Double Wall System Research Articles

Direct Tensile Capacity of Steel-Tube Connections in a Precast Concrete Double-Wall System

This study introduces a new precast concrete (PC) double-wall system designed to simplify the complex fabrication process of existing PC double-wall systems and eliminate laitance and other defects that can occur during the manufacture of concrete panels. An experiment and finite element analysis were conducted on 11 specimens to determine the tensile resistance performance of rectangular steel tubes that maintain spacing to avoid damage to the PC panels during transportation or on-site installation. Specimens varied in terms of the end details of the rectangular steel tubes, such as the presence of welded steel plates or embedded concrete and total length in terms of whether longer or shorter specimens were used. As a result, the specimens showed a 20–30% increase in maximum tensile strength compared to the control specimen according to the end details, except for the case where side steel plates were cut and bent inward. The control specimen filled with concrete was the most suitable for connections when constructing PC double-wall systems. It has significant tensile resistance according to the experiment and finite element analysis and does not require additional construction steps or costs.

Global sensitivity analysis of sound attenuation in double-wall system with porous layer

This paper investigates the acoustic performance of a double-wall system with a porous layer and presents a global sensitivity analysis of sound attenuation. The transfer matrix method is first applied to predict sound transmission through the structure. This method offers a relatively simple and cost-effective way to model the complex acoustic interactions in these systems and provides rich high-frequency information. The method represents sound wave propagation for each layer using a transfer matrix that depends on the thickness and physical characteristics of each material, and interface matrices are introduced to consider boundary conditions between adjacent layers. The poroelastic layer is modeled using the Biot-Allard approach with nine parameters. Then a global sensitivity analysis is performed using Morris and Sobol methods to identify the parameters that have a significant impact on sound transmission loss. The Morris method is used first to eliminate the parameters that have the least impact, and the Sobol method is then employed to analyze the remaining parameters and their interactions in more detail. The study focuses on eleven parameters, including all the physical parameters of the foam, and thicknesses of plates, cavity, and foam. The results of the sensitivity analysis indicate that geometrical parameters such as the thickness of different layers have the most significant impact on the sound transmission loss response in the lower frequency range. In contrast, foam properties such as flow resistivity have more influence in the higher frequency range. Overall, this study is the first to apply sensitivity analysis methods to the problem of sound transmission through double wall systems with porous layers, providing valuable insights into the system’s behavior and its design optimization.

Post-tensioned rocking dissipative timber wall systems: Numerical prediction

Low-damage post-tensioned technologies were born with the aim to obtain structural solutions able to guarantee, in case of seismic events, not only the safeguarding of human life, but also the rapid re-use of the buildings without permanent damage. In this context, structural systems based on rocking dissipative timber walls have been introduced, in which rocking behavior is entrusted to post-tensioned bars, and the dissipative contribution is provided by steel dampers, easily replaceable after an intense seismic event. The paper presents a nonlinear numerical model to predict the response of different configurations of Post-Tensioned (PT)-timber wall systems, particularly useful to support the design phase. More in detail, the geometrical non-linearity due to the rocking behavior of the system and material non-linearities that characterize the dampers are taken explicitly into account. The proposed numerical modelling strategy has been validated on different experimental literature tests performed by non-linear static analyses on both single and double wall systems equipped with different damper configurations. The comparison between numerical and experimental results is performed to demonstrate the effectiveness of the proposed model in predicting the behavior of post-tensioned walls subjected to cyclic loads. Further, parametric analyses have been developed in order to investigate the effect of different parameters, such as wall dimensions, initial post-tensioned force in the bars, number of axial and shear dampers, on the global behaviour of post-tensioned timber systems.

