Search results

Discusses the causes of damp following the insertion of a remedial damp‐proof course and the methods which can be used to detect and prevent it. Details hygroscopic and capillary moisture, the components of the total moisture content of masonry and the uses of a moisture profile with which to measure this. Explores electrical and carbide moisture meters, explaining the pros and cons of each. Reports on alleged failures and reported causes of damp, discussing problems with replastering, condensation and penetrating damp, surface condensation, misreading of signals, bridging. Suggests that the majority of dampness problems can be resolved by undertaking a logical programme of investigation and elimination.

In structural mechanics, systems with damping factor get converted to nonlinear eigenvalue problems (NEPs), namely, quadratic eigenvalue problems. Generally, the parameters of NEPs are considered as crisp values but because of errors in measurement, observation or maintenance-induced errors, the parameters may have uncertain bounds of values, and such uncertain bounds may be considered in terms of closed intervals. As such, this paper aims to deal with solving nonlinear interval eigenvalue problems (NIEPs) with respect to damped spring-mass systems having interval parameters.

Two methods, namely, linear sufficient regularity perturbation (LSRP) and direct sufficient regularity perturbation (DSRP), have been proposed for solving NIEPs based on sufficient regularity perturbation method for intervals. LSRP may be used for solving NIEPs by linearizing the eigenvalue problems into generalized interval eigenvalue problems, and DSRP may be considered as a direct solution procedure for solving NIEPs.

LSRP and DSRP methods help in computing the lower and upper eigenvalue and eigenvector bounds for NIEPs which contain the crisp eigenvalues. Further, the DSRP method is computationally efficient compared to LSRP.

The efficiency of the proposed methods has been validated by example problems of NIEPs. Moreover, the procedures may be extended for other nonlinear interval eigenvalue application problems.

The objective is to study the optimal damper placement of a given number of passive viscoelastic dampers, when the structure (nuclear plant) is subjected to motions from earthquake, in order to reduce the acceleration responses at a particular location, for example, a vibration‐sensitive room (nuclear reactor).

The IDESIGN software including genetic algorithms for the optimisation task has been interfaced with a finite element program, ABAQUS, to create a structural optimisation tool. The tool has been tested on a 3D building structure.

Optimisation results for different constraints on number of dampers shows that eight optimally located dampers results in an overall maximum reduction of 59 per cent of the cost function for the uncontrolled structure. It is also found that six optimally placed dampers are more effective than the fully damped case with 12 dampers.

More powerful computers are needed in order to reduce the computational time for many engineering models. Especially parallel processing would make more efficient use of the genetic algorithm. It is also necessary to perform stochastic finite element analysis to investigate the impact on the cost function due to different earthquakes.

The study of vibration reduction by an optimal number and location of viscoelastic dampers indicate that structures subjected to dynamic forces can be designed both safely and economically.

The tool developed is quite general and is believed to be applicable to many types of structural optimisation analyses.

Research is being carried out into the performance of surveyors undertaking a Homebuyer Report. The background to that research was published in Hollis, M. and Bright, K. (1999), Structural Survey, Vol. 17 No. 2. This paper is a sub‐set of that work and deals with the public perception of survey standards relating to dampness, the duties of the surveyor, and the knowledge requirement for a surveyor working in 1999. It looks at the observation and the reporting of dampness within a sample of ten survey reports completed within a period of two weeks on the same house. The research concludes that there is an unexpectedly high level of reporting that falls below an acceptable standard. Recommendations are made for the improvement of standards, an assessment of the skills required and the requirements for the education process for surveyors.

The purpose of this paper is to propose a virtual testing strategy in order to predict damping due to the joints which are present in the ARIANE 5 launcher.

Since engineering finite element codes do not give satisfactory results, either because they are too slow or because they cannot calculate dissipation accurately, a new computational tool is introduced based on the LArge Time INcrement (LATIN) method in its multiscale version.

The capabilities of the new strategy are illustrated on one of the joints of ARIANE 5. The damping predicted virtually is compared to experimental results, and the approach appears promising.

