scholarly journals PHENOMENA OF INSTABILITY IN NON-CONSERVATIVE DYNAMICAL SYSTEMS

2018 ◽  
Vol 13 (1) ◽  
Author(s):  
Dragan Milašinović
Keyword(s):  
Qualitative Research ◽  
Dynamical Systems ◽  
Internal Friction ◽  
Dynamic Response ◽  
Equilibrium State ◽  
Dynamic Behavior ◽  
Quantitative Research ◽  
Loss Of Stability

If the loading is non-conservative, the loss of stability may not manifest itself as the system going into another equilibrium state, but as exhibiting oscillations of increasing amplitude. To take account of this possibility, we must consider the dynamic behavior of the system, because stability is essentially a dynamic concept. In the paper the author’s theory, named the rheological-dynamical analogy (RDA), is used to examine the phenomena of instability in linear internally damped inelastic (LIDI) dynamical systems. Apart from quantitative research, qualitative research is presented to demonstrate the influence of inelasticity and internal friction on dynamic response.

Influence of the backlash generated by tooth accumulated wear on dynamic behavior of compound planetary gear set

2016 ◽  
Vol 231 (11) ◽  
pp. 2025-2041 ◽  
Author(s):  
Shijing Wu ◽  
Haibo Zhang ◽  
Xiaosun Wang ◽  
Zeming Peng ◽  
Kangkang Yang ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Dynamic Model ◽  
Dynamic Behavior ◽  
Planetary Gear ◽  
Tooth Wear ◽  
Transmission Error ◽  
Gear Transmission ◽  
Tooth Surface ◽  
Contact Ratio ◽  
The Impact

Backlash is a key internal excitation on the dynamic response of planetary gear transmission. After the gear transmission running for a long time under load torque, due to tooth wear accumulation, the backlash between the tooth surface of two mating gears increases, which results in a larger and irregular backlash. However, the increasing backlash generated by tooth accumulated wear is generally neglected in lots of dynamics analysis for epicyclic gear trains. In order to investigate the impact of backlash generated by tooth accumulated wear on dynamic behavior of compound planetary gear set, in this work, first a static tooth surface wear prediction model is incorporated with a dynamic iteration methodology to get the increasing backlash generated by tooth accumulated wear for one pair of mating teeth under the condition that contact ratio equals to one. Then in order to introduce the tooth accumulated wear into dynamic model of compound planetary gear set, the backlash excitation generated by tooth accumulated wear for each meshing pair in compound planetary gear set is given under the condition that contact ratio equals to one and does not equal to one. Last, in order to investigate the impact of the increasing backlash generated by tooth accumulated wear on dynamic response of compound planetary gear set, a nonlinear lumped-parameter dynamic model of compound planetary gear set is employed to describe the dynamic relationships of gear transmission under the internal excitations generated by worn profile, meshing stiffness, transmission error, and backlash. The results indicate that the introduction of the increasing backlash generated by tooth accumulated wear makes a significant influence on the bifurcation and chaotic characteristics, dynamic response in time domain, and load sharing behavior of compound planetary gear set.

DYNAMIC BEHAVIOR OF TELESCOPIC CRANES BOOM

2013 ◽  
Vol 13 (01) ◽  
pp. 1350010 ◽  
Author(s):  
IOANNIS G. RAFTOYIANNIS ◽  
GEORGE T. MICHALTSOS
Keyword(s):  
Dynamic Response ◽  
Dynamic Analysis ◽  
Dynamic Behavior ◽  
Analytical Model ◽  
Constant Velocity ◽  
Steel Beam ◽  
Continuum Approach ◽  
Theoretical Formulation ◽  
Modal Superposition ◽  
Superposition Technique

Telescopic cranes are usually steel beam systems carrying a load at the tip while comprising at least one constant and one moving part. In this work, an analytical model suitable for the dynamic analysis of telescopic cranes boom is presented. The system considered herein is composed — without losing generality — of two beams. The first one is a jut-out beam on which a variable in time force is moving with constant velocity and the second one is a cantilever with length varying in time that is subjected to its self-weight and a force at the tip also changing with time. As a result, the eigenfrequencies and modal shapes of the second beam are also varying in time. The theoretical formulation is based on a continuum approach employing the modal superposition technique. Various cases of telescopic cranes boom are studied and the analytical results obtained in this work are tabulated in the form of dynamic response diagrams.

