bluuebunny/crossref_metadata_2025 huggingface dataset:
A Market Based Distributed Optimization for Power Allocation in Smart Grid
Authors: HomChaudhuri Baisravan , Kumar Manish , Devabhaktuni Vijay
Published: May 2012

The potential of Smart Grid in bringing about a revolutionary change in the production, distribution, and utilization of power has generated much attention among producers and consumers of electric power, policy makers as well as researchers. However, before a smart grid can become fully functional, it requires technological advancements in a number of interdisciplinary domains. In particular, the usage of renewable energy sources is envisioned to result in a massively distributed power generation and distribution system composed of a large number of generating stations operating on disparate renewable technologies. Even though smart grid facilitates run-time optimal allocation of power via extensive instrumentation and information accessibility, the process of optimal power routing becomes challenging due to the massively distributed nature of generation facilities and consumption sites, and due to uncertainty caused by inherent random fluctuations in generation. In this paper, a Market Based technique has been presented for carrying out the optimal allocation for efficient utilization of the energy produced in a Smart Grid. The Market Based Resource Allocation is inspired by concepts from the economic market, where resources are allocated to activities through the process of competitive buying and selling. In the proposed technique, the energy consumers act as the potential energy buyers and the energy producers act as the energy sellers. The paper evaluates the proposed Market Based technique via a number of simulated scenarios of energy consumers and producers in a Smart Grid. The proposed technique optimizes the transmission loss of electric power distribution. Simulation results of the proposed approach are presented at the end of this paper.
A Novel Air Cycling Valve for Combustion Engines
Authors: Braune Steffen , Kramer Klaus-Dietrich
Published: May 2012

This paper describes a novel actuator used as a drive system for an air cycling valve (ACV) for combustion engines. With this actuator concept, which is based on a single-phase synchronous motor, a small construction volume, a high torque density, combined with low power consumption and a robust construction is realized. The ACV enables a torque advance for the combustion engine for lower engine speed and an improvement of fuel economy, associated with a reduction of CO2. It is installed into the inlet manifold with no modification of the cylinder head. Extremely high angular accelerations with high velocities are realized to switch the flap of the air cycling valve in less then two milliseconds with a rotation angle of 45 degree. Described is the design procedure and used control algorithm.
Towards Automated Mechanical Characterization of Biological Samples Using Atomic Force Microscopy (AFM)
Authors: Roy Rajarshi , Chen Wenjin , Cong Lei , Goodell Lauri A. , Foran David J. , Desai Jaydev P.
Published: May 2012

The mechanical properties of biomaterials have long been a subject of interest for researchers due to their potential in predicting biologically relevant questions, like proliferation of cancer in tissue. A popular technique of estimating material properties of biomaterials is the AFM, which consists of a probe that indents the material of interest. However, region localization for AFM indentation is challenging, especially when probing large sections of the tissue. Furthermore, identifying the point of contact between AFM tip and the specimen on the force-displacement curve involves uncertainties that are difficult to predict. In this work, we try to address these two issues. We use a vision-guided positioning system to achieve region localization, and we use a resistance based-electrical circuit to identify the point of contact between AFM tip and the specimen.
Experimental Study on Passive Dynamic Bipedal Walking: Comparing Test Platforms and Effects of Parameter Changes on Gait Patterns
Authors: Rushdi Kazi , Koop Derek , Wu Christine Q.
Published: May 2012

Passive dynamic walking is a gait developed, partially or in whole, by the energy provided by gravity. An improved kneed bipedal walking mechanism was designed and built to study passive gait patterns. The first aim of this study is to determine if testing a passive dynamic biped walker on a ramp is equivalent to testing on a treadmill. Based on the small difference between the gait patterns measured on the two test platforms, testing on a treadmill is equivalent to testing on a ramp. Measurement of the gait parameters were then conducted on the treadmill to evaluate the effects of the treadmill angle of inclination, mass distribution of the biped, treadmill belt speed and length of flat feet. Our experimental results are presented and compared with previous experimental and simulation results. Research on passive dynamic bipedal walking helps to develop an understanding of walking mechanics. Moreover, experimental passive dynamic walking results provide information to validate mathematical models of passive dynamic walking.
Local Onset of Voltage and Calcium Alternans in the Heart
Authors: McIntyre Stephen D. , Mori Yoichiro , Tolkacheva Elena G.
Published: May 2012

A beat-to-beat variation in cardiac action potential durations (APD) is a phenomenon known as electrical alternans. Alternans desynchronizes depolarization, increases dispersion of refractoriness and creates a substrate for ventricular fibrillation. In the heart, APD alternans can be accompanied by alternans in intracellular calcium ([Ca2+]i) transients. Recently, we demonstrated experimentally that the onset of APD alternans in the heart is a local phenomenon that undergoes complex spatiotemporal dynamics as pacing rate increases. Moreover, the local onset of APD alternans can be predicted by measuring the restitution properties of periodically paced cardiac tissue. The purpose of this research is to investigate the interplay between local onsets of APD and [Ca2+]i alternans using 2D simulation of action potential model of cardiac myocytes.
On Robust Disturbance Observer Design Using Semi-Definite Programming
Authors: El-Shaer Ahmed H. , Zhang Tao , Al Janaideh Mohammad
Published: May 2012

