bluuebunny/crossref_metadata_2025 huggingface dataset:
Haemodynamic profile and responsiveness to anandamide of TRPV1 receptor knock‐out mice
Authors: Pacher Pál , Bátkai Sándor , Kunos George
Published: May 2004

The endocannabinoid anandamide and cannabinoid (CB) receptors have been implicated in the hypotension in various forms of shock and in advanced liver cirrhosis. Anandamide also activates vanilloid TRPV1 receptors on sensory nerve terminals, triggering the release of calcitonin gene‐related peptide which elicits vasorelaxation in isolated blood vessels in vitro. However, the contribution of TRPV1 receptors to the in vivo hypotensive effect of anandamide is equivocal. We compared the cardiac performance of anaesthetized TRPV1 knockout (TRPV1−/−) mice and their wild‐type (TRPV1+/+) littermates and analysed in detail the haemodynamic effects of anandamide using the Millar pressure–volume conductance catheter system. Baseline cardiovascular parameters and systolic and diastolic function at different preloads were similar in TRPV1−/− and TRPV1+/+ mice. The predominant hypotensive response to bolus intravenous injections of anandamide and the associated decrease in cardiac contractility and total peripheral resistance (TPR) were similar in TRPV1+/+ and TRPV1−/− mice, as was the ability of the CB1 receptor antagonist SR141716 to completely block these effects. In TRPV1+/+ mice, this hypotensive response was preceded by a transient, profound drop in cardiac contractility and heart rate and an increase in TPR, followed by a brief pressor response, effects which were unaffected by SR141716 and were absent in TRPV1−/− mice. These results indicate that mice lacking TRPV1 receptors have a normal cardiovascular profile and their predominant cardiovascular depressor response to anandamide is mediated through CB1 receptors. The role of TRPV1 receptors is limited to the transient activation of the Bezold‐Jarisch reflex by very high initial plasma concentrations of anandamide.
Numerical Modeling of an Industrial Aluminum Melting Furnace
Authors: Nieckele Angela O. , Naccache Mo^nica F. , Gomes Marcos S. P.
Published: May 2004

For the present work, a numerical simulation of the 100% oxy-firing combustion process inside an industrial aluminum remelting reverb furnace is presented. Three different configurations were analyzed: (i) a staged combustion process with parallel injection jets for oxygen and natural gas, (ii) a staged combustion process with a divergent jet for the oxygen, and (iii) a non-staged combustion process, with parallel jets. In all the cases, the injections were directed towards the aluminum bath, which was maintained at constant temperature. The numerical procedure was based on the finite volume formulation. The κ-ε model of turbulence was selected for simulating the turbulent flow field. The combustion process was calculated based on the finite rate models of Arrhenius and Magnussen, and the Discrete Transfer Radiation model was employed for predicting the radiation heat transfer. The numerical predictions allowed the determination of the flame patterns, species concentration distribution, temperature and velocity fields. This kind of analysis can be a powerful tool for evaluating design options such as the type, number and positioning of the burners. The present work illustrates a preliminary comparison of three types of burners. From the results obtained, the staged combustion process with a divergent jet presented the best configuration, since the flame length was not too long as to damage the refractory wall. Further it presented the largest region with low water vapor concentration close to the aluminum surface.
Nonlinear Periodically Forced Vibration of Stay Cables
Authors: Ni Y. Q. , Zheng G. , Ko J. M.
Published: May 2004

A new method for analyzing nonlinear steady-state dynamic response of three-dimensional sagged stay cables subject to arbitrary periodic excitation is proposed in this paper. Firstly, the nonlinear governing equation of motion of a stay cable with arbitrary sag is formulated in terms of three-node curved finite elements. Then a frequency-domain solution method to obtain the periodically forced response is developed by applying the incremental harmonic balance (IHB) technique to the finite element model. The proposed method is an accurate algorithm in the sense that it accommodates multi-harmonic components and no mode-based model reduction is made in the solution process. Both frequency- and amplitude-controlled algorithms are formulated and are alternatively implemented to obtain complete frequency-response curves including unstable solutions. The proposed method enables direct solution to the sub- and super-harmonic resonances, and gives a way to analyze nonlinear periodic oscillation under parametric excitation and internal resonance. Case study of applying the proposed method to nonlinear dynamic behavior analysis of the Tsing Ma suspension bridge cables is demonstrated. The analysis results show that the side-span free cables of the bridge display distinctly different nonlinear characteristics in the construction stage and in the final stage.
Experimental Investigation of a LiCl-Water Open Absorption System for Cooling and Dehumidification
Authors: Gommed K. , Grossman G. , Ziegler F.
Published: May 2004

