Experiments on Complex Repetitive Impact Dynamics of a Built-Up Beam Structure

2006 ◽  
Author(s):  
Elizabeth K. Ervin ◽  
Jonathan A. Wickert
Keyword(s):  
Experimental System ◽  
Mapping Method ◽  
Problem Area ◽  
Forced Response ◽  
Beam Structure ◽  
Response Characteristics ◽  
Time Histories ◽  
Impact Phenomena ◽  
Repetitive Impact ◽  
The Impact

This paper investigates the experimental dynamics of a beam structure that supports an attached rigid body and that can impact a comparatively compliant base structure. The problem area is motivated by impact phenomena that are observed in certain structures internal to nuclear reactors. The assembly is subjected to base excitation at specified frequency and acceleration, and the resulting displacement and velocity time histories are recorded and used to obtain spectra, phase diagrams, and Poincare´ sections. The measurements validate simulation results obtained by using a constraint and modal mapping method based on the two sets of modes when the structure is in-contact, and when it is not-in-contact. Generalized coordinates are mapped across the impact discontinuities in the modal representation. The forced response simulation predicts the test specimen's response over a range of excitation frequencies. The specimens are fabricated as single integral structures from acrylnitrile butadene styrene plastic through rapid prototyping technology in order to eliminate the undesirable dissipation and flexibility arising from joints and connections. The experimental system can exhibit complex response characteristics, and the influences on complexity of deadband clearance and of asymmetry in the point of impact are examined in the experiments.

Structural Dynamics with Parameter Uncertainties

1987 ◽  
Vol 40 (3) ◽  
pp. 309-328 ◽  
Author(s):  
R. A. Ibrahim
Keyword(s):  
Structural Dynamics ◽  
Structural Parameters ◽  
Normal Modes ◽  
Forced Response ◽  
Experimental Investigations ◽  
Continuous Systems ◽  
Parameter Uncertainties ◽  
Response Characteristics ◽  
Random Eigenvalues ◽  
The Impact

The treatment of structural parameters as random variables has been the subject of structural dynamicists and designers for many years. Several problems have been involved during the last few decades and resulted in new theorems and interesting phenomena. This paper reviews a number of topics pertaining to structural dynamics with parameter uncertainties. These include direct problems such as random eigenvalues and random responses of discrete and continuous systems. The impact of these problems on related areas of interest such as sensitivity of structural performance to parameter variations, design optimization, and reliability analysis is also addressed. The paper includes the results of experimental investigations, the phenomenon of normal modes localization, and the effect of mistuning of turbomachinery blades on their flutter and forced response characteristics.

Impact Test on Steel Structures - An Experimental Investigation

2010 ◽  
Vol 146-147 ◽  
pp. 1514-1518
Author(s):  
Mohd Zaki Nuawi ◽  
Abdul Rahim Bahari ◽  
Shahrum Abdullah
Keyword(s):  
Steel Structures ◽  
Dynamic Responses ◽  
Transient Signal ◽  
Impact Event ◽  
Low Velocity ◽  
Power Spectral ◽  
Time Histories ◽  
Full Capacity ◽  
Impact Phenomena ◽  
The Impact

The dynamic responses of the impact phenomena were studied experimentally using ultrasound transducer mounted at the specimen support to capture non-audible structure-borne acoustic signal generated during the impact event. A series of low velocity as well as full capacity impact tests were analysed. Analysis from the time histories record and the signal energy from the power spectral density show that the transient signal generated during the impact event have relation to the impact velocity and impact energy. This paper can be further studied in order to characterise the material properties.

Modeling and Simulation of a Cold-Engine Test Stand Driveline With Experimental Comparisons

2006 ◽  
Author(s):  
Kamran A. Gul ◽  
Douglas E. Adams
Keyword(s):  
Fuel Injection ◽  
Cold Test ◽  
Forced Response ◽  
Test Stand ◽  
Torsional Vibrations ◽  
Engine Test ◽  
Response Characteristics ◽  
Noise Characteristics ◽  
Torque Measurements ◽  
The Impact

There is a need to develop cold-engine test stands for use in diagnosing cylinder faults and measuring gear noise given the new quieter fuel injection systems in modern engines. When engines run hot, these characteristics are not easily measured. By running the unfired cold-engine as a load using an electric motor and driveline, torque measurements can be used to diagnose assembly faults, damage and noise characteristics. In this paper, two cold-engine test stand drivelines are considered. Both stands experience large torsional vibrations excited by the various engine harmonics. Engine fault diagnosis becomes a challenge when these torsional vibrations degrade the measured torque signals. To solve this problem of torsional vibrations, an engine test stand model is developed to understand the system dynamics and analyze the free and forced response characteristics of the system. The model is used to predict the impact of the changes made to the test stand driveline and the trends observed in the simulation results are compared with experimental results for model validation. It is shown that based on model sensitivity analysis the changes made to the driveline parameters help to reduce the amplitude of the driveline resonances considerably. The developed model can be used to design a cold test stand for production diagnostics.

