Methodology For Dynamic Analysis Research Articles

A parametric study on the dynamic response of planar multibody systems with multiple clearance joints

A general methodology for dynamic modeling and analysis of multibody systems with multiple clearance joints is presented and discussed in this paper. The joint components that constitute a real joint are modeled as colliding bodies, being their behavior influenced by geometric and physical properties of the contacting surfaces. A continuous contact force model, based on the elastic Hertz theory together with a dissipative term, is used to evaluate the intrajoint contact forces. Furthermore, the incorporation of the friction phenomenon, based on the classical Coulomb’s friction law, is also discussed. The suitable contact-impact force models are embedded into the dynamics of multibody systems methodologies. An elementary mechanical system is used to demonstrate the accuracy and efficiency of the presented approach, and to discuss the main assumptions and procedures adopted. Different test scenarios are considered with the purpose of performing a parametric study for quantifying the influence of the clearance size, input crank speed, and number of clearance joints on the dynamic response of multibody systems with multiple clearance joints. Additionally, the total computation time consumed in each simulation is evaluated in order to test the computational accuracy and efficiency of the presented approach. From the main results obtained in this study, it can be drawn that clearance size and the operating conditions play a crucial role in predicting accurately the dynamic responses of multibody systems.

Experimental methodology for the dynamic analysis of slender structures based on digital image processing techniques

There are several problems in engineering where the structural response may be affected by conventional devices for displacement measurements. This work presents an alternative methodology for the experimental dynamic analysis of structures, which cannot be monitored by conventional sensors. This methodology is based on digital image acquisition and processing techniques. The importance of this methodology is that it enables one to perform non-contact displacement measurements, without introducing undesirable changes in the structure's behavior, as for example, in models with an extremely reduced scale. The proposed methodology uses sticking markers of a negligible mass in relation to the structure, facilitating the implementation of the instrumentation of the experimental test. To evaluate the efficiency, precision and accuracy of this methodology, two different experimental tests are carried out and the obtained results are favorably compared with the theoretical results and with the ones provided by conventional sensors. This has shown to be a highly cost-effective and easy to implement experimental procedure for the analysis of very flexible structures, and yet maintains the advantage of dynamic measurements with high resolution.

Inverse First-Order Reliability Method for Probabilistic Fatigue Life Prediction of Composite Laminates under Multiaxial Loading

A new methodology for concurrent dynamic analysis and structural fatigue prognosis is proposed in this paper. The proposed methodology is based on a novel small timescale formulation of material fatigue crack growth that calculates the incremental crack growth at any arbitrary time within a loading cycle. It defines the fatigue crack kinetics based on the geometric relationship between the crack-tip opening displacement and the instantaneous crack growth rate. The proposed crack growth model can be expressed as a set of first-order differential equations. The structural dynamics analysis and fatigue crack growth model can be expressed as a coupled hierarchical state-space model. The dynamic response (structural level) and the fatigue crack growth (material level) can be solved simultaneously. Several numerical problems with single-degree-of-freedom and multiple-degree-of-freedom cases are used to show the proposed methodology. Model predictions are validated by using coupon testing data from open literatu...

Macro Factors in Bond Risk Premia

Are there important cyclical fluctuations in bond market premiums and, if so, with what macroeconomic aggregates do these premiums vary? We use the methodology of dynamic factor analysis for large datasets to investigate possible empirical linkages between forecastable variation in excess bond returns and macroeconomic fundamentals. We find that “real” and “inflation” factors have important forecasting power for future excess returns on U.S. government bonds, above and beyond the predictive power contained in forward rates and yield spreads. This behavior is ruled out by commonly employed affine term structure models where the forecastability of bond returns and bond yields is completely summarized by the cross-section of yields or forward rates. An important implication of these findings is that the cyclical behavior of estimated risk premia in both returns and long-term yields depends importantly on whether the information in macroeconomic factors is included in forecasts of excess bond returns. Without the macro factors, risk premia appear virtually acyclical, whereas with the estimated factors risk premia have a marked countercyclical component, consistent with theories that imply investors must be compensated for risks associated with macroeconomic activity.

A Dynamic Workflow Modelling and Performance Analysis Methodology for Complicated Clinical Pathway with Variations

Clinical Pathway (CP) is very complicated and has many exceptional variations. Generally, its treatment course and control steps can not be totally predefined. Meanwhile, the CP embodies the “Re-flow” therapy features, which is very hard to model, control and manage. Therefore, combined modular modelling method and structure changing mechanisms, a Modular Colored Petri Net with changeable structure (MCPN-CS) workflow modelling method is proposed. A special type of transition called main bus gate (MBG) is introduced to solve the “Re-flow” problem. Moreover, aimed at the variations of the CP, the workflow model for the CP can be reconfigured dynamically by using the mechanism of change-by-modification (CBM) and change-by-composition (CBC). A case study on the osteosarcoma CP evolution workflow modelling is constructed and the modelling is analyzed by presented deadlock detection algorithms (DDA). The result validates that the proposed method can noticeably enhance the flexibility, adaptation, reusability and maintainability workflow model for the CP.

