Numerical simulation of squeezing Cu–Water nanofluid flow by a kernel-based method

The main aim of this paper is to propose a kernel-based method for solving the problem of squeezing Cu–Water nanofluid flow between parallel disks. Our method is based on Gaussian Hilbert–Schmidt SVD (HS-SVD), which gives an alternate basis for the data-dependent subspace of “native” Hilbert space without ever forming kernel matrix. The well-conditioning linear system is one of the critical advantages of using the alternate basis obtained from HS-SVD. Numerical simulations are performed to illustrate the efficiency and applicability of the proposed method in the sense of accuracy. Numerical results obtained by the proposed method are assessed by comparing available results in references. The results demonstrate that the proposed method can be recommended as a good option to study the squeezing nanofluid flow in engineering problems.

Methodology for First Coiled Tubing Application in a Problematic Unconventional Well with Proven 17,500 Psi Bottom Hole Pressure

A deviated newly drilled gas well in Western Caspian Sea in Azerbaijan, with a flowing water reservoir pressure of 17,500-psi and a flowing gas reservoir pressure of 12,200-psi was unable to regain flow after an unsuccessful attempt to bullhead produced water back into the well. During the bullheading operation, there was a peak registered pumping pressure of 12,933-psi without admission of fluid into formation. Producing interval was 5880mTVD with a MASP of 9,700-psi for gas reservoir. Coiled Tubing was the most viable option to identify the problem, to solve it and to regain access to the lower completion and then proceed with interval abandonment program. This being an unconventional well in multiple aspects, presented serious challenges accentuated in Safety, Well Integrity Control, Obstruction Removal, and Well Conditioning Plan Forward. Integrity of completion was believed to be compromised by the high pumping pressures applied during bullheading and a confirmed communication between production tubing and "A annulus". After performing 2 rig site visits, an action plan was issued to adjust the platform for a Coiled Tubing intervention for the first time. Points to be developed in the plan were HSE, Structural Analysis and modifications required for proper equipment accommodation. For well integrity control, it was imperative to evaluate the potential scenarios which could have led to the problematic well status. Completion history and specifications were reviewed to assure each of the potential operating scenarios could be controlled without compromising well integrity. On obstruction removal, simulation software was used to design procedure with optimum string, chemicals, rates and fluids to be used for the operation and which contingency fluids considered to be available offshore. It is challenging to perform effective cleanouts in completions with 2 different sizes of tubings (IDs 3.74" & 2.2") combined with restrictions (1.92" nipple), the success is a function of overcoming limited fluid pumping rates, slow annular velocities, particle sizes, cleaning speeds, among others. Well conditioning for future completion operations was planned depending on successful achievements of the coiled tubing intervention. A total of 14 runs with coiled tubing using different BHA configurations were performed to complete the scope. Well was safely and successfully cleaned from a starting depth of 2,512mMD to a target depth of 5,864mMD (5,610mTVD) by removing mud deposits, consolidated sand bridges and completion restrictions. Throughout the cleanout operation, best practices discussed on planning stage were applied to remove multiple obstructions encountered and dealing with potential corkscrewed casing. By accomplishing the well delivery, it is evident that the methodology followed during the planning stage and execution, was crucial to save the well from being lost or abandoned. There was an uncertainty whether the completion integrity was compromised by the high pressures used during the bullheading operation. Novelty in this intervention was the methodology for the risk assessment for an unconventional live well intervention with a 17,500-psi BHP, unseen pressure in the region. Thorough structural analysis was performed to assure the coiled tubing equipment could be placed safely on the platform to condition the well to regain production

Using Prior Wave Information and Paradata: Can They Help to Predict Response Outcomes and Call Sequence Length in a Longitudinal Study?

