Optimisation of helical geometry of inspection probe for steam generator tubes of the PFBR

The steam generator (SG) tubes of the prototype fast breeder reactor (PFBR) located in Kalpakkam, India, need to be periodically inspected using the remote field eddy current (RFEC) technique. During the pre-service inspection of the SG tubes, it was found that the RFEC probes experienced frequent mechanical breakages. To avoid these failures, changes in the existing structural design of the RFEC probe were required. A helical groove design was proposed to obtain a smooth transition in the variation of stress across the probe during the inspection. It was difficult to calculate the flexural stiffness of the proposed helical geometry probe due to the varying cross-section along its length. In this paper, the smearing approach adopted to calculate the stiffness of the RFEC probe and the sensitivity analysis carried out to determine the optimal design of the probe are discussed. A probe was fabricated based on the helical groove design and tested to qualify its suitability for the SG inspection. The RFEC probe with helical grooves was employed for the pre-service inspection of the SG tubes of the PFBR. More than 200 tubes have been inspected using the proposed design and no mechanical failure of the probe has been observed.

Computer support for the shape formation of helical surfaces with a disk tool

An analytical description of the process of making helical surfaces with a disk tool with a substantiated definition of the objective function is proposed. By analogy with coordinate metrology, it is proposed to adopt a minimum tolerance zone as an objective function. This allows to specify the required solution error and eliminates the need to use normal lines or tangents to the profiles. An example of calculating the profile of a helical groove of a twotoothed end mill, performed with an error of 0.05 mm is presented. Keywords: helical surface, disk tool, computer support, optimization, minimum tolerance. [email protected]

Properties of Oligomeric Interaction of the Cytomegalovirus Core Nuclear Egress Complex (NEC) and Its Sensitivity to an NEC Inhibitory Small Molecule

Herpesviral nuclear egress is a regulated process shared by all family members, ensuring the efficient cytoplasmic release of viral capsids. In the case of human cytomegalovirus (HCMV), the core of the nuclear egress complex (NEC) consists of the pUL50-pUL53 heterodimer that builds hexameric lattices for capsid binding and multicomponent interaction, including NEC-associated host factors. A characteristic feature of NEC interaction is the N-terminal hook structure of pUL53 that binds to an alpha-helical groove of pUL50, thus termed as hook-into-groove interaction. This central regulatory element is essential for viral replication and shows structural–functional conservation, which has been postulated as a next-generation target of antiviral strategies. However, a solid validation of this concept has been missing. In the present study, we focused on the properties of oligomeric HCMV core NEC interaction and the antiviral activity of specifically targeted prototype inhibitors. Our data suggest the following: (i) transiently expressed, variably tagged versions of HCMV NEC proteins exert hook-into-groove complexes, putatively in oligomeric assemblies that are distinguishable from heterodimers, as shown by in vitro assembly and coimmunoprecipitation approaches; (ii) this postulated oligomeric binding pattern was further supported by the use of a pUL50::pUL53 fusion construct also showing a pronounced multi-interaction potency; (iii) using confocal imaging cellular NEC-associated proteins were found partly colocalized with the tagged core NECs; (iv) a small inhibitory molecule, recently identified by an in vitro binding inhibition assay, was likewise active in blocking pUL50–pUL53 oligomeric assembly and in exerting antiviral activity in HCMV-infected fibroblasts. In summary, the findings refine the previous concept of HCMV core NEC formation and nominate this drug-accessible complex as a validated antiviral drug target.

Automated calculation of the profile of a disk cutter for the manufacture of helical grooves

The calculation of the profile of disk cutters, excluding undercutting for any complex profile of the helical groove, is proposed. The feature of the method is in the fact that the profile is specified by a small number of control points, which, using interpolation, is increased by tens or hundreds of times. The rational profile of the cutter is investigated depending on its three setting parameters. A numerical experiment was carried out for the profile of the cutter with the optimization of the setting parameters. Keywords: disk cutter, profile, helical groove, computer-aided design, calculation [email protected]

Static and Rotordynamic Characteristics for Two Types of Novel Mixed Liquid Damper Seals With Hole-Pattern/Pocket-Textured Stator and Helically Grooved Rotor

