bluuebunny/crossref_metadata_2025 huggingface dataset:
Data Center Cooling Efficiency Improvement Through Localized and Optimized Cooling Resources Delivery
Authors: Zhou Rongliang , Bash Cullen , Wang Zhikui , McReynolds Alan , Christian Thomas , Cader Tahir
Published: October 2013

Data centers are large computing facilities that can house tens of thousands of computer servers, storage and networking devices. They can consume megawatts of power and, as a result, reject megawatts of heat. For more than a decade, researchers have been investigating methods to improve the efficiency by which these facilities are cooled. One of the key challenges to maintain highly efficient cooling is to provide on demand cooling resources to each server rack, which may vary with time and rack location within the larger data center. In common practice today, chilled water or refrigerant cooled computer room air conditioning (CRAC) units are used to reject the waste heat outside the data center, and they also work together with the fans in the IT equipment to circulate air within the data center for heat transport. In a raised floor data center, the cool air exiting the multiple CRAC units enters the underfloor plenum before it is distributed through the vent tiles in the cold aisles to the IT equipment. The vent tiles usually have fixed openings and are not adapted to accommodate the flow demand that can vary from cold aisle to cold aisle or rack to rack. In this configuration, CRAC units have the extra responsibilities of cooling resources distribution as well as provisioning. The CRAC unit, however, does not have the fine control granularity to adjust air delivery to individual racks since it normally affects a larger thermal zone, which consists of a multiplicity of racks arranged into rows. To better match cool air demand on a per cold aisle or rack basis, floor-mounted adaptive vent tiles (AVT) can be used to replace CRAC units for air delivery adjustment. In this arrangement, each adaptive vent tile can be remotely commanded from fully open to fully close for finer local air flow regulation. The optimal configuration for a multitude of AVTs in a data center, however, can be far from intuitive because of the air flow complexity. To unleash the full potential of the AVTs for improved air flow distribution and hence higher cooling efficiency, we propose a two-step approach that involves both steady-state and dynamic optimization to optimize the cooling resource provisioning and distribution within raised-floor air cooled data centers with rigid or partial containment. We first perform a model-based steady-state optimization to optimize whole data center air flow distribution. Within each cold aisle, all AVTs are configured to a uniform opening setting, although AVT opening may vary from cold aisle to cold aisle. We then use decentralized dynamic controllers to optimize the settings of each CRAC unit such that the IT equipment thermal requirement is satisfied with the least cooling power. This two-step optimization approach simplifies the large scale dynamic control problem, and its effectiveness in cooling efficiency improvement is demonstrated through experiments in a research data center.
Comparison of Methods for Tracking Control of Nonlinear Uncertain Multi-Body Mechanical Systems
Authors: Udwadia F. E. , Wanichanon T.
Published: October 2013

This paper presents a comparison of several alternative approaches to obtaining tracking control of a nonlinear uncertain system. A real-life multi-body system is in general highly nonlinear and is intrinsically error-prone due to uncertainties in the modeling system. The uncertainty which is time-varying, unknown but bounded, is therefore assumed in this paper, whereby it may arise from two general sources: uncertainty in the knowledge of the physical system and/or uncertainty in the ‘given force’ applied to the system. In this paper, the use of a new, generalized nonlinear controller is illustrated incorporating two control laws—generalized sliding surface control and generalized damping control. The generalized damping control law also provides two control approaches, one with an uncertainty bound and one without the bound on uncertainty. This leads to three sets of closed-form controllers that can guarantee, regardless of the uncertainty, a tracking signal of a desired reference trajectory of the nominal system, which we refer to as our best assessment of the actual real-life situation. A comparison of the use of the proposed three control designs is demonstrated using an example of a control problem in multi-body dynamics. Both the generalized sliding surface controller and the generalized bound damping controller require knowledge of the bound on uncertainty in order to guarantee a tracking signal of a desired reference trajectory within a desired error bound. In contrast, when using the generalized no-bound damping controller, tracking of the nominal system trajectory can be obtained regardless of the knowledge of the uncertainty’s bound. However, the tracking results from the generalized no-bound damping controller are the least optimal when compared with those obtained from the other two controllers. With simplicity and accuracy obtained, all three control approaches can be implemented for a wide range of complex multi-body mechanical systems.
Functional Analysis of Bushing in Four-Link Suspension on K&C Characteristics Using Multibody Dynamics Method
Authors: Song Kang , Chen Xiao-kai , Lin Yi , Ma Zheng-Dong
Published: October 2013

