bluuebunny/crossref_metadata_2025 huggingface dataset:
Greedy Tool Heuristic for Rough Milling of Complex Pockets
Authors: Joneja Ajay , Shaoming Zhu , Lee Yuan-Shin
Published: November 2020

The milling of complex pockets bounded by NURBS surfaces is usually broken into rough and finish milling, with the former taking up the bulk of the machining time. This time can be reduced if the proper combination of end-mills of different sizes are used to machine in different regions. The greedy tool heuristic presented in this paper is a new approach for determination of the machining volume that should be allocated to different tools selected from among a large set of available tools. Subsequent machining planning can then be performed by repeated application of standard 2D milling algorithms. This new approach in multiple-tool rough milling of complex shapes promises to reduce machining time of parts with complex shapes, such as modern moulds and casting patterns.
Some Geometric Techniques to Reduce Build Time in LOM
Authors: Wah Pang King , Joneja Ajay
Published: November 2020

We propose a new CAPP system for the layered manufacturing technology of LOM (laminated object manufacturing). The traditional technique of building wastes much effort and time in generation of rectangular grid patterns to the exterior of the model to facilitate waste removal. In the proposed approach, several geometric properties of the model are exploited to dramatically reduce the waste removal grids. This in turn leads to reduced build-time, with no effect on the build quality. An integrated CAPP system incorporating these ideas has been developed, and an example part is presented to show how the system performs.
Operation Ordering Principles and Intra-Setup Planner: Combining Human Control With Automation in Process Planning
Authors: Sharma Vipin , Hayes Caroline C.
Published: November 2020

We present in this paper 1) operation ordering principles and 2) a customizable process planner, Intra-Setup Planner that implements those principles. The principles and the planner focus on sequencing cutting operations within individual setups for three and five axis prismatic milling applications. There is no general agreement on ordering principles largely because different shops have very different needs. To address a wide range of users’ needs, we have designed both the ordering principles and the Intra-Setup Planner to support flexibility rather than providing a single one-size-fits-all prescription for operation ordering. The Intra-Setup Planner provides a convenient user interface, Rule Editor through which users can select the ordering principles that suit their own situation, an automated planner that will follow the user selected principles, and a Plan Editor to allow final adjustments. The combination of flexible principles and user control maximize the strengths of human and machine intelligence.
Influence of Design Representation on Effectiveness of Idea Generation
Authors: McKoy Felicia L. , Vargas-Hernández Noé , Summers Joshua D. , Shah Jami J.
Published: November 2020

The issue being investigated is the role of the type of representation used for recording design ideas in idea generation techniques for conceptual design. An empirical study was conducted to test the hypothesis that graphical (pictorial) representation is better than textual (sentential) for recording of design ideas. This study used a standard set of outcome measures: fluency, quality, novelty, and variety of ideas generated by use of different representations. The expressiveness of each representation was also studied by examining the ability to convey key design information of an idea. The experiment was designed and data analyzed based on the principles of statistical DOE. The study confirms the hypothesis that graphical representation provide greater benefits for engineering design idea generation than textual representation.
Assessment of Rework Probabilities for Simulatng Product Development Processes Using the Design Structure Matrix (DSM)
Authors: Yassine Ali A. , Whitney Daniel E. , Zambito Tony
Published: November 2020

This paper uses the Design Structure Matrix (DSM) to model and simulate the performance of development processes. Though the simulation is a powerful tool for analyzing process performance, its ability is limited by the quality of input information used in the analysis. DSM simulation requires process data that is hard to assess or estimate directly from development participants. In this paper, we propose a methodology that allows a more practical estimation of an important simulation parameter: rework probabilities. Furthermore, we show how does this assessment method (combined with simulation) allow managers to evaluate process improvement plans based on two resulting process measures: reliability and robustness. The method is illustrated with a real application from the automotive industry.
Research Methods for Design Theory
Authors: Tate Derrick , Nordlund Mats
Published: November 2020

This paper is about the development of design theory, about how research in design theory is — and should be — done. Important works in design theory since 1850 are identified. The current state of design as a pre-paradigm science is explained, motivating the need for a unifying view of design. Given the state of the field, a framework for design theory is presented, and a research process model is proposed as a scientific way of doing research in design theory. These are discussed in light of modern views in the philosophy of science and their criteria for theory evaluation and scientific progress. Research in design can be treated in a scientific manner, but this must be done from a sophisticated view of scientific practice, one with the proper criteria for evaluating progress: at the level of the research program.
Complexity of Planning in Design
Authors: Earl Christopher F. , Eckert Claudia M. , Johnson Jeffrey H.
Published: November 2020

