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Dynamic Modeling and Cascaded Control for a Multi-Evaporator Supermarket Refrigeration SystemGupta, Ankush 1986- 14 March 2013 (has links)
The survey from US Department of Energy showed that about one-third of energy consumption in US is due to air conditioning and refrigeration systems. This significant usage of electricity in the HVAC industry has prompted researchers to develop dynamic models for the HVAC components, which leads to implementation of better control and optimization techniques. In this research, efforts are made to model a multi-evaporator system. A novel dynamic modeling technique is proposed based on moving boundary method, which can be generalized for any number of evaporators in a vapor compression cycle. The models were validated experimentally on a commercial supermarket refrigeration unit. Simulation results showed that the models capture the major dynamics of the system in both the steady state and transient external disturbances. Furthermore the use of MEMS (microelectromechanical) based Silicon Expansion Valves (SEVs) have reportedly shown power savings as compared to the Thermal Expansion Valves (TEVs). Experimental tests were conducted on a supermarket refrigeration unit fitted with the MEMS valves to explain the cause of these potential energy savings. In this study an advanced cascaded control algorithm was also designed to control the MEMS valves. The performance of the cascaded control architecture was compared with the standard Thermal Expansion Valves (TEVs) and a commercially available Microstaq (MS) Superheat Controller (SHC). The results reveal that the significant efficiency gains derived on the SEVs are due to better superheat regulation, tighter superheat control and superior cooling effects in shorter time period which reduces the total run-time of the compressor. It was also observed that the duty cycle was least for the cascaded control algorithm. The reduction in duty cycle indicates early shut-off for the compressor resulting in maximum power savings for the cascaded control, followed by the Microstaq controller and then the Thermal Expansion Valves.
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An experimental and simulation based approach toward understanding the effects of obesity on balance recovery from a postural perturbationMatrangola, Sara Louise 17 October 2011 (has links)
Obesity is associated with an increased risk of falls and subsequent injury. Most falls result from some type of postural perturbation. As such, it is important to understand how obesity influences balance recovery from a postural perturbation. There is limited information on the effects of obesity on balance recovery, and the limited available information is ambiguous. Therefore, the purpose of the research within this dissertation was to investigate the effects of obesity on balance recovery after a postural perturbation in young adults to better understand how obesity contributes to fall risk.
Four separate studies make up this dissertation. The purpose of the first study was to investigate the effects of obesity on balance recovery ability using an ankle strategy in young adults. Normal-weight and obese participants recovered balance using an ankle strategy after three types of postural perturbations: an initial angular displacement, an initial angular velocity from the natural stance, and an initial angular velocity from a prescribed position. Obese participants were unable to recover balance using an ankle strategy as well as normal-weight participants when perturbations involved an initial angular velocity. However, no differences between obese and normal-weight participants were found when perturbations only involved an initial angular displacement. The effect of obesity on balance recovery in young adults was dependent on the perturbation characteristics, and may be explained by a possible beneficial effect of increased inertia on balance recovery after perturbations with little or no initial angular velocity.
The purpose of the second study was to examine the effects of obesity on balance recovery by stepping in young adults. The ankle strategy has the benefit of simplifying the mechanics of balance recovery, but limits generalizability to more realistic fall scenarios where stepping to extend the base of support and recover balance is desired. Similar to the first study, participants attempted to recover balance following two types of postural perturbations: an initial angular displacement from an upright stance (by releasing participants from a static forward lean), and an initial angular velocity while in an upright stance (using a translating platform). In contrast to the first study, the ability to recover balance with a single-step did not differ between young normal-weight and obese adults. These results suggest that the reported increase in fall risk in obese adults is not a result of impaired balance recovery ability (at least among young adults that were tested here).
The third study examined the effects of obesity on body kinematics immediately following a trip-like perturbation in young adults. Obesity was found to increase body angular velocity the perturbation, and that increases in body angular velocity were associated with an increased probability of a failed recovery. These results suggest that when a young obese and young normal-weight individual trip while walking at similar speeds, the young obese individual may be at a greater risk of falling following a trip because the young obese individual will experience a greater body angular velocity. This detrimental effect of obesity on the difficulty of recovering from a trip-like perturbation in young adults is most likely due to how mass is distributed throughout the body and not the amount of mass itself.
