Complicated Engineering Problems Research Articles

A new site classification approach based on neural networks

Site classification is an important procedure for a reliable site-specific seismic hazard assessment. On the other hand, the site conditions at strong-motion stations are essential for accurate interpretation and analysis of the recorded ground motion data obtained from different regions of the world. For some countries with insufficient data on the subsurface geological settings, the required site condition information is not available. This paper presents a new and efficient approach for site classification based on artificial neural networks (ANN) along with a selected set of representative horizontal to vertical spectral ratio (HVSR) curves for four site classes. The nonlinear nature of ANN and their ability to learn in a complex environment make it highly suitable for function approximation and solving complicated engineering problems. Two types of radial basis function (RBF) neural networks, namely, probabilistic neural networks (PNN) and generalized regression neural networks (GRNN) were chosen in this study, as no separate training phase is required, rendering them particularly suitable for site classification. The proposed approach has been tested using data of the Chi-Chi, Taiwan, earthquake ( Mw=7.6) recorded from 87 stations at which the site conditions are known. Analyses show that both the PNN and the GRNN perform very well with similar accuracy in estimating site conditions, with successful rates of 78% and 75%, respectively.

A New Numerical Approach for Adhesive Contacts of Real Engineering Surfaces

Microelectromechanical system (MEMS) and nanotechnology are important directions on the development of the science in twenty-first century. Some of the effects, such as viscous force, surface force, electrostatic force, friction etc., which can be usually ignored on the traditional scale, have become noticeable when the scale has turn to micro or nano scale. Nanotribology is one of the main areas of the indispensable researches on the basic theory and methodology of the effects. The micro/nano adhesive contact which is the foundation of nanotribology is studied in this paper. The earliest study on adhesive contact was done by Bradley. He presented an expression of adhesive force of two contacting rigid spheres. Derjaguin, Muller and Toprov (DMT) gave the relation of the contact area and the applied load of the adhesive contact of two spheres, but they did not consider the elastic deformation due to the adhesive force of the bodies. Johnson, Keudall and Roberts (JKR) provided a theory of the adhesive contact of two elastic spheres. Tabor gave a parameter (Tabor parameter) to interpret the ratio of the elastic deformation with the adhesive force of two contacting bodies. That is to say the DMT model corresponding to small Tabor parameter(<0.1) and the JKR model to large Tabor parameter(>5). Maguis gave a DMT-JKR transition using the Dugdale model in fracture mechanics (M-D model) in the intermediate region between the DMT model and the JKR model. A numerical algorithm of elastic adhesive contact based on the meshless method is presented in this paper. This make it possible to solve the adhesive contact with more complex surface topography and to consider more intricate factors, such as thermal stress, friction, elasto-plastic deformation etc. in the further studies on micro/nano scale adhesive contact problems. The meshless method seems to be a promising approach for contact analyses because of its flexibility in domain descritization and versatility in node arrangements. It can be used to solve a variety of complicated engineering problems. A numerical example of adhesive contact between a micro elastic cylinder and a rigid half-space is carried out to show the feasibility of the algorithm. In the simulation, an effective method of the M-D model is used to save the cost of computation. Compared with the existed solutions, the results solved by the presented algorithm are reasonable.