Connectivities between processes in product developments indicate both conflicts of resources and potential synergies. These represent constraints and potential opportunities in planning design Each product development comprises a network of processes. Similarity between processes is analysed by a layered classification ranging from common components to shared design knowledge. The connectivities between products arising from similarities among products are represented by a multidimensional network. Design planning is described by flows or ‘traffic’ on this network which represents a structural model of complexity. Comparison is made with information based measures of the complexity of designs and processes.
Developing Bayesian Surrogates for Use in Preliminary Design
Authors: Pacheco Jorge E. , Amon Cristina H. , Finger Susan
Published: November 2020

During the preliminary design stages, designers often have incomplete knowledge about the interactions among design parameters. We are developing a methodology that will enable designers to create models with levels of detail and accuracy that correspond to the current state of the design knowledge. The methodology uses Bayesian surrogate models that are updated sequentially in stages. Thus, designers can create a rough surrogate model when only a few data points are available and then refine the model as the design progresses and more information becomes available. These surrogates represent the system response when limited information is available and when few realizations of experiments or numerical simulations are possible. This paper presents a covariance-based approach for building surrogates in the preliminary design stages when bounds are not available a priori. We test the methodology using an analytical one-dimensional function and a heat transfer problem with an analytical solution, in order to obtain error measurements. We then illustrate the use of the methodology in a thermal design problem for wearable computers. In this problem, the underlying heat transfer phenomena make the system response non-intuitive. The surrogate model enables the designer to understand the relationships among the design parameters in order to specify a system with the desired behavior.
A Framework for Flexible Systems and its Implementation in Multiattribute Decision Making
Authors: Olewnik Andrew , Brauen Trevor , Ferguson Scott , Lewis Kemper
Published: November 2020

In this paper, we present a framework for the concept of flexibility in complex system design. This is one of the first of many steps toward developing new design methods for designers that will aid them in development of customizable systems that meet the requirements of multiple customers and multiple tasks. The hope is that this paper will provide both a starting point from which academia and industry can move forward in developing new design methods for flexible systems and a basis for establishing a standard lexicon for use when referring to flexible system design.
Re-Interpretation of Conceptual Design Sketches in Mechanical Engineering
Authors: Pache Martin , Roemer Anne , Lindemann Udo , Hacker Winfried
Published: November 2020

In this paper a case study on conceptual design in mechanical engineering design is presented. At first, an exemplary sketch from the design process is discussed with regard to the modality and level of abstraction of the elements used in this sketch. The possibility to predefine geometry of components, as well as functional features on different levels of abstraction provides clues for reinterpretation of the sketch. Furthermore a remarkable sequence of sketching is presented, that shows how reinterpretation of a sketch can result in significant changes of the conceptual solution. This may be due to the combination of geometrical and functional elements, that gain meaning within the overall context of the sketch only in combination with the other elements. Therefore recombination by reinterpretation may change this context entirely. The proposed mechanisms could not be verified due to the rareness of their occurrence, still these mechanisms may have a significant impact on a design process. Therefore this paper is supposed to provide hypotheses for further research on this subject.
The Role of Intranets to Facilitate Designer/Client Communication
Authors: Challice David , Hogarth Peter
Published: November 2020

Speed of product to the market place was always important. This has become increasingly so with the onslaught of globalisation. What is released on the High Street in the USA today will be sold on the shelves and counters of shops in other continents within days. This has placed pressure on the designer to complete his task or contract with even more alacrity than was the case, even as recently as ten years ago. The cliché “we have the Technology”, is a truism in the world of manufacturing and design, but use of the available technology is, perhaps, not as apparent as it is generally accepted to be.

In order to get the product to the market at the right price demands an ever closer liaison between the product designer and the client. More often than not, the “product” is an enhancement or improvement of one which already exists. In addition, it is not unusual for the designer to be a contractor or 3rd party not physically resident in the premises of the client. As a consequence, communication is rarely conducted face to face but via other means, ie e-mail, telephone etc. Yet, in order to prevent misunderstanding, it is essential that correct information is relayed between the relevant parties. It is also necessary for the information about changes in the product to be available to other members of the client’s company so that the necessary decisions regarding price, sales schedules, re-tooling etc. can be made. Ultimately, these changes will have to be incorporated in the company’s Business Plan.

Research at Bournemouth University suggests that use of the technology available to relay information is not as widespread as it could be. The three major areas of finance, product and design have been approached and the results of the research appear below.
Capstone Design and Manufacture of Hand–Made Small-Sized Electric Vehicle
Authors: Sakamoto Haruo , Uchino Takashi , Kaino Toru , Sawada Tatsuro , Yokoyama Masaaki
Published: November 2020

