bluuebunny/crossref_metadata_2025 huggingface dataset:
Space Cooling Potentials for Ambient Energy Sources Across the US
Authors: Robinson Brian S. , Sharp M. Keith
Published: March 2012

While solar energy provides a source for passive space heating across a variety of climates, other ambient energy sources may be more appropriate for passive space cooling. These ambient resources include ambient air at dry-bulb and wet-bulb temperatures, ground temperature at locations where the soil is cooler than the indoor comfort temperature, and night-sky radiant temperature, which is substantially lower than ambient air in most climates. The focus of this study was on comparing these sources to cooling loads across climates in the US. Using a degree-day approach, annual cooling potentials were calculated for over 800 TMY3 locations. Color-themed maps for each ambient source at several indoor comfort temperature ranges were constructed as visual references for design purposes. In addition, eight US cities (Denver, CO, Los Angeles, CA, Louisville, KY, Madison, WI, Miami, FL, New Orleans, LA, Phoenix, AZ and Washington DC) were selected to represent a range of climate characteristics, including seasonal ambient temperature, diurnal temperature swings, humidity and sky clearness. For each city, an ambient potential to cooling load ratio (ALR) was calculated, with the potential based on an indoor comfort temperature range of 68°F – 72°F and the load calculated with a base temperature of 65°F. ALR, which neglects phase lags between source and load and the associated need for thermal storage, exceeded one for dry-bulb air and for ground temperature for all locations except Miami, New Orleans and Phoenix. Wet-bulb ALR exceeded one for all locations except Miami, and sky ALR exceeded one for all locations. Finally, the effect of limited thermal storage was estimated by calculating daily ambient source fraction, fas, which is the daily ambient cooling potential divided by the daily cooling load. fas thus approximates the cooling potential of systems with one day’s worth of thermal storage, and has an upper limit of one. Fas, the annual sum of fas, equaled one for ground temperature for Los Angeles and Madison and for sky temperature for Denver and Los Angeles. Fas for ground temperature was above 0.9 for all locations except Miami, New Orleans and Phoenix. Fas for sky temperature exceeded 0.6 for all locations. By utilizing all possible combinations of ambient sources, half of the selected locations attained Fas equal to one and the minimum for all locations still exceeded 0.65.
Engineering the Photoanode Using Scalable Hybrid Nanostructures
Authors: Druffel Thad , Vendra Venkat Kalyan , Amos Delaina , Sunkara Mahendra
Published: March 2012

Dye sensitized solar cells (DSSCs) have garnered a great deal of interest as a cost-effective technology for large-scale manufacturing. Engineered inorganic hybrid nanostructures can improve the performance of DSSC’s without affecting the cost effectiveness of the devices. Here, we present a concept of engineered hybrid nanostructures, incorporating appropriate selection of nanowire and nanoparticle materials, to enhance the charge transport and reduce the recombination within the photoanode. Low recombination properties of this photoanode allow flexibility in choosing the redox couple for increasing open circuit voltage.
A Flux Mapping Method for Central Receiver Systems
Authors: Ho Clifford K. , Khalsa Siri S.
Published: March 2012

A new method is described to determine irradiance distributions on receivers and targets from heliostats or other collectors for concentrating solar power applications. The method uses a CCD camera, and, unlike previous beam characterization systems, it does not require additional sensors, calorimeters, or flux gauges on the receiver or target. In addition, spillage can exist (the beam does not need to be contained within the target). The only additional information required besides the digital images recorded from the CCD camera is the direct normal irradiance and the reflectivity of the receiver. Methods are described to calculate either an average reflectivity or a reflectivity distribution for the receiver using the CCD camera. The novel feature of this new PHLUX method is the use of recorded images of the sun to scale both the magnitude of each pixel value and the subtended angle of each pixel. A test was performed to evaluate the PHLUX method using a heliostat beam on the central receiver tower at the National Solar Thermal Test Facility in Albuquerque, NM. Results showed that the PHLUX method was capable of producing an accurate flux map of the heliostat beam with a relative error in the peak flux of 2%.
Enabling Technologies for High Penetration of Wind and Solar Energy
Authors: Denholm Paul
Published: March 2012

