Mohamed S. Gadala

A three-dimensional finite element model of the cervical spine with spinal cord: an investigation of three injury mechanisms.

The spinal cord may be injured through various spinal column injury patterns (e.g., burst fracture, fracture dislocation); however, the relationship between column injury pattern and cord damage is not well understood. A three-dimensional finite element model of a human cervical spine and spinal cord segment was developed, verified using published experimental data, and used to investigate differences in cord strain distributions during various column injury patterns. For a transverse contusion injury, as would occur in a burst fracture, a 33% canal occlusion resulted in two peaks of strain between the indentor and opposing vertebral body and intermediate peak strain values. For a distraction injury, relevant to column distortion injuries, a 2.6 mm axial displacement to the cord resulted in more uniform strains throughout the cord and low peak strain values. For a dislocation injury, as would occur in a fracture dislocation, an anterior displacement of C5 corresponding to 30% of the sagittal dimension of the vertebral body resulted in high peak strain values adjacent to the shearing vertebrae and increased strains in the lateral columns compared to contusion. This model includes more anatomical details compared to previous studies and provides a baseline for mechanical comparisons in spinal cord injury.

A Modified Sequential Particle Swarm Optimization Algorithm with Future Time Data for Solving Transient Inverse Heat Conduction Problems

The particle swarm optimization (PSO) method is modified and employed to solve the inverse heat conduction problem. Since the main drawback of PSO in solving inverse problems is its slow convergence, most of the modifications in this research are aimed at overcoming this downside. A sequential implementation and a multi-criteria optimization formulation are designed to accelerate the convergence in transient multi-sensor applications. The concept of future time steps is used to make the PSO-based inverse analyzer more stable in dealing with measurement noise. All these modifications are found to be effective in improving the behavior of the algorithm.

An FE‐based sequential inverse algorithm for heat flux calculation during impingement water cooling

Purpose – To develop an effective and reliable procedure for the calculation of heat fluxes from the measured temperatures in experimental tests of impingement water cooling.Design/methodology/approach – An inverse heat transfer analysis procedure is developed and implemented into a 2D finite element program. In this method, the least‐squares technique, sequential function specification and regularization are used. Simplifications in the sensitivity matrix calculation and iterative procedures are introduced. The triangular and impulse‐like profiles of heat fluxes simulating practical conditions of impingement water cooling are used to investigate the accuracy and stability of the proposed inverse procedure. The developed program is then used to determine the heat flux during impingement water cooling.Findings – A hybrid procedure is developed in which inverse calculations are conducted with a computation window. This procedure may be used as a whole time domain method or become a periodically sequential o...

Investigation of Error Sources in Temperature Measurement Using Thermocouples in Water Impingement Cooling

The reliability of thermocouples with separation measuring junction in temperature measurement in the cooling process of hot steel plates with impingement jet has been investigated using direct and inverse finite element analysis (FEA). It is concluded that while the attachment of thermocouple wires on surface has negligible influence on surface temperature distribution during air cooling, the conduction of wires in a jet impingement water cooling process has significant effect on the measured temperature. The disturbance of the temperature field due to the introduction of a small hole for the installation of internal thermocouple has also been studied and showed similar but less pronounced effects to those of the surface measurement. An increased distortion of the temperature field is evident when the thermocouple is attached on the top surface directly above the bottom surface of hole.

Boiling Heat Transfer of Multiple Impinging Jets on a Hot Moving Plate

In this research, boiling heat transfer on a hot moving plate caused by multiple impinging water jets in multiple jet rows is studied. An inverse heat conduction code is developed to analyze the readings of thermocouples that are implemented inside the plate in order to find the surface values of temperature and heat flux. Effects of nozzle stagger, plate velocity, and jet line spacing are studied. Nozzle stagger is found to affect the uniformity of heat transfer across the width of the plate. Jet line spacing can affect the heat transfer between two adjacent jet rows. Plate speed is important only in the higher entry temperatures and in the impingement zone.

