bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Bearing Offset and Flexibility on the Mesh Force Distribution of Spiral Bevel Gears
Authors: Mark W. D.
Published: January 2010

For straight or spiral bevel gears of nominal spherical involute design, the resultant total force vector transmitted by the gear mesh, in the absence of friction, lies in the plane of tooth contact. This force vector can be characterized by three scalar components, two orthogonal force components lying in the plane of contact and the resultant moment taken about the nominal center of the zone of contact. Equations for these three generalized force components are derived. The equations are expressed in terms of tooth pair/gear body stiffnesses, bearing/bearing support flexibility influence coefficients, the shaft input torque, deviations of the tooth running surfaces from perfect spherical involute surfaces, and bearing centerline offsets from the positions occupied by the base cone axes of the perfect involute bevel gear counterparts to the actual gears under consideration. Inertial forces arising from transverse and axial vibrations of the gear bodies are assumed to be negligible in comparison with the bearing support reaction forces.
An Extremum Principle for Computation of the Zone of Tooth Contact and Generalized Transmission Error of Spiral Bevel Gears
Authors: Mark W. D.
Published: January 2010

For a given set of forces transmitted by the gears, each of the three components of the generalized transmission error of spiral bevel gears is shown to be stationary with respect to small independent variations in the positions of the endpoints of the lines of tooth contact about their true values. The tangential generalized transmission error component is shown to take on a minimum value at the true endpoint positions. A computational procedure based on the method of steepest descent is described for computing the true line of contact endpoint positions and the three components of the generalized transmission error. A method for computing the Fourier series coefficients of the tooth meshing harmonics of the three generalized transmission error components also is provided.
Optimization of Spherical Joint Attachment in Spatial Linkages
Authors: Stanisˇic´ M. M. , Mirusky W. F.
Published: January 2010

This paper presents the kinematic analysis and optimization technique required for the optimal attachment of a spherical joint (i.e., a ball in a socket) to the ground pivoted link of an RSSR spatial four-bar linkage. The optimization technique is a searching algorithm, which can be applied to the problem of optimal spherical joint attachment in other types of spatial linkages as well. This attachment optimization is necessary if the socket of the joint is to have its maximum ball retention capability. The optimization technique is illustrated by an example.
The Method of Alternate Formulations, an Automated Strategy for Optimal Design
Authors: Hammond C. R. , Johnson G. E.
Published: January 2010

The Method of Alternate Formulations (MAF) is a new method of global information extraction for constrained, nonlinear optimization problems. MAF automatically generates the complete set of candidate solution points for these optimization problems using a symbolic mathematics computer package. MAF uses ideas and techniques from both the Method of Optimal Design and Monotonicity Analysis to reduce and formulate the problem. The reduced problem is repeatedly reformulated to develop state equations and objective functions in terms of all possible variable partitions. Trend analysis on the decision variables in the objective functions yields global information about constraint activity at possible solution points. Trend analysis on all of the possible formulations of the objective functions yields the complete set of candidate solutions. The state equations in each partition of the variables are used to test the feasibility of these candidate solutions, and the best feasible point is selected as the optimum solution. MAF can be used as a preprocessor for standard numerical optimization techniques and can be extended to nonmonotonic problems.
FDL—A Language for Function Description and Rationalization in Mechanical Design
Authors: Lai K. , Wilson W. R. D.
Published: January 2010

Function Description Language (FDL) is a design language which features an English-like syntax. It can be applied at the conceptual stage of mechanical design to describe functions of the elements in a preliminary design. From these description structural information can be deduced and analyzed. Based upon the suggestion and recommendations provided by the system, improvement can be made by the designer such that layout of the product can be simplified and rationalized.
Optimization With Discrete Variables Via Recursive Quadratic Programming: Part 2—Algorithm and Results
Authors: Cha J. Z. , Mayne R. W.
Published: January 2010

A discrete recursive quadratic programming algorithm is developed for a class of mixed discrete constrained nonlinear programming (MDCNP) problems. The symmetric rank one (SR1) Hessian update formula is used to generate second order information. Also, strategies, such as the watchdog technique (WT), the monotonicity analysis technique (MA), the contour analysis technique (CA), and the restoration of feasibility have been considered. Heuristic aspects of handling discrete variables are treated via the concepts and convergence discussions of Part I. This paper summarizes the details of the algorithm and its implementation. Test results for 25 different problems are presented to allow evaluation of the approach and provide a basis for performance comparison. The results show that the suggested method is a promising one, efficient and robust for the MDCNP problem.
On the Conceptual Design of a Novel Class of Robot Configurations
Authors: Tsai Lung-Wen , Freudenstein Ferdinand
Published: January 2010