High penetration of variable wind and solar electricity generation will require modifications to the electric power system. This work examines the impacts of variable generation, including uncertainty, ramp rate, ramp range, and potentially excess generation. Time-series simulations were performed in the Texas (ERCOT) grid where different mixes of wind, solar photovoltaic and concentrating solar power provide up to 80% of the electric demand. Different enabling technologies were examined, including conventional generator flexibility, demand response, load shifting, and energy storage. A variety of combinations of these technologies enabled low levels of surplus or curtailed wind and solar generation depending on the desired penetration of renewable sources. At lower levels of penetration (up to about 30% on an energy basis) increasing flexible generation, combined with demand response may be sufficient to accommodate variability and uncertainty. Introduction of load-shifting through real-time pricing or other market mechanisms further increases the penetration of variable generation. The limited time coincidence of wind and solar generation presents increasing challenges as these sources provide greater than 50% of total demand. System flexibility must be increased to the point of virtually eliminating must-run baseload generators during periods of high wind and solar generation. Energy storage also becomes increasingly important as lower cost flexibility options are exhausted. The study examines three classes of energy storage — electricity storage, including batteries and pumped hydro, hybrid storage (compressed-air energy storage), and thermal energy storage. Ignoring long-distance transmission options, a combination of load shifting and storage equal to about 12 hours of average demand may keep renewable energy curtailment below 10% in the simulated system.
Developing a Flexible Platform for Optimal Engineering Design of Commercial Wind Farms
Authors: Chowdhury Souma , Zhang Jie , Messac Achille , Castillo Luciano
Published: March 2012

In this paper, we develop a flexible design platform to account for the influences of key factors in optimal planning of commercial scale wind farms. The Unrestricted Wind Farm Layout Optimization (UWFLO) methodology, which avoids limiting assumptions regarding the farm layout and the selection of turbines, is used to develop this design platform. This paper presents critical advancements to the UWFLO methodology to allow the synergistic consideration of (i) the farm layout, (ii) the types of commercial turbines to be installed, and (iii) the expected annual distribution of wind conditions at a particular site. We use a recently developed Kernel Density Estimation (KDE) based method to characterize the multivariate distribution of wind speed and wind direction. Optimization is performed using an advanced mixed discrete Particle Swarm Optimization algorithm. We also implement a high fidelity wind farm cost model that is developed using a Radial Basis Function (RBF) based response surface. The new optimal farm planning platform is applied to design a 25-turbine wind farm at a North Dakota site. We found that the optimal layout is significantly sensitive to the annual variation in wind conditions. Allowing the turbine-types to be selected during optimization was observed to improve the annual energy production by 49% compared to layout optimization alone.
Evaluation Criteria and Estimate of Output From a Small-Scale Wind Turbine
Authors: Small Dorothy S.
Published: March 2012

This paper will evaluate a specific site located in southwestern Virginia, providing design criteria that are important considerations at this site. The evaluation will predict the output from a 6 blade HAWT model at the height and location of the site. As a small scale wind turbine, the process of determination of relevant considerations to establish the turbine selection and output are weighted to establish the evaluation criteria. A review of the specific site conditions are presented in detail. This information includes: three-dimensional topographic review, wind and weather profile of the site and surrounding environmental conditions of the site. With this information the decision path for the specific siting is discussed. Characteristics of the site that will be considered to calculate output are: historical data of wind profile of the region, height of tower, affect of other objects and affect of wind turbulence. A discussion of current modeling options will be compared. The design and components of the small scale wind turbine chosen for this application will be compared to other wind turbines of similar size and cost. Considerations of the turbine that are considered are: size of wind turbine, cost of wind turbine, predictable output of the wind turbine based on design of the various wind turbines, requirements for the tower for each turbine and predicted maintenance for each turbine. Initial performance of the selected turbine will be available by presentation of information.
Design and Construction of Grid Attached Storage Simulator
Authors: Lutz Markus , Zimmerle Daniel , Huff Brian , Bradley Thomas
Published: March 2012

Using a Variable Frequency Drive, 15kWh battery pack, and Active Front End control, Colorado State University has designed and built a real-world functional test stand to study the effects of attaching a battery power pack to the grid for grid stabilization. This paper describes the design, analysis, and construction of the Grid Attached Storage simulation laboratory. An in-depth discussion of the design, selection and specifications of components including the LCL filter, transformer, grid attachment, line synchronization card, software control, and safety measurements is discussed. The dynamics and control of grid-attached storage can be investigated using this lab. Battery temperatures, charging/discharging cycles, and battery degradation can also be better understood with the use of this system. Second life batteries can be used as well to investigate their characteristics, economical benefits, and quality of use. Using grid interaction, the batteries can work in a variety of ways including: frequency regulation, V2G simulation of opportunity charging, and renewable energy smoothing.
Review of Combined Space and Domestic Hot Water Heating Systems for Solar Applications
Authors: Dickinson Ryan M. , Cruickshank Cynthia A.
Published: March 2012