Dynamic Behavior of Aircraft Wings Modeled as Doubly-Tapered Composite Thin-Walled Beams

1999 ◽  
Author(s):  
Sungsoo Na ◽  
Liviu Librescu
Keyword(s):  
Composite Materials ◽  
Free Vibration ◽  
Dynamic Response ◽  
Dynamic Behavior ◽  
Transverse Shear ◽  
Dynamical Behavior ◽  
Time Dependent ◽  
Aircraft Wings ◽  
Helicopter Blades ◽  
Thin Walled

Abstract A study of the dynamical behavior of aircraft wings modeled as doubly-tapered thin-walled beams, made from advanced anisotropic composite materials, and incorporating a number of non-classical effects such as transverse shear, and warping inhibition is presented. The supplied numerical results illustrate the effects played by the taper ratio, anisotropy of constituent materials, transverse shear flexibility, and warping inhibition on free vibration and dynamic response to time-dependent external excitations. Although considered for aircraft wings, this analysis and results can be also applied to a large number of structures such as helicopter blades, robotic manipulator arms, space booms, tall cantilever chimneys, etc.

Dynamics and Control of Dual-Hoist Cranes Moving Triangular Payloads

2014 ◽  
Author(s):  
Alexander S. Miller ◽  
Padma Sarvepalli ◽  
William Singhose
Keyword(s):  
Dynamic Response ◽  
Dynamic Behavior ◽  
Bridge Crane ◽  
Response Characteristics ◽  
Dynamics And Control ◽  
System Configurations ◽  
And Control

Certain heavy-lifting applications require the coordinated movement of multiple cranes. Such tasks dramatically increase the complexity of crane operation, especially when the payload has a non-uniform shape. This paper studies the dynamic behavior of a dual-hoist bridge crane moving triangular payloads. Simulations and experiments are used to develop an understanding of the dynamic response of the system. Various inputs and system configurations are analyzed, and important response characteristics are highlighted.

Dynamic Response of a Dual-Hoist Bridge Crane

2013 ◽  
Author(s):  
Ehsan Maleki ◽  
William Singhose ◽  
Jeffrey Hawke ◽  
Joshua Vaughan
Keyword(s):  
Dynamic Response ◽  
Dynamic Behavior ◽  
Bridge Crane ◽  
Response Characteristics ◽  
Manufacturing Facilities ◽  
System Configurations

Cranes are used in manufacturing facilities, throughout nuclear sites, and in many other applications for various heavy-lifting purposes. Unfortunately, the flexible nature of cranes makes fast and precise motion of the payload challenging and dangerous. Certain applications require the coordinated movement of multiple cranes. Such tasks dramatically increase the complexity of the crane operation. This paper studies the dynamic behavior of a dual-hoist bridge crane. Simulations and experiments are used to develop an understanding of the dynamic response of the system. Various inputs and system configurations are analyzed and important response characteristics are highlighted.

Embracing qualitative research: an act of strategic essentialism

2018 ◽  
Vol 13 (4) ◽  
pp. 306-314 ◽  
Author(s):  
Raza Mir
Keyword(s):  
Qualitative Research ◽  
Quantitative Research ◽  
Postcolonial Theory ◽  
Ethical Considerations ◽  
Social Scientists ◽  
Content Type ◽  
Theoretical Approaches ◽  
Strategic Essentialism ◽  
The Common ◽  
Good Research

Purpose The purpose of this paper is to argue that rather than contest the artificial schism produced by social scientists between “qualitative” and “quantitative” research, we should to accept this binary, however, contingently, and use it productively. This would be an act of “strategic essentialism” that would allow us to be productive in the research and inquiry. Design/methodology/approach The paper uses postcolonial theory to make a case for contingent representation, i.e. using artificial categories to carve out a space for heterodox theoretical approaches. Findings Researchers devoted to qualitative research must resist thinking, speaking and evaluating that research using quantitative thinking. Also, while ethical considerations are paramount in qualitative research, we need to debunk the narrow understanding of ethics as “following rules.” Also, qualitative researchers need to be aware of the institutional pulls that the research will be subject to, and also be ready to resist them. Originality/value This paper discusses how good research resists the siren call of institutionalization. It challenges the “common sense” assumptions of the field and brings them into the realm of the questionable. It seeks to theorize the untheorizable, and anthropologize the dominant.

scholarly journals Qualitative Research in COVID 19 Pandemic

2021 ◽  
Author(s):  
Abdolghani Abdollahi Mohammad ◽  
Mohammad Reza Firouzkouhi
Keyword(s):  
Qualitative Research ◽  
Social Interaction ◽  
Quantitative Research ◽  
Social Consequences ◽  
Natural Order ◽  
Medical Procedures ◽  
Epidemiological Models ◽  
Social Event ◽  
The Social ◽  
The Face