Cyclic model of post-tensioned low damage timber walls with dissipative devices

Post-tensioned rocking dissipative timber wall systems born from the idea to obtain structural solutions able to guarantee, after a seismic event, a rapid re-use of the buildings without permanent damage, as well as to guarantee the safeguarding of human life. In this framework, the rocking of timber walls is entrusted to post-tensioned bars, placed in ad hoc cavities of the panel, while the dissipative contribution is provided by steel dampers, which are sacrificial elements subjected to damage easily replaceable after an intense seismic event. In this context, it can be helpful to have a numerical model in order to support the design phase; indeed, the paper presents a non-linear numerical model of post-tensioned rocking dissipative timber walls able to predict the response of this innovative system. In particular, geometrical and material non-linearities, due to the rocking behavior of the system and to the material that characterize the dampers, are taken explicitly into account. Further, the proposed numerical modelling strategy has been validated on literature experimental campaigns performed on both single and double wall systems, with different damper configurations. The comparison between experimental and numerical cyclic responses are shown in term of global results, i.e. force/displacement curves and post-tension variation of the bars. The comparison demonstrates the effectiveness of the proposed model in predicting the behavior of post-tensioned walls subjected to cyclic loads.

Effect of a constrictor plate on behavior of a model steel pipe pile driven in dense sand

This study investigates the effect of a constrictor plate on the drivability and load-carrying capacity of open-ended pipe piles via a series of model pile tests. The model pile had an outer diameter of 88.9 mm and was driven in a dense sand to a depth of 670 mm using an impact hammer. Soil plug lengths were measured using a laser distance meter for the entire process of the pile driving. The model pile further employed a double-wall system to separately measure the annulus resistance, soil plug resistance, and outer shaft resistance. Two tests with a constrictor plate located at 98.4 mm and 200 mm above the pile base and one test without a constrictor plate were performed. The piles with a constrictor plate required about 15–20% more pile driving energy than the pile without a constrictor plate. Results from static load tests showed that the piles with a constrictor plate were able to resist more axial loads than the pile without a constrictor plate by about 25–38%.

Performance of a 56 m deep circular excavation supported by diaphragm and cut-off double-wall system in Shanghai soft ground

The performance of a 56 m deep circular excavation supported by a double-wall system, consisting of an inner circular diaphragm wall and an outer rectangular cut-off wall, in Shanghai soft ground is studied in this paper. The surveyed data (e.g., lateral wall deflections ( δ h), horizontal displacement of soil ( δ s), ground surface settlement ( δ v), soil rebound ( δ v+), earth pressure ( P), pore water pressure ( Pw), and soil stress path) are systematically investigated. The results show that the maximum lateral wall deflections are 0.002% ∼ 0.03% of the excavation depth ( H e). The maximum ground surface settlement ( δ v m) is generally larger than δ h m, which is located at 0.4 ∼ 0.6 H e. Moreover, an innovative formula is proposed to estimate the ground settlement. It is able to distinguish various characteristics of surface settlement in different zones of the settlement profile. The ground surface settlements are mainly induced by surcharge loading and continuous excavation, and they are related to the change in confined water level. The lateral earth and pore water pressures in the active zone are relatively insensitive to the excavation, while the correlation becomes obvious in the passive zone. The findings from this study can be helpful to the design of other similar deep excavations in soft clay.

Ratchetting and Creep Failure in Twin-Wall Turbine Blades Experiencing Severe Thermal and Centrifugal Loading

Abstract Twin-wall structures can be cooled both externally and internally, raising great potential for use in high-temperature applications. However, their increased geometric complexity imposes a range of potential failure mechanisms for consideration in design. The primary aim of this study is to identify the nature of such mechanisms by constructing Bree type interaction diagrams for idealized double-wall systems under cyclic thermomechanical loading that shows the combination of loading conditions for which cyclic plasticity (leading to fatigue failure)-creep ratchetting occur. Through an extension of the classical Bree analysis, we determine analytical boundaries between different regimes of behavior. We also quantify the effects of wall thickness ratio, temperature field, and yield and creep material properties. Local cyclic plasticity is shown to dominate over structural/global ratchetting when the yield strength reduces with temperature and/or when the temperature gradient through the hot wall thickness dominates over the temperature difference between the walls. Thus, we conclude that global ratchetting is unlikely to occur in the practical loading range of Nickel-based twin-wall turbine blades, but instead these systems suffer from local fatigue at cooling holes and excessive creep deformation. This is verified by 3D cyclic finite element (FE) simulations, demonstrating that the analytical approach provides a powerful, cost-effective strategy for providing physical insight into possible deformation mechanisms in a range of thin-walled components; highlighting the key trade-offs to be considered in design; and directing the use of computer methods toward more detailed calculations.

