Analytical Modeling of Wax Plug Transportation during Pipeline Pigging Using a Foam Pig

Summary In our previous article (Gao et al. 2020), a mathematical model including elastic and yield components but not viscous component was developed to predict the wax plug transportation force. In this work, an analytical model was developed to calculate the wax plug transportation force, and the viscous component was introduced into the analytical model to capture some of the time effects. In this analytical model, the viscoelastic behavior of the wax deposit was characterized by a three-parameter model, formulated by adding an additional spring element to the Kelvin-Voight model. The Laplace transformation was used to solve the model. According to the calculated results of the analytical model, the transportation force of the wax plug was observed to slightly increase with time and then tended to level off. To obtain a parameter in the model and verify the model, the pigging experiments were conducted using foam pigs. During the pigging process of the foam pig, the wax plug transportation force in a five-phase wax removal profile was determined by taking the steady wax breaking force from the resistive force of the wax layer. Moreover, the linear increase of the wax plug transportation force per unit contact area with the shear strength of the wax layer was found, as described by the functional relationship in the analytical model. The interfacial lubrication coefficient calculated from the experimental data based on the analytical model is between the coefficient for diesel-prepared deposits and coefficient for oil-A-prepared deposits. Experimental verification results show that the average relative error of the model is 12.47%. Field implication was proposed to illustrate the application of the model and the formation condition of the wax blockage.

Correlation of Reduced-Order Models of a Threaded Fastener in Multi-Axial Loading

Fasteners are represented with varying degrees of fidelity in finite element models in order to meet solver constraints and accuracy requirements. Three reduced-order models are evaluated to quantify how well they perform in terms of calibration effort and accuracy. To baseline their performance, a new series of test data are developed by pulling NAS1351-3-20P screws at angles between pure tension (0°) and pure shear (90°) in 15° increments. First, a nonlinear elastic spring element joins two portions of the fastener shank. Unique load-displacement curves for tension and shear are taken directly from the test data, making it easy to calibrate yet fairly accurate. Second, the fastener is modeled with a solid cylindrical shank. The material properties are only calibrated to the tensile test results; consequently, this model is less accurate for predicting the ultimate shear load, though it comes reasonably close to the ultimate displacement in shear and combined loading. Third, a solid cylinder is divided into tensile and shear regions, and the material properties in each region are calibrated to the corresponding test data. This model deviates further from the ultimate displacement but effectively predicts the ultimate load in combined tension and shear. Each model has advantages, but the first is easiest to implement and most accurate overall.

A Time-Dependent Creep Constitutive Model of Deep Surrounding Rock under Temperature-Stress Coupling

In order to study the creep behavior of the surrounding rock of Hengda coal mine in Fuxin under different temperatures, the triaxial creep test of sandstone is carried out by the MTS815.02 test system. The relationship between damage variables and temperature is constructed based on the Weibull distribution of the meso-probability voxel intensity. Aiming at the nonlinear characteristics of rock creep, a nonlinear viscous pot element and a nonlinear spring element are proposed. The two linear viscous pot elements and one linear spring element in the Nishihara model can be replaced separately. Thus, an unsteady parameter creep model is established. The comparison between the Nishihara model curve and the model and the experimental curves in this article has been added to the article. Furthermore, the superiority of this model can be proved. The results show that the established variable-time aging creep model not only can describe the rock attenuation creep and stable creep deformation characteristics but also can make up for the shortcomings of the traditional creep model that cannot describe the accelerated creep characteristics. Moreover, it predicts the development law of creep deformation well. The model is in good agreement with the test curve, which shows the correctness and rationality of the model. It has guiding significance for actual engineering support and prediction of long-term deformation of surrounding rock.

Creep adjustment of strain gauges based on granular NiCr-carbon thin films

An important property of high-precision mechanical sensors such as force transducers or torque sensors is the so-called creep error. It is defined as the signal deviation over time at a constant load. Since this signal deviation results in a reduced accuracy of the sensor, it is beneficial to minimize the creep error. Many of these sensors consist of a metallic spring element and strain gauges. In order to realize a sensor with a creep error of almost zero, it is necessary to compensate for the creep behavior of the metallic spring element. This can be achieved by creep adjustment of the used strain gauges. Unlike standard metal foil strain gauges with a gauge factor of 2, a type of strain gauges based on sputter-deposited NiCr-carbon thin films on polymer substrates offers the advantage of an improved gauge factor of about 10. However, for this type of strain gauge, creep adjustment by customary methods is not possible. In order to remedy this disadvantage, a thorough creep analysis is carried out. Five major influences on the creep error of force transducers equipped with NiCr-carbon thin-film strain gauges are examined, namely, the material creep of the metallic spring element (1), the creep (relaxation) of the polymer substrate (2), the composition of the thin film (3), the strain transfer to the thin film (4), and the kind of strain field on the surface of the transducer (5). Consequently, we present two applicable methods for creep adjustment of NiCr-carbon thin- film strain gauges. The first method addresses the intrinsic creep behavior of the thin film by a modification of the film composition. With increasing Cr content (at the expense of Ni, the intrinsic negative creep error can be shifted towards zero. The second method is not based on the thin film itself but rather on a modification of the strain transfer from the polyimide carrier to the thin film. This is achieved by controlled cutting of well-defined deep trenches into the polymer substrate via a picosecond laser.