Solar heating systems are widely used in several European countries for domestic hot water heating, and in the past decade, an increasing number of solar combined space and hot water heating systems (typically referred to as “combisystems”) have begun to take precedence. In Canada, however, the majority of all residential solar thermal installations are for heating domestic hot water. To date, various combisystem configurations have been investigated under the auspices of the International Energy Agency, Task 26 and Task 32. Within these tasks, various system configurations were modelled and test procedures developed to allow standard performance evaluations to be conducted. This work, although extensive, has limited application within the North American context. At present, little research has been conducted on the applicability of these systems for residential housing. In particular, due to Canada’s more severe winters, larger solar collector arrays would be required to significantly contribute to the space heating load. This has drawbacks, as much of the solar capacity would not be utilized during the summer, leading to poor economic performance and possible overheating that could accelerate degradation or scald occupants. Therefore, there is a need to optimize the configuration of solar combisystems to avoid over-sizing while maximizing the utilization of solar energy in a safe and economic manner. This paper presents a review of the current literature on solar combined space and domestic hot water heating systems, with a particular emphasis on the work which has been conducted by the International Energy Agency. In addition, a review of combined space and domestic hot water systems currently installed in Canada are also discussed.
Thermocline Energy Storage in the Solar One Power Plant: An Experimentally Validated Thermomechanical Investigation
Authors: Flueckiger Scott , Yang Zhen , Garimella Suresh V.
Published: March 2012

The growing interest in large-scale solar power production has led to a renewed exploration of thermal storage technologies. In a thermocline storage system, heat transfer fluid (HTF) from the collection field is simultaneously stored at both excited and dead thermal states inside a single tank. A granulated porous medium included in the tank provides thermal mass for storage and reduces the amount of HTF volume required. While the thermocline offers a low-cost storage option, thermal ratcheting of the tank wall (generated by filler material reorientation from continuous thermal cycling) poses a significant design concern. A comprehensive simulation of the 170 MWht thermocline tank used in conjunction with the Solar One pilot plant is performed with a multi-dimensional two-temperature computational fluid dynamics model. In operation from 1982 to 1986, this tank was subject to extensive instrumentation, including multiple strain gages along the tank wall to monitor hoop stress. Temperature profiles along the wall material are extracted from the simulation results to compute hoop stress via finite element models and compared with the original gage data. While the strain gages experienced large uncertainty, the stresses computed from the simulation agree reasonably well with the experimental measurements. The maximum predicted hoop stress agrees to within 6.8% of the maximum stress recorded by the most reliable strain gages.
Optimum Microturbine Sizing in Small Scale CHP Systems
Authors: Aghaei Meybodi Mehdi , Behnia Masud
Published: March 2012

Microturbines are ideally suited for distributed generation applications due to their flexibility in connection methods. They can be stacked in parallel for larger loads and provide stable and reliable power generation. One of the main applications of microturbines is operating as the prime mover in a combined heat and power (CHP) system. CHP systems are considered to be one of the best ways to produce heat and power with efficient fossil fuel consumption. Further, these systems emit less pollution compared to separate productions of the same amount of electricity and heat. In order to optimally benefit from combined heat and power systems, the proper sizing of prime movers is of paramount importance. This paper presents a technical-economic method for selecting the optimum number and nominal power as well as planning the operational strategy of microturbines as the prime movers of small scale combined heat and power systems (capacities up to 500 kW) in three modes of operation: one-way connection (OWC) mode, two-way connection (TWC) mode, and heat demand following (HDF) mode. In the proposed sizing procedure both performance characteristics of the prime mover and economic parameters (i.e. capital and maintenance costs) are taken into account. As the criterion for decision making Net Present Worth (NPW) is used. In our analysis we have also considered the impact of carbon tax on the economics of generation. The proposed approach may also be used for other types of prime movers as well as other sizes of CHP system.
Wind-Tunnel Tests of Vertical-Axis Wind Turbine Blades
Authors: Plourde B. D. , Abraham J. P. , Mowry G. S. , Minkowycz W. J.
Published: March 2012

An ongoing research project is investigating the potential of locating vertical-axis wind turbines (WT) on remote, off-grid cellular communication towers. The goal of the WT is to provide local power generation to meet the electrical needs of the tower. While vertical-axis devices are less efficient than their more traditional horizontal-axis counterparts, they provide a number of practical advantages which make them a suitable choice for the present situation. First, the direction of their axis is aligned with the existing tower and its rotation does not interfere with the tower structure. Second, vertical-axis devices are much less susceptible to the direction of wind and they do not require control-systems to ensure they are oriented correctly. Third, vertical-axis turbines have very low start-up wind speeds so that they generate power over a wide range of speeds. Fourth, since vertical-axis turbines rotate at a slower speed compared with horizontal counterparts, they impart a lessened vibration load to the tower. These facts, collectively, make the vertical-axis turbine suitable for the proposed application. The design process involved a detailed initial design of the turbine blade using computational methods. Next, a trio of designs was evaluated experimentally in a large, low-speed wind tunnel. The wind tunnel is operated by the University of Minnesota’s St. Anthony Falls Fluid Laboratory. The tunnel possesses two testing sections. The larger section was sufficient to test a full-size turbine blade. Accounting was taken of the blockage effect following the tests. The experiments were completed on (1) a solid-wing design (unvented), (2) a slotted-wing design (vented), and (3) a capped-and-slotted design (capped). Conditions spanned a wide range of wind speeds (4.5–11.5 m/s). The turbines were connected to electronics which simulated a range of electrical loads. The tested range was selected to span the expected range of resistances which will be found in practice. It was discovered that over a range of these wind speeds and electrical resistances, slots located on the wings result in a slight improvement in power generation. On the other hand, the slotted-and-capped design provided very large increases in performance (approximately 200–300% compared with the unvented version). This large improvement has justified commercialization of the product for use in powering remote, off-grid cellular communication towers.
Performance Analysis of Diffuser-Augmented Composite Marine Current Turbine Using CFD
Authors: Wang Jifeng , Piechna Janusz , Gower Blake , Mu¨ller Norbert
Published: March 2012