Experimental testing and analytical modelling of single and double post-tensioned CLT shear walls

Post-tensioned (PT) timber technology - also called Pres-Lam technology - can provide increased strength/stiffness for mass timber seismic load resisting systems while also providing energy dissipation and re-centering capabilities. Initial experimental tests and practical implementation on PT timber structures in the past 15 years primarily utilized laminated veneer lumber (LVL), with some glulam and cross-laminated timber (CLT) prototypes and real-case applications, and their analytical prediction models were extended and adapted from precast concrete to account for unique characteristics of engineered timber. More recently, CLT has emerged into a more dominant global mass timber product. This paper presents a large-scale experimental study on 8.6 m tall PT CLT single and double wall systems. The PT double walls utilized screwed connections at the in-plane joint and U-shaped flexural plates at the foundation to provide coupling effect and energy dissipation. With screwed connections, the PT double wall partial composite action of approximately 70% was achieved and the system stiffness was almost two times that of two PT single walls without partial composite action but of equivalent length. Analytical prediction models, accounting for the peculiar controlled rocking mechanism and originally developed for PT LVL systems were adopted for PT CLT wall systems, were found to have increased compressive toe strain variability due to the increased material inhomogeneity of CLT with non-edge glued lamella. The timber compressive strains and unique ‘end effect’ bearing phenomenon was investigated for the first time with Particle Tracking Technology (PTT). Extensions to the existing PT double wall analytical prediction model were proposed and validated to capture the unique kinematic rocking mechanism where wall uplift occurs due to the strong and stiff screwed in-plane connection between individual walls.

AN EXPERIMENTALLY VALIDATED LOW ORDER MODEL OF THE THERMAL RESPONSE OF DOUBLE-WALL EFFUSION COOLING SYSTEMS FOR HP TURBINE BLADES

Abstract Transpiration cooling represents the pinnacle of turbine cooling and is characterised by an intrinsic porosity achieving high internal convective cooling, and full coverage film cooling. The quasi-transpiration, double-wall effusion system attempts to replicate the cooling effect of transpiration cooling. The system is characterised by a large wetted area providing high internal convective cooling performance, with a highly porous external wall allowing the formation of a protective cooling film. This paper presents a low-order thermal model of a double-wall system designed to rapidly ascertain cooling performance based solely on the geometry, thermal conductivity, and approximate surface heat transfer coefficients. Initially validation uses experimental data with heat transfer coefficients for the low order model obtained from fully conjugate CFD simulations. A more controlled CFD study is then undertaken with both fully conjugate and fluid only simulations performed on several double-wall geometries to ascertain both overall and film effectiveness data. Data from these simulations are used as inputs to the low order thermal model and the results compared. The low order model successfully captures both the trends and absolute cooling effectiveness achieved by the various double-wall geometries. The model therefore provides a powerful tool whereby the cooling performance of double-wall geometries can be near instantaneously predicted during the initial design stage, potentially allowing geometry optimisation to rapidly occur prior to more in-depth, costly and time-consuming analyses. This benefit is demonstrated via the implementation of the model with input boundary conditions obtained using empirical correlations.

