Nik Kapur

Case study of a data centre using enclosed, immersed, direct liquid-cooled servers

The growth in demand for Information Technology (IT) systems and the requirements to better control carbon emissions is a large challenge for data centre design. Air-cooled data centres are becoming more efficient by layout and the adoption of compressor free cooling, but for higher densities, further efficiencies can be achieved with liquid (water) cooled systems, where liquid is either brought to the cabinet or is fed directly into the IT systems. This paper makes a comparison of the full energy consumption between hybrid air-cooled and direct liquid-cooled systems based on real operational systems using comparable IT components. The results based on real data demonstrate a significant level of energy reduction for a high density data centre solution that uses enclosed, immersed, direct liquid-cooled servers.

Biomechanics of low-modulus and standard acrylic bone cements in simulated vertebroplasty: A human ex vivo study

The high stiffness of bone cements used in vertebroplasty has been hypothesised to contribute to the propensity of adjacent vertebral fractures after treatment. Therefore, new low-modulus cements have been developed; however, there are currently no studies assessing the biomechanical aspects of vertebroplasty with these cements in an ex vivo non-prophylactic model. In this study, we induced wedge fractures through eccentric uniaxial compression to single whole-vertebrae, before and after augmentation with either standard or low-modulus cement. Compressive strength and stiffness of individual vertebrae were measured, on 19 samples from metastatic spines and 20 samples from elderly, osteopenic spines. While both cement types increased the strength of both the metastatic (+34% and +63% for standard and low-modulus cement, respectively) and the elderly vertebrae (+303% and +113%, respectively), none of them restored the initial stiffness of metastatic specimens (-51% and -46%, respectively). Furthermore, low-modulus cement gave a lower total stiffness (-13%) of elderly specimens whereas standard cement increased it above initial levels (+17%). Results show that vertebroplasty with low-modulus cement could provide restoration of the initial stiffness while increasing the strength of fractured elderly vertebrae and hence represent a treatment modality which is closer to pre-augmented behaviour. Also, this study indicates that stiffness-modified cement needs to be optimised for patient/pathology specific treatment.

A unified model for holistic power usage in cloud datacenter servers

Cloud datacenters are compute facilities formed by hundreds and thousands of heterogeneous servers requiring significant power requirements to operate effectively. Servers are composed by multiple interacting sub-systems including applications, microelectronic processors, and cooling which reflect their respective power profiles via different parameters. What is presently unknown is how to accurately model the holistic power usage of the entire server when including all these sub-systems together. This becomes increasingly challenging when considering diverse utilization patterns, server hardware characteristics, air and liquid cooling techniques, and importantly quantifying the non-electrical energy cost imposed by cooling operation. Such a challenge arises due to the need for multi-disciplinary expertise required to study server operation holistically. This work provides a unified model for capturing holistic power usage within Cloud datacenter servers. Constructed through controlled laboratory experiments, the model captures the relationship of server power usage between software, hardware, and cooling agnostic of architecture and cooling type (air and liquid). An exciting prospect is the ability to quantify the amount of non-electrical power consumed through cooling, allowing for more realistic and accurate server power profiles. This work represents the first empirically supported analysis and modeling of holistic power usage for Cloud datacenter servers, and bridges a significant gap between computer science and mechanical engineering research. Model validation through experiments demonstrates an average standard error of 3% for server power usage within both air and liquid cooled environments.

Design of data centre rack arrangements using open source software

In the design of a data centre (DC), engineers are increasingly using specialized commercial computational fluid dynamics (CFD) software packages to predict thermal loads for various cooling configurations. This paper is the first to demonstrate how a set of open source software tools, namely OpenFOAM, Octave and paraview can be used to simulate and visualize the airflow in a real live 55kW private DC, with a particular focus on energy savings and reduction of hotspots.