The conceptual design has been investigated for the kinematic structure of relatively small robots with positive, rigid-body drive elements of minimum complexity in order to maximize rigidity, minimize vibrations and response time and optimize payload. Several novel robot configurations have been conceived and their displacement analysis and static torque analysis derived directly from their kinematic structure. It is believed that these configurations can be advantageous in the design of high-performance robots relative to current designs involving cables and push/pull elements.
A Closed-Form Numerical Method for Calculating the Steady-State Dynamic Response of Rigid-Body Machine Systems
Authors: Farhang K. , Midha A.
Published: January 2010

The rigid-body dynamic response of most single-degree-of-freedom machine systems are known to be governed by second-order, nonlinear, inhomogeneous, ordinary differential equations with variable coefficients. An earlier effort produced a solution algorithm, by linearizing such an equation and expressing it in the first-order form, to obtain the steady-state rigid-body dynamic response. This paper formulates a “closed-form numerical” algorithm for obtaining this steady-state response. It is demonstrated as leading to significant reductions in computation time. Efficient iterative methods, based on the criterion of balance of energy over the fundamental cycle, are formulated to treat the more practical problems involving known forcing and unknown average speed, and those involving unknown forcing and known average speed. In addition, two numerical procedures are proposed to treat problems involving systems with large coefficients of fluctuations. All methods are shown to be efficient and stable through examples involving a four-stroke reciprocating engine.
Two Generalizations of the Isometric Projection in Geometric Design
Authors: Wilde D. J.
Published: January 2010

The well-known pictorial drafting technique of isometric drawing is here generalized in two ways, called “isoclinal” and “axial,” or collectively, “symmetric.” Although the isoclinal projection preserves the useful property of foreshortening adjacent edges equally, and the axial projection foreshortens adjacent normals equally, the directions for these projections usually differ from that for isometric projection. Formulas are derived for the isoclinal and axial directions and their foreshortening factors and rotation matrices. Although intended for three-dimensional computer-aided design, the symmetric projections also can be performed on a drawing board with a protractor. Graphic examples involving design of nonrectangular connectors for three skew structural members and adjacent plates in space are presented.
Optimal Design of a Rotating Bar for Kinetic Energy Storage
Authors: Berger M. , Porat I.
Published: January 2010

A thin homogeneous rotating bar of variable width is considered for the purpose of storing kinetic energy. The objective of the design is to find the shape of the bar for which, in the presence of constraints on the geometry and strength of the bar, the Specific Kinetic Energy (SKE) is maximal. An upper bound for the SKE of a finite length bar is derived and a discrete formulation is presented by which an approximate optimal profile for arbitrary design parameters and rotational speeds can be obtained numerically. Applying a parametric study, in which optimal designs for a sequence of rotational speeds were observed, a general configuration of the exact optimal profile was concluded. The parametric study reveals the existence of three speed intervals, each characterized by a common type of optimal design. The optimal SKE corresponding to the ultimate rotational speed reaches a value very close to the theoretical upper bound, namely, that of a thin ring. The model gives insight into the nature of optimal designs and serves as a simple and rapid computational tool for finding the optimal profile for arbitrary bar parameters and rotational speeds.
On the Application of Straight-Line Linkages to Vehicle Suspension
Authors: Sadler J. P. , Chou H. C. , George G. R.
Published: January 2010

Four-bar linkages which generate approximate straight-line motion are investigated for use in vehicle suspension. The particular suspension geometry studied is the beam-axle type, leading to systems with two degrees of freedom of body roll motion relative to the axle. Kinetostatic analyses of these spring-restrained systems are carried out for a number of cases involving different combinations of loads and linkage geometry. From the predicted orientation of the body relative to the axle various vehicle dynamics parameters can be calculated, including roll center location and roll stiffness. It is found that these parameters, which are normally considered constant, are functions of the suspension linkage, jounce/rebound, and roll angle. Conditions under which the linkage types produce comparable roll performance are established.
Statistical Characteriztion of Position Errors of an Ensemble of Robots and Its Applications
Authors: Menq Chia-Hsiang , Borm Jin-Hwan
Published: January 2010

For the accurate control and implementation of a robot in an integrated manufacturing environment using off-line programming, a knowledge of the absolute positioning accuracy of the robot becomes important. This paper presents a framework which can be used to statistically represent the absolute positioning accuracy for a family of robots. Statistical error measure indices are proposed to represent the position error field over the working space for a family of robots. This error field provides statistical information for the position errors of the end-effector and can be a guide for the determination of the optimal design tolerances of the parts composing of a robot. The second objective of the paper is to introduce a simple interpolation scheme to improve the local position accuracy by teaching one or more task reference frames with which goal positions are mathematically expressed. It will be shown how the method shifts or alters the position error field in order to maintain the desired position accuracy within a desired working area.
Computer-Aided Design of Compact Helical Gear Sets
Authors: Jog C. S. , Pande S. S.
Published: January 2010

