External Wall Surface Research Articles

Internal heat transfer coefficient estimation in three-dimensional ducts through the reciprocity functional approach – An analytical approach and validation with experimental data

In the current paper it is presented and tested an innovative method for estimating internal heat transfer coefficients in ducts adopting only thermal measurements acquired on the external wall surface. This approach is based on the reciprocity functional analysis, which is a powerful non-intrusive inverse problem technique. The adoption of this technique is promising since it avoids intrusive measurements, it is fully non-iterative and the computational time and cost are very limited. In this paper, it is presented an extension of the classical reciprocity functional methodology in the sense that a fully analytical expression, obtained by the integral transform technique, is developed for estimating the internal heat transfer coefficient in a three-dimensional problem. Such methodology, avoiding the solution of linear systems, reduces the computational costs that are massive when the traditional approaches are applied to three dimensional problems. The proposed procedure is first validated adopting synthetic temperature data and then tested using real temperature measurements acquired by an infrared camera. The results highlight that the methodology is able to recover the unknown functions in a very short computational time with a good accuracy.

Design of solar huts

This problem is a solar hut photovoltaic cell in the attached and overhead two installation methods, the type of photovoltaic cells and array mode and inverter type optimization design issues. In question 1, since the photovoltaic cells are attached to the roof and exterior surfaces, the direction and angle of the battery are uniquely determined by the direction and angle of the attached surface. The problem is translated to optimize the installation of a certain type on a single surface area (array) of photovoltaic cells, so that the total amount of solar photovoltaic power generation as much as possible, and the unit power generation costs as small as possible, which is a multi-objective optimization problem. The problem can be discussed in the ideal environment in a single surface area of the battery installation optimization program, and then the actual environment of the multi-surface optimization. In the solution to Problem 1, the unit on the south of the roof of the battery at the moment to accept the solar energy formula is generated. The definition of and is the moment of direct radiation intensity, for the moment the sun and the south of the roof of the plane where the angle, for the level of horizontal radiation intensity, for the south of the roof and the horizontal angle, the planefor the plane, the center of the heart, the vertical upward direction is the axis of the positive coordinate system, obtained with the sun height angle , the sun azimuth , red angle, angle and the sun when the relationship is generated. The conclusion is only installed in the small roof surface type of battery C11, and the rest of the surface is not installed. 35 years of electricity generation is 77126 degrees, the economic benefits of 16,488 yuan, the recovery period of 21.3 years. In question 2, because the photovoltaic cells in the roof and the external wall surface can be installed overhead, the panel orientation and tilt will affect the efficiency of photovoltaic cells. Therefore, in the optimization scheme of Problem 1, the orientation and inclination of the panel on each surface are further adjusted to calculate the optimum orientation and inclination of the panel on each surface. The problem can be in the ideal weather environment to establish the sun running and the battery board efficiency model, and then the measured environment test. The optimal orientation of the panel is southward, and the optimal angle with the ground plane is 39.89 degrees. The conclusion is only installed in the small roof surface type of battery C11, and the rest of the surface is not installed. 35 years of generating capacity of 82165.2 degrees, the economic benefits of 18,998 yuan, the recovery period of 13 years. In question 3, by the optimization of the above two issues, in the building to meet the requirements of the hut under the design of the various aspects of the cabin and battery installation, and further optimize the total power generation of the hut, economic benefits. The whole model solver is run in MATLAB7.0.

Assessment of the possibility of profiting from solar energy through the use of walls with external sheet metal cladding

The possibility of profiting from solar radiation through external walls was studied for an experimental, windowless livestock building. Temperature measurements on the wall surfaces were taken during winter, in two measuring series. On the first day, the average sol-air temperature on the outer surface of the east-facing wall was 7.4 °C and was even up to 2.2 °C lower than temperature of the outdoor air which was 9.6 °C. With the averaged temperature of inner surface of the wall reaching 21.3 °C, heat transfer form the outside into the building was impossible. An identical tendency in temperature distribution on surfaces was noticed on the west-facing wall. In the second measuring cycle, the sun temperature on external wall surfaces increased significantly — 13.3 °C on the eastern side, and 14.1 °C on the western side. They were noticeably higher than the outdoor air temperature which was 9.1 °C. However, the high indoor surface temperatures on the eastern and western walls — 21.2 °C and 21.0 °C respectively, proved that in this case too, the transfer of heat generated by the sun’s radiation into the building was impossible. The tests results imply that we should exclude reheating the building with the heat from sun heat external walls during winter. However, a similar assessment including more measuring series and several objects, could be also be performed during interim seasons.

