Liquid rocket metal tanks and tank components

Significant guidelines are presented for the successful design of aerospace tanks and tank components, such as expulsion devices, standpipes, and baffles. The state of the art is reviewed, and the design criteria are presented along with recommended practices. Design monographs are listed

The Palomar Testbed Interferometer

The Palomar Testbed Interferometer (PTI) is a long-baseline infrared interferometer located at Palomar Observatory, California. It was built as a testbed for interferometric techniques applicable to the Keck Interferometer. First fringes were obtained in July 1995. PTI implements a dual-star architecture, tracking two stars simultaneously for phase referencing and narrow-angle astrometry. The three fixed 40-cm apertures can be combined pair-wise to provide baselines to 110 m. The interferometer actively tracks the white-light fringe using an array detector at 2.2 um and active delay lines with a range of +/- 38 m. Laser metrology of the delay lines allows for servo control, and laser metrology of the complete optical path enables narrow-angle astrometric measurements. The instrument is highly automated, using a multiprocessing computer system for instrument control and sequencing.Comment: ApJ in Press (Jan 99) Fig 1 available from http://huey.jpl.nasa.gov/~bode/ptiPicture.html, revised duging copy edi

Advances in System Identification and Stochastic Optimization

This work studies the framework of systems with subsystems, which has numerous practical applications, including system reliability estimation, sensor networks, and object detection. Consider a stochastic system composed of multiple subsystems, where the outputs are distributed according to many of the most common distributions, such as Gaussian, exponential and multinomial. In Chapter 1, we aim to identify the parameters of the system based on the structural knowledge of the system and the integration of data independently collected from multiple sources. Using the principles of maximum likelihood estimation, we provide the formal conditions for the convergence of the estimates to the true full system and subsystem parameters. The asymptotic normalities for the estimates and their connections to Fisher information matrices are also established, which are useful in providing the asymptotic or finite-sample confidence bounds. The maximum likelihood approach is then connected to general stochastic optimization via the recursive least squares estimation in Chapter 2. For stochastic optimization, we consider minimizing a loss function with only noisy function measurements and propose two general-purpose algorithms. In Chapter 3, the mixed simultaneous perturbation stochastic approximation (MSPSA) is introduced, which is designed for mixed variable (mixture of continuous and discrete variables) problems. The proposed MSPSA bridges the gap of dealing with mixed variables in the SPSA family, and unifies the framework of simultaneous perturbation as both the standard SPSA and discrete SPSA can now be deemed as two special cases of MSPSA. The almost sure convergence and rate of convergence of the MSPSA iterates are also derived. The convergence results reveal that the finite-sample bound of MSPSA is identical to discrete SPSA when the problem contains only discrete variables, and the asymptotic bound of MSPSA has the same order of magnitude as SPSA when the problem contains only continuous variables. In Chapter 4, the complex-step SPSA (CS-SPSA) is introduced, which utilizes the complex-valued perturbations to improve the efficiency of the standard SPSA. We prove that the CS-SPSA iterates converge almost surely to the optimum and achieve an accelerated convergence rate, which is faster than the standard convergence rate in derivative-free stochastic optimization algorithms

Marshall Space Flight Center Research and Technology Report 2019

Today, our calling to explore is greater than ever before, and here at Marshall Space Flight Centerwe make human deep space exploration possible. A key goal for Artemis is demonstrating and perfecting capabilities on the Moon for technologies needed for humans to get to Mars. This years report features 10 of the Agencys 16 Technology Areas, and I am proud of Marshalls role in creating solutions for so many of these daunting technical challenges. Many of these projects will lead to sustainable in-space architecture for human space exploration that will allow us to travel to the Moon, on to Mars, and beyond. Others are developing new scientific instruments capable of providing an unprecedented glimpse into our universe. NASA has led the charge in space exploration for more than six decades, and through the Artemis program we will help build on our work in low Earth orbit and pave the way to the Moon and Mars. At Marshall, we leverage the skills and interest of the international community to conduct scientific research, develop and demonstrate technology, and train international crews to operate further from Earth for longer periods of time than ever before first at the lunar surface, then on to our next giant leap, human exploration of Mars. While each project in this report seeks to advance new technology and challenge conventions, it is important to recognize the diversity of activities and people supporting our mission. This report not only showcases the Centers capabilities and our partnerships, it also highlights the progress our people have achieved in the past year. These scientists, researchers and innovators are why Marshall and NASA will continue to be a leader in innovation, exploration, and discovery for years to come

