Non-linear dynamic analysis of geared systems, part 2

A good understanding of the steady state dynamic behavior of a geared system is required in order to design reliable and quiet transmissions. This study focuses on a system containing a spur gear pair with backlash and periodically time-varying mesh stiffness, and rolling element bearings with clearance type non-linearities. A dynamic finite element model of the linear time-invariant (LTI) system is developed. Effects of several system parameters, such as torsional and transverse flexibilities of the shafts and prime mover/load inertias, on free and force vibration characteristics are investigated. Several reduced order LTI models are developed and validated by comparing their eigen solution with the finite element model results. Several key system parameters such as mean load and damping ratio are identified and their effects on the non-linear frequency response are evaluated quantitatively. Other fundamental issues such as the dynamic coupling between non-linear modes, dynamic interactions between component non-linearities and time-varying mesh stiffness, and the existence of subharmonic and chaotic solutions including routes to chaos have also been examined in depth

Robust Sensitivity Analysis for Multi-Attribute Deterministic Hierarchical Value Models

The Air Force\u27s ability to deploy, employ, and sustain operations in forward locations is a key to mission success. An integral part of this strategy is equipment pre-positioning, to include: vehicles, aircraft support, consumable inventory, and munitions. This research focuses on defining and developing a model to aid decision makers with the afloat pre-positioning and deployment of munitions in an effort to ensure that the right weapons are available when, and where needed. This research places a particular focus on the strategic, global pre-positioning of the Afloat Pre-positioning Fleet (APF) in an effort to minimize the overall response time involved with offloading these ships and transporting their cargo to the intended point of use. The model developed in this study is a mixed integer program that was implemented using the General Algebraic Modeling System (GAMS). The model considers the various aspects of pre-positioning (forward operating locations, Standard Air Munitions Packages, and the APF) in order to optimally locate and configure each APF ship. The methodology for this model was tested and verified using precision-guided munitions data for a number of scenarios

Dynamic analysis of geared rotors by finite elements

A finite-element model of a geared rotor system on flexible bearings was developed. The model includes the rotary inertia of shaft elements, the axial loading on shafts, flexibility and damping of bearings, material damping of shafts and the stiffness and the damping of gear mesh. The coupling between the torsional and transverse vibrations of gears were considered in the model. A constant mesh stiffness was assumed. The analysis procedure can be used for forced vibration analysis of geared rotors by calculating the critical speeds and determining the response of any point on the shaft to mass unbalances, geometric eccentricities of gears and displacement transmission error excitation at the mesh point. The dynamic mesh forces due to these excitations can also be calculated. The model has been applied to several systems for the demonstration of its accuracy and for studying the effect of bearing compliances on system dynamics

Inhomogeneity and anisotropy in Eulerian-Eulerian near-wall modelling

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record This paper tackles the issue of image vorticity in turbulent Eulerian-Eulerian simulations. A pressure-velocity model to account for the no permeability constraint on the fluid- and particle-phase wall normal stress components is proposed. The pressure-velocity model is derived with in a Reynolds-Averaged Two-Fluid model (RA-TFM) framework and is implemented within the open-source CFD toolbox OpenFOAM. We demonstrate that this approach is capable of accounting for the strong near-wall inhomogeneity, a flow feature that hitherto has been neglected in Eulerian-Eulerian modelling. Simulation predictions are validated against benchmark Direct Numerical Simulation data and show a promising step forward in near-wall modelling in Eulerian-Eulerian simulations. The predictions reveal that the approach proposed herein can lead to a satisfactory agreement across all turbulence statistics paving the way for the correct prediction of more complex mechanisms. Finally, the source code of the recently developed solver ratfmFoam and supplementary material used in this work is made available online.University of Exete