Energy and Economic Performance of Plant-Shaded Building Façade in Hot Arid Climate

The use of vegetated walls and intensive plantation around buildings has increased in popularity in hot and arid climates, such as those in the United Arab Emirates (UAE). This is due to its contribution towards reducing the heat gain and increasing the occupants’ comfort levels in spaces. This paper examines the introduction of plant-shaded walls as passive technique to reduce heat gain in indoor spaces as a strategy to lower cooling demand in hot arid climate of Al-Ain city. Experimental work was carried out to analyze the impact of using plantation for solar control of residential building façades in extreme summer. External and internal wall surface and ambient temperatures were measured for plant-shaded and bare walls. The study concluded that shading effect of the intensive plantation can reduce peak time indoor air temperature by 12 °C and reduce the internal heat gain by 2 kWh daily in the tested space. The economic analysis reveals a payback period of 10 years considering local energy tariff excluding environmental savings.

Determination of the crack-initiation and propagation conditions in a styrene-acrylonitrile water-filter housing with external ribs based on destructive pressure tests

Abstract Fatigue cracks were initiated during the operation of a water-filter housing made from styrene-acrylonitrile (SAN). Using a destructive pressure test, it was confirmed that the sharp transition between the wall and the vertical external ribs of the filter housing at the point of the increased external diameter is the critical area of the water-filter housing. This is a consequence of the stress concentration due to the combined action of the sharp edges of the vertical external ribs and the increased stiffness due to the thicker wall and the mounting of the upper part of the housing onto the filter head. During the destructive pressure tests a crack was initiated on the external surface in the same place and spread in the same direction as the fatigue crack during the operation of the water filter. At the critical point the actual loads due to the stress concentrator are approximately 3.2 times higher than that expected based on the water pressure in the pipeline. The tensile strength of the styrene-acrylonitrile from the water-filter housing was comparable with the literature data. The fracture toughness of styrene-acrylonitrile is low and comparable to the fracture toughness of polymethylmethacrylate. The critical crack depth for the occurrence of an uncontrolled rupture for a continuously increasing load is approximately 100 μm, while the plane-strain condition occurs at a thickness of about 1 mm. A rapidly growing crack in the wall tends to grow in a layer of plane-strain conditions, and from the internal- to the external-wall surface. The possibility of determining the fracture toughness with a destructive pressure test of the housing or a pressure vessel with an external surface stress concentrator was achieved.

A new model for exergetic optimum insulation thickness

A new approach is presented to predict the exergetic optimum insulation and the payback period. The calculation method consists of four innovations, namely, heating/cooling degree-hour figures for any given time interval in a day depending on the building working conditions instead of the annual total of degree-hours; the effect of concrete columns on external wall surfaces; the costs of labour and auxiliary equipment utilisation are incorporated into the total insulation cost and finally, the method also determines the optimum insulation depending on whether the purchase of insulation material is financed with cash or bank credit. A concept on energetic and exergetic saving start and end insulation thickness is also introduced into the literature.