The tool which has been developed gives access to calculations which were previously unaffordable with standard computational codes, which may improve the design process of launchers. The code is transferred into ASTRIUM‐ST, where it is being used to build a database of dissipations in the joints of the ARIANE 5 launcher.

The purpose of this paper is to investigate the dynamic stability of liquid hydrogen turbopump rotor system in rocket engine under the effects of seal and internal rotor damping.

The dynamic modeling of a liquid hydrogen turbopump rotor system in rocket engine is presented in this paper with the aid of the finite element technique. The mathematical model takes into account the seal hydrodynamic forces described by Muszynska model and the internal rotor damping, viscous damping, and hysteretic damping. The shooting method and Floquet theory are employed to investigate the effects of seal and internal rotor damping on the nonlinear dynamic stability of two turbopump designs, the original and the modified design with a flexible bearing support.

The numerical results, which are in good agreement with test data, show that the destabilizing effect of internal rotor damping play a key role in the original design. In the modified design, the stability margins are enhanced and the vibration response levels are minimized. The onset speed of instability increases in original design and decreases in modified design as the effects of seal nonlinearities are considered. The predicted results indicate that the seals have a great destabilizing effect in the modified design and the turbine end bearing is the most dangerous hardware in both designs. The system stability analysis shows that the effect of seal length on the system stability is significant comparing with that of seal radius.

The results can be used in the design and operation of a liquid hydrogen turbopump rotor system to improve its stability performance and eliminate its subsynchronous problem.

Since seal and internal damping are two key destabilizing factors in liquid hydrogen turbopumps and the seal nonlinearities are inevitable, the use of nonlinear theory to study their effects on nonlinear stability and dynamic performance can lead to accurate prediction and explain the nature of the subsynchronous motion.

Explores damp in the context of historic buildings, explaining why these structures require an individualistic approach. Outlines historic building materials and construction and the history of damp treatments. Discusses the causes of damp related damage, concentrating on direct penetration of rainwater, rising damp, condensation and hydroscopic salts. Details the principles of historic pointing and rendering, and the differences in modern techniques, touching on preventatives such as leadwork, water repellents and consolidants. Concludes that the primary consideration when working on any aspect of historic building work is that any clash between building conservation and human comfort ought to favour the building.

Capillary rise of water in buildings has been an issue of concern among past and present researchers. Despite the research efforts devoted to the proper elimination of the problem in masonry construction, it still remains a challenge that needs to be addressed. The purpose of this paper is to explore treatment mechanisms that can be used to prevent rising damp in new building infrastructure.

In total, 14 test walls are constructed, conditioned, subjected to various treatments and monitored for four years. The treatments applied to the walls include the use of polyethylene damp proof courses, damp proof coatings and dense concrete bases. The walls are then monitored with reference to the two climate seasons in Ghana.

The results highlight that rising damp is present, as suggested by the constant increase and decrease in the height of the water levels in the walls during the rainy and dry seasons, respectively. The findings further reveal that within the four-year period, the walls treated with the damp proof coatings, together with those with the dense concrete bases performed better than those treated with the polyethylene damp proof courses.

The economic and commercial impact of these preventive mechanisms were not considered in this study. A future research can be directed at these issues.

The proposed treatment mechanisms highlight the effectiveness of some treatments applied to walls to prevent the capillary rise of water from the ground into the superstructure.

Building regulations, especially in Ghana and other tropical settings should be amended to include ways to prevent rising damp phenomena by including effective methods against rising damp during the building design or construction.

Series of studies worldwide have been conducted in laboratories to simulate the capillary rise of water in walls of buildings. This is among the few studies that look at how water rises from actual ground conditions into the walls of buildings.

This paper describes the results for magnetic damping in torsional mode (TEAM problem 16). A total of six solutions are presented and compared with experimental results. The problem is treated as a coupled electromagnetomechanical one. In general numerical predictions agree well with experiment.