Antano Bistricko architektūrinis statybinis palikimas

The nowadays high schools are interested in appreciation from time to time of true worth of their activity. Particularly there emerge an actuality for verification of effectiveness of their links with needs of economic structures and society in whole. They decide to analyse long- time data of achievements and career disturbances of their graduates. Well known subsystems of nowadays Lithuanian high schools commemorate the a jubilee of their origins. Among these nowadays schools, faculties and directions of the science to reckon to technical trend there is a Faculty of Building and Architecture in Kaunas Technological University. For some time there the most notable practical activities and results to be characteristic of the graduates of University are studied. Also there the living peculiarities and distinctions of the most honourable graduates are revealed. Antanas Bistrickas, a builder – engineer, constructor, etc. is quite an interesting person and – a graduate of building department (nowadays Faculty). Antanas Bistrickas was born in 1900. So we may commemorate the jubilee of this event too. As a building engineer A. Bistrickas graduated from University Vytauti in 1933. After graduation he passed a short time on engineering practice. Shortly after that he was called by his professor to occupy a certain duty in the same University he graduated from. Practically all professional life of this person was related with the building engineering branch in the same University to be differently named in times of independent Lithuania and at Soviet time. Some time later he was teaching at Kaunas polytechnic institute when this high school was organized on the basis of technical faculties acting formerly in the structure of the Kaunas State University. There he had a career of engineer, professor, dean of the building faculty, vice – rector, etc. Antanas Bistrickas died in 1971. The basic heritage of Antanas Bistrickas onto practical activity of building engineering contains designing and constructing of the sacral objects, dwelling houses and some verification of strength and exploitability to be distinctive of various building structures after the Second World War. His heritage is worthy of an extensive study from various standpoints, positions and criteria. First of all, this heritage contains an interesting reconnaissance in design of modern sacral objects. It is displayed in architectural forms of sacral buildings especially. Also there can be a new for that time building engineering practice, efforts for adaption of the modern building materials. Particularly there can be mentioned the reinforced concrete, complex concrete with using of a rolled steel beams, reinforced brickwork for high thin elements of building structures and long span floors or overlapings, etc. There may be noted the intensive activity of this person which produced the sustainable noteworthy results in every position he was called to occupy. The most interesting object designed and realized by A. Bistrickas is the church of St. Antonius in Kaunas city. There some quite complicated engineering problems were solved related to hydro – geological situation of soils to be laid on the lot of church. It generates a problem of stability of the church towers and columns, prevention of their deviations and some other difficulties. For example, in the soil supporting footings of towers and columns their loading generates local pressure. Consequently, there may act combined stresses and strains. An irregular loading, as well as combined stresses and strains can be a premise of overloading and limit state in non – rigid flexible soils. In this state large deformations and deviations can be evaluated expecially when the hydro – geological characteristics of soil are variable at various periods of the year. Finally, it can be a premise of crushing of towers and columns. These processes were not exactly studied at the time of church building. There can be considered variants of architectural design of the church appearance. Author produced the five projects on this matter. The most developed variation contains five towers simetrically laid on frontage of the church. The towers generate an impression of vertical dynamics of this building. Joined among them by graduated parapet the frontal composition of the church is based on the image of architectural waves to be decreasing on both sides. Unfortunately, the resource of the customer (parish) was not enough for improvement and realization of this project. Article in Lithuanian

Some improvement to the mutation donor of differential evolution

PurposeThe purpose of this paper is to improve the existing differential evolution (DE) mutation operator so as to accelerate its convergence.Design/methodology/approachA new general donor form for mutation operation in DE is presented, which defines a donor as a convex combination of the triplet of individuals selected for a mutation. Three new donor schemes from that form are deduced.FindingsThe three donor schemes were empirically compared with the original DE version and three existing variants of DE by using a suite of nine well‐known test functions, and were also demonstrated by a practical application case – training a neural network to approximate aerodynamic data. The obtained numerical simulation results suggested that these modifications to the mutation operator could improve the DE's convergence performance in both the convergence rate and the convergence reliability.Research limitations/implicationsFurther research is still needed for adequately explaining why it was possible to simultaneously improve both the convergence rate and the convergence reliability of DE to that extent despite the well‐known “No Free Lunch” theorem. Also further research is considered necessary for outlining more distinctively the particular class of problems, where the current observations can be generalized.Practical implicationsMore complicated engineering problems could be solved sub‐optimally, whereas their real optimal solution may never be reached subject to the current computer capability.Originality/valueThough DE has demonstrated a considerably better convergence performance than the other evolutionary algorithms (EAs), its convergence rate is still far from what is hoped for by scientists. On the one hand, a higher convergence rate is always expected for any optimization method used in seeking the global optimum of a non‐linear objective function. On the other hand, since all EAs, including DE, work with a population of solutions rather than a single solution, many evaluations of candidate solutions are required in the optimization process. If evaluation of candidate solutions is too time‐consuming, the overall optimization cost may become too expensive. One often has to limit the algorithm to operate within an acceptable time, which maybe is not enough to find the global optimum (optima), but enough to obtain a sub‐optimal solution. Therefore, it is continuously necessary to investigate the new strategies to improve the current DE algorithm.

