bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Temperature Fatigue Properties of Single Crystal Superalloys in Air and Hydrogen
Authors: Arakere N. K.
Published: August 2004

Hot section components in high-performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys such as PWA1480, PWA1484, CMSX-4, and Rene N-4 as these materials provide superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over their polycrystalline counterparts. Fatigue failures in PWA1480 single crystal nickel-base superalloy turbine blades used in the space shuttle main engine fuel turbopump are discussed. During testing many turbine blades experienced stage II noncrystallographic fatigue cracks with multiple origins at the core leading edge radius and extending down the airfoil span along the core surface. The longer cracks transitioned from stage II fatigue to crystallographic stage I fatigue propagation, on octahedral planes. An investigation of crack depths on the population of blades as a function of secondary crystallographic orientation (β) revealed that for β=45+/−15 deg tip cracks arrested after some growth or did not initiate at all. Finite element analysis of stress response at the blade tip, as a function of primary and secondary crystal orientation, revealed that there are preferential β orientations for which crack growth is minimized at the blade tip. To assess blade fatigue life and durability extensive testing of uniaxial single crystal specimens with different orientations has been tested over a wide temperature range in air and hydrogen. A detailed analysis of the experimentally determined low cycle fatigue properties for PWA1480 and SC 7-14-6 single crystal materials as a function of specimen crystallographic orientation is presented at high temperature (75°F–1800°F) in high-pressure hydrogen and air. Fatigue failure parameters are investigated for low cycle fatigue data of single crystal material based on the shear stress amplitudes on the 24 octahedral and 6 cube slip systems for FCC single crystals. The max shear stress amplitude [Δτmax] on the slip planes reduces the scatter in the low cycle fatigue data and is found to be a good fatigue damage parameter, especially at elevated temperatures. The parameter Δτmax did not characterize the room temperature low cycle fatigue data in high-pressure hydrogen well because of the noncrystallographic eutectic failure mechanism activated by hydrogen at room temperature. Fatigue life equations are developed for various temperature ranges and environmental conditions based on power-law curve fits of the failure parameter with low cycle fatigue test data. These curve fits can be used for assessing blade fatigue life.
A Characteristic Parameter to Estimate the Optimum Counterweight Mass of Symmetric In-Line Engines
Authors: Stanley R. , Taraza D.
Published: August 2004

Dimensionless relationships that estimate the maximum bearing load of two symmetric in-line engines have been developed. These relationships were empirically determined by averaging the maximum bearing loads of several engine configurations with various geometric and operating parameters. It has been found that the maximum bearing load initially decreases with engine speed, reaches a minimum, and then increases quickly with engine speed. This minimum reflects a transition speed at which the contribution of the inertia force overcomes the contribution of the maximum pressure force to the maximum bearing load. The transition speed increases with an increase of counterweight mass and is a function of the geometric parameters and operating conditions of the engine. Rapid estimation of the main bearing loads is made possible by the use of the dimensionless relationships developed in the paper.
The Qualitative Synthesis of Parallel Manipulators
Authors: Angeles Jorge
Published: August 2004

As shown in this paper, when designing parallel manipulators for tasks involving less than six degrees of freedom, the topology can be laid out by resorting to qualitative reasoning. More specifically, the paper focuses on cases whereby the manipulation tasks pertain to displacements with the algebraic structure of a group. Besides the well-known planar and spherical displacements, this is the case of displacements involving: rotation about a given axis and translation in the direction of the same axis (cylindrical subgroup); translation in two and three dimensions (two- and three-dimensional translation subgroups); three independent translations and rotation about an axis of fixed direction, what is known as the Scho¨nflies subgroup; and similar to the Scho¨nflies subgroup, but with the rotation and the translation in the direction of the axis of rotation replaced by a screw displacement. For completeness, the fundamental concepts of motion representation and groups of displacements, as pertaining to rigid bodies, are first recalled. Finally, the concept of Π-joint, introduced elsewhere, is generalized to two and three degrees of freedom, thereby ending up with the Π2-and the Π3-joints, respectively.
Alternative Multinutating Disk Engine Configurations for Diverse Applications
Authors: Korakianitis T. , Meyer L. , Boruta M. , McCormick H. E.
Published: August 2004