A wound composite material wheel has been developed and is intended to be used for many purposes. One of these applications is marine current turbine. Diffuser-augmented turbines are capable of concentrating the energy in water. If a diffuser shaped shroud encloses a conventional horizontal axis turbine, the low pressure at the exit of the diffuser draws a larger mass flow through the turbine. This permits more power to be extracted from the water. In this paper, numerical analysis of a diffuser-augmented composite material marine current turbine (CMMCT) is developed and compared with a conventional bare turbine. The CFD results show that the extracted power of a diffuser-augmented CMMCT can be 5 times larger than the power extracted by a bare turbine of the same turbine area. The results of the analysis provide an insight into the hydrodynamic design and operation of a diffuser-augmented turbine in order to shorten the design period and improve technical performance.
Numerical Study on Composite Material Marine Current Turbine Under Various Hydrodynamic Conditions
Authors: Wang Jifeng , Piechna Janusz , Qu Yunfei , Mu¨ller Norbert
Published: March 2012

A novel manufacturing approach similar to filament winding has been developed and automated and is able to produce the Composite Material Marine Current Turbines (CMMCT), which have significant advantages over traditional designs. This paper presents numerical results to investigate the performance of these turbines. The numerical approach was performed using Computational Fluid Dynamics (CFD) in a free stream of water with various hydrodynamic flow conditions. Static torque and extracted power are calculated at different rotating speeds in a free stream with various hydrodynamics flow conditions. The calculated results will provide a fundamental understanding of the impeller as a water turbine, and this design method is used to shorten the design process and improve the water turbine’s performance.
Fast Pyrolysis of Biomass With Activated Alumina
Authors: Ates¸ Funda
Published: March 2012

In this study, corncob was chosen as a biomass sample and the pyrolysis of this sample was carried out with or without catalyst at different conditions in a well-swept fixed-bed reactor. In the experimental studies, firstly the raw material was analysed for its moisture, ash, volatile matter and fixed carbon. Then, experiments were conducted with a heating rate of 700 °C/min, mean particle size and between 300–800 °C pyrolysis temperatures with or without catalyst. The catalytic experiments involved a dry mixing of the catalyst with the biomass using an in bed-mode in the nitrogen atmosphere. In the experimental studies, influence of catalyst and temperature on the corncob products was investigated. According to the experimental results; maximum bio-oil yield was obtained as 36.1% and 34.8% with or without catalyst at a pyrolysis temperature of 500°C, respectively. The use of catalyst showed its cracking effect at higher temperatures and the gas yield increased above pyrolysis temperature of 500 °C. Pyrolysis oils were examined by using elemental analysis and GC/MS. According to all results; the use of catalyst can be suggested in the pyrolysis to obtain both good quality fuels and valuable chemicals.
An Examination of the Effect of Reynolds Number on Airfoil Performance
Authors: Burdett Tim , Gregg Jason , Van Treuren Kenneth
Published: March 2012