This paper presents the design strategy for the Computer-Aided Design (CAD) of compact helical gear sets. Using optimization techniques, fundamental gear design parameters such as the number of teeth on the pinion, helix angle, and diametral pitch (or module) are selected subject to constraints on bending stresses, contact stresses, and involute interference limits for both standard and nonstandard gearing. The CAD procedure is illustrated with the help of a design example.
Computer Implementation of an Optimal Conformal Mapping for Gear Tooth Stress Analysis
Authors: Richard M. J. , Pare D. , Cardou A.
Published: January 2010

This paper describes a computerized version of the complex potential approach which is a comprehensive mathematical model for the stress analysis of spur gear teeth. The entire procedure is a basic application of Hirano’s conformal mapping theory in which laws of elasticity have been combined. The main concepts of the method have been explained in previous publications but the work described herein is an appreciable extension of this relatively new approach. The algorithm is eminently well-suited for computer-aided-design of gear teeth; it serves as the basis for an interactive computer program which can model a gear tooth and can calculate the stresses and displacements within the tooth when subjected to a concentrated load. Results are compared with AGMA’s and other published values.
Position Errors Due to Clearances in Journal Bearings
Authors: Wang H. H. S. , Roth B.
Published: January 2010

The positional errors due to clearances in journal bearings intended to approximate revolute joints are analyzed. Equations are presented which relate joint geometry, external loads, and errors. The paper treats the case common in serial chain manipulators where the revolute joint’s nominal rotational angle is controlled, and it is desired to determine the errors that result from the clearances.
An Equality Constrained RQP Algorithm Based on the Augmented Lagrangian Penalty Function
Authors: Chen C. , Kong W. C. , Cha J. Z.
Published: January 2010

In comparative studies of constrained optimization methods the equality constrained recursive quadratic programming procedure has performed very favorably, particularly in terms of required computer time for execution. Biggs has formulated a strategy based on a quadratic penalty function and proved the global convergence of the method. This paper reformulates the procedure based on an augmented Lagrangian penalty function leading to improved performance and reduced sensitivity to the algorithm parameters. The formulation and algorithm are described herein and global convergence is demonstrated. Evaluation results on several test problems are presented to allow comparisons with other algorithms of the same type.
A Vehicle Handling Model With Active Suspensions
Authors: Shannan J. E. , Vanderploeg M. J.
Published: January 2010

This paper presents two vehicle models used to investigate the effects of active suspensions. One is a linear seven degree of freedom ride model. The second is a nonlinear ten degree of freedom ride and handling model. Full state feedback optimal control algorithms are developed for both models. The seven degree of freedom model is used to study ride effects. The active suspension substantially reduced the motion of the sprung mass. The ten degree of freedom model is used to study the effects of the active suspension on the directional response characteristics of the vehicle. The handling characteristics exhibited by the active suspension are very similar to those of the passive suspension. However, the active suspension did significantly reduce sprung mass motions during the handling maneuvers. It is then illustrated that by altering various feedback gains, active suspensions can be made to change the handling characteristics in the nonlinear range.
A Study of Spur Gear Geometry Factor Through Complex Potential Analysis
Authors: Cardou A. , Tordion G. V.
Published: January 2010

Bending stresses in spur gears have been obtained analytically using the Complex Potential Method of the two-dimensional theory of elasticity and conformal mapping of the tooth profile. Effects of profile shift and sliding friction on geometry factor have been studied for 20 deg pressure angle and numbers of teeth ranging from 20 to 150. It has been shown how these results can be applied to obtain a geometry factor corrected to include either the profile or the coefficient of friction effect in a given gear pair.
A Modification of Feasible Direction Optimization Method for Handling Equality Constraints
Authors: Chen Yong , Li Bailin
Published: January 2010

The Feasible Direction Method of Zoutendijk has proven to be one of the most efficient algorithms currently available for solving nonlinear programming problems with only inequality type constraints. Since in the case of equality type constraints, there exists no nonzero direction close to the feasible region, the traditional algorithm cannot work properly. In this paper, a modified feasible direction finding technique has been proposed in order to handle nonlinear equality constraints for the Feasible Direction Method. The algorithm is based on searching along directions intersecting the tangent of the equality constraints at some angle which makes the move toward the interior of the feasible region.
A Strategy of Wave Gait for a Walking Machine Traversing a Rough Planar Terrain
Authors: Qiu Xi-Ding , Song Shin-Min
Published: January 2010