The nutating engine is a new type of internal combustion engine with distinct advantages over conventional piston engines and gas turbines in small power ranges. The engine’s unique arrangement flexibility allows several alternative disk and shaft configurations, each selected for a different application. Variations in cycle temperature ratio and compression ratio during normal operation enable the engine to effectively become a variable-cycle engine, allowing significant flexibility for maximum efficiency or power or other optimizing function for on-ground stationary or for airborne applications. In its basic configuration the core of the engine is a nutating nonrotating disk, with the center of its hub mounted in the middle of a Z-shaped shaft. The two ends of the shaft rotate, while the disk “nutates,” performs a wobbling motion without rotating around its axis. The motion of the disk circumference prescribes a portion of a sphere. A portion of the area of the disk is used for intake and compression, a portion is used to seal against a center casing, and the remaining portion is used for expansion and exhaust. The compressed air is admitted to an external accumulator, and then into an external combustion chamber before it is admitted to the power side of the disk. A companion paper examines the performance potential of the one-disk engine. This paper examines alternative engine configurations. The external combustion chamber enables the engine to operate on a variable compression ratio cycle. In addition, separate disks of unequal size are used for intake and expansion, resulting in distinct and significant power, efficiency, fuel flexibility, and arrangement advantages over conventional piston engines, over gas turbines, and over the basic nutating-engine configuration. The performance of these arrangements is examined for: on-ground power, on-ground efficiency, (auxiliary power, automotive); and for small and light airframe applications for flight Mach numbers from 0 to 1 and altitudes from 0 to 20 km. This publication is the original presentation of the performance potential of several alternative configurations of the basic engine, such as multidisk arrangements, combustion and exhaust disks of different size, and variable-compression ratio (variable cycle) configurations.
Lateral Forces From Single Gland Rotor Labyrinth Seals in Turbines
Authors: Song Bum Ho , Song Seung Jin
Published: August 2004

Even though interest in labyrinth seal flows has increased recently, an analytical model capable of predicting turbine flow response to labyrinth seals is still lacking. Therefore, this paper presents a new model to predict flow response in an axial turbine stage with a shrouded rotor. A concentric model is first developed, and this model is used to develop an eccentric model. Basic conservation laws are used in each model, and a nonaxisymmetric sealing gap is prescribed for the eccentric model. Thus, the two models can predict the evolution of a uniform upstream flow into a nonuniform downstream flow. In turbines with concentric shrouded rotors, the seal flow is retarded in the axial direction and tangentially underturned. In turbines with eccentric shrouded rotors, flow azimuthally migrates away from and pressure reaches its peak near the maximum sealing gap region. Finally, the rotordynamic implications of such flow nonuniformities are discussed and compared against eccentric unshrouded turbine predictions.
The Employment of Hydrogenerated Fuels From Natural Gas Reforming: Gas Turbine and Combustion Analysis
Authors: Bozza Fabio , Cameretti Maria Cristina , Tuccillo Raffaele
Published: August 2004

An integrated method for power plant analysis, including rotating component matching and CFD simulation of the combustion process, is applied to the study of gas turbines supplied with hydrogenated fuels originating from the natural gas reforming. The method proposed by the authors allows estimation of the power plant performance and emission in the gas turbine operating range. A comparison is then carried out between the plant behavior with conventional fuelling and with decarbonised fuel supply. Attention is also paid to the study of the combustion regimes with either natural gas or fuels with increasing hydrogen contents, in order to achieve a realistic insight of both the temperature distributions and the growth of nitric oxides throughout the combustion chamber.
Torque and Angle Controlled Tightening Over the Yield Point of a Screw—Based on Monte-Carlo Simulations
Authors: Toth Go¨ran R.
Published: August 2004

This paper presents a technique, based on Monte-Carlo simulations, of utilizing a screw over its yield point in a controlled fashion, even under simple tightening conditions. The simulations consider the probabilistic nature of different variables necessary to calculate screwed joints. The proposed torque and angle controlled tightening technique can be used in assembly plants as well as in small workshops. The technique predicts permanent elongation, maximum tightening angle, final torque and preload after tightening. Further, a recommendation on the minimum and maximum snug torques prior to application of the angle over the yield point of a screw is also presented.
Analytical Blade Row Cooling Model for Innovative Gas Turbine Cycle Evaluations Supported by Semi-Empirical Air-Cooled Blade Data
Authors: Torbidoni Leonardo , Massardo Aristide F.
Published: August 2004

With the objective of performing reliable innovative gas turbine cycle calculations, a new procedure aimed at evaluating blade cooling performance is presented. This complete analytical (convective and film) blade cooling modeling provides the coolant mass flow and pressure loss estimation, and is a useful tool in the field of innovative gas turbine cycle analysis, mainly when alternative fluids are considered. In this case, in fact, the conventional semi-empirical data based on the use of air as traditional coolant and working media are no longer suitable. So the analytical approach represents a way of properly investigating alternative cooling methods and fluids. In the presented analysis the effects of internal blade geometry on cooling performance are summarized by the Z parameter, which also highly affects the coolant flow pressure losses. Since existing technology represents a natural starting point for the assessment of Z, the model is able to automatically estimate a proper value relying only on available semi-empirical data which were established for air-cooled gas turbine blades. When alternative fluids are considered, the same estimated value of Z is still maintained for the calculation, with the result of investigating the performance of existing blade technology for novel operational conditions. This represents an example of how the analytical approach, supported by conventional air-cooled blade semi-empirical data, appears as an innovative tool in the analysis of novel gas turbine cycles. In fact, the simulation results for the cooled blade were easily employed on the whole system level (gas turbine).
A Feasibility Study of Existing Gas Turbines for Recuperated, Intercooled, and Reheat Cycle
Authors: Bhargava R. , Bianchi M. , Peretto A. , Spina P. R.
Published: August 2004