The standard of living throughout the world has increased dramatically over the last 30 years and is projected to continue to rise. This growth leads to an increased demand on conventional energy sources, such as fossil fuels. However, these are finite resources. Thus, there is an increasing demand for alternative energy sources, such as wind energy. Much of current wind turbine research focuses on large-scale (>1 MW), technologically-complex wind turbines installed in areas of high average wind speed (>20 mph). An alternative approach is to focus on small-scale (1–10kW), technologically-simple wind turbines built to produce power in low wind regions. While these turbines may not be as efficient as the large-scale systems, they require less industrial support and a less complicated electrical grid since the power can be generated at the consumer’s location. To pursue this approach, a design methodology for small-scale wind turbines must be developed and validated. This paper addresses one element of this methodology, airfoil performance prediction. In the traditional design process, an airfoil is selected and published lift and drag curves are used to optimize the blade twist and predict performance. These published curves are typically generated using either experimental testing or a numeric code, such as PROFIL (the Eppler Airfoil Design and Analysis Code) or XFOIL. However, the published curves often represent performance over a different range of Reynolds numbers than the actual design conditions. Wind turbines are typically designed from 2-D airfoil data, so having accurate airfoil data for the design conditions is critical. This is particularly crucial for small-scale, fixed-pitched wind turbines, which typically operate at low Reynolds numbers (<500,000) where airfoil performance can change significantly with Reynolds number. From a simple 2-D approach, the ideal operating condition for an airfoil to produce torque is the angle of attack at which lift is maximized and drag is minimized, so prediction of this angle will be compared using experimental and simulated data. Theoretical simulations in XFOIL of the E387 airfoil, designed for low Reynolds numbers, suggest that this optimum angle for design is Reynolds number dependent, predicting a difference of 2.25° over a Reynolds number range of 460,000 to 60,000. Published experimental data for the E387 airfoil demonstrate a difference of 2.0° over this same Reynolds number range. Data taken in the Baylor University Subsonic Wind Tunnel for the S823 airfoil shows a similar trend. This paper examines data for the E387 and S823 airfoils at low Reynolds numbers (75,000, 150,000, and 200,000 for the S823) and compares the experimental data with XFOIL predictions and published PROFIL predictions.
Evaluation of Energy Efficiency Improvement Program for Rental Homes
Authors: Herrmann Lesley , Krarti Moncef
Published: March 2012

Recently, the city of Boulder, CO has recently approved mandatory energy efficiency standard, called SmartRegs Program, for rental properties. Improving residential energy efficiency is a goal of the city as they strive to meet the green house gas reduction targets of the Kyoto Protocol. However, energy efficiency is typically not implemented in rental units because of a split incentive between landlords and tenants. This paper evaluates the various retrofit measures that improve rental homes energy efficiency as well as the effectiveness of SmartRegs Program. First, various energy efficiency measures are evaluated through walk-through and detailed energy audits to assess their effectiveness in improving the energy performance of rental homes. Based on the results of the energy audits and survey of various stake holders, a set of recommendations have been defined to ensure that the SmartRegs program be successfully implemented in order to improve the overall performance and quality of rental homes. Moreover, it is found that energy efficient can increase the thermal comfort levels and decrease the energy costs for tenants, increase the value of the property for landlords, and help the city meet their green house gas reduction goals.
Nonlinear Energy Harvesting Using Coupled Micro-Scale Oscillator Arrays
Authors: Ramakrishnan Subramanian , Kumar Manish
Published: March 2012

Vibration energy harvesting paradigms that seek to exploit the unique characteristics of nonlinear and stochastic systems are currently emerging as an important aspect of frontier research in energy sustainability. In particular, the ubiquitous nature of ambient mechanical vibrations and recent results obtained in the dynamics of micro and nano scale oscillatory systems together suggest the potential efficacy of vibration energy harvesting for the powering of small scale electronic mobile devices. In this context, the inherent advantages of using nonlinear systems over linear ones for energy harvesting are currently well established. In addition, the inherently random nature of ambient vibrations as well as the emergence of phenomena such as stochastic resonance indicates the imperativeness of a stochastic approach. Computational and experimental studies of energy harvesting involving individual nonlinear oscillators that take into account some of the above mentioned features have recently been reported in the literature. In this article, the authors present a new approach to the problem by introducing an analytical framework based on the Fokker-Planck formalism. In particular, the framework is applied to a nonlinearly coupled array of micro-scale oscillators in order to investigate the potential advantages of stochastic effects in coupled arrays for energy harvesting. The influence of varying coupling strengths as well as noise intensity on harvestable energy is studied for the case of a nonlinearly coupled micro-cantilever array. It is noted that the micro-scale arrays of the type under consideration have already been employed in experimental investigations of energy localization effects and hence are currently available for technological applications. In conclusion, the analytical framework introduced and the results obtained in this article are expected to contribute to a fundamental understanding of how the synergistic effects of nonlinear and stochastic phenomena could contribute to the development of novel methods for efficient vibration energy harvesting.
An Interdisciplinary Graduate Level Course in Battery Systems Engineering
Authors: Schumack Mark , Siavoshani Saeed J. , Benvenuto Mark
Published: March 2012