Studies on Related ms Magnitude Rate Models in Triangular Wave Unloading Section of Calcium Medium-Fine Sandstone

2010 ◽  
Vol 152-153 ◽  
pp. 164-170
Author(s):  
Jie Liu ◽  
Jian Lin Li ◽  
Ying Xia Li ◽  
Shan Shan Yang ◽  
Ji Fang Zhou ◽  
...  
Keyword(s):  
Mechanical Response ◽  
Strain Curve ◽  
Experimental System ◽  
Constant Term ◽  
Lag Time ◽  
Vertical Force ◽  
Time Segment ◽  
Triangular Wave ◽  
Apparent Modulus ◽  
The Impact

Specific to the improvement in the present research of mechanical response under cyclic loading, this paper, taking the calcareous middle- coarse sandstone as the research subject and the RMT-150C experimental system in which data is recoded by ms magnitude as the platform, develops several related models concerning the unloading rate of triangle waves. The unloading process is divided into lag time segment and non-lag time segment, with criterions and related parameters provided as well. The term apparent elastic modulus is defined. The test data analysis shows that there exist a linear relationship between the apparent modulus and instant vertical force before load damage in non-lag time segment. On the preceding basis, a rate-dependent model of triangular wave un-installation section in non-lag time segment is established. Due to the inability of the loading equipment to accurately input the triangle wave, the average loading rate is amended and a constant term is added into it. The model is proved to be reliable, as the predicted value of the deformation rate and the stress strain curve coincides with measured value. At the same time, the impact of the lag time is pointed out quantitatively and a predication model of lag time segment is set up.

scholarly journals Patient preferences for use of virtual consultations in an orthopaedic rehabilitation setting: Results from a discrete choice experiment

2021 ◽  
pp. 135581962110354
Author(s):  
Anthony W Gilbert ◽  
Emmanouil Mentzakis ◽  
Carl R May ◽  
Maria Stokes ◽  
Jeremy Jones
Keyword(s):  
Conceptual Model ◽  
Discrete Choice Experiment ◽  
Discrete Choice ◽  
Patient Preferences ◽  
Choice Experiment ◽  
Best Practice ◽  
Time Of Day ◽  
Problem Area ◽  
Fractional Factorial ◽  
The Impact

Objective Virtual Consultations may reduce the need for face-to-face outpatient appointments, thereby potentially reducing the cost and time involved in delivering health care. This study reports a discrete choice experiment (DCE) that identifies factors that influence patient preferences for virtual consultations in an orthopaedic rehabilitation setting. Methods Previous research from the CONNECT (Care in Orthopaedics, burdeN of treatmeNt and the Effect of Communication Technology) Project and best practice guidance informed the development of our DCE. An efficient fractional factorial design with 16 choice scenarios was created that identified all main effects and partial two-way interactions. The design was divided into two blocks of eight scenarios each, to reduce the impact of cognitive fatigue. Data analysis were conducted using binary logit regression models. Results Sixty-one paired response sets (122 subjects) were available for analysis. DCE factors (whether the therapist is known to the patient, duration of appointment, time of day) and demographic factors (patient qualifications, access to equipment, difficulty with activities, multiple health issues, travel costs) were significant predictors of preference. We estimate that a patient is less than 1% likely to prefer a virtual consultation if the patient has a degree, is without access to the equipment and software to undertake a virtual consultation, does not have difficulties with day-to-day activities, is undergoing rehabilitation for one problem area, has to pay less than £5 to travel, is having a consultation with a therapist not known to them, in 1 weeks’ time, lasting 60 minutes, at 2 pm. We have developed a simple conceptual model to explain how these factors interact to inform preference, including patients’ access to resources, context for the consultation and the requirements of the consultation. Conclusions This conceptual model provides the framework to focus attention towards factors that might influence patient preference for virtual consultations. Our model can inform the development of future technologies, trials, and qualitative work to further explore the mechanisms that influence preference.

Molecular Dynamics Study of Ion Impact Phenomena and Compressive Stress in Thin Films

1993 ◽  
Vol 317 ◽  
Author(s):  
N.A. Marks ◽  
P. Guan ◽  
D.R. Mckenzie ◽  
B.A. PailThorpe
Keyword(s):  
Molecular Dynamics ◽  
Three Dimensional ◽  
Carbon Films ◽  
Loss Mechanism ◽  
Ion Energy ◽  
Lennard Jones ◽  
Impact Phenomena ◽  
Ion Impact ◽  
Dynamics Simulations ◽  
The Impact

ABSTRACTMolecular dynamics simulations of nickel and carbon have been used to study the phenomena due to ion impact. The nickel and carbon interactions were described using the Lennard-Jones and Stillinger-Weber potentials respectively. The phenomena occurring after the impact of 100 e V to 1 keV ions were studied in the nickel simulations, which were both two and three-dimensional. Supersonic focussed collision sequences (or focusons) were observed, and associated with these focusons were unexpected sonic bow waves, which were a major energy loss mechanism for the focuson. A number of 2D carbon films were grown and the stress in the films as a function of incident ion energy was Measured. With increasing energy the stress changed from tensile to compressive and reached a maximum around 50 eV, in agreement with experiment.

