An engine trade study for a supersonic STOVL fighter-attack aircraft, volume 1

The best main engine for an advanced STOVL aircraft flight demonstrator was studied. The STOVL aircraft uses ejectors powered by engine bypass flow together with vectored core exhaust to achieve vertical thrust capability. Bypass flow and core flow are exhausted through separate nozzles during wingborne flight. Six near term turbofan engines were examined for suitability for this aircraft concept. Fan pressure ratio, thrust split between bypass and core flow, and total thrust level were used to compare engines. One of the six candidate engines was selected for the flight demonstrator configuration. Propulsion related to this aircraft concept was studied. A preliminary candidate for the aircraft reaction control system for hover attitude control was selected. A mathematical model of transfer of bypass thrust from ejectors to aft directed nozzle during the transition to wingborne flight was developed. An equation to predict ejector secondary air flow rate and ram drag is derived. Additional topics discussed include: nozzle area control, ejector to engine inlet reingestion, bypass/core thrust split variation, and gyroscopic behavior during hover

Alternate Materials for High-speed Projectile Casing

A high-speed projectile impact is a highly complex dynamic problem that can be simplified with the use of finite element analysis solvers. Abaqus/Explicit was used to evaluate the impact of various projectiles using a plane strain setup. Using a baseline stainless steel projectile, the proposed sandwich construction design was analyzed and compared to the baseline projectile. The overall goal was to see if a new composite casing could perform similarly to the simple baseline projectile. The sandwich construction used stainless steel, tungsten, and silicon-carbide reinforce aluminum as outer and inner shell materials. The core material was created using additive manufacturing of inconel 718. The inconel 718 core is a triply periodic minimal surface structure manufactured to provide the projectile casing with high stiffness and strength while reducing material used to manufacture it. A monolithic concrete target using a brittle cracking model for a projectile hitting a concrete wall in order to simulate a projectile impacting a bunker, road, or other concrete structure. Each projectile was evaluated using either the Johnson-Cook damage model or the Hashin damage model depending on if the shell materials were ductile metals or a metal matrix composite. By implementing the sandwich design, the negatives and benefits can be considered for mission feasibility

Modeling the change of stem form in plantations of young loblolly pine (Pinus teada)

When predicting future stand volumes using present mensurational methods, stem form is often considered as a static variable and thus ignored. This may lead to incorrect estimates since stem form may change during the time period considered. These changes can be further influenced by natural occurrences or by management practices such as thinning. The objectives of this study were to: (1) develop a model to describe the changes in stem form with age in a plantation, and (2) correlate the effects of age at which a loblolly pine (Pinus taeda L.) plantation was thinned with changes in form. The data used were obtained by stem analysis on randomly selected trees in a young loblolly pine plantation which had four thinning treatments: a control (with no thinning), and thinnings at ages 10, 15, and 20 years. Three types of models were used to describe the change in stem form. They consisted of past growth models, taper equations, and the use of the primary units of volume, surface, and length as predictors. The accuracy desired for the past growth models and the taper equations was the capacity to predict the radius inside bark at known heights within 0.25 of an inch 95 percent of the time. In the models using the primary units of volume, surface and length the desired accuracy was predicting these units in 1975 within 5 percent of the means 95 percent of the time. None of the models tested were able to describe the form of the whole length of the stem within the desired accuracy. However the model using the radius at breast height inside bark growth (1970 to 1975) was able to satisfactorily predict the form of the stem up to 50 percent of the total height of the tree. Evaluations of the taper equations showed that for the years 1970 and 1975 there were significant differences in the populations. For the year 1965 no significant differences were found, and evaluation of the regression equations showed no significant differences in stem form between the thinning regimes for that year. Thus it was concluded that thinning at age 10 had no significant effect on the change in stem form, but thinnings at ages 15 and 20 had a significant effect on the change in stem form. Models using the primary units of volume, surface, and length showed that surface and length could be predicted from past values of the primary units within reasonable limits. This was shown for both total (from stump height to the tip) and sectional (based on the tree being composed of bolts of a fixed length) values of the primary units. Predicting volume within reasonable limits was not possible for either total or sectional values. Evaluation of curves showing the change in Girard form class for ages 10 to 22, revealed that the older the stand when thinned the less pronounced is the reduction in the rate of natural increase of Girard form class with young trees overtime

Application of Optimization Techniques to Spectrally Modulated, Spectrally Encoded Waveform Design

A design process is demonstrated for a coexistent scenario containing Spectrally Modulated, Spectrally Encoded (SMSE) and Direct Sequence Spread Spectrum (DSSS) signals. Coexistent SMSE-DSSS designs are addressed under both perfect and imperfect DSSS code tracking conditions using a non-coherent delay-lock loop (DLL). Under both conditions, the number of SMSE subcarriers and subcarrier spacing are the optimization variables of interest. For perfect DLL code tracking conditions, the GA and RSM optimization processes are considered independently with the objective function being end-to-end DSSS bit error rate. A hybrid GA-RSM optimization process is used under more realistic imperfect DLL code tracking conditions. In this case, optimization is accomplished using a correlation degradation metric with the GA process being first applied to generate a “coarse” solution followed by RSM processing which provides the final optimized solution. This work has successfully expanded the practical utility of a previously developed tool, the original SMSE framework, by demonstrating a more efficient, structured means for coexistent waveform design that replaces previous trial and error methods

Feedback Control For Rob ot Formation Maneuvers

This paper develops control strategies for moving multiple-agents in formation, using a virtual structure. The controls are specifically applied to robots. by introducing feedback from the followers to the coordinating mechanism, the robots are shown to better coordinate their motion. Hardware results are presented