In earlier work, a novel open absorption cycle was proposed, capable of producing both cooling and dehumidification for air conditioning, utilizing low-grade heat. The system, referred to as DER (Dehumidifier-Evaporator-Regenerator), uses ambient air in conjunction with an absorbent solution; the air is dehumidified and then employed to produce chilled water in an evaporative cooler. Alternatively, a portion of the dehumidified air may be used directly for air conditioning purposes. The system thus has the potential to provide both cooling and dehumidification in variable ratios, as required by the load. Computer simulations and theoretical investigations were carried out to analyze and predict the performance of the system. The objective of the present study has been to construct a laboratory system to test the concept, identify problems and carry out preliminary design optimization. The characteristic performance of individual components, analyzed theoretically in the simulation, was studied experimentally. Measurements have provided much-needed realistic data about heat and mass transfer coefficients. The performance of the system has been studied under varying operating conditions. The paper describes the operation of the experimental system and presents the measured data and the resulting transfer coefficients.
Analysis of Heat and Moisture Transfer Beneath Freezer Foundations—Part I
Authors: Chuangchid Pirawas , Ihm Pyeonchan , Krarti Moncef
Published: May 2004

This paper provides a numerical solution for simultaneous heat and moisture transfer within frozen soil beneath slab foundations of refrigerated warehouses. The developed solution is validated using data from experimental tests. A parametric analysis is then performed to determine the impact of slab insulation levels and to estimate the time required to reach steady-state ground-coupled heat transfer conditions. Finally, the solution is utilized to determine an effective soil thermal conductivity that could be used in a purely heat conduction model for ground-coupled heat transfer beneath freezers.
Analysis of Heat and Moisture Transfer Beneath Freezer Foundations-Part II
Authors: Krarti Moncef , Chuangchid Pirawas , Ihm Pyeongchan
Published: May 2004

This paper discusses selected results from a numerical solution of two-dimensional heat and moisture transfer within frozen and unfrozen soils beneath freezer slab foundations. In particular, the numerical solution is used to determine soil temperature profiles as well as freezer foundation heat gains. Finally, an effective soil thermal conductivity is successfully utilized in a pure heat conduction model to predict ground-coupled heat gains for freezers.
Design and Performance of the Van Geet Off-Grid Home
Authors: Barley C. Dennis , Torcellini Paul , Van Geet Otto
Published: May 2004

The Van Geet home near Denver, Colorado, demonstrates the successful integration of energy conservation measures and renewable energy supply in a beautiful, comfortable, energy-efficient, 295-m23,176-ft2 off-grid home in a cold, sunny climate. Features include a tight envelope, energy-efficient appliances, passive solar heating (direct gain and Trombe wall), natural cooling, solar hot water, and photovoltaics. In addition to describing this house and its performance, this paper describes the recommended design process of (1) setting a goal for energy efficiency at the outset, (2) applying rules of thumb, and (3) using computer simulation to fine-tune the design. Performance monitoring and computer simulation are combined for the best possible analysis of energy performance. In this case, energy savings are estimated as 89% heating and cooling (compared to 95 MEC), 83% electrical, and nearly 100% domestic water heating. The heating and cooling energy use is 8.96kJ/°Cs˙days˙m20.44Btu/°Fs˙days˙ft2.
A Note on Suhir’s Solution of Thermal Stresses for a Die-Substrate Assembly
Authors: Tsai M. Y. , Hsu C. H. , Han C. N.
Published: April 2004

The well-known, closed-form solution to thermal stresses of a die-substrate assembly is initially provided by Suhir in the mid-1980’s after Timoshenko [1] and Chen and Nelson [2]. It has been revised several times in its die attach (adhesive) peel solution by Suhir [3][4], and Mishkevich and Suhir [5]. However, there still exist some controversies and inconsistencies regarding die stresses, die attach shear and peel stresses, and warpage (deformation) of the assembly. In the study, Suhir’s derivation of the solution is closely examined in details, and the corrections to the solution are suggested and verified by comparing with the finite element results. It is shown that, unlike the original Suhir solution, the corrected one gives very good prediction of thermal stresses and deformations of die-substrate assembly. The limitation of the Suhir solution is also discussed in this study.
Calculating Benzene Concentration Emitted During Tanker Loading
Authors: Majima Takahiro , Yamanouchi Hiroshi , Yamaguchi Katsuji
Published: May 2004

Benzene emissions occur during marine vessel loading operations. These emissions are regulated in several countries. Accordingly, we developed a one-dimensional benzene diffusion model advancing in the vertical direction within cargo tanks. Unlike other models, the model presented in this paper is based on a 1/10 scale modeling of eddy diffusion at the liquid surface during initial loading operations and advection under the tank roof during final loading operations. The model input parameters include loading rate, flow rate, cargo tank size, and temperature dependent saturated concentrations. The validity of the model is demonstrated by comparisons with onboard measurements. Other models exist. However, they are based on empirical estimates rather than rational modeling.
Transient Heat Transfer Between a Semi-Infinite Hot Plate and a Flowing Cooling Liquid Film
Authors: Dorfman Abram
Published: May 2004

