Pulse Forming Network (PFN), which had to be reduced by more than half of its current size in order to install it in the vehicle. Improvement in both the power converters and the PFN hinged on the maturation of wide bandgap (WBG) materials such as SiC. This material provides the capability to build converters that operate at high temperature, high frequency (50-100 kHz), and higher efficiency.

Vehicle Mobility

In a combat vehicle, there are three main users of continuous power: mobility, thermal management, and silent watch. Power is supplied to most of the mobility and thermal loads from the prime mover (the engine), whereas the silent watch is solely supplied from the energy storage (a battery bank), which is also recharged from the engine driven generator. For optimum performance, the power is split between engine and battery for either best fuel efficiency or burst power, according to the specified vehicle duty cycle.

Military vehicles must have the capacity to operate anywhere in the world, under extreme environmental conditions, from the frigid temperatures of the Arctic, to the intense heat of the deserts, and from hard rocky and paved roads, to hilly and soft soil. They must withstand the vibration, shock, and violent twisting experienced during crosscountry travel over rough terrain, and they must be able to operate for long periods of time with very little or no maintenance. However, there are additional requirements that are changing the whole philosophy of vehicle design. Future vehicles must be lighter, faster, and more deployable, but at the same time, more lethal and more survivable.

For a 20-ton vehicle, the power required to meet the acceleration, top speed, and gradeability requirements at 10 kph is about 400-500 kW. In a hybrid electric vehicle, the engine provides most of that power. The engine is normally programmed to operate within the band of optimum efficiency on its fuel map. Boost power for transient operation is supplemented by the stored energy from the battery pack. Thus, for propulsion, a relatively small energy storage system would be sufficient.

Requirements such as acceleration, top vehicle speed, steering at large radii, and cross-country speed depend on the available horsepower from the prime mover and the energy storage device (batteries) getting to the sprockets or wheels when needed for the various vehicle mobility conditions. For all vehicles, the power is transmitted from the prime mover to the wheels or sprockets according to a specific architecture, series, or parallel, depending on the application and duty cycle of the vehicle.

Thermal Management

In the current fleet, in addition to the power demand to operate the vehicle, 10 to 15% of the generated power from the prime mover is needed for the cooling system. For a hydraulic drive using hydrokinetic or hydromechanical transmission, all of the mobility requirements are manageable. For a hybrid electric system, the situation is more complex. The cooling system of a hybrid electric vehicle with the currently available technologies can conceivably be four to six times the size of its mechanical counterpart. Consequently, high-operating-temperature components must be developed to reduce the current hybrid electric cooling requirements.

Silent Watch

The power demand for silent watch is difficult to establish because the requirements are not well defined. However, using high-energy-density batteries such as Li-Ion, it is conceivable to have 25-30 kW-hr of energy onboard the vehicle. This amount of energy storage can support silent watch missions for a duration of two hours if the power requirements do not exceed 10 kW. The amount of energy supply must exceed the amount of energy demand by 50% to account for the system efficiency, degradation at temperature extremes, and cycle life.

High-voltage pulse power is required to power the ETC/ETI, the ETC gun, and the EMA envisioned for future hybrid electric vehicles. Intermediate energy storage for these pulse power loads is achieved through the use of high-energy-density thin-film capacitors, currently utilizing Biaxial-Oriented Polypropylene (BOPP) as the dielectric film. The total amount of energy storage required varies based on such factors as simply achieving ETI or full–blown temperature compensation (ETC), the type of propellant used, the specific armor design, the threats to be countered, and the desired safety factor. This results in intermediate energy storage from tens to hundreds of kilojoules.

The basic building block for these high-voltage pulse power systems is an extremely high-power-density (~4.5 kW/l) 150-kW pulse charger. Depending on factors such as the total amount of intermediate energy storage required, the number of rounds per minute the system is required to fire, and the required rate of recharge for the EMA, additional chargers can be added.