Noncontacting liquid annular seals, such as helical groove seals, are widely used at the impeller interstage and shaft end in the liquid turbomachinery to reduce the fluid leakage and stabilize the rotor-bearing system. However, previous literatures have expounded that the helical groove seal possesses the poor sealing property at low rotational speed condition and suffers the rotor instability problem inducing by negative stiffness and damping, which is undesirable for the liquid turbomachinery. In this paper, to obtain the high sealing performance and the reliable rotordynamic capability throughout full operational conditions of machines, two novel mixed liquid damper seals, which possess a hole-pattern/pocket-textured stator matching with a helically grooved rotor, were designed and assessed for the balance piston location in a multiple-stage high-pressure centrifugal liquid pump. To assess the static and rotordynamic characteristics of these two types of mixed liquid damper seals, a three-dimensional (3D) steady computational fluid dynamics (CFD)-based method with the multiple reference frame theory was used to predict the seal leakage and drag power loss. Moreover, a novel 3D transient CFD-based perturbation method, based on the multifrequency one-dimensional stator whirling model, the multiple reference frame theory, and the mesh deformation technique, was proposed for the predictions of liquid seal rotordynamic characteristics. The reliability and accuracy of the present numerical methods were demonstrated based on the published experiment data of leakage and rotordynamic force coefficients of a helical groove liquid annular seal and a hole-pattern liquid annular seal. The leakage and rotordynamic force coefficients of these two mixed liquid damper seals were presented at five rotational speeds (0.5 krpm, 2.0 krpm, 4.0 krpm, 6.0 krpm, and 8.0 kpm) with large pressure drop of 25 MPa, and compared with three types of conventional helical groove seals (helical grooves on rotor, stator or both), two typical damper seals (hole-pattern seal, pocket damper seal with smooth rotor), and a mixed helical groove seal. Numerical results show that two novel mixed liquid damper seals both possess generally better sealing capacity than the conventional helical groove seals, especially at lower rotational speeds. The circumferentially isolated cavities (hole/pocket types) on the stator can enhance the “pumping effect” of the helical grooves for mixed helical groove seals, by weakening the swirl flow in seal clearance (which results in the increase of the fluid velocity gradient near the helically grooved rotor). What is more, the helical grooves on rotor also strengthen the dissipation of fluid kinetic energy in the isolated cavities, so the mixed liquid damper seals offer less leakage. Although the mixed liquid damper seals possess a slightly larger (less than 40%) drag power loss, it is acceptable in consideration of the reduced (∼60%) leakage for the high-power turbomachinery, such as the multiple-stage high-pressure centrifugal liquid pump. The present novel mixed liquid damper seals have pronounced rotordynamic stability advantages over the conventional helical groove seals, due to the obviously larger positive stiffness and damping. The mixed liquid damper seal with the hole-pattern stator and the helically grooved rotor (HPS/GR) possesses the lowest leakage and the largest effective damping, especially for higher rotational speeds. From the viewpoint of sealing capacity and rotor stability, the present two novel mixed liquid damper seals have the potential to become the attractive alternative seal designs for the future liquid turbomachinery.

Definition of setting total error value at centerless ball grinding

There is defined a total basing error arising during centerless ball grinding using driving disk helical grooves with different forms. On the basis of computations there is offered a design of a driving disk with the trapezoidal helical groove. A design of a supporting knife which allows carrying out efficiently an automatic position correction of the measuring base of operation size during ball grinding is offered.

THE MECHANISM OF OPERATIONAL WEAR OF SPINDLE-NECK COATING OF SPINNING SPINDLES MADE OF AlCu4Mg1 ALLOY DUE TO COOPERATION WITH A STREAM OF YARNS

Results of the investigations of wear of spindle-neck coating with a collapse balloon crown of ring spinning frames, resulting from cooperation with stream of yarn within industrial conditions are discussed in the paper. The study have comprised measurements of the wear of spindle-neck coating made of EN AW-2024 (AlCu4Mg1) alloy after performed burnishing treatment in the course of cooperation with blend of 70 – 80% wool fibres with the addition of 30–20% polyester fibers, causing the greatest wear. Before and after the period of the operation, based on produced outlines of the roundness of the cylindrical part of the burnished neck of the coating, outlines of the cylindricity of the neck of the spindle have been drawn. Next, using the shape-meter, performed measurements were made of the wear on the spindle-neck coating having the form of a helical groove in the direction perpendicular to its run. There were also 2D measurements performed of the roughness on the neck of coating of spinning spindle, and photos were taken of side surface of the wear in form of helical groove, and one has an inserted EDS spectrum for the surface in the location of the precipitation (phase of AlCuFeMnSi type – point 2). Assessment of the surface in friction area between the spindle-neck coating and the stream of the fibres and the microphotography of side surface of the helical groove lead to the conclusion that the wear of the spindle-neck coating made of AlCu4Mg1 alloy, outside the deep grove, occurs as the result of abrasion, while inside the groove as the result of abrasion and oxidation.

INVESTIGATION OF DEPENDENCE IMPACT OF TOOL GEOMETRICAL PARAMETERS AND CUTTING SPEED UPON SHAPING EFFORT AT HELICAL GROOVE CUTTING ON INTERNAL SURFACE OF CYLINDRICAL SHELL

The work purpose was the investigation of dependence impact of tool geometrical parameters upon shaping effort during internal groove cutting. As a realization for the fulfillment of the helical groove processing investigation there was used a software complex based on a finite element method and a computer mathematic system. As a result of the investigations carried out there was obtained a regression equation manifesting the dependence of factors impact upon axial force falling on one tooth of the tool in the set scale of factor parameters. The scientific novelty consists in that in the paper there is considered a new method for helical groove cutting in which a shaping motion is carried out at the expense of the contact interaction of a tool and a billet performing free cutting. The investigation results obtained allowed determining the number of teeth operating simultaneously, that can be used further at cutting mode setting, and also as recommendations during designing tool design.