Heat transfer between a hot, semi-infinite plate and thin liquid film flowing over its surface is considered. As the plate is semi-infinite, the finite cooled portion of the plate and the temperature at the moving film front are time variable. The heat transfer is transient, as opposed to the usual quasi-steady process that exists when the plate is infinite. To investigate the transient heat transfer, solutions describing the temperature fields of the wet and dry portions of the plate are conjugated at the moving film front. The basic characteristics of transient cooling process are found to be governed by a dimensionless parameter named the Leidenfrost number, which is the ratio of the Biot number and the square of the Peclet number. The plate temperatures at the moving front, the film velocity, and the time required to reach the wetting temperature are calculated.
Optimal Synthesis/Design of a Pem Fuel Cell Cogeneration System for Multi-Unit Residential Applications–Application of a Decomposition Strategy
Authors: Oyarza´bal Borja , von Spakovsky Michael R. , Ellis Michael W.
Published: May 2004

The application of a decomposition methodology to the synthesis/design optimization of a stationary cogeneration proton exchange membrane (PEM) fuel cell system for residential applications is the focus of this paper. Detailed thermodynamic, economic, and geometric models were developed to describe the operation and cost of the fuel processing sub-system and the fuel cell stack sub-system. Details of these models are given in an accompanying paper by the authors. In the present paper, the case is made for the usefulness and need of decomposition in large-scale optimization. The types of decomposition strategies considered are conceptual, time, and physical decomposition. Specific solution approaches to the latter, namely Local-Global Optimization (LGO) are outlined in the paper. Conceptual/time decomposition and physical decomposition using the LGO approach are applied to the fuel cell system. These techniques prove to be useful tools for simplifying the overall synthesis/design optimization problem of the fuel cell system. The results of the decomposed synthesis/design optimization indicate that this system is more economical for a relatively large cluster of residences (i.e. 50). Results also show that a unit cost of power production of less than 10 cents/kWh on an exergy basis requires the manufacture of more than 1500 fuel cell sub-system units per year. Finally, based on the off-design optimization results, the fuel cell system is unable by itself to satisfy the winter heat demands. Thus, the case is made for integrating the fuel cell system with another system, namely, a heat pump, to form what is called a total energy system.
A Method for Assessing the Importance of Body Force on Flow Boiling CHF
Authors: Zhang Hui , Mudawar Issam , Hasan Mohammad M.
Published: May 2004

Experiments were performed to examine the effects of body force on flow boiling CHF. FC-72 was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface just prior to CHF. High-speed video imaging techniques were used to identify dominant CHF mechanisms corresponding to different flow orientations and liquid velocities. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed significant sensitivity to orientation for flow velocities below 0.2 m/s, where extremely low CHF values where measured, especially with downward-facing heated wall and downflow orientations. High flow velocities dampened the effects of orientation considerably. The CHF data were used to assess the suitability of previous CHF models and correlations. It is shown the Interfacial Lift-off Model is very effective at predicting CHF for high velocities at all orientations. The flooding limit, on the other hand, is useful at estimating CHF at low velocities and for downflow orientations. A new method consisting of three dimensionless criteria is developed to determine the minimum flow velocity required to overcome body force effects on near-saturated flow boiling CHF.
Stability and Oscillations in an Evaporating Corner Meniscus
Authors: Zheng L. , Plawsky J. L. , Wayner, P. C. , DasGupta S.
Published: May 2004

A Constrained Vapor Bubble Loop Thermosyphon, CVBLT, made of quartz was used to study the stability and oscillations of an evaporating curved wetting film of pentane in a corner. The film thickness profile was measured as a function of heat input, time, and axial position using image analyzing interferometry. The curvatures and apparent contact angles for the evaporating film under various operating conditions were obtained from the measured film thickness profiles. Instability (oscillation) of the liquid film was observed at relatively higher values of the heat input. The behavior of the curvature and the apparent contact angle of an oscillating film with changes in heat input was evaluated. Moving velocities of the oscillating film were calculated from the measured values of the liquid-wall wetted lengths and were found to be directly proportional to the difference between the instantaneous force acting on the curved film and the reference force. Using an augmented Young-Laplace pressure jump model, the effect of the excess free energy at the contact line on the oscillations was demonstrated.
Parameter Setting for a Tubular SOFC Simulation Model
Authors: Lazzaretto Andrea , Toffolo Andrea , Zanon Federico
Published: May 2004

Several empirical assumptions deriving from observations and measurements of the physical processes are involved in the modeling of Solid Oxide Fuel Cells (SOFCs). An insight of the main models proposed in the literature is given to present the characteristics and limits of these assumptions for the various existing configurations. The basic structure and equations of the models are discussed in details, focusing particularly on the parameters that are to be set to achieve reliability and accuracy. According to this discussion, a zero-dimensional model for a tubular Solid Oxide Fuel Cell (SOFC) is then presented. The model demonstrates good capability in predicting SOFC characteristic curves as they appear in the literature.
Combined Effects of Rotating Magnetic Field and Rotating System on the Thermocapillary Instability in the Floating Zone Crystal Growth Process
Authors: Ma Nancy , Walker John S. , Martin Witkowski Laurent
Published: May 2004

