Peter Persson

Modelling local-scale frost variations using mobile temperature measurements with a GIS

Abstract A stepwise linear regression model for local-scale temperature climates for clear and calm summer nights is presented for a heterogeneous and forested area in south Sweden. The spatial variations in measured air temperature 2 m above 5.5 km of roads were modelled from the following independent variables retrieved from a geographic information system (GIS): sky view factor, altitude, relative relief and presence of peat soils. The model explains 88% of the measured variations in air temperature and 87% of the variations in air temperature of a separate validation data set collected along 2.4 km of roads. Distributed model results for a 7.5-km 2 area generates a map with areas delineated that are prone to low temperature and frost after clear-cutting. The map gives useful information for efficient implementation of frost protection measures in forestry and is based on a simple methodology that can be applied in practical forestry.

A flexible portable system for measurement of air temperature and humidity

Abstract The Department of Physical Geography, Lund, has, in cooperation with Chemical Dynamic Sweden AB (CDS) in Skara, Sweden, developed a flexible portable system which can be used for temperature and humidity measurements both from a car or while carried on foot. The major system is composed of two minor systems, the field system and the stationary system. The field system is built around a micrologger from Campbell Scientific Inc. (CSI, Model 21X) and consists of six different sensors (five which measure air temperature and one which measures humidity), a cassette memory, a switch closure and a box with buttons for adding extra information to the memory (location, etc.). The sensors are attached to a mast at different levels (0.2, 1.0, 2.0 and 3.0 m) and are easy to move. The stationary equipment consists of an IBM AT computer, a cassette interface (CSI, Model C20) and a flex-hammer printer. Tests have shown that the accuracy of the temperature measurements is ∼ ± 0.3°C. The accuracy of the humidity measurements is ± 1% RH. The error of the switch closure, which measures the way the car runs, has been measured at 0.03%. It takes the logger 80.5 ms to measure the six sensors and put the values in the memory. This means that it is possible to measure each fifth meter at a speed of 50 km h−1. Tests have shown that 50 km h−1 is the highest speed recommended for car measurements. In our case, we have chosen to make measurements at every 10 m from a car at a speed of 40 km h−1. The system has been used since 1986 in a project concerning nocturnal air temperature in an orchard district and was found to be very convenient and reliable.

Fluid-Structure Interaction Analysis of Vibration Reduction in Pipe Systems

Transmitted vibrations from water-pipe systems, involving supports standing on a concrete slab and the underlying ground, are investigated here. The effects of varying parameters of the supports, such as location, their elastic modulus and their cross-section, on the level of vibrations transmitted by the water-pipe system are analysed in order to minimise vibrations transmitted to sensitive parts in a facility. A finite element model involving use of both finite and infinite elements was employed for analyses in the frequency domain where account was taken of both fluid-structure interaction and soil-structure interaction. It was concluded from the analyses performed that the parameters of the supports had an appreciable effect on the vibration level in the facility.

Predicting structure-borne sound from railway traffic

Since noise exposure can disturb the well-being, acoustical comfort in the built environment is of great importance when constructing new dwellings. Population growth causes densification of cities, which together with space limitation issues, lead to buildings being constructed closer to existing vibration sources such as motorways and railways, and vice versa. Likewise, architectural trends, environmental benefits and cost result in increased use of lighter materials such as wood and hollow-core concrete slabs. Lightweight structures make the achievement of acoustical comfort in dwellings an increasing challenge. A major issue when designing buildings regarded as acoustically pleasant, especially in the low-frequency range, is the lack of reliable prediction models to be used during the design stage of the building. Predictions of structure-borne noise are nowadays mostly made based on measurements performed on existing buildings and engineers’ experience. Hence, it is of interest to develop tools that ...

Prediction Models of Free-Field Vibrations from Railway Traffic

Many cities experience an increasing population leading to a need for urban densification. In these cities, unused land close to railways will have to be developed with new residential and office buildings. The infrastructural demand will also increase, resulting in heavily trafficked roads and railways close to w here people work and live. Annoyance from traffic-induced vibrations and noise is expected to be a growing issue. To predict the level of vibration and noise in buildings caused by railway and road traffic, calculation models are needed.In the present pa per, a simplified prediction model is briefly described. This prediction model is based on the assumption that the ground and railway embankment can be described in an axisymmetric model , to provide the transfer functions between the track and the free-field . In the paper, the error that arise by assuming axisymmetric response is studied by comparing the response in a three-dimensional finite-element model. Transfer functions at several positions in the free-field are compared (Less)

Numerical Study of Reduction in Vibrations Induced by Water-Pipe System

In certain buildings such as synchrotrons and large ground telescopes, strict requirements are stated regarding the vibration levels. Both external and internal vibration sources, for example traffic and indoor water pumps, can have an appreciable effect on the vibration levels in the buildings. The synchrotron research facility MAX IV, which is currently under construction in Sweden, serves as an example case for the analyses. In MAX IV, several water-pipe systems used for cooling purposes will be placed near vibration sensitive equipment. These systems will transmit vibrations, into structural parts of the facility, which could exceed the vibration requirements. Structural modifications of pipe systems are investigated here by means of the finite element method in order to reduce vibration levels in the building. The finite element model employed includes a water-pipe system, adjacent building parts and the underlying soil. The use of fluid-structure interaction is investigated as well as the use of component mode synthesis. This paper focuses on the numerical procedure used as well as the effects on transmitted vibrations by different placements of the pipe supports.