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Mechanical Engineering. 1998;120(10):62-68. doi:10.1115/1.1998-OCT-1.

This article discusses the three federally funded projects that are underway to develop new rocket engines that can make it more affordable to send payloads into orbits. The new RS-68 propulsion system is Rocketdyne's entry in competition to power the US Air Force's new heavy-lift booster. The most ambitious of the new propulsion system designs is Rocketdyne's XRS-2200 linear aerospike engine, a seemingly nozzle-less oxygen/hydrogen powerplant that is designed to send the autonomously controlled NASA X-33 lifting body into orbit. The X-33 is being developed by Lockheed Martin Skunk Works, Palmdale, CA. The key for new launch vehicles, whether they're expendable or reusable, is to get the costs down. The article also highlights that the payload that can be lofted by a launch vehicle depends in large part on engine performance and the ratio of propellant to structural weight. Bell nozzles are designed to offer the best compromise of shape and length for a vehicle and flight path. Rocketdyne's R-68 engine is to be 17 feet tall and 8 feet wide at the base. The key to the R-68 engine design was the selection of hydrogen as the propellant rather than kerosene.

Mechanical Engineering. 1998;120(10):70-72. doi:10.1115/1.1998-OCT-2.

Biomedical researchers are combining electrostatic finite element analysis (FEA) software with laboratory testing to improve treatments for arrhythmia. The researchers used Algor's Superdraw Ill, a precision finite-element model-building tool, to model a 100-by-100-centimeter sheet, which represented a conductive area of the heart. They applied a resistivity value based on a thickness of 1cm to simulate a uniform resistance over heart fibers. The finite element model showed that current through the element faces at the ends of the electrodes was 151 percent larger than current near the electrode center. The researchers also used FEA to determine that the length of the line electrode does not affect the current distribution. In order to confirm the results of the analysis and further test the positioning of the electrode with respect to heart fibers, researchers applied line electrodes in varying positions andorientations on 13 hearts from New Zealand rabbits. Finally, researchers could determine the distribution of the change in transmembrane voltage from a line electrode, made up of a summation of points, using electrostatic analysis.

Mechanical Engineering. 1998;120(10):74-79. doi:10.1115/1.1998-OCT-3.

Product data management (PDM) has proven its value as a critical tool in handling the enormous amounts of technical information companies generate. Now the PDM industry is applying this experience to more affordable systems targeted at smaller organizations. Several suppliers have entered the market with economical approaches aimed specifically at midsized companies. Many companies use PDM to eliminate inefficiencies in the engineering change process. Diebold, Inc. reduced engineering change cycle time by 30 percent through process automation with PDM. IBM is using PDM technology in product development for sharing data among groups, designing tools tightly coupled with release and change processes, interfacing with procurement and other services, and establishing real-time communication of data across the enterprise. Engineers increasingly are using PDM viewing features to track subsystems. Virtual-mockup capabilities enable engineers to import all the parts files for a product designed in Solid Edge, regardless of computer-aided design (CAD) vendor or file format.

Mechanical Engineering. 1998;120(10):80-82. doi:10.1115/1.1998-OCT-4.

Product data management (PDM) has helped engineers shrink the time needed to develop a new cross-country motor coach called Renaissance. Engineers used virtual prototypes to confirm that movable parts in the motor coach would fit properly and to identify interferences before physical prototypes were built. The Renaissance uses some highly innovative technology. It is the only cross-country motor coach built in North America to feature six-wheel anti-lock disc brakes for speedy stops and a steering tag axle that greatly improves manoeuvrability. Motor Coach management believes that the use of computer design eliminated some of the costs associated with building and rebuilding portions of the prototype. It also reduced the cycle time considerably. The entire project, from concept to customer deliveries, took 39 months. The PDM system helped engineers by allowing them to see the association of their files with their designs. Solid modeling and PDM helped engineers slash the Renaissance's parts count by 60 percent, reduce suppliers from 53 to 48, and cut build hours by 45 percent.

Mechanical Engineering. 1998;120(10):88-91. doi:10.1115/1.1998-OCT-5.

This article discusses that ozone levels in the Arctic and Antarctic should begin to recover due to reductions in chlorofluorocarbon production, but greenhouse warming may exacerbate losses of the gas in the polar region. It is important to understand the life cycle of ozone molecules because it plays such a vital role in screening harmful ultraviolet radiation. The concentrations of certain gases, such as these highly reactive chlorine compounds, have a critical effect on ozone levels. The chlorine found in the stratosphere comes principally from chlorofluorocarbons (CFC). A CFC release becomes well mixed throughout the troposphere in about one year. The CFCs, which enter the stratosphere from the tropical upper-troposphere region, have been measured by the Cryogenic Limb Array Etalon Spectrometer on the Upper Atmosphere Research Satellite (UARS). Recent research has suggested that greenhouse warming may lead to significant cooling of the polar region. If so, this cooling may exacerbate ozone losses despite decreasing chlorine and bromine levels.

Mechanical Engineering. 1998;120(10):92-95. doi:10.1115/1.1998-OCT-6.

The driving forces in refrigerant development and selection are varied and sometimes conflicting; however, several options are currently available that consider all aspects of the refrigeration system. There are five major factors that design engineers must consider in selecting a refrigerant for a particular application: performance, safety, reliability, environmental acceptability, and simple economics. The reliability of a refrigeration system depends to a large extent on the chemical stability of the refrigerant and its compatibility with the various system components and the compressor lubricant. Among several groups of alternatives, two—the hydrochlorofluorocarbons (HCFCs) and the hydrofluorocarbons (HFCs)—are the most useful. One of the major challenges in identifying halocarbon alternatives to ozone-depleting substances is to strike a balance between the various affecting factors. In the United States, there is considerable resistance to use of hydrocarbons or ammonia in applications that use halocarbons. This is due to liability concerns arising from their flammability and, in the case of ammonia, also toxicity.

Mechanical Engineering. 1998;120(10):96-99. doi:10.1115/1.1998-OCT-7.

This article explains that substances such as air, water, ammonia, hydrocarbons, and carbon dioxide may provide solutions to the problem of finding environmentally acceptable refrigerants. The search for new and environmentally benign refrigerants to replace the existing chlorofluorocarbons (CFC) and hydrochlorofluorocarbons (HCFC) has led to the introduction of hydrofluorocarbons (HFC). HFCs could be useful as short- and mid-term replacements, but may ultimately not be suitable, owing to their high global-warming potential (GWP). Natural refrigerants still have several technical and safety challenges to overcome, and each has its unique advantages and disadvantages. Refrigerant, carbon dioxide offers a clear advantage over CFCs and HCFCs from the environmental impact standpoint. In addition to its environmental advantages, carbon dioxide also offers certain attractive thermal characteristics that can help it provide substantial potential as a long-term replacement if energy efficiency challenges can be addressed.

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