Stochastic Model Updating of Bolt-Jointed Structure for Structural Dynamics Applications

Structural stiffness exerts from joint connections and contact interfaces are significantly affect the dynamic behaviour of the bolt-jointed structure. Randomness in the joint connections due to the manufacturing variability in the identical bolted joints and uncertainty in contact interfaces due to the assambled and reassambled of the joint structure make sets of the dynamic behaviour of the bolt-jointed structure always inconsistent. On this account, a stochastic analytical model needs to be developed for the bolt-jointed structure to be used for uncertain parameters quantification. Hence, this paper is intended to propose an accurate and efficient stochastic analytical modelling of bolt-jointed structure in predicting the dynamic behaviour of the structure due to the randomness in the joint connections and uncertainty in contact interfaces. The aim of the study was accomplished by investigating four different finite element (FE) models of bolt-jointed structure with different element connectors to represent the bolted joints connections, namely rigid element (RBE), beam element (CBEAM), and 2 types of spring elements namely CELAS and CBUSH. Stochastic modelling was conducted by coupled the appropriate FE models with Latin Hypercube Sampling (LHS) algorithm to provide variability sampling due to the randomness in the bolted joints. The experimental modal analysis was performed by reassembled and disassembled the bolted joints to extract the variability in the dynamic behaviour, and the results were compared with LHS using statistical characteristics. Stochastic model updating then was used to minimise the discrepancies between experimental result and predicted model. The result has shown that the CBUSH is the most appropriate connector to accurately predict the dynamic behaviour of the bolt-jointed structure under variability conditions using the stochastic model updating method.

Stress-Deformed State of the Breed in the Funnel of Depression

Analytical solutions of one-dimensional equations of poroelasticity, describing the stress distribution in the depression (repression) funnel, are obtained in this work. It is shown that the influence of the boundary conditions on the wellbore wall is significant only in a relatively small (~1 m) vicinity of the wellbore bottom zone. It has been established also that in fractured rocks in cased wells, the compressive angular stresses, which largely determine the filtration conductivity of the bottomhole zones, will be less than in uncased wells. A method is described that makes it possible to increase the tightness of preserved wells in depleted fields. The method consists in cutting out a section of the casing pipe above the productive formation, expanding the wellbore in this section, installing a spring metal centralizer in this section, followed by cementing it. The formation of such a rigid element associated with the casing will prevent rock displacement relative to this pipe and ensure the tightness of the near-wellbore zone of the well.

Influence of orthopedic support structure and construction on compression and behavior during stress relaxation

This work was focused on changes of the compression generated by knitted orthopedic supports during the stress relaxation in order to find in which period of the stress relaxation the most significant part of the compression is lost. The influence of knitted structure, elastomeric inlay-yarn insertion density and shape/orientation of the rigid element fixed on the fabric on the compression and its changes under the stress relaxation was also investigated in this study. 11 different knitted structures and constructions were used in this research. It was found that the higher density of elastomeric inlay-yarn insertion into the knitted structure is not only responsible for higher compression generation, but also makes compression degradation during the time slower. In addition, the higher pre-tension of the elastomeric inlay-yarn leads to the faster relaxation process. Moreover, the shape and orientation of the rigid element can significantly affect the compression generation, however behavior of all variants during the stress relaxation is very similar. Evaluation of the tensile force after at least 120-300 s of the stress relaxation has to be used in design algorithm of very different compression products and applied in estimation of the compression at different manufacturing stages of the product.

Assessment of the mutual influence of deformation-strength characteristics of the fastening system elements

The degree of influence has been determined of diversified deformation-strength characteristics of load-bearing elements in the fastening system of the preparatory mine workings, while maintaining them in a laminal massif of soft rocks. The analysis has been performed of multivariate computational experiments of the stress-strain state of the load-bearing elements of the fastening system in the preparatory mine workings from the position of the mutual influence of their deformation-strength characteristics and the support loading as a whole. An analysis is represented of the mutual influence of the operation modes of the mine working support elements between themselves and the fastening system as a whole; it has been studied the stress-strain state of the mine working fastening system with a central hydraulic prop stay, as well as a significant increase in reliability of the support performance has been analysed and determined. The tendency has been substantiated of minimizing the load on the mine working fastening system – increasing the coherence of the diversified operation modes of fastening elements by enhancing preferentially the yielding property of the rigid element. The application has been substantiated of the central yielding prop stays of the strengthening support of a frame in case of intensive rock pressure manifestation in the zone of the stope works active influence.

Cooperation of axisymmetric connection elements under dynamic load

The article presents a method for determining the parameters that define the cooperation of the elements in the axisymmetic connection. The connection, which constitutes a shaft cooperating with a sleeve, has been tested for reaction forces in the connection during shaft rotation in the static sleeve. The shaft was characterized by deliberately modelled roundness deviations in the form of ovality, triangularity and quadrangularity. In addition, the research programme has taken into account the determination of the impact of tolerance of the outside diameter of the shaft. Determination of reaction forces has been carried out using the FEM software. The shaft has been modelled as a rigid element that rotates with a given rotational speed in the deformable sleeve. The conclusions present the impact of roundness deviation types and the tolerance value on reaction forces in the connection restraint. The method presented in the article can be used to predict the behaviour of the elements of axisymmetic connections under dynamic load, which can contribute to forecasting the durability of the connection.

Modeling and Simulation of Big Pendulum Hammer with Natural Coordinates

The dynamic of a type of play equipment, Big Pendulum Hammer, was modeled and simulated in computer and the approach of natural coordinates was adopted to build its equation of motion. In order to obtain appropriate natural coordinates, a two-step selection method was chosen, which based on concept of natural coordinate system (NCS). The two-step method treats selecting natural coordinates for a rigid element as building an actual NCS which should be adapted from a standard NCS. In order to automate the process of adaptation for 18 rigid elements in the model of Big Pendulum Hammer, a four-step self-adaptation method was also adopted, which can help automate the selection of natural coordinates for multi-rigidbody systems.

A Periodical Loaded Dynamical System

In the paper a Preisach hysteresis model is applied to determine the dynamic behavior of a steel column with a mass on the top and loaded by periodically alternating force. The column is considered as a completely rigid element, while the fixed end of the column is modeled with a rotational spring with hysteresis characteristic. In the solution of the non-linear dynamical equation of the motion the fix-point technique is inserted to the time marching iteration. The cycling time of the force is changing. The results are plotted in figures.