The link of multilink suspension usually has bushings at both body connection and wheel carrier connection. These bushings are designed subjected to the function of link. In the studies of vehicle dynamics, bushing could be represented by three translational stiffness and three torsional stiffness as well as corresponding damping. Due to specific location and orientation of each bushing, usually only one of these six stiffness plays an important role. In this paper, effect of bushing on suspension K&C characteristics was investigated with a four-link suspension. Through virtual loading tests, force distribution of suspension bushing was studied to find the relation between bushing stiffness and K&C characteristics. In order to quantitatively measure effect of bushing stiffness on parasitic rate, an “equivalent force” method based on energy conservation was proposed. Similarly, an “equivalent displacement” method was proposed to measure effect of bushing stiffness on suspension compliance. According to theoretical analysis and numerical calculation result, six stiffness of a bushing could be classified into three categories: main function stiffness closely related to suspension behavior, sub-function stiffness affecting parasitic rate or subjected to large load and non-function stiffness to be controlled within an acceptable range.
Dynamic Simulation of an Ejector-Based Cooling System for Residential Solar Air-Conditioning
Authors: Gavioli Stefano , Seynhaeve Jean-Marie , Bartosiewicz Yann
Published: October 2013

A smart and sustainable way to produce cooling power during the hot season is through thermal activated compression. One of the most promising technology is the ejector cycle. An experimental machine based on this technology has been designed and built at Université Catholique de Louvain (UCL). This study presents a dynamic simulation model of a full house incorporating solar collectors to produce domestic hot water and to feed an ejector-based solar air-conditioning machine. The model takes into account geographic location, transient thermal house behaviour, and also integrates a performance map of the ejector cycle based on real measurement campaign. Different types of collectors and storage sizes have been studied as well. In this paper, the developed model is used to analyze and optimize operation and strategy of hot water production and air conditioning. Results show that the full solar solution may cover low energy house needs.
Optimal Design of Combined Heat and Power System Using R-Curve Concept
Authors: Khoshgoftar Manesh Mohammad Hasan , Navid Pooya , Amidpour Majid , Blanco Marigorta Ana Maria
Published: October 2013

In this paper, a new procedure has been introduced for optimal design of utility system in process industries. This method is based on the development of the R-curve concept by using estimation of costs, environmental impacts and exergoeconomic analysis. This new method can be applied for synthesis of site utility system in grassroot problems. In addition, the powerful and accurate cogeneration targeting method has been used. Also, the new graphical representations have been proposed. These curves are easy to be constructed simple to be understood. In this paper, optimal design of site utility has been carried out in the case study, in which the usefulness of this method is clearly demonstrated. The computer code has been provided based on new procedure to optimal design of site utility at fixed heat demand.
Thermal Energy Storages Analysis for High Temperature in Air Solar Systems
Authors: Andreozzi Assunta , Buonomo Bernardo , Manca Oronzio , Tamburrino Salvatore
Published: October 2013

In this paper a high temperature thermal storage in a honeycomb solid matrix is numerically investigated and a parametric analysis is accomplished. In the formulation of the model it is assumed that the system geometry is cylindrical, the fluid and the solid thermophysical properties are temperature independent and radiative heat transfer is take into account whereas the effect of gravity are neglected. Air is employed as the working fluid and the solid material is cordierite. The evaluation of the fluid and thermal behaviors are accomplished assuming the honeycomb as a porous medium. The Brinkman-Forchheimer-extended Darcy model is used in the governing equations and the local thermal non equilibrium is assumed. The commercial CFD Fluent code is used to solve the governing equations in transient regime. Numerical simulations are carried out with storage medium at different mass flow rates of the working fluid and different porosity values. Results show the effects of storage medium, different porosity values, porosity effect and mass flow rate on stored thermal energy and storage time. Results in terms of temperature profiles and stored thermal energy as function of time are presented.
Some Issues in Passive Impact Location Detection Triangulation in Composite Materials Using Embedded Piezoelectric Sensors
Authors: Zamorano-Senderos Bruno , Elvin Niell , Shin Samuel
Published: October 2013

This paper studies some aspects of impact location detection in composites materials using triangulation methods with embedded piezoelectric sensors. The first step of any impact damage evaluation method is to ascertain if an impact has happened and its location. More sophisticated methods (not addressed in this paper) can then be used to determine the type and extent of damage and to estimate the residual life of the structure. We propose a novel sensor array that potentially reduces the number of computations required to locate the position of the impact and reduces the complexity of embedded sensor wiring. Reducing the computational complexity allows the use of lighter, cheaper and less energy consuming electronic devices. The new technique reduces the classical computation from a planar (two dimensional) search to an angular (one dimensional) search. The new technique is experimentally compared with a classical triangulation technique at moderate ballistic speeds (300 m/s). This paper shows that the new technique reduces the computational cost, but also reduces accuracy of impact location.
The Effect of Microstructural Morphologies on the Effective Electromechanical Properties of Piezoelectric Particle Composites
Authors: Tajeddini Vahid , Lin Chien-hong , Muliana Anastasia , Lévesque Martin
Published: October 2013