Designing better nestboxes: double-walled and pale proves coolest under the sun

Context Fauna nestboxes are used for conservation, research and mitigation against tree hollow/cavity loss. Scant attention has been given to the microclimate inside boxes until recently, with concern that nestboxes may be ineffective or a thermal trap because of high internal temperatures during summer. Aim Our study used construction design principles to guide modifications to nestboxes to reduce maximum temperatures inside boxes. Methods Five trials were undertaken, and modifications included addition of thermal mass, creation of a double wall system and painting the box and/or outer wall white. Nestboxes were placed in full sun. Key results The internal temperature difference from ambient between the worst (unpainted box) and the best box design was around 7°C at 30°C, and 9.5°C at 40°C. Painting boxes white had a marked impact on internal temperatures, but the single modification giving most protection from heat gain was construction of a ventilated double wall. This created a shaded air space around the internal box. Painting the outer layer white further improved insulation, and painting both the box and outer layer gave the best result. Conclusion Double-walled, pale nestboxes can provide significant protection from solar heat. Implications Adding an air space to insulate a nestbox has considerable advantages over alternatives − it contributes little weight (compare using denser wood/materials); avoids environmental issues associated with insulators such as polystyrene or foil batts; is inexpensive; is easy to retrofit a second layer around existing boxes and it should improve nestbox longevity as the outer layer protects the inner box from weathering.

Evaluation of the thermal performance of construction systems to reduce the energy consumption in buildings: A case study in a cold semi-arid climate


 
 
 The performance of a three-story laboratory building was analyzed to reduce its annual energy consumption. The analysis was performed through a whole-building simulation approach and dynamic simulations to calculate the potential reduction of heating and cooling energy requirements by evaluating various construction systems. The main objective was to accomplish a decrease in energy consumption without the implementation of sophisticated constructive systems, which are commonly unavailable or unfeasible to apply in developing countries. Therefore, a two-stage analysis was carried out. At the first stage, a set of commonly available construction materials were implemented. From this analysis, it was shown that the use of an insulated concrete wall, double tinted glass, and an insulated terracotta roof corresponds to the optimal combination of materials, resulting in a decrease of 36% on the total annual energy requirements. Finally, from the second stage analysis, where double-wall systems and a green façade were implemented, an additional energy saving of up to 16% was achieved.
 
 

Experimental and Computational Methods for the Evaluation of Double-Wall, Effusion Cooling Systems

Abstract Further improvements in gas turbine efficiency can be sought through more advanced cooling systems—such as the double-wall, effusion system—which provide high cooling effectiveness with low coolant utilization. The double-wall system, as described here, comprises two walls: one with a regular array of impingement holes and the other with a closely packed, regular array of film holes (characteristic of effusion systems). These walls are mechanically and thermally connected via a bank of pedestals which increase coolant wetted area and turbulent flow features. However, a lack of data exists in the open literature on these systems. This study presents a novel experimental heat transfer facility designed with the intent of investigating flat plate versions of such double-wall geometries. Key features of the facility are presented including the use of recirculation to increase the mainstream-to-coolant temperature ratio and the use of infrared thermography to obtain thermal measurements. Some rig commissioning characteristics are also provided which demonstrate well-conditioned, uniform flow. Both coolant and mainstream Reynolds numbers are matched to engine conditions, with the Biot number within around 15% of engine conditions. The facility is used to assess the cooling performance of four double-wall effusion geometries which incorporate various geometrical features. Both overall effectiveness and film effectiveness measurements are presented at a range of coolant mass flows with conclusions drawn as to preferable features from a cooling perspective. The results from a fully conjugate computational fluid dynamics (CFD) model of the facility are presented which utilized boundary conditions obtained during experimental runs. Additionally, a computationally efficient decoupled conjugate method developed previously by the authors was adapted to assess the experimental geometries with the results comparing favorably.

Development and Application of Precast Concrete Double Wall System to Improve Productivity of Retaining Wall Construction

The construction of most apartment underground parking lots utilizes reinforced concrete (RC) structures composed mainly of rebar work and formwork. RC structures lower construction efficiency and significantly delay the construction because they require a large number of temporary materials and wooden formwork. In this study, a precast concrete double wall (PCDW) system was developed to address the existing problems of RC structures and to improve the productivity of retaining wall construction. PCDW is a precast concrete (PC) wall in which two thin concrete panels are connected parallel to each other with truss-shaped reinforcement between them. PCDW can contribute to securing integrity, reducing the delay in construction, and improving quality. An overall process for the member design and construction stage of the PCDW system was proposed, and its improvement effects were examined regarding various aspects in comparison to the RC method.