Some aspects of energy efficient building envelope in high latitude countries

Nowadays, energy conservation in buildings is especially important for countries where high energy consumption in the residential and tertiary sectors causes the high energy intensity of the whole economy. This paper presents some idea of creating energy efficient building envelopes. The focus is on reduction of heat transfer through it. Different structures of external walls are analyzed. In high latitude countries walls should be characterized by high thermal resistance and high thermal capacity (good storage ability). In the paper traditional multilayer wall structures with specific paints on external wall surfaces are analyzed. Paints are characterized by different solar absorptivity. Two extreme cases of solar absorptivity of external wall paints (0.9 for the black paint and 0.1 for the black paint) have been taken into account to give completely different ability of the external wall surface for photo-thermal conversion (of solar radiation). Results show that in moderate or cold climates, if thick thermal insulation is applied as external layer of a building envelope, then the effect of solar absorptivity of a cover paint of external wall surface is not meaningful. In July, when daily solar irradiation is the highest, in the case of the black paint all day long there are small heat gains (about 2kJm−2 in average) with maximum in the night (3.1kJm−2). In the case of the white paint all day long there are small heat losses (about 2.3kJm−2 in average), with maximum in the middle of a day (2.7kJm−2). The effect of the solar absorptivity of the paint, that covers the external surface of the wall, can be seen, but it is very small and perhaps cannot be noticed by inhabitants. However, in the extreme summer weather conditions, i.e. very high irradiance level and high ambient air temperature, what have happened quite often in high latitude countries recently, the considered effect is more strong. Therefore, it would be good to apply envelope of a building, that can change “the skin” from summer to winter. Also modern structures with the Phase Change Materials (PCMs) are analyzed. In simulation study it was assumed that PCMs are applied in the form of light thermal mass panels that are integrated with the external wall structure. A mathematical model of dynamics of a building has been developed. In the paper stress has been put on energy transfer through walls of different structures. The model takes into account the influence of solar radiation on energy balance, including the availability of solar radiation on walls of different location (inclination and orientation). On the basis of the model developed simulation studies have been performed. Selected results of thermal behavior of some multilayer structures of external walls of a building have been analyzed. Through comparative studies some recommendations for creating building wall structures have been formulated. Results (presented in figures) show, how the temperature of a wall surface can increase because of the high solar radiation absorptivity of the surface paint. The temperature is especially high when a thick insulation is used. Because of the insulation the heat transfer through the wall is reduced significantly. If there is no insulation than the heat gained can be conducted (relatively easily) through the wall to the interior of a building, in consequence there are high heat gains in summer, and the temperature of the external wall surface is not high. It is evident that external surface temperature is not the basic parameter that determines the real heat transfer through a wall. Results show that in high latitude countries a wall structure for a standard building (used all year around) must contain thermal insulation as external layer. This is also true when the PCMs are applied in the form of light thermal mass panels. For high latitude countries the recommended structure of an external wall is following: thermal insulation (e.g. mineral wool) at outside (external layer) of thickness of 25cm and PCM thermal mass panel at inside (internal layer) of thickness of 1cm. Such wall structure assures full reduction of the ambient surrounding influence. An external wall made of a brick and a PCM panel does not have high enough thermal resistance (even if thermal capacity is high) to keep the room temperature at the required level. However, such structure could be recommended for the summer season, e.g. for summer houses in a moderate climate or high latitude countries, or for warm climate.

An investigation into the Accuracy of Distance Measurements to an object with the Pulse (Non-Prism) Total Station

In order to achieve the results that meet the specifications of a given project, like engineering surveys (e. g., Surveying of Buildings) , the knowledge of the reliability and accuracy of the surveying equipment is inevitable. The reflectorless total stations are used nowadays for several applications in civil engineering work due to their highly accurate , easy and fast measurements in an automated measuring process. The present paper investigates the accuracy and limits for prismless instrument Total Station especially in relation to observations with large (horizontal and/or vertical) angle of incidence to the reflecting surface , its colours and types, and beam divergence of the measuring signal. This study has been carried out with various surveying field tests by prism and prismless modes, using the pulse (non-prism) TOPCON GPT-2006 Total Station to evaluate the limitations and accuracy of this instrument in surveying the buildings (distance measurements).
 The current study has confirmed that while observations at right angles to an object ( building) are generally well within manufacturer specifications (σ=±10 mm), observations to surfaces of a building from a position that is not at right angles to the surface of the building ( signal beam) can introduce errors.
 Also , this study suggests that the angle of incidence of the measuring signal to the building points ( external and internal corners and wall surface points) has a large influence on the accuracy of that measurement. It is recommended to use horizontal angle of incidence for measuring the detail survey points between (-36 to + 36) degrees from the normal. Also, in case of measurements to a vertical surface, the maximum measured vertical angles of incidence was about forty degrees when using prismatic observations and fifty degrees for reflector less measurements. Some surveying techniques and recommendations are suggested to overcome these problems. Moreover, a good understanding of the non-prism instrument is required to get the required accuracy of the project. When using other total station equipment, the results of the current study can be used as a general guide only. The results of the current practical field experiments, computations and analysis of these tests using various calculations and least squares theory and computer programs (Excel and AutoCAD 2010) are also presented in digital and/or graphical forms.