This study introduces a micromechanical model that incorporates detailed microstructures for analyzing the effective electro-mechanical properties, such as piezoelectric and permittivity constants as well as elastic moduli, of piezoelectric particle reinforced composites. The studied composites consist of polarized spherical piezoelectric particles dispersed into a continuous and elastic polymeric matrix. A micromechanical model generated using three-dimensional (3D) continuum elements within a finite element (FE) framework. For each volume fraction (VF) of particles, realization with different particle sizes and arrangements were generated in order to represent microstructures of a particle composite. We examined the effects of microstructural morphologies, such as particle sizes and distributions, and particle volume fractions on the overall effective electro-mechanical properties of the active composites. The overall electro-mechanical properties determined from the present micromechanical model were compared to those generated using the Mori-Tanaka, self-consistent, and simplified unit-cell micromechanical models.
Power Die Packaging by Substrate Embedding
Authors: Appelt Bernd K. , Su Bruce , Yen Uno , Essig Kay
Published: October 2013

Historically, power die like MOSFETs have been packaged on lead frames using wire bonds as interconnects. To facilitate current carrying requirements, thick wires and sometimes also clips were used, to handle the total electrical and thermal conductivity requirements. As die are being thinned, it has become possible to take advantage of new electrical designs and locate source and drain on opposite sides of the die. Such die can now be easily packaged by embedding the power die in organic substrates. The die is bonded on a Cu pad and covered by prepreg and copper foil during lamination. Source, drain and gate pads are accessed from the top side with laser vias and filled with plated copper. Finally, the top side is patterned and protected with solder mask. An exemplary process flow will be described here. Electrical and thermal modeling data will be presented to demonstrate the performance efficiency while reducing the form factor in accordance with the miniaturization of mobile applications. Aside from single die packages, more advanced packages can be built containing multiple power die and controller die. The basic process flow remains the same but does require some adaptation. If so desired, additional components may be assembled on top of the embedded die package leading to further integration and miniaturization.
Blast Event Recognition Method for Multisensor Data
Authors: Rapo Mark , Whang Chong , Chan Philemon
Published: October 2013

Due to the great concern that blast overpressure can cause mild traumatic brain injury (mTBI), there is strong interest in putting sensors on warfighters to collect theater data for correlation with medical outcomes. One approach is to mount multiple pressure sensors on the warfighter to measure the blast overpressure environment. An event recognition algorithm that is based on the sensor data recordings is needed to reconstruct the incident blast wave that impacts the warfighter. Blast impingement pressure on an object is highly dependent on the angle of incidence at the point of impact; shadowing and recirculating flow effects can complicate the sensor data pattern. Using computational fluid dynamics (CFD) simulation, the present work demonstrates that for a warfighter in an upright posture in an open blast environment, a three-sensor event recognition algorithm can be developed to reconstruct the incident blast wave (generally characterized as a Friedlander wave). Three-dimensional Navier-Stokes’ based CFD simulations were performed to predict pressure recordings at the three sensor locations for a range of horizontal blast waves impacting the warfighter at all angles of incidence. The predicted peak pressures and durations were recorded and stored in a lookup table. Using an inverse problem approach, it was found that based on the three-sensor data recorded for each event, an algorithm exists for reconstructing the blast incident wave. The established event recognition algorithm is limited to warfighters with upright posture in open blast. Work is being continued to generalize and extend the method to include complex blasts involving multiple reflections and other posture orientations.
Design of a Lean Methodology for an Ergonomic and Sustainable Work Environment in Textile and Garment Industry
Authors: Maia Laura Costa , Alves Anabela Carvalho , Leão Celina Pinto
Published: October 2013

This paper presents a methodology to implement Lean Production (LP) in Portuguese Textile and Garment Industry (TGI). Lean Production is a well-known work organizational model being, nowadays, widely implemented in all sort of industries and services companies. LP responds to customers’ demand for on-time delivery of high quality products at reduced costs, through continuous waste elimination (e.g., overproduction, raw materials, energy and water more than necessary, among others). In this methodology is included, besides the Lean tools and techniques, some ergonomics tools in order to assess the ergonomic work conditions and techniques to evaluate the company sustainability. It is expected that, with the involvement of these tools, will allow the implementation of a Lean Production that creates a positive work environment for workers giving special attention to sustainable development.
Numerical Simulation of Two Pass Gas Turbine Blade Internal Cooling Channels With 90 Degree Varying Height Ribs
Authors: Kumar Sourabh , Amano R. S.
Published: October 2013

Improvement in thermal efficiency of gas turbine can be obtained by operating it at high inlet temperatures. In addition to improving the performance, the cons of high inlet temperature is high thermal stresses on the turbine blades. To improve life and performance of the blade, improved cooling technologies are desired. The main objective of this paper is to perform computational analysis of the ribs with varying height and compare this with 90 degree ribbed channel and smooth channels. The numerical analysis is carried out using ANSYS-Fluent, a flow modeling simulation software. The flow is assumed to be steady state and flow turbulence is modeled using the k-ε with Standard Wall Functions. Local heat transfer and friction loss in a square duct roughened with 90 degree ribs with varying height is investigated for different Reynolds number. The pitch of the rib is considered to be 10 times the height of rib which is 0.0635 m. The square cross section of the channel is .0508x .0508 m2. The pitch of rib to rib height ratio varies from 10 to 20 at the center of the channel. There is a rib considered at the turn section as well. The numerical simulation produced higher heat transfer for the varying height ribs as compared to 90 degree ribbed channel and smooth channel.
The Effect of Cement Viscosity in Total Knee Arthroplasty
Authors: Abbruzzese Kevin , O’Laughlin Richard , Lee Daniel , Allan D. Gordon , Paliwal Manish
Published: October 2013

