Modeling and Control of Robot-Structure Coupling During In-Space Structure Assembly

This paper considers the problem of robot-structure coupling dynamics during in-space robotic assembly of large flexible structures. A two-legged walking robot is used as a construction agent, whose primary goal is to stably walking on the flexible structure while carrying a substructure component to a designated location. The reaction forces inserted by the structure to the walking robot are treated as bounded disturbance inputs, and a trajectory tracking robotic controller is proposed that combines the standard full state feedback motion controller and an adaptive controller to account for the disturbance inputs. In this study, a reduced-order Euler-Bernoulli beam structure model is adapted, and a finite number of co-located sensors and actuators are distributed along the span of the beam structure. The robot-structure coupling forces are treated as a bounded external forcing function to the structure, and hence an output covariance constraint problem can be formulated, in terms of linear matrix inequality, for optimal structure control by utilizing the direct output feedback controllers. The numerical simulations show the effectiveness of the proposed robot-structure modeling and control methodology

Guidance and Control Architecture Design and Demonstration for Low Ballistic Coefficient Atmospheric Entry

We propose to develop a robust guidance and control system for the ADEPT (Adaptable Deployable Entry and Placement Technology) entry vehicle. A control-centric model of ADEPT will be developed to quantify the performance of candidate guidance and control architectures for both aerocapture and precision landing missions. The evaluation will be based on recent breakthroughs in constrained controllability/reachability analysis of control systems and constrained-based energy-minimum trajectory optimization for guidance development operating in complex environments

Sedimentology, Diagenesis and Reservoir Characteristics of Eocene Carbonates Sirt Basin, Libya

ABSTRACT The reservoir quality of Middle Eocene carbonates in the intracratonic Sirt Basin (at the northern margin of the African continent) is strongly influenced by depositional facies and various diagenetic modifications. This thesis investigates the petrography, sedimentology, diagenetic evolution and hydrocarbon potential of the Middle Eocene Gialo Formation in the subsurface of the north-central Sirt Basin based on data from core samples and well logs from five boreholes in the Assumood and Sahl gas-fields. Reducing risk in exploration demands an understanding of reservoir facies development, which is governed by the type and distribution of depositional facies and their diagenetic history. Seven major carbonate facies (and 20 microfacies) have been identified in this study and are interpreted as predominantly deposited under shallow-marine conditions within the photic zone, as indicated from their richness in phototrophic fauna and flora. These include lagoon (back-bank), main bank, fore-bank and open-marine facies, all of which were deposited on a homoclinal ramp type of carbonate platform. The type and distribution of the Gialo depositional facies were influenced by basin-floor architecture and environmental controls. The basin floor was shaped through pre-Eocene structural development into a series of elevated platforms and deep troughs. Platform facies were deposited across three broad facies belts: (1) inner-ramp, dominated by dasycladacean molluscan wackestone/packstone, nummulitic-bryozoan packstone, bryozoan wackestone; (2) mid-ramp, dominated by nummulitic packstone and Discocyclina-nummulitic wackestone; and (3) outer-ramp, dominated by fragmented nummulitic packstone. Troughs were dominated by thick successions of lime mudstone containing rare fine skeletal fragments and nummulites, with deposition taking place in a deeper-marine environment, below the photic zone. Present-day reservoir characteristics of the Gialo Formation are the net result of modification to the original depositional characteristics caused by diagenesis. This diagenesis took place on the seafloor, under burial, and in the meteoric diagenetic environment. Early marine diagenetic processes affecting the Middle Eocene Gialo carbonates resulted in micritization of bioclasts. Later diagenesis in meteoric to burial environments resulted in dissolution of aragonitic bioclasts, cementation (syntaxial overgrowths on echinoid grains, and blocky to equant, non-ferroan cements), neomorphism, pressure dissolution, compaction and fracturing. δ18O and δ13C values in the Gialo Formation range between -1.06 and -4.16‰ PDB, and 0.76 and 1.89‰ PDB, respectively. These values are mostly marine values, although some alteration is likely. The more negative oxygen of the cements suggests precipitation within the shallow-burial environment under the influence of meteoric water and / or precipitation at higher temperatures during further burial. The carbon isotopic signatures are typical marine values. There is a strong relationship between porosity and the diagenetic processes that-affected the Gialo sediments. Generally the porosity in the Assumood and Sahl fields is either primary or secondary, enhanced by dissolution and fracturing of the sediments. Reduction in porosity in the investigated sediments is mainly due to cementation and compaction. The common pore-types in the Gialo Formation are intergranular, moldic, intragranular, vuggy and scattered fractures. Porosity ranges from poor to very good (<1% to ~37%) and permeability varies from low to high (<1mD to 100mD). These variations in porosity and permeability are strongly related to facies changes, which were influenced by depositional environment and diagenetic processes. Shallow-water packstones/rudstones containing both primary intergranular and secondary biomouldic porosity have the best reservoir quality. The Gialo Formation is an important gas producing reservoir in the Assumood, Sahl and other surrounding fields. The gas which is generated from the gas-prone Sirt Shale source rock of the northern Ajdabiya Trough possibly migrated onto the Assumood Ridge from the northeast through late Cretaceous, Paleocene and early Eocene carbonates, before being trapped beneath the Augila Shale (Upper Eocene) which is the principal regional seal in the area. This integrated study has helped to understand the reservoir heterogeneity and potential of the Gialo carbonates and based on this current wells are being completed appropriately, as, hopefully, will future wells too. The facies pattern is different from one well to another, which does suggest that there was a strong tectonic control, that is differential tectonic subsidence and/or fault control, or that deposition was controlled by autocyclic processes. The different vertical positions and numbers of transgressive-regressive cycles in each well make formation-wide correlation problematic. The lack of correlation in terms of cycle thickness, as well as facies, between wells, also suggests autocyclic processes. Third and fourth-order relative sea-level (RSL) changes do not appear to have been a major control on deposition during this Middle Eocene time.

