Limited Bandwidth Wireless Communication Strategies for Structural Control of Seismically Excited Shear Structures

Structural control is used to mitigate unwanted vibrations in structures when large excitations occur, such as high winds and earthquakes. To increase reliability and controllability in structural control applications, engineers are making use of semi-active control devices. Semi-active control gives engineers greater control authority over structural response versus passive controllers, but are less expensive and more reliable than active devices. However, the large numbers of actuators required for semi-active structural control networks introduce more cabling within control systems leading to increased cost. Researchers are exploring the use of wireless technology for structural control to cut down on the installation cost associated with cabling. However wireless communication latency (time delays in data transmissions) can be a barrier to full acceptance of wireless technology for structural control. As the number of sensors in a control network grows, it becomes increasingly difficult to transmit all sensor data during a single control step over the fixed wireless bandwidth. Because control force calculations rely on accurate state measurements or estimates, the use of strategic bandwidth allocation becomes more necessary to provide good control performance. The traditional method for speeding up the control step in larger wireless networks is to spatially decentralize the network into multiple subnetworks, sacrificing communication for speed. This dissertation seeks to provide an additional approach to address the issue of communication latency that may be an alternative, or even a supplement, to spatial decentralization of the control network. The proposed approach is to use temporal decentralization, or the decentralization of the control network over time, as opposed to space/location. Temporal decentralization is first presented with a means of selecting and evaluating different communication group sizes and wireless unit combinations for staggered temporal group communication that still provide highly accurate state estimates. It is found that, in staggered communication schemes, state estimation and control performance are affected by the network topology used at each time step with some sensor combinations providing more useful information than others. Sensor placement theory is used to form sensor groups that provide consistently high-quality output information to the network during each time step, but still utilize all sensors. If the demand for sensors to communicate data outweighs the available bandwidth, traditional temporal and spatial approaches are no longer feasible. This dissertation examines and validates a dynamic approach for bandwidth allocation relying on an extended, autonomous and controller-aware, carrier sense multiple access with collision detection (CSMA/CD) protocol. Stochastic parameters are derived to strategically alter back-off times in the CSMA/CD algorithm based on nodal observability and output estimation error. Inspired by data fusion approaches, this second study presents two different methods for neighborhood state estimation using a dynamic form of measurement-only fusion. To validate these wireless structural control approaches, a small-scale experimental semi-active structural control testbed is developed that captures the important attributes of a full-scale structure

STRUCTURAL CONTROL OF A SMALL-SCALE TEST-BED SHAKER STRUCTURE USING A SPONGE-TYPE MAGNETO-RHEOLOGICAL FLUID DAMPER

Semi-active damping devices have been shown to be effective in mitigating unwanted vibrations in civil structures. These devices impart force indirectly through real-time alterations to structural properties. Simulating the complex behavior of these devices for laboratory-scale experiments is a major challenge. Commercial devices for seismic applications typically operate in the 2-10 kN range; this force is too high for small-scale testing applications where requirements typically range from 0-10 N. Several challenges must be overcome to produce damping forces at this level. In this study, a small-scale magneto-rheological (MR) damper utilizing a fluid absorbent metal foam matrix is developed and tested to accomplish this goal. This matrix allows magneto-rheological (MR) fluid to be extracted upon magnetic excitation in order to produce MR-fluid shear stresses and viscosity effects between an electromagnetic piston, the foam, and the damper housing. Dampers for uniaxial seismic excitation are traditionally positioned in the horizontal orientation allowing MR-fluid to gather in the lower part of the damper housing when partially filled. Thus, the absorbent matrix is placed in the bottom of the housing relieving the need to fill the entire device with MR-fluid, a practice that requires seals that add significant unwanted friction to the desired low-force device. The damper, once constructed, can be used in feedback control applications to reduce seismic vibrations and to test structural control algorithms and wireless command devices. To validate this device, a parametric study was performed utilizing force and acceleration measurements to characterize damper performance and controllability for this actuator. A discussion of the results is presented to demonstrate the attainment of the damper design objectives

