scholarly journals Modelisation of Thermally Induced Jitter in a Slender Structure

2021 ◽  
Author(s):  
KATHIRAVAN THANGAVEL ◽  
Maurizio Parisse
Keyword(s):  
Bending Moment ◽  
Basic Mechanism ◽  
Space Vehicles ◽  
Main Body ◽  
Structural Element ◽  
Thermally Induced ◽  
Flexible Appendage ◽  
Thermal Bending ◽  
Slender Structure ◽  
Elastic Transverse

Abstract The thermomechanical interactions of onboard space vehicles is an interesting field of research and study. Since the pioneering paper by Bruno Boley, published in 1954, many authors have given their relevant contribution to the comprehension of phenomena not otherwise investigable if not with a cross-sectoral approach and a multidisciplinary methodology. The anomaly that occurred to the spacecraft Alouette 1, in 1962, marked the beginning of a long series of unexpected events due to unconceivable coupling between the mechanical and thermal behaviour of the system. This work aims to emphasise, by means of a simple model, the basic mechanism responsible for elastic vibrations induced by a thermal shock. This is a widespread event experienced by a spacecraft during the transitions shadow-sun and vice-versa or when a flexible appendage, previously shadowed by the spacecraft's main body, comes to the light as a consequence of an attitude manoeuvre [Ulysses, 1990]. For the investigation, a very slender structure has been considered in order to make the thermal and mechanical characteristic times comparable and realise the conditions of strong coupling. The accurate thermal analysis provides an equivalent thermal bending moment, depending on time, which appears as a boundary condition in the subsequent modal analysis of the structural element, where it plays the role of a trigger of elastic transverse vibrations.

scholarly journals Thermo-hydro-mechanical coupling analysis of a thermo-active diaphragm wall

2018 ◽  
Vol 55 (5) ◽  
pp. 720-735 ◽  
Author(s):  
Yi Rui ◽  
Mei Yin
Keyword(s):  
New Technologies ◽  
Bending Moment ◽  
Diaphragm Wall ◽  
Elastic Model ◽  
Element Analysis ◽  
Thermally Induced ◽  
Mechanical Coupling ◽  
Reversal Effect ◽  
Earth Pressures ◽  
Geotechnical Aspect

Thermo-active diaphragm walls that combine load bearing ability with a ground source heat pump (GSHP) are considered to be one of the new technologies in geotechnical engineering. Despite the vast range of potential applications, current thermo-active diaphragm wall designs have very limited use from a geotechnical aspect. This paper investigates the wall–soil interaction behaviour of a thermo-active diaphragm wall by conducting a thermo-hydro-mechanical finite element analysis. The GSHP operates by circulating cold coolant into the thermo-active diaphragm wall during winter. Soil contraction and small changes in the earth pressures acting on the wall are observed. The strain reversal effect makes the soil stiffness increase when the wall moves in the unexcavated side direction, and hence gives different trends for long-term wall movements compared to the linear elastic model. The GSHP operation makes the wall move in a cyclic manner, and the seasonal variation is approximately 0.5–1 mm, caused by two factors: the thermal effects on the deformation of the diaphragm wall itself and the thermally induced volume change of the soil and pore water. In addition, it is found that the change in bending moment of the wall due to the seasonal GSHP cycle is caused mainly by the thermal differential across the wall during the winter, because the seasonal changes in earth pressures acting on the diaphragm wall are very limited.

scholarly journals Thermal optimization of a high-heat-load double-multilayer monochromator

2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Philipp Brumund ◽  
Juan Reyes-Herrera ◽  
Christian Morawe ◽  
Thomas Dufrane ◽  
Helena Isern ◽  
...  
Keyword(s):  
Heat Load ◽  
High Heat ◽  
Element Analysis ◽  
Synchrotron Source ◽  
Thermally Induced ◽  
Multilayer Mirror ◽  
Thermal Bending ◽  
Absorbed Power ◽  
High Heat Load ◽  
Grazing Angles