Numerical simulations of a double-wall cooling with internal jet impingement and external hexagonal arrangement of film cooling holes

Three-dimensional conjugate computations are conducted to investigate the flow and heat transfer characteristics of a double-wall cooling system with a novel hexagonal arrangement of film cooling holes. Under the same coolant flow rate, the heat transfer and cooling performance of angled holes in the hexagonal arrangement are investigated and compared with those in the counterparts with conventional linear arrangements of external film cooling holes. The boundary condition of numerical simulations maintains the fixed jet Reynolds numbers of 10,000, 20,000 and 30,000 and the corresponding blowing ratios of 0.5, 1.0 and 1.5. Different wall thermal conductivities are respectively used in the numerical computations in order to examine the effects of Biot number of the film cooling wall on the overall cooling performance. Polyhedral meshes and Shear-Stress Transport (SST) k−ω turbulence model have been adopted in the numerical computations to obtain the detailed heat transfer and flow field. The results indicate that the hexagonal arrangement of film cooling holes shows significant advantages for the double-wall cooling scheme to decrease the external surface temperature appreciably. As the Biot number increases the overall cooling effectiveness of the double-wall system shows a downward trend, which decreases by about up to 25% in the Biot number range of 0.3–1.2. With the engine-like turbine Biot number of Bi≈0.56 the hexagonal arrangement improves the total heat transfer quantity inside the film cooling holes by up to 3.8 times, and enhances the overall effectiveness by up to 24.5%, as compared with the linear arrangement of straight circular film cooling holes. The combinations of the increased convective heat transfer inside the film cooling holes and the improved external film coverage induced by the hexagonal arrangement are the main contributions to the improvement of overall cooling performance.

Development of a Steady-State Experimental Facility for the Analysis of Double-Wall Effusion Cooling Geometries

The continuous drive for ever higher turbine entry temperatures is leading to considerable interest in high performance cooling systems which offer high cooling effectiveness with low coolant utilization. The double-wall system is an optimized amalgamation of more conventional cooling methods including impingement cooling, pedestals, and film cooling holes in closely packed arrays characteristic of effusion cooling. The system comprises two walls, one with impingement holes, and the other with film holes. These are mechanically connected via pedestals allowing conduction between the walls while increasing coolant-wetted area and turbulent flow. However, in the open literature, experimental data on such systems are sparse. This study presents a new experimental heat transfer facility designed for investigating double-wall systems. Key features of the facility are discussed, including the use of infrared thermography to obtain overall cooling effectiveness measurements. The facility is designed to achieve Reynolds and Biot (to within 10%) number similarity to those seen at engine conditions. The facility is used to obtain overall cooling effectiveness measurements for a circular pedestal, double-wall test piece at three coolant mass-flows. A conjugate computational fluid dynamics (CFD) model of the facility was developed providing insight into the internal flow features. Additionally, a computationally efficient, decoupled conjugate method developed by the authors for analyzing double-wall systems is run at the experimental conditions. The results of the simulations are encouraging, particularly given how computationally efficient the method is, with area-weighted, averaged overall effectiveness within a small margin of those obtained from the experimental facility.

Determination of the dynamic complex modulus of viscoelastic materials using a time domain approach

Viscoelastic and poroelastic materials are widely used in multilayer panels for noise control. They are usually used as an inner decoupling layer in double wall systems in order to increase the sound transmission loss of a bare plate. In order to correctly simulate the acoustical behaviour of such systems, it is necessary to measure the elastic parameters of these materials (storage and loss moduli, and Poisson's ratio). Physical properties related to pore morphology also need to be determined for open cell structures. Most of the materials used in trimmed panels can show elastic parameters that vary with frequency, thus a quasi-static measurement technique is not accurate enough to consider such viscoelasticity effects. This paper focuses on the estimation of complex modulus as a function of the frequency of isotropic viscoelastic materials. In particular, the tested material is positioned between two plates, with one of them being excited by an electromagnetic shaker. Using a sine burst as an excitation signal, the accelerometric response in the time domain is measured at the top and bottom plates. The time of flight between the plates and the envelope function of time domain acceleration at the top plate are then found. A transfer matrix model of the experimental setup is used to inversely estimate the complex modulus of the materials once the remaining mechanical and physical properties have been fixed. The results will be presented and discussed for different materials and compared with well-established quasi-static and dynamic techniques.