In the present paper, a comprehensive and simple in application design methodology to obtain a gas turbine working on recuperated, intercooled, and reheat cycle utilizing existing gas turbines is presented. Applications of the proposed design steps have been implemented on the three existing gas turbines with wide ranging design complexities. The results of evaluated aerothermodynamic performance for these existing gas turbines with the proposed modifications are presented and compared in this paper. Sample calculations of the analysis procedures discussed, including stage-by-stage analysis of the compressor and turbine sections of the modified gas turbines, have been also included. All the three modified gas turbines were found to have higher performance, with cycle efficiency increase of 9% to 26%, in comparison to their original values.
Analysis, Design, and Modeling of a Rotary Vane Engine (RVE)
Authors: Librovich B. V. , Nowakowski A. F.
Published: August 2004

This paper introduces a mathematical model to analyze the dynamic behavior of a novel rotary vane engine (RVE). The RVE can be considered to have a number of advantages when compared to a majority of other reciprocating engine types. The advantages are found in the simple structure and the small number of moving parts. In this paper the geometrical structure and dynamical behavior of engines with a different number of work units is considered in detail. This has been examined through a study of torque transmission with a particular reference to how this is affected by the noncircular geometry of gear pitch curves. Using the Coulomb friction model, consideration has been given to the mechanical power loss due to friction in different parts of the engine, which must be taken into account. The study also proposes a possible method for balancing of asymmetric cogwheels. The analysis concludes that by using an appropriate design and arrangement of cogwheels and all moving parts, vibration can be attenuated due to impulsive gas torque.
Inlet Fogging of Gas Turbine Engines—Part I: Fog Droplet Thermodynamics, Heat Transfer, and Practical Considerations
Authors: Chaker Mustapha , Meher-Homji Cyrus B. , Mee Thomas
Published: August 2004

The inlet fogging of gas turbine engines for power augmentation has seen increasing application over the past decade yet not a single technical paper treating the physics and engineering of the fogging process, droplet size measurement, droplet kinetics, or the duct behavior of droplets, from a gas turbine perspective, is available. This paper provides the results of extensive experimental and theoretical studies conducted over several years coupled with practical aspects learned in the implementation of nearly 500 inlet fogging systems on gas turbines ranging in power from 5 to 250 MW. Part I of the paper covers the underlying theory of droplet thermodynamics and heat transfer, and provides several practical pointers relating to the implementation and application of inlet fogging to gas turbine engines.
Inlet Fogging of Gas Turbine Engines—Part II: Fog Droplet Sizing Analysis, Nozzle Types, Measurement, and Testing
Authors: Chaker Mustapha , Meher-Homji Cyrus B. , Mee Thomas
Published: August 2004

The inlet fogging of gas turbine engines for power augmentation has seen increasing application over the past decade yet not a single technical paper treating the physics and engineering of the fogging process, droplet size measurement, droplet kinetics, or the duct behavior of droplets, from a gas turbine perspective, is available. This paper provides the results of extensive experimental and theoretical studies conducted over several years, coupled with practical aspects learned in the implementation of nearly 500 inlet fogging systems on gas turbines ranging in power from 5 to 250 MW. Part II of the paper treats the practical aspects of fog nozzle droplet sizing, measurement and testing presenting the information from a gas turbine fogging perspective. This paper describes the different measurement techniques available, covers design aspects of nozzles, provides experimental data on different nozzles, and provides recommendations for a standardized nozzle testing method for gas turbine inlet air fogging.
Inlet Fogging of Gas Turbine Engines—Part III: Fog Behavior in Inlet Ducts, Computational Fluid Dynamics Analysis, and Wind Tunnel Experiments
Authors: Chaker Mustapha , Meher-Homji Cyrus B. , Mee Thomas
Published: August 2004

The inlet fogging of gas turbine engines for power augmentation has seen increasing application over the past decade yet not a single technical paper treating the physics and engineering of the fogging process, droplet size measurement, droplet kinetics, or the duct behavior of droplets, from a gas turbine perspective, is available. This paper along with Parts I and II provides the results of extensive experimental and theoretical studies conducted over several years coupled with practical aspects learned in the implementation of nearly 500 inlet fogging systems on gas turbines ranging in power from 5 to 250 MW. In Part III of this paper, the complex behavior of fog droplets in the inlet duct is addressed and experimental results from several wind tunnel studies are covered.
Simplified Versus Detailed Solid Oxide Fuel Cell Reactor Models and Influence on the Simulation of the Design Point Performance of Hybrid Systems
Authors: Magistri Loredana , Bozzo Riccardo , Costamagna Paola , Massardo Aristide F.
Published: August 2004