This paper presents a linear stability analysis for the thermocapillary convection in a liquid bridge bounded by two planar liquid-solid interfaces at the same temperature and by a cylindrical free surface with an axisymmetric heat input. The two solid boundaries are rotated at the same angular velocity in one azimuthal direction, and a rotating magnetic field is applied in the opposite azimuthal direction. The critical values of the Reynolds number for the thermocapillary convection and the critical-mode frequencies are presented as functions of the magnetic Taylor number for the rotating magnetic field and of the Reynolds number for the angular velocity of the solid boundaries.
A Model of Heat and Mass Transfer Beneath an Ablating Concrete Surface
Authors: Epstein Michael
Published: May 2004

This paper presents a one-dimensional steady-state model of heat and water vapor transport just beneath an ablating concrete surface. In the model an evaporation front separates a dry porous region through which water vapor flows to the ablation front from a semi-infinite region that is partially wet with evaporable water. The predicted water vapor pressures at the evaporation front are quite high and could conceivably cause the concrete to spall. The model is quantitatively compatible with spallation events observed during tests involving the pouring of molten steel onto concrete and is capable of explaining the disparate results obtained in two rather extensive test series on the penetration of induction heated metallic pools into concrete.
Investigation of the Initial Inverse Problem in the Heat Equation
Authors: Masood Khalid , Zaman F. D.
Published: May 2004

We investigate the inverse problem in the heat equation involving the recovery of the initial temperature from measurements of the final temperature. This problem is extremely ill-posed and it is believed that only information in the first few modes can be recovered by classical methods. We will consider this problem with a regularizing parameter which approximates and regularizes the heat conduction model.
Predicting Inlet Temperature Effects on the Pressure-Drop of Heated Porous Medium Channel Flows Using the M-HDD Model
Authors: Narasimhan Arunn , Lage Jose´ L.
Published: May 2004

A Modified Hazen-Dupuit-Darcy (M-HDD) model, incorporating nonlinear temperature-dependent viscosity effects, has been proposed recently for predicting the global pressure-drop of nonisothermal flows across a heated (or cooled) porous medium channel. Numerical simulations, mimicking the flow of a liquid with nonlinear temperature-dependent viscosity, are presented now for establishing the influence of inlet temperature on the pressure-drop and on the predictive capabilities of the M-HDD model. As a result, new generalized correlations for predicting the coefficients of the M-HDD model are derived. The results not only demonstrate the importance of fluid inlet temperature on predicting the global pressure-drop but they also extend the applicability of the M-HDD model.
Critical Heat Flux of Steady Boiling for Subcooled Water Jet Impingement on the Flat Stagnation Zone
Authors: Liu Zhen-Hua , Tong Tie-Feng , Qiu Yu-Hao
Published: May 2004

An experimental investigation was carried out for predicting the critical heat flux (CHF) of steady boiling for a round subcooled water jet impingement on the flat stagnation zone. The experimental data were measured in a steady nucleate boiling state. Three main influencing parameters, i.e., subcooling, impact velocity and jet nozzle size were widely changed and their effects on the critical heat flux were systemically studied. An empirical correlation was obtained using the experimental data over a wide experimental range for predicting the critical heat flux of steady boiling for a round subcooled water jet impingement on the flat stagnation zone.
Theoretical Analysis of a Water Desalination System Using Low Grade Solar Heat
Authors: Al-Kharabsheh S. , Goswami D. Yogi
Published: May 2004

Theoretical analysis of a solar desalination system utilizing an innovative new concept, which uses low-grade solar heat, is presented. The system utilizes natural means of gravity and atmospheric pressure to create a vacuum, under which liquid can be evaporated at much lower temperatures and with less energy than conventional techniques. The uniqueness of the system is in the way natural forces are used to create vacuum conditions and its incorporation in a single system design where evaporation and condensation take place at appropriate locations without any energy input other than low grade heat. The system consists of solar heating system, an evaporator, a condenser, and injection, withdrawal, and discharge pipes. The effect of various operating conditions, namely, withdrawal rate, depth of water body, temperature of the heat source, and condenser temperature were studied. Numerical simulations show that the proposed system may have distillation efficiencies as high as 90% or more. Vacuum equivalent to 3.7 kPa (abs) or less can be created depending on the ambient temperature at which condensation will take place.
Scale Analysis of Combined Thermal Radiation and Convection Heat Transfer
Authors: Kottke Peter A. , Ferguson Timothy P. , Fedorov Andrei G.
Published: May 2004