Analysis of Human Gait Based on Multibody Formulations and Optimization Tools#

Human gait involves complex interaction mechanisms within the human body or with the environment as a result of variable conditions associated to different human activities. Such complexity is evident when trying to describe the characteristics of motor control and coordination exercised by the nervous system on the lower extremities of the human body during gait, under both normal and neuropathological conditions. The purpose of this work is to elucidate the neurological mechanisms that govern human locomotion under such conditions, using an inverse dynamic analysis methodology applied to 3D biomechanical models of the human body, developed on the basis of multibody formulations and optimization tools. The redundant biomechanical problem is solved through a cost function that emulates the dynamic behavior of nervous system involved in human gait and a novel global static optimization method. The outcome of this research is aimed at identifying cost functions describing the neural behavior during gait, keeping in mind their application to neuromuscular rehabilitation.

Dynamic load analysis and design methodology of LCD transfer robot

The objective of the present study is to develop a design methodology for the large scale heavy duty robot to meet the design requirements of vibration and stress levels in structural components resulting from exposure of system modules to LCD (Liquid Crystal Display) processing environments. Vibrations of the component structures significantly influence the motion accuracy and fatigue damage. To analyze and design a heavy duty robot for LCD transfer, FE and multi-body dynamic simulation techniques have been used. The links of a robot are modeled as flexible bodies using modal coordinates. Nonlinear mechanical properties such as friction, compliance of reducers and bearings were considered in the flexible multi-body dynamics model. Various design proposals are investigated to improve structural design performances by using the dynamic simulation model. Design sensitivity analyses with respect to vibration and stresses are carried out to search an optimal design. An example of an 8G (8th-Generation) LTR (LCD Transfer Robot) is illustrated to demonstrate the proposed methodology. Finally, the results are verified by real experiments including vibration testing.

Supplier risk assessment and monitoring for the automotive industry

PurposeThis research aims to develop a supplier risk assessment methodology for measuring, tracking, and analyzing supplier and part specific risk over time for an automotive manufacturer.Design/methodology/approachSupply chain risk literature is analyzed and used in conjunction with interviews from the automotive manufacturer to identify risks in the supply base. These risks are incorporated into the development of a temporal risk assessment and monitoring system.FindingsA framework of risk factors important to the auto manufacturer is presented. A multi‐criteria scoring procedure is developed to calculate part and supplier risk indices. These indices are used in the development of a risk assessment and monitoring system that allows the indices to be tracked over time to identify trends towards higher risk levels.Research limitations/implicationsThere are a number of operational issues identified in the paper that could be investigated in future research. One such issue is the development of alternative risk assessment methods that would increase the sensitivity of the risk analysis.Practical implicationsThe framework is implementable in firms interested in understanding and controlling risk in their supply base. The research stems from an industry project with an automotive manufacturer. The method is designed to be practical and easy to implement and maintain. The system also has a visual reporting mechanism designed to provide early warning signals for potential problems in the supply base and to show temporal changes in risk.Originality/valueThis paper presents a dynamic risk analysis methodology that analyzes and monitors supplier risk levels over time.

Analysis of Small and Medium Russian Banks in Dynamics

This paper focuses on three important issues concerning the Russian banking system: its stability, prevailing patterns of national banks' performance and structural dissimilarities. To examine these issues the methodology of dynamic cluster analysis is applied. The research is based on dynamic cluster analysis of 444 Russian banks for the period of 2 years (from September 2001 to September 2003). Support is found for the hypothesis that the Russian banking sector consists of an excessive number of small banks. There are a significant number of troubled banks, which slow down the development of banking system due to higher risks associated with their activities, insolvency and high accumulated losses. Although, dynamic analysis suggests that some of these institutions are stable, this deceptive stability refers to bankruptcy state. The results argue there is a tendency to overestimate bank performance in terms of their stability and prosperity. The problems of undeveloped financial market, high affiliation with insiders and undercapitalization are serious limiting factors for the evolution of national banking system. Another finding suggests that possible root cause for the decline in its development is ineffective performance of individual financial institutions within the whole banking system. The evidence related to clustering of banks is consistent with other studies in this field. However, proposed framework provides more detailed and precise snapshot. Potential application to regulatory surveillance in commercial banking is discussed.