This paper describes an engineering education attempt in a synthesis class during the 4th year. Since the Kochi University of Technology was inaugurated in April, 1997, engineering education trials had been conducted in the past 4 years. In 1997, 3 student teams participated in an eco-power race held in Kochi, Japan, with hand-made ecological vehicles. In the summer, 1998, three teams participated in the Shikoku Electric Vehicle Rally using light weight vehicles converted into electric cars. The synthesis class was performed based on such past engineering activities out of class. In order to provide an active learning opportunity, a synthetic learning environment is needed rather than just teaching in classes. Manufacturing is also considered to be of great importance for mechanical engineering as well as the basic sciences such as mathematics and physics. As a capstone learning course, a team of four students in the laboratory tried to design and manufacture a hand-made small-sized electric vehicle.
Thermal Behavior of Aluminum Metal-Matrix Composite During Cooling Process
Authors: Okumuş F. , Turgut A.
Published: November 2020

The paper presents a thermal behavior analysis of metal matrix composite lamina and laminates during a cooling process. A long stainless steel fiber reinforced aluminum metal matrix composite lamina and laminate are used for this purpose. Metal matrix composites were manufactured by using modulus under the action of 30 MPa pressure and heating up to 600 °C. The thermal stresses generated during cooling have a profound effect on the distortion and strength of the composite materials. In this study, thermal stresses, residual stresses and effective thermal expansion coefficients as a function of orientation angle of the aluminum metal matrix composite during a cooling process are investigated. The finite element method was used for thermal stress analysis. For this purpose, four noded rectangular elements were used in the ANSYS finite element code.
A Novel Strategy for Probability-Based Failure Avoidance of Operating Technical Systems
Authors: Söffker Dirk
Published: November 2020

Failure and fault avoidance techniques are becoming important methodologies due to economical and ecological risks of modern technologies. The basic methodologies and techniques developing safe systems are connected with reliability engineering technologies or fault detection and isolation (FDI) approaches. The contribution introduces into the ideas of the 1997 firstly published SRCE (Safety and Reliability Control Engineering)-concept. Core of the approach is the development of a history- and load-dependent failure rate, which allows the online-calculation of reliability characteristics, which can be monitored or controlled. The classical definitions of reliability engineering characteristics are unfit due to the fact that they are only ‘driven’ by the time, so effects of changing operating conditions etc. can not be considered directly. The proposed approach solves this problem by introducing a new definition of a failure rate by introducing load- and lifetime-dependent failure rate. This also includes the possibility to consider regenerating/recovering effects of technical systems or components. As an example the determination is illustrated and applied to the monitoring of an automotive tire.
Evaluation of Combustion Chamber Leakage for the Maintenance of Four Stroke Marine Diesel Engines
Authors: Mollah M. A. Hossain
Published: November 2020

Maintenance is becoming increasingly an important element in the upkeep of the modern complex equipment. There are a number of approaches to the maintenance of the equipment such as the break down maintenance and preventive maintenance. Marine diesel engines require proper maintenance to ensure their efficient, safe and trouble-free operation. The preventive maintenance task that is most useful for reducing the overall maintenance, is also known as on-condition maintenance, condition-directed maintenance, or predictive maintenance. This is done by measuring some parameter over time where it has been established that parameter correlates well with the incipient failure conditions. This paper contains the studies of the evaluation of combustion chamber leakage of four stroke marine diesel engines by using a diagnostic device. It describes the methodology to develop the performance limits of the combustion chamber leakage of marine diesel engine and the method of evaluating the condition of diesel engines. The results of model tests of the diagnostic device, Pneumatic Indicator, are also reported. The proposed methodology allows performing the evaluation of the technical condition of a cylinder piston group of marine engines both qualitative and quantitative. Thus the maintenance and repairing works may be performed according to the real condition of the engine, which is extremely useful in decreasing the overall maintenance cost.
Mechanical Noise Identification Using Time-Frequency Representations
Authors: Pan Min-chun
Published: November 2020

Three computation schemes of time-frequency representations (TFRs) have been developed and implemented to identify different components of mechanical noise originated from the transmission system of electrical vehicles.

This study explores the close relationships between three TFRs, i.e. the spectrogram based on windowed Fourier transform (WFT), the Wigner-Ville distribution (WVD), and the smoothed WVD (SWVD). One main purpose is to pursue the efficiency of computing the SWVD of a dynamic signature. The revised scheme can tremendously reduce the computation time to a scale of around 1/90, compared with the original scheme.