This paper is concerned with optimal synthesis of disturbance observers guaranteeing closed loop robust tracking and disturbance rejection performance. The approach presented makes use of internal model-based estimation of exogenous disturbances, where the internal model dynamics is chosen with at least one of its eigenvalues at the origin. The synthesis is then formulated as an H∞ weighted-sensitivity optimization for static output feedback (SOF) gain of a Luenberger observer. A linearization method is then implemented to solve the bilinear-matrix-inequality (BMI) constrained semi-definite program (SDP) for a (sub)optimal static gain.
A Method for Teaching Feedback Control Using the Enhanced Mass-Spring-Damper System
Authors: Kim Dean H.
Published: May 2012

This paper presents a method that the author has developed to teach students about the need for feedback control and to facilitate the understanding of controller implementation. The initial discussion focuses on the limitations of open-loop control to improve performance of the traditional mass-spring-damper system. The key contribution is the introduction of an enhanced mass-spring-damper system with a position sensor and force generator, resulting in voltages as system input and output. This enhanced system provides a foundation for discussion of basic feedback control strategies such as PID-Control in addition to advanced controls concepts. The analysis is provided in time-domain to facilitate the understanding of these important controls concepts.
Foot-Terrain Interaction for a Prototype Silicon Micro-Robot
Authors: Ryou Jeong Hoon , Oldham Kenn
Published: May 2012

Research on dynamics of micro devices indicates that contact forces are complex in a micro-scale environment. Previous work tried to identify how small-scale forces numerically affect a walking micro system, using a similar structure to a micro-robot leg and a simple analytical model for system dynamics. This paper extends that work by focusing on further experimental testing and simulation studies on a prototype micro-robot. Evaluation of experimental data indicates that characteristics of the ground, such as material properties and static charge on the surface should be also considered in understanding foot-terrain interaction. This leads to modifications to the former foot-terrain interaction algorithm. The refined analytical model is validated through experimental comparison.
Qualitative Robustness and Its Role in the Robust Control of Uncertain Engineering Systems
Authors: Devarakonda Nagini , Yedavalli Rama K.
Published: May 2012

This paper addresses the issue of robustness of linear uncertain systems. In addition to the conventional notion of robustness based on quantitative information, in this paper, a new and novel perspective of qualitative robustness is introduced. The qualitative robustness measure is inspired by ecological principles and is based on the nature of interactions and interconnections of the system. Thus, using the proposed framework, the robustness of engineering systems can be assessed both from quantitative as well as qualitative information. This type of analysis from both viewpoints sheds considerable insight on the desirable nominal system in engineering applications. Using these concepts it is shown that a specific quantitative set of matrices labeled ‘Target Sign Stable Matrices’ are the best nominal matrices. These concepts are then extended to closed loop control systems and problem of control design and for ease in design a new set of matrices ‘Target Pseudosymmetric Matrices’ are introduced which enhance the class of desirable closed loop system matrices. Examples are included to illustrate these concepts.
Dynamics of Networks With Stochastically Switched Connections
Authors: Belykh Igor , Hasler Martin
Published: May 2012

This talk discusses the influence of network structure on the dynamics of networks with fast on-off stochastic connections. It is investigated to what extent the trajectories of a stochastically switched (blinking) network follow the corresponding trajectories of its averaged analog where the stochastic connection are replaced with static ones. Four cases have to be distinguished, depending on whether or not the averaged system has a unique attractor and whether or not the attractors are invariant under the dynamics of the blinking system. The corresponding asymptotic behavior of the trajectories of the blinking system is described and illustrative examples are given.
Simultaneous Optimization of Supervisory Control and Gear Shift Logic for a Parallel Hydraulic Hybrid Refuse Truck Using Stochastic Dynamic Programming
Authors: Johri Rajit , Baseley Simon , Filipi Zoran
Published: May 2012

The power management controller of a hybrid vehicle orchestrates the operation of onboard energy sources, namely engine and auxiliary power source with the goal of maximizing performance objectives such as the fuel economy. The paper focuses on optimization of the power management strategy of the refuse truck with parallel hydraulic hybrid powertrain. The high power density of hydraulic components and high charging/discharging efficiency of accumulator with no power constraint make hydraulic hybrid an excellent choice for heavy-duty stop and go application. Two power management strategies for a parallel hydraulic hybrid refuse truck are compared; heuristic and stochastic dynamic programming based optimal controller. For designing a SDP based controller, an infinite horizon problem is setup with power demand from driver modeled as random Markov process. The objective is to maximize system level efficiency by optimizing (i) the power split between engine and hydraulic propulsion unit, and (ii) gear shift schedule. This combines the optimization of powertrain parameters with power management design.
Analysis of an Adaptive Iterative Learning Algorithm for Freeway Ramp Flow Imputation
Authors: Muralidharan Ajith , Horowitz Roberto
Published: May 2012