The performance of a legged system is closely related to the adopted gait. Among the many available gaits, the wave gait possesses the optimum stability [1–3] and has been applied to walking on perfectly smooth terrain. The follow-the-leader (FTL) gait has the least demands for foothold selection and is the most suitable for walking on rough terrain [14]. In this paper, a strategy of wave gait which enables a hexapod to traverse two-dimensional, rough terrain is developed. This strategy applies a quasi FTL mode in walking and hence it has the advantages of both wave gait (optimum stability) and FTL gait (easy control on rough terrain). During walking, the legs move according to the wave gait and the two forelegs are adjusted to avoid forbidden areas. The maximum foot adjustment is determined by the current foot positions and the foot positions in the following one or two step(s). In order to improve the stability, different methods of foot adjustments and body adjustments are evaluated and integrated into the strategy. Finally, this strategy is verified by using computer graphics simulations.
An Efficient Rate Allocation Algorithm in Redundant Kinematic Chains
Authors: Huang M. Z. , Waldron K. J.
Published: January 2010

This paper addresses a basic problem which arises in the coordination of serial chain manipulators, namely, that of decomposing a given end effector velocity state into a set of joint rates. Such a problem is indeterminate for manipulators with kinematic redundancy. A novel method of solving the rate distribution problem for the class of fully revolute-jointed, serial manipulators is developed. The technique is an extension of the axial field solution scheme developed initially for solving the force allocation problem in a statically indeterminate parallel chain system. The basis of the solution method lies in the dualities of velocity and force systems between series and parallel mechanisms. The method offers an efficient means of rate coordination and is especially useful in the control of manipulators with high degrees of redundancy. Two examples have been given for illustration. It is shown that the minimum norm solution, obtainable commonly from pseudoinverse, can also be achieved using this new efficient algorithm.
Application of Kinematically Compatible Rolling-Contact Pairs to the Design of Low-Friction Rocker-Pivots
Authors: Chew M.
Published: January 2010

The concept of rolling-contact has been applied to reduce friction at highly loaded rocker-pivots without the use of rolling element bearings. Various configurations for a rolling motion at the pivot are discussed. As an example, this rolling-contact concept is applied to the pivot of a valve-train rocker. Problems relating to stability and motion distortion of the rocker are addressed and solved, resulting in significant friction reduction at the pivot.
Simulation of Dual Drive Branched Gear Systems During Selective Engagement of the Prime Movers
Authors: Inoue Y. , Seireg A.
Published: January 2010

This paper describes a digital simulation of the vibration and impact in a dual drive branched gear system during the engagement and disengagement of the prime movers. A nonlinear transient response analysis is carried out to illustrate the influence of system inertia, the tooth backlash, rate of clutch engagement and disengagement, friction etc. on tooth separation and dynamic tooth loads. The simulation procedure which is based on the phase-plane-δ method provides a general and effective tool of analysis for this class of problems. The existence of an optimal backlash condition for the idle pinion, which minimizes the dynamic tooth load, is illustrated.
An Operation Strategy for Mathematical Modeling in Optimum Design of Machine Construction
Authors: Kowalski J.
Published: January 2010

The paper describes an operation strategy, based on the systems approach, to enable quality control for design of products. The ideas outlined make possible a two-level hierarchic modeling system controlled according to principles of classification of product models. Elements of the optimization theory for model-based design are given, including an application example for the optimum design of a self-loading trailer assembly.
Optimal Design of Mechanical Systems With Constraint Violation Stabilization Method
Authors: Chang C. O. , Nikravesh P. E.
Published: January 2010

This paper presents a comprehensive optimal design procedure for constrained dynamic systems. The constraint violation stabilization method for dynamic analysis of mechanical systems is briefly reviewed. A direct differentiation method is used to form the equations of design sensitivity analysis based on a constraint violation stabilization method. The sensitivity equations and the equations of motion are integrated simultaneously to obtain the system response, as well as the state sensitivity matrices. All integrations are performed using a multistep predictor-corrector method. The first order design sensitivity matrix is used to calculate the gradient of cost function and the performance constraint during the optimization procedure. An optimization routine is linked to the analysis/sensitivity algorithm. Two examples are given which illustrate the effectiveness of this method for determining the optimal design of a system.
Analysis and Design of Basic Linkages for Harmonic Motion Generation
Authors: Midha A. , Cipra R. J. , Farhang K.
Published: January 2010

This paper deals with basic planar linkages driven by relatively small cranks, and as a consequence generating approximate simple harmonic motion at the output members. A unique approach is presented to yield the kinematic equations, as exemplified by planar crank-rocker and offset slider-crank linkages. The method involves the presumption of a mean linkage configuration and a small motion excursion therefrom. Its validity is demonstrated by means of several error plots, generated for varying, nondimensional linkage parameters and a constant mean transmission angle. These plots also serve to illustrate the order of approximation involved for a particular combination of parameters. Finally, the synthesis of a crank-rocker linkage for a representative set of requirements is exemplified using the equations developed herein.
An Optimum Design Algorithm for Gear Systems Incorporating Surface Temperature
Authors: Lin Tylor T. C. , Seireg A.
Published: January 2010

