Search

This paper addresses the maintenance of a halo orbit around the L1 point of the Sun-Earth system in a circular restricted three-body problem. To this effect, a trajectory tracking problem is formulated and solved by designing various controllers using the linear quadratic method and Lyapunov stability theory. The linear quadratic formulations are performed using two approaches: the first one linearizes the equations of motion at several operating points, while the second approach uses a state-dependent coefficient system matrix that requires solving the state-dependent Riccati equation (SDRE). To handle the nonlinearity and to reduce the computational complexity as compared to the linear quadratic method, the controller is also derived using Lyapunov stability theory. The proposed controllers are tested for their effectiveness in reducing the orbit insertion errors as well as for disturbance rejection. The disturbances being considered are primarily due to the eccentricity of Earth's orbit around the Sun, solar radiation pressure, and the gravitational pull of the Moon. The simulation results are presented to delineate the performances of the proposed controllers. The superiority of a Lyapunov theory-based controller over the LQR-based controllers is demonstrated. [ABSTRACT FROM AUTHOR]

This study outlines a method for identifying high-quality recycled concrete aggregate (RCA) obtained after mechanical treatment. In the present approach, the physical and mechanical properties of RCA are considered as quality parameters. As a first step, mechanically treated (Los Angeles) RCA is produced with 28 combinations of charges and drum revolutions. Twenty-eight sets of mechanically treated RCA are produced, each with different physical and mechanical properties. Furthermore, the 28 sets of RCAs are compared using the performance-based quality optimization approach. The performance index for each set of RCAs is calculated applying a multicriteria decision-making approach named "technique for order of preference by similarity to ideal solution." This approach considers physical and mechanical properties as a response and the combination of charges and drum revolutions as alternatives to obtain the performance index of alternatives. Based on its performance, the leading rankings RCAs are selected for an experimental study to validate the methodology. As a result of RCA's optimized quality, recycled aggregate concrete (RAC) has excellent physical, mechanical, and durability characteristics that agree with natural aggregate concrete (NAC) composed of parent aggregate. The 28- and 91-day compressive strengths of RAC exceed those of NAC by 8.5% and 30.65%, respectively. Flexural strength, split tensile strength, fracture energy, ultrasonic pulse velocity (UPV) values, rapid chloride-ion penetration test values, water absorption, and abrasion resistance are comparable with NAC. The quality optimization approach identifies RCA with superior shape, texture, and elastic properties. An RCA with optimized qualities also strengthens the new interfacial transition zone and old interfacial transition zone as well as RAC's associated properties. The RAC's dynamic modulus of elasticity is superior to the reported values and is 0.95 fractions of NAC. Optimized quality of RCA reduces the sorptivity of RAC compared with the reported values. The RAC may not have equivalent sorptivity to NAC without lowering RCA parts, whether mortar-attached, mortar-covered, or mortar-only type aggregate or applying other treatments that may increase the production cost. This research presents a standard procedure for identifying mechanically treated recycled concrete aggregate with properties (physical properties and mechanical properties) similar to those of the parent aggregate (natural aggregate). The method demonstrated in this study may be adapted to real-life worksite conditions—but not exactly. In Los Angeles abrasion machines, recycled concrete aggregates obtained from a source can be processed by varying drum revolutions and charges. Based on the charges and drum revolutions selected for treatment, treated recycled concrete aggregate can be prepared with different sets of physical and mechanical properties. Based on the present research, the physical and mechanical properties of treated recycled concrete aggregate can be compared between these sets. In this way, recycled concrete aggregates can be produced that resemble their parent aggregates. Using this process, recycled concrete aggregates may be used to replace natural aggregates without compromising the concrete's physical, mechanical, or durability properties. [ABSTRACT FROM AUTHOR]