Neil Popplewell

Tuned liquid dampers for controlling earthquake response of structures

Numerical simulations of a single-degree-of-freedom (SDOF) structure, rigidly supporting a tuned liquid damper (TLD) and subjected to both real and artificially generated earthquake ground motions, show that a properly designed TLD can significantly reduce the structures response to these motions. The TLD is a rigid, rectangular tank with shallow water in it. Its fundamental linear sloshing frequency is tuned to the structures natural frequency. The TLD is more effective in reducing structural response as the ground excitation level increases. This is because it then dissipates more energy due to sloshing and wave breaking. A larger water-depth to tank-length ratio than previous studies suggested, which still falls within the constraint of shallow water theory, is shown to be more suitable for excitation levels expected in strong earthquake motions. A larger water-mass to structure-mass ratio is shown to be required for a TLD to remain equally effective as structural damping increases. Furthermore, the reduction in response is seen to be fairly insensitive to the bandwidth of the ground motion but is dependent on the structures natural frequency relative to the significant ground frequencies. Finally, a practical approach is suggested for the design of a TLD to control earthquake response. Copyright

Sequencing jobs on a single machine: A neural network approach

Abstract This paper presents an approach for single machine job sequencing problems that is based on artificial neural networks. A problem is classified first by one type of neural network into one of a number of categories. The categorization is based on the problem’s characteristics. Then another neural network, which is specialized for a particular category, applies a previously ‘learnt’ relationship to produce a job sequence that aims to better satisfy the given objective. The learning is acquired in these networks after a training process in which the network is exposed repeatedly to a set of example problems and their solutions. The trained network thereby learns predominant relationships between given problems, and the output sequences that optimally meet the desired objective. The advantage of such an approach is that it allows what amounts to a ‘customized’ heuristic to be established for problem subsets and various objectives without having to deduce an algorithm in advance. The methodology and its implementation is described for several of the more common sequencing objectives, as well as for a hypothetical objective that minimizes a cost function exhibiting a limited exponential behavior.

A Search-Based Heuristic For The Two-Dimensional Bin-Packing Problem

AbstractA heuristic algorithm combining priority rules with a restricted search procedure is presented for solving the two-dimensional, bin-packing problem. The method of solution is one of problem reduction, where the initial problem is decomposed into subproblems that are solved separately. The search procedure acts to minimize the number of subproblems created in the decomposition, while the priority rules force the search process to give due weight to the less combinatorially-inclined pieces. The algorithm was tested using four heuristic rules for assigning priorities, and data from two previously published algorithms. A good improvement was generally observed.

Surface roughness measurements in finish turning

A new approach is proposed for the on-line measurement of the maximum peak-to-valley roughness,Rmax, of a finished-turned surface in the feed direction. The method is based on solving the inverse problem of light scattering by using a linear least-square estimate of the angular scattered light pattern reflected from a surface. A laser system has been developed to capture the light reflected under different cutting conditions. The effects of the ambient room light as well as the workpieces rotational speed and methods for thier compensation are also discussed. Good correlation was found between the optical and stylus-measuredRmax.

Application of neural networks for surface roughness measurement in finish turning

A laser system which incorporates a charge-coupled-device (CCD) sensor is developed to measure, in real lime, the maximum peak-to-valley surface roughness, R max. produced during finish turning. A three-layer neural network is used in conjunction with a back-propagation learning algorithm to predict R max, by quickly recognizing the angular scattered light patterns (ASLP) reflected from the workpiece in the feed direction. The predicted R max values have a maximum error of about 10% when compared to conventional stylus measurements.

Intelligent robotic assembly

Abstract It is normal when programming a robotic manipulator to provide the end effectors orientation and position at the pick up and drop off locations. Additional sensory information and intelligence is needed, however, to detect the presence of a part as well as its location if the assembly site cannot be controlled precisely by employing expensive jigs or fixtures. This paper investigates, for this purpose, the application of solely an inexpensive laser sensor mounted unobtrusively to the end effector of a CRS robot having customized hardware and open software. Data from the sensor is converted into a single “Feature Value Vector” to recognize a part and accurately determine its location by using a neural network and back propagation training. The procedures viability is tested by assembling a set of tightly meshing gears under poor ambient lighting.