Directed Energy Weapons

The most likely DEW to be integrated into a vehicle platform is the Solid State Heat Capacity Laser (SSHCL), which will be integrated onto a hybrid electric ground combat vehicle in order to provide forward air defense against unmanned aerial vehicles (UAVs), helicopters, and other low-flying craft, as well as area-wide active protection against incoming threats including mortars and missiles. The system will generate a 100-kW laser output at ~10% electrical efficiency, meaning the hybrid electric vehicle will need to provide 1 MW for short durations (several seconds).

Although the power management and distribution to both types of loads is feasible within the hybrid architecture, the integration burden is extremely challenging in a 20-ton vehicle, and depends to a great extent on the pulsed load specifications. Currently, it is difficult to envision a hybrid electric combat vehicle without the development and maturation of the emerging technologies in power semiconductors and energy storage. However, in the last ten years, these technologies have progressed by more than one order of magnitude.

This article was written by Gus Khalil, Eugene Danielson, Edward Barshaw, and Michael Chait of the U.S. Army TARDEC in Warren, MI. For more information, click here.

Posted in: Articles, Aerospace, Electric power, Hybrid electric vehicles, Military vehicles and equipment

Detecting Improvised Explosive Devices in Urban Areas

Improvised explosive devices (IEDs) are rudimentary bombs that generally consist of commonly found non-military materials. Although common IED threats include roadside bombs, suicide bombers are another emerging problem in the IED arena. Suicide bombers carrying personal-borne IEDs (PBIEDs) are extremely hard to detect or stop. Because no IED emplacement is necessary, a suicide bomber can quickly strap on an IEDladen vest and move to the kill zone. Placed in the proper urban environment, this weapon is capable of inflicting serious structural damage and killing hundreds of people in mere seconds.

Research has been done to detect magnetic materials used in IEDs in urban environments using a wireless sensor network. Using the magnetic detectors in the wireless sensor nodes, magnetic behaviors and patterns are analyzed to differentiate a person carrying an IED and a person possessing magnetic material like jewelry or keychains. Using wireless sensor nodes instead of standard metal detectors enables the detectors to remain hidden to outside observers. The small nodes easily blend into the indigenous environmental settings to provide stealth.

All IEDs require a power source to initiate the weapon. Most initiators are battery- operated electrical devices, but there are other means of initiation. Spring-loaded initiators require no electrical power to function. The IED initiator detonates the weapon and begins the bombing sequence. Common initiators are blasting caps and fuse igniters. Electrical initiators can be triggered in various ways, including a button, radio frequency, and optical. The IED switch arms the weapon after the initiator sequence begins. The switch could be an arming switch, fuse, or both for redundancy. Once the IED is armed, the internal circuit is complete and detonation occurs shortly thereafter.

One of the first solutions to detect IEDs was to detect the frequency spectrum used by the IED initiator devices. By correctly analyzing the frequency spectrum used by the remote triggers, troops successfully jammed the frequencies and prevented IEDs from being triggered. Electromagnetic pulse jamming also destroyed IED circuitry.

Unmanned Aerial Vehicles (UAVs) use mounted cameras to take pictures of probable IED areas and then come back for more images. The Buckeye camera mounted on a UAV uses an electro-optical sensor capable of producing threedimensional images. Using imagery software or the human eye, the pictures are analyzed against pictures from the same area, but taken at a different time. Scrutinizing the images to the nearest pixel, experts can determine if suspicious IED activity has occurred in a region.

Magnetic Wireless Sensor Networks

A wireless sensor network (WSN) is formed from a series of wireless network nodes or motes, generally in an ad-hoc configuration. Each node contains a small processor to handle sensing duties. Nodes are able to relay information using a predetermined routing protocol such as ZigBee. Due to the wireless constraints, each WSN node needs a self-contained power source such as batteries.

A standard WSN uses the nodes for their physical sensing capabilities in conjunction with a base station, which receives information from the nodes and passes it to another source to process the data. Since the base station receives input from the WSN nodes, it has higher power requirements and must always coordinate data delivery out of the network. Each node contains sensing capabilities appropriate for the network application and needs. Nodes cannot process or analyze the information, but can forward information to either another node or the base station.