The recent introduction of plug-in hybrid electric and fully electric vehicles by major automotive manufacturers signals the advent of technologies that can help us move away from petroleum and towards a more sustainable transportation future. As the demand for electric vehicles grows, there will be an increased need for engineers who can design battery systems that satisfy the stringent energy storage and power delivery demands of passenger vehicles. This paper describes a new course at the University of Detroit Mercy intended to teach students about battery systems engineering. The course is offered as part of a newly-established Advanced Electric Vehicle graduate-level certificate program. The design of a battery system is highly interdisciplinary in nature. Engineers must address mechanical concerns such as packaging, vibration, torsional loads, impact resistance and thermal management; electrical aspects such as those associated with battery monitoring and control; and the electrochemical phenomena that governs capacity, power delivery and absorption, degradation and operating temperatures. A key challenge in the course design was tailoring the material to students with diverse backgrounds which include undergraduate degrees in mechanical, electrical and chemical engineering. The paper describes the development process for the course outcomes, the typical student audience, the structure of the team delivery and the topics covered including examples of lecture material and student assignments. It concludes by summarizing student and instructor feedback along with plans for future course delivery.
Assessing Wind Resource Potential in the Built Environment
Authors: Stewart Susan W. , Haupt Sue Ellen , Cole Julia A.
Published: March 2012

This study addresses the issue of siting wind turbines on existing structures in the built environment for optimal performance. Annually averaged wind power maps were produced over the surface of two different building types using a Detached Eddy Simulation (DES) model in order to assess the feasibility of building integrated wind under various wind resource conditions. The modeling approach was first applied to a cubical geometry for which validation of the CFD results was possible with existing field measurements. A pitched roof building was also modeled to study the power density over top of typical residential shaped structures. The average annual power density for twenty-seven locations over the top of the modeled structures was analyzed under varying wind direction distributions (wind roses). The overall results of this study have the potential to inform the wind energy and built environment communities on best practices for siting wind turbines on or near buildings.
Rule-Based and Expert Icing Screening Approaches for Wind Energy Measurements: Impacts, Methods, and Improvements
Authors: Harris James C. , Womeldorf Carole A.
Published: March 2012

Wind resource assessments produce hundreds of thousands of measurements every year. Before determination of the wind power density, a function of the velocity cubed, those values are screened to remove erroneous data points. Typical categories of erroneous data are sensor malfunction, tower shading, and icing. Identification of tower shading is a well established procedure dependent on the mounting direction of the sensor booms. Most instrument malfunctions are clearly extended flat lines and typically only affect one sensor at a time. Sensor icing of anemometers and directional vanes, on the other hand, can be subtle and affect more than one sensor simultaneously and can require an experienced evaluator’s assessment. Designation of icing results in the removal of lower velocity data. If too few points are removed the wind velocity will be underestimated, while if too many points are removed the wind velocity can be exaggerated, both of which can have a significant influence on the power density due to the cube effect. And experts frequently disagree. Much of this disagreement is driven by the difference between rule based approaches and operator judgment approaches. A comparison of different screening approaches for icing is described in this work. Three different rule-based approaches are compared against a visually-based expert determination that combines multiple sensors, including temperature, humidity, directional vanes and anemometers with several rule based approaches. Relative impacts of different approaches can affect from 1.09% for a visually-based expert approach to 5.03% for a rule-based standard deviation approach.
Experimental Study of Solar Air Heating System Based on Unglazed Transpired Collector
Authors: Gao Lixin , Bai Hua , Fang Xiumu
Published: March 2012

An experimental rig was set up to test the thermal performance of a solar air heating system based on an unglazed transpired collector of 2.5 m2. The experiment was carried out at Harbin Institute of Technology in the city of Harbin, which is located in northeastern China, at latitude 45°41′ N and longitude 126°37′ E. The tests were spread over a number of days, in which the 4-day experimental data within the period were selected as the sample for analysis. Experimental results show that solar collector’s surface temperature and exit air temperature increase with increasing solar irradiation. The influence of ambient temperature on surface temperature and exit temperature is negligible. Temperature rise decreases with increasing air flow rate, while collector efficiency increases with increasing air flow rate. For an air flow rate of 100 m3/h in Test 1, the average air temperature rise and collector efficiency were 28.86°C and 72% respectively; for an air flow rate of 235 m3/h in Test 2, the average air temperature rise and collector efficiency were 11.52°C and 78% respectively. Higher airflow rate tends to operate the collector at lower surface temperature, which results in lower overall heat losses from the collector to the surroundings, therefore increasing airflow rate reduces air temperature rise and enhances the collector efficiency. The average efficiency of the experimental solar air heating system in the 4-day experiment period was 72%, 78%, 61%, and 72% respectively, which are higher than most conventional glazed flat-plate solar air collectors. With better coordination with architectural design at early stage in a project, this building-integrated solar air heating system can be both aesthetically and technically viable.
Maximizing the Life Cycle Primary Energy Savings of an Integrated Solar Absorption Cooling and Heating System for a Medium-Sized Office Building in Los Angeles, California
Authors: Hang Yin , Qu Ming
Published: March 2012