High-efficiency hybrid systems (HS) based on the coupling of solid oxide fuel cells (SOFCs) and gas turbines (GT) are analyzed in this paper through the use of two different approaches: simplified and detailed SOFC models. The simplified model, already presented by the authors, is very useful for HS design and off-design analysis. The detailed model, developed by the authors and verified through the use of available experimental data, allows the complete description of the SOFC reactor’s internal behavior to be obtained. The detailed model can also be utilized for HS modeling. Both models are presented and discussed in this paper, and they are compared to each other. The results obtained for the stand-alone SOFC reactor, and the HS design point configuration are presented and carefully discussed, also taking into account the nonlinear SOFC response.
Siemens Westinghouse Advanced Turbine Systems Program Final Summary
Authors: Diakunchak Ihor S. , Gaul Greg R. , McQuiggan Gerry , Southall Leslie R.
Published: August 2004

This paper summarizes achievements in the Siemens Westinghouse Advanced Turbine Systems (ATS) Program. The ATS Program, co-funded by the U.S. Department of Energy, Office of Fossil Energy, was a very successful multiyear (from 1992 to 2001) collaborative effort between government, industry, and participating universities. The program goals were to develop technologies necessary for achieving significant gains in natural gas-fired power generation plant efficiency, a reduction in emissions, and a decrease in cost of electricity, while maintaining current state-of-the-art electricity generation systems’ reliability, availability, and maintainability levels. Siemens Westinghouse technology development concentrated on the following areas: aerodynamic design, combustion, heat transfer/cooling design, engine mechanical design, advanced alloys, advanced coating systems, and single crystal (SC) alloy casting development. Success was achieved in designing and full scale verification testing of a high-pressure high-efficiency compressor, airfoil clocking concept verification on a two-stage turbine rig test, high-temperature bond coat/TBC system development, and demonstrating feasibility of large SC turbine airfoil castings. The ATS program included successful completion of W501G engine development testing. This engine is the first step in the W501ATS engine introduction and incorporates many ATS technologies, such as closed-loop steam cooling, advanced compressor design, advanced sealing, and high-temperature materials and coatings.
New Pneumatic Cylinders for Improving Servo Actuator Positioning Accuracy
Authors: Krivts Igor L.
Published: August 2004

Positioning accuracy of pneumatic servo actuators depends on parameters of the actuator and control system, and also on the friction force. This paper reports on new constructions of the pneumatic cylinders, which are the integral part of the servo actuator. Experimental examination of these servo actuators has shown that they could provide improved accuracy performance over the system with ordinary pneumatic cylinder.
A General Formulation for Designing Interference-Fit Joints With Elastic-Plastic Components
Authors: Baldanzini Niccolo`
Published: August 2004

A general approach for designing interference-fit joints constituted of elastic-plastic components is presented. The wide applicability range of the method was achieved removing restrictive assumptions about material characterization and yield criterion, which were included in previous theoretical models. Because of the general approach, the model is solved with an iterative procedure. The theory has been successfully validated by a result comparison with finite element models.
Injection System Design Optimization by Considering Fuel Spray Characteristics
Authors: Kegl Breda
Published: August 2004

This paper considers optimal design of an electronic control diesel fuel injection system by considering fuel spray characteristics. The proposed design procedure relies on the assumption that the atomization of fuel spray influences the diesel engine performance, fuel consumption and harmful emission significantly. As a measure of spray atomization the Sauter mean diameter is employed. The design problem is formulated in a form of a multiobjective optimization problem taking into account the Japanese 13 Mode test for diesel engines of commercial vehicles. Two different transformations from the multiobjective to the standard form are proposed and the results are compared to each other. The design variables of the injection system are related to the shape of the cam profile, to the nozzle geometry and to the control parameters influencing the injection quantity and timing. The geometrical properties of the cam profile as well as some injection parameters are kept within acceptable limits by the imposed constraints.
Analysis of Fully Reversed Sequences of Rotations of a Free Rigid Body
Authors: Koh Sung K. , Ananthasuresh G. K. , Croke Christopher
Published: August 2004