We present an adaptive iterative learning based flow imputation algorithm, to estimate missing flow profiles in on ramps and off ramps using a freeway traffic flow model. We use the Link-Node Cell transmission model to describe the traffic state evolution in freeways, with on ramp demand profiles and off ramp split ratios (which are derived from flows) as inputs. The model based imputation algorithm estimates the missing flow profiles that match observed freeway mainline detector data. It is carried out in two steps: (1) adaptive iterative learning of an “effective demand” parameter, which is a function of ramp demands and off ramp flows/ split ratios; (2) estimation of on ramp demands/ off ramp split ratios from the effective demand profile using a linear program. This paper concentrates on the design and analysis of the adaptive iterative learning algorithm. The adaptive iterative learning algorithm is based on a multi-mode (piecewise non-linear) equivalent model of the Link-Node Cell transmission model. The parameter learning update procedure is decentralized, with different update equations depending on the local a-priori state estimate and demand estimate. We present a detailed convergence analysis of our approach and finally demonstrate some examples of its application.
Optimal Control of Engine-Starts for Drivability of Parallel Hybrid Electric Vehicles
Authors: Kum Dongsuk , Peng Huei , Bucknor Norman
Published: May 2012

The parallel hybrid electric vehicle (HEV) with a single pre-transmission electric motor (the P2 configuration) has a challenging drivability issue during engine-starts because the motor must simultaneously provide the propulsion torque demand and start the engine. The goal of this study is to present a design process to achieve optimal balance between these two conflicting goals. We first develop a control-oriented HEV powertrain model to accurately predict the engine, clutch, and vehicle dynamics. Assuming that the clutch torque can be accurately estimated and perfectly cancelled, an optimal engine-start control problem is formulated to minimize engine-start time while accurately supplying the driver torque demand simultaneously. This nonlinear constrained optimal control problem is solved numerically using Dynamic Programming (DP). DP results show that a proper constant clutch pressure level, which leads to constant torque disturbance that is easy to cancel out using the motor, can achieve near-optimal performance. Furthermore, the DP control policy is found to be time-invariant, and thus can be directly implemented in the form of a full state feedback controller.
A New Architecture for Set-Point Control of Robotic Manipulators With Time-Varying Input/Output Delays
Authors: Liu Yen-Chen , Chopra Nikhil
Published: May 2012

In this paper we study the classical set-point control problem for rigid robots when there are time-varying delays in the input-output channels. It has been demonstrated earlier that scattering variables together with additional gains can be utilized to stabilize the closed loop system in the presence of time-varying delays. However, this architecture is not able to guarantee asymptotic regulation to the desired configuration, and the stability depends on the maximum rate of change of the time-varying delays in the communication. Hence, in this paper, we present a new architecture where scattering variables and position feedback are utilized to guarantee stability and asymptotic convergence of the regulation error to the origin while simultaneously relaxing a significant assumption on the rate of change of delays. The proposed algorithm is numerically verified on a two-degree-of-freedom manipulator.
Single-Input Planar Navigation via Proportional Heading Control Exploiting Nonholonomic Mechanics or Vortex Shedding
Authors: Fairchild Michael J. , Hassing Peter M. , Kelly Scott David , Pujari Parthesh , Tallapragada Phanindra
Published: May 2012

We present a strategy for coupled steering and motion generation applicable to a class of single-input planar robotic vehicles. We demonstrate this strategy through simulations of two different vehicles under closed-loop control, the first a novel variation of the Chaplygin sleigh and the second a fishlike swimmer in an ideal fluid. The dynamics of the former are influenced by a nonholonomic constraint and the dynamics of the latter by a hydrodynamic force associated with vortex shedding. The juxta-position of these two systems highlights a link between nonholonomic mechanics and hydrodynamics explored in a prior paper.
Hydraulic Cylinder Velocity Control With Energy Recovery: A Comparative Simulation Study
Authors: Troxel Ned A. , Yao Bin
Published: May 2012

A valve configuration including a hydraulic accumulator for energy recovery is proposed for velocity control of hydraulic cylinders. A control design incorporating a low-level adaptive robust controller and high-level logic is presented. The benefits of independent cylinder pressure control, regeneration flows, and the proposed energy recovery system are compared. Simulation results show the proposed configuration provides significant energy savings compared to the other system configurations following the same velocity trajectory. An explanation of the advantages of the proposed configuration over previous configurations is given, showing why the proposed configuration makes increased recycling of system flows possible. Results for constant pressure source and a load-sensing pump show that different control objectives are appropriate for different supply pressure setups. Additional applications and further study of the proposed configuration are discussed.
Passivity Based Nonlinear Control of Hydraulic Actuators Based on an Euler-Lagrange Formulation
Authors: Li Perry Y. , Wang Meng
Published: May 2012