ULTRASONIC MEASUREMENT OF DIMENSIONAL AND MATERIAL PROPERTIES

A computer model‐based inversion procedure is used to simultaneously determine the elastic constants and wall thickness of a typical steel pipe from the experimentally determined cut‐off frequencies of three guided wave modes as well as the pipe’s mass density and outer diameter. Nominal values for the unknown parameters agree well with those found from conventional tension and torsion tests performed on a short piece of the pipe cut from one end.

Modal Analysis of Transient Ultrasonic Guided Waves in a Cylinder

Loaded cylinders are ubiquitous in industrial applications (e.g., pipes carrying pressurized fluids). Defects in a cylinder reduce the load that can be carried safely; catastrophic failure of a cylinder can be costly in terms of both economics and loss of life. An apparent dichotomy exists presently in the literature. To date, analyses are performed predominantly in the wave number-frequency domain and tend to focus on a single mode or relatively few modes (e.g., [1] – [3]) to minimize computational requirements. Excitation of a single mode, while permitting straightforward interpretations, is difficult to achieve in practice, requires specialized transducers (see, e.g., [2]), and potentially limits the types of defects that can be detected (see, e.g., [4]). Waves generated and subsequently scattered by a transient multi-modal excitation, on the other hand, are much easier to excite practically and have the potential to quickly detect and characterize more defects, albeit with more interpretation effort. An understanding of the behaviour of multi-modes excitations is of great interest in Non-Destructive Testing (NDT). While direct time integration is capable of considering multiple modes in a single analyses, it sheds little insight into modal interactions. A Semi-Analytic Finite Element (SAFE) computational approach [5] is adopted here that ameliorates the shortcomings of single mode and direct time integration analyses and provides information on the relative contribution of each mode. This approach, while computationally expensive, allows many “what if? ” questions to be posed that give insight into the sensitivity from variations, for example, in material properties and cylinder geometries. This understanding is a prerequisite for developing and understanding solutions to inverse problems, including the development of robust artificial intelligence that can automate the interpretation. To overcome the difficulties with computational expense, parallel computing techniques are applied, that are implemented on readily available personal and high performance micro-computers. Practical implementation difficulties, including vast storage requirements, numerical artifacts arising from the use of finite memory widths, and minimization of waiting times, are overcome by adopting appropriate computer science techniques. The ultimate feasibility and field applicability of ultrasonic inspection of structures using elastic waves depends upon a meaningful interpretation of measured data which can come only from knowledge of the physics of guided wave propagation and scattering that is presently unavailable. The approach presented here is a first step in this direction.

Inversely Found Elastic and Dimensional Properties

The ability to simultaneously measure a homogeneous, isotropic pipe’s elastic properties and wall thickness from its known mass density, outer diameter and the cut-off frequencies of three ultrasonic guided wave modes is demonstrated for a typical steel pipe. This inverse procedure is based upon simulated results computed by using an efficient Semi-Analytical Finite Element (SAFE) forward solver. The Young’s modulus, shear modulus, and wall thickness agree very well with those found from conventional but destructive experiments. On the other hand, Poisson ratios agree within their assessed uncertainties.

Wind Tunnel Studies on the Galloping of Lightly-Iced Transmission Lines

The aerodynamics involved in the galloping of lightly-iced transmission lines were studied in a series of wind tunnel experiments. A representative section of a lightly-iced conductor produced in an outdoor freezing rain simulator was used throughout. In the first set of experiments aerodynamic loads were measured on a static model at different wind speeds and angles of attack. These experiments showed that the well-established den Hartog criterion does not predict an instability at wind speeds associated with transmission line galloping. A second set of experiments examined the effects of different steady rotational motions on the aerodynamic loads. Automated controls were used to rotationally oscillate the model in a repeatable manner at various angles of attack and rotational amplitudes as well as frequencies. The drag remained consistent with quasi-steady values, while the lift was affected by the rotational motion. This rotation-induced lift was enhanced by ice surface irregularities, but further studies were needed to fully assess its importance.© 2010 ASME