Near-wall modelling in Eulerian–Eulerian simulations

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordThe near-wall region in turbulent Eulerian–Eulerian (E–E) simulations has hitherto received little to no attention. A standard approach to modelling this region is through the employment of single-phase wall-functions in the fluid-phase and it is unclear whether such an approach is capable of capturing the turbulent fluid-particle interaction in the near-wall region. In order to both investigate and alleviate E–E models reliance on single-phase wall-functions we propose an E–E elliptic relaxation model to account for the near-wall non-homogeneity which arises in wall-bounded flows. The proposed model is derived within an E–E framework and enables the full resolution of the boundary layer and arbitrary wall sensitivity. The model is then compared against the conventional kf−εf turbulence model with standard single-phase wall-functions. Additionally, the modelling is compared against a low-Re number turbulence model. The elliptic relaxation model is implemented within the open-source CFD toolbox OpenFOAM, applied to a vertical downward-facing channel and validated against the benchmark experimental data of Kulick et al. [1]. Model results show marked improvements over the conventional turbulence model across mean flow and turbulence statistics predictions. The use of conventional single-phase wall functions were shown to negatively impede on the prediction of the velocity covariance coupling term and as a result the particle fluctuation energy. Moreover, this also lead to an underestimation of the near-wall volume fraction accumulation. Finally, the elliptic relaxation model, E-E model and accompanying validation cases are made open-source.University of Exete

Reynolds-Averaged Two-Fluid Model prediction of moderately dilute fluid-particle flow over a backward-facing step

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record In this work a Reynolds-Averaged Two-Fluid fully coupled model (RA-TFM) for modelling of turbulent fluid-particle flow is implemented in OpenFOAM and applied to a vertically orientated backward-facing step. Three particle classes with varying mass loadings (10–40%) and different Stokes number are investigated. Details of the implementation and solution procedure are provided with special attention given to challenging terms. The prediction of mean flow statistics are in good agreement with the data from literature and show a distinct improvement over current model predictions. This improvement was due to the separation of the particle turbulent kinetic energy kp, and the granular temperature Θp, in which the large scale correlated motion and small scale uncorrelated motion are governed by separate transport equations. For each case simulated in this work, turbulence attenuation was accurately predicted, a finding that is attributed to separate coupling terms in both transport equations of kp and εp

Fully-coupled pressure-based two-fluid solver for the solution of turbulent fluid-particle systems

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordA fully-coupled pressure-based two-fluid solver for the solution of turbulent fluid-particle flows is presented. The numerical framework details several crucial aspects: implicit treatment of the phase-velocity-pressure coupling, the implicit treatment of inter-phase momentum transfer and finally the solution algorithm. The two-fluid solver is implemented within the open source tool-box foam-extend which is a community driven fork of OpenFOAM. The coupled solver is verified against a standard segregated implementation of the two-fluid solution algorithm and validated against benchmark experimental data. The coupled solver shows marked improvements in convergence, stability and solution time. The coupled implementation is capable of solving to a tolerance that is six orders of magnitude smaller in residual error and 1.7 times quicker than the segregated solver. Additionally, the sequentially solved system of phase-energies experienced performance improvements when solved in conjunction with the coupled solver

Working with refugees during COVID-19: social worker voices from Turkey

This short essay aims to share social workers’ experiences of working with refugees during the COVID-19 pandemic in Turkey. Three of the authors work in different non-governmental organizations (NGOs) in different cities. NGOs play a vital role in the delivery of psychosocial support services to refugees in Turkey and have been inevitably affected by the pandemic. The major practice challenges are being unprepared for tele-social work, a decrease in financial resources, increasing barriers to resources, and threats to refugee children’s wellbeing. Finally, suggestions are made for the near future

Adaptation of heritage architecture in Al Asmakh, Doha: insights into an urban environment of the Gulf

This is the author accepted manuscript. The final version is available from Taylor & Francis (Routledge) via the DOI in this record.This paper examines the continuing legacy and occupation of Doha’s vernacular architecture of the early oil period, drawing on techniques from architecture, contemporary archaeology and anthropology. Historical and contemporary inhabitation is examined, as well as the experiences of today’s resident migrant communities. The ongoing significance of Al Asmakh’s vernacular architecture within Qatar’s heritage discourse is considered. Particular attention is given to adaptations undertaken by today’s multinational residents, and the role they play as custodians of Qatar’s architectural heritage. This is a companion piece to the study of vernacular architecture by Eddisford & Carter (2017).National Priorities Research Program (NPRP) Qata