Finite-element analysis is used to study the thermal deformation of a multilayer mirror due to the heat load from the undulator beam at a low-emittance synchrotron source, specifically the ESRF-EBS upgrade beamline EBSL-2. The energy bandwidth of the double-multilayer monochromator is larger than that of the relevant undulator harmonic, such that a considerable portion of the heat load is reflected. Consequently, the absorbed power is non-uniformly distributed on the surface. The geometry of the multilayer substrate is optimized to minimize thermally induced slope errors. We distinguish between thermal bending with constant curvature that leads to astigmatic focusing or defocusing and residual slope errors. For the EBSL-2 system with grazing angles θ between 0.2 and 0.4°, meridional and sagittal focal lengths down to 100 m and 2000 m, respectively, are found. Whereas the thermal bending can be tuned by varying the depth of the `smart cut', it is found that the geometry has little effect on the residual slope errors. In both planes they are 0.1–0.25 µrad. In the sagittal direction, however, the effect on the beam is drastically reduced by the `foregiveness factor', sin(θ). Optimization without considering the reflected heat load yields an incorrect depth of the `smart cut'. The resulting meridional curvature in turn leads to parasitic focal lengths of the order of 100 m.

Load History for SSFU Under Multimodal Wave Spectra

2013 ◽  
Author(s):  
Matteo Mattioli ◽  
Michele Drago ◽  
Federico Quondamatteo ◽  
Roberto Bruschi
Keyword(s):  
Bending Moment ◽  
Development Project ◽  
Load History ◽  
Structural Element ◽  
Sea State ◽  
Fatigue Assessment ◽  
Hull Girder ◽  
Ongoing Development ◽  
Wind Sea ◽  
Term Analysis

This paper presents results from an ongoing development project which aims at increasing the knowledge for the estimation of extremes conditions and fatigue assessment of structural element (i.e. topside) of Ship Shaped Floating Units (SSFU) in a complex environment-load conditions. The method can be extended for the calculation of total bending moment to connections and hull-girder system. In some world geographical context, such as those of West Africa and Offshore Brazil, the environmental conditions are characterized by co-existence of waves and swells propagating in different directions. In these conditions load history for SSFU are strictly linked to comprehension knowledge of site specific environment. Loads pertain to various frequency ranges, for instance the long-period response of a morning, quasi-static response to swell, dynamic response to shore-crested sea and structural resonance of flexible components as flares etc. This paper aims at developing a new method for establishing load history at site in case of metocean climate including combination of several (up to 3 or 4) sea state components, such as those of main swell, secondary swell and wind sea. The method is applicable to both extreme conditions and fatigue assessment as results of a “combined-event approach”. The results are compared and discussed. They show that the use of different approaches, long and a short term analysis with deterministic and probabilistic computation of vessel heading, provide a reasonably conservative estimate of the vessel responses. Differences from the conventional method, i.e. unimodal spectrum and equivalent sea state, are also presented.

scholarly journals Thermal Bending of the Rotor Due to Rotor-to-Stator Rub

2000 ◽  
Vol 6 (2) ◽  
pp. 91-100 ◽  
Author(s):  
Paul Goldman ◽  
Agnes Muszynska ◽  
Donald E. Bently
Keyword(s):  
Transfer Problem ◽  
Constant Load ◽  
Load Force ◽  
Rotor Vibration ◽  
Thermally Induced ◽  
Vibrational Response ◽  
Contact Stage ◽  
Thermal Bending ◽  
The Stability ◽  
Transient Thermal

The rotor thermal bending due to the rotor-to-stator rubbing can lead to one of three types of observed rotor lateral motion: (1) spiral with increasing amplitude, (2) oscillating between rub]no-rub conditions, and (3) asymptotical approach to the rotor limit cycle. Based on the machinery observations, it is assumed in the analytical part of the paper that the speed scale of transient thermal effects is considerably lower than that of rotor vibrations, and that the thermal effect reflects only on the rotor steady-state vibrational response. This response would change due to thermally induced bow of the rotor, which can be considered to slowly vary in timefor the purpose of rotor vibration calculations. Thus uncoupled from the thermal problem, the rotor vibration is analyzed. The major consideration is given to the rotor which experiences intermittent contact with the stator, due to predetermined thermal bow, unbalance force, and radial constant load force. In the case of inelastic impact, it causes an on/off, step-change in the stiffness of the system. Using a specially developed variable transformation for the system with discontinuities, and averaging technique the resonance regimes of motion are obtained. These regimes are used to calculate the heat generated during contact stage, as a function of thermal bow modal parameters, which is used as a boundary condition for the rotor heat transfer problem. The latter is treated as quasi-static, which reduces the problem to an ordinary differential equation for the thermal bow vector. It is investigated from the stability standpoint.