Metagenomic-based Surveillance of Pacific Coast tick Dermacentor occidentalis Identifies Two Novel Bunyaviruses and an Emerging Human Ricksettsial Pathogen.

An increasing number of emerging tick-borne diseases has been reported in the United States since the 1970s. Using metagenomic next generation sequencing, we detected nucleic acid sequences from 2 novel viruses in the family Bunyaviridae and an emerging human rickettsial pathogen, Rickettsia philipii, in a population of the Pacific Coast tick, Dermacentor occidentalis in Mendocino County sampled annually from 2011 to 2014. A total of 250 adults of this human-biting, generalist tick were collected from contiguous chaparral and grassland habitats, and RNA from each individually extracted tick was deep sequenced to an average depth of 7.3 million reads. We detected a Francisella endosymbiont in 174 ticks (70%), and Rickettsia spp. in 19 ticks (8%); Rickettsia-infected ticks contained R. rhipicephali (16 of 250, 6.4%) or R. philipii (3 of 250,1.2%), the agent of eschar-associated febrile illness in humans. The genomes of 2 novel bunyaviruses (&gt;99% complete) in the genera Nairovirus and Phlebovirus were also identified and found to be present in 20-91% of ticks, depending on the year of collection. The high prevalence of these bunyaviruses in sampled Dermacentor ticks suggests that they may be viral endosymbionts, although further studies are needed to determine whether they are infectious for vertebrate hosts, especially humans, and their potential role in tick ecology

Aeroelastic Wing Shaping Control Subject to Actuation Constraints.

This paper considers the control of coupled aeroelastic aircraft model which is configured with Variable Camber Continuous Trailing Edge Flap (VCCTEF) system. The relative deflection between two adjacent flaps is constrained and this actuation constraint is accounted for when designing an effective control law for suppressing the wing vibration. A simple tuned-mass damper mechanism with two attached masses is used as an example to demonstrate the effectiveness of vibration suppression with confined motion of tuned masses. In this paper, a dynamic inversion based pseudo-control hedging (PCH) and bounded control approach is investigated, and for illustration, it is applied to the NASA Generic Transport Model (GTM) configured with VCCTEF system

LMI-Based Fuzzy Optimal Variance Control of Airfoil Model Subject to Input Constraints

