The Experts below are selected from a list of 69 Experts worldwide ranked by ideXlab platform

V D Pellegrini - One of the best experts on this subject based on the ideXlab platform.

  • UNRELENTING THIGH PAIN IN THE WELL FIXED FEMUR: A Solution Option
    2018
    Co-Authors: V D Pellegrini
    Abstract:

    Conventional wisdom holds that aseptic failure of proximal ingrowth femoral stems should be addressed by revision to a longer femoral stem dependent upon more distal fixation. This is a reliable and time-honoured strategy with a high likelihood of success provided secure initial fixation of the revision stem is obtained. Yet, stems reliant upon more distal diaphyseal fixation are accompanied by a greater risk of physiologic thigh pain attributable to the differential in flexural stiffness of the femoral shaft compared with the prosthetic stem.Contemporary proximal ingrowth femoral stems have become the most popular device used in total hip arthroplasty and are traditionally reserved for primary procedures. Nevertheless, the flat tapered design offers a tight fit between the medial and lateral endosteal cortices of the femur, unimpeded by an increasing anteroposterior dimension of the stem, and provides a secure geometrical block to rotational movement of the stem. In instances when the primary stem is not...

  • UNRELENTING THIGH PAIN IN THE WELL FIXED FEMUR: A Solution Option
    Journal of Bone and Joint Surgery-british Volume, 2013
    Co-Authors: V D Pellegrini
    Abstract:

    Conventional wisdom holds that aseptic failure of proximal ingrowth femoral stems should be addressed by revision to a longer femoral stem dependent upon more distal fixation. This is a reliable and time-honoured strategy with a high likelihood of success provided secure initial fixation of the revision stem is obtained. Yet, stems reliant upon more distal diaphyseal fixation are accompanied by a greater risk of physiologic thigh pain attributable to the differential in flexural stiffness of the femoral shaft compared with the prosthetic stem. Contemporary proximal ingrowth femoral stems have become the most popular device used in total hip arthroplasty and are traditionally reserved for primary procedures. Nevertheless, the flat tapered design offers a tight fit between the medial and lateral endosteal cortices of the femur, unimpeded by an increasing anteroposterior dimension of the stem, and provides a secure geometrical block to rotational movement of the stem. In instances when the primary stem is not fit to the endosteal cortex on the anteroposterior radiograph, such as with the Corail or SROM devices, the opportunity may exist for revision with a flat tapered proximal ingrowth stem that is upsized to abut the endosteal femoral cortex. Such a strategy preserves the diaphyseal femur for subsequent revision in these typically young patients and avoids the issue of thigh pain in this active population. Likewise, revision of a well-fixed long stem that is associated with unrelenting thigh pain may be similarly accomplished by revision to a flat proximal ingrowth stem provided the integrity of the upper femur can be maintained during the revision. A prophylactic cerclage wire around the proximal femur is a helpful adjunct when using flat tapered proximal ingrowth stems in the revision setting.

S. David Stulberg - One of the best experts on this subject based on the ideXlab platform.

  • Dual mobility for chronic hip instability: a Solution Option.
    Orthopedics, 2010
    Co-Authors: S. David Stulberg
    Abstract:

    A dual-mobility acetabular component consists of a large, fixed, porous-coated acetabular component and a bipolar femoral component. These components are often called tripolar components. This configuration provides a stable, well-fixed implant platform against bone and 2 articular interfaces, a large polyethylene surface directly apposed to the highly polished metal shell, and a standard sized (28 mm, 32 mm) femoral head captured within polyethylene. The dual-mobility cup was designed to reduce the incidence of dislocations in patients at increased risk of instability (eg, patients undergoing revision). The cup appears to offer a safe, effective, durable Solution to hip instability. The concept has extensive laboratory and clinical support. Although the long-term durability of dual-mobility cups, particularly in young, active, large patients, is not known, the tested wear rates of the dual-mobility design with the current generation of highly cross-linked polyethylene are significantly lower than any previously reported wear rates. The recently released anatomic dual-mobility cup seeks to reduce the potential for iliopsoas impingement while retaining the stability and wear characteristics of the original dual-mobility design.

  • Dual Mobility for Chronic Instability: Solution Option
    Seminars in Arthroplasty, 2010
    Co-Authors: S. David Stulberg
    Abstract:

    The purpose of this paper is to: (1) define the concept of a dual mobility acetabular component; (2) present the clinical issue that a dual mobility cup seeks to address; and (3) review the clinical and laboratory data available on dual mobility acetabular components.