Aseptic loosening of the tibial implant remains one of the major reasons of failure in Total Knee Arthroplasty (TKA). Currently, there is no consensus on the role that cement viscosity at the time of application to the bone plays in ensuring the long-term success of the arthroplasty. The purpose of this study was to investigate the relationship between cement viscosity and aseptic loosening of tibial implants. Three cements (Depuy 2, Palacos R (high viscosity cements) and Simplex-P, a medium viscosity cement) were compared during TKA through radiographic analysis and mechanical loading tests using surrogate tibia. Cement penetration was measured from radiographs of the constructs and analyzed according to the Knee Society Total Knee Arthroplasty Roentgenographic Evaluation System. Simplex-P had the maximum cumulative penetration in seven zones in the mediolateral view, and three zones in antero-posterior view. Simplex exhibited maximum penetration in zone 7 in the antero-posterior view, and in zone 3 in the lateral view. For the mechanical tests the TKA constructs were subjected to cyclic compressive loading in the sagittal plane. Simplex-P had the smallest micro-motion in sagittal plane, the results were significant when compared to Palacos R. The consistently superior performance of Simplex-P suggests that cement viscosity does indeed play a role in arthroplasty success. These results have direct clinical relevance for TKA patients suffering from aseptic loosening.
Creativity in Multi Objective Problem Solving
Authors: El-Sayed Mohamed E. M. , El-Sayed Jacqueline A. J.
Published: October 2013

Problem solving is one of the main activities in achieving design and research goal. While problem solving in general is an activity aiming at transforming unacceptable state of reality to acceptable state of reality, problem solving in engineering is usually a means for tackling other activities such as design and research. By breaking down design and research into a set of engineering problem solving activities, the goals of complicated design and research projects can be achieved. For this reason, the transitions from design or research to problem solving in some cases are unidentifiable. The identification of the problem solving activity goals and the transition between the three activities, however, are essentials for creativity and achieving the desired objectives especially when dealing with conflicting objectives and constraints.

In this paper, design, research, and problem solving are distinguished as realization activities performed in different reality domains with different beginning and ending states. These three activities use modeling and simulation as basic elements of mapping between realities to perform analysis and integration. While analysis and simulation are mainly the analytical actions, modeling and integration are mainly the creative actions. With these distinctions, the identification of problem solving activity goals, and transitions between activities, can be easily realized. Also, creativity and dealing with conflicting objectives can be greatly facilitated. To demonstrate these concepts and their implications some illustrative examples are discussed.
Development of a Numerical Model to Predict Residual Stress Based on Acoustoelastic Effect Using Critically Refracted Ultrasonic Longitudinal (LCR) Waves
Authors: Srinivasan Malur N. , Joshi Shrijwal , Zhou Jiang
Published: October 2013

The paper contains the development of mathematical model of the ultrasonic wave travelling through the medium which has been critically refracted known as critically refracted longitudinal wave or Creep wave. This wave is very sensitive to the residual stress induced in a medium. The mathematical model uses ultrasonic wave as a compressive stress source, which shows a relation of stress with the time travel. The result shows that when the stress is increased by 400 MPa the time travel jumps from 3187 to 3158 ns.
Diesel Engine Injector Waveform Monitoring in Real-Time for Fuel Efficiency
Authors: Farooqi Q. R. , Anwar S. , Snyder B.
Published: October 2013

This paper presents the development, experimentation and validation of a reliable and robust system, which can be easily calibrated for different engine platforms, to monitor the injector pulse generated by an Engine Control Module (ECM) and feedback the corresponding fueling quantity to the real-time computer in a closed-loop Controller in the loop (CIL) bench in order to achieve optimal fueling. This research utilized Field Programmable Gate Arrays (FPGA) and Direct Memory Access (DMA) transfer capability to achieve high speed data acquisition and delivery. The research is conducted in two stages, first stage was to study the variability involved in the injected fueling quantity from pulse to pulse, from injector to injector, between real injector stators and inductor load cells, over different operating conditions. Different thresholds were experimented to find out the best start of injection (SOI) threshold and the end of injection (EOI) threshold that captured the injector “on-time” with best reliability and accuracy. Second stage involved development of a system that interprets the injector pulse into fueling quantity; the system can be easily calibrated to be used over various platforms. Finally, the use of resulting correction table was found to capture the fueling quantity with best accuracy.
Intertube Thermal Resistance in Double-Wall Carbon Nanotube
Authors: Chen Weiyu , Ni Zhonghua , Yang Juekuan , Zhang Yan , Li Deyu , Chen Yunfei
Published: October 2013