A passivity framework for hydraulic actuators is developed by consideration of the compressibility energy function for a fluid with a pressure dependent bulk modulus. The typical actuator’s mechanical and pressure dynamic model is shown to be the Euler-Lagrange equations for this energy function. A passivity property for the actuator is exhibited in which the hydraulic supply rate contains the compressibility energy, instead of just being P · Q. A storage function for the pressure error is then proposed based on the physical compressibility energy and the pressure error dynamics is shown to be a passive two-port subsystem. Control laws are derived using the storage function. A case study is presented to compare the new passivity based approach and the traditional backstepping approach for a trajectory tracking application. In this example, the proposed approach is less sensitive to velocity measurement error and requires lower feedback gains than the traditional approach.
Robust Control of a Surface Vehicle With Disturbances
Authors: Lee DongBin , Nataraj C. , Burg Timothy C.
Published: May 2012

In this paper, a new approach for robust control of a surface vehicle is presented. This approach uses a sliding mode controller with an additional robust term. A nonlinear dynamic model which is complicated by environmental disturbances is presented for a surface vehicle, dividing the model into the rigid-body portion, and a portion containing disturbance terms that the robust controller will reject. Following that, a robust approach based on sliding mode controller is developed for tracking desired trajectories in finite time while compensating for disturbances such as hydrodynamics, wind, wave, and currents based on Lyapunov-type stability analysis. Finally numerical simulation results are shown to demonstrate the validity of the proposed controllers.
On-Line Identification of Fuel Injection Timing Using Cylinder Balancing
Authors: Kim Yong-Wha , Van Nieuwstadt Michiel , Yoo In Kwang
Published: May 2012

Identification of the injection timing drift in modern diesel engine is investigated. The cylinder balancing action which is most common in modern diesel engine is utilized in locating the injection timing (injection timing with the minimum cylinder balancing correction). To find the minimum, several approaches are examined, including a parameterization based approach, sliding mode based self optimizing control and the simplex search. The proposed approaches are evaluated with experimental data from a vehicle.
Numerical Analysis of Effects of Centrifugal Compressor Impeller Design on Overall- and Flow Field Performance
Authors: Hildebrandt A. , Franz H. , Jakiel C.
Published: May 2012

The present paper deals with two different subjects in the field of centrifugal compressors, namely impeller design and its aerodynamic analysis. The paper provides results of aerodynamic design of low specific speed centrifugal compressor impellers. The design objective is the improvement of the efficiency of a 2D-impeller by means of a 3D-impeller design. The design volume flow and isentropic pressure coefficient of the 3D-impeller should be similar to the one of the 2D-impeller. The numerical CFD (Computational Fluid Dynamics) analysis comprises non-dimensional results of overall impeller and stage performance as well as flow details (circumferentially averaged fluid properties in the impeller exit plane). Furthermore, the paper presents the analysis of secondary flow development of different impellers in comparison with a 2D-impeller of prismatic blade profile. The numerical analysis focuses on understanding of different development of the impeller secondary zone. Results show a direct correlation between the overall performance and secondary flow of the different impellers providing more insight into the aerodynamic philosophy of design of centrifugal compressor impellers.
Aerodynamic Measurements on a Low Pressure Turbine Cascade With Different Levels of Distributed Roughness
Authors: Montis Marco , Niehuis Reinhard , Fiala Andreas
Published: May 2012

The effect of surface roughness on the aerodynamics of a highly loaded low-pressure turbine airfoil was investigated in a series of cascade tests conducted in a high speed facility. Profile loss and aerodynamic loading of three different surface roughnesses with a ratio of the centerline average roughness to the profile chord of 1.1 · 10−5, 7.1 · 10−5 and 29 · 10−5 were analysed. Tests were carried out under design outlet Mach number, outlet Reynolds number ranging from 5 · 104 to 7 · 105 and inlet turbulence level of 2.5% and 5%. The mid span flow field downstream of the cascade and the loading distribution on the profile were measured for each investigated operating point using a five hole probe and surface static pressure taps. Additional measurements with a hot wire probe in the profile boundary layer under reference conditions (Re2th = 2 · 105) were also conducted. Experimental results show a loss reduction for the highest roughness under reference conditions, due to the partial suppression of the separation bubble on the suction side of the profile. At high Reynolds numbers a massive boundary layer separation on the suction side is observed for the highest roughness, along with a large increase in total pressure loss. The middle roughness tested has no effect on the loading distribution as well as on the loss behaviour of the airfoil under all investigated flow conditions.
Gas Turbine Failure due to Water Wash and Extraction Line Blockage
Authors: Ali Abdulmajeed A.
Published: May 2012

