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Open access

Žanesa Ljevo, Mladen Vukomanović and Suada Džebo

Abstract

Although the quality of a process affects the quality of the end product, there is currently an insignif­icant amount of knowledge about the quality of project management (PM) processes that directly affect the quality of the delivered product (constructed building). This study presents a proposal for modeling the impact of the quality of the PM process on the quality of the con­structed building. The quality of the PM process is rep­resented by the main quality factors and product quality indicators. It presents the results of the interviews that were conducted and study cases that were analyzed in Bosnia and Herzegovina with a variety of project partici­pants (with different managerial perspectives) in terms of the indicators of quality of the delivered product. All par­ticipants, regardless of managerial perspective, believe that the most important indicator of the quality of prod­ucts for each phase of the project is “customer satisfaction in the end phase”, the measurement of which is different for each project phase that is presented. The results of the factor analysis of the definition and the planning phases show that 11 variables, namely, the quality factors of the PM process, can be grouped into three new factors, which is described as 66.61% (77.046%) of the basic set of vari­ables.

Open access

Miroslav Pástor, Peter Frankovský, Martin Hagara and Pavol Lengvarský

Abstract

Anchoring parts of technical systems are often damaged due to the heavy forces acting on these systems during their operation. For that reason, various modifications are suggested and created on the anchoring screws, which should help to reduce the mechanical stress values in a place of the first load-bearing thread of a female screw. For the determination of stress fields on the surface of a plane model of a threaded joint, two non-contact optical methods were used – conventional transmission photoelasticimetry and modern digital image correlation.

Open access

Stefan Segla

Abstract

The paper deals with static balancing of various kinds of mechanisms and manipulation devices using spring balancing mechanisms. In case of parallelogram robots and manipulation mechanisms a spring balancing mechanism exerting a constant force is used. Problems of static balancing of variable payloads are also presented and investigated in the paper. Static balancing is formulated as an optimization problem with the objective function expressing minimization of the forces acting in the driving joints. As design variables geometrical variables and spring stiffnesses and their unloaded lengths are used. Optimization Toolbox for Use with Matlab and GOOD (Generator Of Optimal Designs) are used to solve the static balancing problems. The optimized mechanisms are evaluated by using multibody dynamics programs taking into account friction effects in mechanism joints. The results of static balancing optimization show essential reduction of the gravity load in drive joints and consequently driving forces with important energy savings.

Open access

Ivan Virgala, Tomáš Lipták and Ľubica Miková

Abstract

In the paper the locomotion of snake robot is introduced considering locomotion in straight and curved pipe. For the straight pipe locomotion was designed traveling wave locomotion pattern with sine-like wave which expands from rear of the robot to its front. For the locomotion in curved pipe was designed approach which is based on inverse kinematic model including besides primary task also secondary tasks, namely kinematic singularities avoidance task, obstacle avoidance task and joint limit avoidance task. For final inverse kinematic model was used approach of weight matrices by which can be stated the priorities of particular tasks. Both case studies were tested by experimental snake robot in order to verify introduced methodology for locomotion in the straight and curved pipe.

Open access

Michal Kelemen, Alexander Gmiterko and Darina Hroncová

Abstract

The paper deals with bristled in-pipe machine simulation. Simulation model is developed and experimentally identified properties are added into the model to achieve high coincidence of the model with real machine. Simulation gives the answers to some selected problems.

Open access

Pavel Élesztős, Roland Jančo and Vladimír Voštiar

Abstract

Welding is a complex technological process in which local heating takes place up to the melting point of the connecting and the additional material. Phase and crystallization processes are a strong non-linear function of the cooling rate. This non-linear function multiplies the complexity of the numerical simulation and optimization of the welding process. Lately, optimization with genetic algorithm has become the trend to optimize systems that behave in a non-linear manner and contain a number of local extremes. Genetic algorithm is therefore a method by which we seek an absolute extreme. It is a method which seeks a solution to near absolute extreme. In this paper the use of the genetic algorithm for welding process optimization is described.