Simple order-of-magnitude relationships predicting heat transfer in limiting cases of combined convection and radiation problems in boundary layer flows are found using the method of scale analysis. Key nondimensional groups are developed that help identify the fundamental interactions between thermal radiation and convection modes of heat transfer for two cases of laminar, two-dimensional convection heat transfer from a semi-infinite vertical wall. The first case is that of heat transfer from a gray wall with a specified heat flux to a surrounding non-participating medium and considers both forced and natural convection effects. The second case is that of heat transfer from a black wall with a specified temperature to an optically thick, gray, nonscattering medium and considers forced, natural, and mixed convection effects. The scale analysis results are presented in terms of the local Nusselt number. They include closed form expressions for order-of-magnitude estimates of the heat transfer rate, and dimensionless parameters that indicate the dominant mode of heat transfer and correlate experimental data well. The scale analysis results are validated against both experimental data and theoretical results.
Investigation of Steady-State Drawing Force and Heat Transfer in Polymer Optical Fiber Manufacturing
Authors: Reeve Hayden M. , Mescher Ann M. , Emery Ashley F.
Published: May 2004

The force required to draw a polymer preform into optical fiber is predicted and measured, along with the resultant free surface shape of the polymer, as it is heated in an enclosed cylindrical furnace. The draw force is a function of the highly temperature dependent polymer viscosity. Therefore accurate prediction of the draw force relies critically on the predicted heat transfer within the furnace. In this investigation, FIDAP was used to solve the full axi-symmetric conjugate problem, including natural convection, thermal radiation, and prediction of the polymer free surface. Measured and predicted shapes of the polymer free surface compared well for a range of preform diameters, draw speeds, and furnace temperatures. The predicted draw forces were typically within 20% of the experimentally measured values, with the draw force being very sensitive to both the furnace wall temperature and to the feed rate of the polymer.
Natural Convection From a Tube Bundle in a Thin Inclined Enclosure
Authors: Liu W. , Davidson J. H. , Kulacki F. A.
Published: May 2004

Natural convection heat transfer coefficients for a rectangular array of eight tubes contained in a thin enclosure of aspect ratio 9.3:1 and inclined at 30 deg to the horizontal are measured for a range of transient operating modes typical of a load side heat exchanger in unpressurized integral collector-storage systems. Water is the working fluid, and thermal charging is accomplished via a constant heat flux on the upper boundary. All other boundaries are well insulated. Results for isothermal and stratified enclosures yield the following correlation for the overall Nusselt number: NuD=0.728±0.002RaD0.25,4.0×105⩽RaD⩽1.4×107. The flow field in the enclosure is inferred from measured temperature distributions. The temperature difference that drives natural convection is also determined. The results extend earlier work for the case of a single tube and provide limiting case heat transfer data for a tube bundle that occupies the upper portion of the collector storage.
Subtle Issues in the Measurement of the Thermal Conductivity of Vacuum Insulation Panels
Authors: Wessling Francis C. , Moser Marlow D. , Blackwood James M.
Published: May 2004

Vacuum insulation panels have values of thermal conductivity that are extremely low ∼4mW/ms˙K compared to the thermal conductivity of most common insulations. Typical ASTM test methods are not designed for testing these very low thermal conductivity materials. An apparatus has been built and tested that uses a thin foil heater and vacuum chamber to test vacuum insulation panels. Several different measurement configurations are studied to determine the effects of the parasitic heat losses. The differences between the ASTM standards and this technique are described and the rationale explained. A new ASTM technique for vacuum panels appears to be needed.
Aerodynamically and Structurally Coupled Vibration of Multiple Co-Rotating Disks
Authors: Park Jung Seo , Shen I. Y.
Published: May 2004

This paper studies vibration of multiple, co-rotating, identical disks coupled by air flow and structural flexibility. In particular, the study focuses on coupled vibration of disk modes with two or more nodal diameters. First, frequency response functions of multiple co-rotating disks are measured in air and in vacuum to study the effects of aerodynamic coupling. In vacuum, vibration modes from each rotating disk are aerodynamically uncoupled; therefore, corresponding travelling waves from each disk have the same natural frequency. When the air is present, the air couples the corresponding travelling waves and rearranges them into a group of N traveling waves with distinct frequencies, where N is the number of the disks. A perturbation analysis is developed to prove the phenomenon of frequency splitting. Aside from the air coupling, finite element analyses and experimental measurements indicate that the flexibility of the clamp and spacers between the disks can also couple the disk vibration in the same manner. Moreover, the aerodynamic coupling is more significant for disk modes with high number of nodal diameters (e.g., 4-nodal-diameter modes). In contrast, structural coupling through spacer flexibility is more pronounced for disk modes with low number of nodal diameters (e.g., 2-nodal-diameter modes). Also, parametric studies using FEA indicate that frequency splitting from structural coupling will remain significant over a wide parameter range.
Quarter-Cycle Switching Control for Switch-Shunted Dampers
Authors: Larson Gregg D. , Cunefare Kenneth A.
Published: May 2004