A. Unger - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear analysis using a modal-based reduction technique
    Composite Structures, 1995
    Co-Authors: D. Shalev, A. Unger
    Abstract:

    This paper presents a Solution to nonlinear formulated problems using eigenfunctions computed by a linear free vibration Solution. The system of equations is extremely reduced. The Solution is unique in its formulation as the governing equations represent the problem continuously and do not require an iterational or incremental Solution. Energy consideration is used and the Ritz method is applied to render the governing equations. The eigenfunctions are computed by a linear Solution Option of the F.E. code MSC/NASTRAN. Several numerical examples are presented and compared to Solutions from the literature.

D. Shalev - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear analysis using a modal-based reduction technique
    Composite Structures, 1995
    Co-Authors: D. Shalev, A. Unger
    Abstract:

    This paper presents a Solution to nonlinear formulated problems using eigenfunctions computed by a linear free vibration Solution. The system of equations is extremely reduced. The Solution is unique in its formulation as the governing equations represent the problem continuously and do not require an iterational or incremental Solution. Energy consideration is used and the Ritz method is applied to render the governing equations. The eigenfunctions are computed by a linear Solution Option of the F.E. code MSC/NASTRAN. Several numerical examples are presented and compared to Solutions from the literature.

Bhola Thapa - One of the best experts on this subject based on the ideXlab platform.

  • AN INVESTIGATION OF THE EFFECT OF PARTICLE SHAPE AND SIZE IN HYDRAULIC TURBINES
    2009
    Co-Authors: Hari Prasad Neopane, Ole Gunnar Dahlhaug, Bhola Thapa
    Abstract:

    Sediment erosion is caused by the dynamic action of sediment flowing along with water impacting against a solid surface. Hydraulic turbine components operating in sediment-laden water are subject to abrasive and erosive wear. This wear not only reduces the efficiency and the life of the turbine but also causes problems in operation and maintenance, which ultimately leads to economic losses. This is a global operation and maintenance problem of hydropower plants. The high sediment concentration combined with high percentage of quartz content in water causes severe damage to hydraulic turbine components. Withdrawal of clean water from the river for power production is expensive due to design, construction and operation of sediment settling basins. Even with the settling basins, 100 % removal of fine sediments is impossible and uneconomical. A number of factors can influence the process of sediment erosion damage in hydro turbine components. The erosion intensity depends on the sediment type and its characteristics (shape, size, hardness, concentration etc.), hydraulic design and operating conditions of turbine (flow rate, head, rotational speed, velocity, acceleration, turbulence, impingement angle etc.), and material used for the turbine components. All these factors are needed to be considered for predicting the erosion. Therefore, dealing with sediment erosion problems requires a multidisciplinary approach. More research and development is needed to investigate the relationship between the particle movement and erosion inside a turbine and to establish the operating strategy for the turbine operating in sediment-laden water. In order to achieve the main objective of this PhD study, the overall research methodology adopted for this work ‘sediment erosion in hydro turbines’ include; experimental studies, numerical simulation, and field studies. This research work is based on result from laboratory experiment, and numerical simulation. A previously made test rig (Thapa, 2004), was reviewed and modified to create a strong swirl flow in curved path. This flow was found similar to the flow between the guide vane outlet and the runner inlet of a Francis turbine. The flow in the guide vane cascade was simulated in order to verify the particle separation process and to investigate the relation of the velocity and the drag coefficient with different shape and size of the particle. There was a provision to introduce particles, with sizes ranging from 1 to 10 mm, and to observe the motion of the particles from Plexiglas windows located on the cover of the tank using a high-speed digital camera. When a particle is flowing in swirl flow, drag force and centrifugal force are two major forces influencing the particle equilibrium. The equilibrium of these two forces provides a critical diameter of the particle. While, a particle larger than the critical diameter move away from the centre and hit the wall, a particle smaller than the critical diameter flows along with the water, and ultimately sinks. For critical diameter, the particle continues to rotate in the turbine. Different shapes and sizes of particles were tested with the same operating conditions and found that triangularly shaped particles were more likely to hit the suction side of the guide vane cascade. Furthermore, this study supports the concept of separation of particles from streamlines inside the test rig, which led to the development of an operating strategy for a Francis turbine processing sediment-laden water. This study also permitted experimental verification of the size and the shape of a particle as it orbits in the turbine, until either the velocity components are changed or the particle became smaller. The steady state numerical simulations were carried out on the Cahua power plant Francis turbine design, mainly at two operating conditions with varying particle size, shape, and concentration using ANSYS CFX. The predictions of erosion, based on the Lagrangian calculation of particle paths in a viscous flow, are described for stay vanes, guide vanes, and runner vanes of a Francis turbine, for which the results of the field tests have been available for verification. The flow simulation was obtained through use of a commercially available computational fluids dynamics (CFD) code, namely ANSYS CFX. The code utilizes a finite-volume, multi-block approach to solve the governing equations of fluid motion numerically on a user-defined computational grid. The flow Solution procedure first generates the computational grid. A pre-processor is available in the software to perform this task. Second, the Solution Option such as inlet and boundary conditions, turbulence model, and discretization scheme, are specified. The final step is running the flow solver to generate the actual flow field simulation. Sediment erosion analysis of a Francis turbine gives an indication of relative erosion intensity and critical zones of erosion damage of the turbine components. The most realistic numerical prediction of erosion is found on a turbine blade. The highest velocities and accelerations occurred at outlet of the runner blade and more erosion was predicted especially at the pressure side of the blade outlet and at the lower cover. Furthermore, unexpected sediment erosion was found at the suction side of the guide vane where concept of critical diameter can be utilized. It has been concluded that if the particle size in the water is more than critical particle sizes, the turbine should not be operated at low guide vane opening. The numerically obtained erosion pattern and the field test observation and inspection at Cahua Francis turbine components are in good qualitative agreement. The encouraging agreement shows that, for this application, numerical simulation really can be used in a predictive manner. This information may serve as an input in an early stage of turbine design process to identify the regions where special surface treatment is necessary in order to increase the lifetime of the components for new hydropower projects involving risks of sediment erosion. The size of a particle is inversely proportional to the velocity of the particle, and it was determined that spherically shaped particles had higher settling velocities than particles with other shapes. However, non-spherical shape of the particles will tend to have lower settling velocities because both decreases in spheroid and increases in angularity tend to decrease velocities. Moreover, larger cross-sectional areas tend to be directed perpendicular to the transport path. As a result, higher coefficient of drag, higher rotational motion and more separation of flow are likely to occur and hence more erosion rate was predicted. The roles played by the shape of the particle significantly affect erosion rate prediction inside the Francis turbine components. Furthermore, it has been found that the erosion process is strongly dependent on the particle size, shape, concentration, and operating conditions of the turbine. The reduction of the erosion is not only linked to the reduction of particle velocity but also is linked to the reduction of separation of flow, which further depends on shape, size, and concentration of the particle. The significant reduction of erosion rate can be achieved by operating turbine at best efficiency point. The full load operation reduced efficiency, increased turbulence, and increased relative velocity of flow at outlet of the blades. The present knowledge and findings, although may not be enough to deal with this problem completely, can be utilised to achieve one major step forward in sediment erosion prediction and prevention.

  • ALTERNATIVE DESIGN OF A FRANCIS TURBINE FOR SAND LADEN WATER
    2007
    Co-Authors: Hari Prasad Neopane, Ole Gunnar Dahlhaug, Bhola Thapa
    Abstract:

    Sediment erosion is caused by the dynamic action of sediment flowing along with water impacting against a solid surface. Hydraulic turbine components operating in sediment-laden water are subject to abrasive and erosive wear. This wear not only reduces the efficiency and the life of the turbine but also causes problems in operation and maintenance, which ultimately leads to economic losses. This is a global operation and maintenance problem of hydropower plants. The high sediment concentration combined with high percentage of quartz content in water causes severe damage to hydraulic turbine components. Withdrawal of clean water from the river for power production is expensive due to design, construction and operation of sediment settling basins. Even with the settling basins, 100 % removal of fine sediments is impossible and uneconomical. A number of factors can influence the process of sediment erosion damage in hydro turbine components. The erosion intensity depends on the sediment type and its characteristics (shape, size, hardness, concentration etc.), hydraulic design and operating conditions of turbine (flow rate, head, rotational speed, velocity, acceleration, turbulence, impingement angle etc.), and material used for the turbine components. All these factors are needed to be considered for predicting the erosion. Therefore, dealing with sediment erosion problems requires a multidisciplinary approach. More research and development is needed to investigate the relationship between the particle movement and erosion inside a turbine and to establish the operating strategy for the turbine operating in sediment-laden water. In order to achieve the main objective of this PhD study, the overall research methodology adopted for this work ‘sediment erosion in hydro turbines’ include; experimental studies, numerical simulation, and field studies. This research work is based on result from laboratory experiment, and numerical simulation. A previously made test rig (Thapa, 2004), was reviewed and modified to create a strong swirl flow in curved path. This flow was found similar to the flow between the guide vane outlet and the runner inlet of a Francis turbine. The flow in the guide vane cascade was simulated in order to verify the particle separation process and to investigate the relation of the velocity and the drag coefficient with different shape and size of the particle. There was a provision to introduce particles, with sizes ranging from 1 to 10 mm, and to observe the motion of the particles from Plexiglas windows located on the cover of the tank using a high-speed digital camera. When a particle is flowing in swirl flow, drag force and centrifugal force are two major forces influencing the particle equilibrium. The equilibrium of these two forces provides a critical diameter of the particle. While, a particle larger than the critical diameter move away from the centre and hit the wall, a particle smaller than the critical diameter flows along with the water, and ultimately sinks. For critical diameter, the particle continues to rotate in the turbine. Different shapes and sizes of particles were tested with the same operating conditions and found that triangularly shaped particles were more likely to hit the suction side of the guide vane cascade. Furthermore, this study supports the concept of separation of particles from streamlines inside the test rig, which led to the development of an operating strategy for a Francis turbine processing sediment-laden water. This study also permitted experimental verification of the size and the shape of a particle as it orbits in the turbine, until either the velocity components are changed or the particle became smaller. The steady state numerical simulations were carried out on the Cahua power plant Francis turbine design, mainly at two operating conditions with varying particle size, shape, and concentration using ANSYS CFX. The predictions of erosion, based on the Lagrangian calculation of particle paths in a viscous flow, are described for stay vanes, guide vanes, and runner vanes of a Francis turbine, for which the results of the field tests have been available for verification. The flow simulation was obtained through use of a commercially available computational fluids dynamics (CFD) code, namely ANSYS CFX. The code utilizes a finite-volume, multi-block approach to solve the governing equations of fluid motion numerically on a user-defined computational grid. The flow Solution procedure first generates the computational grid. A pre-processor is available in the software to perform this task. Second, the Solution Option such as inlet and boundary conditions, turbulence model, and discretization scheme, are specified. The final step is running the flow solver to generate the actual flow field simulation. Sediment erosion analysis of a Francis turbine gives an indication of relative erosion intensity and critical zones of erosion damage of the turbine components. The most realistic numerical prediction of erosion is found on a turbine blade. The highest velocities and accelerations occurred at outlet of the runner blade and more erosion was predicted especially at the pressure side of the blade outlet and at the lower cover. Furthermore, unexpected sediment erosion was found at the suction side of the guide vane where concept of critical diameter can be utilized. It has been concluded that if the particle size in the water is more than critical particle sizes, the turbine should not be operated at low guide vane opening. The numerically obtained erosion pattern and the field test observation and inspection at Cahua Francis turbine components are in good qualitative agreement. The encouraging agreement shows that, for this application, numerical simulation really can be used in a predictive manner. This information may serve as an input in an early stage of turbine design process to identify the regions where special surface treatment is necessary in order to increase the lifetime of the components for new hydropower projects involving risks of sediment erosion. The size of a particle is inversely proportional to the velocity of the particle, and it was determined that spherically shaped particles had higher settling velocities than particles with other shapes. However, non-spherical shape of the particles will tend to have lower settling velocities because both decreases in spheroid and increases in angularity tend to decrease velocities. Moreover, larger cross-sectional areas tend to be directed perpendicular to the transport path. As a result, higher coefficient of drag, higher rotational motion and more separation of flow are likely to occur and hence more erosion rate was predicted. The roles played by the shape of the particle significantly affect erosion rate prediction inside the Francis turbine components. Furthermore, it has been found that the erosion process is strongly dependent on the particle size, shape, concentration, and operating conditions of the turbine. The reduction of the erosion is not only linked to the reduction of particle velocity but also is linked to the reduction of separation of flow, which further depends on shape, size, and concentration of the particle. The significant reduction of erosion rate can be achieved by operating turbine at best efficiency point. The full load operation reduced efficiency, increased turbulence, and increased relative velocity of flow at outlet of the blades. The present knowledge and findings, although may not be enough to deal with this problem completely, can be utilised to achieve one major step forward in sediment erosion prediction and prevention.