This paper presents a study of fuzzy optimal variance control problem for dynamical systems subject to actuator amplitude and rate constraints. Using Takagi-Sugeno fuzzy modeling and dynamic Parallel Distributed Compensation technique, the stability and the constraints can be cast as a multi-objective optimization problem in the form of Linear Matrix Inequalities. By utilizing the formulations and solutions for the input and output variance constraint problems, we develop a fuzzy full-state feedback controller. The stability and performance of the proposed controller is demonstrated through its application to the airfoil flutter suppression

Relationship between Weather, Traffic and Delay Based on Empirical Methods

The steady rise in demand for air transportation over the years has put much emphasis on the need for sophisticated air traffic flow management (TFM) within the National Airspace System (NAS). The NAS refers to hardware, software and people, including runways, radars, networks, FAA, airlines, etc., involved in air traffic management (ATM) in the US. One of the metrics that has been used to assess the performance of NAS is the actual delays provided through FAA's Air Traffic Operations Network (OPSNET). The OPSNET delay data includes those reportable delays, i.e. delays of 15 minutes or more experienced by Instrument Flight Rule (IFR) flights, submitted by the FAA facilities. These OPSNET delays are caused by the application of TFM initiatives in response to, for instance, weather conditions, increased traffic volume, equipment outages, airline operations, and runway conditions. TFM initiatives such as, ground stops, ground delay programs, rerouting, airborne holding, and miles-in-trail restrictions, are actions which are needed to control the air traffic demand to mitigate the demand-capacity imbalance due to the reduction in capacity. Consequently, TFM initiatives result in NAS delays. Of all the causes, weather has been identified as the most important causal factor for NAS delays. Therefore, in order to accurately assess the NAS performance, it has become necessary to create a baseline for NAS performance and establish a model which characterizes the relation between weather and NAS delays

Attitude Control System Design for CubeSats Configured with Exo-Brake Parachute

This paper develops a novel attitude control strategy for an Earth orbiting CubeSat spacecraft by utilizing the exo-brake parachute to modulate the atmospheric drag forces as a source of attitude control authority, enabling orbital exo-sail maneuvers. In particular, the spacecraft attitude controls can be realized through the two dimensional exo-sail maneuvers in pitch and yaw directions. The uncertain atmospheric drag induced disturbance torque is estimated through an adaptive parameter estimation process which makes use of the adaptive least-squares minimization techniques. The covariance updating law with a variable forgetting factor is adopted and it can be shown that the convergent rate for the estimation errors can be chosen at the same level as the forgetting factor, in order to meet the design needs. The proposed approach is best suited for Earth orbiting micronano-satellite applications, which are configured with exo-brake parachute. With integration of exo-sail actuation mechanism and disturbance estimation, we demonstrate through simulations that exo-sail induced control torque for CubeSat attitude maneuver is feasible

How to Improve Pavement Life Cycle Cost Analysis: A Case Study of Minnesota

Life cycle cost analysis (LCCA) frameworks are used by some transportation agencies for economic assessment, but there have been challenges implementing the approach, particularly in the characterization of initial and future costs of materials, as well as their associated uncertainties. This research brief presents a case study which focused on characterizing initial and future pay item costs as a function of project size for a probabilistic LCCA of the entire life cycle including user cost impacts.This research was carried out by the CSHub@MIT with sponsorship provided by the Portland Cement Association and the Ready Mixed Concrete Research & Education Foundation. CSHub@MIT is solely responsible for content

Adaptive Disturbance Torque Estimation for Orbiting Spacecraft Using Recursive Least-Squares Methods

This paper develops a novel disturbance torque estimator for an orbiting spacecraft by using the adaptive least-squares parameter estimation technique. The disturbance estimation is first formulated as an adaptive least-squares minimization problem using a set of polynomial functions and then integrated with the feedback momentum estimator. The covariance update law with a variable forgetting factor is used, and it is shown that the convergent rate for estimation errors can be made at the same level as the forgetting factor. The proposed approach is particularly suited for orbiting small or microsatellite applications, where the momentum management capacity is often limited. The onboard estimated disturbance torque input can then be used as a part of control resource for spacecraft momentum management. The simulation results demonstrate the efficacy of the proposed concept