Introduction: Quantitative research is not suitable for COVID pandemic research because it does not cover the social consequences of qualitative research. COVID 19 is a social event that is important because of the disruption of the natural order of society. To defeat the disease, social interaction is needed, so qualitative research is appropriate to find the challenges and experiences of society. Therefore, due to the inconsistency of people's health behaviors with epidemiological models, people's vulnerability in epidemics, unexpected consequences or surprising results, extracting participants' experiences from medical procedures and revealing flexibility in the face of social problems, the use of qualitative research in this pandemic that will be important.

scholarly journals Quantitative and Qualitative Approaches to Generalization and Replication–A Representationalist View

2021 ◽  
Vol 12 ◽  
Author(s):  
Matthias Borgstede ◽  
Marcel Scholz
Keyword(s):  
Qualitative Research ◽  
Boundary Conditions ◽  
Quantitative Research ◽  
Deductive Reasoning ◽  
Syntactic Structure ◽  
Inductive Reasoning ◽  
Statistical Testing ◽  
Bottom Up ◽  
Qualitative Approaches ◽  
Case Based

In this paper, we provide a re-interpretation of qualitative and quantitative modeling from a representationalist perspective. In this view, both approaches attempt to construct abstract representations of empirical relational structures. Whereas quantitative research uses variable-based models that abstract from individual cases, qualitative research favors case-based models that abstract from individual characteristics. Variable-based models are usually stated in the form of quantified sentences (scientific laws). This syntactic structure implies that sentences about individual cases are derived using deductive reasoning. In contrast, case-based models are usually stated using context-dependent existential sentences (qualitative statements). This syntactic structure implies that sentences about other cases are justifiable by inductive reasoning. We apply this representationalist perspective to the problems of generalization and replication. Using the analytical framework of modal logic, we argue that the modes of reasoning are often not only applied to the context that has been studied empirically, but also on a between-contexts level. Consequently, quantitative researchers mostly adhere to a top-down strategy of generalization, whereas qualitative researchers usually follow a bottom-up strategy of generalization. Depending on which strategy is employed, the role of replication attempts is very different. In deductive reasoning, replication attempts serve as empirical tests of the underlying theory. Therefore, failed replications imply a faulty theory. From an inductive perspective, however, replication attempts serve to explore the scope of the theory. Consequently, failed replications do not question the theory per se, but help to shape its boundary conditions. We conclude that quantitative research may benefit from a bottom-up generalization strategy as it is employed in most qualitative research programs. Inductive reasoning forces us to think about the boundary conditions of our theories and provides a framework for generalization beyond statistical testing. In this perspective, failed replications are just as informative as successful replications, because they help to explore the scope of our theories.

scholarly journals Financial Implications of Capital Controls Enforcement on Large-Cap Companies Listed on the Athens Stock Exchange

2021 ◽  
Vol 9 (1) ◽  
pp. 20-34
Author(s):  
Aikaterini Derdemezi ◽  
◽  
Kanellos Toudas ◽  
Paraskevi Boufounou ◽  
Georgios Georgakopoulos ◽  
...  
Keyword(s):  
Qualitative Research ◽  
Financial Performance ◽  
Mixed Method ◽  
Quantitative Research ◽  
Stock Exchange ◽  
Investment Decisions ◽  
Capital Controls ◽  
Senior Executives ◽  
Negative Effects ◽  
Athens Stock Exchange

The aim of this study is to examine the effects of the capital controls on the process and financial performance of large-cap companies operating in Greece listed on the Athens Stock Exchange. More specifically, the markets’ behavior is studied, as well as the reactions of the investors after the announcement of the implementation of the measure. The mixed method (quantitative research with questionnaires and qualitative research with interviews with financial managers and senior executives) was used. The main findings of the research are that the measure of capital controls: was deemed necessary and effective based on its aims, which were (a) the protection of the mass withdrawal of deposits and (b) the stabilization and security of the financial system had a significant effect on increasing the use of electronic banking. But also had significant negative effects: on the investment decisions of companies, on their competitiveness and reputation abroad, on the ability to raise new capital, on their liquidity and therefore on their ability to cope with key functions, as well as on their imports and exports. Keywords: Capital controls, listed large-cap companies, crisis, Athens Stock Exchange, Greece.

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