The Empirical Risk-Return Relation: A Factor Analysis Approach

A key criticism of the existing empirical literature on the risk-return relation relates to the relatively small amount of conditioning information used to model the conditional mean and conditional volatility of excess stock market returns. To the extent that financial market participants have information not reflected in the chosen conditioning variables, measures of conditional mean and conditional volatility - and ultimately the risk-return relation itself - will be misspecified and possibly highly misleading. We consider one remedy to these problems using the methodology of dynamic factor analysis for large datasets, whereby a large amount of economic information can be summarized by a few estimated factors. We find that three new factors, a volatility, risk premium, and real factor, contain important information about one-quarter ahead excess returns and volatility that is not contained in commonly used predictor variables. Moreover, the factor-augmented specifications we examine predict an unusual 16-20 percent of the one-quarter ahead variation in excess stock market returns, and exhibit remarkably stable and strongly statistically significant out-of-sample forecasting power. Finally, in contrast to several pre-existing studies that rely on a small number of conditioning variables, we find a positive conditional correlation between risk and return that is strongly statistically significant, whereas the unconditional correlation is weakly negative and statistically insignificant.

Optimization of steering linkage and double-wishbone suspension via R-W multi-body dynamic analysis

By employing R-W (Roberson and Wittenburg) methodology of multi-body dynamic analysis, both the original and reduced digraph representation of a steering linkage and double-wishbone suspension system were made. The kinematical and constrain equations of this system was obtained after a deducing of its incident matrices and tach matrices. Finally, an optimization model of a steering and suspension mechanism aiming to minimize the steering error was established. The optimization model took the influence caused by wheel bouncing to the steering performance into account and employed two weight functions in order to simulate the actual working condition. This procedure was verified by an example of a passenger vehicle, a group of desirable design variables were defined. Kinematische Analyse und Optimierung der Einrichtungen der Doppelquerlenker-Radaufhangung und Lenkung

DYNAMIC RESPONSE EVALUATION OF A FRAMED TYPE TURBO-GENERATOR FOUNDATION INCORPORATING DYNAMIC MODULUS AND OPERATING SPEED VARIATIONS

Framed type foundation structures supporting turbo-generator machinery in a power plant have stringent vibration limits to ensure proper functioning of turbine generators without any breakdown. Current dynamic analysis methodology for such dynamically sensitive structures involves modal synthesis considering a single value of operating speed for the machinery and a uniform dynamic modulus for the frame material, which cannot be realized in site conditions. Such variations in the dynamic modulus across the whole structure and running speed of the machinery during normal operation have a profound impact on its dynamic performance which may result in alarmingly increasing amplitudes leading to subsequent breakdown of the machinery. A new methodology is outlined that combines the effects of the two variations by way of considering an enhanced range of speeds on either side of the operating speed for the modal synthesis process. This study shows the effects of variations in the dynamic modulus and operating speed on the peak dynamic response of a typical framed turbo-generator foundation structure. The modal synthesis process adopted in the study includes the significant modes in the sub-resonant range and a band of modes around the operating speed to obtain the peak response of the framed structure.

Methodology for dynamic analysis of offloading operations

The relative positioning between the Floating, Production, Storage and Offloading (FPSO) and the shuttle vessel during offloading should be analysed carefully, since the safety of the operation is of primary concern. In order to avoid collision, the shuttle vessel is kept away from the FPSO through the force of a tug-boat or by a dynamic positioning system. In both cases it is convenient to perform a preliminary study of their dynamics in order to obtain a guideline to set the best reference as well as a control approach. This paper presents a methodology for studying the dynamics and control of FPSO and shuttle vessel in tandem configuration systematically, using two software tools. The first tool allows the study of static solutions and the results have shown complex behavior, with a multiplicity of static equilibrium solutions the number and stability properties of which vary according to the combinations of the environmental conditions and vessel parameters. The second tool performs dynamic analysis of the FPSO-shuttle vessel, making it also possible to include a dynamic positioning system. Some results are compared with those obtained experimentally.

Revolute joints with clearance in multibody systems

A computational methodology for dynamic analysis of multibody mechanical systems with joint clearance is presented in this work. Clearances always exist in real joints in order to ensure the correct relative motion between the connected bodies being the gap associated to them a result of machining tolerance, wear, and local deformations. Clearance at different joints is the source for impact forces, resulting in wear and tear of the joints, and consequently the degradation of the system performance. The model for planar revolute joints is based on a thorough geometric description of contact conditions and on a continuous contact force model, which represents the impact forces. It is shown that the model proposed here lead to realistic contact forces. These forces correlate well with the joint reaction forces of an ideal revolute joint, which correspond to a null joint clearance. The application to the analysis of a simple planar multibody system illustrates the use of the different models proposed.

