Constant Radial Force Research Articles

Analysis of Ship Propulsion Shafting Vibration Using Coupled Torsional-Bending Model

The paper describes a coupled torsional-bending model of ship propulsion system vibrations. The developed model is based on the modified model of the Jeffcott rotor. In order to test the model and determine the coupled torsional-bending vibrations, several cases were analyzed. First, a reference case corresponding to a fully axisymmetric ship propulsion system is set up. Then, the influence of the constant radial force in the vertical direction at the position of the stern bearing was analyzed, such as the conditions of navigation of the ship at calm sea under partial or fully loaded hull. Finally, the case of sailing on rough sea is analyzed, when the propeller racing occurs due to the stern lifting out of the sea. For simplicity, the harmonic law of amplitude changing of the vertical radial force on the stern tube bearing as well as of the propeller load was adopted. Based on the results of numerical analysis, it was found that the proposed model well describes the case of coupling of torsional and bending vibrations of the propulsion system.

The effect of coupled lateral and torsional vibrations of an unbalanced Jeffcott rotor supported by roller bearings

In this paper, an unbalanced Jeffcott rotor supported by the roller bearings is modelled, and the dynamic differential equations are obtained by the Lagrange’s equations. The fourth order Runge–Kutta method is employed to simulate this system in two cases. Simulation results show the combined effect of the coupled lateral and torsional vibrations and the variable compliance vibration of the rotor. In the case of that only a large and constant radial force is applied, the sum and difference between variable compliance and rotational frequency components of the torsional vibrations of the disk are induced because of the roller bearings’ rotation. And when they are near to the natural frequency of the torsional vibration, the resonance peaks appear. In the case of that a large and constant radial force and a harmonic torque are simultaneously applied, the two components, the sum and difference between rotational frequency and the frequency of the external torque, of the lateral vibrations of the disk are induced. When the frequency of the external harmonic torque approximatively equal to a special value, the two frequency band lines, variable compliance and the sum of rotational frequency and the frequency of external torque, intersect near the natural frequency of the lateral vibration, and the vibration may aggravate.

TCT-394 Impact of inadequate angiographic results after pre-dilatation on clinical outcomes following drug-coated balloon treatment for in-stent restenosis

Drug-coated balloons (DCBs) have emerged as a treatment for in-stent restenosis (ISR); however, due to the lack of a permanent metallic cage and constant radial force, outcomes may be affected by the results of pre-dilatation. The purpose of this study was to investigate clinical outcomes following

Burnishing tool actuators and their influence on the burnishing force components

The article presents the results of studies on measuring components of force of diamond burnishing of surfaces with variable radius of curvature. The impact of structural elements of burnishing tools of different types on components of burnishing force was analyzed. The impact of different actuators of burnishing tools on components of burnishing force was analyzed. The design of the burnishing tool with an air receiver (bellows with compressed air as an actuator) with a parallelogram-type mounting of the indenter on the four flat posts, which ensures burnishing of profiled and other types of surfaces with constant radial force, was proposed.

Experimental evaluation of stent retrievers’ mechanical properties and effectiveness

BackgroundFive randomized controlled trials recently appeared in the literature demonstrating that early mechanical thrombectomy in patients with acute ischemic stroke is significantly related to an improved outcome. Stent retrievers are...

Rindler modified Schwarzschild geodesics

The mysterious attractive constant radial force acted in the past on Pioneer spacecrafts - the so-called Pioneer anomaly - is considered within the context of Rindler acceleration. As an idea this is tempting since it is reminiscent of the cosmological constant. Fortunately the anomalous force acts radially toward the sun so that it differs from the mission of a cosmological constant. Without resorting to the physical source responsible for such a term we investigate the modified Schwarzschild geodesics. The Rindler acceleration naturally affects all massive / massless particle orbits. Stable orbits may turn unstable and vice versa with a finely-tuned acceleration parameter. The overall role of the extra term, given its attractive feature is to provide confinement in the radial geodesics.

An Adolescent Patient with Coarctation of Aorta Treated with Self-Expandable Nitinol Stent

Transcatheter treatment of aortic coarctation, with balloon angioplasty or stent implantation, is now an acceptable alternative to surgical repair. However these procedures may result in complications, such as vascular wall injury and re-stenosis of the lesion. A nitinol self-expandable stent, when deployed at the coarctation site, produces low constant radial force, which may result in a gradual widening of the stenotic lesion leaving less tissue injury ('stretching rather than tearing'). For an adolescent with a native aortic coarctation, a self-expandable stent of 20 mm diameter was inserted at the discrete stenotic lesion of 5 mm diameter without previous balloon dilatation procedure. No further balloon dilatation was done immediately after the stent insertion. With the self-expandable stent only, the stenosis of the lesion was partially relieved immediately after the stent deployment. Over several months after the stent insertion, gradual further widening of the stent waist to an acceptable dimension was observed.