This paper presents a computer-based procedure for the optimum design of gear systems which selects the basic gear parameters to provide the best balance between the meshing elements for strength, surface durability, wear resistance and surface temperature. The emphasis is on the selection of the number of teeth in the different gears which provide the specified transmission ratio and maximize the load-carrying capacity of the system with special attention to the minimization of the maximum contact temperature.
Inclining Work-Arbor Taper Hobbing of Conical Gear Using Cylindrical Hob
Authors: Mitome K.
Published: January 2010

The inclining work-arbor taper hobbing is considered one of the most practical methods to cut a conical gear. But an exact hobbing theory has not been made clear, and besides an ideal hobbing machine available inpractical use has not been developed so far. In this paper, an exact kinematic analysis of this taper hobbing is presented, and an imaginary generating rack is obtained. A gear generated by this rack is defined as an ideal gear. Practical hobbing of conical involute gears is discussed. A hobbing machine having an inclining rotary table is tested, and some test gears are cut and inspected. And it is confirmed that the ideal gear can be considered representative of the gear cut by this taper hobbing, and the hobbing machine with an inclining rotary table has a practical utility. Finally, grinding of the conical involute gear based on the principle of this taper hobbing is presented.
Fiber-Reinforced Sandwich Plates Under Static Loads—Proposals for Their Optimization
Authors: Eschenauer H. A. , Fuchs W.
Published: January 2010

In order to satisfy the permanently increasing specification demands on machines and plants, the structural members and units of the constructions have to be designed in an “optimal” way. Nowadays more and more composite structures are attaining such new fields of application where one-component materials are not able to fulfill the higher demands. Typical examples are light constructions with optimal stiffness at various loadings. In this paper, a detailed investigation of the deformation behavior of a simply supported sandwich plate under static loads is carried out. Then, an optimal design method is formulated as a nonlinear multiobjective optimization problem by adopting the two conflicting objectives “minimal deformation” at “minimal weight,” including a set of constraints. The application of an optimization strategy is shown by means of a special preference function and sequential linearization as optimizer. Finally, some results of this procedure are discussed concerning the optimal design of sandwich plates.
Determination of Linkage Parameter and Pair Variable Errors in Open Chain Kinematic Linkages Using a Minimal Set of Pose Measurement Data
Authors: Ibarra R. , Perreira N. D.
Published: January 2010

During the manufacture of robotic systems differences between actual and nominal link lengths and orientations occur. In addition, errors between nominal and actual pair variables result from sensor and controller errors. Thus, when a robotic system attempts to perform a desired task using nominal motion planning schemes and nominal linkage kinematics, it will perform an actual task that is usually quite different from that desired. A procedure for determining the differences between the nominal and actual linkages parameters, pair variables, and tasks is presented. The approach can be used on all modern-day robots, as it incorporates solution techniques for the nonsquare and singular matrices that typically occur. An example using a PUMA 560 is included.
A Theoretical and Experimental Investigation of Contact Loss in the Clearances of a Four-Bar Mechanism
Authors: Bengisu M. T. , Hidayetoglu T. , Akay A.
Published: January 2010

The dynamic behavior of a four-bar mechanism with a clearance at any one of its connections is described using a quasi-static model. Prediction of separation at the joints is based on the deviation of the model at these positions from the zero-clearance values. Corresponding experimental studies have verified the theoretical results satisfactorily. Furthermore, the present model was applied successfully to similar cases published earlier. The existing criteria on the prediction of contact loss are discussed and a new criterion is offered.
Low Cost Thin-Film CdS-Based Solar Cells—Progress and Promise
Authors: Barnett Allen M. , Meakin John D.
Published: January 2010

The direct conversion of sunlight to electricity using thin film solar cells is potentially a low cost renewable source of energy. A major factor contributing to the low projected costs is the very small quantities of materials required as the active layers of the cells can be as little as 2 μm thick. The efficiency of solar cells will have to exceed ten percent to achieve economic power generation. Until 1976 no thin film solar cells with above seven percent efficiency in sunlight had been reported, but since then the Institute of Energy Conversion has successively reported 7.8, 8.55 and 9.15 percent. This paper will describe the loss minimization methodology utilized to achieve these increases in performance. Analysis shows that efficiencies as high as 14–16 percent for CdS-based solar cells are achievable. The research and development necessary to achieve these high efficiencies will be described. The feasibility of an extremely low cost manufacturing process capable of producing solar cells costing 250 dollars/kWatt will be discussed. Recent progress in development of low-cost thin-film devices shows great promise that direct conversion of sunlight to electricity can make a measurable contribution to the electrical energy supply both nationally and internationally.
Photovoltaic Electric Power Generation from a Utility Perspective
Authors: Goodman F. R.
Published: January 2010