A Hot Gas Path Inspection (HGPI) of GE Co-Generation train revealed an extensive failure of the turbine blades and vanes in the first, second, third stages and combustion chamber cross firing tubes. Subsequent investigation effort indicated that commissioning activities of associated compressor water wash system allowed large volumes of water to penetrate the compressor and combustion chamber due to improper instrumentation interlock configuration of MOV-20TW-1 (Offline compressor water wash motor operated valve) and MOV-20TW-3 (Online compressor water wash motor operated valve). The field wiring for the valves was incorrectly interchanged causing the offline water wash valves to be operated while commanding the online water wash valves to operate and vice-versa. Compressor water wash system is typically used to remove fouling deposits from compressor components to maintain the equipment efficiency, power output and reduce corrosion rate. Vendor recommends daily online water wash while the offline water wash shall be performed whenever the equipment is not working. As a result, cross firing tubes were exposed to sudden quenching during the water wash activities causing tube fragmentation, which found its way through the exhaust stream to the turbine chamber — colliding with associated buckets and nozzles — eventually resulting in the reported damage. Water seeped into the air extraction line and settled in the dryer skid system, resulting in desiccant contamination. Following turbine shutdown for correcting the instrumentation loop configurations of subject MOVs, the contaminated desiccant flowed to the combustion chamber, blocking the extraction line and the drain lines. After successful configuration of compressor water wash system MOVs, the turbine was put back in operation mode. The contaminated desiccant blocked the air passage of the combustion chamber, which consequently melted the cross firing tubes and contributed to the overheating of first stage buckets. Investigation concluded that the inadequate pre-commissioning procedure — for the Co-Generation train compressor water wash interlock system — were the root cause behind the subject incident. The immediate cause was determined to be water penetration to the compressors and combustion chamber internals during machine operation.
A Multi-Section Droplet Combustion Model for Spray Combustion Simulation
Authors: Wang F. , Sayma A. I. , Peng Z. J. , Huang Y.
Published: May 2012

Since 1960s, from experimental observation, there are several stages for liquid droplets in multi-phase combustion: pure heating, pure evaporation without individual droplet combustion, and individual droplet combustion (burning) with individual flame around which enhances evaporation. As for individual burning droplets, they have envelope flame or wake flame regimes. From experimental and theoretical research, in liquid fuel combustion chambers, according to the space between the droplets, there are four typical droplet group combustion modes. Generally, the external group combustion mode and the internal group combustion mode are the two main modes, and there are individual burning droplets in multiphase combustion. Up to now, based on the literature information, no matter in Reynolds Averaged Navier Stokes (RANS) method, Large Eddy Simulation (LES) method or Point Direct Numeral Simulation (PDNS) method, droplets in multi-phase combustion are treated as pure evaporation points, corresponding to the bright blue flame condition, i.e., small droplets in hot gas mixture with the pure evaporation stage, so in species equation and energy equation, the droplet points are mass source and heat sink. As for the individual droplets burning mode, in point source simulation method, corresponding to the big droplet in cold gas phase mixture with yellow trail flame condition, the source terms in the species equation and energy equation should be the mass sink and heat source. The individual burning droplets affects the NO formation because the flame around the droplet has higher temperature than the local gas phase mixture mostly for the quasi-stoichiometric ratio reaction in individual droplet flame. In this paper, a new spray combustion model with the consideration of individual droplets combustion mode is brought forward. The existing modeling approach is extended with an ignition criterion and a droplet combustion correlation. The ignition criterion, which judges the droplet stage between pure evaporation and burning, and the droplet combustion correlation, which integrates the micro-scales droplet burning effects into point source term frame, are both selected from pioneer’s experimental work and added to the present existing widely used multi-phase combustion model. Then a jet spray flame is tested by the new model with RANS and LES method. The prediction results are compared with the literature experimental results. New model gives better simulation results in downstream regions. According to the results, this model added the individual droplet combustion mode in multi-phase combustion model, while its combustion correlations are quite rough at present. More verify studies should be carried in the future.
Analytical Investigation of the Effects of Induction Motor Transients on Compressor Drive Shafts
Authors: Srinivasan Anand
Published: May 2012

Centrifugal compressors driven by induction motors are most common in the turbomachinery industry. When sudden transients occur in the driver due to upsets in electrical supply to the motor, the air-gap torque generated by the motor undergoes a transient spike. This in turn gets transmitted through the coupling to the drive-shaft of the driven equipment, causing momentary high spikes in vibration that are torsional in nature, and can sometimes result in shaft torques that can create catastrophic damage to driven equipment components. In order to analytically predict these peak torques that can occur during transients, a complete drive-train torsional model needs to be created for the mechanical system, and the driving torque values need to be derived from the motor electrical system of equations. Various line faults are possible with induction motor driven equipment. A generalized analytical procedure based on motor electrical parameters to predict the peak shaft torques of compressor drive shafts is investigated in this paper. The effects of shaft transients due to 3-phase short circuits and reclosures are analyzed. The simulation has been performed for an industrial compressor train, and has been presented from a mechanical system point of view, rather than electrical. Comparisons and inferences are also made based on the simulation results.
Thermal Properties and Phase Analysis of Titania Doped Yttria-Zirconia Ceramics for Use as High Temperature Thermal Barrier Coatings (TBCs)
Authors: Romualdez L. J. , Kibsey M. , Huang X. , Kearsey R.
Published: May 2012