Open access

Davit L. Aghayan, Egidijus Pelanis, Åsmund Avdem Fretland, Airazat M. Kazaryan, Mushegh A. Sahakyan, Bård I. Røsok, Leonid Barkhatov, Bjørn Atle Bjørnbeth, Ole Jakob Elle and Bjørn Edwin

Abstract

Background

Laparoscopic liver resection (LLR) of colorectal liver metastases (CLM) is increasingly performed in specialized centers. While there is a trend towards a parenchyma-sparing strategy in multimodal treatment for CLM, its role is yet unclear. In this study we present short- and long-term outcomes of laparoscopic parenchyma-sparing liver resection (LPSLR) at a single center.

Patients and methods

LLR were performed in 951 procedures between August 1998 and March 2017 at Oslo University Hospital, Oslo, Norway. Patients who primarily underwent LPSLR for CLM were included in the study. LPSLR was defined as non-anatomic hence the patients who underwent hemihepatectomy and sectionectomy were excluded. Perioperative and oncologic outcomes were analyzed. The Accordion classification was used to grade postoperative complications. The median follow-up was 40 months.

Results

296 patients underwent primary LPSLR for CLM. A single specimen was resected in 204 cases, multiple resections were performed in 92 cases. 5 laparoscopic operations were converted to open. The median operative time was 134 minutes, blood loss was 200 ml and hospital stay was 3 days. There was no 90-day mortality in this study. The postoperative complication rate was 14.5%. 189 patients developed disease recurrence. Recurrence in the liver occurred in 146 patients (49%), of whom 85 patients underwent repeated surgical treatment (liver resection [n = 69], ablation [n = 14] and liver transplantation [n = 2]). Five-year overall survival was 48%, median overall survival was 56 months.

Conclusions

LPSLR of CLM can be performed safely with the good surgical and oncological results. The technique facilitates repeated surgical treatment, which may improve survival for patients with CLM.

Open access

Pavel Kraus, Juraj Úradníček, Miloš Musil and Michal Bachratý

Abstract

The evaluation of disk brake squeal is nowadays performed using Finite Element Model. In this standard procedure the thermal effects are omitted. The omission is done because of long computing time of fully coupled brake system thermo-structural transient analysis. This paper is presenting an effective uncoupled thermo-structural FEM procedure. This method is applied on a pin-on-disc system and its time effectiveness is compared to standard full coupled transient analysis.

Open access

Justín Murín, Mehdi Aminbaghai, Vladimír Goga, Vladimír Kutiš, Juraj Paulech and Juraj Hrabovský

Abstract

In this paper, results of numerical simulations and measurements are presented concerning the non-uniform torsion and bending of an angled members of hollow cross-section. In numerical simulation, our linear-elastic 3D Timoshenko warping beam finite element is used, which allows consideration of non-uniform torsion. The finite element is suitable for analysis of spatial structures consisting of beams with constant open and closed cross-sections. The effect of the secondary torsional moment and of the shear forces on the deformation is included in the local finite beam element stiffness matrix. The warping part of the first derivative of the twist angle due to bimoment is considered as an additional degree of freedom at the nodes of the finite elements. Standard beam, shell and solid finite elements are also used in the comparative stress and deformation simulations. Results of the numerical experiments are discussed, compared, and evaluated. Measurements are performed for confirmation of the calculated results.

Open access

Milan Žmindák

Abstract

In this paper the concept of generalized form of proportional damping is proposed. Classical modal analysis of non-conservative continua is extended to multi DOF linear dynamic systems with asymmetric matrices. Mode orthogonality relationships have been generalized to non-conservative systems. Several discretization methods of continua are presented. Finally, an expression for derivatives of eigenvalues and eigenvectors of non-conservative system is presented. Examples are provided to illustrate the proposed methods.