A substantial research and development effort is presently taking place on a worldwide basis to improve the viability of photovoltaic systems in terrestrial applications for direct conversion of sunlight to electricity. The utility-related applications of photovoltaic systems can be categorized as either centralized generation facilities or dispersed generation facilities. Technical, economic and other problems associated with utilizing photovoltaic systems in both application categories are discussed. The advantages and disadvantages of centralized versus dispersed generation are presented. The advantages and disadvantages of different photovoltaic devices for various applications are given. Factors which are expected to influence, either favorably or unfavorably, the future widespread deployment of photovoltaic systems in terrestrial applications are provided. The current program at the Los Angeles Department of Water and Power for assessing the potential future impacts of photovoltaic conversion is discussed.
Structural Cost Optimization of Photovoltaic Central Power Station Modules and Support Structure
Authors: Sutton P. D. , Stolte W. J. , Marsh R. O.
Published: January 2010

The results of a comprehensive study of photovoltaic module structural support concepts for photovoltaic central power stations and their associated costs are presented. The objective of the study has been the identification of structural cost drivers. Parametric structural design and cost analyses of complete array systems consisting of modules, primary support structures, and foundations were performed. Area related module cost was found to be constant with design, size, and loading. A curved glass module concept was evaluated and found to have the potential to significantly reduce panel structural costs. Conclusions of the study are: array costs do not vary greatly among the designs evaluated; panel and array costs are strongly dependent on design loading; and the best support configuration is load dependent.
The Effect of Natural Soiling and Cleaning on the Size Distribution of Particles Deposited on Glass Mirrors
Authors: Roth E. P. , Anaya A. J.
Published: January 2010

The particle size distribution and the reflectance properties of silvered glass mirrors exposed in an outdoor environment have been measured to determine the separate effects of natural soiling and natural cleaning (wind and rain). The wavelength dependent diffuse reflectance was correlated with the particle size distribution function for mirrors exposed to increasing periods of outdoor exposure. These measurements have indicated the significant role of small particles (radii ≲ 5 μm) in the soiling of exposed mirrors and in the subsequent reflectance loss over the solar spectrum.
Uncertainty in Determining Thermal Performance of Liquid-Heating Flat-Plate Solar Collectors
Authors: Streed E. R. , Waksman D.
Published: January 2010

Thermal performance measurements of eight types of liquid-heating flat-plate solar collectors were conducted with two to four collectors of each type at four outdoor test sites. Tests were performed in accordance with the procedure prescribed by ASHRAE Standard 93-77. Statistical analysis of data sets for each collector type within test sites and between test sites was done using ASTM recommended methods to evaluate test method measurement uncertainty.
Ammonia Turbine Design for Ocean Thermal Energy Conversion (OTEC) Plants
Authors: Kostors C. H. , Vincent S. P.
Published: January 2010

During the optimization studies of a 10-MWe (net) OTEC power system the ammonia turbine design study led to selection of a four-stage, double-flow axial turbine yielding 89.6 percent efficiency at 1800 rpm. To maximize power at off-nominal conditions, variable nozzles are used for the first stage. The turbine is directly connected to a four-pole, 60-Hz synchronous generator having 97.2 percent efficiency. This study was limited to state-of-the-art hardware designs for axial- and radial-flow turbines, single- and double-flow designs, and variations in the base diameter and number of turbine stages. The gasdynamic calculation procedure and the effects of the turbine generator control scheme, turbine blade design, materials (annealed AISI Type 403 steel is chosen for the blading), and seals and bearings are addressed in this paper. The estimated mass-production cost of the turbine-generator set is approximately $150/kWe at 10-MWe (net) size in 1979 dollars. Single-flow-axial and radial-inflow turbines would have lower performance without sufficiently lower cost to be cost-effective, since each percentage point of turbine efficiency is estimated to be worth 17 to $28/kWe.
Theoretical and Experimental Study of an Air Solar Collector with an Evacuated Tube Cover
Authors: Alben R. , Hardcastle K.
Published: January 2010

Theoretical calculations and experimental data on an evacuated tube solar collector with an air heat transfer medium are presented. The collector is a conventional flat plate design except that the front cover, instead of being made up of one or two sheets of flat glass, consists of a raft-like arrangement of evacuated glass tubes. The calculations indicate that an evacuated tube cover, together with a high heat transfer absorber, could give a solar collector with superior thermal performance. Experimental measurements are given for an air collector using uncoated evacuated tubes and a screen absorber. Results on internal temperatures are used to infer the effectiveness of the heat transfer between the absorber screen and the air flow. When account is taken of the measured absorber properties, the performance of the evacuated tube cover is in reasonable accord with the theory.
Transient Response of a Latent Heat Storage Unit: An Analytical and Experimental Investigation
Authors: Green T. F. , Vliet G. C.
Published: January 2010