Significant interest has been generated by the possibilities of active vibration control through the implementation of state switching, with a specific implementation embodied through piezoceramic shunting. A state-switched absorber (SSA) is a vibration absorber that has the unique ability to change its resonant state amongst multiple distinct resonant states while in motion, thereby increasing the effective bandwidth over that of a single frequency device and thereby allowing control of multi-frequency, transient, and time-varying disturbances. In contrast, a switch-shunted damper (SSD) is a variant of an SSA that is used to increase the damping of the structure to which the damper is applied. Active vibration control applications discussed in the literature indicate the potential advantages of SSDs which employ piezoelectric ceramics as switchable springs with control algorithms that require switching states at points of non-zero strain. However, consideration of the constitutive equations for piezoelectric materials indicates a discontinuity in the electrical and mechanical conditions imposed by switching the stiffness at non-zero strains. A prototype SSD has been built and tested to experimentally investigate switching control logic and electrical and mechanical discontinuities at switching points; experimental measurements with this prototype SSD indicate that quarter-cycle switching algorithms which include switching states at a condition of maximum strain yield enhanced damping effectiveness but also leads to the generation of potentially undesirable mechanical transients.
Identification of Multi-Degree of Freedom Systems With Nonproportional Damping Using the Resonant Decay Method
Authors: Naylor Steven , Platten Michael F. , Wright Jan R. , Cooper Jonathan E.
Published: May 2004

This paper describes an extension of the force appropriation approach which permits the identification of the modal mass, damping and stiffness matrices of nonproportionally damped systems using multiple exciters. Appropriated excitation bursts are applied to the system at each natural frequency, followed by a regression analysis in modal space. The approach is illustrated on a simulated model of a plate with discrete dampers positioned to introduce significant damping nonproportionality. The influence of out-of-band flexible and rigid body modes, imperfect appropriation, measurement noise and impure mode shapes is considered. The method is shown to provide adequate estimates of the modal damping matrix.
Simulation and Characterization of Particle Damping in Transient Vibrations
Authors: Mao Kuanmin , Wang Michael Yu , Xu Zhiwei , Chen Tianning
Published: May 2004

Particle damping is a technique of providing damping with granular particles embedded within small holes in a vibrating structure. The particles absorb kinetic energy through particle-to-wall and particle-to-particle frictional collisions. While the concept of particle damping seems to be simple and it has been used successfully in many fields for vibration reduction, it is difficult to predict the damping characteristics due to complex collisions in the dense particle flow. In this paper, we utilize the 3D discrete element method (DEM) for computer simulation and characterization of particle damping. With the DEM modeling tool validated with experimental results, it is shown that the particle damping can achieve a very high value of specific damping capacity. Furthermore, simulations provide information of particle motions within the container hole during three different regions and help explain their associated damping characteristics. The particle damping is a combination of the impact and the friction damping. The damping is found to be highly nonlinear as the rate of energy dissipation depends on amplitude. Particularly, the damping effect results in a linear decay in amplitude over a finite period of time. These characteristics are examined with respect to a simple single-mass impact damper and a dry-friction damper. It is concluded that the particle damping is a mix of these two damping mechanisms. It is further shown that the relative significance of these damping mechanisms depends on a particular arrangement of the damper. This study represents an effort towards a deeper understanding of particle damping to provide a comprehensive methodology for its analysis and design.
Photocatalytic Oxidation of Benzene in Air
Authors: Einaga Hisahiro , Ibusuki Takashi , Futamura Shigeru
Published: May 2004

Photocatalytic oxidation of benzene in air at room temperature was studied in order to obtain the information on its reactivity on the photoirradiated TiO2 catalyst. The objective of this paper is to describe in detail the dependence of the rate for benzene photooxidation on humidity, initial benzene concentration, and incident light intensity, since they are important factors for construction of VOC control system utilizing solar energy. The reaction mechanism is also discussed to understand the decomposition behavior of benzene.
Experimental Investigation of Natural Convection Heat Loss From a Model Solar Concentrator Cavity Receiver
Authors: Taumoefolau T. , Paitoonsurikarn S. , Hughes G. , Lovegrove K.
Published: May 2004

Natural convection heat loss inevitably occurs in cavity-type receivers in high concentrating solar dishes, downward focusing systems and solar towers. In most applications, it can contribute a significant fraction of total energy loss, and hence it is an important determining factor in system performance. To investigate natural convection losses from cavity type receivers, an electrically heated model receiver, was tested at inclinations varying from −90 deg (cavity facing up) to 90 deg (cavity facing straight down), with test temperatures ranging from 450 to 650 deg C. Ratios of the aperture diameter to cavity diameter of 0.5, 0.6, 0.75, 0.85 and 1.0, were used. In addition to measurements of overall heat loss, the Synthetic Schlieren technique was used to visualize the flow pattern out of the cavity. Numerical modeling of the convection losses from the cavity was carried out for positive angles with the commercial computational fluid dynamics software package, Fluent 6.0. Good agreement was found between the numerical flow patterns at the aperture region with the schlieren images and between measured and predicted values for heat loss. Of the previously published work that has been reviewed, a model proposed by Clausing, A. M., 1981, “An Analysis of Convective Losses from Cavity Solar Central Receivers,” Sol. Energy 27 (4) pp. 295–300 shows the closest prediction to both numerical and experimental results for downward facing cavities despite its original use for bigger-scale central receivers.
Advanced Thermal Energy Storage Technology for Parabolic Trough
Authors: Tamme Rainer , Laing Doerte , Steinmann Wolf-Dieter
Published: May 2004