Numerical aspects of non-coaxial model implementations

Abstract This paper ascertains the reasons for the numerical problems when the yield vertex non-coaxial model is implemented in the finite element analysis to predict the behaviour of complicated geotechnical engineering problems. The numerical problem, reflected in the failure of convergence in the non-linear solutions in ABAQUS, is likely to happen when a smaller non-coaxial plastic modulus is used. It is found that a large non-coaxial influence at the start of elastoplastic loading, which causes the predominance of non-coaxial plastic strain rate over the coaxial plastic strain rate in stress–strain responses, is the reason for the numerical problem. The original yield vertex non-coaxial model is modified to overcome the numerical problem. Instead of a constant non-coaxial plastic modulus in the original yield vertex non-coaxial model, the non-coaxial modulus is made a function of cumulative deviatoric plastic strain. It shows that the modified non-coaxial model retains the functions of the original non-coaxial model. Meanwhile, it overcomes the non-convergence problem when a smaller non-coaxial plastic modulus, representing a larger non-coaxial influence, is used.

A unified fractional step method for compressible and incompressible flows, heat transfer and incompressible solid mechanics

PurposeThis paper aims to present briefly a unified fractional step method for fluid dynamics, incompressible solid mechanics and heat transfer calculations. The proposed method is demonstrated by solving compressible and incompressible flows, solid mechanics and conjugate heat transfer problems.Design/methodology/approachThe finite element method is used for the spatial discretization of the equations. The fluid dynamics algorithm used is often referred to as the characteristic‐based split scheme.FindingsThe proposed method can be employed as a unified approach to fluid dynamics, heat transfer and solid mechanics problems.Originality/valueThe idea of using a unified approach to fluid dynamics and incompressible solid mechanics problems is proposed. The proposed approach will be valuable in complicated engineering problems such as fluid‐structure interaction and problems involving conjugate heat transfer and thermal stresses.

Particle swarm optimization-based parameter identification applied to permanent magnet synchronous motors

The high-performance application of high-power permanent magnet synchronous motors (PMSM) is increasing. PMSM models with accurate parameters are significant for precise control system designs. Acquisition of these parameters during motor operation is a challenging task due to the inherent nonlinearity of motor dynamics. This paper proposes an intelligent model parameter identification method using particle swarm optimization (PSO). PSO, an intelligent computational method based on stochastic search, is shown to be a versatile and efficient tool for this complicated engineering problem. Through both simulation and experiment, this paper verifies the effectiveness of the proposed method in identification of PMSM model parameters. Specifically, stator resistance and load torque disturbance are identified in this PMSM application. Though PMSM is presented, the method is generally applicable to other types of electrical motors, as well as other dynamic systems with nonlinear model structure.

Controlling the Conversation

American automakers adopted computer controls to deal with complicated engineering problems only when pushed by forces beyond their control.