This paper presents the variation of interface thermal resistance between two single-wall carbon nanotubes versus overlap length by using nonequilibrium molecular dynamics method. The simulation model is constructed through pulling the inner tube out a double wall carbon nanotube with a distance. The overlap length between the inner and outer nanotubes is proportional to the contact area, which acts as a variable in controlling the heat transport between the inner and the outer nanotubes. Simulation results show that the intertube thermal conductance increases almost linearly with increasing the overlap length. The rectification effect is undetectable due to the fixed atoms that prevent rotation of the carbon nanotubes and resulting in constant intertube coupling strength.
Optimization Under Uncertainty of Manifold Microchannel Heat Sinks
Authors: Sarangi Suchismita , Bodla Karthik K. , Garimella Suresh V. , Murthy Jayathi Y.
Published: October 2013

Conventional microchannel heat sinks provide good heat dissipation capability but are associated with high pressure drop and corresponding pumping power. The use of a manifold system that distributes the flow into the microchannels through multiple, alternating inlet and outlet pairs is investigated here. This manifold arrangement greatly reduces the pressure drop incurred due to the smaller flow paths, while simultaneously increasing the heat transfer coefficient by tripping the thermal boundary layers. A three-dimensional numerical model is developed and validated, to study the effect of various geometric parameters on the performance of the manifold microchannel heat sink.

Apart from a deterministic analysis, a probabilistic optimization study is also performed. In the presence of uncertainties in the geometric and operating parameters of the system, this probabilistic optimization approach yields an optimal design that is also robust and reliable. Uncertainty-based optimization also yields auxiliary information regarding local and global sensitivities and helps identify the input parameters to which outputs are most sensitive. This information can be used to design improved experiments targeted at the most sensitive inputs. Optimization under uncertainty also provides a quantitative estimate of the allowable uncertainty in input parameters for an acceptable uncertainty in the relevant output parameters. The optimal geometric design parameters with uncertainties that maximize heat transfer coefficient while minimizing pressure drop for fixed input conditions are identified for a manifold microchannel heat sink. A comparison between the deterministic and probabilistic optimization results is also presented.
Active Vibration Control of Flexible Rotor-Shaft System Subject to Earthquake
Authors: Sharma P. , Gupta S. , Das A. S. , Dutt J. K.
Published: October 2013

This paper presents the results of a numerical simulation to actively control transverse vibration of a flexible rotor shaft subject to seismic base excitation. The active control force is applied over an air gap by an electromagnetic actuator. Equations of motion of the rotor-shaft-system have been drawn up after discretizing the rotor continuum with finite beam elements and taking into account rotor flexibility, internal friction forces due to rotor material damping, inertial forces due to base motion, gyroscopic forces and non-linear electromagnetic control forces from the actuator in addition to harmonic excitation due to unbalance in the steadily spinning rotor-disc. A MATLAB code in the SIMULINK domain has been created for this purpose and the equations developed are solved numerically in the time domain to get the response at each nodal point. Numerical simulation of vibration response of the disc in a single-disc rotor-shaft-system is compared with and without the control action when the rotor base is excited with the El-Centro earthquake data. The comparison shows a remarkable reduction of response amplitude and improvement of rotor-shaft-system stability in comparison with no control action. Hence the usefulness of an electromagnetic actuator is proposed for safe and sound operation of rotor-shaft systems even under the seismic base excitation.
Cooling Methods for High Temperature Polymer Electrolyte Fuel Cell Stacks
Authors: Supra Jen , Janßen Holger , Lehnert Werner , Stolten Detlef
Published: October 2013

One promising future application for a high temperature polymer electrolyte fuel cell (HT-PEFC) stack coupled with a reformer is an auxiliary power unit (APU) for mobile applications using diesel or kerosene which is also used for the main engine. Despite of the high efficiency of a HT-PEFC, the stack has to be cooled during operation. Hence, this work focuses on the investigation of different cooling strategies regarding the complete system, the use of heat transfer oil as cooling medium is fixed in this contribution. In detail, three cooling methods to maintain operating temperature in stacks with more than 1 kW electrical power and large active areas (> 200 cm2 per cell) were analyzed. In the first method heat transfer oil flows through the stack in internal channels that are located on the backside of the cathode-side bipolar plate. In the second cooling arrangement the oil flows through capsuled cooling cells, which are arranged between every third electrochemical cell. For the third cooling method the excellent heat conducting properties of heat pipes are used. Outside the stack, the heat is removed by heat transfer oil from the overlapping heat pipes. These three methods were evaluated experimentally and with CFD simulations. In this paper the detailed measurements of the temperature distributions are presented containing the overall result that all cooling methods are applicable to maintain the temperatures of large HT-PEFC stacks during the operation in an APU system.
Effect of Fluid Dynamic Parameters on the Performance of a Radial Flow Pressure Exchange Ejector
Authors: Umar Muhammad , Garris Charles A.
Published: October 2013

The “Pressure exchange” is a novel concept in turbomachinery whereby two fluids, at different energy levels, come in direct contact with each other to transfer energy and momentum between them through non-steady interface pressure forces. The rotating jets of the high pressure primary fluid, often referred to as pseudoblades, resemble solid blades on the impeller of a conventional turbomachine. The low pressure secondary fluid, ahead of the pseudoblades, is pressurized by the action of interface pressure forces.