To assess the validation of these TFR schemes, firstly, four synthetic signals are designed and processed. Secondly, the developed TFRs are applied to distinguish different spectral components of transmission noise, and identify their sources. This study takes an electrical scooter with a continuous velocity transmission (CVT) system as a test bench. The CVT-belt noise, helical-gear whine noise, and fan noise can be clearly identified via the processing of the TFRs. These obtained conclusions can be used as references for machine element modification to improve annoying noise.
A Time-Frequency Envelope Estimation Method for Detection of Bearing-Localized Defects
Authors: Nikolaou Nikolaos G. , Antoniadis Ioannis A.
Published: November 2020

This paper proposes a new method for the estimation of the envelope of signals resulting from rolling element bearing-localized defects, based on the use of a shifted Morlet wavelet family. Using a time-frequency representation of the signal, the method is designed in a way that can exploit the underlying physical concepts of the modulation mechanism, present in the vibration response of bearings with localized defects. Systematic selection criteria for the automated choice of the critical parameters that characterize the Morlet wavelet family are used. The method is evaluated by using actual vibration signals measured from bearings with defects at different locations.
A New Sparse Solver for Kinematics Simulation of Multibody Systems in Natural Coordinates Based on Tearing Methods
Authors: Funes Francisco Javier , Jiménez José Manuel , Rodríguez José Ignacio , de Jalón Javier García
Published: November 2020

This paper presents a new method for the factorization of the sparse system of linear equations arising from the kinematic simulation of multibody systems using natural coordinates. A special reordering of the jacobian matrix of the mechanism constraint equations will be described. This reordering depends only on the topology of the mechanism. In open-chain systems the matrix can be reordered to a block triangular form. For closed-loop systems this matrix can take a bordered block triangular form, with very few columns in the border. A modification of the Harwell’s implementation of the P5 algorithm from Erisman et al. [1] is used for reordering the rows and columns of the matrix. A new method of factorization is described. This method reduces the number of floating-point operations and the fill-ins. An efficient way for solving the least-squares problem arising from over-determined systems is explained.
Contact Dynamics of Reconfigurable Space Systems With Numerical Verification Method
Authors: Takahashi Takashi , Matunaga Saburo
Published: November 2020

In order to analyze dynamics of space systems, such as cluster satellite systems and the capturing process of damaged satellites, it is necessary to consider such space systems as reconfigurable multibody systems. In this paper, we discuss the numerical computation of the dynamics of the ground experiment system to simulate the capturing and berthing process of a satellite by a dual-manipulator on the flat floor as an example. We have previously discussed the efficient dynamics algorithm for reconfigurable multibody system with topological changes. However, the contact dynamics, which is one of the most difficult issues in our study, remains to be discussed. We introduce two types of the linear complementarity problem (LCP) concerned with contact dynamics. The difference between the two types of LCP is whether impacts can be considered. Dynamic systems with impacts and friction are non-conservation systems; moreover the LCP is not always solvable. Therefore we must check if the solutions of the numerical computation are correct, or how accurate they are. In this paper, we derive the method of numerical computation with guaranteed accuracy of the LCP for contact dynamics.
Improved “Order-N” Performance Algorithm for the Simulation of Constrained Multi-Rigid-Body Dynamic Systems
Authors: Anderson Kurt S.
Published: November 2020

This paper presents an algorithm for the efficient numerical analysis and simulation of modest to heavily constrained multi-rigid-body dynamic systems. The algorithm can accommodate the spatial motion of general multi-rigid-body systems containing arbitrarily many closed loops in O(n + m) operations overall for systems containing n generalized coordinates, and m independent algebraic constraints. The presented approach does not suffer from the performance (speed) penalty encountered by most other of the so-called “O(n)” state-space formulations, when dealing with constraints which tend to actually show O(n + m + nm + nm2 + m3) performance. Additionally, these latter formulations may require additional constraint violation stablization procedures (e.g. Baumgarte’s method, coordinate partitioning, etc.) which can contribute significant additional computation. The presented method suffers less from this difficulty because the loop closure constraints at both the velocity and acceleration level are directly embedded within the formulation. Due to these characteristics, the presented algorithm should offer superior computing performance relative to other methods in situations involving both large n and m.
Velocity Transformation Matrix of a Revolute-Spherical Massless Link
Authors: Yoo Wan-Suk , Sohn Jeong-Hyun , Lim O-kaung , Hong Keum-Shik
Published: November 2020

Since the contribution of lightweight components in the total energy of a system is small, the inertia effects are sometimes ignored via replacing them to massless links. A massless link, which is sometimes called as a composite joint, connects two adjacent bodies keeping the relative degrees of freedoms. For a revolute-spherical massless link, one edge is connected to an adjacent body with a revolute joint and the other edge is linked to another body with a spherical joint. Using velocity transformation technique, it is possible to combine the generality of Cartesian coordinates in modeling and the efficiency of relative coordinates in simulation. In this paper, velocity transformation matrix of a revolute-spherical massless link is formulated and implemented as a joint module in a vehicle dynamic analysis program. Numerical examples are presented to verify the formulation.
On the Modeling of Shells in Multibody Dynamics
Authors: Bauchau Olivier A. , Choi Jou-Young , Bottasso Carlo L.
Published: November 2020

Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material non-linearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of shells are treated in a rigorous manner, and the material nonlinearities can be handled when the constitutive laws stem from the existence of a strain energy density function. The efficiency and robustness of the proposed approach is illustrated with specific numerical examples that also demonstrate the need for integration schemes possessing high frequency numerical dissipation.
Study on Derivation and Application of Mean Axis for Deformable Beam by Means of the Absolute Nodal Coordinate Multibody Dynamics Formulation
Authors: Takahashi Yoshitaka , Shimizu Nobuyuki
Published: November 2020

There are three basic finite element formulations which are used in the dynamics analysis of flexible beams undergoing large rotation and deformation. These are the floating frame of reference approach, the finite segment method and the large rotation vector approach. Recently, the absolute nodal coordinate formulation was proposed by A.A.Shabana et al. In this formulation, elastic forces are lead by approximating the slope of the beam at an arbitrary point on the neutral axis of the beam in terms of the slope of the simple support axis of the beam.

In this paper, we propose the mean axis of the planar Bernoulli-Euler beam for the absolute nodal coordinate approach. The origin and the orientation of this axis are selected so as to minimize the total deformation of the concerned beam. And the selected axis can be simply described by the nodal coordinates of the beam element. Using the mean axis instead of the simple support axis, the elastic forces of the beam element may be more precisely calculated. Finally, we show numerical examples to demonstrate effectiveness of this approach.
Absorbed Power As an Indicator of Health Risk Associated With Whole-Body Vibration Exposure
Authors: Xie X. Y. , Bhat R. B. , Boileau P.-E.
Published: November 2020

The human body behaves like a vibrating physical system having mass, elastic and damping properties. In order to study the biodynamic behavior of the body, it is common practice to model the body as a lumped single or a multiple-degree-of-freedom (MDOF) system. Standards have been developed using the frequency-weighted root-mean-square (rms) acceleration input to the body as the primary measure of whole-body vibration exposure. In this paper, absorbed power during exposure to vertical whole-body vibration is considered as a potential indicator of the physical stress affecting comfort and health. A four-degree-of-freedom biodynamic model is chosen to represent the body and the absorbed power for the different body segments and the total body is computed. On the basis of the model and of the guidance provided in ISO 2631-1:1997 relating vibration exposure with health risk, computations are carried out to define a health guidance caution zone based on absorbed power.
Experimental Validation of a Dynamic Model for Flexible Link Mechanisms
Authors: Caracciolo R. , Gasparetto A. , Trevisani A.
Published: November 2020

This paper presents an experimental validation of a finite element approach for the dynamic analysis of flexible multi-body planar mechanisms. The mathematical model employed accounts for mechanism geometric and inertial non-linearities and considers coupling effects among rigid-body and elastic motion. A flexible five-bar linkage actuated by two electric motors is employed as a test case. Experimentally determined link absolute deformations are compared with the numerical results obtained simulating the system dynamic behavior through the mathematical model. The experimental and numerical results are in good agreement especially after the very first transient period.
Comparison Between Flexible Multibody Tracked Vehicle Simulation and Experimental Data
Authors: Nakanishi Toshikazu , Isogai Koji
Published: November 2020

In this investigation, a comparison between planar multibody tracked vehicle simulation and experimentally obtained acceleration data is presented. On the simulation, rigid and flexible bodies are used and its results are compared. The data of flexible body are obtained by experimental modal test. From the modal test five modes are selected and used for the simulation. A method to determine the contact stiffness is presented. The calculation results show that using flexible body simulation, it is possible to get relatively good agreement with experimental acceleration data. Even using flexible body, to improve the closeness of the calculated and experimental results, one has to carefully select the contact parameters.
Closed Form Solutions to the Equation of Motion Avoiding Mass Matrix Inversion and Eigenvectors Decomposition
Authors: Reaud Karine , Vallee Claude , Fortune Danielle
Published: November 2020

Solutions of the vibrations equations are generally obtained, in the linear case, by methods involving either matrix exponential computation or matrix eigendecomposition. However, these methods lead to a loss of symmetry because of the necessary inversion of the mass matrix. In doing so, one can introduce ill-conditioned matrices and, thus, compute eigenvectors with poor accuracy. In order to avoid these inconveniences, our method, which is an extension of Le Verrier-Souriau algorithm, provides solutions to the vibrations equations without inverting the mass matrix or computing eigenvectors. Moreover, we can solve damping systems even when the damping matrix has no specific properties such as the Basile property.
Identification of Multi-Body Dynamics by External Force/Torque Measurements
Authors: Grotjahn Martin , Heimann Bodo
Published: November 2020

Analytical simplification and regrouping rules are presented which lead to a formulation of the base force/torque equations of tree-structured multi-body system which is linear with respect to a dynamic parameter vector of minimal dimension. The rules depend only on the kinematic parameters. They can be easily implemented in standard computer algebra programs. Furthermore, a new approach is presented for identification of the system’s dynamics by external force/torque measurements. It does not require optimized trajectories for parameter excitation. The method is applied to the identification of a 6-d.o.f. standard industrial robot by base force/torque measurements. A comparison to results of a conventional identification approach shows the efficiency of the presented identification method.
Lund’s Contribution to Rotor Stability: The Indispensable and Fundamental Basis of Modern Compressor Design
Authors: Gunter Edgar J.
Published: November 2020