Buildings are responsible for 41% of the primary energy use in the United States. Due to the negative environmental impact from fossil fuel, people are trying to use renewable energy resources to provide energy to the buildings. Integrated solar absorption cooling and heating (SACH) technology can be one of the promising solutions to this issue. Due to the nature of solar energy, integrated SACH has many drawbacks, such as discontinuity of generation, thus backup system driven by fossil fuel should be included to the system configuration as well. Therefore, optimization is highly required during the design stage. This paper presents the development of a method to optimize an integrated SACH system. Regression analysis is used to identify the relationship between the life cycle primary energy savings (PES) and the system factors according to the data provided by experiments. In order to obtain an accurate model to estimate the problem using small number of experimental trials, the method of central composite design (CCD) from design of experiments (DE) is used as a key technique. The experimental trials are conducted in TRaNsient SYstems Simulation (TRNSYS). Finally, the optimization problem is formulated and solved by including the model as the objective function and the physical constraints of the system factors. A case study was conducted to apply this optimization method to the design of an integrated SACH system installed in a medium-sized office building in Los Angeles.
Passive geoacoustic inversion with a single hydrophone using broadband ship noise
Authors: Gervaise C. , Kinda B. G. , Bonnel J. , Stéphan Y. , Vallez S.
Published: March 2012

An inversion scheme is proposed, relying upon the inversion of the noise of a moving ship measured on a single distant hydrophone. The spectrogram of the measurements exhibits striations which depend on waveguide parameters. The periodic behavior of striations versus range are used to estimate the differences of radial wavenumber between couples of propagative modes at a given frequency. These wavenumber differences are stacked for several frequencies to form the relative dispersion curves. Such relative dispersion curves can be synthesized using a propagation model feeded with a bottom geoacoustic model. Inversion is performed by looking for the bottom properties that optimize the fit between measured and predicted relative dispersion curves. The inversion scheme is tested on simulated data. The conclusions are twofold: (1) a minimum 6 dB signal to noise ratio is required to obtained an unbiased estimate of compressional sound speed in the bottom with a 3 m s−1 standard deviation; however, even with low signal to noise ratio, the estimation error remains bounded and (2) in the case of a multi-layer bottom, the scheme produces a single depth-average compressional sound speed. The inversion scheme is applied on experimental data. The results are fully consistent with a core sample measured around the receiving hydrophone.
Loudspeaker line array educational demonstration
Authors: Anderson Brian E. , Moser Brad , Gee Kent L.
Published: March 2012

This paper presents a physical demonstration of an audio-range line array used to teach interference of multiple sources in a classroom or laboratory exercise setting. Software has been developed that permits real-time control and steering of the array. The graphical interface permits a user to vary the frequency, the angular response by phase shading, and reduce sidelobes through amplitude shading. An inexpensive, eight-element loudspeaker array has been constructed to test the control program. Directivity measurements of this array in an anechoic chamber and in a large classroom are presented. These measurements have good agreement with theoretical directivity predictions, thereby allowing its use as a quantitative learning tool for advanced students as well as a qualitative demonstration of arrays in other settings. Portions of this paper are directed toward educators who may wish to implement a similar demonstration for their advanced undergraduate or graduate level course in acoustics.
Mathematics summer schools for acoustics research training
Authors: Attenborough Keith , Wright Matthew , Umnova Olga
Published: March 2012

Mathematical methods are important for research in many aspects of acoustics. Most researchers in acoustics in the United Kingdom do not have access to master level courses to broaden their postgraduate study, so they advance their fundamental mathematical methodologies taught at undergraduate level through independent learning. They develop their mathematical skills as appropriate rather than being made aware of the potential of advanced mathematical tools at the onset of their research career. Attempts to improve this situation were made through summer schools held in 2003 and 2005 at Southampton University and in 2007 at Salford University. The background to these Summer Schools, their content and structure, recruitment figures and student feedback are reported together with conclusions about their performance and role particularly in respect of PhD completion.
Raising public awareness of acoustic principles using voice and speech production
Authors: Howard David M.
Published: March 2012

Public engagement with science, technology, and engineering is seen as being increasingly important as the numbers of school leavers choosing to read for degrees in these areas is typically dropping. Engagement with pupils during their school years is seen as being a key element in influencing their choices of career for which seeds are sown from the primary years. Acoustics is an excellent vehicle for public engagement since the demonstrations can be appreciated directly by the sense of hearing and the underlying principles also apply in many branches of physics and engineering. This paper describes a number of demonstrations that have been employed during science engagement events for schools and the general public in the context of the principles of acoustics and human speech production. The apparatus used, which in some cases has been purpose-built, is described along with the activities themselves. In addition, a way to quantify the success of the process is proposed that involves a single button press on entry to and exit from an event.
Place-pitch manipulations with cochlear implants
Authors: Macherey Olivier , Carlyon Robert P.
Published: March 2012