The current paper seeks to provide an insight into the complex flow phenomena occurring inside the radial flow pressure exchange ejector. This research presents the results of the first successful numerical simulation to explore the effects of primary to secondary total pressure ratio and primary to secondary total temperature ratio on the performance of a radial flow pressure exchange ejector.
Simulation Model and Experimental Validation of a CHP Plant With Micro Gas Turbine
Authors: Badami Marco , Ferrero Mauro , Portoraro Armando
Published: October 2013

The paper deals with a simulation model, developed in Matlab Simulink®, of a small-scale Combined Heat and Power (CHP) plant based on a recuperated micro gas turbine (mGT). A minimum data set, mainly obtainable from datasheets, was defined, that allows the model to simulate different mGT plants in the small-scale range with a good accuracy. The model implements the mass, energy and momentum equations of the main components of the power plant. A double control system has also been developed, with the aim of maintaining the rotational speed of the turbine /compressor assembly at the nominal fixed value, and at limiting the Exhaust Gas Temperature (EGT) below the limit value. The model has been validated by means of experimental data obtained from a commercial mGT (100 kWel, 170 kWth), installed at the Politecnico di Torino, whose energetic characterization has been performed both at rated and at partial load conditions. The layout and the characteristics of the measurement system are also described in the paper.
Nonlinear Control Modeling for Arrays of Coupled Mechatronic Transducers
Authors: Xiros Nikolaos I.
Published: October 2013

A typical mechatronic oscillator involving a tuned resistor-inductor-capacitor circuit driven by a voltage source and coupled to a mass-spring-damper mechanical subsystem is analyzed in order to develop a nonlinear control model. The analysis is approached using the Volterrra/Wiener framework of nonlinear systems combined with the Hilbert Transform. The former is needed since the coupling between the electrical and mechanical parts is lost, should standard linearization is adopted. The latter is needed since a very important characteristic of the system, due to the presence of the capacitance, is frequency selectivity. To use this very frequency selectivity in an application, involving more than one transducer units, modulation of the carrier signal, amplitude modulation in this case, must be implemented. Carrier modulation enables multiple units, structurally identical otherwise but for the capacitance value adjusting the tuning frequency setting, in the same application. Both a low-pass and a band-pass model are developed and subsequently simulation runs are performed. Since the modulation method employed is not of the suppressed-carrier type, the equilibrium point is of dynamic rather than static nature, corresponding to initial values for current and displacement. The model is enhanced by superimposing an external disturbance in form of a baseband force acting on the mass payload of the mechanical subsystem. Then, the response of the system to monochromatic and polychromatic excitations is investigated; making sure among others none of the constraints is violated. The transducer configuration investigated here can be employed as an energy harvesting device in cases where vibrational or oscillatory motion of a mass is involved, e.g. ocean wave energy concepts, Vortex-Induced Vibrations etc., especially if no physical contact between the driving process and the driven circuit is feasible or practical.
Finite Element Modeling and Analysis of Photovoltaic Modules
Authors: Hasan Osama , Arif A. F. M. , Siddiqui M. U.
Published: October 2013

A Photovoltaic (PV) module consists of layers of different materials constrained together through an encapsulant polymer. During operation, it experiences mechanical and thermal loads due to seasonal and temperature variations, which cause breakage of interconnects owing to fatigue and laminate warpage. This is due to the fact that there is a coefficient of thermal expansion (CTE) mismatch because of the presence of unlike materials within the laminate. Therefore, thermo-mechanical stresses are induced in the module. Glass, being the thickest of all in the module, plays a significant role in the stressing of components. The lifetime of today’s PV module is expected to be 25 years and this period corresponds to the guarantee of the manufacturer. Its high reliability will help it to reach grid parity. But the problem is that it is not convenient to wait and assess its durability. Qualification standards such as ASTM E1171-09 are useful in predicting a module’s failure.