A fully reversed (FR) sequence of rotations is defined as a series of rotations of a free rigid body about its body-fixed axes such that the rotation about each axis is fully reversed at the end of the sequence. Due to the non-commutative property of finite rigid body rotations, an FR sequence can effect non-zero changes in orientation of the rigid body even though the net rotation about each axis is zero. The FR sequences are useful for attitude maneuvers of miniature spacecraft that use elastic deformation-based microactuators and for other airborne or neutrally buoyant underwater vehicles where actuations effecting orientation change are restricted. This paper considers the kinematics of six-rotation FR sequences and discusses if each of them is capable of producing any desired change in orientation. It is concluded that out of a total of 24 six-rotation sequences, 12 are capable of this but not the remaining 12. The results are proved using mathematical formalism and are also interpreted using numerical computations and graphical visualization.
Geometric Tailoring: A Design for Manufacturing Method for Rapid Prototyping and Rapid Tooling
Authors: Sambu Shiva , Chen Yong , Rosen David W.
Published: August 2004

The goal of fabricating functional prototypes quickly is hindered by a mismatch of material properties between production materials and those used in rapid prototyping (RP) machines, such as stereolithography. Even when rapid tooling (RT) technologies are utilized for injection molded parts, differences in mold materials cause differences in molded part properties. To compensate for these material and process differences, a design for manufacturing (DFM) method is introduced, called geometric tailoring. The idea is to modify dimensions of prototype parts to match key characteristics of production parts, such as stress and deflection behaviors. For RP parts, the geometric tailoring DFM method integrates two sub-problems, one for achieving functional requirements by matching part behaviors, and one for RP process planning to incorporate manufacturing capabilities and limitations. For parts fabricated by RT, an additional sub-problem is integrated, namely injection molding process planning. Problem decomposition is critical due to the coupled nature of the sub-problems. A problem decomposition and solution procedure is presented. The geometric tailoring method is shown to enable the matching of prototype to production part behaviors, while improving manufacturability.
Forward Problem Singularities of Manipulators Which Become PS-2RS or 2PS-RS Structures When the Actuators are Locked
Authors: Di Gregorio Raffaele
Published: August 2004

The instantaneous forward problem (IFP) singularities of a parallel manipulator (PM) must be determined during the manipulator design and avoided during the manipulator operation, because they are configurations where the end-effector pose (position and orientation) cannot be controlled by acting on the actuators any longer, and the internal loads of some links become infinite. When the actuators are locked, PMs become structures consisting of one rigid body (platform) connected to another rigid body (base) by means of a number of kinematic chains (limbs). The geometries (singular geometries) of these structures where the platform can perform infinitesimal motion correspond to the IFP singularities of the PMs the structures derive from. This paper studies the singular geometries both of the PS-2RS structure and of the 2PS-RS structure. In particular, the singularity conditions of the two structures will be written in a new form. This new form will directly bring to a new geometric interpretation of their singularity conditions and to the exhaustive enumeration of the geometric conditions identifying their singular geometries. Such an enumeration will reveal that some geometric conditions were not identified in the literature. Finally, the use of the obtained results in the design of parallel manipulators which become either PS-2RS or 2PS-RS structures, when the actuators are locked, will be illustrated.
Contribution of Gear Body to Tooth Deflections—A New Bidimensional Analytical Formula
Authors: Sainsot and P. , Velex P. , Duverger O.
Published: August 2004

The magnitude and variation of tooth pair compliance affects tooth loading and gear dynamics significantly. This paper presents an improved fillet/foundation compliance analysis based on the theory of Muskhelishvili applied to circular elastic rings. Assuming linear and constant stress variations at root circle, the above theory makes it possible to derive an analytical formula for gear body-induced tooth deflections which can be directly integrated into gear computer codes. The corresponding results are in very good agreement with those from finite element models and the formula is proved to be superior to Weber’s widely used equation, especially for large gears.
Theory for Topology Synthesis of Parallel Manipulators and Its Application to Three-Dimension-Translation Parallel Manipulators
Authors: Jin Qiong , Yang Ting-Li
Published: August 2004

A systematic theory for topology synthesis of parallel manipulators considering basic requirements such as kinematics, dynamics, control, and actuation is built. The kernel part of the theory is its proper application of a new mobility formula, output character equation of parallel manipulators, and units for single-opened-chains that have topological features. A feasible methodology for synthesizing parallel manipulators is also given, by which a detailed application is focused on the synthesis of three-dimension-translation parallel manipulators. The result synthesized encompasses not only most known mechanisms, but also some novel mechanisms with fine performances, such as simple forward/inverse kinematics and decoupling of input-output parameters that especially benefit control of theses structures.
A New Cycloid Drive With High-Load Capacity and High Efficiency
Authors: Li Xin , He Weidong , Li Lixing , Schmidt Linda C.
Published: August 2004

A patented double crank ring-plate-type cycloid drive is introduced in this paper. The new drive requires no output unit and places no limit on the size of the tumbler bearing. The drive is able to transfer larger torque than a typical existing planetary cycloid drive. The newly designed double crank ring-plate cycloid drive preserves the standard advantages of planetary pin-cycloid drives. Its working principles, advantages and design issues are discussed. Promising results from prototype testing are presented.
Stiffness Modeling of the Soft-Finger Contact in Robotic Grasping
Authors: Ghafoor Abdul , Dai Jian S. , Duffy Joseph
Published: August 2004

