"wai sun shum"
121846846
Longitudinal vibration frequencies of steadily whirling rodsa)
Past researchers suggested that "static instabilities" exist at certain rotational speeds of whirling rods. This paper shows these instabilities are an artefact of the material constitutive laws that are being used well outside their range of applicability. An alternative approach is developed where strains due to rotation are separated from the superimposed vibration. This enables the generally predicted lowering of longitudinal natural frequencies with rotational speed shown to be simply a result of the bulk changes in the geometry of whirling rods. Steady state equations of whirling rods are formulated in Lagrangian coordinates. Due to the nonlinear nature of the governing equations, an original numerical method is applied to solve the problem. Numerical results are compared with analytical results obtained from the linearized uniaxial model. There is close agreement between these two models at low angular velocities. However, at high angular velocities, discrepancies between them arise, confirming tha.
W Shum Rodney Entwistle
120266757
Dynamic motion of whirling rods with Coriolis effect
Longitudinal vibrations coupled with transverse vibrations of whirling rods are investigated. It is known that longitudinal and transverse vibrations are governed by second and fourth order differential equations, respectively. Due to the Coriolis effect, a system of equations that governs the longitudinal and transverse displacements will be constructed by coupling these two equations together. Solutions of the equations assume small oscillations of vibration being superimposed on the steady state of the whirling rod. Exact and approximate solutions are obtained from the proposed governing equations, where the approximate solutions on displacements and natural frequencies are acquired by neglecting the Coriolis effect. A proposed numerical scheme known as complete function collocation method is implemented to solve the governing equations coupled with longitudinal and transverse displacements. The approximate results on both longitudinal and transverse natural frequencies show that natural frequencies are decreasing while the angular velocity of the rod is increasing. Exact and numerical results on both longitudinal and transverse natural frequencies show that there are no predictable trends whether natural frequencies are increasing or decreasing while the angular velocity of the rod is increasing.
W Shum Zhang Lin
108501806
Effect of internal partitions on the performance of under floor air supply ventilation in a typical office environment
This paper presents a case to investigate the effect of partitions in an office on the performance of under floor air supply ventilation system via computational fluid dynamics. The assessment is in terms of thermal comfort and indoor air quality with the use of a validated computer model. The results indicate that the partitions may significantly affect airflow and performance of a under floor air supply ventilation system. In particular, the presence of a gap above the partition wall is able to improve air distribution owing to less air re circulation in the upper zone. Its effect on thermal comfort and indoor air quality indicators are evaluated.
Zhang Lin Tin-tai Chow Chin-Fu Tsang K F Fong L S Chan W Shum Luther Tsai
110363708
Effect of Ventilation System on Smoke and Fire Spread in a Public Transport Interchange
In this report, a large eddy simulation (LES) model is used to investigate the conventional types of ventilation system design in the context of a public transport interchange. Various airflow patterns based on two of the most popular ventilation designs (mixing and displacement) are simulated to determine their effect on the fire. The simulation program chosen is the fire dynamics simulator (FDS) published by National Institute of Standards and Technology (NIST) It is found that increased airflow causes the fire temperature to increase by as much as 500 K. Extraction of smoke mixture by fans (exhaust only system) significantly decreases the spread of smoke and fire. Ventilation inlets located at the ground level help to increase the smoke and fire intensity in the occupied zone. Displacement ventilation increases fire intensity and current.
Zhang Lin Tin-tai Chow Chin-Fu Tsang K F Fong L S Chan W Shum
109592687
Complete function collocation method for solving preliminary cable stayed bridge pretension forces
A proposal for a numerical method based on the complete solution collocation method is presented to solve the cable stayed bridge engineering structural problem. This complete function collocation method is presented from the viewpoint of calculating the pretension forces required for the final completed bridge structure, which is one of the most important and practical considerations in cable stayed bridge design. The complete function collocation method is used to calculate stay cable forces by solving a set of partial differential equations. The study shows that this mesh free collocation method can be used to solve practical structural engineering problems and provides an alternative to traditional finite element methods. A simple two dimensional cable stayed bridge is presented and is solved to illustrate this numerical method. Governing equations of deformation for a bridge structure are formulated in either Eulerian or Lagrangian coordinate systems according to the situation. Point loads due to sta.