In this work, material of each component of the PV module is characterized and then the implementation of material models is discussed. A Finite-Element (FE) model of 36 cell PV module is developed using 2D layered shell elements in ANSYS. A single temperature cycle of ASTM E1171-09 is simulated after lamination procedure and 24 hour storage at constant temperature. The FE model is validated by simulating an experimental procedure in the literature by determining change of cell gap during the temperature cycle. Finally, parametric studies are performed with respect to lamination thickness.
Analytical Solutions to Transient Conduction Heat Transfer Problems With Discrete Heat Generating Sources in Cylindrical Coordinates
Authors: Perez Eduardo , Romero Edwar , Meza Omar
Published: October 2013

Heat transfer mechanisms are virtually present anywhere where energy is involved; heat conduction is one of those mechanisms. Pure conduction heat transfer can be found mainly in aerospace applications especially when aircrafts are in shadows occulted from sunlight and temperatures drop to extremely low values. In these cases resistance heaters are activated in order to preserve temperatures inside the aircraft within values where circuitry does not stop working. Resistance heaters should be embedded such that appropriate thermal control is achieved. In addition conduction heat transfer is of special interest in fundamental theory for science and engineering. Typically this kind of problems are solved by means of numerical analysis or specialized software which most of the times are more time consuming and more expensive in terms of computational resources. In the other hand, traditional analytical methods such as separation of variables can be used to solve simple heat conduction problems, but do not work for problems where discrete heat generation sources are present. The purpose of this work is to present an analytical method to solve transient conduction heat transfer problems in geometries with embedded discrete heat generating sources. The Green’s Functions were used to formulate the mathematical model to find analytical solutions to transient conduction heat transfer problems for circular plates with embedded discrete heat generating sources. Two cases of embedded heat generating sources are discussed: a thin circular wire in the form of an arc, and a circular region. Results found in the present work were taken for long values of time and compared to those reported by Venkataraman et al who found results for similar problems under steady state conditions. Results were in excellent agreement. Final equations found with the technique presented here are in the form of summations series similar to those found using the separation of variables method.
Waste Heat Recovery and Saving Fresh Water Consumption in Power Plants
Authors: Jeong Kwangkook
Published: October 2013

A section to delineate ‘waste heat recovery’ has been written to contribute for the ASME Power Plant Cooling Specification/Decision-making Guide to be published in 2013. This paper informs tentative contents for the section on how to beneficially apply waste heat and water recovery technology into power plants. This paper describes waste heat recovery in power plant, current/innovative technologies, specifications, case study, combined cycle, thermal benefits, effects on system efficiency, economic and exergetic benefits. It also outlines water recovery technologies, benefits in fresh water consumptions, reducing acids emission, additional cooling effects, economic analysis and critical considerations.
Effects on Dust Emission From an Inclined Flat Solar Panel
Authors: Li Zhen , Lan Chuanjin , Ma Yanbao
Published: October 2013

Flat solar panels array is one of the typical geometries used in photovoltaic (PV) power plants. The presence of these inclined solar panels can significantly accelerate or decelerate wind speed and distort the wind velocity profiles near the ground when wind flows around, which leads to considerable changes in dust emissions determined by shear stress at ground surface. To understand the fundamental principle of the effects of a flat solar panel on the dust emission rate at ground surface, the incompressible viscous flow past an inclined flat plate with ground effect was numerically investigated based on finite volume method. Results indicate that the presence of an inclined plate has little impact on the ground when the gap between the plate and ground is larger than twice plate length at tilt angle of 25° and Reynolds number of 300. However, as the gap is decreased the vortex clusters behind the plate are flattened and restrained by the ground, which results in the change of the shear stress at the ground surface. Both the magnitude and the distribution of shear stress at the ground surface can be significantly changed by varying the distance between the plate and the ground. The results demonstrate the possibility to adjust the strength and distribution of surface shear stress hence change the dust emission rate on the ground by an inclined flat plate.
Numerical Simulation of Thermal Performance of a High Aspect Ratio Thermal Energy Storage Device
Authors: Zhao Jingde , Alvarado Jorge L. , Languri Ehsan M. , Wang Chao
Published: October 2013

Heat transfer analysis of a high aspect ratio thermal energy storage (TES) device was carried out numerically. The three dimensional numerical study was performed to understand the heat transfer enhancement which results from internal natural convection in a high aspect ratio vertical unit. Octadecane was used as phase change material (PCM) inside TES system, which consisted of six corrugated panels filled with PCM. Each panel had a total of 6 tall cavities filled with PCM, which were exposed to external flow in a concentric TES system. Unlike traditional concentric-type TES devices where heat transfer by conduction is the dominant heat transport mechanism, the high aspect ratio TES configuration used in the study helped promote density-gradient based internal convection mechanism. The numerical model was solved based on the finite volume method, which captured the whole transient heat transfer process effectively. The time-dependent temperature profiles of the PCM inside a single TES panel are compared with the experimental results for two cases. Numerical and experimental results of the two cases showed a reasonable agreement. Furthermore, convection cells were formed and sustained when the PCM melted within the space between the solid core and the walls. The promising results of this numerical study illustrate the importance of internal natural convection on the speed of the PCM melting (charging) process.
Substrate Effect on Modulus of Elasticity and Hardness of Thin Film Under Nanoindentation Test
Authors: Ahmed Mesbah U. , Tarefder Rafiqul A.
Published: October 2013