Optical analysis of glass bead retro-reflective materials for urban heat island mitigation

Retro-reflective (RR) envelopes can reduce the urban heat island (UHI) effect. To develop a lower cost method for imparting RR properties to external wall surfaces, this research measures RR performance of RR surfaces made with glass beads. 8 glass bead RR samples were created, as well as 1 prism and 1 capsule type for comparison. Their angular retro-reflectance and angular distribution were measured by an emitting–receiving optical fiber system developed in our laboratory. It shows that the retro-reflectance of all RR samples at low incident angle with respect to the perpendicular is better than at high angles. The RR capacity of glass bead samples with a refractive index of 1.9 is better than those of 1.5. The retro-reflectance of prism sample is much larger than the all glass bead samples at incident angles up to about 60–70°. The performance decreased sharply at incident angles of 70° and above. At high incident angles, the glass beads are slightly better than prisms. This could make them better suited to apply to outer walls with the goal of reducing reflection of midday sunlight onto streets and buildings. Also, considering their simple construction, glass beads may be more cost-effective the prism in reducing UHI.

Energy performance analysis of variable thermal resistance envelopes in residential buildings

This paper evaluates potential energy savings associated with dynamic insulation materials (DIMs) – material assemblies that can change their thermal resistance through a controlled exchange of liquid or gaseous media – in the exterior walls of buildings. In the analysis, a two-step control strategy is considered to modify the R-value of DIMs based on the temperature difference between internal and external wall surfaces. Using a simulation environment capable of modeling DIMs, a comparative analysis is carried out to evaluate the impact of DIMs on the heating and cooling energy end-uses for single-zone residential buildings in three US climates. Several design and operating conditions are considered to assess the performance of DIMs and their potential energy use savings. The results indicated that variable thermal resistance envelope materials (RSI-0.5/RSI-2.5) have the potential to reduce annual cooling energy use in residential buildings on average by 15% and up to 39% for all three US climates and annual heating energy use by 10% on average for mild US climates depending on the window sizes and internal heat gains.

In situ U-value measurements for today's Cypriot houses

The present work aims to establish the thermal characteristics and actual thermal behaviour of typical residential houses in Cyprus under real weather conditions. For this purpose, a wireless web-based monitoring system has been deployed covering 44 different houses, geographically spread all over Cyprus. Construction materials varied amongst each house, resulting in a theoretical U-value range of 0.467–1.389 W/m2 K. Calibrated temperature sensors were installed and measurements were conducted at 30-min intervals for each individual house. The indoor air temperature of each house, the outside (ambient) air temperature, and the internal and external wall surface temperatures have continuously been monitored for a period of 15 months. Processing the above-mentioned data has led to the establishment of the mean indoor air temperature of the typical Cypriot residence and calculation of the U-value for each individual wall, facing north, south, east and west, including the roof, comprising the building envelope. Variations of the calculated U-value of up to 25% for each wall orientation were observed, even though construction materials of each wall remain the same. Furthermore, deviations of up to 30% from the theoretical U-value calculation were also observed.

Some Aspects of Energy Efficient Building Envelope in High Latitude Countries

Nowadays, energy conservation in buildings is especially important for countries where high energy consumption in residential and tertiary sectors causes the high energy intensity of the whole economy. This paper presents some idea of creating energy efficient building envelope. The focus is put on reduction of heat transfer through it. Different structures of external walls are analyzed. In high latitude countries walls should be characterized by high thermal resistance and high thermal capacity (good storage ability). In the paper traditional multilayer wall structures with specific paints on external wall surfaces are analyzed. Paints are characterized by different solar absorptivity. Also modern structures with the Phase Change Materials are analyzed. In simulation study it was assumed that PCMs are applied in a form of the light thermal mass panels that are integrated with the external wall structure. Mathematical model of dynamics of a building has been developed. In the paper stress has been put on energy transfer through walls of different structures. The model takes into account the influence of solar radiation on energy balance, including availability of solar radiation on walls of different location (inclination and orientation). On a base of the model developed the simulation studies have been performed. Selected results of thermal behavior of some multilayer structures of external walls of a building have been analyzed. Through comparative studies some recommendations for creating building wall structures have been formulated.