The final study examined the relationship between relative strength and functional capability in young adults, and how obesity influences this relationship. To compare relative strength used during a functional task (i.e. balance recovery from a forward fall), the obese and normal-weight individual should complete the task with identical kinematics. Forward dynamic simulations were used to address this research question, instead of human subjects testing, to achieve identical kinematics. Differences in peak relative torques were found between the normal-weight and obese model, with the largest differences seen at the hip. These findings suggest that young obese individuals use greater relative strength at some joints than young normal-weight individuals to perform the time-critical task of balance recovery, and that these differences in relative strength demands may limit functional capability in young individuals who are obese. / Ph. D.
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Design and Simulation of a Towed Underwater VehicleLinklater, Amy Catherine 07 July 2005 (has links)
Oceanographers are currently investigating small-scale ocean turbulence to understand how to better model the ocean. To measure ocean turbulence, one must measure fluid velocity with great precision. The three components of velocity can be used to compute the turbulent kinetic energy dissipation rate. Fluid velocity can be measured using a five-beam acoustic Doppler current profiler (VADCP). The VADCP needs to maintain a tilt-free attitude so the turbulent kinetic energy dissipation rate can be accurately computed to observe small-scale ocean turbulence in a vertical column.
To provide attitude stability, the sensor may be towed behind a research vessel, with a depressor fixed somewhere along the length of the towing cable. This type of setup is known as a two-part towing arrangement.
This thesis examines the dynamics, stability and control of the two-part tow. A Simulink simulation that models the towfish dynamics was implemented. Through this Simulink simulation a parametric study was conducted to see the effects of sea state, towing speed, center of gravity position, and a PID controller on the towfish dynamics. A detailed static analysis of the towing cable's effects on the towfish enhanced this dynamic model. The thesis also describes vehicle design and fabrication, including procedures for trimming and ballasting the towfish. / Master of Science
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DYNAMIC MODELING AND CONTROL OF REACTIVE DISTILLATION FOR HYDROGENATION OF BENZENEAluko, Obanifemi 16 January 2010 (has links)
This work presents a modeling and control study of a reactive distillation column
used for hydrogenation of benzene. A steady state and a dynamic model have been
developed to investigate control structures for the column. The most important aspects of
this control problem are that the purity of the product streams regarding benzene need to
be met. At the same time as little toluene as possible should be converted. The former is a
constraint imposed by EPA regulations while the latter is tied to process economics due
to the high octane number of toluene. It is required to satisfy both of these objectives
even under the influence of disturbances, as the feed composition changes on a regular
basis. The dynamic model is used for developing transfer function models of two
potential control structures. Pairing of inputs and outputs is performed based upon the
Relative Gain Array (RGA) and PI controllers were designed for each control structure.
The controller performance was then compared in simulation studies. From our results,
control structure 2 performed better than control structure 1. The main advantage of CS2
over CS1 is noticed in the simulation of feed composition disturbance rejection, where
CS2 returns all variables back to steady state within 3 hrs while it take CS1 more than 20
hrs to return the temperature variables back to steady state.
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A System Dynamic Study in Steel Industry for the Strategy of CO2 MitigationChen, Chun-Da 29 June 2007 (has links)
The development of steel industry makes progress simultaneously with economy and society of a country. The steel industry is an important industry for each country. From 2001, there was an insufficient supply gap of steel due to strong demand of China, which pushes main integrated steel works to increase their capacities. However, the mitigation pressure of the emission of Green House Gas make a limitations for capacity expansion. The objective of this study is to make appropriate policies for integrated steel works to cope with new operation environment.
From the analysis of steel industry, this study discovers the features and the related operation issues of global steel industry. The relationship between production and CO2 emission was investigated, and the casual loop among the production, revenue, and CO2 emission was analyzed. A dynamic model was developed by system dynamics approach and related tools to simulate the dynamic relationship between the revenue and CO2 emission of steel work. After thorough tests of reliability, model behavior, and policy implications, this model was used to investigate the influence of main operational and environmental parameters on the revenue of steel work. The appropriate production policies for steel works was also proposed.
Simulation results showed that, there was no universal production policy without the economic penalty for CO2 emission, but keeping the production under regulation limit was the most suitable strategy after the implementation of economic penalty. Increasing energy utilization efficiency, the ration of R&D budget in annual profit, and lowering the growth rate of production would facilitate the revenue increase of steel work. The simultaneous adjustment of these parameters could downgrade the negative effect of economic penalty.
The main strategy to cope with the pressure of the CO2 mitigation is to reduce the unit cost of mitigation. Four approaches can be adopted by the steel work to tackle the CO2 mitigation. They are (1) carefully scheduling the capacity expansion of steel work, (2) actively deriving the legislation of economic penalty for CO2 emission, (3) reducing the unit cost for CO2 mitigation, (4) enhancing the power of R&D activities.