In the early design of compressors and turbines, it was of importance to locate the rotor critical speeds so as to insure that a turbo rotor would not be operating at a critical speed. As compressor and turbine design became more sophisticated, a more detailed analysis of the rotor damped critical speeds and rotor log decrements was necessary. With compressors and turbines operating at higher speeds, under high power levels, and at multiples of the first critical speed, the problem of stability or self-excited whirling is of paramount importance. The onset of self-excited motion may lead to large amplitudes of motion with possible destructions of the rotor or the inability of the compressor to operate at peak power levels. Encountering this phenomenon with a compressor on an off-shore oil platform can mean millions of dollars of lost production. Self-excited whirling can be caused by fluid-film bearings, seals, Alford-type cross-coupling forces, or internal shaft friction, to name a few of the excitation mechanisms.

The problem of computing the approximate values of the rotor log decrement under full speed and loading conditions requires the solution of a complex eigenvalue problem. The computation of the rotor complex roots is an order of magnitude more difficult than the problem of undamped critical speed calculations. J. W. Lund presented the first practical numerical procedure for computing turbo-rotor log decrements. The mathematical transfer matrix method pioneered by Lund has allowed industry to develop and stabilize a vast array of rotating machinery leading to the savings to industry of millions of dollars. Without the procedures of Lund, for example, it would not have been possible to resolve stability problems encountered with both the hydrogen and oxygen space shuttle pumps. This paper briefly presents some of the attributes of the Lund stability procedure and its unique characteristics.
Some Unusual Cases of Rotor Instability
Authors: Olsson Karl-Olof
Published: November 2020

In the paper presented here three peculiar cases of rotor instability are presented. The first is a tilting-pad bearing used as an intershaft bearing in a two-spool gas turbine. It was initially chosen for its good stability properties. However, in a deeper study it was found that those benefits are greatly reduced when both inner shaft and outer bearing are rotating. The second case comprises a turbine which showed a very strange performance with vibrations alternating between heavy and mild amplitudes. The periods were a couple of minutes long. After a more elaborate instrumentation was installed it was found that vibrations were synchronous and that the rotor experienced continuos changes of vibrations interrupted by sudden changes of amplitude. This revealed that non-linearity and thermal effects coupled to the rotor vibrations must be incorporated to understand the behavior. Many hypotheses were tested and the one coming closest to explaining the case was one incorporating thermal bending caused by heat conduction through an annulus partly filled with oil. The third case is a simple one of more pure curiosity, where a rotor was provided with a substantial amount of inner damping, and just according to the school book showed dynamic instability.
Jorgen W. Lund: Theories Versus Tests
Authors: Tonnesen Jorgen
Published: November 2020

The contribution of the late Professor Jorgen W. Lund in the field of rotor dynamics and fluid film bearings is presented in a condensed form with the emphasis on the experimental work and results that confirm and support many of Dr. Lund’s theories and analyses. Included are subjects of rotor balancing by the influence method, unbalance response of a flexible rotor, damped critical speeds of flexible rotors and fluid film bearing’s static, dynamic and thermal properties.
Rotordynamics Involving Axial Rubbing Against a Disk
Authors: Childs Dara W. , Siddiqui Nameer A.
Published: November 2020

Test results are presented involving axial rubbing of a test rotor with an overhung disk to investigate test results cited by Den Hartog [1]. Point rubbing was introduced via a rod on the inside (motor-drive side) and outside faces of the overhung disk for multiple operating conditions (running speeds below and above the critical speed) and multiple shaft configurations. For supercritical running speeds, no change in the response spectrum was observed. For subcritical running speeds, a slight increase of response at twice running speed was observed.

“Face” axial rubbing was introduced by forcing a contact between the outside face of the disk and a flat surface. Rubbing at running speeds below the critical speed produced: (i) a small backwards component at the running speed frequency, (ii) a large backward-whirl component at twice running speed, and (iii) a very large, twice-running-speed, forward-whirl component. Rubbing at running speeds well above the critical speed produced a subsynchronous forward component near the critical speed. The large twice-running-speed results due to rubbing at the outside face were comparable to Den Hartog’s. However, point rubbing on the inside face did not produce the subsynchronous backward-whirl response cited by Den Hartog.