Mistuning and Damping of a Radial Turbine Wheel. Part 1: Fundamental Analyses and Design of Intentional Mistuning Pattern

2021 ◽  
Author(s):  
Alex Nakos ◽  
Bernd Beirow ◽  
Arthur Zobel
Keyword(s):  
High Stress ◽  
Forced Response ◽  
Experimental Investigations ◽  
Detailed Knowledge ◽  
Turbine Wheel ◽  
Operation Conditions ◽  
Radial Turbine ◽  
Influence Coefficients ◽  
Modes Of Vibration ◽  
The Impact

Abstract The radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. Contrary, the use of intentional mistuning (IM) has proved to be an efficient measure to mitigate the forced response. Independently, the presence of aerodynamic damping is significant with respect to limit the forced response since structural damping ratios of integrally bladed rotors typically take extremely low values. Hence, a detailed knowledge of respective damping ratios would be desirable while developing a robust rotor design. For this, far-reaching experimental investigations are carried out to determine the damping of a comparative wheel within a wide pressure range by simulating operation conditions in a pressure tank. Reduced order models are built up for designing suitable intentional mistuning patterns by using the subset of nominal system modes (SNM) approach introduced by Yang and Griffin [1], which conveniently allows for accounting both differing mistuning patterns and the impact of aeroelastic interaction by means of aerodynamic influence coefficients (AIC). Further, finite element analyses are carried out in order to identify appropriate measures how to implement intentional mistuning patterns, which are featuring only two different blade designs. In detail, the impact of specific geometric modifications on blade natural frequencies is investigated.

Forced Response Sensitivity of a Mistuned Rotor From an Embedded Compressor Stage

2015 ◽  
Author(s):  
Fanny M. Besem ◽  
Robert E. Kielb ◽  
Nicole L. Key
Keyword(s):  
Experimental Data ◽  
Forced Response ◽  
Symmetric System ◽  
Response Analysis ◽  
Cfd Simulations ◽  
Forcing Function ◽  
Wear And Tear ◽  
The Individual ◽  
The Impact ◽  
Interblade Phase Angle

The frequency mistuning that occurs due to manufacturing variations and wear and tear of the blades can have a significant effect on the flutter and forced response behavior of a blade row. Similarly, asymmetries in the aerodynamic or excitation forces can tremendously affect the blade responses. When conducting CFD simulations, all blades are assumed to be tuned (i.e. to have the same natural frequency) and the aerodynamic forces are assumed to be the same on each blade except for a shift in interblade phase angle. The blades are thus predicted to vibrate at the same amplitude. However, when the system is mistuned or when asymmetries are present, some blades can vibrate with a much higher amplitude than the tuned, symmetric system. In this research, we first conduct a deterministic forced response analysis of a mistuned rotor and compare the results to experimental data from a compressor rig. It is shown that tuned CFD results cannot be compared directly with experimental data because of the impact of frequency mistuning on forced response predictions. Moreover, the individual impact of frequency, aerodynamic, and forcing function perturbations on the predictions is assessed, leading to the conclusion that a mistuned system has to be studied probabilistically. Finally, all perturbations are combined and Monte-Carlo simulations are conducted to obtain the range of blade response amplitudes that a designer could expect.

scholarly journals Exploiting Thermochronology to Quantify Exhumation Histories and Patterns of Uplift Along the Margins of Tibet

2021 ◽  
Vol 9 ◽  
Author(s):  
Kevin P. Furlong ◽  
Eric Kirby
Keyword(s):  
Thermal History ◽  
Data Sets ◽  
The Tibetan Plateau ◽  
Tectonic History ◽  
Time Histories ◽  
Major Fault ◽  
History Of ◽  
Cooling Behavior ◽  
Exhumation Rates ◽  
The Impact

The utilization of thermal-chronological data to constrain mountain building processes exploits the links among rock uplift, exhumation, and cooling during orogenesis. Conceptually, periods of rapid uplift and associated denudation will lead to cooling of rocks as they approach Earth’s surface. The linkage between uplift and exhumation can be complex, but in practice exhumation is often assumed to directly track uplift. The reconstruction of temperature-time histories via thermochronologic systems provides a proxy method to relate the cooling of rock as it is exhumed toward the surface to orogenesis. For the rapid exhumation rates that can occur in active orogenic systems the thermal history will be complex as a result of heat advection, rates of propagation of thermal perturbations, and other processes that affect the cooling behavior. These effects become amplified as exhumation rates increase, and in regions experiencing exhumation rates greater than ∼0.2–0.3 mm/yr (0.2–0.3 km/Ma) simple assumptions of cooling through a constant geotherm will bias the subsequent interpretation. Here we explore, through a suite of generalized models, the impact of exhumation rate and duration on the resulting thermal history and apparent age results. We then apply lessons from these simple exhumation systems to data sets from the high-relief ranges along the eastern margin of the Tibetan Plateau to determine exhumation histories constrained by those data. The resulting exhumation histories provide constraints on the onset of Cenozoic exhumation, the subsequent pace of exhumation, and on the tectonic history of one of the major fault systems in the central Longmen Shan.

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