The availability of storage capacity plays an important role for the economic success of solar thermal power plants. For today’s parabolic trough power plants, sensible heat storage systems with operation temperatures between 300°C and 390°C can be used. A solid media sensible heat storage system is developed and will be tested in a parabolic trough test loop at PSA, Spain. A simulation tool for the analysis of the transient performance of solid media sensible heat storage systems has been implemented. The computed results show the influence of various parameters describing the storage system. While the effects of the storage material properties are limited, the selected geometry of the storage system is important. The evaluation of a storage system demands the analysis of the complete power plant and not only of the storage unit. Then the capacity of the system is defined by the electric work produced by the power plant during a discharge process of the storage unit. The choice of the operation strategy for the storage system proves to be essential for the economic optimization.
Thermal Performance of Unvented Attics in Hot-Dry Climates: Results from Building America
Authors: Hendron Robert , Farrar-Nagy Sara , Anderson Ren , Reeves Paul , Hancock Ed
Published: May 2004

As unvented attics have become a more common design feature implemented by Building America partners in hot-dry climates of the United States, more attention has been focused on how this approach affects heating and cooling energy consumption. By eliminating the ridge and eave vents that circulate outside air through the attic in most new houses and by moving the insulation from the attic floor to the underside of the roof, an unvented attic becomes a semiconditioned space, creating a more benign environment for space conditioning ducts. An energy trade-off is made, however, because the additional surface area (and perhaps reduced insulation thickness) increases the building loss coefficient. Other advantages and disadvantages, unrelated to energy, must also be considered. This paper addresses the energy-related effects of unvented attics in hot-dry climates based on field testing and analysis conducted by the National Renewable Energy Laboratory.
Simulation of a Solar Stirling Engine Operating Under Various Weather Conditions on Mars
Authors: Badescu Viorel
Published: May 2004

A solar stirling engine based on a horizontal selective flat-plate converter is analyzed in this work. A detailed model for the heat losses towards the atmosphere is presented. The engine’s output power is maximised numerically. The analysis is based on meteorological data measured at Viking Landers sites during clear sky and dust storm conditions. All the computations were performed for a solar collection area similar in size with that of Mars Pathfinder’s Sojourner. The efficiency of converting solar energy into mechanical work at noon is as high as 18%. The power provided by the engine is as high as 16 W during autumn and winter. These results suggest that under the Martian environment the performance of properly designed solar Stirling engines is comparable with that of PV cell power systems.
Thermal Performance of Danish Solar Combi Systems in Practice and in Theory
Authors: Andersen E. , Shah L. J. , Furbo S.
Published: May 2004

An overview of measured thermal performances of Danish solar combi systems in practice is given. The thermal performance varies greatly from system to system. Measured and calculated thermal performances of different solar combi systems are compared and the main reasons for the different thermal performances are given. Further, a parametric study on two solar combi system types is performed. Based on the investigation it can be concluded that the thermal performance first of all is influenced by the space heating consumption during the summer period and that the systems in practice perform as theoretically expected.
Design of Nonproportional Damped Systems via Symmetric Positive Inverse Problems
Authors: Starek L. , Inman D. J.
Published: May 2004

This paper summarizes the authors’ previous efforts on solving inverse eigenvalue problems for linear vibrating systems described by a vector differential equations with constant coefficient matrices and nonproportional damping. The inverse problem of interest here is that of determining symmetric, real, positive definite coefficient matrices assumed to represent mass normalized velocity and position coefficient matrices, given a set of specified complex eigenvalues and eigenvectors. Two previous solutions to the symmetric inverse eigenvalue problem, presented by Starek and Inman, are reviewed and then extended to the design of underdamped vibrating systems with nonproportional damping.
An Experimental Study of the Acoustic Oscillations by Flows Over Cavities
Authors: Amandole`se Xavier , He´mon Pascal , Regardin Clotilde
Published: May 2004

We present an experimental study of acoustic oscillations induced by an internal airflow over a shallow and a deep cavity. The Kelvin-Helmholtz instability is interacting with an acoustic mode of the cavity or of the duct, leading to a resonance which produces a very high sound level. The influence of upstream boundary layer thickness and neck thickness is studied. Some results obtained by modifying the upstream lip shape, by crenel addition, are also given.
Modeling of Granular Particle Damping Using Multiphase Flow Theory of Gas-Particle
Authors: Wu C. J. , Liao W. H. , Wang M. Y.
Published: May 2004

A theoretical model based on multiphase flow theory of gas-particle is developed to evaluate the granular particle damping characteristics. Expressions for the drag forces of the equivalent viscous damping and the Coulomb friction damping are formulated respectively. The nonlinear free vibration of an exemplified cantilever particle-damping beam is analyzed by using the averaging method based on the first approximation. Numerical results are also presented to illustrate general characteristics of the particle-damping beam. An experimental verification is performed, and a good correlation between the theoretical results and the experimental data shows that the theoretical work in this paper is valid.
Nonlinear Tensile Properties of Bovine Articular Cartilage and Their Variation With Age and Depth
Authors: Charlebois Mathieu , McKee Marc D. , Buschmann Michael D.
Published: May 2004

