Roger Powell

Implicit state-estimation technique for water network monitoring

Abstract This paper presents a new implicit formulation of the standard weighted least squares (WLS) state-estimation problem for water networks with very low measurement redundancy. The formulation is based on the loop equations and the state variables are the unknown nodal demands. The minimisation problem is solved using a Lagrangian approach. It is shown that the method can be applied to weak demand indicators, such as property counts, rather than direct demand information which is often unreliable. Furthermore, a new leak detection scheme is derived from the method. This method is investigated under idealised noise-free conditions in order to demonstrate the principles and to gauge the potential of the scheme. The application of the scheme in more realistic circumstances of uncertainty is also discussed.

Calibration and comparison of chlorine decay models for a test water distribution system

This paper investigates the kinetics of monochloramine as disinfectant in a 1.3 km water pipe. A novel procedure for the correction of chlorine meter errors is introduced and applied. Parameter estimation using nonlinear optimisation procedures is used to identify decay coefficients for monochloramine models with a single coefficient or two coefficients as used in EPANET. Important difficulties in fitting these parameters which come about because of the model structure are highlighted. Finally, results of decay coefficients are presented and investigated for flow, inlet chlorine concentration and temperature dependence.

GRIDCC: real-time workflow system

The Grid is a concept which allows the sharing of resources between distributed communities, allowing each to progress towards potentially different goals. As adoption of the Grid increases so are the activities that people wish to conduct through it. The GRIDCC project is a European Union funded project addressing the issues of integrating instruments into the Grid. This increases the requirement of workflows and Quality of Service upon these workflows as many of these instruments have real-time requirements. In thispaper we present the workflow management service within the GRIDCC project which is tasked with optimising the workflows and ensuring that they meet the pre-defined QoS requirements specified upon them.

Constrained state estimation with applications in water distribution network monitoring

This paper investigates the effects of imposing bounds on the measurements used in weighted least-squares (WLS) state estimation. The active limits for such bounds are derived and algorithms based on linear and quadratic programming kernels are presented. Using the lower limit for the bounds, the constrained WLS scheme becomes an adaptive maximally constrained scheme: M-WLS. For some networks, the poor prior knowledge of the global error characteristic results in some measurements having less influence than would be expected from the local error characteristics of their transducers. By using M-WLS estimation, the influence of such measurements on state estimation may be improved. Analysis of the adaptive bounding of the scheme can also lead to identification of critical measurement discrepancies. For the purpose of illustration, results are presented using simulated measurements; the head measurements (pressures) are consistent with nominal demands (nodal flows) and the demand measurements are generated b...

A parametric model of biofilm shedding in a test water distribution system

Abstract This paper investigates particle counts as an indication of water quality in a 1.3 km water pipe. The observations from an extensive sampling schedule are used to develop a parametric model that describes the response of particle counts to a step increase of flow. The model is represented as a linear system with a biofilm shedding profile as input and a dynamic shear-off function as transfer function. The parameters of the shear-off function and the biofilm shedding profile (BSP) can both be identified. Results show that the net shear-off decreases with the introduction of monochloramine, that for an unchlorinated system shedding from the pipe walls is highest in the initial part of the system and that in the chlorinated system shear-off is highly non-uniform. The model gives insight into the underlying processes and the BSP provides a snapshot of the state of the system in terms of particle shear-off.

An Approach for Validation of Digital Anti-Forensic Evidence

ABSTRACT e-crime is increasing and e-criminals are becoming better at masking their activities. The task of forensic data analysis is becoming more difficult and a systematic approach towards evidence validation is necessary. With no standard validation framework, the skills and interpretation of forensic examiners are unchecked. Standard practices in forensics have emerged in recent years, but none has addressed the development of a model of valid digital evidence. Various security and forensic models exist, but they do not address the validity of the digital evidence collected. Research has addressed the issues of validation and verification of forensic software tools but failed to address the validation of forensic evidence. The forensic evidence collected using forensic software tools can be questioned using an anti-forensic approach. The research presented in this paper is not intended to question the skills of forensic examiners in using forensic software tools but rather to guide forensic examiners to look at evidence in an anti-forensic way. This paper proposes a formal procedure to validate evidence of computer crime.

A Generalized Reduced Gradient Approach to Expansion of Water Distribution Networks

The paper explores the use of the generalized reduced gradient method(GRG) in the design of expansion in water distribution networks. In the optimisation model, the objective function includes capital cost of pipelines and operating cost of pumping stations. The main constraints are a set of nonlinear hydraulic equations, upper and low bounds of diameters, and a minimum requirement of pressure head at all nodes. A modified Newton-Raphson technique is used in the hydraulic simulation to accelerate calculation and the convergence and consistency of the algorithm is investigated. An extension of the method that includes multiple demand loadings is also described.

Operational space control in hexapod robot for humanitarian demining applications

In this paper, we present an operational space inverse dynamics control law to control the motion of a six-legged robot for the humanitarian demining applications. The controller will ensure the tracking of a given centre of gravity (CoG) trajectory to keep it inside the supporting polygon formed by the stance legs. By achieving this, the balance of the body of the robot will be ensured. Additionally, the controller is capable to execute multiple tasks simultaneously. The control strategy consists of two stages. The first one is to generate a reference acceleration consistence with the robot dynamics. The second is to generate the torque that will give the desired acceleration in the task. We present a simulation on the robot that we designed in SolidWorks.

Continuous landmines scanning using legged robot with manipulator arm over rough terrain

In this paper, we introduce a new scanning technique for detecting landmines and unexploded ordnance (UXO). The manipulator arm carried by a hexapod robot is capable of scanning rough terrain using a typical mine detector. To speed up the landmine detection and marking, both scanning and moving forward will be done simultaneously. The controller will perform two tasks. The first task is to keep the sensor-head in a fixed level with respect to the ground and the second task is to keep the base of the arm within a specified range of position and orientation. A coupling between the velocity of the end-effector and the velocity of the manipulator base (robot body) is created to ensure the efficiency of the whole process. To verify the feasibility of our design, three experiments will be performed using simulation in MATLAB. The manipulator was modelled using SolidWorks.

Quadratic programming for inverse kinematics control of a hexapod robot with inequality constraints

In this paper, we present an inverse kinematics control law to control the motion of a six-legged robot intended for use in humanitarian demining. We exploit a Quadratic programming (QP) method to resolve the constrained kinematic redundancy problem and we include both inequality and equality constraints such as joint rate and joint angle limits. The problem of redundancy resolution is considered at the inverse differential kinematics level. Task prioritization for the hexapod robot with sensor head has been used to address the issue of robot balance, walking and manipulator motion. This work describes the whole-body control framework, based on task prioritization with inequality constrained QP applied at different levels. The algorithm has been tested on a three degrees of freedom leg as part of a six legged robot with sensor head carrier arm. We present a simulation on the robot using MatLab.