This paper investigates the soft-finger contact by presenting the contact with a set of line springs based on screw theory, reveals the rotational effects, and identifies the stiffness properties of the contact. An elastic model of a soft-finger contact is proposed and a generalized contact stiffness matrix is developed by applying the congruence transformation and by introducing stiffness mapping of the line springs in translational directions and rotational axes. The effective stiffnesses along these directions and axes are hence obtained and the rotational stiffnesses are revealed. This helps create a screw representation of a six-dimensional soft-finger contact and produce an approach of analyzing and synthesizing a robotic grasp without resorting to the point contact representation. The correlation between the rotational stiffness, the number of equivalent point contacts and the number of equivalent contours is given and the stiffness synthesis is presented with both modular and direct approaches. The grasp thus achieved from the stiffness analysis contributes to both translational and rotational restraint and the stiffness matrix so developed is proven to be symmetric and positive definite. Case studies are presented with a two-soft-finger grasp and a three-soft-finger grasp. The grasps are analyzed with a general stiffness matrix which is used to control the fine displacements of a grasped object by changing the preload on the contact.
Transformation of an EGT Grammar: New Grammar, New Designs
Authors: Li and Xin , Schmidt Linda C. , He, Weidong , Li, and Lixing , Qian Yuanmei
Published: August 2004

True design with grammars lies in the creation of the grammar rules, not in the application of the rules to generate design alternatives. Existing grammars can be modified to describe new languages of designs [1–4]. Studying an epicyclic gear train graph grammar leads to purposeful relaxation of grammar rules and subsequent discovery of new designs. A revised new EGT grammar is presented, which is designed to generate a wider selection of valid EGTs.
A Combined Penalty and Recursive Real-Time Formulation for Multibody Dynamics
Authors: Cuadrado J. , Dopico D. , Gonzalez M. , Naya M. A.
Published: August 2004

The continuously improved performance of personal computers enables the real-time motion simulation of complex multibody systems, such as the whole model of an automobile, on a conventional PC, provided the adequate formulation is applied. There exist two big families of dynamic formulations, depending on the type of coordinates they use to model the system: global and topological. The former leads to a simple and systematic programming while the latter is very efficient. In this work, a hybrid formulation is presented, obtained by combination of one of the most efficient global formulations and one of the most systematic topological formulations. It shows, at the same time, easiness of implementation and a high level of efficiency. In order to verify the advantages that the new formulation has over its predecessors, the following four examples are solved using the three formulations and the corresponding results are compared: a planar mechanism which goes through a singular position, a car suspension with stiff behavior, a 6-dof robot with changing configurations, and the full model of a car vehicle. Furthermore, the last example is also analyzed using a commercial tool, so as to provide the readers with a well-known reference for comparison.
Infinitely Variable Transmission of Racheting Drive Type Based on One-Way Clutches
Authors: Benitez F. G. , Madrigal J. M. , del Castillo J. M.
Published: August 2004

An infinitely variable transmission (IVT), based on the use of one-way action clutches, belonging to the family of ratcheting drives is described. The mechanical foundations and numerical simulations carried out along this research envisage a plausible approach to its use as gear-box in general mechanical industry and its prospective use in automobiles and self-propelled vehicles. The system includes one-way clutches—free wheels or overrunning clutches—and two epicyclic gear systems. The output velocity, with oscillatory character, common to the ratcheting drives systems, presents a period similar to that produced by alternative combustion motors, making this transmission compatible with automobile applications. The variation of the transmission is linear in all the working range. The kinematics operating principles behind this IVT is described followed by a numerical simulation of the dynamic analysis. A prototype has been constructed and tested to assess its mechanical efficiency for different reduction ratios. The efficiency values predicted by theory agree with those experimentally obtained on a bench-rig testing equipment.
An Integrated Framework for Optimization Under Uncertainty Using Inverse Reliability Strategy
Authors: Du Xiaoping , Sudjianto Agus , Chen Wei
Published: August 2004