Harnessing the Mechanics of Thin-Walled Metallic Structures: from Plate-Lattice Materials to Cold-Formed Steel Shear Walls

Thin-walled structures have received a lot of interest during the last years due to their light weight, cost efficiency, and ease in fabrication and transportation, along with their high strength and stiffness. This dissertation focuses on the mechanical performance of thin-walled metallic structures from cold-formed steel shear walls and connections (PART I) to plate-lattice architected materials (PART II) via computational, experimental, and probabilistic methods. Cold-formed steel (CFS) shear walls subjected to seismic loads is the focus of PART I of this dissertation. An innovative three-dimensional shell finite element model of oriented strand board (OSB) sheathed CFS shear walls is introduced and benchmarked by nine different experimental studies. Particular attention is given to the fastener behavior since they are governed by significant inherent variability and they represent a dominant failure mechanism in CFS shear walls. Shear fastener behavior is experimentally determined and introduced into the finite element approach. To further address the connection variability, an extensive parametric analysis accompanied by Monte Carlo simulations are conducted. Design recommendations for higher capacity sheathings (fiber cement board (FCB) and steel-gypsum (SG) composite board) that are not currently enabled in design specifications are also introduced. Architected plate-lattice materials subjected to uniaxial compression is the focus of PART II of this dissertation. Architected materials are structures whose mechanical performance is governed by their geometry rather than their constituent material. Plate-lattices are composed of plates along the planes of crystalline structures. They represent the stiffest and strongest existing materials, since they can reach the Hashin-Shtrikman and the Suquet upper bounds. The stability and imperfection sensitivity of plate-lattices are evaluated in this work via elastic and plastic shell finite element analyses. Plate-lattice geometries of cubic symmetry are examined, such as the simple cubic (SC), the body-centered cubic (BCC), the face-centered cubic (FCC) structures and their combinations (SC-BCC, SC-FCC) over a range of relative densities between $\rho$*=0.5\% and $\rho$*=25\%. Imperfections are characterized by modal shapes at five different imperfection amplitudes. Finally, knockdown factors are recommended for these metamaterials

Lateral capacity and seismic characteristic of hybrid cold formed and hot rolled steel systems

This thesis addresses the application of hybrid cold-formed steel (CFS) - Hot-Rolled Steel (HRS) structures, as a new lateral force resisting system for light weight steel framed buildings in seismic regions. The study considers hysteretic behaviour, as well as maximum lateral load resisting capacity through comprehensive testing and advanced numerical analyses. The study identifies the advantages and disadvantages of the proposed hybrid system and provides in depth knowledge about performance characteristics of this innovative structural system, in order to facilitate the use of this system in earthquake-prone regions. The project is divided into three main parts: experimental, numerical and analytical studies. A comprehensive literature review is performed as a part of this study, in order to discover the existing gaps in the current knowledge regarding the structural performance of CFS structures and the methods for lateral performance enhancement. The literature review suggests that although CFS walls are not new, and have been used as non-structural components for many years, their application as main load-bearing structural frames is relatively new. That is, appropriate guidelines that address the seismic design of CFS structures have not yet been fully developed in the literature. In addition, the lateral design of these systems is not adequately detailed in the available standards of practice. There have been several attempts to improve the seismic performance of such structural system by different bracing or sheathing configurations. However, there is minimal background information available on hybrid systems such as hot rolled-cold formed structures. In this study, a series of CFS-HRS hybrid shear walls are constructed in order to investigate the lateral behaviour of the walls with different configurations to obtain the optimum combination of HRS and CFS. Different configurations are considered to provide the most efficient load transfer pattern from cold formed steel part of the wall to the Hot Rolled section, which is responsible for withstanding the lateral loads. The CFS part is aimed to transfer lateral loads to HRS part without any internal local failure. The ideal failure condition is the HRS yielding. Therefore, the optimum rigidity of the HRS part is of great importance to prevent any local failure happening prior to reaching the maximum lateral capacity of the HRS. For each experimental specimen, the hysteretic envelope curve is plotted, and different characteristics are evaluated. Since the failure mode of such systems is very complicated, the test results will provide the possible failure modes to be utilised for any further investigation or any optimisation analysis in numerical and analytical studies. In addition, Non-linear finite element (FE) analysis is employed using the ABAQUS software [1], in order to investigate the seismic performance of the proposed hybrid shear walls in multi-storey light steel frames. The nonlinear analysis accounts for different structural characteristics, including material non-linearity, geometric imperfection and residual stresses. The numerical models are verified based on experimental test results. The principal objective of this part of the study is aseismic optimisation of the proposed hybrid system and finding the corresponding dimensions and configurations to improve the strength and stiffness to achieve the objective. Using the hybrid wall panel system, a 4-storey building in an earthquake prone region is designed as per the relevant codes of practice. For the designed 4-storey building, the CFS part of the panel only bears the gravity loads, while a hot rolled steel collector transfers the lateral load to the HRS part acting as the main lateral load resisting system. Finally, the building is designed using different lateral load resisting systems and the results are compared with those from the proposed hybrid system in terms of cost. Furthermore, based on the real failure mode shapes obtained from test specimens, a Finite Strip Method program is developed to evaluate the elastic buckling mode shapes of a single stud with an arbitrary section detail. The code is helpful for design of CFS studs as explained in Chapters 3 and 5