Titania doped YSZ ceramic samples were subjected to calorimetric, thermal and microstructural analyses to assess the value of titania as a dopant for use as thermal barrier coating in modern gas turbine engines. The primary objective of titania addition was to effectively stabilize the tetragonal phase at operating temperatures while lowering the thermal conductivity. Powder blends with 5, 10, and 15 wt% titania added to standard 7YSZ powder were sintered at 1200°C for 325hrs after plasma spraying. Basic physical properties related to the thermal conductivity of the material such as bulk densities and Young’s modulus were determined. Phase analysis of all samples was performed using x-ray diffraction techniques so the percentage of monoclinic, tetragonal, and cubic phases could be determined. For all titania samples, it was shown that the composition was predominantly tetragonal with slightly decreasing amounts of monoclinic phases present with increasing titania content. The results of calorimetric analysis showed a marginal decrease in the specific heat capacities of the sintered titania doped samples. Similarly, thermal diffusivities were lowered by the addition of titania, though only slightly, since it has been previously shown that diffusivity is more strongly linked to sample porosity. Using these results, the experimental thermal conductivities for all titania doped samples were determined and compared to theoretical conductivities based solely on the mechanical properties of the ceramic. The results showed a decrease in thermal conductivity with the addition of titania, though with higher values than that predicted from the theoretical model. Experimental thermal conductivities were also shown to decrease with temperature initially, while increasing slightly at higher temperatures, which is most probably due to the radiation effect.
Functional Analysis and Exergoeconomic Evaluation for the Combined Production of Electromechanical Power and Useful Heat of a Cogeneration Power Plant
Authors: Irrazabal Bohorquez Washington Orlando , Barbosa Joa˜o Roberto
Published: May 2012

In the Ecuadorian electrical market, several sugar plants, which significantly participate in the local electricity market, are producing their own energy and commercializing the surplus to the electrical market. This study evaluates the integral use of the sugar cane bagasse for productive process on a Cogeneration Power Plant in an Ecuadorian Sugar Company [8]. The electrical generation based on biomass requires a great initial investment. The cost is around US$ 800/kW installed, twice the US$ 400/kW initial investment of conventional thermoelectric power plant and almost equal to the US$ 1,000/kW initial cost of hydroelectric power plant [5]. A thermoeconomic study was carried out on the production of electricity and the sales of the surplus of 27 MWe average produced by the power plant. An operational analysis was made using instantaneous values from the estimated curves of demand and generation of electricity. From the results, it was concluded that the generated electricity costs are 0.0443 US$/kWh, while the costs of the electricity from Fossil Power Plants (burning fuel oil, diesel fuel and natural gas) are in the range 0.03–0.15 US$/kWh and from Hydroelectric Plants are about 0.02 US$/kWh. Cogeneration power plants burning sugar cane bagasse could contribute to the mitigation of climatic change. This specific case study shows the reduction of the prospective emissions of greenhouse gases, around 55,188 ton of CO2 equivalent yearly for this cogeneration power plant.
The Cost of Flow Control in a Compressor
Authors: Evans Simon W. , Hodson Howard P.
Published: May 2012

This paper documents an analysis performed to estimate the cycle cost of flow control in a compressor. The analysis is based on a series of experiments conducted in a low-speed compressor cascade at high incidence. In these experiments, flow control was applied to delay a turbulent separation on the suction surfaces of the blades in the cascade. The flow control methods studied include boundary layer suction and both steady and pulsed vortex generator jets. Endwall control was also applied to remove corner separations. Tip gaps and endwall suction were both studied for this purpose. The flow control methods studied were able to successfully delay a separation occurring on the suction surface of the blades, reducing the loss coefficient. The mass flow rates and jet supply pressures required to achieve control in each case were used to model a single flow-controlled blade row in a typical turbofan cycle using cycle analysis software. The cost of control to the cycle was calculated as the polytropic compressor efficiency increase required to maintain thrust relative to a conventional cycle with no flow control. The results of the analysis show that the benefits of flow control significantly outweigh the cost. They also show that boundary layer suction coupled with endwall suction yields the lowest cycle cost. This is because of the small pressure difference required to drive suction, which allows reinjection of the aspirated air a short distance upstream of the flow controlled blade row.
Overview of Fuel Injection Techniques for Scramjet Engines
Authors: Huang Wei , Wang Zhen-guo , Luo Shi-bin , Liu Jun , Xia Zhi-xun , Lei Jing , Jin Liang , Wang Zhong-wei , Pourkashanian Mohamed , Ma Lin , Ingham Derek B.
Published: May 2012