W Shum Chin-Fu Tsang Zhang Lin
122132735
Eulerian and Lagrangian formulations of steady rotating annuli
It is interesting to ask if there are any fundamental differences between Eulerian and Lagrangian formulations in structural dynamics problems. Steady rotating annuli formulated in both Eulerian and Lagrangian coordinates are exemplified for the present study. Nonlinear strain displacement relationships for radial vibration only without circumferential motion in polar coordinates are derived. Linear and nonlinear strain displacement relationships are implemented to form the governing equations and are compared to check for the validity of small strain analysis. By including the Poisson's effect, the resulting governing equations are nonlinear equations with material density redistribution and plate thickness variation. Analytical solutions of the linearized versions of nonlinear Eulerian and Lagrangian governing equations by keeping material density and plate thickness constant are offered. Fundamental issues in existence and uniqueness of analytical solutions are discussed between linear Eulerian and linear Lagrangian formulations. Furthermore, the fundamental difference of imposing free edge boundary conditions in Eulerian and Lagrangian coordinates is emphasized. Results show that there are in general insignificant differences between Eulerian and Lagrangian descriptions for circular plate problems, although the approaches to solve the problems in the two formulations are quite different.
W Shum Zhang Lin
120082350
Simulation of Cable stayed Bridge Pretension Forces by Complete Function Collocation Method with Cell Partition
Complete function collocation method (CFCM) without cell partition had been applied by Shum et al. to study cable stayed bridge pretension forces. This paper is intended to extend this numerical method with cell partition for a more accurate prediction of transverse natural frequencies of stay cables under gravity body force and longitudinal deformation of bridge deck and bridge pylon subject to point loads. The objective of the proposed numerical method with cell partition is to divide the computational domain into subintervals called cells, where solution in each cell of the whole domain is then locally approximated by a truncated complete function, in contrast to the global approximation of a solution using one truncated complete function for the whole computational domain using CFCM without cell partition. Comparing to the previous results, CFCM with cell partition can predict natural frequencies of stay cables under gravity force, longitudinal bridge deck and bridge pylon deformations subject to poin.
W Shum Z Lin
186711796
Vibration modes of steady whirling rods and dynamic roatating annuli
Chapter 1 gives the aims and scopes of the book. Chapter 2 is the literature review. Chapter 3 develops an alternative approach to predict natural frequencies of whirling rods. Nonlinear steady equations of whirling rods are formulated. An original numerical method is applied to solve for rod shape profiles under whirling motion. Classical receptance approach is then applied to solve for the natural frequencies from the deformed geometry of the whirling rod. Conditions for existence and uniqueness of solutions are derived. Chapter 4 investigates in plane vibration of annuli. Two different model equations that govern rotational motions of annuli are scrutinized. Solutions of the equations assume small oscillations of vibration being superimposed on the steady state of the annulus while it is rotating. Exact and approximate solutions are obtained, where the approximate solutions are acquired by ignoring the Coriolis effect. A proposed numerical scheme is implemented to solve the governing equations coupled with radial and circumferential displacements. Chapter 5 provides critiques on current work. Finally, Chapter 6 is the summary.
W Shum
123952034
Vibration frequencies of whirling rods and rotating annuli
Static Whirling Rods Past researchers suggested that "static instabilities" exist at certain rotational speeds of whirling rods. This thesis shows these instabilities are an artefact of the material constitutive laws that are being used well outside their range of applicability. An alternative approach is developed where strains due to rotation are separated from the superimposed vibration. This enables the generally predicted lowering of longitudinal natural frequencies with rotational speed shown to be simply a result of the bulk changes in the geometry of whirling rods. Steady state equations of whirling rods are formulated in Lagrangian coordinates. Due to the non linear nature of the governing equations, an original numerical method is applied to solve the problem. Numerical results are compared with analytical results obtained from the linearized uniaxial model. There is a close agreement between these two models at low angular velocities. However, at high angular velocities, discrepancies between them arise, confirming that the nonlinear strain displacement relationship has significant effect on the results and the inferred "static instabilities" This approach first solves the "static" problem of the deformed geometry of a highly strained whirling rod before longitudinal natural modes are determined by classical methods. Furthermore, conditions for existence and uniqueness of solutions are derived. Dynamic Rotating Annuli In plane modes of vibration of annular plates are investigated. Two different models of equations one from Bhuta and Jones and the other from Biezeno and Grammel that govern the rotational motions of annuli will be studied. Since Biezeno and Grammel's model was originally derived in Eulrian coordinates, their model will be transformed to the Lagrangian coordinates for the purpose of comparison with Bhuta and Jones' model. The solutions of the equations assume small oscillations of vibration being superimposed on the steady state of the annulus while it is in rotation. Exact and approximate solutions are obtained for the Bhuta and Jones' model, where the approximate solutions on in plane displacements and natural frequencies are acquired by ignoring the Coriolis effect. A proposed numerical scheme is implemented to solve
W Shum
111912374
Time domain prediction of acoustics in domains with realistic boundaries
W Shum