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Reduced Order Modeling for Vapor Compression Systems via Proper Orthogonal DecompositionJiacheng Ma (8072936) 04 December 2019 (has links)
<p>Dynamic
modeling of Vapor Compression Cycles (VCC) is particularly important for
designing and evaluating controls and fault detection and diagnosis (FDD)
algorithms. As a result, transient modeling of VCCs has become an active area
of research over the past two decades. Although a number of tools have been
developed, the computational requirements for dynamic VCC simulations are still
significant. A computationally efficient but accurate modeling approach is
critically important to accelerate the design and assessment of control and FDD
algorithms where a number of iterations with a variety of test input signals
are required. Typically, the dynamics of compressors and expansion devices
evolve on an order of magnitude faster than those of heat exchangers (HX)
within VCC systems. As a result, most dynamic modeling efforts have focused on
heat exchanger models. The switched moving boundary (SMB) method, which
segments a heat exchanger depending on thermodynamic phase of the refrigerant,
i.e. subcooled liquid, two-phase and superheated vapor, and moves control
volumes as the length of each phase changes, can reduce the computation time
compared with the finite volume (FV) method by solving fewer equations due to a
smaller set of control volumes. Despite the computational benefit of the SMB,
there is a well-known numerical issue associated with switching the model
representations when a phase zone disappears or reappears inside of a heat
exchanger. More importantly, the computational load is still challenging for many
practical VCC systems. This thesis proposes an approach applying nonlinear
model order reduction (MOR) methods to dynamic heat exchanger models to
generate reduced order HX models, and then to couple them to quasi-static
models of other VCC components to complete a reduced order VCC model. To enable
the use of nonlinear model reduction techniques, a reformulated FV model is
developed for matching the baseline MOR model structure, by using different
pairs of thermodynamic states with some appropriate assumptions. Then a
rigorous nonlinear model order reduction framework based on Proper Orthogonal
Decomposition (POD) and the Discrete Empirical Interpolation Method (DEIM) is
developed to generate reduced order HX models. </p><p>
</p><p> The proposed reduced order modeling approach
is implemented within a complete VCC model. Reduced order HX models are
constructed for a centrifugal chiller test-stand at Herrick Labs, Purdue
University, and are integrated with quasi-static models of compressor and
expansion valve to form the complete cycle. The reduced cycle model is
simulated in the Modelica-based platform to predict load-change transients, and
is compared with measurements. The validation results indicate that the reduced
order model executes 200 times faster than real time with negligible prediction
errors.</p><br>
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Enantioselective nanofiltration using predictive process modeling: bridging the gap between materials development and process requirementsBeke, Aron K. 10 1900 (has links)
Organic solvent nanofiltration (OSN) is a low-energy alternative for continuous separations in the chemical industry. As the pharmaceutical sector increasingly turns toward continuous manufacturing, OSN could become a sustainable solution for chiral separations. Here we present the first comprehensive theoretical assessment of enantioselective OSN processes. Lumped dynamic models were developed for various system configurations, including structurally diverse nanofiltration cascades and single-stage separations with side-stream recycling and in situ racemization. Enantiomer excess and recovery characteristics of the different processes were assessed in terms of the solute rejection values of the enantiomer pairs. The general feasibility of stereochemical resolution using OSN processes is discussed in detail. Fundamental connections between rejection selectivity, permeance selectivity, and enantiomer excess limitations are revealed. Quantitative process performance examples are presented based on theoretical rejection scenarios and cases from the literature on chiral membranes. A model-based prediction tool can be found on www.osndatabase.com to aid researchers in connecting materials development results with early-stage process performance assessments.
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Dynamics of Affordance ActualizationNordbeck, Patric C. January 2017 (has links)
No description available.