As one of the most promising hypersonic propulsion systems for hypersonic vehicles, the scramjet engine has drawn an ever increasing attention of researchers worldwide. At present, one of the most important issues to be dealt with is how to improve the fuel penetration and mixing efficiency and make the flame stable in supersonic flows. Further, how to reduce the structural weight of the engines is an urgent issue that needs to be considered. The ongoing research efforts on fuel injection techniques in the scramjet engine are described, mainly the cavity flame holder, the backward facing step, the strut injection and the cantilevered ramp injection, and the flow field characteristics and research efforts related to these fuel injection techniques are summarized and compared. Finally, a promising fuel injection technique is discussed, namely a combination of different injection techniques, and the combination of the cantilevered ramp injector and the cavity flame holder is proposed. This is because it can not only stabilize the flame, but also shorten the length of the combustor, thus lighten the weight of the scramjet engines.
Investigation of Self-Recycling-Casing-Treatment (SRCT) Influence on Stability of High Pressure Ratio Centrifugal Compressor With a Volute
Authors: Yang Mingyang , Martinez-Botas Ricardo , Zhang Yangjun , Zheng Xinqian , Bamba Takahiro , Tamaki Hideaki , Li Zhigang
Published: May 2012

Large feasible operation range is a challenge for high pressure ratio centrifugal compressor of turbocharger in vehicle engine. Self-Recycling-Casing-Treatment (SRCT) is a widely used flow control method to enlarge the range for this kind of compressor. This paper investigates the influence of symmetrical/asymmetrical SRCT (ASRCT) on the stability of a high pressure ratio centrifugal compressor by experimental testing and numerical simulation. Firstly, the performance of the compressor with/without SRCT is tested is measured investigate the influence of flow distortion on the stability of compressor as well as the numerical method validation. Then detailed flow field investigation is conducted by experimental measurement and the numerical method to unveil the reasons for stability enhancement by symmetrical/asymmetrical SRCT. Results show that static pressure distortion at impeller outlet caused by the volute can make passages be confronted with flow distortion less stable than others because of their larger positive slope of T-S pressure ratio performance at small flow rate. SRCT can depress the flow distortion and reduce the slope by non-uniform recycling flow rate at impeller inlet. Moreover, ASRCT can redistribute the recycling flow in circumferential direction according to the asymmetric geometries. When the largest recycling flow rate is imposed on the passage near the distorted static pressure, the slope will be the most effectively reduced. Therefore, the stability is effectively enhanced by the optimized recycling flow device.
Evaluating Complex Inlet Distortion With a Parallel Compressor Model: Part 1—Concepts, Theory, Extensions, and Limitations
Authors: Cousins William T. , Davis Milt W.
Published: May 2012

Modeling compression systems using parallel compressor theory has been used for the analysis of compression system operability since the 1960s. Parallel compressor models have been traditionally designed and used for the analysis of circumferential distortion effects as a means to evaluate the impact of various inlet flow field disturbances on compressor operation. This paper (the first of two) provides a review of the parallel compressor concept and discusses extensions to the original theory. These extensions include the incorporation of dynamic response, application to complex distortions, and the application to inlet swirl. Understanding these effects and the application of parallel compressor theory extensions is required to produce analytical models and computer simulations that can be used to enhance the development testing and the understanding of the response of gas turbine compression systems. Once a computer simulation has been constructed for a particular test article, it can be exercised and results compared against test results where distortion-generator devices (such as distortion screens) have been used, generally with favorable accuracy. The usefulness of the extended parallel compressor model is derived from its ease of use, simplicity, and ability for quick turn-around of results. It is often more desirable to have an analysis capability that is easy and quick to use than to have one that is extremely accurate, especially when understanding basic physics is of primary concern during a test operation. Extreme accuracy may require large amounts of computer resources and take days or weeks to compute a single performance point. While this may be acceptable for design, the limitations of high-fidelity simulations make them impractical to use due to the time constraints imposed by the pace of testing. Applying a timely analysis capability, using a parallel compressor simulation can provide a new physical understanding of the effects of complex distortion during the testing process when comparing the analytical and test results. This concept is presented in two companion papers: the first paper, Part 1, concentrates on the parallel compressor concepts, theory and limitations of the methodology while the second paper, Part 2 [1] presents applications of the approximate methods developed and compares results with experimental data.
Evaluating Complex Inlet Distortion With a Parallel Compressor Model: Part 2—Applications to Complex Patterns
Authors: Davis Milt W. , Cousins William T.
Published: May 2012