Setting for the Application of Phase Change Paraffin in Block Masonry

This paper studies the insulation properties of masonry filling paraffin composite phase change material. With high density polyethylene (HDPE) as wrapping materials and solid-liquid mixing paraffin as phase change materials, solid-liquid mixed paraffin phase change material with different amount of admixture is prepared, and the problem of flowing after paraffin phase change is then solved. The phase change temperature and the phase change latent heat of composite phase change material with different amount of admixture are tested. The results showed that the composite material with 30% of 52 # solid paraffin, 70% of liquid paraffin, 70% of HDPE coating performs best as to the phase transition temperature and latent heat. On this basis, This paper studies the composite phase change wall with phase change materials 0%, 33%, 66% and100%. Results show that the composite phase change material wall’s heat preservation performance has significantly improved. the temperature fluctuation range of internal and external wall surface is 4.2 °C lower than unfilled wall.

Tree canopy shade impacts on solar irradiance received by building walls and their surface temperature

Shading coefficients are used to predict the seasonal and diurnal benefit of architectural shading devices. It is more difficult to model the impact of tree shade on building thermal performance, and data is rare and varies greatly with species and season. We established a range of tree shade amounts and shade qualities from which to develop simple, robust models that predict external wall surface temperatures. We measured percentage shade cover, solar irradiance and external surface temperature on north and west sun-bearing walls of three identical buildings in spring and summer 2010/11. One building was shaded by tall Angophora trees, another by smaller Fraxinus trees and one was unshaded.Tree shade reduced wall surface temperatures by up to 9 °C and external air temperatures by up to 1 °C. The smaller trees did little to reduce external wall surface temperatures, and moving the tall trees further away from the building wall eliminated their cooling benefits. Wall surface temperatures were best predicted by shade cover and solar irradiance, and was most poorly predicted by shading coefficients, that varied greatly through the day and the season, as tree height and leaf area index increased.Trees can reduce external solar irradiance loads when they are close enough and tall enough to shade the majority of the wall. To simulate the thermal performance benefits that trees provide, it is necessary to account for seasonal, growth and phenological changes in tree shade amount and quality.

Seismic and vibration tests for assessing the effectiveness of GFRP for retrofitting masonry structures

Full-scale shake table seismic experiments and low-amplitude vibration tests on a masonry building are carried out to assess its seismic performance as well as study the effectiveness of a new multifunctional textile material for retrofitting masonry structures against earthquakes. The un-reinforced and the retrofitted with glass fiber reinforced polymer (GFRP) strips masonry building was subjected to a series of earthquake excitations of increasing magnitude in order to progressively induce various small, moderate and severe levels of damage to the masonry walls. The performance of the original and retrofitted building states is evaluated. Changes in the dynamic characteristics (lowest four modal frequencies and damping ratios) of the building are used to assess and quantify the damage states of the masonry walls. For this, the dynamic modal characteristics of the structure states after each earthquake event were estimated by performing low-amplitude impulse hammer and sine-sweep forced vibration tests. Comparisons between the modal results calculated using traditional accelerometers and those using Fiber Bragg Grating (FBG) sensors embedded in the reinforcing textile were carried on to investigate the reliability and accuracy of FBG sensors in tracking the dynamic behaviour of the building. The retrofitting actions restored the stiffness characteristics of the reinforced masonry structure to the levels of the original undamaged un-reinforced structure. The results show that despite a similar dynamic behavior identified, corresponding to reduction of the modal frequencies, the un-reinforced masonry building was severely damaged, while the reinforced masonry building was able to withstand, without visual damage, the induced strong seismic excitations. The applied GFRP reinforcement architecture for one storey buildings was experimentally proven reliable for the most severe earthquake accelerations. It was easily placed in a short time and it is a cost effective solution (covering only 20% of the external wall surfaces) when compared to the cost for full wall coverage by GFRPs.

Impact of non-uniform urban surface temperature on pollution dispersion in urban areas

Airflow pattern through street canyons has been widely studied to understand the nature of pollution dispersion in order to develop guidelines for urban planners. One of the major contributing parameters in pollution dispersion is thermal-induced flow caused by surface and air temperature difference. However, most of the previous studies assumed isothermal condition for street canyons. Those addressed the thermal-induced flow, have assumed a uniform wall surface temperature distribution. The external building wall surface temperature distribution is not uniform, and is influenced by many factors including the wall surface characteristics, and shading. The non-uniform temperature distribution significantly impacts on 3-dimensional airflow within street canyons. Moreover, effect of intersection is barely considered in the literature where L/H<3 (L and H are respectively length and height of street canyon). This Paper reports the development of a 3-dimensional model to study the effect of non-uniform wall surface temperature distribution on the pollution dispersion and flow pattern within the short street canyons (L/H<3). For this purpose, a computational fluid dynamics (CFD) model is developed to investigate these effects on pollution dispersion in various prevailing wind velocities and directions. Moreover, active and passive techniques to reduce the level of concentration are examined. The study clearly shows that thermal-induced flow dominates during fair-weather condition.