Technique for Analyzing Relationship Between Unbalanced Load and Structural Deterioration in Outside Facilities

In order to provide telecommunication and FTTH services, NTT have installed so many facilities such as utility poles and optical cables. The number of poles is about 11.8 million and the total length of all installed cables is about 2.3 million km. These facilities are now maintained and inspected visually by on-site maintenance staff at great expense. Therefore, we are researching a novel outside-facility renovation technology that increases cost-effectiveness by ensuring the long-term safe use of facilities. When a utility pole is newly constructed, it is designed under the assumption of a maximum load such as wind pressure being applied to the pole via cables and auxiliary attachments. However, the loads can become imbalanced when the guy wire cannot be tensioned as they cross private land or when there are obstacles, etc. We call this condition that unbalanced loads occur. Unbalanced loads are one of the key reasons for the structural deterioration of utility poles. After the deterioration occurs, the risk of pole collapse increases, because deflection and inclination are generated and finally the cracks propagate until collapse. The conventional solution is to replace the damaged pole. However, in many cases, the loads are created by other contiguous poles, so unbalanced loads occur again. Therefore, we are developing a method that can identify the reason by regarding sets of utility poles as "facility systems" and analyzing unbalanced loads quantitatively by FEM. In our research, simulation accuracy is improved by determining the quantitative differences obtained by comparing the calculated results obtained by FEM with measured values obtained by using a reaction wall. The simulations of structural degradation due to unbalanced loads taking into account the deformation of cables due to wind velocity and air temperature in addition to various material properties such as hysteresis and the sectional model of the utility poles. In addition to the above, the effect of soil is considered as a spring element, and the analysis involves the elements of horizontal spring (Kxi, Kzi) and vertical spring (Kv). While the calculated and the measured values show good agreement, there is some small error. This error is considered to be due to the influence of parameters such as tensile and compressive strength, and we aim to improve the simulation accuracy by considering these effects in the future.

Implementation and experiment of a novel piezoelectric-spring stage for rapid high-precision micromotion

A precision micromotion stage is significant in the microelectronics-manufacturing field to realize high-performance tasks. The output position error and limited frequency response influence the working performance and efficiency of the micromotion stage. A novel piezoelectric-based (PZT) reciprocating micromotion stage with a special spring-PZT structure is proposed in this paper to cater to the high manufacturing demands and achieve rapid precision micromotion performance. This structure is designed to use a high-stiffness spring element as the flexure deformation structure, by utilizing the linearity of the spring, for achieving precise output/input ratio and high-frequency response. The feasibility of the micromotion stage is explored through theoretical analyses, including a dynamic response analysis, frequency response analysis, output displacement, and rapidity analysis of the specialized spring-PZT structure. For the inherent hysteresis challenge of the PZT-based structure, a feedforward subdivided proportional–integral–derivative method is adopted for system implementation. Subsequently, an optimal design of the stage is established, and the expected motion performance is verified experimentally. Finally, a series of experiments in terms of output ratio property analysis, dynamic hysteresis characterization, tracking error performance, and response rapidity are conducted for different micromotion frequencies and strokes. It is indicated that the stage can achieve nanometre-level precision and high-frequency micromotion simultaneously, which could be applied in the microelectronics manufacturing for rapid precision micromotion operations.

Evaluation of a Macro Lump Plasticity Model for Reinforced Concrete Beam-Column Joint under Cyclic Loading

Lateral deformations of reinforced concrete (RC) frames under extreme seismic excitation are highly affected by the stiffness of their beam-column joints. Numerous models have been proposed to simulate the responses of RC beam-column joint under cyclic loading. Development of RC beam-column joint model based on macro modeling using spring elements becomes more popular because of its considerably simple application for seismic performance evaluation purposes. In this study, a simple modification to previously developed macro-spring element-based model for RC beam-column joint is done and is used to simulate the behavior of seven external and five internal RC joints under cyclic loading in SAP2000. The model consists of several spring elements to define column, beam, joint, and bond-slip responses according to its individual moment-rotation relationships. Overall, the analysis results show that the modified model can simulate well the cyclic behavior of RC beam-column joints when are compared to previously available experimental results

Monolithic Leg Design With Compliant Knee Joint for Bipedal Robots: Design and Preliminary Results

Design and control of human-like robots mimicking the motion using biped legs are still in demand. However, the vast majority of the biped robots are too heavy due to the number of actuators and their bulky design. Compliant designs can mimic the motions in nature through the large deformation of their compliant members and have the ability to be designed as a single piece thereby reducing the overall weight and increasing the performance of the mechanism. Biped robots specifically designed for walking currently existing in the literature often arranged in series form. Although serial design leads high flexibility, each link carries its actuator compromising the overall weight and stability. This paper presents the design and development of a bioinspired leg for biped robots without the requirement of actuation of the knee or addition of a spring element. Each leg is designed as a single piece by exploiting a compliant knee joint, 3D printed using TPU filament and actuated through a cam design using a servo motor. Servo motor is also attached to the trunk which serves as the torso of the robot body. Zero moment point (ZMP) analysis is performed by adopting simple cart-table and inverted pendulum methods. Stiffness of the compliant knee is obtained from multibody dynamic simulations in MSC Adams. The preliminary testing of the bio-inspired biped robot reveals that the robot performs successful periodic gait.