The mesh-networking feature of the motes allows them to communicate with each mote in the network. Additional motes can be added to the network or motes can be removed from the network seamlessly. The magnetic detection capability within the motes uses a twoaxis magnetic field sensor to detect electronic voltage perturbations around the sensor. The passive infrared sensors detect dynamic changes in the thermal radiation environment within immediate vicinity of the sensor. The mote also contains a dormant microphone to detect acoustic changes within its environment. Each mote contains four magnetic and passive infrared sensors placed within a cubicle housing to provide nearly 360-degree coverage.

Placing a WSN by entry and exit points of urban buildings provides a stealthy means of detecting IED materials. The accuracy of the mote detectors allows observers to distinguish normal routines from suspicious IED activities. The WSN can be set up to alert security officials of possible IED activity, and used in conjunction with standard surveillance methods to provide a more complete and accurate depiction of actual activities taking place in real time.

WSN Deployment

In IED detection, the network looks for patterns of activity that appear suspicious and raises alerts when a certain level of confidence has been achieved in the prediction. Ferrous materials compose a large number of IEDs, making magnetic sensors a logical choice for detecting IEDs. However, magnetic sensors alone may not be sufficient in confirming IED presence because the network may be susceptible to false positives (the network falsely detecting IEDs) or false negatives (failure of the network to detect IED). Using a combination of different sensor modalities could mitigate both possibilities.

The urban environment presents many challenges. Large crowds provide many variables unbeknownst to the planning process. For example, the presence of a metal shopping cart in a grocery store is a common occurrence; thus, another reason to use metallic sensors in conjunction with other detection characteristics. Another issue is the emplacement of the wireless sensor nodes. Although relatively small, they must be carefully placed to avoid accidental detection.

To find the optimum deployment scenario, various tests were conducted using the motes, 18" orange safety cones to elevate the motes from the ground, and steel buckets and staples to simulate metallic IED material. The initial setup kept the metal bucket in a fixed position and the mote was walked along a straight-line path over the bucket. The spacing was too great and the motes had trouble detecting magnetic material unless extremely close to the mote.

To test if large amounts of metal at a specified distance would give the same magnetic reading as smaller amounts of metal at a closer distance, a keychain was placed 6" from the mote. The keychain gave readings just as strong as a bucket placed 3' away from the mote.

Another test used a basic rectangular configuration of motes placed at fivemeter intervals. A steel bucket was traversed through various paths around the motes. These various paths often produced dead spots. The mote was then placed 1.5' away from a wall. Metal was placed at varying heights of the wall to determine how high the metal could be detected by the sensor mote. Results showed that a 2.5' height was the maximum distance that still provided consistent results.

In another test, two motes represented an entrance or doorway to an urban building. The motes were placed at 2' intervals. This interval was later increased to 4, 8, and 12'. A subject carrying a metal bucket traversed the network. Final tests were conducted with two and three subjects traversing the network with differing amounts of metal. The 2 and 4' configurations were tested as a means of providing network redundancy and avoiding blind spots inside the mote area. The motes were able to detect strong magnetic signals from the bucket and provided many data points for detection by the mote software.

The mote intervals were then expanded to 8 and 12'. The 8' configuration still provided reliable and consistent results. The 12' configuration showed some readings, but was not consistently able to detect metal from 6' away. So, an 8' interval between motes was optimal for the six-mote network, providing redundancy of motes while avoiding blind spots within the network (see figure).

Overall, a wireless sensor network using only magnetic detection is not a complete solution for the IED problem. The strengths of a WSN include low power requirements, adaptability, and relative ease of use. For controlling entrances to buildings such as shopping malls, places of worship, or office buildings, a cost-effective WSN implementation would be possible. It would require a configuration that leaves no holes in detection and provides redundancy to prevent network failure.

This article was written by Lieutenant Matthew P. H. O’Hara of the United States Navy. For more information on the Navy’s IED detection technologies, click here.

Posted in: Articles, Aerospace, Security systems, Sensors and actuators, Defense industry, Personnel, Magnetic materials, Hazards and emergency management