Applications of ground penetrating radar in the Three Gorges Project, China

During the Three Gorges Project (TGP) on the Yangtze River in China, a number of complicated engineering and geological problems had to be solved. A quick and high resolution non-destructive method was needed to find buried geological defects and engineering quality problems in order to guarantee the project schedule and engineering quality. Ground penetrating radar (GPR) was one technique which was effectively applied to detect the extension of inhomogeneous weathering of granite prior to excavation, to map the extent and attitude of large faults and weathering of alternative layers, and to check the engineering quality of concrete work for TGP during construction. In this paper, three case histories are discussed.nThe detection results proved consistent with the results of excavation with the performance of GPR obvious. As a large scale, high technology and difficult construction, The Three Gorges Project(TGP) is the largest and most ambitious infrastructure project in the world. Geological exploration and surveys have been conducted for more than 30 years providing a wealth of data prior to construction. Like other large hydroelectric engineering projects, the TGP was faced with many complicated engineering, geological and technology problems during construction, such as outlining inhomogeneous weathering layers in granite during excavation, determining the occurrence of large faults and weathering of alternative layers, detecting the position of seepage in the embankment, checking the engineering quality of the work, and so on. If these problems could not be rapidly solved during construction, they would delay the construction process and affect construction quality. As a high resolution non-destructive detection technique, GPR was able to rapidly and economically solve some of the problems encountered during TGP construction which other geophysical methods could not accomplish. Through test, research and practical application, successful results were obtained using GPR to solve the engineering problems mentioned. In this paper, three case histories are presented. The first shows the delineation of inhomogeneous layers in granite, the second illustrates the definition of faults and weathering of alternative layers, and the third demonstrates the checking of the engineering quality of work for the TGP. The detection results were confirmed by on-site inspection.

Proof of the Young–Laplace Equation Using the Theory of Calculus of Variations Applied to Petroleum Fluids

Computer technology has advanced rapidly in the past two decades. Many complicated petroleum science and engineering problems have been solved numerically using computers. Consequently, less attention has been paid to analytical methods. Higher education institutions have a tendency to offer more numerical analysis courses and less advanced mathematics courses than before. As a result, the analytical skills of graduating petroleum scientists and engineers are declining. This article demonstrates that analytical methods are still favorable in solving some petroleum science and engineering problems. The demonstration example is the proof of the Young–Laplace equation using the theory of Calculus of Variations applied to petroleum fluids.

High-Performance Computing for Large-Scale Analysis, Optimization, and Control

Research papers published on parallel processing, supercomputing, and distributed computing since 1994 are reviewed in this article. The focus is on review of the archival journal articles published in three areas: analysis, optimization, and control. The review is divided into three main sections: (1) parallel processing on dedicated shared memory and distributed memory parallel machines; (2) distributed computing on a cluster of networked workstations; and (3) parallel computing and object-oriented programming. The great majority of the journal articles published since 1987 deal with fundamental issues and academic problems. The trend in the future, at least in part, should be more toward solution of large-scale and complicated real-life engineering problems, the kind of problems that cannot be solved readily by conventional uniprocessor computers.

Penalty-combined method and applications in solving elliptic problems with singularities

The simplest penalty technique is proposed for matching the Ritz-Galerkin and finite elements methods in solving elliptic problems with multiple singularities. The advantage of this method over the nonconforming combination is its simplicity, without dealing with direct constraints. Error bounds are provided to guide the choice of the penalty constant P c. Moreover, when P c is chosen properly large, the numerical solutions from the penalty combined method will approach those from the nonconforming combination. Numerical experiments are carried out for Motz's problem to justify the proposed coupling technique. This technique is also applied to the study of potential flow of wind over buildings where there exist multiple singularities and multiple coupling interfaces among different numerical methods. On the whole, the penalty combined method is useful for solving complicated engineering problems.

Complex Stress Paths and Validation of Constitutive Models

Abstract The solution of complicated soil engineering and soil structure interaction problems requires the use of realistic constitutive equations and failure criteria. A recent international workshop held at Case Western Reserve University was aimed at assessing the predictive capability of presently available models for granular noncohesive soils. The results of tests conducted on hollow cylinders at Case and on cubes at the University of Grenoble were used to test the various models. This paper highlights some of the realities of soil testing when the equipment used induces different boundary conditions to the soil samples. It evaluates the predictions submitted to the workshop and examines the adequacy of the various classes of models in predicting simple and complicated stress paths using results obtained from standard tests.

