ALE stress update for transient and quasistatic processes

A key issue in Arbitrary Lagrangian–Eulerian (ALE) non-linear solid mechanics is the correct treatment of the convection terms in the constitutive equation. These convection terms, which reflect the relative motion between the finite element mesh and the material, are found for both transient and quasistatic ALE analyses. It is shown in this paper that the same explicit algorithms can be employed to handle the convection terms of the constitutive equation for both types of analyses. The most attractive consequence of this fact is that a quasistatic simulation can be upgraded from Updated Lagrangian (UL) to ALE without significant extra computational cost. These ideas are illustrated by means of two numerical examples. © 1998 John Wiley & Sons, Ltd.     

A Workcell for the Development of Robot-Assisted Surgical Procedures

This paper describes a robotic workstation for the development of new robot-assisted surgical procedures. This work is motivated by the difficulties and cost associated to the development of surgical robots, often requiring large investments and several re-designs which limit wider use of this technology. The approach presented here consists of using a general purpose robotic workcell to develop the hardware and the surgical aspects of new robot-based surgical systems, before committing to a completely new system design. The workcell is based on a clean room PUMA 260 manipulator, suitably enhanced to expand and improve its capabilities, and on a vision-based operator interface. Two new robot-assisted surgical procedures have been developed and tested using this set-up: percutaneous discectomy and knee osteoctomy. By using the robotic workcell, engineers and surgeons are able to define many aspects of the two procedures, such as surgical gestures, workspace of the robot, and calibration procedures, without incurring a large, up-front investment. First, the article describes the configuration of the workcell, the enhancements to the PUMA manipulator and the surgical procedures developed with this setup. Then the results of the tests and the lessons learned using the workcell are discussed in some detail.     

A New Multilevel Conversion Structure for Grid-Connected PV Applications

A novel scheme for three-phase grid-connected photovoltaic (PV) generation systems is presented in this paper. The scheme is based on two insulated strings of PV panels, each one feeding the dc bus of a standard two-level three-phase voltage-source inverter (VSI). The inverters are connected to the grid by a three-phase transformer having open-end windings on the inverter side. The resulting conversion structure performs as a multilevel power active filter (equivalent to a three-level inverter), doubling the power capability of a single VSI with given voltage and current ratings. The multilevel voltage waveforms are generated by an improved space-vector-modulation algorithm, suitable for the implementation in industrial digital signal processors. An original control method has been introduced to regulate the dc-link voltages of each VSI, according to the voltage reference given by a single maximum power point tracking controller. The proposed regulation system has been verified by numerical simulations and experimental tests with reference to different operating conditions.     

Implementation of a direct control algorithm for induction motorsbased on discrete space vector modulation

The basic concept of direct torque control of induction machines is investigated in order to emphasize the effects produced by a given voltage vector on stator flux and torque variations. The low number of voltage vectors which can be applied to the machine using the basic DTC scheme may cause undesired torque and current ripple. An improvement of the drive performance can be obtained using a new DTC algorithm based on the application of the space vector modulation (SVM) for prefixed time intervals. In this way a sort of discrete space vector modulation (DSVM) is introduced. Numerical simulations and experimental tests have been carried out to validate the proposed method     

Binary spatial partitioning of the central‐difference time integration scheme for explicit fast transient dynamics

This paper proposes a generalization of the explicit central‐difference time integration scheme, using a time step variable not only in time but also in space. The solution at each element/node is advanced in time following local rather than global stability limitations. This allows substantial saving of computer time in realistic applications with non‐uniform meshes, especially in multi‐field problems like fluid–structure interactions. A binary scheme in space is used: time steps are not completely arbitrary, but stay in a constant ratio of two when passing from one partition level to the next one. This choice greatly facilitates implementation (via an integer‐based logic), ensures inherent synchronization and avoids any interpolations, necessary in other partitioning schemes in the literature, but which may reduce numerical stability. The mesh partition is automatically built up and continuously updated by simple spatial adjacency considerations. The resulting algorithm deals automatically with large variations in time of stability limits. The paper introduces the core spatial partitioning technique in the Lagrangian formulation. Some academic numerical examples allow a detailed comparison with the standard, spatially uniform algorithm. A final more realistic example shows the application of partitioning in simulations with arbitrary Lagrangian Eulerian formulation and fully‐coupled boundary conditions (fluid–structure interaction). Copyright © 2008 John Wiley & Sons, Ltd.     

Complications and surgical indications in 144 cases of nonmetastatic osteosarcoma of the extremities treated with neoadjuvant chemotherapy

From September 1986 to December 1989, 144 patients with osteosarcoma of the extremities were treated with combined surgery and neoadjuvant chemotherapy. The disease-free survival was 79% for good responders (necrosis greater than 90%) and 72% for poor responders (necrosis less than 90%), and the local recurrence rate was low. Improvement in long-term prognosis and the increase of limb-sparing surgery determine a higher rate of immediate and late complications. Most of the complications were observed in limb-salvage procedures; 63% of these procedures presented one or more complications. In nine rotationsplasties, there were four complications, and in 13 amputations no complications were observed. Therefore, 55% of patients were affected by surgical complications. Twenty-eight complications were considered minor (not requiring surgery), whereas 77 complications were major. Functional results, evaluated according to Enneking's new system, were higher than 50% in two thirds of the limb-salvage procedures. Complications in limb-salvage procedures are more influenced by the type of reconstruction than by the surgical procedure used. Probably the most troublesome consequence of surgical complications in osteosarcoma is the deviation or delay in administering postoperative chemotherapy, which jeopardizes survival.     

Strengthening of Brick Masonry Arches with Externally Bonded Steel Reinforced Composites

The objective of this study is to investigate the efficiency of an innovative technique for strengthening masonry arches, based on the use of high strength steel cords embedded in either an epoxy (steel reinforced polymer) or mortar matrix (steel reinforced grout). Ten prototypes of brickwork arches strengthened by composite laminates were tested under a monotonic vertical load applied at the quarter-span. Load tests were performed to compare the behavior up to collapse of strengthened masonry arches; the influence of the types of reinforcement (steel and carbon fibers) and matrices (epoxy and cementitious), as well as location of the strengthening layer (intrados, extrados, and both) and the presence of anchorage systems has been investigated. The experimental results highlight the enhanced strength of the arches reinforced with steel cords, as well as the role of the mechanical anchoring with regard to the resulting final strength.     

Steady-state and transient performance evaluation of a DTC schemein the low speed range

In this paper, a direct flux and torque control scheme for industrial application is analyzed in order to emphasis the drive performance at standstill and in the low speed range. The control strategy utilizes the torque and rotor flux commands to determine the reference value of the stator flux. In order to improve the low speed performance a closed loop estimator is employed to evaluate the rotor flux. The validity of the control scheme is verified by simulations and experimental tests of an induction motor drive system