Analysis of a nonslipping kinematic whirl condition (comparable to classical dry friction whipping) for the face of an overhung disk against a stationary surface predicts reverse asynchronous whirl; however, testing over a wide range of parameters failed to produce this response. None of the present test results produced the types of very high vibration levels and grave consequences that have been produced in test rigs for conventional, radial dry-friction whirl and whip.
Modal Estimation of Gyroscopic Effect in Rotordynamic Systems
Authors: Sawicki Jerzy T.
Published: November 2020

A new approach for uncoupling the equations of motion typical for rotordynamical systems is presented. The method does not neglect the speed dependent effects, like gyroscopic effects, and can be particularly valuable in the controller design of actively controlled rotors. In the presence of hysteretic type of damping, the resulting uncoupled gyroscopic systems come with an equivalent viscous damping, equivalent in a sense of the same natural frequency and decay rate. The approach is illustrated through the example of technical interest. The generated results demonstrate that the developed approach is correct and straightforward.
Modeling and Stability Analysis of Turboprop Engine Installations
Authors: Alkhatib Rabih , Golnaraghi Farid
Published: November 2020

In this paper a simple formulation of dynamic model of a turboprop installations has been presented incorporating aerodynamic forces. A four-bladed propeller-engine is simplified to have six rigid-body degrees of freedom. The engine is connected to the nacelle through resilient elements in order to reduce vibration transmission from the engine to the airplane structure. The aerodynamic forces acting on the propeller are modeled utilizing quasi-steady airfoil theory by considering their effect as reaction forces. Using the formulated dynamic model, an analysis of the stability of the engine-mount is conducted by deriving a second order eigenvalue problem. The system natural frequencies are found to be dependent on the rotational speed. At lower speeds, the aerodynamic forces have a stabilizing effect on the system. At higher rotational frequencies, the engine reaches a speed after which the system becomes unstable. The use of soft resilient mounts maximizes the vibration isolation but lowers instability threshold speed.
Optimal Sensor and Actuator Configuration for Structural Identification
Authors: Papadimitriou C. , Christodoulou K. , Pavlidou M. , Karamanos S. A.
Published: November 2020

A methodology is presented for designing cost-effective optimal sensor and actuator configurations useful for structural model updating and health monitoring purposes. The optimal sensor and actuator configuration is selected such that the resulting measured data are most informative about the condition of the structure. This selection is based on an information entropy measure of the uncertainty in the model parameter estimates obtained using a statistical system identification methodology. The optimal sensor and actuator configuration is selected as the one that minimizes the information entropy. A discrete optimization problem arises which is solved efficiently using genetic algorithms. This study also addresses important issues related to robustness of the optimal sensor and actuator configuration to unavoidable uncertainties in the structural model, as well as issues related to the optimal sensor and actuator configurations designed to monitor multiple damage scenarios. The theoretical developments are illustrated by designing the optimal configuration for a 40-DOF two-dimensional truss structure subjected to an impulse hammer excitation.
Instant Chaos, Extreme Parametric Uncertainty, and Sustained Chaotic Transients in Nonlinear Continuum Mechanics
Authors: Schwartz Ira B. , Triandaf Ioana , Wood Yvette , Georgiou Ioannis T.
Published: November 2020

Bifurcation to high-dimensional hyperchaos is observed in a driven coupled pendulum-flexible rod system. When the rod is in resonance with the pendulum, the system changes from a low dimensional attractor to a high dimensional attractor abruptly. It is shown that high dimensional chaotic dynamics is hysteretic, and exhibits extreme sensitivity with respect to small parameter changes. Such sensitivity poses a problem in obstructing predictability in mechanics. A brief discussion of sustaining chaos to prevent resonance is included.
Biomechanical Considerations in Antenatal Care of High Risk Pregnancies
Authors: Bhat Rama B. , Bhat Padmavathi P.
Published: November 2020

Preterm labor is an important issue in the field of Obstetrics and Gynacology. The earlier the diagnosis, the better the prevention of preterm labor. This study examines the static and dynamic loads on the cervix, which is one of the causes of preterm labor, from a biomechanical point of view. A simple biomechanical model is formulated to assess the loads bearing on the cervix. Results indicate the need for extreme caution warranted in cases of high risk pregnancies in highly dynamic environments. In view of the very delicate nature of the issue, it is essential to formulate better simulation models using indirectly gathered data.
POD (K-L) Analysis of the Interaction Free Dynamics of a Beam/Pendulum Configuration: An Experimental Study
Authors: Georgiou Ioannis T. , Schwartz Ira B.
Published: November 2020

This work presents an analysis of the experimental free dynamics of a coupled beam/pendulum configuration. The analysis, which is based on the method of Proper Orthogonal Decomposition, identifies the characteristics of the active degrees-of-freedom dominating the dynamics. Depending on the level of energy a motion is initiated, the interaction dynamics bear distinct signatures of reduced slow dynamics and distinct signatures of the interaction dynamics created by instabilities of reduced slow and fast dynamics.
Dynamics and Control of an Elastic Guideway Under a Moving Mass
Authors: Reckmann Hanno , Popp Karl
Published: November 2020

Lightweight structures under moving loads occur in robotics, ground transportation and in space stations. Increasing velocities lead to an excitation of structural vibrations with high amplitudes. This phenomenon may affect the precision of machine tools and robots and the safety of transport operations. An example of such a lightweight structure is a flexible beam under a moving load. In this paper we investigate the possibility of active vibration control of the elastic beam using a king post truss system (KPTS). The system is excited by both a mass moving with constant velocity and a mass performing an accelerated motion. The aims are to minimize the vibrations of the system and the transverse deflections under the moving mass.