Pitch can be conveyed to cochlear implant listeners via both place of excitation and temporal cues. The transmission of place cues may be hampered by several factors, including limitations on the insertion depth and number of implanted electrodes, and the broad current spread produced by monopolar stimulation. The following series of experiments investigate several methods to partially overcome these limitations. Experiment 1 compares two recently published techniques that aim to activate more apical fibers than produced by monopolar or bipolar stimulation of the most apical contacts. The first technique (phantom stimulation) manipulates the current spread by simultaneously stimulating two electrodes with opposite-polarity pulses of different amplitudes. The second technique manipulates the neural spread of excitation by using asymmetric pulses and exploiting the polarity-sensitive properties of auditory nerve fibers. The two techniques yielded similar results and were shown to produce lower place-pitch percepts than stimulation of monopolar and bipolar symmetric pulses. Furthermore, combining these two techniques may be advantageous in a clinical setting. Experiment 2 proposes a method to create place pitches intermediate to those produced by physical electrodes by using charge-balanced asymmetric pulses in bipolar mode with different degrees of asymmetry.
Pulse propagation in an elastic medium with quadratic nonlinearity (L)
Authors: Qu Jianmin , Nagy Peter B. , Jacobs Laurence J.
Published: March 2012

This letter examines the propagation of an acoustic pulse in an elastic medium with weak quadratic nonlinearity. Both a displacement pulse and a stress pulse of arbitrary shapes are used to generate the wave motion in the solid. By obtaining the explicit solutions for arbitrary pulse shapes, it is shown that for a sinusoidal tone-burst, in addition to a second order harmonic field, a radiation induced static strain field is also generated. These results help clarify some confusion in the recent literature regarding the shape of the propagating static displacement pulse.
Reflectance of acoustic horns and solution of the inverse problem
Authors: Rasetshwane Daniel M. , Neely Stephen T. , Allen Jont B. , Shera Christopher A.
Published: March 2012

A method is described for solving the inverse problem of determining the profile of an acoustic horn when time-domain reflectance (TDR) is known only at the entrance. The method involves recasting Webster’s horn equation in terms of forward and backward propagating wave variables. An essential feature of this method is a requirement that the backward propagating wave be continuous at the wave-front at all locations beyond the entrance. Derivation of the inverse solution raises questions about the meaning of causality in the context of wave propagation in non-uniform tubes. Exact reflectance expressions are presented for infinite exponential, conical and parabolic horns based on exact solutions of the horn equation. Diameter functions obtained with the inverse solution are a good match to all three horn profiles.
Properties of the acoustic intensity vector field in a shallow water waveguide
Authors: Dall’Osto David R. , Dahl Peter H. , Woong Choi Jee
Published: March 2012

Acoustic intensity is a vector quantity described by collocated measurements of acoustic pressure and particle velocity. In an ocean waveguide, the interaction among multipath arrivals of propagating wavefronts manifests unique behavior in the acoustic intensity. The instantaneous intensity, or energy flux, contains two components: a propagating and non-propagating energy flux. The instantaneous intensity is described by the time-dependent complex intensity, where the propagating and non-propagating energy fluxes are modulated by the active and reactive intensity envelopes, respectively. Properties of complex intensity are observed in data collected on a vertical line array during the transverse acoustic variability experiment (TAVEX) that took place in August of 2008, 17 km northeast of the Ieodo ocean research station in the East China Sea, 63 m depth. Parabolic equation (PE) simulations of the TAVEX waveguide supplement the experimental data set and provide a detailed analysis of the spatial structure of the complex intensity. A normalized intensity quantity, the pressure-intensity index, is used to describe features of the complex intensity which have a functional relationship between range and frequency, related to the waveguide invariant. The waveguide invariant is used to describe the spatial structure of intensity in the TAVEX waveguide using data taken at discrete ranges.
Evidence of Doppler-shifted Bragg scattering in the vertical plane by ocean surface waves
Authors: Lynch Stephen D. , D’Spain Gerald L.
Published: March 2012

A set of narrowband tones (280, 370, 535, and 695 Hz) were transmitted by an acoustic source mounted on the ocean floor in 10 m deep water and received by a 64-element hydrophone line array lying on the ocean bottom 1.25 km away. Beamformer output in the vertical plane for the received acoustic tones shows evidence of Doppler-shifted Bragg scattering of the transmitted acoustic signals by the ocean surface waves. The received, scattered signals show dependence on the ocean surface wave frequencies and wavenumber vectors, as well as on acoustic frequencies and acoustic mode wavenumbers. Sidebands in the beamformer output are offset in frequency by amounts corresponding to ocean surface wave frequencies. Deviations in vertical arrival angle from specular reflection agree with those predicted by the Bragg condition through first-order perturbation theory using measured directional surface wave spectra and acoustic modes measured by the horizontal hydrophone array.