Reliable production of microalgae biomass using a novel microalgae platform

A microalgae platform, consisting of four photobioreactor units incorporating a novel biomimetic design, has been installed at the Biosolar Center in Koethen, Germany. The novel photobioreactor consists of a flexible, tubular double-wall hose system (silicone based) with integrated temperature control in a closed cycle. The modular-arranged platform system (total cultivation volume 1700 L) has been designed for stable long-term cultivation of microalgae biomass in outdoor use. Cultures with Scenedesmus and Chlorella species have been grown outdoors at their optimal growth temperature (avg. 26 °C) for 145 days during spring and summer and were tested successfully for the stable production of microalgae (avg. biomass productivity 0.3 g L−1 day−1 (max. 0.75 g L−1 day−1)) with an overall photosynthetic conversion efficiency of 7.2 % based on photosynthetically active radiation. The average calorific value of the produced biomass is 23.25 MJ kg−1 with defined product quality (content relating to biomass dry weight: proteins 0.40 g g−1, lipophilic compounds 0.38 g g−1 and total carotenoids 11 mg g−1). This outdoor concept is continuously adjustable to maintain an optimal environment for microalgae cultures (in particular light entry, temperature control and limiting of oxygen levels).

Reduction of construction noise while building a recording studio

While a new recording studio was being built within a large Audio and Video complex, construction noise had to be adequately controlled, in order to allow for the already existent audio recording studios and TV sets to continue with their normal activities along the building process. The noise was reduced by making a double wall system in the façade overlooking the construction area. Use was made of the already existing external wall, adjacent to the construction site, as the first wall of the system, and a second one was added in the exterior side of that wall in order to complete the double wall system, which contributed with a few dB's in the low frequency range, while getting a considerable noise level reduction in the high frequencies range to the overall noise reduction of the original wall. Producers and performers who were actually working in the existing studios were satisfied by the results obtained once the adaptation was complete. Details of the wall and its expected acoustical behavior are presented and discussed.

A FINITE ELEMENT PLATE FORMULATION FOR THE ACOUSTICAL INVESTIGATION OF THIN AIR LAYERS

Double wall systems consisting of thin plates separated by an air gap are common light-weighted wall structures with high transmission loss. Generally, these plate-like structures are modeled in a finite element analysis with shell elements and volume elements for the air (fluid) layer. An alternative approach is presented in this paper, using shell elements for the air layer as well. First, the element stiffness matrix is obtained by removing the thickness dependence of the variational form of the Helmholtz equation by use of a power series. Second, the coupling between the acoustical shell element and the elastic structure is described. To verify the new shell element, a simple double wall system is considered. Comparing the predicted sound field with the results from a commercial FE software (with a single layer of volume elements) a very good agreement is observed. At the same time, employing the new elements with a third-order power series (4 DOFs per node), the calculation time is reduced.

Modeling the sound transmission through complex structures with attached noise control materials

This paper discusses three extensions of the Transfer Matrix Method (TMM). The first deals with the modeling of the transmission loss of sandwich–composite panels. A wave based model is recalled and used to derive a simpler model based on identifying effective properties of an equivalent orthotropic panel. An experimental case study is presented to show the accuracy of these models when used to predict practical sound transmission problems involving single wall sandwich–honeycomb panels and double wall sandwich–honeycomb with an absorbing material filling the cavity between the two panels. In the second extension, the use of the TMM to predict the response of panels under various types of excitations is discussed. A wave based method is presented and compared with Finite Element Method (FEM) predictions for two types of excitations: Turbulent Boundary Layer (TBL) and point source. The comparison shows that the method allows for accurate predictions of the frequency averaged Transmission Loss (TL). Finally, the use of the TMM to model double wall systems with mechanical links is presented and numerically validated using FEM. It is found that the method captures well the decrease of the TL due to the insertion of the links and the effect of the excitation nature on this decrease.