Seismic retrofit of RC frames

The main purpose of this paper is to present the numerical simulation of different strategies for the seismic retrofit of reinforced concrete frames, comparing the obtained solutions with the experimental results, and evaluating benefits concerning their structural behaviour under the seismic action. This work is based on the study of a RC frame, representative of the typical construction of the 70s, which has been submitted to real scale experimental tests at the Elsa Laboratory in Italy, involving the use of some retrofitting techniques. The numerical simulation of such tests, as well as the application of a non-linear dynamic analysis methodology to evaluate the structural behaviour and the structural safety improvement of the various retrofit techniques adopted, is presented. The aim is, therefore, to contribute for developing and calibrating a procedure that enables the evaluation of the efficiency of the different retrofit solutions, their possibilities and fields of application.

Revolute joints with clearance in multibody systems

A computational methodology for dynamic analysis of multibody mechanical systems with joint clearance is presented in this work. Clearances always exist in real joints in order to ensure the correct relative motion between the connected bodies being the gap associated to them a result of machining tolerance, wear, and local deformations. Clearance at different joints is the source for impact forces, resulting in wear and tear of the joints, and consequently the degradation of the system performance. The model for planar revolute joints is based on a thorough geometric description of contact conditions and on a continuous contact force model, which represents the impact forces. It is shown that the model proposed here lead to realistic contact forces. These forces correlate well with the joint reaction forces of an ideal revolute joint, which correspond to a null joint clearance. The application to the analysis of a simple planar multibody system illustrates the use of the different models proposed.

Coupled BEM–FEM solutions for direct time domain soil–structure interaction analysis

A coupled BEM–FEM methodology is presented for 3D wave propagation and soil–structure interaction analysis in the direct time domain. The employed boundary element method (BEM) uses a new generation of the Stokes fundamental solutions that utilize the B-Spline family of polynomials. A standard finite element methodology for dynamic analysis along with direct integration in time is coupled to the BEM through a staggered solution approach. Each method provides initial conditions to the other at the beginning of each time step. Formulation and computational aspects of the proposed coupling scheme are discussed. A number of numerical examples are presented for the validation and demonstration of the general nature of the proposed methodology.

Guidelines for terms related to chemical speciation and fractionation of elements. Definitions, structural aspects, and methodological approaches (IUPAC Recommendations 2000)

Abstract This paper presents definitions of concepts related to speciation of elements, more particularly speciation analysis and chemical species. Fractionation is distinguished from speciation analysis, and a general outline of fractionation procedures is given. We propose a categorization of species according to isotopic composition of the element, its oxidation and electronic states, and its complex and molecular structure. Examples are given of methodological approaches used for speciation analysis. A synopsis of the methodology of dynamic speciation analysis is also presented.

Automatic generation of dynamic clamping forces for machining fixtures

Automatic fixture configuration analysis is an essential issue in the context of computer-integrated manufacturing. In this paper, a general methodology for fixture configuration verification is presented, which is based on force closure and clamping equilibrium. The inclusion of a new clamping equilibrium criterion ensures a robust clamping layout and hence reduces the possibility of workpiece displacement within a fixture. For clamping force analysis, a new method for directly generating the minimal clamping intensity for planar fixtures is presented. Next, we develop a general friction methodology of dynamic clamping analysis and planning for arbitrary-shaped workpieces based on nonlinear programming. The objective of the presented algorithm is to determine a spectrum of minimum sustainable clamping forces for a machining process based on a proposed criterion of maximum friction. The set of variable clamping intensities is determined such that it is just enough to counterbalance the dynamic cutting forces. This approach is more realistic than other systems with static cutting conditions and frictionless contacts. The concept of maximum clamping forces is also proposed and a computation method is presented. The non-approximation representation of contacting forces presented in this algorithm guarantees the existence of an optimal clamping solution. Moreover, it makes the algorithm robust and reliable. Case studies are included to demonstrate the effectiveness and capabilities of the methodology.

Dynamic analysis of small signal voltage instability decoupled from angle instability

This paper presents a methodology for dynamic analysis of short term small signal voltage instability in a multi-machine power system. The formulation of the problem is done by decoupling the angle instability from the voltage instability. The method is based on the incremental reactive current flow network (IRCFN), where the incremental reactive current injection at each bus is related to the incremental voltage magnitude at all the buses. Small signal stability using the eigenvalue analysis is illustrated utilizing a single-machine load bus (SMLB) and three-machine system examples. The role of a static var compensator (SVC) at the load bus is also examined.