Mechanical properties of thin film under nanoindentation test by Finite Element Analysis (FEA) have been studied in this literature. An axi-symmetric bi-layer model has been developed in commercial finite element analysis software, ABAQUS. Aluminum (Al) comprises the thin film whereas Silicon (Si) comprises the substrate. This model has been simulated using the loading condition that mimics real nanoindentation test, i.e. an indenter has been probed to a predefined depth onto Al-thin film. Modulus of elasticity and hardness of thin film have been calculated by existing empirical relationship. Substrate effect on determination of film modulus and hardness has been investigated by varying the substrate modulus. It has been observed that substrate effect is pronounced on film modulus determination whereas hardness is not significantly sensitive to this effect. Depth of indentation has also been varied over a long range to observe the indentation effect on these parameters. It is obvious that film modulus is increased with depth increment. However, hardness variation is not regular. Different friction condition is also in the scope of this study. It has been observed that friction does not affect modulus of elasticity. It, however, affects hardness of thin film. This is attributed to the dissipation of the energy needed to overcome friction at film-indenter interface.
Lyapunov-Based Attitude Tracking Control of a Quadrotor UAV
Authors: Ayoubi Mohammad A. , Sendi Chokri
Published: October 2013

In this paper, we use the Newton-Euler formulation to derive the equations of motion of a quadrotor unmanned aerial vehicle. We use the Modified Rodrigues Parameters to describe the attitude motion of a quadrotor for large attitude angles. Then, a globally stable feedback law for the problem of attitude tracking control of the vehicle was derived based on the Lyapunov’s direct method. Simulation results confirm that the proposed controller can track a reference attitude signal in the presence of parameter uncertainty, time delay, and slow time-varying external moments.
Influence of Edge-Boundaries on the Cohesive Behaviour of an Adhesive Layer
Authors: Biel Anders , Walander Tomas , Stigh Ulf
Published: October 2013

In comparison with other adhesives e.g. epoxies, polyurethane adhesives (PUR) are soft. In automotive applications, the thickness of PUR-adhesive layers is between about 2 to 5 mm. Since these adhesives cure by moisture, the width of the joints is limited. Often, the width is only marginally larger than the thickness of the layer.

In numerical FE-simulations it is now common to represent epoxy adhesive layers by cohesive elements. With this model, both stress distribution and fracture can be modelled using mesh sizes that allows for large-scale analyses. Material properties are usually the result from experiments with coupon type specimens, e.g. the double cantilever beam specimen (DCB). With PUR-adhesives this approach is problematic. The adhesive is very flexible and effects from the edge-boundaries cannot be ignored.

In order to study the influence of the edge-boundaries in peel loading, experiments with the DCB-specimens are performed. Specimens with a layer thickness of 3 mm and three different widths between 10.6 mm to 40.6 mm are studied. The PUR-adhesive SikaFlex-UHM is used. All the experiments are performed at a constant loading rate. The cohesive law is measured.

The experimental results show that the maximum peel stress is increasing with an increasing width of the specimen, i.e. when the influences from the edges decrease. When the width increases from 10.6 mm to 40.6 mm, the maximum evaluated peak stress increases from about 5 MPa to about 7 MPa. From visual inspections during the experiments it is conjectured that crack growth starts with voids initiating inside the adhesive. At a critical point, the voids rapidly reach the surface and crack growth starts.
Robotic Sound Source Localization Using Bio-Inspired Acoustic Sensors
Authors: Sawaqed Laith , Liu Haijun , Yu Miao
Published: October 2013

In sound source localization, there is a fundamental size limit; the smaller the size, the smaller the directional cues that are relied on to pinpoint the sound source. As such, it is challenging to develop miniature sound source localization robotic system where space is too confined to employ conventional microphone arrays without compromising localization performance. Our previous studies show that through mechanical coupling with well-tuned structural parameters, directional microphones inspired by the parasitic fly Ormia ochracea can amplify the minute interaural time delay (ITD) by more than ten times, which enables the reduction of device size significantly while maintaining localization performance. In this paper, Cramer Rao lower bound (CRLB) is derived for the fly-ear inspired sensor and the conventional directional microphones to study the effects of mechanical coupling on the decrease of the theoretical lower bound of azimuth estimation. This improvement gives mobile robots the capability to reactively localize sound in an indoor environment. Using this miniature sensor, new sound source localization method is proposed to localize a stationary sound source in 2-D (azimuth and elevation). In the proposed sound localization method, Model-Free Gradient Descent (MFGD) optimization method, one of the main challenges is to choose the appropriate cost function to achieve minimum number of iterations and the smallest absolute error. To this end, different cost functions are proposed and investigated with different control schemes. Simulation results showed the ability of this technique to solve the ambiguity problem and localize the sound source.