An analytical and experimental investigation of the transient thermal response of a latent heat storage unit is presented. Emphasis is placed on characterization of an entire storage unit rather than a single constituent storage element. In the analysis, two coupled governing partial differential equations that describe the model are derived and solved numerically. In the experimentation, a baffled shell and tube type heat exchanger was fabricated to provide data for a preliminary evaluation of the model. The experimental unit used water as the shell side HFT and poly(ethylene oxide) as the PCM contained within glass tubes. A comparison of experimental and analytical results shows that the analysis predicts somewhat conservative results.
Optimization of Flow Passage Geometry for Air-Heating, Plate-Type Solar Collectors
Authors: Hollands K. G. T. , Shewen E. C.
Published: January 2010

The effect of the choice of shape and dimensions of the air flow passages in plate-type, air-heating solar collectors is assessed. Particularly examined is their effect on the overall heat transfer coefficient Upf between the air stream and the plate, which has an important effect on collector efficiency. It is emphasized in this study that in comparing various designs of flow passage, they should be compared for the same pressure drop Δp suffered by the air in passing through the collector, and for the same mass flow rate m per unit of collector area. On the basis of this type of comparison, two main conclusions are drawn. First, when the length of the air flow passage L is made less than about 1 m, Upf increases dramatically with decreasing values of L. Second, outside the transition regime, the value of Upf for a V-corrugated absorber plate is from 47 to 300 percent higher than that for a flat absorber plate, depending on whether the flow is laminar or turbulent, and on whether the V-corrugated plate is thermally bonded to the back plate. The first conclusion has led to a proposal for a novel air-heating solar collector design, called the “short-path” design.
Analysis and Design of Hybrid Double-Absorption Cooling Systems for Low Grade Thermal Energy Applications
Authors: Peng C. S. P. , Howell J. R.
Published: January 2010

A hybrid double-absorption system using LiCL-H2O solution as a working fluid is proposed in this paper. This system can operate at low source temperature (55–80°C), requires lower blower power than a desiccant system, and has a higher system C.O.P. A modification of this system, a double absorption-evaporation system that provides even higher C.O.P. is also proposed. Both closed and open regeneration of the working fluid are considered in the system design. Performance equations for these hybrid systems are presented. A computer code HYBRID is written to do parametric analyses for these systems under steady-state conditions. The operating range and optimum design conditions are determined through both theoretical analysis and computer simulation. It is shown that these hybrid absorption systems have definite advantages over conventional absorption and desiccant systems for low grade thermal energy applications.
Blade Fatigue Life Assessment With Application to VAWTS
Authors: Veers P. S.
Published: January 2010

A cursory analysis of the stress history of wind turbine blades indicates that a single stress level at each wind speed does not adequately describe the blade stress history. A statistical description is required. Blade stress data collected from the DOE/ALCOA Low Cost experimental turbines indicate that the Rayleigh probability density function adequately describes the distribution of vibratory stresses at each wind speed. The Rayleigh probability density function allows the distribution of vibratory stresses to be described by the RMS of the stress versus time signal. With the RMS stress level described for all wind speeds, the complete stress history of the turbine blades is known. Miner’s linear cumulative damage rule is used as a basis for summing the fatigue damage over all operating conditions. An analytical expression is derived to predict blade fatigue life. Input to the blade life expression includes a basic blade S-N curve, RMS stress versus wind speed data, the probability density function of vibratory stress, and the probability density function which describes the wind speed distribution. The implications of the assumptions and the limitations of this approach are discussed.
Transient Response of Solar Collectors
Authors: Mather G. R.
Published: January 2010

A transient response model is developed for collectors whose dynamic behavior is controlled predominantly by the absorber surface and heat-transfer fluid. Such collectors can be described adequately by two differential equations for which exact solutions are possible. The equations are solved for the case of evacuated-tube collectors, and the solutions are found to exhibit qualitatively new transient phenomena. In particular, it is found that fluid flow rates, thermal masses, and heat-transfer coefficients are important factors in determining the overall response of a collector, and that the functional form of the response depends on how these parameters are related. The model is compared with test results for four evacuated-tube collectors whose heat-transfer configurations and fluid flow rates encompass a broad range of transient response regimes. Excellent agreement is obtained in all cases. In addition to providing a detailed insight into the problem of collector dynamics, the model is a potentially useful tool for obtaining information about heat-transfer coefficients and fluid flow distribution effects.
Performance of a Cross-Cooled Desiccant Dehumidifier Prototype
Authors: Worek W. M. , Lavan Z.
Published: January 2010

