Dynamics of risers analysed by means of the segment method, with consideration of bending and torsional stiffness

The paper presents the application of the finite segment method to the analysis of coupled bending torsional vibrations of risers. The method is formulated by means of joint coordinates using multibody methods for kinematics and dynamics. A new approach to calculating bending and torsion moments is presented. The mathematical model and computer program enable us to analyse both free and forced vibrations of risers caused by the motion of the base (vessel or platform) as well as hydrodynamic forces. The model is validated by comparing frequencies of free and forced vibrations calculated from the authors’ own models with the results presented by other researchers. Natural frequencies are also compared with analytical solutions. The influence of sea currents and of the initial twisting of the riser on its natural and forced vibrations is analysed.

Planar dynamic modelling of round link chain drives considering the irregular polygonal action and guide rail

Round link chain drives can be sorted into the transmission, parallel conveyor and non-parallel conveyor systems according to their applications and guide rail’s layouts. The polygonal action in these systems is irregular. Compared with the literature, this paper proposes a more accurate modelling approach to capture the dynamic behaviour of round link chain drives, which can consider both the irregular polygonal action and non-parallel guide rail’s layout. The dynamic models of the three types of round link chain drives are developed based on the finite segment method. The chain is divided into multiple discrete segments that are connected by Kelvin models. To account for the irregular polygonal action, the sprocket is equivalent to an irregular polygon. To consider the non-parallel guide rail’s layout in the conveyor system, the chain segment out of the guide rail and the corresponding sprocket are treated as a swinging-block mechanism. The proposed approach is applied to model a scraper conveyor. Simulation results show that the irregular polygonal action and non-parallel guide rail’s layout greatly increase the fluctuation of the chain tension force.

Influence of Sea Current on Stabilization of Moments and Forces in Risers

One of the important aspects in the design of floating, production, storage, and offloading (FPSO) systems is to ensure a fairly constant load on risers despite the base motion caused by sea waves. The paper presents the authors’ own formulation of the finite segment method for dynamic analysis of risers and its application to the solution of a dynamic optimization problem. This task consists in defining vertical displacements of the top of the riser which compensate horizontal movements of the vessel or platform caused by sea waves. Compensation involves stabilizing the bending moment in the risers or the force in the connection of the riser and the wellhead. The model takes into account the influence of the sea by means of Morison equations. Different sea current profiles are considered. Calculation of vertical displacements of the top of the riser is carried out in order to stabilize the force or the bending moment for a defined function of horizontal displacements of the riser.

A Finite Segment Method for Skewed Box Girder Analysis

A finite segment method is presented to analyze the mechanical behavior of skewed box girders. By modeling the top and bottom plates of the segments with skew plate beam element under an inclined coordinate system and the webs with normal plate beam element, a spatial elastic displacement model for skewed box girder is constructed, which can satisfy the compatibility condition at the corners of the cross section for box girders. The formulation of the finite segment is developed based on the variational principle. The major advantage of the proposed approach, in comparison with the finite element method, is that it can simplify a three-dimensional structure into a one-dimensional structure for structural analysis, which results in significant saving in computational times. At last, the accuracy and efficiency of the proposed finite segment method are verified by a model test.

Studying and Simulation Analysis for Rubber Track of Rescue Robot

Rubber track of Rescue Robot was dispersed into limited number of track blocks by the method of finite segment method used in flexible multibody dynamics. The two neighbor track blocks were connected by springs and dampers, then the moldel was become a multi-rigid-body system with flexible joint. Rubber track was modeled with the help of macro command used in the secondary development of virtual prototype technique software named ADAMS. Flexible connection was realized by the method of adding Bushing, and then a new method was proposed to build rubber track model. The obstacle-surmounting simulation of climbing the barrier of single step was carried out. It intuitively reflected the stress and deformation under the condition of climbing barrier. The method mentioned above laid good foundation for studying obstacle-surmounting abilities of the rubber-tracked robots and dynamic characteristic of the tracks.

The Study of Modeling Methods Based on Applied Mechanics for Sling of Tower Crane with ADAMS

Along with the rapid development of construction industry, tower crane becomes the indispensable machine in building trade. Using a simple and effective modeling method for sling is a crucial step in the analysis of tower crane. The 6 different models for sling of the tower crane were established by using the finite segment method of ADAMS in this paper, and the simulation of the sling based on applied mechanics was done. The conclusion was drew that in the modeling of sling, a rigid rod can substitute for sling, in the case that the resistance and axial stretching deformation of the sling were neglected. So a simple modeling method was given for sling of tower crane in a special case.

Use of Finite Element and Finite Segment Methods in Modeling Rail Flexibility: A Comparative Study

Safety requirements and optimal performance of railroad vehicle systems require the use of multibody system (MBS) dynamics formulations that allow for modeling flexible bodies. This investigation will present three methods suited for the study of flexible track models while conclusions about their implementations and features are made. The first method is based on the floating frame of reference (FFR) formulation which allows for the use of a detailed finite element mesh with the component mode synthesis technique in order to obtain a reduced order model. In the second method, the flexible body is modeled as a finite number of rigid elements that are connected by springs and dampers. This method, called finite segment method (FSM) or rigid finite element method, requires the use of rigid MBS formulations only. In the third method, the FFR formulation is used to obtain a model that is equivalent to the FSM model by assuming that the rail segments are very stiff, thereby allowing the exclusion of the high frequency modes associated with the rail deformations. This FFR/FS model demonstrates that some rail movement scenarios such as gauge widening can be captured using the finite element FFR formulation. The three procedures FFR, FSM, and FFR/FS will be compared in order to establish differences among them and analyze the specific application of the FSM to modeling track flexibility. Convergence of the methods is analyzed. The three methods proposed in this investigation for modeling the movement of three-dimensional tracks are used with a three-dimensional elastic wheel/rail contact formulation that predicts contact points online and allows for updating the creepages to account for the rail deformations. Several conclusions will be drawn in view of the results obtained in this investigation.

Shear Lag Effect of Continuous Curved Box Girder with Initial Curvature

The homogeneous solutions of the governing differential equations for shear lag are used as the displacement patterns of the finite segment are presented. A finite segment model with consideration of initial curvature, bending, torsion and shear lag is established. In addition, the tests of the two-span continuous curved box girder and numerical calculations of the model tests by finite segment method and finite element method are made. The results of the model tests and numerical calculation are consistent with each other. An actual example was given to investigate the shear lag effect of a continuous curved box girder under load. The research results show that the initial curvature has an obvious influence on the shear lag effect of a continuous curved box girder.