In this work, we propose an integrated framework for optimization under uncertainty that can bring both the design objective robustness and the probabilistic design constraints into account. The fundamental development of this work is the employment of an inverse reliability strategy that uses percentile performance for assessing both the objective robustness and probabilistic constraints. The percentile formulation for objective robustness provides us an accurate evaluation of the variation of an objective performance and a probabilistic measurement of the robustness. We can obtain more reasonable compound noise combinations for a robust design objective compared to using the traditional approach proposed by Taguchi. The proposed formulation is very efficient to solve since it only needs to evaluate the constraint functions at the required reliability levels. The other major development of this work is a new search algorithm for the Most Probable Point of Inverse Reliability (MPPIR) that can be used to efficiently evaluate percentile performances for both robustness and reliability assessments. Multiple strategies are employed in the MPPIR search, including using the steepest ascent direction and an arc search. The algorithm is applicable to general non-concave and non-convex performance functions of random variables following any continuous distributions. The effectiveness of the MPPIR search algorithm is verified using example problems. Overall, an engineering example on integrated robust and reliability design of a vehicle combustion engine piston is used to illustrate the benefits of our proposed method.
Multi-Objective Optimization of the Handling Performances of a Road Vehicle: A Fundamental Study on Tire Selection
Authors: Miano Carlo , Gobbi Massimiliano , Mastinu Giampiero
Published: August 2004

The optimization of the handling behavior of road vehicles is dealt with in this paper. Both a linear and a nonlinear model have been considered. A number of analytical solutions to the equations of motion have been derived for the linear model. The objective functions (i.e. performance indices) to be optimized for a steering step input maneuver were the sideslip angle gain, the yaw velocity peak response time, the yaw velocity overshoot and the initial yaw acceleration. The front and rear tire cornering stiffness have been considered as the design variables to be optimized. The derived optimal solutions can be used during preliminary design for the definition of the best vehicle handling performance. The tire cornering stiffness of a number of actual road vehicles comply with the corresponding values coming from the optimization process proposed in the paper.
A Novel Compliant Mechanism for Converting Reciprocating Translation Into Enclosing Curved Paths
Authors: Mankame Nilesh D. , Ananthasuresh G. K.
Published: August 2004

This paper introduces a novel contact-aided compliant mechanism that uses intermittent contacts to convert a single translatory reciprocating input into two output curves, which intersect to enclose a two dimensional region. Contact interactions endow contact-aided compliant mechanisms with enhanced kinematic and kinetostatic capabilities. The mechanism described in this paper is designed to undergo large deformations repeatedly, without yielding by avoiding flexural joints and by using contacts to obtain the desired deformation. A single-material, joint-free and planar design makes the mechanism easy and economical to fabricate at the macro or micro scales. The design is validated experimentally by manufacturing and testing macro scale prototypes. Two potential applications that motivated this mechanism are also noted.
Rigid Body Motion Characteristics and Unified Instantaneous Motion Representation of Points, Lines, and Planes
Authors: Ting Kwun-Lon , Zhang Yi
Published: August 2004

The article presents a unified algebraic approach for the modeling of the instantaneous motions of all linear elements, such as points, lines, and planes, embedded in a rigid body. The paper first addresses the Clifford algebra based displacement operator and its higher derivatives from which the coordinate-independent characteristic numbers with simple geometric meaning are defined. With Clifford algebra, the paper also presents the computation method and examples to demonstrate the process of obtaining the displacement operator and the characteristic numbers. Because of the coordinate independent feature, no tedious coordinate transformation typically found in the conventional instantaneous invariants method is needed.
A Study of Displacement Distribution in a Piezoelectric Heterogeneous Bimorph
Authors: Li, Qiang , Lovell, Michael , Mei, and Junfeng , Clark William
Published: August 2004

Piezoelectric heterogeneous bimorphs have extensive applications in the MEMS area. In order to formulate their displacement distribution more conveniently, a concise analytical solution is described herein. This solution integrates all of the important influence factors, such as geometry and material properties, into a single expression. Secondary effects such as shear, residual stress induced curvature, and electrostiction, are not considered, but they are found to be minimally important based on the accuracy of the predicted results. The expression is verified using the finite element method, and shown to be straightforward compared to the more complicated couple-field FEM analysis for a specific range of materials and thicknesses. The method is subsequently shown to be capable of quickly estimating the displacement in a bimorph beam, making it a useful tool for designing piezoelectric structures.
Large Eddy Simulation of the Anti-Erosion Characteristics of the Ribbed-Bend in Gas-Solid Flows
Authors: Fan J. R. , Luo K. , Zhang X. Y. , Cen K. C.
Published: August 2004

In order to find out the ribs with the best anti-erosion efficiency, the erosion effects in three 90° duct bend gas-solid flows with different ribs are investigated and compared with that in the bare bend. Three different kinds of ribs are studied, which have square cross section, isosceles right-angled triangle shape cross section and isosceles triangle shape cross section, respectively. The arrangement and the geometry dimensions of the ribs are the same. The gas phase flow field is solved by the large eddy simulation technique considering the interaction between the gas and the particles, whereas the particles are tracked by Lagrangian method. The results exhibit that the erosion rates of all the ribbed bends are greatly reduced due to the adding of the ribs compared with that of the bare bend. Among the three different kinds of ribs, the isosceles right-angled triangle ribs have the highest anti-erosion ability. The reason is that the particle impact velocity on the walls in the isosceles right-angled triangle ribbed bends is decreased to the utmost and the corresponding particle impact angle is altered adequately due to the special shape of the ribs. In addition, the rib erosion rate, the sidewall erosion rate and the bend wall erosion rate are calculated separately. It is found that the rib erosion rate is half of the wall erosion rate, and the sidewall erosion rate is so low that it can be omitted compared with the bend wall erosion rate.
Computations of Air/Fuel Preparation Process in a Port-Injected Spark-Ignition Engine During Cold-Starting Phase
Authors: Zeng Yangbing , Lee C. F.
Published: August 2004