The dynamic nature of rotor thermal bending due to unsteady lubricant shearing within a bearing

1994 ◽  
Vol 445 (1924) ◽  
pp. 273-290 ◽  
Keyword(s):  
Journal Bearing ◽  
System Stability ◽  
Source Distribution ◽  
Time Varying ◽  
Dynamic Nature ◽  
Thermally Induced ◽  
Speed Range ◽  
Thermal Bending ◽  
Bearing Design ◽  
Rotor Dynamic

The influence upon the temperature distribution within a hydrodynamically lubricated journal bearing of a time varying journal orbit is considered and the oscillatory source distribution arising as a result of unsteady shearing of the lubricant is examined with respect to axes which rotate with the journal. The time dependent thermal bend induced in a rotor by such a process has been evaluated and incorporated into a rotor dynamic model for the assessment of system stability. Techniques have been developed enabling calculations to be carried out on an idealized rotor-bearing configuration and the speed range over which instability occurred was established. The rate of growth of the unstable vibrations together with the rate and direction of ‘spiralling’ of the thermal bend vector were also determined. Features of rotor and bearing design having an influence on such thermally induced instability are assessed.

Time-Variant Reliability of RC Structures

2016 ◽  
Vol 847 ◽  
pp. 407-414
Author(s):  
Bruno Palazzo ◽  
Paolo Castaldo ◽  
Alessio Mariniello
Keyword(s):  
Reinforced Concrete ◽  
Probabilistic Approach ◽  
Bending Moment ◽  
Structural Safety ◽  
Time Variability ◽  
Structural Element ◽  
Rc Structures ◽  
Geometrical Properties ◽  
Proposed Model ◽  
Strength And Stiffness

Reinforced concrete structures are generally affected by degradation phenomena, which results in a time variability in strength and stiffness beyond the baseline conditions which are assumed in structural design, in particular when the concrete is exposed to an aggressive environment. Therefore, structural safety should realistically be considered time-variant. This paper provides a probabilistic approach to predict the time-evolution of the mechanical and geometrical properties of a reinforced concrete structural element (i.e., bridge pier) subjected to corrosion-induced deterioration, due to diffusive attack of chlorides, in order to evaluate its service life. The proposed model is based on Monte Carlo simulations in order to evaluate time variant axial force-bending moment resistance domains, with the aim to estimate the time-variant reliability index. Finally, an application to estimate the expected lifetime of a deteriorating reinforced concrete bridge pile is proposed.

Numerical Calculation of Micro-Plie in Slope Engineering

2014 ◽  
Vol 644-650 ◽  
pp. 5113-5120
Author(s):  
Xiao Song Tang ◽  
Jian Ping Xin ◽  
Ying Ren Zheng
Keyword(s):  
Shear Failure ◽  
Bending Moment ◽  
Soil Mass ◽  
Calculation Model ◽  
Plastic State ◽  
Soil Slope ◽  
Structural Element ◽  
Deformation And Failure ◽  
Pile Deformation ◽  
Rock And Soil

In order to conduct the numerical simulation of rock and soil slope strengthened by the micro-pile with reinforced bar, FEM strength reduction is combined with the program of FLAC which possesses the function of analyzing tensile and shear failure. The micro-pile is under plastic state due to its mechanic features. Solid element and ideal elastic-plastic constitutive model of Mohr-Coulomb are applied as the rock and soil mass and pile. The calculation model can work out the safety factor of slope, the dynamic changing process of pile deformation and failure, the failure mode of slope after strengthened by micro-pile. Then the structural element of pile is used to simulate piles, which can obtain the bending moment and shear force. The beam element is used to simulate the coupling beam. So the layout principle of inner force before the failure can be calculated.

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