Tensile stiffness of articular cartilage is much greater than its compressive stiffness and plays an essential role even in compressive properties by increasing transient fluid pressures during physiological loading. Recent studies of nonlinear properties of articular cartilage in compression revealed several physiologically pertinent nonlinear behaviors, all of which required that cartilage tensile stiffness increase significantly with stretch. We therefore performed sequences of uniaxial tension tests on fresh bovine articular cartilage slices using a protocol that allowed several hours to attain equilibrium and measured longitudinal and transverse tissue strain. By testing bovine cartilage from different ages (6 months to 6 years) we found that equilibrium and transient tensile modulus increased significantly with maturation and age, from 0 to 15 MPa at equilibrium and from 10 to 28 MPa transiently. Our results indicate that cartilage stiffens with age in a manner similar to other highly hydrated connective tissues, possibly due to age-dependent content of enzymatic and nonenzymatic collagen cross links. The long relaxation period used in our tests (5–10 hours) was necessary in order to attain equilibrium and avoid a very significant overestimation of equilibrium modulus that occurs when much shorter times are used (15–30 minutes). We also found that equilibrium and transient tensile modulus increased nonlinearly when cartilage is stretched from 0 to 10% strain without any previous tare load. Although our results estimate a nonlinear increase in tensile stiffness with stretch that is an order of magnitude lower than that required to predict nonlinear properties in compression, they are in agreement with previous results from other uniaxial tension tests of collagenous materials. We therefore speculate that biaxial tensile moduli may be much higher and thereby more compatible with observed nonlinear compressive properties.
Determination of Poisson’s Ratio of Articular Cartilage by Indentation Using Different-Sized Indenters
Authors: Jin Hui , Lewis Jack L.
Published: May 2004

Articular cartilage is often characterized as an isotropic elastic material with no interstitial fluid flow during instantaneous and equilibrium conditions, and indentation testing commonly used to deduce material properties of Young’s modulus and Poisson’s ratio. Since only one elastic parameter can be deduced from a single indentation test, some other test method is often used to allow separate measurement of both parameters. In this study, a new method is introduced by which the two material parameters can be obtained using indentation tests alone, without requiring a secondary different type of test. This feature makes the method more suitable for testing small samples in situ. The method takes advantages of the finite layer effect. By indenting the sample twice with different-sized indenters, a nonlinear equation with the Poisson’s ratio as the only unknown can be formed and Poisson’s ratio obtained by solving the nonlinear equation. The method was validated by comparing the predicted Poisson’s ratio for urethane rubber with the manufacturer’s supplied value, and comparing the predicted Young’s modulus for urethane rubber and an elastic foam material with modulii measured by unconfined compression. Anisotropic and nonhomogeneous finite-element (FE) models of the indentation were developed to aid in data interpretation. Applying the method to bovine patellar cartilage, the tissue’s Young’s modulus was found to be 1.79±0.59MPa in instantaneous response and 0.45±0.26MPa in equilibrium, and the Poisson’s ratio 0.503±0.028 and 0.463±0.073 in instantaneous and equilibrium, respectively. The equilibrium Poisson’s ratio obtained in our work was substantially higher than those derived from biphasic indentation theory and those optically measured in an unconfined compression test. The finite element model results and examination of viscoelastic-biphasic models suggest this could be due to viscoelastic, inhomogeneity, and anisotropy effects.
Computational Fluid Dynamics (CFD) Study of the 4th Generation Prototype of a Continuous Flow Ventricular Assist Device (VAD)
Authors: Song Xinwei , Wood Houston G. , Olsen Don
Published: May 2004

The continuous flow ventricular assist device (VAD) is a miniature centrifugal pump, fully suspended by magnetic bearings, which is being developed for implantation in humans. The CF4 model is the first actual prototype of the final design product. The overall performances of blood flow in CF4 have been simulated using computational fluid dynamics (CFD) software: CFX, which is commercially available from ANSYS Inc. The flow regions modeled in CF4 include the inlet elbow, the five-blade impeller, the clearance gap below the impeller, and the exit volute. According to different needs from patients, a wide range of flow rates and revolutions per minute (RPM) have been studied. The flow rate-pressure curves are given. The streamlines in the flow field are drawn to detect stagnation points and vortices that could lead to thrombosis. The stress is calculated in the fluid field to estimate potential hemolysis. The stress is elevated to the decreased size of the blood flow paths through the smaller pump, but is still within the safe range. The thermal study on the pump, the blood and the surrounding tissue shows the temperature rise due to magnetoelectric heat sources and thermal dissipation is insignificant. CFD simulation proved valuable to demonstrate and to improve the performance of fluid flow in the design of a small size pump.