A numerical study has been performed of the air/fuel preparation process in a cold-starting port-injected spark-ignition engine. The latest models were implemented for spray impingement and multicomponent vaporization of the droplet and wall film accounting for finite diffusion in the liquid. The infinite diffusion model was found insufficient for predicting vaporization in this engine, and the single-component fuel representation yields results significantly different from those from the multicomponent one. The operating parameters studied included injection timing, swirl, speed, target path, enrichment, and fuel accumulation. In-cylinder measurements were compared and good agreement was achieved. Detailed quantitative analysis of the air/fuel preparation of the engine was reported.
A Simulation Model for Hot Spring Thermal Energy Conversion Plant With Working Fluid of Binary Mixtures
Authors: Bai Ou , Nakamura Masatoshi , Ikegami Yasuyuki , Uehara Haruo
Published: August 2004

Hot spring thermal energy conversion (STEC) is a system that converts heat energy into electricity using the temperature difference between hot spring water and sea/river water. This paper describes dynamic model construction for the transient performance of STEC plant, which uses a recently developed power cycle with binary mixtures as working fluid. The mathematical models were constructed based on thermodynamics and structural features of the power cycle for representing the timely dependent state variables of the working fluid. Confidence in the accuracy of the developed models has been established by comparison of the simulation results with those obtained experimentally in a pilot STEC plant.
Nonparametric Modeling of Random Uncertainties for Dynamic Response of Mistuned Bladed Disks
Authors: Capiez-Lernout E. , Soize C.
Published: August 2004

The random character of blade mistuning is a motivation to construct probability models of random uncertainties. Recently, a new approach known as a nonparametric model of random uncertainties, based on the entropy optimization principle, was introduced for modeling random uncertainties in linear and nonlinear elastodynamics. This paper presents an extension of this nonparametric model for vibration analysis of structures with cyclic geometry. In particular this probability model allows the blade eigenfrequencies uncertainties and the blade-modal-shape uncertainties to be modeled.
A Pareto-Based Genetic Algorithm Search Approach to Handle Damped Natural Frequency Constraints in Turbo Generator Rotor System Design
Authors: Angantyr Anders , Aidanpa¨a¨ Jan Olov
Published: August 2004

The detailed design of a turbo generator rotor system is highly constrained by feasible regions for the damped natural frequencies of the system. A major problem for the designer is to find a solution that fulfills the design criterion for the damped natural frequencies. The bearings and some geometrical variables of the rotor are used as the primary design variables in order to achieve a feasible design. This paper presents an alternative approach to search for feasible designs. The design problem is formulated as an optimization problem and a genetic algorithm (GA) is used to search for feasible designs. Then, the problem is extended to include another objective (i.e., multiobjective optimization) to show the potential of using the optimization formulation and a Pareto-based GA in this rotordynamic application. The results show that the presented approach is promising as an engineering design tool.
Strategies for Reduced NOx Emissions in Pilot-Ignited Natural Gas Engines
Authors: Krishnan S. R. , Srinivasan K. K. , Singh S. , Bell S. R. , Midkiff K. C. , Gong W. , Fiveland S. B. , Willi M.
Published: August 2004

The performance and emissions of a single-cylinder natural gas fueled engine using a pilot ignition strategy have been investigated. Small diesel pilots (2–3% on an energy basis), when used to ignite homogeneous natural gas-air mixtures, are shown to possess the potential for reduced NOx emissions while maintaining good engine performance. The effects of pilot injection timing, intake charge pressure, and charge temperature on engine performance and emissions with natural gas fueling were studied. With appropriate control of the above variables, it was shown that full-load engine-out brake specific NOx emissions could be reduced to the range of 0.07–0.10 g/kWh from the baseline diesel (with mechanical fuel injection) value of 10.5 g/kWh. For this NOx reduction, the decrease in fuel conversion efficiency from the baseline diesel value was approximately one to two percentage points. Total unburned hydrocarbon (HC) emissions and carbon monoxide (CO) emissions were higher with natural gas operation. The nature of combustion under these conditions was analyzed using heat release schedules predicted from measured cylinder pressure data. The importance of pilot injection timing and inlet conditions on the stability of engine operation and knock are also discussed.