The system to be analysed and controlled is time variant due to the moving mass. The fast motion of the mass leads to a highly dynamic system with a fast changing system matrix. We use control inputs at fixed positions for control of the system with distributed parameters. The system is modelled by a finite element approach to implement the moving mass in the system description. To reduce the numerical complexity of the system a modal transformation is applied and numerical investigations of the system are performed.

We apply two different control strategies to reach the aims. The first one is an optimal discrete time approach which allows to reach both aims. The second one is an adaptive control strategy with a simple model to minimize the deflection under the moving mass. The numerical results are compared with experimental data. In the case of a constant mass velocity the optimal control strategy leads to a reduction of the deflection under the moving mass of more than 98% compared to the uncontrolled system. The reduction of the deflection under the moving mass applying adaptive control results in a smaller reduction of about 96%.
Parametric Control of an Axially Moving String via Fuzzy Sliding-Mode and Fuzzy Neural Network Methods
Authors: Lai Cheng-Liang , Huang Jeng-Sheng , Chao Chang-Po
Published: November 2020

The parametric fuzzy sliding mode control (FSMC) and parametric fuzzy neural network control (FNNC) methods, in the present study, is applied to suppress vibration of the axially moving string system, which is driven by adjusting the axial tension. Due to the difficulty of utilizing fuzzy logic control (FLC) to obtain the linguistic control rules, the stability and robustness are not guaranteed. The sliding-mode control is then incorporated in the scheme of FLC to generate the control rule bases in order to meet the requirement of stability and robustness. In additions, for the purpose of improving system performance, the Genetic Algorithm (GA) is applied to search for the optimal parameters of the fuzzy sliding mode controller. Beside the aforementioned method of fuzzy sliding mode control plus GA, the on-line learning algorithm Fuzzy Neural Network (FNN) accompanied with sliding mode characterization is also developed and applied to achieve control goal. In this method, the parameters of FNN are adjusted in the direction that minimizes sliding mode variables SṠ where S of the switching function for vibration suppression. Simulations are conducted to verify the effectiveness of control designs. The results show the performance of FSMC with GA in general is favorable to others.
Coupled Torsion-Lateral Stability of a Shaft-Disk System Driven Through a Universal Joint
Authors: DeSmidt Hans A. , Wang K. W. , Smith Edward C.
Published: November 2020

Understanding the instability phenomena of rotor-shaft and driveline systems incorporating universal joints is becoming increasingly important because of the trend towards light-weight, high-speed supercritical designs. A non-dimensional, periodic, linear time-varying model with torsional and lateral degrees-of-freedom is developed for a rotor shaft-disk assembly supported on a flexible bearing and driven through a U-Joint and stability is investigated with Floquet Theory. It is shown that the interaction between torsional and lateral dynamics results in new regions of parametric instability that have not been addressed in previous investigations. The presence of load inertia and misalignment causes dynamic coupling of the torsion and lateral modes, which can result in torsion-lateral instability for shaft speeds near the sum-type combinations of the torsion and lateral natural frequencies. The effect of angular misalignment, static load-torque, load-inertia, lateral frequency-split, and auxiliary damping on the stability of the system is studied over a range of shaft operating speeds. Also, the effectiveness of auxiliary lateral viscous damping as a means of stabilizing the system is investigated. Finally, a closed-form technique based on perturbation expansions is derived to determine the auxiliary damping necessary to stabilize the system for the least stable case (worst case).
Forced Dynamics of an Orbiting Conducting Tether
Authors: Pasca Monica
Published: November 2020

Orbiting electrodynamic tethered systems are subjected not only to the gravity gradient but also to the electromagnetic drag forces that are generated by the interaction of the current flowing in the tether with the local magnetic field, according to the Lorentz law. This feature makes it possible to think of using such a system in order to de-orbit a satellite at the end of its life, taking advantage of the orbital energy lost in producing electric power.

The configuration of such a system is deeply discussed in this paper with reference to a parametric analysis based on two different mechanical models, both of them considering the tether mass and elasticity and an electric current generated at one end that interact with the Earth’s ionosphere. The magnetic field variation along the orbit is considered, giving raise to forced oscillations of the system around its equilibrium configuration.