Design of a pressurized lunar rover

A pressurized lunar rover is necessary for future long-term habitation of the moon. The rover must be able to safely perform many tasks, ranging from transportation and reconnaissance to exploration and rescue missions. Numerous designs were considered in an effort to maintain a low overall mass and good mobility characteristics. The configuration adopted consists of two cylindrical pressure hulls passively connected by a pressurized flexible passageway. The vehicle has an overall length of 11 meters and a total mass of seven metric tons. The rover is driven by eight independently powered two meter diameter wheels. The dual-cylinder concept allows a combination of articulated frame and double Ackermann steering for executing turns. In an emergency, the individual drive motors allow the option of skid steering as well. Two wheels are connected to either side of each cylinder through a pinned bar which allows constant ground contact. Together, these systems allow the rover to easily meet its mobility requirements. A dynamic isotope power system (DIPS), in conjunction with a closed Brayton cycle, supplied the rover with a continuous supply of 8.5 kW. The occupants are all protected from the DIPS system's radiation by a shield of tantalum. The large amount of heat produced by the DIPS and other rover systems is rejected by thermal radiators. The thermal radiators and solar collectors are located on the top of the rear cylinder. The solar collectors are used to recharge batteries for peak power periods. The rover's shell is made of graphite-epoxy coated with multi-layer insulation (MLI). The graphite-epoxy provides strength while the thermally resistant MLI gives protection from the lunar environment. An elastomer separates the two materials to compensate for the thermal mismatch. The communications system allows for communication with the lunar base with an option for direct communication with earth via a lunar satellite link. The various links are combined into one signal broadcast in the S-band at 2.3 GHz. The rover is fitted with a parabolic reflector disk for S-band transmission, and an omnidirectional antenna for local extravehicular activity (EVA) communication. The rover's guidance, navigation, and control subsystem consists of an inertial guidance system, an orbiting lunar satellite, and an obstacle avoidance system. In addition, the rover is equipped with a number of external fixtures including two telerobotic arms, lights, cameras, EVA storage, manlocks, a docking fixture, solar panels, thermal radiators, and a scientific airlock. In conclusion, this rover meets all of the design requirements and clearly surpasses them in the areas of mobility and maneuverability

Model Validation and Simulation

The Bauhaus Summer School series provides an international forum for an exchange of methods and skills related to the interaction between different disciplines of modern engineering science. The 2012 civil engineering course was held in August over two weeks at Bauhaus-Universität Weimar. The overall aim was the exchange of research and modern scientific approaches in the field of model validation and simulation between well-known experts acting as lecturers and active students. Besides these educational intentions the social and cultural component of the meeting has been in the focus. 48 graduate and doctoral students from 20 different countries and 22 lecturers from 12 countries attended this summer school. Among other aspects, this activity can be considered successful as it raised the sensitivity towards both the significance of research in civil engineering and the role of intercultural exchange. This volume summarizes and publishes some of the results: abstracts of key note papers presented by the experts and selected student research works. The overview reflects the quality of this summer school. Furthermore the individual contributions confirm that for active students this event has been a research forum and a special opportunity to learn from the experiences of the researchers in terms of methodology and strategies for research implementation in their current work