Hydrodynamic and Thermal Behavior of Journal Bearings using Upwind Petrov-Galerkin FEM

A novel approach to modeling plain journal bearings is presented. The journal is assumed to be cut open at the oil supply groove and modeled in Cartesian coordinates. The streamline upwind Petrov-Galerkin (SUPG) finite element method is used to develop the three-dimensional model. The model is validated using Boncompain, Costa, and Dowsons experimental data and compared to Khonsaris analytical method. The maximum deviation from the measured temperatures is 10 per cent for Costas data and the predictions of 51.2°C from the model are 0.3°C lower than Dowsons experimentally measured peak temperature. The model shows rapid convergence, stabilizing in only three iterations. The cavitation interface thermal boundary conditions need not be specified. Side leakage predictions are within 2.8 percent of the measured value whereas Martins analytical method achieves an accuracy of 11.2 percent.

Unsteady CFD Simulation for High Speed Centrifugal Compressor Operating Near Surge

Centrifugal compressor surge and stall are an instabilities flow and system phenomenon, which can lead to a loss of engine power, large pressure transients and, in some cases, failure of the compressor and bearing system. Three-dimensional, compressible, unsteady Navier-Stokes equations are solved, using the sliding mesh at the interface between the moving and stationary parts. The investigated computational domain is composed of inlet pipe, inlet bell, impeller followed by a diffuser. The impeller side cavities are included in the computational domain, to make the simulation more close to the actual case. The present article focuses on the unsteady pressure and velocity results within the impeller and diffuser, at an operating condition close to the surge of the compressor. The computational data compares favorably with the measured data, from literature, for the same compressor and operational point. The pressure fluctuation results are analyzed for the surge and design operating conditions. Through the acquisition of both velocity and transient pressure data, the time evaluation of the unsteady flow during surge is revealed.Copyright

Three-Dimensional Modeling of Thermohydrodynamic Lubrication in Slider Bearings Using Streamline Upwind Petrov-Galerkin Method

A three-dimensional thermohydrodynamic lubrication model which couples the Reynolds and energy equations is developed in the finite-element program Sepran. The model uses the streamline upwind Petrov-Galerkin method. Model results indicate the peak temperature is not on the mid-plane surface. This position shifts toward the mid-plane as the width-to-length ratio is reduced from 10 to 1 as well as when pressure boundary conditions are altered in such a way that the inlet/outlet pressure is higher than the side pressure. The adiabatic temperature profiles of an infinite slider and a square slider are compared. The wider slider shows a higher peak temperature. The side flow plays a major role in determining the value and position of the peak temperature. Model results also indicate peak side flow at a width-to-length ratio of 2.

Rolling element bearing fault diagnostics using acoustic emission technique and advanced signal processing

Acoustic emission (AE) signal generated from defects in rolling element bearings are investigated using simulated defects and experimental measurements in this paper. Rolling element bearings are crucial parts of many machines and there has been an increasing demand to find effective and reliable health monitoring technique and advanced signal processing to detect and diagnose the size and location of incipient defects. Condition monitoring of rolling element bearings comprises four main stages, which are, statistical analysis, faults diagnostics, defect size calculation, and prognostics. A modified and effective signal processing algorithm is designed to diagnose localized defects on rolling element bearing components under different operating speeds, loadings, and defect sizes. The algorithm is based on optimizing the ratio of Kurtosis and Shannon entropy to obtain the optimal band pass filter utilizing wavelet packet transform (WPT) and envelope detection. Results show the superiority of the developed algorithm and its effectiveness in extracting bearing characteristic frequencies from the raw acoustic emission signals masked by the background noise under different operating conditions.

Study on the 2-D Simulation of the Cooling Process of Steel Strips on a Run-Out Table

The cooling process of steel strips on the run-out table (ROT) is simulated using 2-D modelings. The effect of nonuniform heat flux in the width direction on the coiling temperature is investigated using transverse 2-D modeling. The coiling temperature difference may be up to 20°C when there is a 15% HTC difference across the width. In the 2-D longitudinal simulations, a time-space shift scheme is developed and used to specify the heat transfer conditions on ROT. It is found that the longitudinal heat transfer is fairly localized and concentrated around the entrance and exit of the impingement zones. It is also found that the temperature differences between 1-D and 2-D modeling are, generally, less than 3°C. These 2-D simulation results suggest that the 2-D modeling may have a modest impact on the accuracy of prediction of coiling temperature of steel strips during the ROT cooling process.