A comparison of the implementation and performance of the Nanbu and Bird direct simulation Monte Carlo methods

Since Bird [Phys. Fluids 6, 1518 (1963)] first proposed the idea of direct simulation Monte Carlo (DSMC) techniques in order to model rarefied gas flows, a concern has been that his method does not provide a solution to the Boltzmann equation. Several simulation schemes have now been developed and, in a review of these methods, Nanbu [J. Phys. Soc. Jpn. 52, 3382 (1983)] showed that only his method [J. Phys. Soc. Jpn. 49, 2042 (1980)] gave a true solution to the Boltzmann equation. However, Nanbu’s simulation method is also the most computationally expensive scheme and in his review paper he recommended the use of the Bird technique for complicated engineering problems. Nanbu’s method also suffers from the apparent disadvantage that momentum and energy are not conserved at each collision. With the advent of the supercomputer the relative expense of the methods will inevitably be of lesser importance so that the testing of the Nanbu method in an engineering context is desirable. A detailed study of the implementation and performance of the Bird and Nanbu simulation schemes has therefore been carried out with reference to the expansion of a gas into vacuum. The results reported herein show, however, that in addition to increased computational overheads, the Nanbu method suffers from further defects that make its implementation more difficult. It is concluded that the Nanbu method is generally less flexible than that of Bird and that greater care must be exercised if meaningful results are to be obtained using the Nanbu approach.

A mixed-mode crack analysis of rectilinear anisotropic solids using conservation laws of elasticity

A very simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems in rectilinear anisotropic solids is presented. The analysis is formulated on the basis of conservation laws of anisotropic elasticity and of fundamental relationships in anisotropic fracture mechanics. The problem is reduced to a system of linear algebraic equations in mixed-mode stress intensity factors. One of the salient features of the present approach is that it can determine directly the mixed-mode stress intensity solutions from the conservation integrals evaluated along a path removed from the crack-tip region without the need of solving the corresponding complex near-field boundary value problem. Several examples with solutions available in the literature are solved to ensure the accuracy of the current analysis. This method is further demonstrated to be superior to other approaches in its numerical simplicity and computational efficiency. Solutions of more complicated and practical engineering problems dealing with the crack emanating from a circular hole in composites are presented also to illustrate the capacity of this method.

Some data obtained with an experimental MHD-power plant

In the report a brief account is given of a large experimental complex MHD-power plant for open-cycle operation with combustion products of natural gas. The main distinguishing feature of such a plant in comparison with existing ones consists in the fact that with its help it is possible to investigate not only the MHD-generator itself but also other complicated components of MHD-power plants as well as to investigate the operation of major components of the MHD-power plant. Presumably the question as to the prospective application of open-cycle MHD-power plants for large-scale power generation can be answered only after the solution of complicated research and engineering problems associated with the development of a large-scale commercial pilot plant. Another distinguishing feature of the described plant lies in the fact that it is intended for a long-period service. The report gives main parameters of the plant, describes the technological scheme and its major components: the combustion chamber, the MHD-channel, the magnet system, facilities for injection and recovery of ionizing seeding, high-temperature air preheaters, end heat-exchanger systems, current inverting systems, etc. Also the report gives a summary of the obtained experimental results. The MHD-generator output power amounted to 30 kW. The comparison of the results on thermal and gasdynamic investigation carried out in the MHD-channel with theoretical calculations made on a refined one-dimensional flow model showed that they agree After the investigations carried out on the described plant conditions were obtained not only for further wide-scale magnetohydrodynamic thermophysical and electrophysical investigations of MHD-power plants but also for the continuation of the work for investigating a simultaneous operation of the MHD-generator with other components of the plant as well as for developing more rational designs of the components and conditions for their operation.

Representation of nonlinear characteristics by linear elements

THE solution of the modern complicated electrical engineering problems needs simpler methods than dealing with a large number of equations in a large number of unknowns; simpler experimental solutions are introduced in the form of simple equivalent circuits or a collection of such circuits with variable constants (to represent more than one case) and measuring instruments in a suitably designed machine called analogue computer. Hence the importance of facilitating the solution of nonlinear characteristics of magnetic circuits, neglecting hysteresis, by the steady-state response of linear elements and using the ordinary measuring instruments (ammeter and voltmeter) is clear.