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DYNAMIC MODELING, STABILITY ANALYSIS AND CONTROL OF AC/DC INTERCONNECTED MICROGRID USING DQ-TRANSFORMATIONSarker, Partha Sarathi January 2018 (has links)
In recent years, there have been significant changes in power systems due to the integration of renewables, distributed generation, switched power loads, and energy storage systems, etc. Locally these AC/DC microgrids include both DC generation (such as solar PV) and AC generation (such as wind generation), various DC and AC loads, converters and inverters, and energy storage systems, such as storage batteries and supercapacitors. DC systems are often characterized as low inertia systems whereas AC generation and systems are usually high inertia and high time constant systems. As such, various components of the microgrid will have different temporal characteristics in case of disturbances, such as short circuit, load switchings, etc. which may lead to instability of the microgrid. This research develops the first principle model for coupling the AC and the DC subsystem of an integrated AC/DC microgrid utilizing the dq-framework. The developed model is highly nonlinear and captures the dynamic interaction between the AC and DC subsystems of the microgrid. Lyapunov stability is used to evaluate the stability of the complete system. Simulation results show that the AC and DC subsystems are tightly dynamically coupled so that any disturbance in one subsystem induces transients in the other subsystem. Induced transients due to pulse loads on the AC and DC subsystems clearly show that generator damper winding alone may not be enough to mitigate transients in the microgrid. Addition of prime mover and excitation system controllers for the generator improves the transients primarily on the AC subsystem. Thus, a battery storage with a charge/discharge controller was also added to the DC subsystem. Simulations of the AC/DC microgrid with all three controllers validate the smooth operation of the system for all types of disturbances. The proposed method can be extended in modeling microgrid with multiple generators and various types of loads. / Electrical and Computer Engineering
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Design and Implementation of Articulated Robotic Tails to Augment the Performance of Reduced Degree-of-Freedom Legged RobotsSaab, Wael 24 April 2018 (has links)
This dissertation explores the design, and implementation of articulated robotic tail mechanisms onboard reduced degree-of-freedom (DOF) legged robots to augment performance in terms of stability and maneuverability. Fundamentally, this research is motivated by the question of how to improve the stability and maneuverability of legged robots. The conventional approach to address these challenges is to utilize leg mechanisms that are composed of three or more active DOFs that are controlled simultaneously to provide propulsion, maneuvering, and stabilization. However, animals such as lizards and cheetahs have been observed to utilize their tails to aid in these functionalities. It is hypothesized that by using an articulated tail mechanism to aid in these functionalities onboard a legged robot, the burden on the robot's legs to simultaneously maneuver and stabilize the robot may be reduced. This could allow for simplification of the leg's design and control algorithms.
In recent years, significant progress has been accomplished in the field of robotic tail implementation onboard mobile robots. However, the main limitation of this work stems from the proposed tail designs, the majority of which are composed of rigid single-body pendulums that provide a constrained workspace for center-of-mass positioning, an important characteristics for inertial adjustment applications.
Inspired by lizards and cheetahs that adjust their body orientation using flexible tail motions, two novel articulated, cable driven, serpentine-like tail mechanisms are proposed. The first is the Roll-Revolute-Revolute Tail which is a 3-DOF mechanism, designed for implementation onboard a quadruped robot, that is capable of forming two mechanically decoupled tail curvatures via an s-shaped cable routing scheme and gear train system. The second is a the Discrete Modular Serpentine Tail, designed for implementation onboard a biped robot, which is a modular two-DOF mechanism that distributes motion amongst links via a multi-diameter pulley. Both tail designs utilize a cable transmission system where cables are routed about circular contoured links that maintain equal antagonistic cable displacements that can produce controlled articulated tail curvatures using a single active-DOF. Furthermore, analysis and experimental results have been presented to demonstrate the effectiveness of an articulated tail's ability to: 1) increase the manifold for center-of-mass positioning, and 2) generate enhanced inertial loading relative to conventionally implemented pendulum-like tails.
In order to test the tails ability to augment the performance of legged robots, a novel Robotic Modular Leg (RML) is proposed to construct both a reduced-DOF quadrupedal and bipedal experimental platform. The RML is a modular two-DOF leg mechanism composed of two serially connected four-bar mechanisms that utilizes kinematic constraints to maintain a parallel orientation between it's flat foot and body without the use of an actuated ankle. A passive suspension system integrated into the foot enables the dissipation of impact energy and maintains a stable four point-of-contact support polygon on both flat and uneven terrain.
Modeling of the combined legged robotic systems and attached articulated tails has led to the derivation of dynamic formulations that were analyzed to scale articulated tails onboard legged robots to maximize inertial adjustment capabilities resulting from tail motions and design a control scheme for tail-aided maneuvering.
The tail prototypes, in conjunction with virtual simulations of the quadruped and biped robot, were used in experiments and simulations to implement and analyze the methods for maneuvering and stabilizing the proposed legged robots. Results successfully demonstrate the tails' ability to augment the performance of reduced-DOF legged robots by enabling comparable walking criteria with respect to conventional legged robots. This research provides a firm foundation for future work involving design and implementation of articulated tails onboard legged robots for enhanced inertial adjustment applications. / Ph. D.
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