Self-Expanding Stent and Delivery System for Aortic Valve Replacement

Currently, aortic valve replacement procedures require a sternotomy and use of cardiopulmonary bypass (CPB) to arrest the heart and provide a bloodless field in which to operate. A less invasive alternative to open heart surgery is transapical or transcatheter aortic valve replacement (TAVR), already emerging as a feasible treatment for patients with high surgical risk. The bioprosthetic valves are delivered via catheters using transarterial or transapical approaches and are implanted within diseased aortic valves. This paper reports the development of a new self-expanding stent for minimally invasive aortic valve replacement and its delivery device for the transapical approach under real-time magnetic resonance imaging (MRI) guidance. Made of nitinol, the new stent is designed to implant and embed a commercially available bioprosthetic aortic valve in aortic root. An MRI passive marker was affixed onto the stent and an MRI active marker to the delivery device. These capabilities were tested in ex vivo and in vivo experiments. Radial resistive force, chronic outward force, and the integrity of bioprosthesis on stent were measured through custom design dedicated test equipment. In vivo experimental evaluation was done using a porcine large animal model. Both ex vivo and in vivo experiment results indicate that the self-expanding stent provides adequate reinforcement of the bioprosthetic aortic valve and it is easier to implant the valve in the correct position. The orientation and positioning of the implanted valve is more precise and predictable with the help of the passive marker on stent and the active marker on delivery device. The new self-expanding nitinol stent was designed to exert a constant radial force and, therefore, a better fixation of the prosthesis in the aorta, which would result in better preservation of long-term heart function. The passive marker affixed on the stent and active marker embedded in the delivery devices helps to achieve precise orientation and positioning of the stent under MRI guidance. The design allows the stent to be retracted in the delivery device with a snaring catheter if necessary. Histopathology reports reveal that the stent is biocompatible and fully functional. All the stented bioprosthesis appeared to be properly seated in the aortic root.

ROBERT HOOKE'S THREE-BODY PROBLEM

During the winter 1679, R. Hooke challenged I. Newton to predict the dynamics of an object submitted to a constant radial force. This correspondence made a strong impact on I. Newton, who wrote four years later "De Motu", the real ancestor of "The Principia", published in 1687. R. Hooke's problem can be physically linked to the dynamics of a sphere sliding on an inverted cone due to gravitational effects. If the symmetry axis of the cone is parallel to the gravitational field, the ball executes stable precessions. Breaking this symmetry induces the appearance of chaotic motions. After having derived the equations related to the position of the sphere, we analyze its dynamics, and we perform an approximated Floquet analysis that is compared to our numerical results.

Generating surface of a tool for shaping the internal surface of the shaft in a low-pressure turbine

Continuous shaping of the internal surfaces of a shaft in a low-pressure turbine by a single contacting working roller is considered, on the basis of semifree strip grinding with constant radial force, in the absence of a servo system. Formulas for semifree grinding that permit the determination of the basic parameters corresponding to the product specifications are established.

Analytical Solution of Direct Dynamics Problem in Cylindrical Coordinates

In this study, the analytical solution of the direct dynamics problem that mostly requires some numerical techniques is developed for two important cases. In the first case, two coupled differential equations of the motion of a particle acted upon by the constant radial force \IF\N\Dr\N and tangential force \IF\Nθ are solved. The analytical solution for the case of variable radial force \IF\N\Dr\N = -\Ikr\N and the constant tangential force \IF\Nθ is considered as a second stage. The present method is applied to some practical engineering problems.

“Snapping” Torsional Response of an Anisotropic Radially Loaded Rotor

A rotor system with two orthogonal lateral and two angular (torsional) degrees of freedom is considered. The rotor has asymmetry of the lateral stiffness and is laterally loaded with a constant radial force and a rotating unbalance. Constant driving and load torques are applied to the rotor. The important part of the research includes an analysis of “snapping” action, when, during rotation, the rotor experiences a peak of torsional acceleration. This occurs when the “strong stiffness” axis of the anisotropic rotor passes under the axis of the sideload. The numerical simulation of the analytical model exhibits a snapping (accelerated) torsional response of the rotor at twice synchronous frequency (2×), and it is especially pronounced at 1× and 2× torsional resonances. The snapping response can initiate a rotor crack in the area of stress concentration, can stimulate existing crack propagation, and can be a cause of the coupling failure. The analytical results are obtained by the Averaging Method application. They confirm the numerical results and show the possibility of combination resonance occurrences. The synchronous dynamic stiffness for the frequency range around 1× lateral resonance is analytically obtained. The specific shape of the quadrature dynamic stiffness component can serve as a shaft crack indicator and can be used for early detection of a lateral crack on the rotor.

Optimization of Hybrid Gas Lubricated Conical Bearings

The motion of a short symmetrical rotor without loading by a constant radial force is described. The rotor under consideration is mounted in two hybrid conical gas lubricated bearings. It is assumed that the symmetric bearing's foundation is supported by flexible damped elements. An optimum angle of conical gas bearings which gives the maximum stability of the motion of the rotor with respect to the self-excited, cylindrical vibrations is sought. For this purpose a linear method of analysis is used. The optimum angle of the conical bearing is established for a certain family of conical gas films. The conditions of its existence in terms of parameters describing properties of the gas films and of the characteristic parameters of flexible damped elements is found. Finally, the existence of an optimum stiffness of elastic elements of support with respect to the creation of self-excited whirl vibrations of the rotor and foundation is proved.