This paper is the second paper (Part 2) in a companion set and presents results of computer simulations using a parallel compressor model developed with the extended concepts presented in the previous paper (Part 1). The computer model, constructed using the parallel compressor theory with extensions, has been exercised and compared with test results from several gas turbine engines to demonstrate the usefulness of this simulation technique. Distortion patterns used in the tests were created using distortion-generator devices such as distortion screens. A technique to simplify complex distortion patterns through approximate means is presented. This simplification is implemented based upon the flow physics of the compression system, thus allowing the model to better represent the distortion pattern while providing minimal impact on the simulation output and the comparison to the test results. The usefulness of the extended parallel compressor model is demonstrated from its ease of use, simplicity, and ability for quick turn-around of results. Applying a timely analysis capability using the demonstrated parallel compressor model provides an additional physical understanding of the effects of complex distortion on compression system operation.
Efficient Gradient-Based Algorithms for the Construction of Pareto Fronts
Authors: Shankaran Sriram , Barr Brian
Published: May 2012

The objective of this study is to develop and assess a gradient-based algorithm that efficiently traverses the Pareto front for multi-objective problems. We use high-fidelity, computationally intensive simulation tools (for eg: Computational Fluid Dynamics (CFD) and Finite Element (FE) structural analysis) for function and gradient evaluations. The use of evolutionary algorithms with these high-fidelity simulation tools results in prohibitive computational costs. Hence, in this study we use an alternate gradient-based approach. We first outline an algorithm that can be proven to recover Pareto fronts. The performance of this algorithm is then tested on three academic problems: a convex front with uniform spacing of Pareto points, a convex front with non-uniform spacing and a concave front. The algorithm is shown to be able to retrieve the Pareto front in all three cases hence overcoming a common deficiency in gradient-based methods that use the idea of scalarization. Then the algorithm is applied to a practical problem in concurrent design for aerodynamic and structural performance of an axial turbine blade. For this problem, with 5 design variables, and for 10 points to approximate the front, the computational cost of the gradient-based method was roughly the same as that of a method that builds the front from a sampling approach. However, as the sampling approach involves building a surrogate model to identify the Pareto front, there is the possibility that validation of this predicted front with CFD and FE analysis results in a different location of the “Pareto” points. This can be avoided with the gradient-based method. Additionally, as the number of design variables increases and/or the number of required points on the Pareto front is reduced, the computational cost favors the gradient-based approach.
Air Flow Modulation for Refined Control of the Combustion Dynamics Using a Novel Actuator
Authors: Giuliani Fabrice , Lang Andreas , Gradl Klaus Johannes , Siebenhofer Peter , Fritzer Johannes
Published: May 2012

A specific actuator able to modulate the air feed of a gas a burner at a given frequency and amplitude is presented. The Combustion Department at the Institute for Thermal Turbomachinery and Machine Dynamics at the Graz University of Technology has experience on the study of combustion instabilities in gas turbines using a flow excitor. The stability of an industrial burner is tested at elevated pressure and temperature conditions in the frame of the NEWAC project. For practical matters of operation among which the possibility to induce progressively a perturbation when the flame conditions are all set, the need was expressed to design, construct and validate a flexible actuator able to set an air flow modulation at a given frequency and at a desired amplitude level, with the possibility during operation to let these two factors vary in a given range independently from each other. This device should operate within the 0–1 kHz range and 0–20% amplitude range at steady-state, during transients, or follow a specific time sequence. It should be robust and sustain elevated pressures. The objective is to bring a perturbation in the flow to which the combustor will respond, or not. For elevated levels of pulsation, it can simulate the presence of vortex-driven combustion instabilities. It can also act as a real-time actuator able to respond in frequency and in phase to actively damp a “natural” combustion instability. Other issues are a better and quicker mixing due to the enhanced turbulence level, and pushing forward the blow out limits at lean conditions with controlled injection dynamics. The basic construction is the one of a siren, with an elevated pressure side where the air is throttled, and a low pressure outlet where the resulting sonic jet is sheared by a rotating wheel. A mechanism allows to let vary the surface of interaction between the wheel and the jet. Two electro-motors driven by Labview set both frequency and amplitude levels. This contribution describes the actuator’s principles, design, operation range and the results of the characterisation campaign.
Parametric Study of Fluidic Oscillators for Use in Active Boundary Layer Control
Authors: Mack Marion , Niehuis Reinhard , Fiala Andreas
Published: May 2012

A parametric study was conducted to identify the main factors influencing the frequency produced by fluidic oscillators with the goal of using the actuator to trigger boundary layer transition through the excitation of Tollmien Schlichting waves. Test bench conditions were chosen to match the static pressure at the actuation position on the candidate blade profile for a cascade exit Mach number of 0.6 and Reynolds numbers from 60,000 to 200,000. The inlet vs. outlet pressure ratio and the position and geometry of the outlet holes were all varied. Additionally, the effect of the oscillator’s scale and the feedback channel geometry were considered. The flow at the exit was measured using a hot wire, while Kulite pressure transducers were used to measure pressure fluctuations within the device. This paper shows that fluidic oscillators can achieve frequencies of 10 kHz and that the parameters considered play an important role in the performance of these devices.