Fungal Fruiting and Dispersal Following Timber Harvest

Forest-dwelling fungi are critical to ecosystem function in their roles as decomposers and nutrient cyclers, food sources, pathogens, and mycorrhizal symbionts. In northern New England, a region with a substantial timber industry, the degree to which fungal communities are resilient to timber harvest, as well as their ability to recolonize post-disturbance, may impact ecosystem function and forest regeneration. In this thesis, we investigate the impacts of (1) timber harvest on fungal fruiting, an important element of fungal reproduction, and (2) the dispersal mechanisms by which fungi may re-colonize harvested areas. In Chapter 1, we investigate the impact of timber harvest on epigeous fungal fruiting patterns. Fruiting has important impacts on fungal reproduction and ecosystem function. Forest disturbances such as timber harvest impact moisture, host availability, and substrate availability, which in turn may drive changes in fungal fruiting patterns and community structure. We surveyed mushrooms in 0.4-ha patch cuts (18 months post-harvest) and adjacent intact hardwood forest in northern New Hampshire, USA, to document the effects of timber harvest on summer fruiting richness, biomass, diversity, and community structure of ectomycorrhizal, parasitic, and x saprobic mushroom taxa. Fungal fruiting richness, diversity, and community heterogeneity were greater in intact forests than patch cuts. Among functional groups, ectomycorrhizal fruiting richness, diversity, and biomass were greater in unharvested areas than in the patch cuts, but parasitic and saprobic fruiting did not differ statistically between the two forest conditions. Our findings suggest that timber harvest simplifies fungal fruiting communities shortly after harvest, in particular triggering declines in ectomycorrhizal taxa which are important symbionts facilitating tree establishment and regeneration. Multi-aged silvicultural practices that maintain mature forest conditions adjacent to and throughout harvested areas through deliberate retention of overstory trees and downed woody material may promote fungal fruiting diversity in regenerating stands. In Chapter 2, we compare fungal spore dispersal between wind and small mammals. Spore dispersal has important impacts on fungal diversity and ecosystem function. Dispersal can occur via several mechanisms, but wind is perhaps the best-studied and is often assumed to be the primary dispersal mechanism for most aboveground fungi. Mycophagy is another commonly reported dispersal mechanism, particularly as performed by small mammals, which are often speciose and abundant in forested systems. Few studies directly compare wind- and mammalfacilitated spore dispersal. Thus, it is unclear whether these pathways are complementary or redundant in the taxa they disperse and the ecosystem functions they provision. Here we compare the diversity and morphology of fungi dispersed by wind and three species of small mammals (Myodes gapperi, Napaeozapus insignis, and Tamias striatus) in recently harvested patch cuts using a combination of microscopy and Illumina sequencing. We demonstrate that fungal communities dispersed by wind and small mammals differ in taxonomy and species xi richness, as well as functional group membership. A large proportion of wind-dispersed spores belong to wood saprotrophs, litter saprotrophs, mycoparasites, and plant pathogens, whereas most spores dispersed in mammal scat come from mycorrhizal and unspecified saprotrophic taxa. We note substantial dispersal of truffles, mushrooms, AM sporocarps, jellies, and crusts by small mammals. In addition, we find that mammal-dispersed spores are larger on average than wind-dispersed spores, but do not differ in melanization or the presence of ornamentation. We quantify dispersal distances of small mammals by modeling home range and core area size using kernel density estimators from mark-recapture survey data, finding the distance to be comparable to those reported in the literature for wind-based dispersal. Our findings suggest that wind- and small mammal-facilitated dispersal are complementary processes, which highlights the importance of maintaining robust small mammal communities, particularly following timber harvest

Re-entrant magnetic field induced charge and spin gaps in the coupled dual-chain quasi-one dimensional organic conductor Perylene2_2[Pt(mnt)2_2]

An inductive method is used to follow the magnetic field-dependent susceptibility of the coupled charge density wave (CDW) and spin-Peierls (SP) ordered state behavior in the dual chain organic conductor Perylene$_2$[Pt(mnt)$_2$]. In addition to the coexisting SP-CDW state phase below 8 K and 20 T, the measurements show that a second spin-gapped phase appears above 20 T that coincides with a field-induced insulating phase. The results support a strong coupling of the CDW and SP order parameters even in high magnetic fields, and provide new insight into the nature of the magnetic susceptibility of dual-chain spin and charge systems.Comment: 6 pages, 6 figure

Reverse-engineering of the rule-of-half in order to retrofit an assessment procedure based on resource consumption

The German evaluation procedure for the Federal Transport Infrastructure Plan (‘Bun-desverkehrswegeplan’) is a large-scale and comprehensive modeling, simulation, and eval-uation effort. An important component of the evaluation procedure is a cost-benefit analy-sis, based on the concept of resource consumption. This concept means that new transport infrastructure causes changes in the consumption of time, money, safety, environment, etc. In this paper, we show that — assuming elastic demand for the facility under consideration — the current approach is not in line with basic consumer theory. This stems from incon-sistencies between the behavioral model and the evaluation method: ignoring unobserved attributes of the different transport modes in the evaluation can lead to quite different eco-nomic gains than when these attributes are considered. Current practice in other EU coun-tries avoids this problem typically by applying the so-called rule-of-half, or by directly deriving the logsum term from the underlying logit model. However, a change in the Ger-man assessment procedure towards one of these best-practice approaches for the upcoming Federal Transport Infrastructure Plan in 2015 seems politically not feasible. We therefore propose an easily applicable procedure to include the logic of the rule-of-half into the exist-ing evaluation approach. We show that the resulting calculation yields the same result as the rule-of-half while maintaining the rest of the former evaluation method. Finally, we discuss how another German assessment scheme for urban public transit projects, which is currently under revision, fits into the proposed procedure.BMVBS, 960974/2011, Review and further development of the assessment methodology with a focus on the benefits components of the benefit-cost-analysis of the German national transport assessment exerciseDFG, 92485222, Detaillierte Evaluation verkehrlicher Maßnahmen mit Hilfe von Mikrosimulatio

Watseka Affordable Housing

Students will design a small residential dwelling that will fit into the affordable housing development currently under consideration in Watseka.  The design will include architectural, structural, mechanical, and electrical design.  Substantial completion of design documents is required