A cross-cooled desiccant dehumidifier prototype was constructed and tested. The cross-cooled dehumidifier prototype was constructed in the form of a cube with a side dimension of 0.6 m. The cooling was achieved by passing air through rectangular channels perpendicular to the process channels which are lined with desiccant sheets consisting of 9 μm Syloid 63™ silica gel held in a Teflon web. The process for the manufacture of the silica gel sheets was developed at the Illinois Institute of Technology. The performance of the dehumidifier prototype was parametrically studied in a test bed that simulates the performance of a cross-cooled desiccant cooling system. The system was tested over a range of operating conditions typically encountered in field installations of such systems. The performance parameters studied are moisture cycled, cooling capacity, and coefficient of performance.
Biofouling Monitors for Noncylindrical OTEC Heat Exchanger Tubes
Authors: Kuzay T. M. , Panchal C. B. , Gavin A. P.
Published: January 2010

Heat-transfer monitors (HTMs) have been used since 1976 to measure the reduction in the seawater heat-transfer coefficient due to buildup of biofouling and corrosion products inside circular tubes of shell-and-tube heat exchangers being developed for ocean thermal energy conversion (OTEC) plants. For OTEC heat exchangers (HXs) with other tube geometries, special, modified HTMs, which we call STMs, are being sought. The analytical approaches and calibration results to date are summarized for STMs of two types: (i) an STM simulating a rectangular seawater passage in a compact, aluminum, plate-fin HX, and (ii) an STM for a helical stainless-steel tube. The development of type 1 has been successful. A software change is needed for type 2.
A Simple Formula for Calculating the Optimal Frequency for Cleaning Concentrating Solar Collectors
Authors: Bergeron K. D.
Published: January 2010

A formula for the interval between solar collector cleanings is presented which minimizes the energy user’s annual operating costs (including backup energy costs). Results are applicable to both thermal and electric power systems and, with slight modification, to flat plate collectors.
Gradient Zone Constraints in a Salt-Stratified Solar Pond
Authors: Newell T. A. , Boehm R. F.
Published: January 2010

An operational condition is defined for a salt-stratified solar pond. A criterion based on empirical evidence is formulated which shows a limit is approached as steady operating conditions are attained. For sodium chloride ponds, the criterion indicates a dependence between salt and temperature gradients during steady-state conditions. At the present time, appropriate data for explaining the physical basis of this relationship are not available. Significant results are found as a result of the gradient zone criterion. First, the gradient zone criterion leads to an explanation for the formation of an upper convecting zone. Results obtained with the gradient zone criterion relate to salt maintenance in a pond. Depending on the temperature operating conditions of a pond, a specific amount of salt must be in the pond. Also, salt concentration levels maintained in the upper and lower convecting zones are shown to significantly affect a pond’s thermal energy performance.
An Experimental Investigation of a Stationary Reflector/Tracking Absorber Solar Collector at Intermediate Temperatures
Authors: Fruchter E. , Grossman G. , Kreith F.
Published: January 2010

This paper describes the design, construction, and testing of a concentrating solar collector based on the Stationary Reflector/Tracking Absorber (SRTA) principle. The system consists of a fixed, 2.5-m dia, spherical mirror which focuses solar radiation on a movable, cylindrical absorber tracking the sun. This work is an extension of earlier tests with a similar collector in which output temperatures up to 150°C were obtained with water. The present system, using a mineral-oil-based heat transfer fluid, was capable of heating the fluid up to 300°C under steady-state conditions. The direct radiation efficiency ranged from 50 percent at low temperatures up to 30 percent near 300°C, showing the SRTA to be an effective concentrating collector for the intermediate temperature range which can be constructed at relatively low cost.
Incident Angle Modifiers for Flat-Plate Solar Collectors: Analysis of Measurement and Calculation Procedures
Authors: Thomas W. C. , Dawson A. G. , Waksman D. , Streed E. R.
Published: January 2010

Existing test procedures for measuring and rating thermal performance require the determination of the angular response of collectors in order to account for non-normal incident beam irradiance. Angular response measurements for four different types of collectors, each type tested by three different laboratories, are presented and analyzed. Substantial differences, both within and between laboratories, are reported for the same type collectors. An analysis of the measurement procedure shows that experimentally determined angular response parameters are subject to relatively large uncertainties. The problem results to a large extent from measuring collector efficiencies at non-normal incident angles where measurement uncertainty is of the same order of magnitude as the efficiency reduction attributable to these off-normal angles. Other factors which can affect angular response measurements and the method of correlating results are also discussed. A theoretical analysis shows that shading of the absorber by the collector air space side- and end-walls for non-normal incident angles can be of the same order of importance as the decrease in the transmittance of the cover assembly. While this situation complicates an analytical approach, it is concluded that calculations are adequate to depict the angular response of conventional flat-plate tube-in-sheet collector designs. A simplified analytical procedure and nomographs are presented for rapid calculation of incident angle modifiers. The predicted seasonal performance of solar energy systems and clear-day ratings of typical flat-plate collectors are shown to be relatively insensitive to large uncertainties in incident angle modifiers. Typically, the values of these calculated quantities could be affected by approximately five percent as a result of uncertainty in the test-derived angular response parameter.