In recent years the use of paradata for nonresponse investigations has risen significantly. One key question is how useful paradata, including call record data and interviewer observations, from the current and previous waves of a longitudinal study, as well as previous wave survey information, are in predicting response outcomes in a longitudinal context. This article aims to address this question. Final response outcomes and sequence length (the number of calls/visits to a household) are modelled both separately and jointly for a longitudinal study. Being able to predict length of call sequence and response can help to improve both adaptive and responsive survey designs and to increase efficiency and effectiveness of call scheduling. The article also identifies the impact of different methodological specifications of the models, for example different specifications of the response outcomes. Latent class analysis is used as one of the approaches to summarise call outcomes in sequences. To assess and compare the models in their ability to predict, indicators derived from classification tables, ROC (Receiver Operating Characteristic) curves, discrimination and prediction are proposed in addition to the standard approach of using the pseudo R2value, which is not a sufficient indicator on its own. The study uses data from Understanding Society, a large-scale longitudinal survey in the UK. The findings indicate that basic models (including geographic, design and survey data from the previous wave), although commonly used in predicting and adjusting for nonresponse, do not predict the response outcome well. Conditioning on previous wave paradata, including call record data, interviewer observation data and indicators of change, improve the fit of the models slightly. A significant improvement can be observed when conditioning on the most recent call outcome, which may indicate that the nonresponse process predominantly depends on the most current circumstances of a sample unit.

An Ordinary Differential Equation Formulation for Multibody Dynamics: Nonholonomic Constraints

A method is presented for formulating and numerically integrating ordinary differential equations of motion for nonholonomically constrained multibody systems. Tangent space coordinates are defined in configuration and velocity spaces as independent generalized coordinates that serve as state variables in the formulation, yielding ordinary differential equations of motion. Orthogonal-dependent coordinates and velocities are used to enforce constraints at position, velocity, and acceleration levels. Criteria that assure accuracy of constraint satisfaction and well conditioning of the reduced mass matrix in the equations of motion are used as the basis for updating local coordinates on configuration and velocity constraint manifolds, transparent to the user and at minimal computational cost. The formulation is developed for multibody systems with nonlinear holonomic constraints and nonholonomic constraints that are linear in velocity coordinates and nonlinear in configuration coordinates. A computational algorithm for implementing the approach is presented and used in the solution of three examples: one planar and two spatial. Numerical results using a fifth-order Runge–Kutta–Fehlberg explicit integrator verify that accurate results are obtained, satisfying all the three forms of kinematic constraint, to within error tolerances that are embedded in the formulation.

An Ordinary Differential Equation Formulation for Multibody Dynamics: Holonomic Constraints

A method is presented for formulating and numerically integrating ordinary differential equations (ODEs) of motion for holonomically constrained multibody systems. Tangent space coordinates are defined as independent generalized coordinates that serve as state variables in the formulation, yielding ODEs of motion. Orthogonal dependent coordinates are used to enforce kinematic constraints at position, velocity, and acceleration levels. Criteria that assure accuracy of constraint satisfaction and well conditioning of the reduced mass matrix in the equations of motion are used as the basis for redefining local coordinates on the constraint manifold, as needed, transparent to the user and at minimal computational cost. The formulation is developed for holonomically constrained multibody models that are based on essentially any form of generalized coordinates. A spinning top with Euler parameter orientation coordinates is used as a model problem to analytically reduce Euler's equations of motion to ODEs. Numerical results using a fourth-order Nystrom integrator verify that accurate results are obtained, satisfying position, velocity, and acceleration constraints to computer precision. A computational algorithm for implementing the approach with state-of-the-art explicit numerical integrators is presented and used in solution of three examples, one planar and two spatial. Performance of the method in satisfying all three forms of kinematic constraint, based on error tolerances embedded in the formulation, is verified.

Descent Symmetrization of the Dai–Liao Conjugate Gradient Method

Symmetrizing the Dai–Liao (DL) search direction matrix by a rank-one modification, we propose a one-parameter class of nonlinear conjugate gradient (CG) methods which includes the memoryless Broyden–Fletcher–Goldfarb–Shanno (MLBFGS) quasi-Newton updating formula. Then, conducting an eigenvalue analysis, we suggest two choices for the parameter of the proposed class of CG methods which simultaneously guarantee the descent property and well-conditioning of the search direction matrix. A global convergence analysis is made for uniformly convex objective functions. Computational experiments are done on a set of unconstrained optimization test problems of the CUTEr collection. Results of numerical comparisons made by the Dolan–Moré performance profile show that proper choices for the mentioned parameter may lead to promising computational performances.