Effects of coefficients of solar reflectivity and infrared emissivity on the temperature and heat flux of horizontal flat roofs of artificially conditioned nonresidential buildings

Nonresidential buildings such as shopping centers, supermarkets and factories are constructions characterized as having large roof surfaces in comparison to their external wall surfaces. When conditioned artificially, these buildings become great consumers of electricity. To reduce this consumption, insulation materials are usually used. Notwithstanding the effectiveness of such a procedure, both the cost and environmental issues (the heat-island effect) have been considered as limiting factors for its usage. In this study, we analyze the effect of the application of selective coatings (with very high reflectance for solar radiation and high emittance for infrared radiation) on the surface temperature of the roof and the heat flux that crosses it. Two roof concepts were considered, namely metal roofs both with and without conventional mass-insulation, i.e. an insulating board on the internal side or between two metal foils. The methodology adopted to solve the proposed problem was based on the heat transfer analysis of a roof composed of multiple layers. External air temperature and solar radiation are considered time-varying. The results obtained show the benefits of selective coatings in terms of reductions in both roof temperature and heat flux and, consequently, alleviation of the urban heat-island effect and reduction of electricity consumption.

Study on the culture of aerial microalga on external wall surfaces using ajellyfish protein extract as a growth medium

クラゲ由来混合タンパク質を用いた気生微細藻類による壁面緑化の基礎的研究を行った。まず，本学八王子キャンパス内において乾燥したコンクリート壁面，樹皮( スギ製棒杭)，石像，スチール製看板塗装面などの表面から気生微細藻類の緑色コロニーを採集した結果，緑藻綱に属するElliptochloris reniformis(E. reniformis)を単離することができた。また，東京湾の夢の島付近から採取したミズクラゲからコラーゲンやムチンなどを含むタンパク質を抽出することができた。E. reniformis は，ミズクラゲ由来混合タンパク質(ムチンなど)を有機窒素源として取り込むことで増殖することが分かった。さらに，そのタンパク質が藻細胞による壁面緑化の初期段階において栄養の供給源の一つになったものと考えられる。したがって，クラゲの有効利用方法および抽出されたタンパク質が気生微細藻類による壁面緑化の助長材料として初期段階において利用可能であること，気生微細藻類の持つ基物着生能力に着目した壁面緑化が可能であることが分かった。

The effect of the orientation and proportion of a plant-covered wall layer on the thermal performance of a building zone

The aim of the present work is to analyse thoroughly the influence of the orientation and proportion (covering percentage) of plant-covered wall sections on the thermal behaviour of typical buildings in the Greek region during the summer period. As to the effect of construction parameters, the layer position of masonry/insulation has been also considered. The investigation has been carried out using a thermal-network model that adequately simulates the building zone under assumption; its validation was based on experimental results from a recently reported study. The model makes provision for several heat-flow paths in order to take into account the leaf cover on the external wall surface, heat transfer through the surfaces that constitute the building envelope, and natural ventilation. The influence of orientation and covering percentage of plant foliage for walls with different configurations was studied using representative outdoor environmental data for the zone location at a specific time period.

円筒形構造物の風荷重に関する風洞実験

Wind loads for designing thin circular cylindrical structures, such as oil-storage tanks and silos, have been studied in a turbulent boundary layer, aiming at accumulating information for the revision of the AIJ Recommendation for Storage Tanks and Their Supports (1996). Wind pressure distribution on the roof, in the case of enclosed structures, was measured, the results of which are compared with the specifications of the AIJ Recommendations for Loads on Buildings (2004). The effects of open top on the pressure distributions on the external and internal wall surfaces are also investigated. Furthermore, the characteristics of instantaneous pressure distributions on the external surface are discussed by using a conditional sampling technique and the POD (Proper Orthogonal Decomposition) analysis.